Tom. M

That same S4 did 282 hp and 300 ft-lbsl with a x-cross over and rrfpr.......and last time..in almost totally stock form it put 260ish...(don't remember the torque)..but using 20% loss...the 260 equates to 325...still better than published numbers..and it had 170k miles plus on it..
My GT at 170,000 miles dynoed (totally stock)..at 283 hp and 285torque (333hp and 335ft-lbs) using 15% loss...basically factory numbers...
When I added the X crossover (through stock system) it put down 295rwhp..or 347at the crank...

If you spend some time looking over all the different dyno numbers from the different dyno's you'll see that dynojets are typically optimistic..and some others are lower....but...the use comes in apples to apples comparison...
I've seen a 5sp GTS dyno at just over 300hp (Marc T called it a strong GTS)..and Ive seen slightly modded GTS's do 335 (with GT Cams and full Ott exhaust treatment). Never seen an AT GTS dyno..but theoretically..it should be in the 280 plus range..and the 5sp's should be 295 plus..
All of course with the double hump torque curve...

Another aspect of the discussion is the power delivery...if you have a GTS with 280hp and a S4 with 280hp...both to the wheels, which car will win a race?...My bets on the GTS due to its always higher torque at low RPM..and better gearing....

The same with a GTS vs a GT..gonna be closer..for sure..

Later,
Tom
midlman@rennlist.net
89GT

Ketchmi

Didn't anyone else notice that Roger's runs start at a considerably higher RPM? I believe his flappy is working but he started his runs at about 3400rpm vs. 2750 for Jim's runs. It also appears that Roger rolled into the throttle whereas Jim may have just pegged it to the floorboard. I see most flappy's activate at 3800-4000rpm on the dyno and it may not have had a chance to show up on Roger's dyno runs since he started at a higher rpm.

The A/F ratios are consistant with what I have seen out of a stock GTS. They all seem to run on the leanish side until 4500+ rpm. (even S4's) As far as the numbers, it appears that the GTS isn't as strong as Porsche proclaimed. I think it has great room to grow but it is not as optimised at the S4.

For the record, I did get 293rwhp out of Bigs's GTS without cats and with a less than optimum X-over. Our final production piece should be even better. He is over 280 rwhp right now with the "less than the best" cats. I think with the final production piece and a bit of fuel tuning, his could easily see over 300rwhp without cats. Not too shabby for a car that started at 265rwhp...

ROG100

Dave thanks for the input.
I will double check my "flappy"today just to be safe.

Providing my flappy is OK and I don't have a inlet manifold R&R in my near furure I will be fitting your X pipe and a RRFR.
Hope I get close to Bigs numbers.

We fitted Jim M's X pipe yesterday and the whole project took about an hour including removing the stock exhaust.
Fine workmanship Dave - fitted like a glove.

I will let Jim talk about performance and noise after he has played for a while.

ROG100

No I did not - Why?

worf928

Sorry. 2 many werdz in this post.... going back to my cave now.

I did notice this - and retracted my remark about a/f ratio. But, you're right, I didn't realize that the consequence is that the one hump in the Auto's curve is the second hump.

So, Rog, your flappy may in fact be working and all we see on your chart is the second hump. The #2 test is easy to do though.

I don't buy that there is something fishy from the factory. I just cannot see Porsche shipping out engines with less than the rated rwhp.

We are talking about a (roughly) 10% shortage of horsepower. I will offer below some theories other than 'GTS motors just suck...'

Apples and Apples. We are (at least I am) concerned about why a stock GTS cannot make expected output. I see absolutely no reason to think that anything other than a well-running stock GTS is required to make stock numbers. No performance mods. Just stock. If the car won't make stock numbers then something's not right. (Or GTS motors just suck...)

Performance mods should push the car beyond stock output.

Baseline(s):

My '91 GT made 294 DynoJet-measured rwhp, SAE corrected. OEM wheels on OEM rubber. The only modification was an RMB. If someone wants to claim that the RMB is good for X, Y, or Z, rwhp then please provide DynoJet charts before and after with at least two runs for each condition. (I do not believe that the RMB - without any other modifications - will provide a statistically meaningful change in dyno numbers.) The car did have freshly cleaned and balanced injectors.

On the same day we had an '89GT put down 289 rwhp. This GT had chips, but was pinging.

On the same day we had a stock (except for RMB) '90GT pull 277 rwhp. (This GT made IIRC about 10 more rwhp after the owner indexed his cams to spec.)

Pretty much no matter which way you slice the above numbers you will come to the conclusion that these cars were making factory-spec or better output.

Now, interestingly enough, three years later, my '91 put down 285 rwhp. On the same dyno. The only difference was 17" wheels and three years of driving.

Looking closely at the A/F numbers for the 5-speed GTS 271 rwhp run and the 294 rwhp run on my '91 I note the following (91 numbers are from raw data, 93 numbers from raw Mark I Eyeball):

RPM 91 93
2300 14.7 N/A
3000 14.2 17.0
3800 13.6 15.0
4200 13.4 14.0
4800 13.3 13.5
5200 13.0 13.0
5600 12.3 12.2
5900 11.9 11.5
6200 11.5 10.6
6400 11.4 11.0

Maximum power is 12.6. But, the power curve is comparatively insensitive between a/f ratios of 12 and 13. But, power drops off rapidly outside of this range.

Note that the a/f curve for my '91 is much flatter than the GTS. The GTS is very lean until 5200 and then goes very rich quickly. So, the GTS is not making the best power except in a small rpm range. (If Rog gets the raw data we can put the runs on the same chart and compare.)

Theories:

1 - A/F curve. The GTS A/F needs to be flatter and in the 12 to 13 range. Why isn't it?

Unburned fuel from bad injector spray patterns? Might this account for the super rich condition late in the WOT run and the 'slope' of the curve?

Might bad fuel delivery volume and/or pressure account for the lean condition early in the run? In-tank pump OK? Fuel lines occluded? How many folks religiously use Techron to keep the fuel system clean?

2 - Condition of Mass-Air Sensor? John Speake might be able to opine on how a bad MAS might be reflected in A/F measurements from a WOT run. The MAS is the only sensor involved in a/f during a WOT run. (No Lambda loop.)

3 - 17" wheels versus 16" wheels. The factory-spec numbers are brake-horsepower numbers. We use a rule of thumb to factor out drive-line loss. 17" wheels require more force to accelerate (rotational acceleration) than 16" wheels. I believe that the rule of thumb is 1-2% per additional inch of diameter. (Note, that my '91 lost 9 rwhp with 17" rims - and three years of driving.)

4 - Cam timing off? Due to one belt-tooth slip during last t-belt R&R? (See '90 GT above.)

5 - the GT has 10:1 motor. The GTS has a 10.4:1 motor. The GTS has the exact same engine management system and intake air system as the GT - although one would assume that the ECU's parameters are different. Or, the other way 'round: The GTS does not have any new sensors, or changes to intake paths, or changes to combustion chambers to facilitate better control of the higher-compression combustion.

Ergo: The GTS will be more susceptible to detonation due to bad-octane gas, buildup of crud in the combustion chambers, and any marginality in the engine cooling system.

Any of the above, or all of the above could contribute to low GTS dyno numbers.

So, .... I think the issue with GTSs is that getting maximum stock power requires that the car be 'more healthier' than would be the case for an S4 or GT.

Our GTS is not Dyno-ready yet. But when it is, I will put my position to the test.

Lastly, note that measurement variability can also play a part in these comparisons. What is the condition of the DynoJet? What is the condition of the sensors feeding data to the DynoJet software? Does the operator hook everything up to the car the same way every time? I would expect at least 1% variability from run-to-run and at least 2% day-to-day. The theory of the inertial-mass dyno is sound. But, it needs the sensor data (rpm, temp, etc.) to be as exact as the unchanging mass of the drum.

Or, in other words, a 2 or 3 hp difference from run-to-run or day-to-day is noise. It doesn't necessarily mean that that new gizmo on your car really makes 2 hp.

ROG100

Dave,
Do not stay in your cave to long!!!!

My car is reasonably well maintained, however I have yet to do a top end R&R which will happen this winter if the weather ever cools down.

New MAF about a year ago, I run on Chevron and use Techron every couple of months. I do about 5k miles a year.

Injectors definitely need cleaning and resetting I am sure.

On the day I did the dyno run I filled up with Premium, about 3/4 of a tank and drove maybe 20 miles prior to the dyno.
For the last two months I have been running Chevron plus instead of premium.
This could have been partially to blame for low numbers.

I will know about the "flappy" tomorrow, to busy today.

I have decided to run one more set of dyno numbers in a couple of weeks after some continued use of Premium gas and ensuring that the flappy works.
This will ensure I get some of the data you require, and also satisfy my curiosity prior to doing the mods that I have waiting.

Thanks to all for the interesting input.

worf928

Thank you Rog. It (the previous) just seems like the obvious response to notions that "GTS engines just suck..." (We know they eat (oil.) But I'm going to need some arm twisting and data before I support the Suck Theory.)
Miles? Vacuum leaks could contribute to lean running.
OK. So, I'm inclined to think that the fuel system is not gummed up. And that the Mass-Air Sensor is not part of the problem.
Given the above I suspect your injectors are clean. Balanced? Dunno. But, bad spray patterns come from dirty injectors.

Do you have any recent emission's testing results? Either from a static idle test or a rolling test?

IIRC the GTS wants 93+ octane. Check your flap. (I'll see if I can remember to do this too.)
In order to maximize the information you obtain here are my suggestions:

Prior to DynoDay:

- verify operation of in-tank pump (takes about 20 minutes and you needs some test leads)

- verify operation of knock sensors and Spanner in Knock Counting mode (IIRC spec is 50 knocks per 10k revolutions. As long as the Spanner counts a few knocks during some WOT street driving you know that the sensors and the Spanner work.)

- verify flappy operation at 4k.

- borrow a fuel pressure gauge and install it on the fuel rail (like the super-charged guys)

- verify stock pressures (~45 PSI idle and ~55 PSI during throttle plate opening)

- verify vacuum and vacuum drop to your fuel pressure regulator and dampeners.

- do the auto transmission hack Sterling suggested so that you can get data over the entire rev range

On DynoDay:

- Fill up with the best gas you can find
- Do the dyno runs with the Spanner in Knock Counting mode.
- Remove the flappy's cap and watch it during the run
- Watch fuel pressure during the run (should stay in the 45+ range.)

worf928

This something Rog can check with the Spanner before DynoDay.

In fact, Roger, good idea to get a clean bill of health from your Spanner for everything.

Jim M.

Wow! Thanks everyone for your input. As Roger stated in the first post neither he or I know much about these dyno chats or how to interpret them. To add some facts: The ambient temp. was 93F, during all the pulls on both cars. I have an external fuel pressure guage on my fuel rail in (preperation for the RRFPR). During all 3 pulls the guage was up near 60PSI. We also have a guage for Rogers car and will install it prior to the next dyno session. My plugs (on the 5-spd) have always looked rich to me, so I may have dirty injectors. However I use a bottle of Techron every 5K miles. I have 18" wheels (285's), while Roger has the stock 17's" (275's) We had both just fueled with 93 octane. Mine is always with 93 while Roger has been using the middle grade for around town use. I plan to put the spanner on mine to check the knock sensors and if that finds no problems I plan to check the cam timing. If that fails to find any problems I'll probably pull the injectors and have them cleaned and balanced. My emmissions tests always pass with flying colors and my milage both on the highway and in town are average for a GTS. Roger had a problem two years ago with an emissions test that turned out to be a bad MAF I believe. I have an RMB on the 5-spd, but I agree I don't think it makes any difference. (Sure doesn't make it sound any better!) I believe my intake system is in good condition, I have avacuum guage in the car and will pull 24"HG when I take my foot off the gas and it idles at 20-22"HG.

Keep the input coming, I'm learning!
Jim Mayzurk
93 GTS 5-spd

worf928

Actually, Sterling, you are very, very correct. The Spanner will only tell Roger if the switch is getting triggered but it most certainly will not tell him if the plate is opening to full.

bigs

Yes. My thread was titled: "Where Are My Ponies?"

IIRC, my curves and numbers are very similar to these. But I'm at altitude, and I'd expect your numbers to beat mine.

Edit: I have brand new 30# injectors in my car, but Ketchmi has tuned them properly on the dyno. (I had bad injectors, and we decided to go with 30# injectors plus a RRFPR - just in case I decide to S/C the car.)

I am also puzzled as to why a fair number of GTS's seem to show disappointing numbers when dynoed. Good thoughts and worthwhile reading here.

worf928

It seems Jim, that both you and Roger should have some healthy GTSs - given the information provided. With the frequent use of Techron (and/or Chevron gas), your good fuel pressure, and Rog's new MAS the 'funkiness' of both of your a/f curves is more puzzling. Your a/f curves in particular show a LOT of variation in the three runs.

In your first run where the a/f curve stays above 14 until ~3.2k rpm and then drops off a cliff has me wondering if the operator was part-throttling until ~3k?

The O2 loop will keep the a/f ratio above 14 until the WOT switch is engaged.

Dyno runs from 928s with non-operational WOT switches standout: the a/f ratio is a nice stoichiometric ~14.7 for the whole run. (And the power is poor.)

Are you guys planning on using the same DynoJet again?

mark kibort

you just cant rev the car to 4k and have the flappy work. you have to see it work on start up, or you have to put it under load. quick revs (real quick) to 4-6k sometimes shows the flappy move, but not always. best way, jack your car up in the rear, use jack stands, start the car, get car in 5th gear 3000rpm and push the acclelerator while pushing the brake. try and get 50%75% load on the engine and not let the revs get away. someone else watching fappy, should see it move.

you can always short flappy out by connecting vacuum directly to the flappy device and watch it peg open.

sometimes its the electrical connection to the flappy that has a bum connection
Mk

ErnestSw

Roger's flappy is working properly. We watched it do its thing on start up and at 4K yesterday. As far as I'm concerned it's not Roger's ponies we're looking for, it's Jim's.
350HP - 20% = 280HP Roger made 276 which is close enough.
350HP - 15% = 297.5HP Jim made 275 which leaves 20HP on the table.

mark kibort

that is kind of low for a GTS at 5.4 liters!!

compression look good?


I wonder what it could be?

mk