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Same Power Different Boost

Brezza

By Brezza,
in Engines & Forced Induction

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

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.

Yeah look @ people like Paul who are making ~420rwkw on stock manifolds, E85, 2.8l and 23-25psi

Pretty big difference.

Im almost the same power for boost as you on PULP, also have a junk exhaust atm.

Brezza Proficient

Brezza

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Posted

Yeah look @ people like Paul who are making ~420rwkw on stock manifolds, E85, 2.8l and 23-25psi

Pretty big difference.

Im almost the same power for boost as you on PULP, also have a junk exhaust atm.

Yea well Paul has a full twin 3 inch so his is ideal!

i think the 2.8L and twin 3inch exhausts from turbo would make a fair difference.

i dont think i'd get close to that power on a 2.6L even with a 3in from the turbo back.

bigmikespec Veteran

bigmikespec

Posted
Posted (edited)

Stock manifolds are not the issue here. Enough of us flow over 400rwkw with them.

I'd put new type A tomei springs in and see how you go.

I want to earn what you are! You can put Supertech ones in there considering Supertech make them for Tomei, no JDM tax.

Edited by bigmikespec
GTSBoy Grand Master

GTSBoy

Posted
Posted

My thought ref the dyno graphs. The boost on the 25 psi run looks a lot like you have valve float. Look at the peaks of the boost line vs the peaks of the power line. They don't line up. It is making more power when the boost is lower on each fluctuation and less power when the boost is higher.

rob82 Mentor

rob82

Posted
Posted

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.

You haven't tuned enough ba xr6t's have you. They run conical springs which is good for fuel economy but not for holding a valve on it's seat when the revs and exh back pressure are high. What you see is a massive dip in power at the reonant point of the spring and then the power comes back towards the rev limit.

But Ive also seen what you've seen in regards to swapping springs in and making more power even when the only symptom is slightly low power.

The interesting thing on the low boost graph is that the power falls away high in the rev range suggesting that springs are possibly not up to the task. Bangs some springs in and stabilize your boost and I think you'll be on the right path.

HYPED6 Collaborator

HYPED6

Posted
Posted

You haven't tuned enough ba xr6t's have you. They run conical springs which is good for fuel economy but not for holding a valve on it's seat when the revs and exh back pressure are high. What you see is a massive dip in power at the reonant point of the spring and then the power comes back towards the rev limit.

This is true, I have tuned many an XR6 turbo. Did 2 last week actually. I wont normally touch them without putting springs in them first.

Rolls Grand Master

Rolls

Posted
Posted (edited)

My thought ref the dyno graphs. The boost on the 25 psi run looks a lot like you have valve float. Look at the peaks of the boost line vs the peaks of the power line. They don't line up. It is making more power when the boost is lower on each fluctuation and less power when the boost is higher.

Sensors can lag, I had one that lagged massively (had a problem) making my car look like a laggy piece of shit with the boost plot, but the power curve didn't match the boost curve. Oscillations like that could very well have lag attached to them which is why they don't line up.

Most the sensors have response times in the ms range but if it is hooked up funny or has problems I have seen it before.

Edited by Rolls
HYPED6 Collaborator

HYPED6

Posted
Posted

After looking at your graphs Im not sold its your springs.

Sensor lag is a consideration. Having them closer to the engine is better for speed, but the factory 4 wire sensors that come with old DD dynos are super slow.

A proper 5 wire should be used as they are much faster and more accurate in richer mixtures...... but that's another story so.......

Back to the story at hand......

Looking at your graphs I would say a fair bit of timing has been pulled over 24psi. Following the graphs as the boost comes up, power actually drops.

As the boost comes down power comes back up. I think if you had the boost control sorted, so the timing at full throttle wouldn't be jumping all over the place with boost pressures there would be gains to have.

Its not in the mixtures because they don't follow the same pattern. I wouldn't be pulling your springs just yet.

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