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Carl Fausett 10-15-2004 09:46 PM

New Supercharged 1990 GT Results
3 Attachment(s)
The dyno chart below has both before-and-after runs on it.

Started October 1st, finished October 14th. This was a stock Murph928 kit -
no frills. Customer did request the Polished Upgrade - that is why the head unit and intercooler are so shiny.

The car is a 1990 GT 5 spd. All stock everywhere, including exhaust.

283 HP at RW before (325 HP at the crank) is now 405 HP RW (465 HP at crank)

275 FtLbs at RW before (316 FtLbs at crank) is now 386 FtLbs (444 FtLbs at crank) increase of 140 HP and 128 Ft Lbs of torque.

Air/Fuel ratio was constant at 11.5:1 Idle 750 RPM steady.
Boost gauge showed about 7 psi at 6,000 RPM.

I have video of the dyno runs that I will post Monday.

Donald 10-15-2004 10:12 PM

The curves dip a bit from around 3,5-700 rpm. Could this be the flappy, and has anyone tried locking it open or closed to evaluate the effect?
Good numbers; well done.

slate blue 10-16-2004 12:37 AM

Why are the lines so shaky?

Ispeed 10-16-2004 01:01 AM

Would that be the knock sensors retarding timing and then restoring normal timing?
BTW, I thought GTs weren't good candidates for s/c because of cams and other stuff?

Donald 10-16-2004 01:53 AM

pressure wave harmonics?

worf928 10-16-2004 01:53 AM

Originally Posted by 928andRC51
Would that be the knock sensors retarding timing and then restoring normal timing?

I was going to postulate the same hypothesis. Both curves are a little 'wiggly' but the boosted curve is very wiggly.

But, looking at O&N's curve - it's not wiggly. I'm wondering if the GT was in good health to start with? Ideally, we'd see another GT curve before and after. Perhaps, GTs simply need to have the came timing physically retarded en passant with boosting? Perhaps someone can twist Gretch's arm(s) a bit harder and get his beastie strapped to a dyno so we can have two GT data points? (My interest is not academic since I want to boost one of my GTs.)

Also, I wonder if the DynoJet model and software revision was the same in Carl's test and O&N's test: the measurement methods should never be ruled out as sources of uncharacterized variation.

Donald 10-16-2004 01:58 AM

Hmmm, it does appear though that the squiggly becomes worse above 3,700 which could be exacerbated by the lengthened intake.

Old & New 10-16-2004 03:43 AM

It's probably just noise. Imagine what the car would feel like if the torque curve were really like that! My chart had "smoothing" set to max. Without smoothing, there was a little bit of the same effect, but not as pronounced as what is shown above.

John Veninger 10-16-2004 07:25 AM

Very nice numbers and nice installation!
I do have to agree with others on the wiggly graph for both before and after boost. Bad knock sensors or crappy fuel?
I'm also wondering why the HP drops out before 6K compared to the NA that keeps rising through 6K.
Did you measure the A/F during the run?

Tony 10-16-2004 12:32 PM

You should be able to "hammer" the knock sensors right?

Carl Fausett 10-16-2004 12:44 PM

Here is the deal on the squiggley lines...

We saw that too and played withg them a bit while we were on the dyno...

We dialed the FMU out a tad to achieve 12:1 air fuel ratio and the squiggly lines almost completely disappeared - they mirrored the squiggleyness (sp?) of the before chart exactly. We actually poicked up a little more HP at 12:1 air/fuel ratio too.

But - we set it back and deleivered the car at 11.5:1 air/fuel ratio because that is a safer, richer, air/fuel level for day to day driving with a supercharged car. Especially a GT with the slightly hotter Compression ration and cams. We wanted a slight richness safety factor - but then the squiggly lines came back....

We were talking about this with the dyno operator too - and he suggested we do a 3rd gear pull - and we did - and he was right - the lines were very much smoother in 3rd gear. He said that was caused by the rate of sampling of the DynoJet software, the whole 3rd gear pull was maybe 4 seconds long where in 4th gear the pull lasted maybe 7 or 8 seconds so there were many more samples taken. Not sure if that is true - but the 3rd gear pull was almost perfectly smooth compared to the same pull in 4th gear.

However - for YOU guys :-) I thought if I compared a 3rd gear pull after the SC install (even though it was orettier) to a 4th gear pull before the SC was installed I'd get shot.

So - I posted 4th gear pull before-and-after just to be accurate and fair. Squiggly lines or not.

Honestly - they went away in 3rd gear, and they went away in 4th gear with a slightly leaner mixture too. So we knew that the dynojet and the FMU in the car were both consistent and accurate and responding to adjustments.

Fastest928 10-16-2004 12:45 PM

How many original miles on the GT? Stock head gaskets? What is the octane of the fuel, is it 91-92 octane gas (pump gas)?

Good numbers. Looks like a stroker with a tick less torque!



Donald 10-16-2004 01:06 PM

Repeat my query re: the flappy-

GoRideSno 10-16-2004 02:11 PM

Nice looking install Carl!
We should coordinate our presentations at Sharktoberfest to make sure we are not covering any of the same stuff. You can e-mail me @ [email protected].

I notice that you have stated this car was making 7 psi yet 8 psi is written on the chart after the run. Was it 7 or 8?

IIRC this is the first SCed GT to be dynoed?

Anyone how similar the 85-86 and GT cams are?

As far as the comments about the flappy effecting the curves go, this may be correct but I wouldn't expect it to. For comparison the chart below is with not only no flappy but also a completely different manifold than stock. "87 S4 automatic, just under 7psi, x-pipe, SUPERMODEL intercooled setup. This chart shows a very slight dip at about 3700rpms. It also shows about 62 more CHP at about 3700rpms. :D
By Sharktoberfest I hope to have dyno charts for:
94GTS automatic intercooled Twin-screw at 5psi.
86.5 5speed non-intercooled Jag/Eaton M112 at 4psi
86.5 5speed Intercooled Twin-screw at ? psi
Andy K

Carl Fausett 10-16-2004 02:30 PM

Q: are there other GT's with the Murph928 kit on them?
A: Yes, I think so. I think stuartph and jorj7 here on the rennlist have them - but I am not certain of all if Tim's customers before we started doing sales/marketing for them. I am sure Tim is watching this thread and will answer. Then there is Lagavaulin - probably the most documented and photographed installation of all - and a host of S4's too.

Q: from Marc Thomas/DEVEK
A: 27,000 miles on the car, all original. Stock head gaskets of course. 91 Octane pump fuel. I drove it about 200 miles after the SC install and we were deliberately hitting the boost hard, often.

Passed a State Trooper who was stopped at the side of a country road going the other way at about 85+ MPH and I was at WOT and accelerating... thought for sure I'd bought the farm. But, as I went by and my eyes met his... (I wondered why he was standing outside his Cruiser at the right front fender on the side of the road)... he was taking a leak! I smiled. He frowned. He did not give chase.

Anyway, I digress - the point of the anecdote is we romped on it for 200+ miles and never hit the knock sensors once. Not once. Hit the RPM limiter once -but never the knock sensor.

Jean-Louis: if your listening - I put in a strong plug for him to bring this car to you for a pre-emptive timing belt replacement. He has 27,000 miles and 14 years on original timing belt. I think he will be calling you for an appointment.

Q: from Donald - "the flappy"
A: I do not understand the question. What is the flappy on a LH car that you are refering to?

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