Project 480: Engine: 15cc is a bridge too fare

The next part of the engine build I’m going to cover is more to do with the rules then to do with Horse Power, or at least the interaction between the two.

Within the Classic Thunder championship, like with most motorsports championships, cars are divided up into groups called classes. The classes are grouped by engine capacity, and then there are some multipliers added for certain setups.

The classes are divided out like this:
Class B – 2,901cc to 3,600cc
Class C – 2,151cc to 2,900cc
Class D – 1,701cc to 2,150cc
Class E – 1,401cc to 1,700cc
Class F – Up to 1,400cc

The following rules also apply cumulatively;
• Forced induction is subject to an equivalency factor of 1.7
• Rotary engines are subject to an equivalency factor of 1.8
• Cars on List 1a or 1b tyres move down one class
• Cars running sequential gearboxes move up one class
• Cars with any original suspension mounts not visible (see section 5.8) move up one class
• Cars using engine block AND cylinder head AND transmission casings AND number of forward gears AND original suspension pickup points AND glass windscreen AND has the engine in the original location (+-15mm) AND, if using forced induction, uses the original inlet AND exhaust manifolds AND original capacity supercharger/turbocharger unit as the original car move down one class

Let’s see how the 480 fits in to this. The engine displacement is 1721cc, but as the Volvo is turbocharged we need to times the CCs by 1.7. So this brings it up to 2925.7, this means it just scrapes into class B. This is not a good place to be for two reasons, first we are at the very bottom of the class and secondly the target BHP for that class is 400bhp, well out of range of the little 480.

Target BHP for the classes:
Class D – 230BHP
Class C – 300BHP
Class B – 400BHP

Target Class

In fact the target class we want is Class D. To do this we need to reduce the CC of the engine and run with semi-slick road tyres to drop us down a further class. Using semi-slick tyres wont drop my lap times down that much, and in relation to driving in a class that is running 70bhp more then me it’s going to be a life saver.

Reduction

We have two options here, drop the CC down or increase the CCs to the max in that class.

I don’t think boring out the engine to up it’s CC is necessarily a good idea. It will mean that the weight limit will be increased (as weight is linked to CC), and it means that everything else in the engine will have to be upgraded.

The next option is to reduce the engine down by 15.15cc. This would put it at the very top of the class C. The first way I thought of doing this, was a little unconventional, and that is to skim the cylinder head and piston crowns down by 0.73mm. This would then reduce the chamber down by 15.15cc. But after checking with the CTCRC, this would not give a reduced CC as the calculate it. They calculate CC by the Bore and Crank Stroke – which to honest is how everyone else does it. So, as I’m not reducing them, it would still remain at 1721cc, even though if you filled the chamber with water it would be 15.15cc less.

This leaves me with two options reduce the Stroke or reduce the Bore:

Reducing Stroke

Reduce the stroke of the crank, this can be done it two ways, get a custom crank made, which will be very pricy indeed. Or reground the crank so that with the use of oversized bigend bears the conrod would be moved down thus reducing the stroke. I would then have to skim the cylinder head to match things up. After speaking with one racing shop, the reduction I need to make of 0.73mm would be to much to make as the largest bigend bearings available is 0.75mm and would not give enough room for balancing. This is a real shame as it’s going to be the cheapest option and I would have the added advantage of having a balanced crank too. I’m still very hopeful about this option and when I get a chance I’m going to call round and see if I can find somewhere else that might be able to do it.

Reducing Bore

To reduce the bore things get very messy. First job is to “sleeve” the cylinder block. This involves drilling the cylinders out to a size larger then you need, then adding in a cylinder of metal (sleeve) in under pressure. When that is all done we bore out the cylinder out to the smaller size you require. We then need to reduce the size of the pistons to fit, this is is done by make brand new costume pistons based on the design of the piston that was in there before. We then also need to match the head to fit the new piston and cylinder block. It’s a lot of work and more then my entire budget for the build. This is pretty much ruled out.

Other Options?

There is a rule we could use to are benefit here but what it gives with one had it takes with the other. “Cars using engine block AND cylinder head AND transmission casings AND number of forward gears AND original suspension pickup points AND glass windscreen AND has the engine in the original location (+-15mm) AND, if using forced induction, uses the original inlet AND exhaust manifolds AND original capacity supercharger/turbocharger unit as the original car move down one class” This means that if I run with mainly modified stock parts rather then fully custom, then I can drop down a class and not need to reduce the engine size. The problem with this is that you have to run with the stock turbo and the one fitted to the 480 was small, a Garrett T2. This means that the turbo becomes the main blocker in getting extra power out of the engine. Can I get 230+bhp out of a Garrett T2? I’m not sure.

Research tells me that the AFR (Air Flow Rate) on it will cures me problems, but I have seen documentation saying that it can be good for up to 260bhp. I can grind out the inlet and outlet as well as use an external waste gate. If I use an oversized external waste gate and create almost it’s own separate exhaust for it, then I could use this to stop the turbo become an air flow blocker but, but as the RPM and air flow increases the turbo will become less and less effective.

The stats that I have found on the turbo are that it’s a TB0262, and the details on the internals are:

Compressor			Turbine
Inducer Wheel Dia(mm)	Exd Whl Dia(mm)	Trim	Ind Whl Dia(mm)	Exd Whl Dia(mm)	Trim
47.12	35.48	57	37.24	48.01	66

This is just internet research so I would need to take the turbo off the car and check to be sure it’s correct. I had a look at the current Garrett specs and an equivalent turbo GT2056, an it’s giving me a BHP range of 140bhp – 260bhp. So might be ok, but that is a modern turbo.

Capacity referred to in the turbo reg is the internal capacity of the turbo, I’m not sure how you work that out, but if I can work that out I can replace the current turbo with another of the same capacity, but hopefully find a more efficient turbo.

Conclusion

This is a prime example of the balancing act you have to do between: Budget, Competitiveness, Rules, Time and Ability. This balancing act is something I’ll be wrestling with throughout the build.

I need to do more research in to regrinding the crank and modifying the stock components. If anyone has any ideas or solutions to this please add them to the comments below.