Manifold Design and Turbine Housing - expensive lesson learnt

[R34GTT-R]

so split pulse is for trust turbo's and flange is same for 30 series and t series trusts??

[GTR-Ben]

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.

Well I am not going for insane power at high RPM.. 400rwhp with great torque even would be great for a start. It is a street car.

Im not to sure on what affects it? .69 AR with a 50mm exaust wheel? How does A/R compare to wheel size?

As for my manifold, the Subzero one I have actually a split design also... goes from 2 lots of 3 into 2 and straight to the turbo.

Is it vital to have a matching turbo with split entry design? or am I now forced to get the proper turbo or another manifold..

Damn more things just keep proping up...

[GTR-Ben]

I took some more photos to compare etc. I tried to take some of the exhaust fins on the dual entry T88 but I couldn't get it to show up. The fin design is rather different to that of a single entry turbo. I would imagine mixing the two would cause problems..

Subzero Manifold.

Trust T88 Turbo.

Single inlet T04.

Sorry if the links disappear.. free host.

[R34GTT-R]

so the t88 stay dual till it hits the turbine?. ANd are HKS and TRUST flange the same?Because mine is 3 runners and 3 runners until it hits exhaust housing.wouldnt this accelerate the flow?

[Steve]

It depends on the turbo, not all trust and HKS turbos are built like that (called split pulse), but of course some are. Usually seems to be the big hp turbo setups, which would alos explain the longer pipe design as they are built to perform at the top end.

[Steve]

Ben, just noticed another interesting thing, the sub zero manifold has grouped sequentially firing cylinders to each side of the split - I am thinking along the lines of what happens in my manifold, ie the pulses will collide with eachother and possibly cause back pressure? Or am I mixing up the firing order/grouping of the runners?

The nissans fire 1,4,2,5,3,6 dont they? Looks like the Jap manifold seperates the grouping.

[GTR-Ben]

The firing order for the RB is 153624. Thanks for pointing that out, I never considered it.

So looking at the manifold, it will fire. Right, Left, Right, Right, Left, Left.

The HKS manifold seems to just bank 3 from each side.

Getting really confused with all this.. I guess all I can do it try things and see what happens.

Quite interesting though.

[Roy]

Dont want to sound as though im assasinating parts on your car, but the welding on that manifold isnt the best...it has a fair bit of undercut/or excess penetration. You can see the variance on overall diameter at the weld.

Depending on the wall thickness and the unsuported weight of the turbo on the manifold, then you may find that this manifold may be a lttle more susceptible to cracking.

[Roy]

.69 AR with a 50mm exaust wheel? How does A/R compare to wheel size?

A/R, area/radius. So its a ratio of the area of the hole through the housing, and the distance from the area's centre to the centre of the turbine wheel.

As its only a ratio, it doesnt mean a 0.69 Housing from a GT25 is the same size as a 0.69 housing off a GT30, as obviously the turbine wheel on the GT30 is goin got be larger in daimeter.

Meaning that the radius (length from centre of area to centre of turbine) is going to be larger for a GT30 to accomodate the larger wheel. In turn as the radius is going to be larger the Area will have to be larger to maintain the ratio of 0.69...making sense?

[GTR-Ben]

Thanks for that ROY.

I know the welding on the manifold isn't the best.. I just had a GTR head and that manifold was attached.. so it's better than having nothing right?

It had a very heavy turbo attached... and didn't seem to hurt the manifold too much.

The HKS one above had a couple of small cracks with the T88 attached.

Is there anything I can do to the SubZero manifold to improve the welds??

So a T04 with a 50mm exaust wheel and an A/R of .69 is rather small?..

[GTS-t VSPEC]

Steve, Sorry to here about your dramas:( I have a custom manifold with a GT30 (0.64housing) and it's making over 300rwkw. Mine is still stock cams, stock headgasket. I'm personally not entirely convinced that it is the manifolds fault, as my mate has the larger housing on his and it's not nearly as laggy as yours.

[Sydneykid]

Hi Steve, can I just make sure I have the facts right...

Previously, 0.61 A/R, 9.0 to compression, standard cams, standard cam timing, boost at 3,000 rpm, max power 256 rwkw at 1 bar.

Now, 0.87 A/R, 8.6 to compression, 256/8.8 inlet & 264/9.0 exhaust cams, exhaust cam timing 6 degrees retarded, boost at 3,700 rpm, max power ? rwkw at ? bar.

There are a couple of bits of missing information (or maybe I simply missed them), plus you don't mention ignition timing. The lower compression ratio should have allowed more advance. How much? On the other hand it will have cost you around 250 rpm in boost build, of the 700 rpm you have "lost".

My humble opinion, I don't think it has anything to do with the length of the primary pipes. I have previously done back to back with a standard RB20 manifold and a GTSR tuned length (low, rear mount) manifold. It made more power everywhere and I don't think you could get longer primary pipes than a GTSR set.

Maybe fill in the missing bits of data if you can, but my guess right now would be something else is wrong. Unless the manifold has very severe interference problems. But that seems unlikely given the previous results.

What I would do;

1. do a leak down test

2. check the ignition timing with a timing light every 1,000 rpm from 2,000 rpm to 8,000 rpm.

3. Measure the primary pipe length and ID and feed it into any of the online exhaust design software. That will tell you the tuned rpm for your size of engine. It should also tell you the severe reversion rpm's (there should be 3).

4. If none of the above sheds any light, then I would stick the standard cams back in at standard timing.

5. Then work your way through the stages.

Hope that helps.

[Steve]

Ben, by comparison the HKS GT3037 has a 84mm exhaust wheel. I suppose you could say ARs are not ARs:)

Correct me if I am wrong, transposition of formula:

A/R = .69 therefore, A= R x .69

By increasing the Radius, the Area will therefore increase too, to use arbitary figures:

if R = 30mm, x .69 = an Area of 20.7

if R = 45mm, x .69 = an Area of 31.05

Add to these figures that you have a bigger exhaust wheel, and quite possibly a bigger exhaust opening, and you can see that a small turbo with an AR of 0.8 could be alot smaller than a bigger turbo with an AR of 0.6

So it is probably a bit inaccurate saying a certain size AR is suitable for a specific hp IMHO.

[Freebaggin]

Ben, by comparison the HKS GT3037 has a 84mm exhaust wheel.  I suppose you could say ARs are not ARs:)

Correct me if I am wrong, transposition of formula:

A/R = .69 therefore, A= R x .69

By increasing the Radius, the Area will therefore increase too, to use arbitary figures:

if R = 30mm, x .69 = an Area of 20.7

if R = 45mm, x .69 = an Area of 31.05

Add to these figures that you have a bigger exhaust wheel, and quite possibly a bigger exhaust opening, and you can see that a small turbo with an AR of 0.8 could be alot smaller than a bigger turbo with an AR of 0.6

So it is probably a bit inaccurate saying a certain size AR is suitable for a specific hp IMHO.

The HKS 3037S or 3037 has a 60mm large and 55mm exducer diameter, exactly the same as the GT30 series Garrett, again, it's all on http://www.hksusa.com/categories/more.asp?id=1092

The 84 refers to trim (which is small diameter squared divided by large diameter squared x 100). Plenty of Garrett sites to confirm numbers.

But anyway, it's all gotta add up to less turbo response at low RPM...lower comp ratio, larger duration cams (particularly exhaust), larger A/R exhaust housing. As we know things get magnified on turbo engines and are cumulative. Really the only thing that may have helped broaden the power range is the increased cam lift.

GTS-T VSPEC, What boost are you running to achieve that power? I assume you are runing stock pistons as well. I have GT30/40 with stock exhaust manifold, internal wastegate, stock head and pistons. I have 253rwkW at 17psi with 15° timing and 11.8 a/f ratio and want to start pushing it harder and need to go the next step.

Steve, great thread, good on ya for opening up discussion.

[Steve]

paul, I know that something is wrong, I am not saying the longer runners are the entire fault, and I agree that boost should be alot earlier than where it is, even with a manifold with longer runners (although they will make a difference to how boost is made). I am thinking that there must be some sort of crazy interferance happening where the runners join - what else could it be? If you know something I dont, please do tell.

freebaggin, oops, my bad, it was late and I was tired when I posted that one, sorry for the misleading info.

Sydneykid, 1 bar of boost now happens at around 5000rpm, so lag has increased by 2000rpm. Positive boost doesnt start building until just before 4000rpm.

Richard who tuned the car, and has done a couple in this trim, said he couldnt understand why it was taking so much ign timing, didnt say exactly how much, but did say 20odd degrees more than he would expect. He did a great job of improving off boost driveability and getting the lag down - before he started it was around 800-1000rpm more lag.

I dont know what rwkw, it hasnt been on a dyno, only street tuned.

Before I go replacing the cams, I will change the turbine housing, Richard said he wants to have a good look at the manifold - which is understandable, next will be the inlet cam, then the exhaust cam. Only thing delaying me is that I paid over $1700 more than I was quoted to get the cams etc changed, and with christmas around the corner, well it may be a back seat for a while.

If it isnt the manifold, what the hell could it be? Cams are a good thing, turbo is a good thing, head gasket has the CR above a GTR CR, so it wont be hurting things too much. The 0.87 is the recommended AR for that turbo for the street (by HKS) and shouldnt useable boost in after 4000rpm, which is where I need to get it back to.

[Steve]

Sydneykid, also, you wouldnt have a URL for online exhaust design software would you?

Cheers

[Warpspeed]

Steve, one thing you can do yourself for minimal cost is go out and get yourself a degree wheel and a cheapie dial indicator.

Without actually changing anything, find out exactly where the inlet and exhaust valve opening and closing points are.

I still think the engine is not producing enough exhaust flow. Excessive advance requirement strongly suggests a serious combustion problem. The two biggest influences here are compression ratio and exhaust dilution from reversion.

[Steve]

Could you explain how to use a degree wheel and dial indicator?

I agree that the problem is insufficient exhaust gas velocity, but wouldnt the reversion be caused by a poorly designed manifold?

[Steve]

I knew as soon as I drove the car that something was seriously amiss.

I first thought that perpaps my cams had been incorrectly installed, but I just have so much trouble believing that the HKS step one cams are causing so many problems - surely this would have come to light before.

Richards first thought was that something had been installed incorrectly, but he checked everything and its ok - I really wish it wasnt:)

Another anomoly, the idle is almost perfect (apart from intermittent hunting) there is absolutely no lumpy idle sound?

Its pretty frustrating, but if you can give me a heads up on how to use the degree wheel and dial indicator, I will give it a go.

Cheers

Steve

[JimX]

How do you dial a cam in? Is there a level of adjustment between the cam and the lug that the cam wheel sits on? Where exactly does the dial sit and how does it measure what angle the cam is at?

These are things I've wondered for a long time but before now couldn't be bothered learning. Installing your own cam wheels piques your curiosity