Bseriescivic5

Ok guys I really want to know who is right in this topic:

Booosh wrote:
after seeing this,

why run 9:1 cr when you could run say 9:5.1 or 9:8.1 ...still lowering compression, but

you can make the same power as 9:1 w/ lower boost on a higher compression motor.

just for an example: (not real)

9:1 @18psi 400whp
9:8.1 @18psi 450whp...

make sense or am i missing something...

so on the 9:8.1 you could run 16psi...having it spool faster...and still get to your 400whp mark

so what im asking is...

WHY DOES EVERYONE GO 9:1 , how come you RARELY see a higher cr motor built ?


You're missing something because the power difference isn't going to be nearly as massive as you're tryin to illustrate. The difference between 9.0:1 and 9.8:1 might be made up with a half of a pound of extra boost, not 2 or more psi. The 9.0:1 motor provides you with a much larger safety net when you're running pump gas, so it makes sense to run a slightly lower compresion ratio for safety. Trying to make power using the engine's compression is silly when you can do it with the turbocharger and have a motor that is less likely to detonate on pump gas at any given power level.

Bseriescivic5

bump need answer

JDogg

do a search, this has been beaten to death, pump gas = as low as you can get the compression, race gas... compression needs to be chosen with your specific power goals/turbo setup in mind.

B18 CYA

Lower compression leaves you more room for error. A car on pump gas with 9:1 pistons, running 18lbs of boost making 400whp will have a lesser chance to detonate than a car with 9.8:1 running the same amount of boost and almost the same power level.

Bseriescivic5

See i did search it, and im not sure i agree with it. I know you have more room for error with low compression, but i thought u could make alot more power with a highercompression motor on boost

JDMTurboEG6

basically a motor thats running 9:1 comp is generally going to be more reliable and easier on the wallet than a motor running 9.8:1 comp

Bseriescivic5

well mine is running 10:6:1.....hehehe and its gonna see 15+psi

0BoostedJeff

im running 10.2:1 compression and plan on running 35psi or more in the future

Its all in the tuning.

Bseriescivic5

I agree, my setup will be tuned by jeff evans. However my car is a street car so thats the only thing im worried about (daily driver)

nasteboyii

Your a silly boy

Basically these guys have hit it right on the head, SAFER WINDOW, in other words lower compression has more chance for error in tuning or fuel quality, were higher compression does not, along with the higher compression engine can get away with a smaller turbo like a .48 .63 like someone we know did,

TUNING TUNING TUNING is always the key
and ur not going to run 400 hp every day on the street not to mention u not goin to make the power on PUMP gas

d

Bseriescivic5

I understand. so basically long story short, a low compression motor needs to be supplemented by lots of air from the turbo, whereas a high compression motor doesnt need as much boost to make the same power at a given boost level

adseguy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bseriescivic5 &raquo;</TD></TR><TR><TD CLASS="quote">I understand. so basically long story short, a low compression motor needs to be supplemented by lots of air from the turbo, whereas a high compression motor doesnt need as much boost to make the same power at a given boost level</TD></TR></TABLE>

Yep, because the high compression engine is more efficient then the lower compession. Jeff Evans did a dyno comparrison of an engine with 9.0:1 compression then changed it to a 10.0:1 he saw about (I think if I remember correctly) 10-20whp difference on a 300whp motor. It's not that much of a gain, you'd be better off making the head flow better at high RPMs ie:cams, severe porting, and all that good stuff.

I would have thought that race cars use high compression (at least in the honda worls), but I just learned that Tony1's 9second car is using 9.0:1......just food for thought .

Bseriescivic5

yeah makes sense. But on a side note, my builder (nasteboyii) decided to go with 10.6:1 primarilly becuase we wernt sure when it would be ready for the turbokit and its going to be a daily driver, so even without boost it will still have good power to get around. And again when it does see boost it will be tuned properly, and be making about 275wheel on the street daily driven.

nasteboyii

and because i have NO FEAR

this guy cant stay outta the pedal, so a small turbo on small boost will be plenty

d

Bseriescivic5

Lol thats not true............I let out when im ahead......hehehehe