Well another shop has failed to go through with doing my exhaust system so i guess i'll be getting the custom tubes inc piping done and wanted to see what everyones thoughts was for exhaust sizing for me because i am running 9:1 CR with the 2.6" pulley on the m45 and i just think that since im running lower CR than everyone elseon this board (i picked up a few tenths in the 1/4 mile by doing this somehow) that 2.5" exhaust would be a overkill on my power. I have 2.25" now with a HUGE amount of low end and a decent top end but we all know the charger dies on top end so what you guys think based on knowing my CR and what charger im running.
double-posting FTL.
fortune cookie say:
better a delay than a disaster.
BOOSTED wrote:who cares, i dont.
We care because it's stupid and annoying and a total waste of JBOs bandwidth.
I used to race cars, now I race myself.
5K PB: 24:50
10K PB: 54:26
Team Vision Racing (aka hypsy) wrote:BOOSTED wrote:who cares, i dont.
We care because it's stupid and annoying and a total waste of JBOs bandwidth.
then just delete it, simple.
here's the thing...changing your compression ratio has no effect on your volumetric efficiency. A engine with 12:1 and a engine with 8:1 will flow similar amounts of air at a given rpm, if everything else is identical.
here's another thing...you're not going to notice any loss in low end power by changing your exaust from 2.25 to 2.5. Especially on a fi motor.
The only thing that you will lose power (dramatically) is by changing the size of your header primaries, since going to too large of primaries would cause reversion...depending on your cam profile/cam timing. (typically on N/A)
Also you would never drop any time in the 1/4 by going with a lower compression. In the range of 1-17:1, you always will gain power by raising compression. The only way you would gain power over something with a higher compression, is if you were running higher boost levels.
2000 z24
1985 z28
http://www.cardomain.com/ride/825536
i actually did gain tenths though from going from the stock CR to 9:1, i went from 14.1 -13.9 and gained 2 mph
I highly doubt you'd make more power with a lower cr.
I would attribute any improvement to conditions or driving.
If everything remains constant, and you lowered your cr, you WILL lose power. It's like contradicting physics. the higher the cr, the more efficiently heat is transfered into pressure.
Are you positive it's 9:1? Are you still running the stock head gasket?
look at deisels. They have 18-22 cr's. they have a much lower bsfc than gasoline engines.
Anyways...go with 2.5". It's nowhere near overkill.
2000 z24
1985 z28
http://www.cardomain.com/ride/825536
1) compression has no effect on exhaust sizing
2) no way in HELL that a 2.5" would make less power on a FI or well built NA motor than a 2.25" exhaust
3) the only way to increase horsepower and decrease compression is to advance the timing more
4) lets just say ur at 10 psi (example) so 24.7 psia and about 110degrees farenheit going into ur motor then being combusted (that added temp increases pressure even more). this pressure gradient will be more than what ur boost gauge said (10psi) b/c of the added heat. so in ur CC u have 24.7+ psia and outside of it (header) u will have 14.7 psia. REVERSION WILL NEVER OCCUR UNDER THESE CONDITIONS, u have the piston pushing the mixture out as well as the pressure difference. BIG IS GOOD under these conditions. just dont go too big or u'll kill ur exhaust velocity.
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EFFICIENCY DETECTIVE
Fast cars. I respect them ALL. Brand elitism is for fanbois and benchracers
daily: 99 civic Si
deceased: 95 cavy '00 LD9 auto swap (vandalized)
