The 18R-GTE reference manual ...

[Norbie]

Yeah, I'm struggling to see how a massive lump of iron like the 18R block could warp as well.

[Steve M]

22Rs have better reinforcing around the main bearings. Struts are thicker and generally better.
Still, I won't be chasing 600hp, so if it is good enough for Finnish drag racers, the stock block should be ok for me.

[JustenGT8]

Hi all,
I'm ordering the flanges for the turbo exhaust manifold today...well maybe tomorrow given the late notice 12mm mild steel, $25 plus post....who's in? Need to get cash to me asap. If they turn out cheaper because we get good numbers it'll be postage inclusive.

[Steve M]

Is that price for both the head flange and the T3 flange?

I want 3 head flanges and 1 flange to suit RB25 turbo, I think that is a T3.
I'll repeat this post to your PM and the 18RGTE thread

cheers,

[The Witzl]

i thought the RB25 had the T28 flange??

[RA23]

That just reminded me of another turbo 18RG a mate built here in Canberra. He used Jag pistons which were 92mm from memory and gave a comp ratio of around 12:1. I have to say it was a very impressive performer. Handled 6psi no probs and was a total torque monster. Spooled up a CT26 like you wouldn't believe. Never fully developed it as needed much bigger injectors and ran out of bucks...not sure where it ended up.

This little experiment was inspired by some Porsche racers that run 13:1 comp ratio and up around 15psi of boost. Goes to show that with the right gear hi comp ratio turbos are very feasible and make for great performers. If the UZ ever gets a set of forgies i'll be very tempted to stick with the stock 10:1 and wouldn't ever go lower than 9:1

That would have been with very high octane fuel I assume, and all sorts of cooling everywhere.
That makes me wonder what the maximum practical boost level is that would you be able to handle with (lets say) 10:1 and 98 octane fuel. I know the intake temp is dependent on the comp ratio of the compressor (I can work that out) , but I have no info on the relation between octane ratio and compression.
Would there be graphs of detonation threshold for given octane ratings? Rules of thumb?
I don't just want to whack something together, only to find out that I can only run 3 psi before I run into detonation trouble.

[Norbie]

There's really no relationship between CR and octane, there are too many external factors influencing when detonation will occur. Head material, combustion chamber design, even cam timing all come into the equation.

[JustenGT8]

Nope, just pump fuel. As for cooling, the stock 22 rad and a supra FMIC...nothing special at all really.

My current proj runs 10:1 comp and 13psi no probs at all. I know of a very similar combo that ran 18psi and i plan to run 16psi once i find the time to tweek a few niggling issues.

For rules of thumb there really aren't any other than run the least boost you can to get the hp you want.

[RA23]

There's really no relationship between CR and octane, there are too many external factors influencing when detonation will occur. Head material, combustion chamber design, even cam timing all come into the equation.

Thanks for your comment.
I realise that it is not straightforward, but for an 18RGEU with stock cams, running 98 octane, I was hoping to find some relationship between intake temperature, boost level and CR, that would give me some direction in my turbo project.
Just taking the safe option and dropping the CR to 7 is not an option for me, as the engine will be gutless on low revs and you need about 5 psi or so before you are even back on "stock" N/A CR=10 performance. And that is throughout the rev range.
I would prefer at least a CR of 9, maybe 10, but only if I can run up to about 1bar (15psi) . This is where I think piston cooling comes in (as one of the measures), but I have not worked out yet how to do that with the 18RG block.

[RA23]

Nope, just pump fuel. As for cooling, the stock 22 rad and a supra FMIC...nothing special at all really.

My current proj runs 10:1 comp and 13psi no probs at all. I know of a very similar combo that ran 18psi and i plan to run 16psi once i find the time to tweek a few niggling issues.

For rules of thumb there really aren't any other than run the least boost you can to get the hp you want.

Thanks Justen, that is good news. I'll start looking for piston options around 10:1. I'll also try and find the most efficient compressor around, to limit the temp increase in the intake.

[JustenGT8]

Just use a forged version of the stock 9.7:1 and you are sweet, plus you know all clearances etc will be spot on. ARIAS do an off the shelf that used in my 18RGT and i'm sure most will have something to suit.

[Steve M]

Right you are there Witzl. My memory failed me on that one. There are just too many letters numbers involved with modern engines.

Anyway, I'm definately in for three head flanges.

[Cobzzz]

just to say love the info

oh and also having a nissan stagea, most if not all rb25det's come with t3 flanges.

Ian

[Steve M]

Ohhh, now hy head hurts,

Is anyone able to post up T3 and T28 bolt patterns.

Cobzzz, would you happen to know what the compressor wheel from an RB25 45v4 is made from? It weights almost nothing, it's totally matt black and feels like plastic. I realise it wouldn't be plastic, but the little mazda BP compresor wheel we've got weighs heaps more.
I'd like to find out what it is made of before I use it.

[RA23]

Just use a forged version of the stock 9.7:1 and you are sweet, plus you know all clearances etc will be spot on. ARIAS do an off the shelf that used in my 18RGT and i'm sure most will have something to suit.

Thanks, Justen

18rg is not listed here:
http://www.ariaspistons.com/toyota.html
So I assume you used something else as a replacement?
Anyway I'll give their Australian distributors a ring on Monday.