Manifold Design and Turbine Housing - expensive lesson learnt

[Merli]

Also, I am pretty sure Merli is using 256/264, and he has good boost from just under 4krpm, and he is using a HKS 3040 with a larger turbine housing from memory.

Just to clear this up:

I was using an HKS GT3040 (0.87 exhaust housing) on an HKS exhaust manifold with Tial external wastegate.

My engine was completely stock. That is, stock cams, gaskets, EVERYTHING. I did buy some JUN 264/272 cams for it, but I decided that they were too big, and I decided to sell the car anyway, so they never made it into the engine.

Boost started to build from 2500rpm, and I had 1.2 bar by 4000rpm. This dropped to 3800rpm after I installed an HKS exhaust cam gear. I would predict 1.8 bar by about 4500rpm or less.

With a larger exhaust camshaft, you should really be getting boost earlier than I was!

[Al]

Great read pplz.

Unfortunately your knowledge was well exceeded mine, so i can't have any input .

But it is threads like this that makes the rest of us aware and mindful .

[Steve]

Thanks for that Merli, that sounds like a sweet setup you had, 1.2bar in by 3800rpm and I would be very, very happy.

[Warpspeed]

Hi again Steve, sorry it took so long to get back.

Disconnecting the VVT is not a fair test. I am not sure if it goes to the fully advanced or fully retarded position when disabled.

If the cam fully advances, the overlap will be rather large, possibly enough to cause a lot of reversion. Also the cams you now have probably open and close a bit more aggressively than stock. So both valves will be at higher lifts as well as open together longer.

If the cam fully retards, inlet closing will be extremely late, and this will really reduce low end and mid range torque. You really should not be using VVT with that cam, it will go a lot better at a fixed position.

The engine must make enough torque off boost to generate enough exhaust flow to start the fun in the turbine. If you cripple the engine with excessively low compression, or a highly unsuitable valve timing it will not be able to light up the turbo, and it is no fault of the turbo.

Try putting the stock inlet cam back in, if it helps, then go back to the 256, disconnect the VVT and set it to a suitable position. If it is still crook with the stock cam, at least you will then know the problem is definitely in the exhaust side of things.

With an untried combination of parts, sometimes some completely unexpected mode of operation can trick you. The only way you can narrow it down and figure out what is actually happening is to try changing a few things.

[Roy]

Steve, my manifold is made by Trust and came with the turbo and Trust wategate. Do you know the diam tube/pipe used to make the manifold.

Im no expert, but like you the research i have done would have me believe the performance would be influenced more by the runner diameter, quality of the blend points and integration of the wastegate... more so then the 6-1 equal length layout, perhaps the collector/blend point for all 6 runners isnt ideal?

I have read that the longer the runners the softer the transition onto boost, the shorter the harder the hit. You have said your runners are "long"

This is exactly the same as my manifold, although mine has been ceramic coated black...

[Merli]

HKS Manifold. If you zoom in or something you can see that it goes from 3 into 2 just before it goes into 1.

Just to clarify this one too,

That's an exhaust manifold for a much larger turbo, one with a twin scroll exhaust compressor.

See how it doesn't actually merge into one opening at the turbo flange? It's seperated and stays as two different exhaust pulses...

In the HKS range, the only turbos with twin scroll exhaust housings are the T04R, T04S and the new T04Z... Even the T51R KAI/SPL have one opening, albeit a massive vband attachment

The HKS exhaust manifold for an RB25 with more reasonably sized turbo won't look anything like this one pictured above.

[Merli]

Here's the HKS exhaust manifold for the RB25DET.

Notice how smooth the bends are, whilst taking the most direct path to the turbo.. Oh..... and they're nice and shiny too

[Guest RedLineGTR]

Hope it all works out in the end. Cheers Rob

[Steve]

Roy, with mine, all 6 come together, but I dont think the angle that they joint at is particularly good. All the jap ones I have seen seem to blend alot smother (like in your photo) where as mine is sort of a BOOSTD described, all colliding together just before exiting.

I am not sure what ID of the pipe is. I didnt want a savage hit of boost, no good for daily driving, well in traffic anyway:)

Warpspeed, I will be trying the cam, straight after I see if I can give a smaller turbine housing a go. If I get good results from the housing swap, I think it would be fair to say its the manifold that is causing the main of the grief. I am a bit hesitant to blame the inlet cam, as they are the smallest made for GTS, so its a bit hard for me to get my head around it being such a massive step backwards.

I was under the impression that the cam stays in the fully retarded position, as disconnecting it with stock cams killed the mid range. Also, I have seen back to back with and without the VVT on stock cams, and the without had a big hole in the middle.

[Warpspeed]

o/k Steve, I understand what you are saying.

Something is not right, and you have made more than one change, so you need to go back to what you had that worked, and then try a few things.

My gut still tells me that the exhaust flow is just not there. The smaller housing will almost certainly be better, but it may, or may not be the best solution.

The exhaust cam change is guaranteed to work and be completely non critical. The inlet cam phasing is far more critical than you probably realise. It is extremely easy to stuff up the inlet valve timing with only small change either way.

I suggest you fit a degree wheel and measure the exact opening and closing points of inlet and exhaust. You might be in for a surprise.

[Cubes]

A while back I was talking to Tim from RPM.

He said he had a fiddle with exhaust a/r's, while keeping a record of the backpressure in the exhaust manifold/turbo.

For 900hp he settled on a .81 or .87 I can't remember exactly. For 300-350rwkw he suggested I stick with the .61-.69 exhaust housing as there is not excessive back pressure. IF I remember correctly. he said some thing along the lines of the exhaust back pressure was around 2 x the inlet pressure. When going from a larger exhaust housing to a smaller exhaust housing he said top end didn't appear to suffer at all. I asked "what about reversion" he said generally you try to pump a little more timing in to it as it helps prevent or minimize the reversion as the explosion begins earlier.

something like that, don't take what I said literally as it was some time ago I spoke about this with him.

Maybe you should have a word to Tim @ RPM Steve.

[Warpspeed]

A while back I was talking to Tim from RPM.

He said some thing along the lines of the exhaust back pressure was around 2 x the inlet pressure. When going from a larger exhaust housing to a smaller exhaust housing he said top end didn't appear to suffer at all. .

Actually the 2 x boost pressure is not a bad turbine inlet pressure to aim for on a tractable everyday road car. Most of the factory turbo systems run about that amount. Any less and the boost threshold stats to get a bit high, any more and the top end power starts to suffer.

I believe measuring the turbine inlet pressure and dump pipe pressures are just as important as knowing what boost you are running. A surprising number of turbo guys have not a clue what is going on in the exhaust side of things.

[GTR-Ben]

Just to clarify this one too,

That's an exhaust manifold for a much larger turbo, one with a twin scroll exhaust compressor.

See how it doesn't actually merge into one opening at the turbo flange? It's seperated and stays as two different exhaust pulses...  

In the HKS range, the only turbos with twin scroll exhaust housings are the T04R, T04S and the new T04Z... Even the T51R KAI/SPL have one opening, albeit a massive vband attachment

The HKS exhaust manifold for an RB25 with more reasonably sized turbo won't look anything like this one pictured above.

Yeah your right there merli.. i didn't look close enough.

That manifold has a T88 34D attached to it..

[GTR-Ben]

A while back I was talking to Tim from RPM.

He said he had a fiddle with exhaust a/r's, while keeping a record of the backpressure in the exhaust manifold/turbo.

For 900hp he settled on a .81 or .87 I can't remember exactly. For 300-350rwkw he suggested I stick with the .61-.69 exhaust housing as there is not excessive back pressure. IF I remember correctly. he said some thing along the lines of the exhaust back pressure was around 2 x the inlet pressure. When going from a larger exhaust housing to a smaller exhaust housing he said top end didn't appear to suffer at all. I asked "what about reversion" he said generally you try to pump a little more timing in to it as it helps prevent or minimize the reversion as the explosion begins earlier.

something like that, don't take what I said literally as it was some time ago I spoke about this with him.

Maybe you should have a word to Tim @ RPM Steve.

So I have a T04 with a .69 exaust housing. Some people have said this will be too small on a RB30DET setup?

[Merli]

Yeah your right there merli.. i didn't look close enough.

That manifold has a T88 34D attached to it..

There you go Steve... You have to get a T88-34D now

It's been decided and it's final

And GTR-Ben, grab 0.87 exhaust housing for your turbo... it's relatively cheap, a straight bolt on that you can do with minimal tools, and find out!!! But yes, it sounds like you'd be restricting your engine's top end breathing with that sized exhaust compressor.

[R34GTT-R]

Here are some pics of my so called HKS manifold which will be bolted to a 3037s 87ar in next couple of weeks.Now ya got me peaking on when boost will come on.Steve do your manifold runners look like mine?

http://www.skylinesaustralia.com/forums/at...tachmentid=7022

http://www.skylinesaustralia.com/forums/at...tachmentid=7028

[Steve]

R34GTT-R, mine is similar, in that they collect 6-1, but my runners are a bit longer and tuned length.

But then again, If it were me, I would be trying to acquire the street type HKS one, as Merli posted the pic of. I was told that apparently the single collector before the turbine housing is used to blend and accellerate the gasses before it hits the turbo.

Good luck

[Cubes]

Steve.

So whats the peak power you now have.

Ben, Try it with the smaller exhaust a/r first. The tests tim has done has shown that it makes bugger all difference with the larger a/r unless you are up over 650-700hp. Depends if you want more power in the last 1000rpm of your rev range or would prefer more power in the 3000rpm prior to that last 1000rpm. Bolt it in and see how it goes.

[Steve]

Joel, I dont know - hasnt been on a dyno, just street tuned.

[Merli]

Here are some pics of my so called HKS manifold which will be bolted to a 3037s 87ar in next couple of weeks.Now ya got me peaking on when boost will come on.Steve do your manifold runners look like mine?

http://www.skylinesaustralia.com/forums/at...tachmentid=7022

http://www.skylinesaustralia.com/forums/at...tachmentid=7028

I'm sorry mate, but that isn't like any HKS manifold I've ever seen before...

I'm not sure how it'll go with the split pulse manifold going to a single inlet GT3037 either... Might be interesting to say the least