Everybody wants to have a streetable car, so they lower the compression and throw boost at it. question is would it be better to have 8.5:1 and more boost or 9.5 with less boost and make up the power difference with the compression. assuming all equal that you have enought fuel and not to much timing, intercooled, with a good tune. what you think. is 8:1 to low to make power when not in boost( ie..street cuising)
when the compression is lower is there less throttle response, not as much torq

 

You will make more hp with the lower CR/higher boost setup. Why? Well, unlike NA, if you have a larger combustion space (volume above the piston at TDC) the mass of the air fuel charge will be larger even though the displacement is the same. This is not true for an NA setup, which primarily fills the cylinders passively. And it assumes the flow from the blower is not maxed out.

Is a relatively low compression car a problem off boost? No. Besides, when you want to go fast, the boost is there.

Rich Krause

 

It basically comes down to compressing the air - you can do it via pistons or via some other means (blower, etc.) A centrifugal blower has a higher effeciency than a piston type compressor (your motor), so moving the same mass of air you will always be better off with lower compression/more blower. The issues occur on a street car when you have a compressor setup such that it only supplies it's peak flow at high rpm's. Then you have to make a compromise between engine compression and blower compression.


Chris

 

or add some nitrous to help u get off the line

sideways_into_"planning a dual power adder motor"_3rd

 

thanks guys thats what i wanted to know. rich... when you run the 224/236 114lsa cam do you find that the engine "hunts". i have heard you guys discussing this before but asked about it. will a good tune rid this problem?? i dont have any specs for the motor yet, as far as what im gonna have built, but im just curious

 

The cam runs pretty nicely without too much fiddling. Obviously, a blower car with a new cam needs WOT tuning of both the AF ratio and the timing. But very little is needed for part throttle drivability.

Rich Krause