-5's Vs Rs's On A Larger Then Stock Motor

[rockabilly]

so 87 is

87 divided by 28 times 1000 correct?.

87/28 3.107 x 1000 = 3107rpm

[rockabilly]

so the graph only goes to 6500 rpm?.

[Piggaz]

Here is my little story. I have been wondering the same thing the last 6 months or so. This is what I have found.

I bought my gtr with plain bearing -5's. Now with

Cams, 10.25 @ 292

Good after market front mount

Very good fuel

Stock dumps

Stock but ported exhaust manifolds

After market exhaust

After market ECU

Fuel systems to support anything I threw at it

Made around 490 rwhp on around 20 psi. Boost control was rubbish. Needed one solenoid per turbo and a 32x32 table just to get any descent control.

If I rung its neck.... (shut the wastegates) it would spike to 2 bar as it came on to boost and 22 psi at 850rpm it would make 530 rwhp. Rubbish.

Now I thought that this was under powered. So made some 2.5inch dumps. No difference

Shortly after one turbo died.

I bought some shiny new -10's.

Made some 3 inch dump pipes. Twin 3 inch front pipe to single 4 inch system.

Engine now makes 400rwhp on 10psi. Much better

Bloody thing hits another brick wall at 480 rwhp!!!! Regardless of boost levels. Regardless of ignition timing or fueling etc.

Now. I believe its the standard exhaust manifolds. I really do believe that is the key to making big power out of these turbos.

At the moment I am currently fitting a single turbo charger. Its the only thing I am changing so it will be a reasonable back to back.

Has any one else seen anything else similar?

When my car was on the dyno a few weeks ago we went from 1.7 to 2.0 bar. I made an extra 12 kw (414rwkw) or something stupid so we pegged it back to 1.7 bar. I think my exhuast is too small but also I reckon my head port doesnt match my setup. Its a little lethargic down low but doesnt make mega numbers up top.

Are manifolds stock or port matched. N1GTR's manifolds are standard and makes more power then that.

Those 292 cams are bloody MASSIVE!

[GTScotT]

Here is my little story. I have been wondering the same thing the last 6 months or so. This is what I have found.

I bought my gtr with plain bearing -5's. Now with

Cams, 10.25 @ 292

Good after market front mount

Very good fuel

Stock dumps

Stock but ported exhaust manifolds

After market exhaust

Do not just keep throwing money at it. Find a real mechanic if you cannot get the thing to work.

You have not mentioned anything about the motor itself. What sort of head work do you have to support 292x10.25 cams and what sort of motor have you got that would do the 10,000rpm those cams imply?

If the answer is none you have some major issues. I am horrified of the thought of this thing.. I would personally put pencil to paper and plot exactly what I want from it and the setup I anticipate will get me there. I would then pull the motor out and strip it back to a long motor, refitting only parts that suit what I have set out to plan.

No number of band aids, double sided tape, sikaflex or zip ties will stop cut wrists from bleeding out. Get onto a real fix, maybe even start your own thread in the members ride section to properly introduce yourself and the car so you may start an active discussion to help your cause.

It honestly does sound like you have a hungry money pit, see below.

[R31Nismoid]

Ye stock manifolds have made over 400rwkw on a number of cars, they certainly are not the issue.

[Piggaz]

Gav how long have you had your Tomei manifolds on your car? I have been through two sets. Cracks, holes blown in runners and the last set didnt make it to 2000 kms. Alot of that was on E85 (second set) too.

[GTRNUR]

Gav how long have you had your Tomei manifolds on your car? I have been through two sets. Cracks, holes blown in runners and the last set didnt make it to 2000 kms. Alot of that was on E85 (second set) too.

I'd be having a good look at your tune, and your EGT's. These manifolds shouldnt crack if your tune was correct for normal unleadded fuels.

While switching to an alcohol based fuel in theory lowers combustion temps and EGT's, the way many people are setting up their E85 engines with higher compression means the common target afr charts dont produce an EGT that is in the safe range. Ive heard stories of melted exhaust valve guides in alcohol based fuel engines that run compression at the higher end of the scale, so it stands to reason that a moderate increase in EGT's could certainly cause stress cracks in in a manifold.

[Tangles]

I never stop enjoying looking @ that difference

an amazing difference in midrange!

[Piggaz]

an amazing difference in midrange!

Damn right it is. If you look up the hot side of the turbo's they are exactly the same.

Gav, were the turbo's modified in anyway or were they straight out of the box and bolted up?

[SimonR32]

so the graph only goes to 6500 rpm?.

6800rpm by the calculations... But I do believe Gav runs 4.3's so would be more along the lines on 7200rpm

Edited January 9, 2011 by SimonR32

[Piggaz]

I'd be having a good look at your tune, and your EGT's. These manifolds shouldnt crack if your tune was correct for normal unleadded fuels.

While switching to an alcohol based fuel in theory lowers combustion temps and EGT's, the way many people are setting up their E85 engines with higher compression means the common target afr charts dont produce an EGT that is in the safe range. Ive heard stories of melted exhaust valve guides in alcohol based fuel engines that run compression at the higher end of the scale, so it stands to reason that a moderate increase in EGT's could certainly cause stress cracks in in a manifold.

Thats a good point. My engine is 9.0:1 comp so it is highish. Next time I go back I might mention it to Yavuz (the tuner) and see what he reckons? Either way im back on ported stockers.

[rockabilly]

could anyone overlay my graph onto avs please. just for comparisons..thanks

[R31Nismoid]

Either way im back on ported stockers.

Ah already done...

Notice any difference?

[Gav]

Gav how long have you had your Tomei manifolds on your car? I have been through two sets. Cracks, holes blown in runners and the last set didnt make it to 2000 kms. Alot of that was on E85 (second set) too.

Actually, I'm not overly impressed with the Tomei manifolds for that reason. I had cracks in the first set that I had welded. Then I found they had burn't through on the outside of the runners. I'm on my second set now and if these fail I'm going back to cast iron units.

On the graph I posted, I did forget to mention I'm running GTS-4 ratios. I'll track down an updated E85 dump graph showing the other set-ups with RPM on the X axis.

[Piggaz]

Ah already done...

Notice any difference?

It could be placebo but it feels like there is. But that could be just my head. I want to get another set and extrude hone them and really get it spot on! So many people swear by the stockers.... and going by Gav's post above me he has had issues with the Tomei's aswell!

[Granthem]

RPM = (SPEED / 28) * 1000

to work out RPM from a speed based dyno plot, assumes 4th gear with 4.11 diff gears

This doesnt really work for mine, as I doubt my car makes 340rwhp @ 6250rpm. Its more like 7250rpm. Hmmmm.

[r32-25t]

It could be placebo but it feels like there is. But that could be just my head. I want to get another set and extrude hone them and really get it spot on! So many people swear by the stockers.... and going by Gav's post above me he has had issues with the Tomei's aswell!

Leave the things alone

[Piggaz]

Gav, were your -5's straight out of the box or were the tinkered with?

[Gav]

Gav, were your -5's straight out of the box or were the tinkered with?

With the exception of HKS actuators they are bog stock.

These did need a freshen up with seals and other bits and pieces (maybe bearings) recently after around 5,000 km of mainly hard track time. Still have the same exhaust and compressor wheels 'tho.

[Nee-san]

Like most cylindrical tubes there is such a thing as too much fiddling