fatboyee

*don't know where else to post this, so gen was my first option. mods please move if needed*

ok for all you turbo guru's out there:

how much boost can be run 'safely' on an intercooled motor (built: forged pistons, head studs, copper gasket, rod bolts.... most of the basic good shit) with 9:1 cr?

my last motor was 8:1 and was easily taking 18psi, some are running as much as 25+.

i had to go with a 9:1 piston b/c of a screw up in my ordering and have settled for what i can get for my schedule. i understand that in theory i won't be able to run as many # of boost, but 'boost is just a number' anyway right?

Crate

if i ever boost i wanna run 9.5 =] higher compression just means you need to tune better... i dunno. just play with it? i doubt anyone could tell you exactly.

Boosted2003

Alot of volvo people run 8.7:1 and 8.2:1 varying from 25 pounds a holset turbo to 45 pounds on 9 liter truck turbos.

xnenon

You can safley run 18+ lbs with that built motor and 9:1, and youll just be making more hp than the 8:1...just get it tuned.

ToyotaTechGeek

you know, what will really matter is how much you can manipulate your ignition timing and fuel map.

HighPSI TSi Guy

compression doesn't mean anything in a built motor for boost threshold.. usually when people talk about high comp motors blowing due to high compression it's because most high comp stock motors aren't built to take the stress of boost. boost IS compression. the strength of the rods/pistons/block is what determines how much boost you can hold, no matter what compression you run.

MORE IMPATIENT

i disagree, detonation is something that needs to be taken into account, lets say i have a fully built block running 12:1 compression, even on 116 race gas you will have a hard time tuning to a mild setting of boost because of your detonation barrier, sometimes in the pump gas and race gas dyno pulls, you reach a certain point where its no longer safe to boost withouth lowering compression...besides the fact that most high compression pistons have a large dome on them with sharper edges which promote detonation, a mild compression (say 9.5-10) is where i think the most power with a built motor can be made, you can run lots of boost(which theoretically equal more HP per lb of boost than a point of compression does), and you dont have to worry as much about detonation cause of piston design, not to mention higher compression pistons flow less out of the chamber then low compression pistons which in turn would create a slower exhaust ventilation and a hotter combustion chamber, making power with compression is all in the tuning,but there comes a limit when making power with high compression becomes hazardous to you investment........

subaruboy

it's been said elsewhere on this board...

Buy "Maximum Boost" by Corky Bell

Best damn book I ever bought... just got it a week ago and I'm reading it like an old bitch reads romance novels.

Also, I have "Turbochargers" By Hugh Machines... another good book, but old... covers carb'd engines mostly.

Maximum Boost has suggestions, warnings, and all the mathmatical equations you would need to answer all of your questions.

They're not hard to work out on paper if you have a scientific calculator, and are not a moron.

I'm trying to prep to eventually boost my brother's 3.4L DOHC Z34, and build my Daytona whenever one falls in my lap... and Maximum Boost has put a lot more confidence under my belt than i had before

HighPSI TSi Guy

if you build an engine right and have half an idea how to tune you shouldn't be detonating much on C16.... boost IS compression. more compression means your limit of boost pressure will be less because you're putting the same load on the engine with less boost pressure. generally people use a compression that is just high enough to to spool their turbo, so that they can run larger turbos at higher boost where they have better efficiency. they are relative.

Boosted2003

Totally agree.

if you build an engine right and have half an idea how to tune you shouldn't be detonating much on C16


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