maXmood

iTrader: (16)

i'm going internals now and would like ur feedback on internals with FI application. (searched, can't find any direct info).

to brief you, i'm running vortech sc, with 2.87" pulley, and almost all boltons except for headers. car produced 304whp on DJ (very low considering what the guys usually get). now i'm going internals because alot of oil blowby and smoke, seems like a damaged piston ring. i'm having the engine opened in few days to see what was the cause of this, and what damage did it cause.

now i have the option of going with 8.8:1 or 11:1 pistons. which one would be better for FI and specifically superchargers?

bear in mind i'm 5AT.

thanks
max

350Zdj

iTrader: (3)

11:1 is high comp. too hi for FI applications. It's only good for N/A builds.

Forged Low comp is the way to go.

Cux350z

iTrader: (162)

but dont go as low as 8.8......since youre running a SC your peak boost will be a lot less and a 8.8cr will make your low end really suffer.

snobes

try something a bit higher than 8.8 like 9.0-9.5 (if its an option).
your supercharger only flows a certain amount of air, going a higher compression than 8.8 will give you a bit more power for the same boost.

(all things being equal going from 10.3 to 8.8 u will lose power, but a built motor will allow more power/boost )

304whp is insanely low for 2.87 (even with 5AT) are you running big heavy rims as well? have you seen a graph of your boost to make sure its not belt slip or leak? or its one low reading dyno

EDIT: Cux350z beat me :P

350Zdj

iTrader: (3)

Is the stock CR 10.3:1 available in forged form?

If so, this is also a good option if you think you're going to part-out and sell the Z in few years from now.

tylerxfire

iTrader: (15)

if u can id go with the stock ratio just forged if your sticking with the vortech..if u go low ratio ur power will suffer even more...how can u only make that power with the 2.87..i dont care what dyno it is that is waaay off..seems there was a problem from the start with the car..

Z1 Performance

iTrader: (564)

The only real valid comparison is what other Z's make on that dyno as well. Otherwise, I wouldn't sweat it. The dyno is a tool, it's not omnipotent.

For compression, the difference between 8.8 and 9, is indescernible.

Yes, you can use 11:1 on a S/C car, and even a moderate turbo setup. You're talking a modest increase vs stock...nothing earth shattering. It is not "too high" - the net result will all be in the assembly and tuning, just like it is with any setup. The higher the compression, with boost, the lower your margin for error as far as tuning, but the supercharger affords you a fairly easy setup to tune in the first place. His boost threshold and overall performance is going to be somewhat limited by virtue of where he lives and the weather there. More than a guys have boosted their stock HR engines, with alot more stress (and revs) vs what this setup would be (you can only rev the S/C setups but so high). So given that a stock HR compression is 11:1, a DE setup, with proper forged internals, balanced and blueprinted as any built motor should be, there is no reason 11:1 would not work well for this setup. If it were me, I'd also consider a proper water injection system as a 'part 2' to this build...once the engine is fully broker in, tuned, and running where you're happy. I think it would give a good safety margin and a good addition for your setup, and help combat the high AIT I'm sure you get.

Max - custom compression ratios can be done too (for example, can easily do stock compression, but forged), as a custom order. Lead times are the issue as they typically take 4-6 weeks or so to make (albeit cost is the same). They can do it faster too, for an added fee. All the piston manufacturers offer this.

Erdem

iTrader: (2)

yep I'm going to build my motor soon enough too with a Vortech Also.. and I'm going for stock CR..

but if u decide to go with a turbo setup later, it will *** u up a little..
I'm staying with the Vortech, therefor the 11:1 CR..

And also, I have heard a lot of bad things about low CR SC's..

maXmood

iTrader: (16)

Thanks for the input, guys... i'm trying to understand/decide whether to go with one or the other.

true about the low output, but we do have crappy fuel here, plus, the base dyno was 210 only.

i just hope with these internals i get more of the hidden power of the SC, and make it a reliable engine.

in that case then, 11:1 will be my choice.

Adam, what kind of water injection system? i have a meth kit, but haven't got it installed yet.. it's gonna be installed along with the internals.

seymore4

iTrader: (27)

If I were doing it I'd go stock or just a little less, maybe 9.5:1

The effective compression ratio is what matters in the end, you can run more boost with lower compression but its gonna suck ***** when you're not in boost

str8dum1

iTrader: (11)

like others have said, with the supercharger, stock compression or higher. 11:1 would be my choice.

maXmood

iTrader: (16)

^yea, sticking with 11:1...

now, oversized bore, what's the limit to oversize the bore and that would still keep it safe?

Quamen

iTrader: (14)

I have heard of .040" over for NA applications, but with FI I would stick to .020" over unless the block is sleeved.

11:1 is really the way to go as others have stated. If you ever want more power, just switch E85 and crank the boost. You shouldn't have any problems.

Z1 Performance

iTrader: (564)

.020 is just fine assuming the block is in good shape in the first place...that's a very standard overbore to do

if you've got methanol already, that would work too

as for a setup "sucking ***** when you're not in boost" - on a s/c car, that would be when you're just cruising (no load) and in that case, who cares

rh_334

iTrader: (2)

just out of curiosity wouldnt higher compression spool quicker on a TT?

has anyone really looked into how cams affect "dynamic compression"? im wondering if this is they GTM's Boost cams exhaust duration decreases with each stage?

SoundPerformance

11-1 and flex fuel/E85 would be my choice!

maXmood

iTrader: (16)

block was inspected, slight scratches from rings.. so going with .020 as suggested by you guys..

Adam, you got the those parts readily available?

lanceccs

I am considering a high comp SC build too but I am on HKS SC with 320 whp. Also purchasing a 90 mm pulley from GTM to max out the boost from the HKS SC unit. By then it should be in around 360-380 whp.

If I am getting 360-380 whp on a stock engine, what should I be expecting when I high comp it to 11:1?

It will be revving faster? Better response? How much increase in whp should I be expecting when pushed to the max with HKS SC.

What would be the max comp I could consider, with methodol kit spraying water? 12? Possible?

Resmarted

iTrader: (2)

11.1!

The only reason why you couldn't do it is if the NA pistons are thinner to save weight and increase response. In fact, on my next build (in... years) I'd like to run high comp pistons on a big twin setup. Ideally I'd have sleeves, billet crank, and a dry sump but first I want to finish this build (LOL). I know some of the big hp porsche's are running pretty high comp pistons, and some of the HPF (over priced douchers cough) turbo cars have pretty damn high compression ratios. Specifically VR alexander comes to mind... twin gt35r's and I've heard some rumors that he ran above 9.0 comp pistons (RIP).
The gt2 rs (which next to the carrera gt, and in-front of the spyder the coolest porsche everrrr) has a 9.0 comp ratio on a 3.6 flat six with 620hp...

High compression isn't necessarily BAD, it's just far more prone to detonation. It does have benefits, as it reduces turbo lag and helps to make more power all over the place (mainly though off boost). I think in a supercharged setup you are more than fine with nearly any N/A piston. I take it you are going with wiesco? Especially with meth (as z1 stated) it should be a great combo.

edit:
i realized i put "." instead of "-", but i'm only editing to troll proof my dgafosb (dont give a fack or shat bricks)

maXmood

iTrader: (16)

i went and bought the 8.8:1 cr, because with our environment, stock cr pistons are **** to detonation with a little adjustment to timing.. so it's gonna be really bad to go with higher cr.

i put the build on hold since it's summer time, but now the weather is changing, i guess it's time to start now.