Went to Chassis Dyno, have question.


135 CI of Pure Power
Nov 6, 2003
Went the the Dyno, made several pulls.

Here is the problem/question.

Power was good at 26.5 psi of boost pressure.
Upped the boost to 31 psi and saw very little change, almost none!

What would cause this?

Probably out of the...

efficiency range of the turbo. Adding more boost just increases the temperature that negates the added boost.
What turbo are you running?
HTH, CaptRob
Not sure of this, but maybe you reach a point where the heads will not flow enough in the time allowed by valve opening to make use of any additional air flow??? is that possible here?
Turbo is the following specs:

T04E Compressor Housing with T04E 50trim Wheel
.63 A/R T3 Turbine Housing with Stage III Wheel

Actually we had two cars dyno.

Car 1, the one mentioned had the problem.
Car 2, ran fine.

Cars are identical except for a ported head.
Car 1 has the ported head, big valves.
Car 2 has a stock head

Car 2 seen an increase all the way up to 34 psi, before we called it a day.

Car 2 made more power than car 1.
Originally posted by TrboVan
Car 2 made more power than car 1.

Let me add,
Car 1 made more power at 26 psi vs car 2 at 26 psi.

Car 1 made same HP @ 26.5 psi that it took car 2 to make at 33 psi
Originally posted by Quick6
Not sure of this, but maybe you reach a point where the heads will not flow enough in the time allowed by valve opening to make use of any additional air flow??? is that possible here?

Are you talking a cam change is in order?
Wow, lots of views but many comments or suggestions.

Is there a better section of the forum for the question at hand?
The first reply you got hit the nail on the head. Car #1 is flowing more air at the same boost and maxes out the turbo's airflow capabilities at 26 psi; it takes Car #2 until 34 psi to do the same. If you step up the turbo size on Car 1, you will see gains. If you had turbo discharge temperature gauges, I would bet you'd see the temp on car #1 go through the roof after 26 psi.
We have been looking at the same thing on our 240sx. Do you have enough fuel? We think that we are running out of turbo. Either way, you need both to make more horsepower.:)
Not running out of fuel.
Even tried an extra fuel injector direct into intake tract.
I notice a rating on this thread.

Can you tell me what is so bad about it?
(Or are you hiding behind the keyboard again?)
I don't like the thread rating system. :mad:

Cowards give it a bad rating and don't have to reply. I've seen many good posts get 1 star so don't sweat it. I don't think many here care anyways..

The One Star Bandit strikes again ;)

Yes, this self appointed editor hides behind his keyboard. He finds all of my posts :)

I like your post, I learned something from it ....

I do have lots more information to bring to the table.
I will do that in a few minutes.

LOOK! It's a troll, it's a post whore, no, no, it's the 5 star bandit!

He just took care of that one star bandit by bumping the tread to a whopping 3 stars! Not good enough for Star Search, but it sure helps your self esteem! :D
Okay, I am NOT convinced it is the Turbo, and here is why:

Map for Car #1 (27 psi)

Map for Car #2 (34 psi)

Car #1 actually has better numbers (according to compressor map)

Your thoughts?
How did you determine the airflow? A rough rule-of-thumb that seems to work well is hp=10*airflow in lb/min so you are using about 390 flywheel hp. What did you get on the dyno for rwhp?
Hmm. Sounds reasonable as to hp and air. Any chance you had a wbo2 sensor to get the actual air-fuel ratio? Assuming this was with race gas and higher timing (25+ degrees) you could probably use 0.5 as the bsfc and calculate the actual airflow just to compare. Otherwise I'm out of ideas just now, sorry.