What do you guys think..valve float?

[Techno Duck]

Went up to CT for a dyno day with a few guys from Rennlist. Dyno'ed my n/a 944 as i was really curious to see what power it was making.

The car made 125.7whp @5900rpm and on my last pull made 136whp @ 7k rpm. As you can see the dyno plot is all over the place. Everyone seemed to think it was due to valve float. The engine has very mild work done to it.

-Full SFR 2.5'' exhaust and no cat
-Run was made with FRWilk's chip however i had it switched off and was using the stock fuel map
-Rebuilt head with 5 angle valve job but with original valve springs
-Engine is in pretty good tune.. all new vac lines and hoses, Magnecore wires..relativley new cap and rotor and maybe 10k miles on the FPR.
-Stock airbox and paper filter
-Cleaned and flowtested injectors with less than 10k miles on them
-A/C delete
-Engine has 99,800 miles on it
-Pull done in 4th gear on load type dyno



What do you guys think? Im not really sure what else could be causing a power drop off like this. Any ideas?

It was an interesting day.. one Rennlister made 602whp @ 28psi on his stock displacement 951 .

[parish8]

did they log a/f ratio for you? is there any way to log timing on these things?

doesn't look like valve float to me. valve float usualy kicks in at high rpm and then drops hard when it hits. your graph is all over the place. i have seen graphs like that with tires that were sliping on the dyno but at 125rwhp thats not a problem.

did it sound ok? could you hear the power modulating like the dyno numbers are showing?

[VINMAN]

Definately not valve float. I've never seen spikes and drops like that. I agree with Parish that you would hear a difference in the engine sound with a reading like that.

[jkrustchinsky]

thats off, i cant belive our n/a cars hardly push 130hp, thats awful

[Techno Duck]

130whp is pretty good for a stock motor.. rated at 147hp they 'should' put down around 125whp if you account for drivetrain loss. I figure 125whp is pretty good considering its 20 years old and has just under 100k miles on it.

Anyway, the car sounded fine throughout the RPM range and runs great. Unfortunetley the dyno did not have a wideband hookup.. and i cant see the worth in installing a standalone system in the car. (Though my turbo has one for obvious reasons).

BTW, here is a short video of the pulls made

http://s24.photobucket.com/albums/c47/porsche951/?action=view&current=TechnoDuck.flv

[parish8]

if it sounded good and feels good on the street then i doubt those numbers are correct. you should be able to hear changes in power like that on the dyno if it is real.

125rwhp seems prety good to me too. especialy on a loaded dyno.

[fast924S]

How did you pull 7k rpm with the stock Maps??? The dyno chart does look funny from 5-6K rpm it jumps all over but it sounds good on the video. Do the run again with the FR wilk chip ON

[Techno Duck]

The first run with the FRWilk chip was worse than with the stock maps (or atleast with the chip set to stock maps). Its possible what the loaded dyno read as 7000 rpm could be a bit off as we had to calibrate the dyno for each car. Basically i ran the car at 3000rpm in 4th gear..so it could possible be off around 200rpm.

Anyhow the first run with the FRWilk chip made 115whp... im not sure what that was about. Something is probably amiss, im just not sure what.

[fast924S]

Yea, That doesnt sound right, Wish you had some A/F ratios . Thing is 125hp doesnt sound bad for this engine, but the dyno chart looks funny. Thing is if it was a lean condition you would have low power all the time not up and down like it is. It could also be a dyno/software error. As much of a PITA as it would be I would try to go somewhere else to get the dyno run down and try to keep as many things as I could the same as the last run. If it does it again then you know its your car.

Where in CT did you get the dyno done?

[Techno Duck]

It was done at a place in Danbury. It is unfortunate i dont have a/f's and i probably wont be dynoing this car again any time soon (or ever). I might be up in that neck of the woods again before the end of the year at Farnbacher Loels (also in Danbury) but im not sure yet.

The tech definietley knew what he was doing and a few other guys ran without issue.

[idontknow]

Nice oscillations there. Does the FR'd chip results have (roughly) the same wave pattern?

My $.02:
If it's just your car and nobody else noticed the same Id hazard to guess that the AFM may be creaking as it opens. The valleys are when the barn door is sticking and the peaks would be when the door creaks open.

Or possibly the wiper contacts aren't giving proper resistance values.

The test is run in WOT so I wouldn't place the blame on the O2 sensor.

Care to post the FR'd results for S&Gs?

[Schumi]

...am I the only one who wants to hear more about the 602rwhp 951? pics?!

[Rick V]

JMO, those readings are a problem with the dyno. If your car was actually running like that it would be hammering badly, and you would have backed out.............fast! I doubt it was valve float, since the car still runs, those peaks/vallys are huge. Not your problem. You didn't have some allterain tires on it did you?

[jackpine savage]

Originally Posted by Schumi

...am I the only one who wants to hear more about the 602rwhp 951? pics?!

No you're not! A stock 951?! WOW!

From my tuning experience with two wheeled racing creatures I'd have to say this is a fuel related issue;

a. A bad load of fuel from recent pumping.

b. Fuel filter is loaded with crap as well, as a result.

I have experienced this firsthand and it has lead me to avoid fueling up a vehicle, 2 wheels or 4, near a weekend when the fuel tankers dump fresh loads for the weekend drivers. The tip off I see in the dyno sheet is that it cleans up, relatively, at higher RPMs.

[924Sman]

You don't suppose the stock air intake with the head opened up and the exhaust opened up and using old springs has any effect?! I will bet those springs are weak after 20 years.

From where I sit it appears the air in and out are now substantially different. You have a stock airbox while the head and exhaust are opened for more flow and not getting it due to the restrictive stock box.

Just a hunch is all

Dal

[fast924S]

924Sman, Its a good idea but I dont think in would cause peaks and drop offs like that. If it was Restricted it would just vally out or not make anymore power and peak out early. If it was valve float it would happen in the upper RPMs and you would have a huge HP drop and you would hear it

[Brando]

Dyno problem.

OR

The resolution between RPM ranges and HP/TQ readings is set VERY fine.

Here's what a dyno should look like on a stock 944:


Sure there are peaks and valleys, but in actuality they are minor slopes and slight inclines. What you showed would be (if it were your car):

Running on 2/3 cylinders.
SEVERE fuel/spark problem (too much, too little, etc)
Wheels slipping on the dyno.

You mentioned they had to "re-configure" the dyno for each car... Usually you do it once, set the number of cylinders and go. Also, you run in 3rd gear, 3rd OR 4th if it's a 6-speed. Go somewhere a competent operator is -- these guys messed up somewhere. I hope you didn't pay for that.

[parish8]

everything i have ever heard says to dyno in your 1-1 gear or direct drive gear. 4th gear would be the closest to that on these cars. where does dynoing in 3rd come from?

[HondaDustR]

Originally Posted by parish8

where does dynoing in 3rd come from?

Youtube...

[onZedge]

If the dyno is actually correct, it could be anything(s)...

-ignition problem
-slipping clutch
-bald, um... racing depth tires
-fuel pressure problem
-faulty AFS signal
-big vacuum leak
-DYNO OPERATOR ERROR