Jim Mayzurk and I dynoed our cars this morning to get some bench mark numbers before we do some mods.
Both 93 GTS's, same fuel, same dyno, same time, temp, elevation ect ect.

Our numbers are very similar as you can see from the charts below.

Are they low? Is the auto OK and the 5 speed low?
Should the 5 speed and the auto be the same (we thought there was a 15% v 20% difference)

On the auto should there be a flappy dip as I do not see one.

Both Jim and I know nothing about the interpretation of the charts and would appreciate the boards thoughts.

 

I was pulling 280RWHP on my'87S4 5 speed pre supercharger.

 

With no mods on a Dynojet? Frankly, I doubt it.

 

Are you referring to Adam's post?

My '91 pulled 294 rwhp on a DynoJet - stock except for RMB. Yes I have the charts and witnesses.

The GTSs:

The auto's flappy is non-operational.

I have not seen a GTS dyno chart until now. The 5-speeds A/F curve seems to stay too lean too long. A/F curves always start lean - a throttle tip-in transient - but they should quickly drop to less than 14 and remain between 13 and 12 for the entire run. Max power is around 12.6. But, the A/F curves in the GTS charts are hard to read 'cause they're all smushed together.


EDIT: Roger - if you have the raw numbers - I can plug them in to excell with other dyno jet numbers for comparative purposes.

 

With and RMB, Maganflow cats, on a dynojet. No big deal, Pal.

 

Dave,
Thanks for your input.
If my flappy was working - it works when I pull a vacuum on it - what would you expect me to see?
Would the Spanner tell me if it works or not? Any other ideas?

So a GTS has less power than an S4 at the wheels?
Roger

 

Dave,
I will go back and ask for the raw numbers. Is it a file that they could email to me?
Roger

 

You mean that the actuator works when you disconnect the line at the solenoid and apply vacuum? If so good - 'cause that's the hard part. However, that doesn't mean that the system works.

Look at the 5-speed torque curve. You will see two distinct humps. The low-rpm hump is larger in amplitude than the second hump but the second hump is visible. Then look at your auto's torque curve and you will see no second hump at all.

To check your flappy system you need to do at least two additional checks:

1) the start-up check. Pull the rubber cap and see if the flappy rotates at start-up.

2) the 4k test: Rev the motor past 4k and the flappy should cycle.

>Would the Spanner tell me if it works or not? Any other ideas?

Yes. But, it will only confirm #1.

If #1 is ok and number #2 is not ok you have a vacuum storage problem up-stream of the solenoid. (Possibly the vacuum check valve.)

If both #1 and #2 are ok then the next time you dyno pull the rubber cap and make sure. On a WOT run the flappy will depend upon stored vacuum to operate.

Shouldn't. Given two equally-healthy stock cars, the GTS curves should be higher than S4 or GT curves all the way across. (I don't have DynoJet curves for a GTS but I have seen various non-DynoJet curves.)

You are loosing 20, maybe 30 ft-lbs of torque because of the lack of the second 'flappy' hump. Since horsepower is torque times RPM and since the second hump is in the higher range of the curve...

Theoretically yes. However, practically maybe not. They should be able to copy the exported-to-text file to floppy if they cannot e-mail it. Worst case they can print the raw numbers and you could type them into a spreadsheet. (I've always had to do it that way; it takes about 15 minutes including a double-check of data entry.)

Comparing the various curves on the same scale can be eye-opening.

 

Ignore the above. I just looked at the charts again - the auto and 5-speed charts have different x-axis ranges. The different ranges and y-axis compression make it difficult for me to compare them by eye with the a/f curves I have.

 

Dave,
Thanks and I will work on the flappy tomorrow.

How come both cars are fairly equal? Jims car is extremely well maintained and the flappy is working.
Why such low numbers when compared to an S4.

I seem to remember "Bigs" starting a thread like this.
I will go and search.

 

270-odd horsepower is - I would think - a bit low. I would expect 295 to 310+ rwhp for a healthy 5-speed GTS. Ergo, I suspect Jim's 5-speed is not totally healthy. If you dyno again, see if you can use the Spanner in knock sensing mode during the run. The a/f curve doesn't look right for either of the GTS. It is definitely too rich at high rpms for best power. But, I cannot say how it compares to other 928s because of the axis issues. More data is needed.

If you twisted my arm and made me guess right now as to the issue I would say it was dirty injectors. One or more injectors may have crappy spray patterns that cause the O2 loop to richen the mixture too much. Or they may all be nasty and the knock sensors are backing out the timing. Or both.

CarChick's GTS initially ran like poop until I replaced the fragged in-tank fuel pump and sent the injectors out.

 

I pulled 244.3 RWHP at 6,000 rpm and 273.1 ft/lbs at 3,250 on a Mustang Dyno at Curry's last October. I realize the Mustang dyno and Dynajet dyno seem to have different readings.

130,000 miles and everything seems to work right.

 

If you use the Auto 20% loss on my car that gives you (350-70) 280 RWHP. Maybe once the flappy is fixed I might get there.
Using the numbers quoted in one of the above posts - S4 = 280rwhp the S4 would appear to be more powerfull than the GTS.
Mine is 275rwhp
Jims is 276rwhp
Bigs 265rwhp IIRC Though at a higher altitude
Bills was 244rwhp

I am going to Dyno my S4 when it is ready.
The S4 seems a better "bang fo the buck"

What does a 89S4 auto put out at the engine? 310HP so take off the 20% and you get 248hp.

I guess we have a lot of missing HP on the GTS??????

 

Over the years, many people have commented that Porsche has underrated their engines. Many people have dynoed their 928S and 928S4s showing numbers a little higher than represented in the owners manual. Then we have the varying reads from the different types of dyno machines to complicate things.

I am now kinda wondering why the GTS are generally reading "low". Are they so fragile that it is common to lose 10+ HP? Maybe Porsche stopped underrating the HP in 1993? Maybe many of us we have gotten too generous of dyno readouts.

If you were not on a dynojet, your numbers are probably very good. If you guys were on a dynojet, Rogers run would suggest no underrating of HP by the Porsche factory. Jim's has about 5% loss which it looks like people have ideas on how you can overcome it. Once you get it back to around 290 rwhp, this still leaves me wondering how/why S4 5 speed dynos are sooooo close to that. GTSs should have 30 more HP (20-25 rwhp) than an S4 right?

Anyone have insight on this? Maybe it is simply a matter that those that own a GTS are less likely to dyno and less likely to pursue performance modifications so we do not have very much dyno experience to compare to.

 

James-Man,

I have noticed the same thing. I have noticed very few GTS' dyno where you would think they would and the pre GTS' dyno higher.
Tom M had an S4 with 165K (?) that dynoed at near factory #'s .