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Compression Ratios

yogibear

By yogibear,
in Engines & Forced Induction

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yogibear Community Regular

yogibear

Posted
Posted

ok starting to come to end of my build not long to go now :) cant wait :) , BUT how do you work out what compression ratios are needed?

obviously my machinist is going to work out what it will be But he isnt too sure what compression i need, he suggested 9.5 to 1 ???

just some info on the motor

rb30 full forged bottom end will be reving too 8k too 8.5krpm

head will be ported , cams , bigger valves , etc

turbo is unsure i was going to be ruining a to4z but a few people saying not too , and their is better options out their for what i want, witch is around 800rwhp on E85.

will mainly be using E85

not sure what other info you need just ask

thanks for any info

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TiTAN Grand Master

TiTAN

Posted
Posted

i thought i can chnage a fair amount with differnet head gaskets?

and just so i know , what Compression should i be aiming for?

you can lower the compression with bigger head gaskets, you cant raise it as the compression figures for the pistons are based off 1-1.2mm head gaskets and you wont get one thin enough to make a big difference without running into issues with the pistons hitting the head.

idealy on E85 you want to try and aim high as your builder has said 9.5-10:1 if you can (arias make pistons off the shelf for the RB30 to do 9.8:1)

bradsm87 Proficient

bradsm87

Posted
Posted

o ok fair enough :), how much more lagy would a GT4088R be?

me allways up for more info guys :)

A GT4088R is only a little bit laggier than a T04Z because the GT4088R is a more modern turbo. Even that will be at it's very limits to make 800rwhp. Still too laggy for circuit IMO. The turbo I'd be looking at is the new GTX3582R. It flows similarly to a GT4088R but is a smaller, more responsive turbo. It's because of the new billet compressor wheel. A GTX3582R with a T4 twin scroll 1.06 turbine housing should make 700rwhp and an absolutely INSANE midrange. It'd hit boost early and hard and just PULL all the way to the redline. It'd definately FEEL faster than a GT4088R with 800hp.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

honestly 600rwkw and circuit, you have gotta be kidding!

think of the heat, braking, oil/water temps.

id be doubtful there is many, if any such GTR's around.

the closest i can think of was the street driven Racepace GTR which on full race fuel ran around with about 450-500, i remember seeing it had actually twisted the turbine housing.

Now think about the heat over years...

The other car that comes to mind is the Russ/High Octane which is an outright race car, still isn't 600 @ the rubber because i dare say its pointless :)

outright power is nothing compared to a well sorted and reliance brake/suspension/aerotrack car.

I agree the GTX35 sure does look like one the choice.

tm_r33 Experienced

tm_r33

Posted
Posted

I just picked my engine up from the builder and I am running 9.3 compression ratio. I used arias pistons. Obviously head gasket or decking will affect the comp ratio slightly. Im running 25 head on forged 3 litre bottom and obviously with decent cams and valve springs and appropriate head work. Ill be running a gt35 turbo and hope for about 400 rwkw to start with.

Imho that will be plenty of power for a pure circuit car. Its a 33 gtst by the way.

f**k peddling an 800 hp car around a track lol

zebra Grand Master

zebra

Posted
Posted

LOL @ 600rwkw circuit car! Marks car has I'm told around 520kw at the treads and it's is on struggle street putting it down with some of the best suspension/tyres money can buy, let alone having another 100hp.

But you say that it will be mainly E85 to run 9.5-9.8:1 it would have to be ONLY on E85 you wont get away with PULP and 9.8:1 unless you rev limit it to 4k rpm and 2psi.

Oh btw will this be 4wd (GTR) or 2wd?

Doesnt say in the thread anywhere

XKLABA Grand Master

XKLABA

Posted
Posted (edited)

the bsm car made around the 450rwkw mark from memory and dave he said it was a scary ride and i've been in the car with him around easten creek and he can really drive, 600rwkw on a track is never going to be used a so very pointless, even on street it would be dangerous at best that kind of power is only any good for dedicated drag cars or dyno whores

Edited by XKLABA
R31Nismoid Grand Master

R31Nismoid

Posted
Posted

Over 400-450rwkw (550-600rwhp) would be the region given you can pretty much get 380-400rwkw now on PULP with a big motor

I highly doubt you'll get bored when over a 2-3 year period you see seconds upon seconds drop off your lap time.

As that's where you'll find the fun... And i hate to say it, spend more money :P

Learning to actually drive a high powered car etc.

If all you have is a built motor and not much else then you'll have more problems to worry about then getting bored.

Suspension/braking/cooling/tyres/gearbox and overall reliability will be more of a worry than how much power you'll be making.

Heat is a MAJOR issue and you could spend half a year getting it right.

If you get bored you can always upgrade the turbo later once you've had a few seasons of roundy roundy. ;)

With that power you'll also be well into the 10's to boot so it'll be good overall that's for sure.

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

I also had a look @ your For Sale thread last night as i was reading the forum...

Honestly, your cars setup now, won't even handle 400rwkw on the circuit.

You brakes will run out after a lap or two, you'll certainly have cooling issues and without a wing IMO it'll be all over the place if there is any higher speed cornering and so on.

Suspension might be ok, but you'll need adjustable arms and all sorts of stuff to help it along.

It just sounds to me like you have a big motor and little else to support it :)

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