331 Dyno #'s Dead @ 5100 RPM (Long)

[Dark_5.0]

Originally Posted by Fox-4-Cobra

Car is a real Cobra (#4709) I bought it from a friend who was the original owner (bone stock down to air silencer when purchased).

I've read that the 93's had a 65mm but 94-95's had a 60mm. No idea why they went smaller with the more restrictive intake inlet. I checked several places and even measured mine before ordering another one.

Well i just learned something.

[Rev]

I think the AF ratio should be near 13. Total timing advance should be 36 or maybe even a little more with those heads.

Rev

[Fox-4-Cobra]

Went back in with new 65mm TB and C&L 76mm MAM kit. Gained 14.5 HP and 9 ft lbs TQ. Timing was bumped and clutch was fine so I guess the GT-40 heads must be killing me.

Twisted Wedges or AFR's will be my next purchase after I can save a little jack in the next few months. I'll post an update after that and let you guys know how it goes.

Thanks for the help!

[fiveohpatrol]

post your air/fuel curve from either run, it really sounds like you're going lean and not making the power it should

[andy669]

The heads should not be the problem. I have seen 330rwhp with a stock cam, 306, GT40 intake, shorty headers.

Take a 3 1/2 inch floppy with you to the dyno. Have them save your files to it, then email them to me. I have WinPep and can post all the info.

Andy

[Dark_5.0]

Originally Posted by andy669

The heads should not be the problem. I have seen 330rwhp with a stock cam, 306, GT40 intake, shorty headers.

Take a 3 1/2 inch floppy with you to the dyno. Have them save your files to it, then email them to me. I have WinPep and can post all the info.

Andy

I am with this guy

[Fox-4-Cobra]

I did not clarify in my update post that the peak HP stayed put from 5100-5300 before dropping this time.

I dont know much about the computer systems and programs that work with the Dyno's. Would I have to get another run or would they have it saved from my tune so they could check it with the next upgrade? I would love to get it and e-mail it to you guys.

I figured the GT-40 Irons would hold me back some but felt the car would put out 275-295 RWHP as is. I was originally planning to use those heads until winter and then replace them for something better. If it's not the heads then I'am at a total loss for what would be holding me back.I did not expect over 300 RWHP with the GT-40 Irons with just a mill job and 3 angle on them. I have tried replacing the TB, Fuel Filter, Plug Wires and MAM and gained so little

I'll call the shop and see if I can get something worked out if they save the programs. Hate to drop another $ 100-150 on a retune without heads.

Appreciate the help guys.

[andy669]

They will have them saved and they might even be able to email them to you. The files are only 4k each. Did the dyno operator have any ideas? Where was the fuel pressure, and did the tuner note the injector duty cycle?

Andy

[Fox-4-Cobra]

[QUOTE=andy669]They will have them saved and they might even be able to email them to you. The files are only 4k each. Did the dyno operator have any ideas? Where was the fuel pressure, and did the tuner note the injector duty cycle?

I will call them Tuesday morning and ask them to e-mail them to me. The operator thought the heads and intake were killing the power potential of the shortblock. I dont think the fuel pressure was checked, I did not have a guage on it or an adjustable regulator. That is an obvious oversight on my part, probably could have picked up a few HP there. The duty cycle of the injectors was not discussed either.

I'am ignorant to what can and cant be checked via the computer during a tune/chip burn session. Hopefully I can get that e-mailed to me and forward it to you. Again maybe I was way off with expectations out of this combo (275-295 RWHP), and figured with new heads 310-330 RWHP. But I would like to maximize it for now until new heads are purchased this fall.

I have a cousin with a 94 Vette and a big mouth that keeps asking about it. Right now I'm too embarrased to let people know it's stroked to a 331.

Thanks for all of the help.

[fiveohpatrol]

well that vette has a 350, and you should be able to whoop him even with your car not making all of its potential hp. The pre LS-1 Vette's are WEAK (ZR-1's not included )

[rwhite65]

As far as the cousin goes, tell him you have some tuning issues right now. You can spank him when you get your combo dialed in....depending on his year of vette.
Ryan

Originally Posted by Dark_5.0

Cars running the cobra ecu almost never dyno well.

I would expect to put out over 350RWHP with my top end on a 331.

What was your AFR.

I'm guessing one of your problems...and probably the main one...is the stock Cobra computer. From what I have heard...they suck! Do the conversion to the regular Mass-Air 5.0 computer. I may be wrong but I believe it's the A9L. A guy on another board I'm on did the computer conversion and picked up a TON of power. You should seriously look into this Fox-4-Cobra.

[andy669]

The tuner should be able to get around the limitations of the stock computer with no problems. Heres the picture of the printout that Fox-4-Cobra emailed me. The place he dynoed at wouldnt send him the whole file.

The only thing that stands out to me is that the numbers are low. It looks like its holding the power pretty decent before he stopped the pull. You cant tell exactly what the air-fuel is, but it looks like its in the 13.5 range.

With flat-tops and 93 octane, 28 degrees is about all those chambers want for timing. I dont think thats the problem.

I'd really like to know exactly what the injectors were doing. From there I'd look at valvetrain geometry. Also, what spark plugs are you running? The next time you go back to the dyno, take a 3.5" floppy and tell them you want the files saved to it, otherwise you will go elsewhere.

Andy