Same Power Different Boost

[GTR_JOEY]

you should be able to see valve float in a dyno graph

[bigmikespec]

I am starting to think that the issue is the turbo's.

Don't matter if it was ok on 25psi before, fact is that your turbo's were out of puff before on 25psi, and when you free'd up the engine a little the turbo's are out of puff on 20psi and still making the same power because its flowing its maximum amount of air.

remember boost is your mortal enemy, the less boost you run the better.

Don't compare your -5 results to other peoples, different cars, different engines, different elevaion, different dyno's... etc etc so please don't tell me (ohhh but it should be making X amount of HP) this is tuning not maths.

An engine is a big air pump, the more air that goes in and out the more power you will make, so you had your turbos running at its max air flow and instead of upgrading them you just made it easier for them to flow the same amount of air at a lesser boost pressure, which is a mod done well if you ask me!

If you want to move forward in power then upgrade those turbo's. Grab a big single T51r or something and then start pumping some serious air into the engine or leave it how it is and be happy with what you got.

^^^ yes!

[Brezza]

I gotta say that the type b's and -5's are a great match when you're pumping some air through those turbo's

i'd definitely reccomend putting those cams on a rb26 when you've got those turbo's and are wanting to shoot for 350kw because the gains are to be had everywhere! the low end response isnt really effected much at all. it actually makes more grunt lower in the rev range, and when on boost the car pulls hard right to redline!

definitely a damn good street cam, and it can sound a little lumpy on idle if you want it to be.

having 360kw at the wheels all day everyday is a pretty good feeling.

i wouldnt mind changing the exhaust (dump & manifolds) if it was an easy enough job to do myself. but to pay someone a whole day's work isnt really worth it if its not going to net any gains.

i do wonder how the car would sound with 3in exhaust off the turbo's to a 4in cat back?

i'm still working on getting a graph from the tuner.

[The Mafia]

hey mate, further to what GuiltToy said, try and picture this.

I must say though, I am no expert, this was a very wild guess at what could be happening, and just an explaination on boost resistance vs flow.

Remember, boost is evil, and flow is your friend.

26psi is where you were, and 20psi is where you are now. Remember, boost isn't how much air is flowing through your engine, its how much your engine is resisting it.

Edited March 7, 2012 by The Mafia

[HYPED6]

you should be able to see valve float in a dyno graph

Im no expert.......... but how?

[GTR_JOEY]

well someone correct me if im wrong, but you will see flat spots at the top end of dyno graph where the engine is reving hard

[mico]

Im no expert.......... but how?

yeah u are thinkin springs too.

[Rolls]

Im no expert.......... but how?

Sometimes see weird dips at the top end that get worse and worse

[HYPED6]

Sometimes see weird dips at the top end that get worse and worse

I still have never seen this.

I have seen more boost, same power and same RPM ceiling. I have also seen engines with "good springs" that make good power to 9000rpm.... at 36psi boost

Then change the springs, same power curve but 80 more rwhp on the same boost pressure.........

Maybe on a NA LS engine they may do "funny" things in the top end...... never on an rb.

[Rolls]

Yeah I am only going by what Ive been told. Often it does what you said, just kills the top end power and the curve still looks smooth.

[HYPED6]

Everything being equal, More boost, no more power = Valve springs.

Providing you have all the supporting mods to handle the power.

when looking for power..... there are certain things that play a huge part in how your springs will perform.

I think I have said too much all ready.

[Guilt-Toy]

springs.... I was making 380kw at wheels with springs that were 360,000km old from a RB25 vct head.

GTR springs are much better then rb25 ones.. I have upgraded since the new cams went in.

[FineLine]

I'm with hyped 6, Too many times now we've seen good builds not perform only to change out valve springs and get the desired results.

[HYPED6]

This is true. I have seen standard 2JZ springs handle well over 30 psi. I have also seen them fall over well and truly at 23 psi

I have seen standard 1JZ springs handle high 40's....... even 50 psi. But the 50 was on gas, so I cant rely on that.

Again, 1JZ standard springs..... 26 psi.... nothing more.

I have also seen aftermarket RB26 springs handle 21 psi........ and not a psi more. Not even half a psi more. Replace nothing but the springs and stopped at 32psi.

RB30 aftermarket springs..... topped out at 46 psi. Replace the springs and got up to 51 psi and made a bucket lead more power. Still yet to wind it up further.

Now remember, all things being equal... Every engine here has, the turbo, exhaust, intercooler, fuel system and correct fuel for the application.

Im in no way saying that springs are 100% your issue. But if everything...... and I mean everything, not most things will support or over support the power level for your engine then springs may be the next option.

Edited March 8, 2012 by HYPED6

[r33_racer]

Have you measured the exhaust back pressure in the manifolds before the turbos?

Im not refuting the valve spring theory as that is most likely the problem, its always the silent killer that people overlook.

But is it possible that maybe the intake to exhaust pressure ratio is getting out of hand also (around 2:1 or maybe closer to 3:1) hence why the 25psi runs are going silly... Unless others have achieved greater numbers on similar setups with these turbos with no backpressure issues.

[HYPED6]

Have you measured the exhaust back pressure in the manifolds before the turbos?

Im not refuting the valve spring theory as that is most likely the problem, its always the silent killer that people overlook.

But is it possible that maybe the intake to exhaust pressure ratio is getting out of hand also (around 2:1 or maybe closer to 3:1) hence why the 25psi runs are going silly... Unless others have achieved greater numbers on similar setups with these turbos with no backpressure issues.

Im not being silly. And im throwing this out to any one on the forum that tunes.

Has any one ever measured pressure in an exhaust manifold?

[R31Nismoid]

I still have never seen this.

I have seen more boost, same power and same RPM ceiling. I have also seen engines with "good springs" that make good power to 9000rpm.... at 36psi boost

Then change the springs, same power curve but 80 more rwhp on the same boost pressure.........

Maybe on a NA LS engine they may do "funny" things in the top end...... never on an rb.

Often people misinterpret the dips on the newer DD sheets that can get a little wavy simple due to the resolution/scale of the graph as opposed to anything else and then springs are an issue - and thus the 'connection' is made, albeit incorrectly.

Yeah I am only going by what Ive been told.

[Brezza]

Everything being equal, More boost, no more power = Valve springs.

Providing you have all the supporting mods to handle the power.

when looking for power..... there are certain things that play a huge part in how your springs will perform.

I think I have said too much all ready.

i'm not ruling springs out, but i think you might be onto something here? the cams are still pretty mild. 260 degree 9.15lift they're a drop in, no relieving the head and no requirement for aftermarket springs. that's not to say that the std ones arent tired. but they should be up to the task.

This is true. I have seen standard 2JZ springs handle well over 30 psi. I have also seen them fall over well and truly at 23 psi

I have seen standard 1JZ springs handle high 40's....... even 50 psi. But the 50 was on gas, so I cant rely on that.

Again, 1JZ standard springs..... 26 psi.... nothing more.

I have also seen aftermarket RB26 springs handle 21 psi........ and not a psi more. Not even half a psi more. Replace nothing but the springs and stopped at 32psi.

RB30 aftermarket springs..... topped out at 46 psi. Replace the springs and got up to 51 psi and made a bucket lead more power. Still yet to wind it up further.

Now remember, all things being equal... Every engine here has, the turbo, exhaust, intercooler, fuel system and correct fuel for the application.

Im in no way saying that springs are 100% your issue. But if everything...... and I mean everything, not most things will support or over support the power level for your engine then springs may be the next option.

again the case might be that the exhaust is not up to the task, or manifolds are not flowing enough? or possibly turbo's are going outside of their efficiency?

from my understanding the main difference between -7's, -5's and -10's are the exaust housing? so in theory they can flow much more? so that got me thinking it might be more likely that the exhaust manifold or the dump pipe (mainly dump pipe - i think its a 65mm max, could be 60mm) these things might be choking the engine from breathing more?

Have you measured the exhaust back pressure in the manifolds before the turbos?

Im not refuting the valve spring theory as that is most likely the problem, its always the silent killer that people overlook.

But is it possible that maybe the intake to exhaust pressure ratio is getting out of hand also (around 2:1 or maybe closer to 3:1) hence why the 25psi runs are going silly... Unless others have achieved greater numbers on similar setups with these turbos with no backpressure issues.

I'm getting the dyno graphs emailed from the tuner and i'll put them up when they come.

also, does anyone know how hard it is to change the manifolds and dump pipes? i've got the manual for the GTR and have read through the steps to removing the turbo's and in theory it doesnt sound too hard. but when you add in the limited working space and possibly tight nuts then its so much harder.

[r33_racer]

Im not being silly. And im throwing this out to any one on the forum that tunes.

Has any one ever measured pressure in an exhaust manifold?

I dont tune...but I have on several occassions with our race car when diagnosing problems on the dyno. We have a 1/8th npt bung in the collector on our manifolds so its possible if a problem occurrs where back pressure is the suspected culprit.

[EAT26]

I'm getting the dyno graphs emailed from the tuner and i'll put them up when they come.

also, does anyone know how hard it is to change the manifolds and dump pipes? i've got the manual for the GTR and have read through the steps to removing the turbo's and in theory it doesnt sound too hard. but when you add in the limited working space and possibly tight nuts then its so much harder.

I would dare say it's not your manifolds, standard manifolds have proven to flow quite well to a certain point to which I believe is over 400kw.

What was your power figure before E85? and what are the exact mods?

I am running -5s and was putting out 350rwkw at 21psi on BP98, before my rebuild and I have a restrictive exhaust... Tomei dumps, restrictive front pipe, 3" cat and 3" to 3 1/2" Kaki exhaust.

Not to compare apples to oranges but Xr6Turbo engines their valve springs tend to start floating around the 13psi mark even when the car only has 10 thousand+ kms on it, its a known problem with the ford engines. Working on the same theory with Rb26s that are a minimum 10 years old you have to add fatigue to the scenario...

This is why when I got my engine rebuilt, I got Supertech springs put in just for a little more peace of mind.