Jump to content
SAU Community

Recommended Posts

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

Link to comment
https://www.sau.com.au/forums/topic/346997-compression-ratios/
Share on other sites

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)

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.

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.

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

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

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

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.

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 :)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Nah - but you won't find anything on dismantling the seats in any such thing anyway.
    • Could be. Could also be that they sit around broken more. To be fair, you almost never see one driving around. I see more R chassis GTRs than the Renault ones.
    • Yeah. Nah. This is why I said My bold for my double emphasis. We're not talking about cars tuned to the edge of det here. We're talking about normal cars. Flame propagation speed and the amount of energy required to ignite the fuel are not significant factors when running at 1500-4000 rpm, and medium to light loads, like nearly every car on the road (except twin cab utes which are driven at 6k and 100% load all the time). There is no shortage of ignition energy available in any petrol engine. If there was, we'd all be in deep shit. The calorific value, on a volume basis, is significantly different, between 98 and 91, and that turns up immediately in consumption numbers. You can see the signal easily if you control for the other variables well enough, and/or collect enough stats. As to not seeing any benefit - we had a couple of EF and EL Falcons in the company fleet back in the late 90s and early 2000s. The EEC IV ECU in those things was particularly good at adding in timing as soon as knock headroom improved, which typically came from putting in some 95 or 98. The responsiveness and power improved noticeably, and the fuel consumption dropped considerably, just from going to 95. Less delta from there to 98 - almost not noticeable, compared to the big differences seen between 91 and 95. Way back in the day, when supermarkets first started selling fuel from their own stations, I did thousands of km in FNQ in a small Toyota. I can't remember if it was a Starlet or an early Yaris. Anyway - the supermarket servos were bringing in cheap fuel from Indonesia, and the other servos were still using locally refined gear. The fuel consumption was typically at least 5%, often as much as 8% worse on the Indo shit, presumably because they had a lot more oxygenated component in the brew, and were probably barely meeting the octane spec. Around the same time or maybe a bit later (like 25 years ago), I could tell the difference between Shell 98 and BP 98, and typically preferred to only use Shell then because the Skyline ran so much better on it. Years later I found the realtionship between them had swapped, as a consequence of yet more refinery closures. So I've only used BP 98 since. Although, I must say that I could not fault the odd tank of United 98 that I've run. It's probably the same stuff. It is also very important to remember that these findings are often dependent on region. With most of the refineries in Oz now dead, there's less variability in local stuff, and he majority of our fuels are not even refined here any more anyway. It probably depends more on which SE Asian refinery is currently cheapest to operate.
    • You don't have an R34 service manual for the body do you? Have found plenty for the engine and drivetrain but nothing else
    • If they can dyno them, get them dyno'd, make sure they're not leaking, and if they look okay on the dyno and are performing relatively well, put them in the car.   If they're leaking oil etc, and you feel so inclined, open them up yourself and see what you can do to fix it. The main thing you're trying to do is replace the parts that perish, like seals. You're not attempting to change the valving. You might even be able to find somewhere that has the Tein parts/rebuild kit if you dig hard.
×
×
  • Create New...