on a boosted motor would 8:1 be too low? and if not too low how much psi/hp could a built dohc zc hold w/8:1 (and a t3 .42/.48)

 

Why are you going that low? I can only assume that you are using a headgasket that is larger than 3mm. Your turbo and the tuning will be the limiting factors for max hp. What size exhaust will you be using?

 

Why run such low compression with such a tiny turbo?

With a turbo that size you might as well stay with a stock engine considering the turbo's efficiency will run out around 7-10psi.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dee &raquo;</TD></TR><TR><TD CLASS="quote">Why are you going that low? I can only assume that you are using a headgasket that is larger than 3mm. Your turbo and the tuning will be the limiting factors for max hp. What size exhaust will you be using?</TD></TR></TABLE>no i didnt plan on it being that low (i made a mistake on my calculations) and the hg is oem (it's the pistons that make my comp low) and the exhaust is 2.5

 

That turbo will probably start choking severely in the 180~200whp range. Are you willing to get a larger compressor (T4)? What is the intended usage?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dee &raquo;</TD></TR><TR><TD CLASS="quote">That turbo will probably start choking severely in the 180~200whp range. Are you willing to get a larger compressor (T4)? What is the intended usage? </TD></TR></TABLE>yeah i plan on getting a bigger turbo....will a t4 comp. help the t3? my hp goal is atleast 275whp......right now the plan for the car is weekend driver, use to go to school...when i move i plan on garaging it and going track only

 

I think it will be difficult to get 275whp with the AR.48 exhaust housing. I might have an extra 50 or 60 trim T4/T3 AR63.. Hell I think I have an N trim T4 AR.36 housing/blade too.....hahahahaha. I'll check my extra parts when I get home tonight. I am running a T67/T3 so I have no use for my footlocker full of turbos.

 

that would be awesome...let me know

 

i ran 8.5:1 pistons previsouly, i would not recommend running that low a CR.

On my new biuld i am going 9:1

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by turbotime &raquo;</TD></TR><TR><TD CLASS="quote">i ran 8.5:1 pistons previsouly, i would not recommend running that low a CR.

On my new biuld i am going 9:1</TD></TR></TABLE> i wish i could change it but i cant (my engine is done)....but my comp is about 8:1

 

Is the motor fully built? If it is just turn the boost way up and run that turbo into the ground.

 

What about using the thinnest HG you can get from cometic? You could take a bit off the head also...

 

There isn't anything wrong with running low CR. people make a lot of power on pump gas with low CR. the honda community is the only community that i know of that thinks 9:1+ is best for boosting on pump gas.

 

sure you can make power on 8:1 but with the same amount of boost you can make more power on 9:1.

I wouldnt recommend shaving your head or running a real thin headgasket...

Stick with what you have, tune it, and if you want more low end power (which is where higher CR pistons will help with) then just get new pistons, simple as that.

I would try it out first before you make all these plans to change it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nonvtecD &raquo;</TD></TR><TR><TD CLASS="quote">Is the motor fully built? If it is just turn the boost way up and run that turbo into the ground.</TD></TR></TABLE> well i have eagle rods, srp pistons (std. bore), arp headbolts, ti. springs and retainers, delta cams, new oem gaskets/seals

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyphear &raquo;</TD></TR><TR><TD CLASS="quote">There isn't anything wrong with running low CR. people make a lot of power on pump gas with low CR. the honda community is the only community that i know of that thinks 9:1+ is best for boosting on pump gas.</TD></TR></TABLE>

Dude you are totally lost. Do you know why cars were produced with ultra low 7.5~8.5:1 compressions? Proper turning was not available so ultra low compression was the band-aid for that problem. A setup with 9:1 compression and 10psi will produce more power throughout the ENTIRE powerband of an engine. And to top it off it will be just as safe. Now if you were to say 10~10.5:1 compression then we would have a different story because a sloppy tune would kill the engine with ease. Lower compression is more forgiving when your tune is a bit off the mark. Actually, people in all of the boosted communities KNOW 8.5~9.5:1 compression will give optimal performance on a street car that is using pump gas.

hatchinprogress - I have the turbo and turbo parts below:
(HKasS) AR.50 46 trim T4/T3 stage 3 AR.63 (needs rebuild)
(HKasS) AR.60 52 trim T4/T3 stage 3 AR.63 (haven't checked the CHRA)
(HKasS) AR.60 60 trim T4/T3 stage 3 AR.63 (holding for a japanese friend)
(HKasS) T300 (T3 super 60 with AR. 63 ex housing) .... I need check it out
(HKasS) T4 AR.36 N trim housing and blade
I think I have some more crap down at the shop.

Eventhough I will hook you up with a turbo or turbo parts for cheap I will suggest getting the correct pistons since SRP's are not that expensive.

 

DEE...............pm sent

 

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

Dude you are totally lost. Do you know why cars were produced with ultra low 7.5~8.5:1 compressions? Proper turning was not available so ultra low compression was the band-aid for that problem. A setup with 9:1 compression and 10psi will produce more power throughout the ENTIRE powerband of an engine. </TD></TR></TABLE>

Yes, im totally lost. and so is the WORLDS FASTEST PUMP GAS CAR running 7.5:1 CR. they must not have any tuning available either. read up for a few hours man.

Here is a link for you to read that shows higher CR doesn't help low end power (much). http://forums.evans-tuning.com...=1612

 

I fully agree with Cyphear on this one! Give me low CR and higher boost any day.

 

Dee- the most powerful built 2jz's in the US are running 8.1-8.3 c/r. and these cars are running only race fuel. as far as the most powerful street driven 2jz's that are built, they run the factory c/r of 8.5:1 they dont go even close to 9.1 what does 9.1 and above offer that you cant get with 8.1 except a smaller window for failure? nobody gets trophies for making the same power while running 2 psi less. I also dont know of any European turbo car that has close to 9.1 and their octane is way higher than ours.

IMO if you have to rely on compression to make the extra HP, then you have a few restrictions on your setup that you need to address.

 

low boost is the cure for crappy tunning or lack of parts.

9:1 compression is just as safe as 8:1 but will build more power at the same BOOST levels. We are talking about a street car and not a deep pockets race car that is running 4 bar of boost.

 

yeah, it is a bit better to have more compression, but i dont think he's not giong to like his engine...i think he'll be more than happy with it. just turn the boost up a bit.

i would definitely get a bigger turbo.

low compression isnt that bad.

i'd rather have in the 8.5 and up area, but 8:1 isnt that bad. not by any means. run it man.....tune it and crank it up!

i personally have a a6 at with srp's that work out to be around 8.5:1, and it feels fine. i was running a .42/.48, not i'm running a .60/.48, and it feels much better at higher boost..

i plan on switching that out for something better ASAP though.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Boostage &raquo;</TD></TR><TR><TD CLASS="quote">Dee- the most powerful built 2jz's in the US are running 8.1-8.3 c/r. and these cars are running only race fuel. as far as the most powerful street driven 2jz's that are built, they run the factory c/r of 8.5:1 they dont go even close to 9.1 what does 9.1 and above offer that you cant get with 8.1 except a smaller window for failure? nobody gets trophies for making the same power while running 2 psi less. I also dont know of any European turbo car that has close to 9.1 and their octane is way higher than ours.

IMO if you have to rely on compression to make the extra HP, then you have a few restrictions on your setup that you need to address.</TD></TR></TABLE>
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