i might be getting a deal on a single cam turbo Ef. it was knocking so he's having weisco 8.1:1 compression pistons and eagle rods put in it.... isnt 8:1 wayyy to low? how much boost would u run on that with a descent tune? 20psi? of course other stuff will be added.. cam, p/p, fuel pump, injectors, bla bla bla

 

sounds good lots of guys run 8:1 pistons

 

do they? on how much boost? i feel a little better now. i was thinkin like 20psi.. yay or nay

 

up

 

depends on tune and if the block is sleeved.

 

no sleeves... safe tune

 

well that is really going to depend on the turbo 20psi on a straight t3 compared to 20psi on say a sc61 is about 200 whp difference

 

good point, i forgot to mention size cuz.... i dont know. the kid im getting it from probably doesnt even know where the turbo goes. ill figure out what it is when i get a closer look, its pretty descent size tho

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lsvtecSIrex &raquo;</TD></TR><TR><TD CLASS="quote">i might be getting a deal on a single cam turbo Ef. it was knocking so he's having weisco 8.1:1 compression pistons and eagle rods put in it.... isnt 8:1 wayyy to low? how much boost would u run on that with a descent tune? 20psi? of course other stuff will be added.. cam, p/p, fuel pump, injectors, bla bla bla</TD></TR></TABLE>

8:1 is too low, IMO. Many people have run that compression with success though.

BTW, installing low compression pistons is not the answer to knocking. The tune is what needed to be fixed. I would never suggest lowering compression to "make up" for a bad tune.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lsvtecSIrex &raquo;</TD></TR><TR><TD CLASS="quote">i might be getting a deal on a single cam turbo Ef. it was knocking so he's having weisco 8.1:1 compression pistons and eagle rods put in it.... isnt 8:1 wayyy to low? how much boost would u run on that with a descent tune? 20psi? of course other stuff will be added.. cam, p/p, fuel pump, injectors, bla bla bla</TD></TR></TABLE>Don't count on that to fix the knock for more than a week or two.

 

said id post in hear rather than start another thread, im using wiesco 8.6-8.9 ratio pistons on my new build, is this compression ratio ok. too low ........????

 

8:1 isnt going to kill you but to say it's going to band-aid a "knocking" problem is ... I dont know. Wrong? I would pass on the car. Car below is a local car. 7.8:1 compression. 2.4 liter. Made 550whp on 93 octane and meth injection. Tuned by Brad Brooks. I think the last time it went to the track it pulled a 10.0 @ 136? Brad, Chet or someone can correct me. Has no problem running with 1K bikes on the street



RIGHT CLICK SAVE TARGET-AS

 

If i were to do it again, I'd probably drop to 8.0 like above to give more room to push the pump gas boost.

 

why would u pass? he's throwin 600 cash on top for my car... so maybe mill the head a little to get back some compression? and then i should have enough to get everything else i need

 

Well according to http://www.zealautowerks.com/dseries.html my vitara's have a static CR of 8.13. In all honesty, i could never tell the difference from stock CR.

If its a good buy why not pick it up??

 

IMO 8:1 is too low. i would at least go 9:1..maybe even 9.5:1.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sohc_turd &raquo;</TD></TR><TR><TD CLASS="quote">my vitara's have a static CR of 8.13. In all honesty, i could never tell the difference from stock CR.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by cuin9sec &raquo;</TD></TR><TR><TD CLASS="quote">IMO 8:1 is too low. i would at least go 9:1..maybe even 9.5:1. </TD></TR></TABLE>

Why run 9.5:1, so you can imagine in your head all that extra throttle response you're getting from it? This guy just said he didn't notice a difference between stock and 8.1:1 Vitara's, so who cares.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tokes1320 &raquo;</TD></TR><TR><TD CLASS="quote">Why run 9.5:1, so you can imagine in your head all that extra throttle response you're getting from it? This guy just said he didn't notice a difference between stock and 8.1:1 Vitara's, so who cares.</TD></TR></TABLE>

*** dynos are worthless. Don't go below 9s compression. Sub 350whp, go 10:1 compression.

 

i wouldnt trust high boost on 10:1 but what do i know. sohc turd whats your set up..

 

8:1 is good for peace of mind with high boost and detonation along with a good tune. the bottom end and thottle response well suck but boost will make up for it

 

thanks. and with a milled vtec head it should add a little comprssion too. maybe 8.5:1?

 

Its personal preference, my first setup was a boosted mini-me, and now my current Vitara setup. I personally havn't noticed a significant difference in off-boost throttle response between the two ends of the spectrums.

I like the fact that ive got a higher knock ceiling on pump gas. You decide what/how you want to build your build and go from their.

A simple answer to the original poster's question, yes, the lower compression is just fine.

 

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

*** dynos are worthless. Don't go below 9s compression. Sub 350whp, go 10:1 compression.</TD></TR></TABLE>

And what might you have to back up your bold claim?


My *** dyno is actually better than most non eddy brake dynos when comparing off -boost throttle response.

 

http://www.evans-tuning.com/_i...e.jpg

Amazing, a full compression ratio adds torque everywhere! Raising your compression ratio inceases your VE. Increasing your VE = good.

 

There are a lot of factors to consider when using low compression ratios but effective rpm range (power band) and turbo spool (quick or late) are probably the most important.

High revving motors that suffer from no-low-end syndrome will suffer more in the low end of the rpm range if the compression is lowered too much. Adding a quick spooling turbo to a high revving will not cure any problems because the turbo will run out of juice before the motor hits its sweetspot in the RPM range. A turbo that is matched to low compression high revving engine's powerband will give the motor a Jekyl/Hyde personality. Turtle with two broken legs on the low end and a Jack Rabbit on speed on the top side type performance equates to a very shitty streetcar.

A SOHC motor with a quick spooling turbo will not suffer much because the quick spool of the turbo will make up for the loss of compression. The lower compression will also allow you to run higher boost levels than a high compression motor. You actually have to run higher boost on a low compression setup if you want to make the same power as high compression setup with the same exact turbo. This will lead to yet another issue..... boost range of the turbo.


In the old days 7.0~8.5:1 compression was the norm for many factory turbo cars and factory backed race cars. Carbs, mechanical fuel injection, crappy ignition setups and the belief that compression ratios above 8.5:1 would cause a Chernobyl meltdown in your engine made the low, by today's standards, compression a STANDARD.

Once better ways to tune a setup became available many tuners began to raise the compression ratio because they found they could make more horsepower by bumping the ratio by as little as half of a point (0.5:1). With the discovery of better tuning solutions, "low compression" on a boosted setup was called a "band-aid" for poor tuning. Better safe than sorry .

Factory turbo cars still run 8.0~9:0: compression ratios for reliability reasons.

Just thought I'd add my 2yen to the thread