Rotec Cycles

Sponsor of BRISCA F1 Stockcar # 92

F1 Engines

Many people are interested in the engines used in F1 Stockcars so I thought I would add a bit of info to maybe help peoples understanding. I will base this info on "Chevy" engines but as I will explain, many of the engines nowadays do not use any original GM parts. In no way is this a definative review, just a bit of information which may lead to a bit more understanding..... 

A summary of "standard" Chevy engines which have commonly been used are below. As standard, blocks are designed to be over bored to allow rebores due to wear - for racing this is often used just to increase capacity and torque/power.

Small Block (physically smaller block than the Big Block so size and weight savings. Engines listed are based on GM blocks with changes to bore/stroke).

350 cu in: 4.00" bore x 3.48" stroke. Base standard engine from GM

355 cu in: 4.03" bore (30 thou over standard) x 3.48" stroke

360 cu in: 4.06 bore (60 thou over standard) x 3.48" stroke

383 cu in: 4.03" bore (30 thou over standard) x 3.75" stroke - commonly classed as a "stroker" engine

388 cu in: 4.06" bore (60 thou over standard) x 3.75" stroke

 

400 cu in: 4.125" bore x 3.75" stroke. Base standard engine from GM

406 cu in: 4.155" bore (30 thou over standard) x 3.75" stroke

413 cu in: 4.185" bore (60 thou over standard) x 3.75" stroke

Stroke possible up to 4" so can achieve up to 440 cu in

 

Big Block, engines listed are based on GM blocks with changes to bore/stroke: 

396 cu in: 4.094" bore x 3.76" stroke. Base standard engine from GM

402 cu in: 4.124" bore (30 thou over) x 3.76" stroke

408 cu in: 4.154" bore ( 60 thou over) x 3.76" stroke

427 cu in: 4.25" bore x 3.76" stroke. Base standard engine from GM

433 cu in: 4.28" bore (30 thou over standard) x 3.76" stroke

439 cu in: 4.31" bore (60 thou over standard) x 3.76" stroke

 

454 cu in: 4.25" bore x 4" stroke. Base standard engine from GM

482 cu in: 4.25" bore x 4.25" stroke (stroker crank)

460 cu in: 4.28" bore (30 thou over standard) x 4" stroke

489 cu in :4.28" bore (30 thou over std) x 4.25" stroke (stroker crank)

467 cu in: 4.31" bore (60 thou over standard) x 4" stroke

496 cu in: 4.31" bore (60 thou over standard) x 4.25" stroke (stroker crank)

Stroke possible up to 4.5" and 100 thou oversize bore so can go to 535 cu in.

 

502 cu in: 4.468" bore x 4" stroke. Base standard engine from GM

533 cu in: 4.468" bore x 4.25 stroke (stroker crank)

509 cu in: 4.5" bore (30 thou over standard) x 4" stoke

540 cu in: 4.5" bore (30 thou over standard) x 4.25" stroke (stroker crank)

516 cu in: 4.53" bore (60 thou over standard) x 4" stroke

548 cu in: 4.53" bore (60 thou over standard) x 4.25" stroke (stroker crank) 

Stroke possible up to 4.5" and 130 thou oversize bore

I have just used the standard rebore sizes of +30 thou and +60 thou + 4.25" stroker cranks to give an idea of typical engine sizes. Depending on block thickness it may be possible to bore out blocks to more than 60 thou but the majority of standard mass produced blocks usually make this a risky business. Unless you really know what you are taking on, for racing purposes it is probably bettter to limit engines to those shown and use aftermarket blocks to go for the larger bores and strokes.

After Market Engines

For some time, companies like Dart and World Products have been building blocks for Chevy's and Fords to allow increase bores and strokes. The tallest deck Dart big block can be bored to 4.7" use a 5.5" stroke - Dart recommend a maximum of 750cu in which is over 12 litres......... A tad big for our purposes but it shows what can be achieved. It should also be remembered that as after market blocks from Dart and World Products allow for thicker cylinder walls they weigh more than GM standard blocks and certainly going to the tall deck options for the big engine sizes can be a significant increase. 

The equivalent in small blocks can be bored to 4.185" and use a 4.125" stroke to give a 454cu in small block, which with weight savings over a big block can be very useful for our racing.

Engine Torque/Power Output

There are various reasons why engines have progressed to present status but limitations on size of engines due to limits of blocks (max bore and stroke possible),  availability of good blocks, limitations on power output due to strength of components, etc.....

Drivers are looking for good torque output from their engine (power is derived from torque) and for our tracks a flat torque/speed curve is the way to go.

For example, torque can be increased by:

- Increasing engine capacity (bore and/or stoke)

- Increasing compression ratio

- Increasing max revs

- More agressive cam

- Improving air flow to and exhaust flow from the engine

...........etc

Whichever way you go, increase in torque comes at a cost if reliability is required as there are greater loads on the components. Whilst GM used uprated components to increase power outputs, the after market industry has gradually built up to the point that you can select non GM parts to build "Chevy" engines.

As you increase the power from an engine, it's build quality has to be increased if you want reliablity. Following is a basic idea of the power outputs from "standard" engines - bare in mind there were many different versions of engines ie "truck" or "high performance" which obviously has a big bearing on the power output of a particular engine: 

"Standard" 350 cu inch Chevy: 200 to 300 bhp, GM performance 300 to 350 bhp

"Standard" 454 cu inch Chevy: 400bhp, GM Performance 425 bhp

From above you can see that there is a bit of work to increase the power outputs to those used in F1 engines although a decent 454 on shale might give a white top driver a chance, he would be swamped on tar. Although 2 bolt main engines (main beaings fixed with 2 bolts) have been used, majority of engines are based on 4 bolt main blocks. Both small and big blocks had options of the 4 bolt mains, some for truck built engines and some for performance engines, I've seen it quoted that its OK to use 2 bolt main small blocks upto 400bhp and I know some 2 bolt big blocks have been used above 500 bhp but personally for our sort of racing I would stick with 4 bolt main blocks.

If you are going to increase the torque/power of an engine, then you have to consider the strength of the components being used. In general, the safe way to go for the first step is for all the rotating elements to be forged ( crank, rods and pistons) and the strength of bolting used needs to improved. There are limits to how much a block can be bored to keep sufficient wall thickness. Components such as rods (even forged ones) may have power limitations and their design need to change (ie from I to H beam designs for powers over 500 bhp and obviously, these changes come at a cost. The experience required to build reliable competative engines is also considerable and the complexity increases as the torque/power output increases - back in 1973 I used standard road engines and blew them up fairly frequently, with the power outputs of todays engines I wouldn't stand a chance at building a reliable engine unless I invested in all the tools and made a clean room to make a start + spent a lot of money for specialised machining work!!

As we are fixed with max 101 octane fuel (can readily buy 99 octane at most garages) we are limited on compression ratio we can use - remember that many racers in the USA can use race fuel and their 13.5:1 compression ratios are no use to us! I understand we can nudge upto max 11:1 but probably safer at say 10.7:1. So you can't just compare BHP you need to know the compression ratio of the engine - it costs a lot in power and dosh to reduce the CR so an enginge that looks good in American mags might not prove to be much use to us. One of the other areas that needs a good looking at is the valve gear as you need your small block to run at higher revs to make the power and this is another area that can't be skimped on other wise you will have problems with valve bounce or valves hitting pistions........

Engine specialists would give definative information on what is now possible but based on product information I have found, you can build small blocks up to 454 cu in (now used by many drivers) and big blocks in the region of 620 cu in. This is all made possible by the development of aftermarket blocks that allow larger bore and strokes and overall increase in block strength.

Whilst there are no limitations on engine size or power for a F1 engine, the small tracks and tyre regulations do limit useful torque/power that can be used and therefore do allow a more equal playing field as spending money is not necessarily an advantage. We previously used an original GM 454 big block which was a "special hi performance" build with forged parts as standard - this had been upgraded and produced about 530hp (for comparison purposes only) and has a very flat torque curve. Changes from standard included Dart Aluminium Heads, Dart Intake Manifold, Racing Pistons, Camshaft with roller followers (allows more agressive cam to be used), MSD distributor and ignition system, Aluminium high flow Water Pump, Baffles Sump. We had a rev limit of 6000 rpm and a relatively low compression ratio. 

So if we had the choice and money, what would be the way to go? Well since after market blocks have been available for small blocks, engine sizes have gradually been increasing and as stated previously you can now get a 454 cu in small block which is substantially lighter than the big block but can be developed to produce reliable power over 600bhp. Originally it seemed that with the higher reving small blocks (needed to rev higher to make the power), more frequent engine rebuilds were required (compared to a big block where we have been advised to rebuild every 50 or so meetings). However, with the small block development where it is at present, it seems that they too can now easily go to 50 meetings before a rebuild and have sufficient power/torque so that gearing can be selected to cover all tracks and engine revs can be varied instead. Not only that but the weight saving can be used to enable more steel to be used in the chassis construction to increase the overall chassis strength.

 I won't go into the full details here but the the equation for bhp is as follows:

Bhp= Torque(ft lbs) x Engine revs (rpm)

                      5252(constant)

 

When we talk about flat torque curves, this is based on the dyno results when the engine was tested and unlike the peeky torque curve for the high reving GP F1 engines which need gear changes to keep within the rev band to give high torque, we are looking for a flat torque curve to get traction all the way through our rev range. Incidentally just think how fast you could be hit into the fence if you had to have your foot on the clutch to change down going into a corner.........does'nt bear thinking about!

Following is from the dyno report for our original 454 big block engine after it's last rebuild in January 2007, remember you use the equation above to work out the bhp - the dyno measures torque:

Engine speed (rpm)      Torque (ft lbs)         Power (bhp)

          3500                        496.0                       330.5

          4000                        483.2                       368.0

          4500                        507.9                       435.1

          5000                        504.0                       479.8 

          5500                        495.7                       519.1

          5900                        478.8                       537.8 (max bhp)

          6000                        462.2                       528.1

 

Now thats what you call a flat torque curve - between 3500 rpm and 6000 rpm the maximum variation is 45.7 ft lbs.

When people talk about a driver having a more powerful engine it may true but the deciding factor is still how that torque can be transferred to the track. Things like using a higher compression ratio with cam to suit can often be distinguished by how the engine sounds at tick over but when some one wants to know why our car was faster than one with a mega small block that produces 650 ft lbs torque (thats maybe 730 bhp!!!) it is still ultimately down to car set up not ultimate power - at least it is with the tyres we can use at present.

When I get the dyno results for our new 434 cu in small block and 496 cu in big block, I will update this section 

               

 

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