supercharging question about compression

Drowzysleeper · Post by **Drowzysleeper** » Fri Apr 20, 2007 2:43 am

it has been a long week. and this post has helped me out and maybe answered some other peoples questions. i should be better of boosting that a vtec motor considering i have some forged internals. well thanks to all that chimed in help me decide to go ahead with the turbo kit.

nitrousjunky · Post by **nitrousjunky** » Wed Apr 25, 2007 12:10 am

i thought it was cool last year when i dynod my ls with a 75 shot of nitrous it made a lot of torque for a honda...

this is complety un tuned
n/a 152hp & 126ft-lb air/fuel 12.9
nitrous 200hp & 191ft-lb air/fuel 11.2

Drowzysleeper · Post by **Drowzysleeper** » Wed Apr 25, 2007 5:23 pm

thats pretty good how much was your nos setup? you know the guy i bought my motor from i think. his name is joe from troy.

nitrousjunky · Post by **nitrousjunky** » Thu Apr 26, 2007 12:29 pm

yes i do, i have the intake manifold that was on that motor.

Drowzysleeper · Post by **Drowzysleeper** » Thu Apr 26, 2007 5:27 pm

do you know if there was anything wrong with it and what it had done? i really dont know about the compression ratio i was just told that it was 10.5 to 1

nitrousjunky · Post by **nitrousjunky** » Fri Apr 27, 2007 2:26 am

no idea.

big pipe · Post by **big pipe** » Fri Apr 27, 2007 7:31 am

i would think that (imight be way off here but) if you take two identical engines. one is at 11;1 cr, the other is at 8;1 compresssion. on the motor there would only be around a 5 percent diff, high comp. make 140, low comp making 125. the differance in boost you could feed it would WAY more than make up for it...example the high comp.. motor making 140 would only hold 8 psi putting it around 200, on the other hand the low comp. engine accepting 13 psi would make 250hp.... offf boost performance would be slightly less (stock engine) but when the boost is added i would give up 10 motor hp for 40 more hp when the turbo spools up... but like i said, i could be way off here

Drowzysleeper · Post by **Drowzysleeper** » Sat Apr 28, 2007 2:39 pm

thats interesting. but i could always build me a turbo kit put it on and then start building my spare for boost.

shinigami · Post by **shinigami** » Sat Apr 28, 2007 5:57 pm

See the one thing you guys aren't factoring into the high vs low comp battle is exhaust gas speed. the higher the compression the faster the exhaust gas is going to exit the exhaust ports, thus causing quicker turbo spool. This is one of the major reasons that all the new turbo cars are seeing boost between 1500-2000 rpms. I'm far to tired and hungover to whip out the mathmatical calculations this morning so we'll just leave it at this:

Higher compression is harder to tune, will be more likely to predetonate, produces more hp and torque, causes your turbo to spool quicker, and thus-forth gives you a superior power band. With 93 octane, proper cooling (fmic/rad/oil) and proper tuning you can run 10.0:1 comp and up to 25lbs of boost assuming that your thermal effeciency is around 78%, and that your static intake temp is somewhere between 60 and 95 degrees.

Low compression, is easier to tune due to margin of error allocated, produces less hp and torque, causes longer turbo lag, but is less likely to blow from inferior tuning. at 8.5:1 compression you can run something around 30lbs on 93 octane (again assuming 78% thermal effeciency, proper cooling, and a static intake temp between 60-95 degrees)

If you have anymore questions i'd be more than obliged to answer them.

nitrousjunky · Post by **nitrousjunky** » Sat Apr 28, 2007 9:22 pm

i have been wanting to turbo my car for a while now at 11 to 1 compression on 8lb's.