angela_itr

Ok I was all set to go for 9:1 compression ratio when I get my block built. But then I talked to someone who said the difference in offboost power between stock ITR compression and 9:1 would be really noticeable, and I'm not sure I want to change the characteristics of the car that much.

On the stock block with T3/4 turbo, it spooled up real quick and there was no lag at all, just instant fun.

So 1) will 9:1 CR feel really different to my stock setup while offboost? and 2) would something like 9.8:1 be better for what I'm after?

I assume the lower the CR, the safer the engine... but it'll be tuned by Mase so I don't think that will be a problem anyway. I thought if it was too low, I'd have to run more boost just to make up for the power lost due to the low CR.. or is that a myth?

crispydee

I went from a stock B16 at 8 psi to running 9:1 at 8 psi and there was no power loss, no extra lag the only difference is that the power is delivered smoother, which in my opinion is better anyway.

vtec.dc2

i noticed difference going from stock to 10:1... its not night/day, but different enough for me to notice response time.. so i'd think there would be noticable difference from stock to 9:1// why so low? are you planning to run tons of hp?

angela_itr

You don't notice the car is more sluggish until its on boost? Stock ITR compression is much higher than a B16 though, 10.6:1 seems a long way from 9:1 - surely I would feel this off boost?

Bump for more opinions

angela_itr

Well the block's being sleeved and built by Earl, so I hope to be looking at somewhere in the region of 350whp, maybe more I dunno. I guess that'll be down to what mase considers is safe.

But as driveability is so important to me, specially on UK roads which means lots of around-town driving rather than top end cruising, I wouldn't like it to feel sluggish off-boost.

CRVRX

I would ask Earl what he recomends....

If I was building a 350whp motor I would keep it around 10-1 and with the correct size turbo you will have very little lag, if any.
Once you start making 450+ you have a harder time tuning , at that point I drop them to 9-1 ish.

vtec.dc2

well, because turbo is part of my powerband and that includes low end, i don't normally accelerate without boost, unless its cruising but its still always going in/out.. its been some time, but i do remember quicker response while 10.6:1 compression. however, 10:1 is still doing the job.

while compression had some effect, most of my powerband is controlled by my turbo size.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by angela_itr &raquo;</TD></TR><TR><TD CLASS="quote">You don't notice the car is more sluggish until its on boost? Stock ITR compression is much higher than a B16 though, 10.6:1 seems a long way from 9:1 - surely I would feel this off boost?

Bump for more opinions </TD></TR></TABLE>

swlabhot

Angela, the CR on our blocks is 11:1. 10:6 US counterpart. I didn't really notice much 'lag' or sluggishness when going from 11 to 9.1 CR at all. I certainly would not recommend sacrificing that extra reliability or bigger margin for error by going any higher than 9.8 imo. The difference isn't really night and day. Besides, you might want 350hp now but who know how long your power urge would last? Once you block is built you're certainly not going to strip it to down the cr just so you can run higher boost for safety are you? Solid tune or not.....

my 2 pence..

tgreaves

On all my motor I keep the compression ratio between 9.5:1 and 10:1..

angela_itr

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by swlabhot &raquo;</TD></TR><TR><TD CLASS="quote">Angela, the CR on our blocks is 11:1. 10:6 US counterpart. I didn't really notice much 'lag' or sluggishness when going from 11 to 9.1 CR at all. I certainly would not recommend sacrificing that extra reliability or bigger margin for error by going any higher than 9.8 imo. The difference isn't really night and day. Besides, you might want 350hp now but who know how long your power urge would last? Once you block is built you're certainly not going to strip it to down the cr just so you can run higher boost for safety are you? Solid tune or not.....

my 2 pence..</TD></TR></TABLE>

Thanks I guess my dilemma is street driveability vs making big power. I enjoyed the stock setup so much because it was still so quick for blasting around town, which is where most of my driving is. But yeah, I guess I should plan for a bout of boost fever and 350whp suddenly not being enough

So 9.8:1 seems a good compromise to me - any more opinions?

freakie

Angela, whats available in terms of fuel?

I've always considered the t3/t4 abit too big for our cars.

angela_itr

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by freakie &raquo;</TD></TR><TR><TD CLASS="quote">Angela, whats available in terms of fuel?

I've always considered the t3/t4 abit too big for our cars. </TD></TR></TABLE>

97/98 RON fuel is readily available here in the UK.
Various people told me the t3/4 would be too big when I got the kit, but it works well IMO. I guess it takes a bit longer to spool up than a smaller turbo, but I think thats why the high ITR compression helped as it didn't seem like there was any lag. Hence my fretting about going for too low CR...

Seraph0

The CR difference seriously won't make much difference at all. All the testing I have seen has shown a negligable difference in spool time with up to a 2 point CR difference. But that's a whole different arguement not worth getting into.

I think your 9.8:1 plan is just right. Anything between 9.5 and 10.0. If you can get 97/98 octane (is RON the same as octane?) then you are very well setup for high CR + boost.

angela_itr

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MarkC &raquo;</TD></TR><TR><TD CLASS="quote">The CR difference seriously won't make much difference at all. All the testing I have seen has shown a negligable difference in spool time with up to a 2 point CR difference. But that's a whole different arguement not worth getting into.

I think your 9.8:1 plan is just right. Anything between 9.5 and 10.0. If you can get 97/98 octane (is RON the same as octane?) then you are very well setup for high CR + boost. </TD></TR></TABLE>

Thanks Am feeling more comfortable about it now, think I'm gonna go for 9.8:1. RON = Research Octane Number, so I guess it is the same as octane.

Finland

Just keep it stock, run 10 Psig tuned and relax. Once it breaks, then knock it down to 9, or 9.5 to 1.

angela_itr

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Boondock Saint &raquo;</TD></TR><TR><TD CLASS="quote">Just keep it stock, run 10 Psig tuned and relax. Once it breaks, then knock it down to 9, or 9.5 to 1.</TD></TR></TABLE>

It already broke, cracked a ringland hence the block is being built and I need to choose some pistons

Finland

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by angela_itr &raquo;</TD></TR><TR><TD CLASS="quote">It already broke, cracked a ringland hence the block is being built and I need to choose some pistons </TD></TR></TABLE>

post some pictures of yourself, you sound hot.

angela_itr

lol, being hot = broken pistons?

Finland

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by angela_itr &raquo;</TD></TR><TR><TD CLASS="quote">lol, being hot = broken pistons? </TD></TR></TABLE>

yes.

_entropy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by angela_itr &raquo;</TD></TR><TR><TD CLASS="quote">

It already broke, cracked a ringland hence the block is being built and I need to choose some pistons </TD></TR></TABLE>

Does that maybe tell you something?

Go 9:1. I prefer my 8.8:1 street motor than I did my 10:1 motor. More comfortable running 9:1 on pump gas. 97/98 RON is the same as our 93/94 octane. The "benefits" from higher compression arn't worth the tradeoffs for a street motor.

FOrSfEd

I personally would go with a 10.1 set up, but thats just me. 9.1 or even 9.5 is just to low for me. Yes margin of error is lowered but what is a lil more time tuning.

_entropy

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by FOrSfEd &raquo;</TD></TR><TR><TD CLASS="quote">I personally would go with a 10.1 set up, but thats just me. 9.1 or even 9.5 is just to low for me. Yes margin of error is lowered but what is a lil more time tuning.</TD></TR></TABLE>

Why? My 10:1 and 9:1 setups feel exactly the same in terms of boost response and off boost driving. There really isn't anything to be gained by high compression on the street.

00ITR #543

I've done both 10.5:1 and 9:1, fully built on boost. I personally like the 9:1 bored out to 84.5mm.. You get a lot more low end torque out of boost, good throttle response etc etc... Lag is negligable with big turbos. Boost response is good with low comp (used 60-1 and sc61). Didn't notice a drop off out of boost compared to high comp at all.

9:1

boostedblack99

Mase is here with me now up in Minnesota, and he says:

"run 9:1 like i told you, you wont notice any adverse effects between stock and 9:1."

angela_itr

Ok 9:1 it is - thanks