New Car Build
19th January 2010
Things have progressed but the snow did'nt actually help with the masterplan! Spent about
14 hrs on the car (total 201hrs), completed all the coilover mounts on the chassis so I could have the car rolling. More or less sorted the seat belt mountings - just a bit different as we are using a Hooker harness with ratchet. Picked up the new 434 SBC - even though it's built using mainly S/H bits it's a corker! Also made a couple of engine lifting plates and sorted some parts we needed for the 496 BBC going in the old car. Some of the pics are a bit dark but hope you can still see whats going on!
Bolt on rear coilover mounting - took some making but it looks the part, keeps the coilover unit vertical but every thing is pretty well protected by the wheel. Local strengthening plate added on the inside welded to the 3mm side plate. Will be maing a spare later.....
Looking back at the rear outside coilover mounting - a couple of holes still to drill but someone needed my drill bits at the shop + my Landy!!
Front inside coilover mounting, will be adding protection tubing later. I used 1" bar and drilled it 1/2" on the lathe to make the bolt on section. The support is made from 60x40x3 HT box the inside one is set at 15 degrees (shown) and ouside one at 25 degrees. I made templates at the sides of both of the box sections to mark out the tube cutout - the tube goes down and bends in towards the centre of the chassis at this point.
New 434 SBC in the back of the Landy having just picked it up. This the part exchange deal we did with Peter Knight to swap with bits of our original BBC- the block, heads are second hand Dart parts but after the man has done his work I doubt if we will notice but it was the only way we were going to afford this little beauty. Thats our original Demon Oval Race Carb which had only been used a couple of times on the original BBC. Out of interest even turned sideways we had to pack the engine for transport - the BBC would not fit sideways!!
Closer view of the Demon carb on top of the Dart intake manifold
25th November 2009
As usual, a busy trip home again - never enough time to do what you want! Managed to spend 25 hrs on the car (total 187 hrs) mostly spent on the suspension and sorting out the fuel tank. The small block is ready for the new car but think we need to go for a "fitting" for the engine mounts before coming home. Also heard that the big block for the old car has arrived in the UK so we should have it soon. We will have to see how much time Si has to sort the old car out as he fancies racing in December - I won't be back home till after that so I will have to leave him with it! Based on the normal December at the shop, that sounds like a busy Christmas....
This is a pic of the bits for the fuel tank. As I've said before this is based on using seemless ally tubing to make a cylindrical tank. It took a fair bit of time to cut ou t the end pieces, baffle (put in position for photo) and I even broke a hole saw.
The complete tank after a visit to the specialist welder we use for the shop for welding ally and titanium frames,etc.
Inside rear coil over mounts. We decided to follow the design from the old car which has bottom axle mountings which keep the coil overs well protected. Top mount is a bolt on arrangement and you can see from the weld heat marks that theres a stiffening plate welded on the inside. The caliper mount has to be relocated - this was on the axle when we bought it.
Pic shows the rear outside coil over mounting on the axle - again this is a bottom mount which keeps the coil over tucked away. It does mean that the coil over is mounted at an angle and not vertically (angled from the side, vertical from the rear) but this really only affects the spring rating we use. I did not take a photo of the top mounting - this too is a bolt on design. You can just see the bent tube which I have used to make this. Again, the caliper mount has to be moved. Subsequent to this photo, I have completed the bolt on top mount.
27th September 2009
As I explained last time, not much time at home with new job schedule but I've just put in another 20 hrs taking the total to 162 hrs. Much of that was spent welding and grinding but continued making suspension bars and a bit more general work on the chassis - easier to describe with photos! I understand engine is just waiting for the dyno so should be available next time I'm home. Also I decided to hang fire installing bumpers, etc until we have some Goodyear tyres on rims so we have the correct dimensions when we decide what rims and offsets to use. We are also looking at using the original car for shale so we are looking for another engine.......................
Back axle located with all bars fitted (not final) and triangulation fitted to down bars, etc
21st July 2009
WellI was very busy this time home but unfortunately this was wrecking the kitchen and not building our car! Barney managed a bit of time on the car fitting the remaining down bar and machining threaded inserts for the rear suspension bars - I was limited to temporarily installing both axles usinf existing suspension bars. So we are set up for installing the bumpers and side nerf bars but it's not happened yet! Between us we've spent 12 hrs on the car so thattakes us to 142hrs so far. It looks like I will have to spend longer at work in the UAE so I'm not going to be able to do anything on the car for some time......................
23rd June 2009
As stated previously, the boys have completed the roll cage and this time home, I completed the 3mm plate under the seat, base fixings for the seat and plating the roll cage sides with 3mm plate + I spent some time on suspension mountings. I estimate that between us we have spent 30 hrs on the car so thats a total of 130hrs so far.
We are now at the position where we need to mount the axles then put on bumpers and side nerf bars - bumpers and nerf bars are welded and waiting so we are not in a bad state. However, we still await the engine so it does look like we can get the car ready in time..............
Roll cage all together
The panhard and suspension mounting brackets shown on top of the chassis needed a bit of modification to open them up to use on 40mm box (supplied for 1 1/2" box, 38.1mm).
3mm plate tacked in position - these have now been welded top and bottom.
One of the down bars from car to front of car is fitted and we will be having a steepish bonnet line - this is high on the front hoop and there will be curved fillet plate to blend this into the cage side. The cage side is higher at the rear hoop which is not too clear on the pics - also because I took the pics standing, the cab sides look lower than they really are. Photographer I am not!!! But in the "flesh" it's looking pretty cool.
31st May 2009
I've no photos yet but Si and Barney has been continuing work on the roll cage and from the pics sent to my phone, everything is looking cool. Had a few phone calls from them for guidance on how I want things and it's great to start getting progress when I am away - up to now it wasn't easy for any of them to take over as I had not put everything down on drawings and anyway I change things as I go along! Cage is tacked together so there will be a good welding session but the time is in the fabrication. When I put on the photos I will check and see how many man hours they have put into the car and update the info.
25th May 2009
Well to say the roll cage has to be built around full containment seats is a fair comment! 20 hours (total100 hours so far) further on, the seat is well and truely located with 20 bolts holding it in and very time consuming bracketry! I also fitted the 3mm plate behind the seat to get all the fiddley bits completed in one go. It's bank holiday but I've got to catch a plane - however Si and some of the team are free to play so I hear they have been working on the roll cage so hopefully there will be some good progress on the car whilst I am away!! I will keep track on the hours they put in to keep things up to date but I was pleased with the progress I made with the tricky bits and things should really start moving now............
This is a view of the bracket on the seat back/shoulder restraint
Rear view with additional cross tube behind the head rest
This view shows the three fixing locations on the seat, one at the top of the seat "bucket" and two on the head rest.
3mm plate going in behind the seat
Still some welding to complete on the rear plate and i've still to install the seat belt mounts and the cross tube for the belts. Think we will go for a new set of ratchet belts which will complement the seat and make for a very secure driver.
27th April 2009
Had to make a few mods to accomodate the new back axle - slightly different mountings from our existing axle + I duffed up on the location of the mount for the rear panhard bar, anyway all sorted and axle is temporarily in place to help with seat location.
Started roll cage construction and completed all the main bends. Rules allow front to back or side to side main hoops - most use front to back these days which has some advantages, ie, you can use a smaller roof plate as the front roof cross member can be positioned to suit. Anyway, just to be different, we have gone for a side to side cage design which will give a different look + the cage is wider down to cab height at the front which also means that the down bars from roll cage cab height to front of car start wide of the chassis at the roll cage so with a slight bow this allows engine removal/installation without having to mess about - engine mounts normally get in the way if installed first. At the end of the day, it will give a different look so it will be in the eyes of the beholder.
In all spent about 20 hours on the car so up to a total of 80 hours. Roll cage bending takes a bit of thought particularly as the front hoop has two bends which each have bends in two planes (easier to see on photos) but theres more brain cells destroyed working out and cutting some of the tube to tube cuts which are a tad more tricky on the side to side design. Anyway, I will attempt to describe whats happening in the photos......
Back axle positioned and on brick to give approximate running height which gives the location of the axle central mounting.
Rear cage hoop being positioned - this angles back 20 degees so photo is a bit misleading. Thers a 50mm raised section in the top of the hoop. The seat will be installed at the same 20 degree angle.
Rear cage tacked in position and front cage being set up. Bends at cab side height on the front cage slope backwards and also in to the chassis. From the side, the front legs are at right angles to the chassis although it does not look like it from the photo! - in this photo the bottom of the front cage legs still need to be pulled in a couple of inches.
Front hoop positioned and tacked + bars from rear hoop to chassis installed.
Perspective makes this shot look a bit wierd but it does give a different view of the cage. Incidentally, the back axle needs moving about 1" to the inside
17th April 2009
No more progress on the build - I should be able to update that at the end April. However, a radical change in plans as the new engine will be delayed in completion to June..........Based on status of the build, it looks like the plan will now change to concentrating on completing the new car and forget about installing the engine in the old car - the engine delay should mean that by the time it arrives the new car should be ready for it and instead of spending time on modifications to fit the small block in the old car (new firewall, floor, fixing new engine mounts, exhaust, new bonnet, etc) I will be at the stage where I can do this on the new car. There will be some "cheating" involved as up to date I have done all the work on the new car and to get us out on track asap Si and the team will have to help with stuff like front fire wall, floor, brakes, bodywork, painting, build up after painting, etc. We will be getting some engine mountings off Bruno and he is busy as well so all in all it looks like it may be an interesting few months...........
Incidentally, although it's not available straight away, the old chassis (all sorted with new bumpers, etc) without axles but with big block engine mounts, exhaust headers, fuel tank, bodywork and probably quite a few other bits will end up on E Bay with a 99p start price and no reserve but the buyer would have to arrange collection, ie trailer and a few guys to help lift it.
30th March 2009
Finally managed to get some spare time at home to work on the car but the majority of the 20 hours (now total of 60 hours) I did get to spend on the build was almost continuous welding. We now have bumpers and side nerf bars ready to go on the car and I completed much of the welding on the chassis - with the 40x40 double box on the X bracing, that was considerably more welding than on a normal chassis.
With the good news that a small block in now going in the new car, I have been looking at how I am going to use the available weight and whilst not really adding to the structural integrity, the roll cage will be lengthened. Fortunately I had not started bending tube, so this time away I will redesign the cage and hopefully next time home I will start work on the cage. Going back in October 08, I meansioned about reworking the former, however on a few trial bends it showed that the former needed higher sides to control the high tensile pipe I am using - after making the steel side extentions to go on the cast iron former, I borrowed the oven to preheat the former to 200 deg C, welded on the steel side extensions with special rods then put the former back in the oven and switched it off to allow it cool down slowly to prevent cracking. This worked fine but my tube was not playing the game and was flexing the sides of the former, so on went Mk1 attempt to clamp the top of the former - this first attempt was not strong enough so a heavy duty Mk11 design was used and I am finally getting there! I was contemplating aquiring a US type bender which uses double formers to control the pipe and is a better way of doing things but it looks as though we are on a winner.........
I am now considering using roll cage tube for the down bars from cab to front of car + more use of 40x40 box in the "sump guard" which is now more of a bottom chassis, all of which will be using the additional available weight to strengthen the chassis.
5th February 2009 - Second batch of photos
When I completed my play in the garage this trip home, I have spent a total of 40 hrs working on the car - the status so far:
I have fabricated angled bracing to the sump guard to make a 'framed structure' that will also tie in the the front and rear axle radius bar mountings. In this photo, I have only completed one side of the chassis.
A closer view of the triangulation
Angled bracing has now been fabricated on both sides of the chassis and this is one of the 4 axle radius arm mountings that use a bolted socket at the top and welded bottom for easy replacement. We will be using the same type of sliding mount as I used for the panhard bars. All 4 axle radius arm mountings have been installed but triangular strengthening plates still require to be installed for the chassis mounted 'sockets'
5th February 2009
This is status after 27 hours - I will add more photos when I get chance of the progress to date
The front and back axle panhard bar chassis mountings use 40x 40 box and slider mountings. The chassis mountings are bolted into a fabricated socket on the chassis and welded to the sump guard frame on pads
This is one of the panhard bar chassis mounting sockets welded to the underside of the chassis - replacement of one of the vertical bars is easy with just easy welding onto the sump guard frame.
Another view of the panhard bar mounting and slider. Decision has now been made to employ the same system for the front and back axle chassis radius arm mountings.
View of the rear of the chassis showing panhard bar mounting and sump guard angle bracing to back bumper
4th February 2009
First of all a bit of a catch up! These are the photos of where I was up to after 22 hrs:
This is where I had finished, main sump guard frame welded in position and plating added for front bumper bracing, front nerf bar bracing and back bumper bracing.
View at front bumper bracing - plates cover the 'honeycombe' of box sections.
View of plating for back bumper bracing
I managed to get a lot more work done this time at home and when I get chance, I will add the photos.
2nd January 2009
Unfortunately no more photos at present and not much happened since early November due to very limited time spent at home. After the last set of photos I did spend a further 4 hours in the garage making a total of 22hours so far. I welded on strengthening plates for the front/rear bumper supports + front nerf bar supports, fitted the main sumpguard frame with four verticals and marked out the front and rear suspension bar chassis mounts ready for drilling.
3rd November 2008
This is the final set of photos I took during my last "play" at home. At this stage I have spent a total of 18 hours in the garage and a few too many of those were spent fitting the X bracing that was a tad challenging! But effectively I have a full flat chassis which still has to be fully welded. To minimise distortion, I will wait until the sump guard, rollcage and down bar from cage to front bumper cross bracing are installed. I have actually completed more of the build but someone had
grabbed the camera so you will have to wait until I am home again!
The completed X bracing, only tacked but it's in there!
I have now assembled the rear of the chassis which of course is welded onto the back bumper cross bracing. This view is looking at the top of the chassis. This is a fairly conventional layout because you still have cage mountings to consider but the back bumper support cross bracing means that we can use 2 x 40x40x2.5 box for the rear bumper bracing. It's true that this does not (usually!!) get as much hammer as the front bumper but we had to introduce some strengthening on the existing car which had some "issues" even using lighter bracing. The rear section of 80x40 box is flush with the main chassis to make plating the cab sides easier. The lower piece of box on the rear add on section of chassis is 60x40x3 box just to give a greater surface area for rear bumper mounting.
This is a view of the underside of the chassis - it's easier to turn over without bumpers on so I will add those later. The temporary bracing is still installed but this will be removed and the correct bracing installed when the roll cage and seat position is finalised. I have sorted out a new Kirkey series 53 full containment seat which was not cheap but is an excellent piece of kit and should help protect Si when he tries to demolish my work! There will be extra roll cage work to install this.
1st November 2008
First section of X tacked in position. 40x40x2.5 is used for the X. Bottom opposite diagonal will also be a single piece and others will cut to fit.
This is a cut out for the end of each X piece. 5 cuts a piece and 8 pieces to make. Actually I made an extra one cos I duffed up with the "handing" of one! Cutting and fiting the X took much more time that I expected but thats how it goes.
View at front bumper cross bracing. As before it ends up with 20mm above the main rail and wil also be the same below. There are no other bracings going in and the "nodes" at the ends of the front bumper cross bracing will take all the loading - the end of the X bracing support the "nodes" and give extra support area for the bumper bracing. If you look at the "honeycomb" of the connected boxes, this provides substantial strength for bumper bracing. Compare this to a "conventional" chassis with 70x70 box.
View at radiator cross bracing.
Top section of X tacked in place. It will be a while before I install the front bumper as its not needed until the end but each corner will have 3 bracings to the "nodes" a V to the front on the "nodes" and the bumper bracings to the end. All these will be made from 2 off 40x40x2.5 box.
Back bumper cross bracing (2off 60x40x3)
again plated and inserts used in the end
100mm of each box. With chassis the right
way up, the main rail is flush with the top of
the cross bracing.
Another view of the radiator cross bracing
showing the 20mm deep top and bottom
overhang on the chassis.
View of the front bumper cross bracing.
The 40 deep main rails look a bit "lost"
relative to the depth of the bracing but
the masterplan should be a bit clearer
when the X bracing is added. I have
said before that we have a similar front
bumper bracing on the existing car but
this is built around the main rails:
30th October 2008
First of many.... Remember that the main rails only run between the bumper cross bracings so they are just under 3m long (on a "normal" car with the main rails running between bumpers the main rails are more like 3.65m long).
The bumper bracings are the full chassis width, front is 3 off 40x40x 2.5 and rear is 2 off 60x40x 3. Also shown is the radiator cross bracing and you can just see how the overalpping is going to work at the front of the chassis.
Other cross member you can see is just a temporary one.
This is the front bumper bracing. As well as being plated, it has inserts in the ends of the box to stop crushing. The main rails are vertically central on the cross bracing.
This is a view of the radiator cross brace as it overlaps the main rails top and bottom
General Information
Following might be of help:
Materials: I have purchased all box and circular section steel in high tensile grade � only exception is 25x25x2.5 which the stockholder could not locate.
I stayed with mild steel for plate as it is more readily available . Note that as my steel stockholder is part of a nationwide group, they do not keep HT box in stock so it took a couple of days to deliver. Point is it probably came from the midlands/ north so it�s not a �southern� thing. Remember to always request a copy of the material certificate for your HT steel � if the stockholder can�t supply this don�t buy it. I�ve spoken to some who didn�t have a clue about HT steel and would have supplied MS steel telling me it was HT steel.
Steel costs (June 08):
3mm MS Plate: 2m2 �39.25+vat
5mm MS Plate: 2m2 �65.16 + vat
80x40x4 HT box based on 1off �67.01 + vat
60x40x3 HT box based on 3off each �42.50 + vat
40x40x2.5 HT Box based on 7 off each �25.85 + vat
25x25x2.5 MS Box based on 5 off each �10.60 + vat
48.3 dia x4 HT Circ based on 4 off each �40.00 + vat
42.4dia x 3.2 HT Circ based on 2 off each �36.00 + vat
Box and circular based on nominal length bars of 7.5m
Roll Cage
Remember that whilst you get the added benefit of the extra strength for the roll cage using the HT grade � you need a decent pipe bender!! Incidentally, there are a few variations on the actual size of bending dies � for my bender the 1 �� die was a tad too small and the 2� too big � I am grinding the 1 �� die for a good fit. A good fit is the best way to get minimum distortion of the pipe and it�s worth the time to do this correctly.
Fuel Tank
Rules require either minimum 1.5mm thick steel or minimum 3mm thick aluminium for fabricating the tank. Normally these are rectangular which means 12 main welded seams, we had a chat about this and I suggested we could try a tubular tank to reduce seams + also this is the better stronger shape to use in our sport � ie you don�t see many fuel tankers with rectangular tanks! In addition our rules state tank capacity of maximum 20.5 litres (approx 4.5 gallons).
Best material I located was 10� O/D �� thick (approx 6mm thk) seamless Aluminium Tube � we decided to use this even though it is thicker than required but to limit our tank capacity to 3 gallons. I managed to buy an offcut of this + some 6mm plate (both tube & plate are a weldable spec). Tank length will be about 12�. Overall tank will be more secure due to shape and thickness and will have 50% less welded seams than a rectangular tank.
Selection of Main Rails and Bracings
I�ve already said that the deal is to get at least equivalent strength for lower weight compared to a �conventional� car with 70 x70 main rails and framing is the way to go to achieve this. However, you have to look at the overall chassis because whilst you can do a good job to ensure the car is strong with regard to say bending from vertical loads or from compression, with a F1 Stock Car
you can never forget bumper bracings. With say a space frame chassis you will often see bumper bracings split and supported on the two �main� rails but it is not easy without adding weight to have the equivalent strength of a conventional car. Personally, I prefer to use the benefits of framing to achieve the overall strength but not to compromise the most important aspect of bumper bracing.
So I could save weight by using HT 70x70x3.6 box but what are the other alternatives? Well both 60x 60 and 80 x 40 have been used, dropping to
60 x 40 or 50 x 50 leads to a more space frame solution. So for info a comparison of what I considered:
Section weight(kg/m) Area(cm2) Section Mod (Vert/Horiz)(cm3)
70x70x3.6 HT 7.46 9.56 20 / 20
60x60x4 HT 6.97 8.96 15.7/ 15.7
80x40x4 HT 6.97 8.96 11.5 / 17.8
As the areas are vary similar, there not much in regarding compression loadings but obviously, the dimensions of the section has the most influence on the section modulus. However, even though 80x40x4 has a relatively low section modulus for vertical loading when used flat, this is easy to rectify using framing.
What made my mind up was not just looking at the numbers but how I could design the bracing. Whilst I am using some of the weight I have saved, using
2 pieces of 40x40x2.5HT box for main bracing means that the chassis internal
bracing can overlap the main rail with 20mm top and bottom of the rail. This appealed to me due to the strength this will give the whole structure + gives
good strong mounting areas for external bracing for bumpers, etc.
Finally, it�s �you pays your money takes your choice� and how this stands up on the track is what matters�������.
I�ve already covered tying in the down brace to the main rails to improve the vertical resistance to bending by making a 3D frame. Well providing this is done correctly it has a substantial effect � I checked by calculation and results as follows:
70x70x3.6HT box � down tube not installed or not tied to main rails
vertical Section Modulus = 20cm3 (from front
of chassis to cage)
80x40x40HT box � down tube structurally tied to main rails, section modulus
is as follows:
At bumper bracing: 34.7cm3
At Front Roll Cage Post: 142cm3
Now that�s the difference that structural bracing makes, up to 7X the resistance to bending for minimal weight used. For my calcs I have assume using 42.4 dia x 3.2 HT tube for the down tube, bracings will be 25x25x2.5 box (1.74kg/m) � I will be using about 3m so assuming you are going to use a down tube anyway, that�s 5.22kg to increase the strength 1.7X to 7X. Way to go!
Selection of Materials
So the idea is to save some weight in the chassis but have equal if not more strength than a �conventional� car with 70 x 70 main rails.
First thing is choice of materials � well theres no real choice as far as I am concerned, we need to take advantage of using high tensile steel. I remember in my early offshore days � if the design was say for Norwegian waters then a lower design temperature was used and so stronger steels were required. At that time the normal mild steel specification for box section was
BS 4360 43C, the high tensile steel developed was BS 4360 50C which was designed to give the same strength as 43C but at -20degC or so. Whilst the
Specifications have been superceded, the similar steels are still available - typical specs are:
Mild steel EN 10219:2006 Grade S235JRH
High Tensile steel EN 10219:2006 Grade S355J2H
Many steel stockholders only stock the mild steel but can get hold of the high tensile if you harass them enough. It�s not easy to give exact price differences as you pay less per item when you buy multiples + overall discounts, etc. However, this time I ended up with a few requotes because I was quoted the wrong specs, for example for one length (nom 7.5m) 80 x 40 x 4 box I was quoted �58.57 +vat for mild steel and �65.16 + vat for HT steel (as part of a decent size order). Always request copy certificates for all the steel and remember to segregate/ mark which is high tensile!
So what are the differences? Well the grade designation gives the real info,
The 235 and 355 refer to the minimum Ultimate Tensile Strength (UTS) of the steel, the units are actually N/mm2.
The UTS is the limit on the steel deforming elastically in tension � below this number, the steel will return to it�s original size, above this it�s permanently distorted. So effectively the UTS is a good comparison. If you look at a certificate it will give the actual test UTS for your steel and will normally be more than the grade required minimum strength.
So to demonstrate how the steel selection can affect us I have compared the max loading that can be applied in tension to 70mm x 70mm box of varying thickness & material
Section Cross Sectional Area Weight Material Max Tensile Load
mm2 kg/m kN
70x70x5 1300 10.1 MS (235) 305.5
70x70x3.6 1062 7.46 HT(355) 377.0
Now as this is a comparison don�t have to bother about the units but the bigger the number the better so if you use 3.6mm thk HT instead of 5mm thk
MS, you save about 2.5kg/m and in addition its 23% stronger in tension.
OK so we are more concerned about how this equates to compression, well it�s the same providing there is sufficient support as the rail gets longer (won�t go into it here but this is determined by the slenderness ratio). For us, the normal internal chassis bracing performs this job and the increased strength applies also to compression. I would not back off from using strengthening pads for the likes of bumper bracings but say for a normal chassis, you can save about 19kgs just on the two main rails. Incidentally, the slenderness ratio is also a good reason for using braced down bars from the cab height on the roll cage to front of chassis as the resulting frame ensures the chassis stays where it should and does and not bend like a banana (the affliction of my first car!).
Only other consideration is that technically if you were welding HT steel instead of MS steel to operate at -20 degrees C you would need to use different welding rods (ie winter racing in Iceland!!). However, for our temperatures, good general rods for carbon steel are fine (I buy mine from the BOC stockist and we checked and compared specifications).
So if you are with me so far you should be asking the question �but won�t this affect the resistance to bending?� Well for the same 70x70 comparison, the section modulus is reduced for the 3.6thk box due to there being less material but the steel strength has increased � it just comes out in favour of the HT steel.
Overall Chassis Design
So far all I�ve done is advising some of the main materials and some aspects of the design. Whilst I might be going through some of the items already covered in the �Structural Design� page, some of you may not have read or understood what I was wittering about!
There are obviously many aspects which have to be assessed in designing a chassis and I will attempt to take you though some of them and then explain why I am going a certain way.
Resistance to bending in the vertical plane is very good on the rear of the car due to the roll cage inc side plating, however, it�s a different story at the front of the car. From the roll cage forward, cars used to have to rely on a basically flat chassis with a bit of sump guard to help. It�s a good move to use a down tube /box from cab height on the roll cage to the front of the car but this needs to be structurally tied to the chassis to achieve the best benefits. The down tube can be in say 40mm box/ equivalent tube and ideally this should be braced to the chassis using a triangulated design with say 25mm box or similar small dia tube - this substantially increases the resistance to vertical bending at the front of the chassis and changes a flat chassis to a 3 dimensional frame. If the down tube/box is not tied to the chassis, then on it�s own it is only giving a marginal increase in strength as it will easily deform under load (but it at least will help with engine protection).
Triangulation if used correctly can reduce weight for the same strength and I aim to lighten up in some areas to allow additional weight in priority areas.
Probably most damage in our racing is to the front bumper and bracing hence bent front axle��. and majority of heavy chassis damage is in this same area. We�ve seen some changes in designs in recent years to overcome this and allow strong bracing without damaging the chassis. Over bracing of the front bumpers has always happened and get a good wack on the bumper end and instead of the bracing giving way, the main chassis rail is distorted then the rail gives way. I covered what we do on Si�s existing car in the �Structural Design� page with photos of the arrangement � this allows better bracing which means we can take a bigger hit and hopefully carry on racing. The same can happen on the rear bumper bracing but it is not as frequent as front end damage.
We�ve been pleased with the design used on the present car but I decided to go one step on and actually end the main rails at the front and rear bumper chassis cross bracings and take those bracings the full width of the car. This is used a fair bit on F2�s and what I have done is made the ends of the front bumper cross bracing �nodes� which take all the chassis loadings. These areas have to be strong so I took quite some time deciding the best approach
Weight Considerations
We are already on the �back foot� cos of our engine + LD axle. Unless you weigh your engine you have to go on estimates but based on what we are allowed in the rule book, we have to consider (info I have found):
Big/ Small Block full cast iron engine: GM big block 675 lbs (307kg)
GM small block 575 lbs (261kg)
From info I have found it looks like you can add about 10lbs (4.5kg) for an aftermarket block as they are strengthened around the cylinders but it also depends how much you bore it out to and light weight cranks, etc!
As above but with Ally heads: GM big block 606 lbs (275 kg)
GM small block 535 lbs (243kg)
All the above will not include starter motors, alternators, etc, and obviously the substantial engine mountings.
A couple of years back, we did weigh the engine but with mountings on + bell housing and starter motor and worked out our complete engine weight (GM big block with Ally heads) without mountings as 300kgs which compares with the above.
Overall we are carrying about 30kg more than an ally headed small block. Note that due to the larger size of big block heads, changing to ally heads saves a bit more weight compared to doing the same thing with small bock heads.
Although ally blocks are not allowed in the rules, I found that changing to ally blocks would save a further 59kg on a big block and 41kg on a small block at 2 to 3 times the cost for the block.
Regarding the back axle, I weighed our LD axle and complete with discs, callipers, hubs and brackets and it came to 144kg � I�m not sure if I kept a check on the Transit axles we used to use but I think the saving was about 20kg.
So for example, when we are racing on tar, we will be competing with cars
that can have about 50kgs more weight in their chassis. Which is why the likes of FWJ�s (to name but one!) tar car has plenty of additional bracing on the chassis.
So do we stay conventional with a 70mm x 70mm x 5mm chassis and compromise on relatively week bumper bracing and nerf bars or do we look at alternatives? Well I decided to digress from the norm and try and achieve 1350kg + fuel weight (car must be no less than 1350kg prior to and after racing without topping up the fuel tank).
For reference, Si�s existing car weighs about 1385kg but that�s with our mods to front and rear bumper bracing and a bit of extra weight used to achieve inside & rear weight requirements so if I don�t get carried away we should be fine.
So the plan is to build a new car based on using our existing big block engine and an LD back axle. To construct a strong car which will be close to the minimum weight limit is not an easy task and normally compromises have to be made which do affect the strength of the car. We are up against cars running competitive small blocks which allows much more weight to be used in the chassis to make the car stronger (at least it should! But some waste it on ballast). We could save some weight running a transit back axle but these are not as strong as the trusted LD and as we want a dual surface car I think it preferable to stick with the LD axle and work around all the extra weight.
At times it is easy to ignore weight concerns vs aesthetic appearance so the design has to be practical. For example, many people seem to prefer the long cab designs that are common these days but whatever weight you add on you have to compromise somewhere else. Whilst we too would prefer to use a longer cab design, it�s not practical due to addition weight, ie, and extra 12� length in the roll cage costs approximately 13kg due to extra cage tube, 3mm side plate and extra side tubes in the cage. Remember the rules require 3mm plating from front to rear of cage � not the same problem with roof plate as minimum size is required but it must be welded to cage on all four sides.
Presently, whilst I know the approximate dimensions of our cage, we have not decided on the final design although it will be governed to some extent by the new seat we intend to use.
With regard to the overall structural design of the car, it is possible to look outside the normal 70mm x 70mm box section chassis by designing a framed structure with equivalent (or greater) strength. I�ve previously given my views on down tubes which add no real structural integrity to the chassis due to inadequate bracing and often the same goes for the �engine protection� tube running from roll cage to the front of the chassis � for minimum additional weight this can be structurally tied to the chassis and truly be part of the frame.
With the exception of some details that I will sort as we go along, the design is complete and I will explain things as we go along hopefully with a few pics to help.
The first thing to say is that the chassis will not be conventional as the main rails do not run from bumper to bumper but instead between front and rear bumper support cross bracings and those cross bracings are full outside chassis width. This will be clearer when I have some pics when I have got that far, to date, I have cut all my chassis plates, cut and welded the front and rear cross braces � the front is made up from 3 off 40mm x 40mm x 2.5mm HT box to make 120mm deep x 40mm brace and the rear from 2off 60mm x 40mm x 3 HT box to make 80mm deep x 60mm brace. As these braces have to take main rail loading, to prevent them being crushed they are being plated at the ends + I�ve added internal stiffeners at the ends of each bracing. I�m just up to the point where I am welding on the plating for these bracings and have also cut the �main� rails and much of the chassis cross bracing.
The main rails are 80mm x 40mm x 4mm HT box section with 80mm side horizontal and the internal bracing (front X and radiator cross bracing) will be made from 40mm x 40mm x 2.5 HT box section, each cross bracing is made up of 2 pieces of box to make 80mm x 40mm which will overlap and be welded to the main rails. It will make more sense when you see the pics!
