First off, this topic of optimal CR for turbo set-up may have been covered before in another thread but I was unable to come across it in searching. With that being said, here goes...

I am in the process of putting together my LS/V-T set-up and have stumbled across a deal on a set of Wiseco 81.5mm 8.3-8.6:1 CR pistons. Yes, I plan on taking my ls block to 81.5 mm already so no need to ask about that.

I am wondering about this CR because I had planned on running something between 9.0-9.5:1 but this deal has me wondering the pros and cons of running a 8.3-8.6:1 CR. The turbo will be a Garrett .60AR. My plans are to make 350-400whp. I am looking on insight of running this 8.3-8.6:1 CR, the pros and cons of it, and personal thoughts. Any and all input is helpful and appreciated. I understand that some goals and other things are unclear. If you need more info on aspects like that, please feel free to ask and I will gladly respond.

TIA

 

I don't think ~.5 compression point will make a world of difference.

Let's see what the gurus say

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by awdgsx96 &raquo;</TD></TR><TR><TD CLASS="quote">I don't think ~.5 compression point will make a world of difference.

Let's see what the gurus say </TD></TR></TABLE>

You are def right and I had the same thought. From 8.6:1 to 9.0:1 is not that much of a difference. On the other hand, 8.3:1 compared to 9.0:1 or 9.5:1 is a good bit of difference. Wiseco's site says the 8.6:1 comes with the head being decked at .030.

Right now, my b16 head is at the machine shop and has been resurfaced. I am unsure of how much it was taken "down" but I know I am going to ask when I go to pick it up next week.

I agree with you...Let's see what the gurus say

 

Garrett .60ar doesn't really tell much about your turbo. That's just the compressor housing ar size, what turbo is it? And what kind of fuel do you plan to run? How much boost? What will the primary use be?

 

Turbo's raise dynamic compression....8.5ish : 1 will be ****

 

I would go 9:1 or higher for more out of boost throttle response

 

Harder to tune high compression boost applications blah blah blah.

If he can get the deal he is talking about on the pistons, why not? ~.5 compression point will not make that much of a difference

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by awdgsx96 &raquo;</TD></TR><TR><TD CLASS="quote">Harder to tune high compression boost applications blah blah blah.

If he can get the deal he is talking about on the pistons, why not? ~.5 compression point will not make that much of a difference</TD></TR></TABLE>

I was on the same thinking page as you about the ~.5 CR not making that much of a difference. Still wanting to hear some more input.

Input from guys running this low of a compression would be awesome

 

You need to lay out what your goals are, and what the use of the car will primarily be in the end.

IMO, for a street/strip car, anything below 9.0 is really doggy out of boost, and your throttle response and "peppyness" down low will really suffer.

Don't skimp on something so integral to save a few bucks.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by a1320addict &raquo;</TD></TR><TR><TD CLASS="quote">You need to lay out what your goals are, and what the use of the car will primarily be in the end.

IMO, for a street/strip car, anything below 9.0 is really doggy out of boost, and your throttle response and "peppyness" down low will really suffer.

Don't skimp on something so integral to save a few bucks.</TD></TR></TABLE>

what you talking about a 8.8 piston can cost the same as a 9.0 lol
but anyway the 8.8CR is just so he can run a higher boost on pump gas if he wants to an even more boost on C14 or C16. also if you milled the head an/or block the lower CR is gonna get bumped up anyway

i would go with a 8.7CR or 8.5CR just because it gets hot here like 91-100+ outside and florida has like horrible humidity on top of that. my V8 pings on 87 because of heat but then again its a dodge ram with 8.94:1 CR

 

just beecause the pistons are 8.3-8.6 doesnt mean thats what yours will be.


that # is quoted for an ls motor, so right off the bat using a vtec head with different head cc volumes will raise the compression around .5 point. combine that with a head resurface and deck mill in the motor build and you are right around 9-9.5:1 which is optimal.

i used to use the low comp wisecos in my 81 and 81.5mm lsvtec builds over the past few years and the compression works itself out to be around 9:1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BlackT5 &raquo;</TD></TR><TR><TD CLASS="quote">I would go 9:1 or higher for more out of boost throttle response</TD></TR></TABLE>

+1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BlackT5 &raquo;</TD></TR><TR><TD CLASS="quote">I would go 9:1 or higher for more out of boost throttle response</TD></TR></TABLE>

You aren't going to notice .5 in compression, that's like 5 whp.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">just beecause the pistons are 8.3-8.6 doesnt mean thats what yours will be.


that # is quoted for an ls motor, so right off the bat using a vtec head with different head cc volumes will raise the compression around .5 point. combine that with a head resurface and deck mill in the motor build and you are right around 9-9.5:1 which is optimal.

i used to use the low comp wisecos in my 81 and 81.5mm lsvtec builds over the past few years and the compression works itself out to be around 9:1 </TD></TR></TABLE>

are you talking to me ??? cause the reason i want compression ratios in the 8's is because i have a lot of stuff done an being done such as getting the head ( stock LS ) combustion chambers reshaped to 47cc or 50cc if possible through endyne on top of the the combustion chambers are being reshaped the proper size for a 83mm bore something most guys often dont do

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by a1320addict &raquo;</TD></TR><TR><TD CLASS="quote">IMO, for a street/strip car, anything below 9.0 is really doggy out of boost, and your throttle response and "peppyness" down low will really suffer.

Don't skimp on something so integral to save a few bucks.</TD></TR></TABLE>

Thats why you don't run a big turbo at low boost. Get one the right size and crank the boost, then you won't have to worry about 'off boost' power - you'll have boost quicker anyways.

10:1 for 9psi...8:1 for 29psi

 

i'm going to be running 10:1-11:1 CR on my next LS-T. i'm done with that low comp stuff. i'll always be running racegas so i'm not worried abt it. and just so everyone knows. every pt of CR is 10HP to the wheels

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by a1320addict &raquo;</TD></TR><TR><TD CLASS="quote">You need to lay out what your goals are, and what the use of the car will primarily be in the end.

IMO, for a street/strip car, anything below 9.0 is really doggy out of boost, and your throttle response and "peppyness" down low will really suffer.

Don't skimp on something so integral to save a few bucks.</TD></TR></TABLE>

When the build is complete, the car will be a strip car...1/8th mile. My goal is to make 350-400whp on stock sleeves (I know I will be able to do that) @ 81.5mm.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by blackeg &raquo;</TD></TR><TR><TD CLASS="quote">just beecause the pistons are 8.3-8.6 doesnt mean thats what yours will be.


that # is quoted for an ls motor, so right off the bat using a vtec head with different head cc volumes will raise the compression around .5 point. combine that with a head resurface and deck mill in the motor build and you are right around 9-9.5:1 which is optimal.

i used to use the low comp wisecos in my 81 and 81.5mm lsvtec builds over the past few years and the compression works itself out to be around 9:1 </TD></TR></TABLE>

Humm interesting. Like I said earlier, I am not sure how much was taken off the head for the resurface but I will be able to provide that information next week when I get it back. I was not thinking about it being quoted for a LS motor so with the b16 head the CR being raised ~.5 mm + whatever difference the resurface will make.

So far, I def appreciate the input, thoughts, and feedback

Also, just to throw a quick question in the mix...Which size wastegate would be best: 38 or 44mm?

Thanks again guys!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by bigbadboy &raquo;</TD></TR><TR><TD CLASS="quote">i'm going to be running 10:1-11:1 CR on my next LS-T. i'm done with that low comp stuff. i'll always be running racegas so i'm not worried abt it. and just so everyone knows. every pt of CR is 10HP to the wheels</TD></TR></TABLE>

I had a 10.8:1 turbo B16 and now I have a 9.0:1 turbo B16 and to be honest, my lower compression one feels a hell of a lot better. Out of boost feels the same...

High compression and boost is stupid, if you understood how a turbo works you would realize it effectively raises your CR anyway.