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[qwr]

Hey guys,
I'm new to FSAE but not to turbocharging. I have done some extensive searching on the cbr 600f4i topic though and have pretty much come up dry.
Alot of teams that run turbos seem to lower the CP quite a bit. It is obvious why you would do this but, my question is. Since we are limited to 600cc displacement. Lowering CP would in advertantly cause displacement to increase over 600ccs.

For people running turbos. What PSI maxes out the duty cycle of the stock injectors? And are you experiencing overheating problems with turbo overspool?

I Just need to get the ball rolling a preposal before anything can be done. Just searhing out my options any input would me much appreciated
thanks alot
Jason

[qwr]

Hey guys,
I'm new to FSAE but not to turbocharging. I have done some extensive searching on the cbr 600f4i topic though and have pretty much come up dry.
Alot of teams that run turbos seem to lower the CP quite a bit. It is obvious why you would do this but, my question is. Since we are limited to 600cc displacement. Lowering CP would in advertantly cause displacement to increase over 600ccs.

For people running turbos. What PSI maxes out the duty cycle of the stock injectors? And are you experiencing overheating problems with turbo overspool?

I Just need to get the ball rolling a preposal before anything can be done. Just searhing out my options any input would me much appreciated
thanks alot
Jason

[Dan Deussen @ Weber Motor]

Hello Jason,

I assume you mean CR (compression ratio) when you write CP.

Lowering the CR by either shimming the head with a thicker gasket or milling the piston domes does not change the displacement.

Displacement is defined as the swept volume of the piston and that will not change unless you alter the bore or stroke.

[Pete M]

What Dan said.

Also, any 600 cc bike injectors should work fine as they're all good for at least 100 hp, which is about the most you can make with the restrictor in place.

Not sure what you mean by "turbo overspool". If you overspeed a turbo, either you'll blow the engine up due to overboost, or the CHRA in the turbo will come apart from the forces involved. You may overheat due to the increase in average power you're making if you don't size your cooling system appropriately, but this isn't really related to overspeeding the turbo.

[Orion ZyGarian]

I'd think you'd have to be doing something serious or seriously stupid to overspeed a turbo nowadays...wastegates are your friend! Use them!

Besides, it would be hard to overspin a turbo with 600cc's of displacement I would think.

Regardless I too wonder what the most common way of lowering the CR has been for turbo users; has anyone gone so far as to have lower comp pistons in addition to the thicker headgasket?

[Drew Price]

Remember that using a thicker head gasket, or using shims will alter or possibly eliminate the effectiveness of the quench area of the combustion chambers (depending on engine used, head design, etc). That is without adding any material of course.

I would be wary of machining down stock piston crowns into dished pistons, especially on some of the 600cc pistons I have see out of engines, there does not seem to me very much extra material, and unless your tuner really knows what they are doing, you may be fairly likely do be able to destroy stock pistons pretty easily. There are probably dished pistons available, and 4 custom pistons usually don't run over ~$1000, right?

I have seen claims of charge pressures in the 12-15psi range, there are past threads for specific cars that go a little more in depth about individual setups.

You could find what power level you can support with the stock injectors by just finding out what their max rated flow is (at what fuel pressure), and whether or not they are capable of sustained flow (some aren't, and I don't know anything about the CBR engines).

Best,
Drew

[qwr]

Over spool meaning. The inducer size is larger then the restrictor plate. therefore the turbo will spin faster to move the same volumetric amount of gas. Lowering the compression ratio keeping everything else stock would cause displacement to rise. but if you decreased the CR to a ideal turbo range lets say 9.5-10 the head would have to be significantly shaved to keep the same displacement.

Once again when i say over spool i don't mean OVER boost. Since the Restrictor plate is smaller then the inducer and the compressor wheel it will cause the turbo to spin faster due to the vacume created between the turbo and the restrictor plate.
Thanks again guys
Jason

[qwr]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">

Regardless I too wonder what the most common way of lowering the CR has been for turbo users; has anyone gone so far as to have lower comp pistons in addition to the thicker headgasket? </div></BLOCKQUOTE>

I have lowered CP with a thicker MLS Headgasket before. Does wonders but for Hi-psi. i would think twice, but my current project is going to be running 21psi on a MLS headgasket.

[Biggy72]

The displacement is only calculated on bore and stroke. It has nothing to do with the compression ratio, shape of the piston or anything else. So unless you bore an engine out, or put in a new stroked crank with shorter rods then the displacement will be the exact same.

[VFR750R]

XU, changing compression ratio does not change displacement. No change in head chamber, dish volume or head gasket thickness changes displacement. Displacement is defined by the stroke and bore only.

The restrictor will not force the turbo to speed up, nor will it have to to displace more volume of air, it will mearly displace the same volume of air at a lower pressure (same volume at the inducer, but lower MASS flow rate).

the turbo can overrev due to the restrictor, and that is a good reason to have a wastegate control that has more variables then just boost. This overspeed will increase the charge temperature as the Pressure ratio rises across the compressor, but it is only an issue after choke and does not directly cause engine overheating, but can cause damaging detonation. Simple alogrithims of wastegate position with RPM or reducing boost demand with RPM both do an adequete job although more advanced techniques can be more accurate and robust.