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

[Dark_5.0]

I dynoed 255 RWHP with ported stock heads, stock TB, stock cam, cobra intake and all the bolt ons on the stock 302.

You probably have bigger issues than the TB and MAM.

[Fox-4-Cobra]

You might be right!

I cant figure out what else could be causing it, the engine starts dropping HP drastically. The tuner said he thought the MAM, TB, GT-40 Irons and Cobra upper and lower were to restrictive for the extra cubes. I had always read that the aforementioned parts were good to atleast 5600 RPM even with the extra stroke. I figured they would be a limiting factor but not to that extent.

Can anybody think of anything I might have missed. The springs were new and good to .600 lift. It has #24lb injectors so it's not starving for fuel. The E-Cam, heads, TB & MAM sizes work well together and should make peak at 5600 on a 5.0. I have seen and read about stock long block 94-95 Cobra's with similar set ups (Cam, Exhaust,GT-40's 3 angle & Surfaced) getting better numbers. I did not expect over 300 RWHP but thought the extra stoke and slightly higher CR would net around 270-290 RWHP and 310-325 RWTQ.

[lx mike]

331 engine with parts that are better suited to a 302. i would think torque would have been a lil better due to the engine size.

[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.

[rwhite65]

I think the torque should be higher. What about your timing and ignition?
Ryan

[Fox-4-Cobra]

Timing was set at 10 degrees so the tuner could do what he wanted with it via the chip. The AFR was 13.9 according to the print off.

My post initial post is unclear, prior to 5100 RPM's the torque line was pretty flat and the HP was heading up. At 5100 RPM's the HP did not flatten out and then drop it just drastically dropped. No plataue (sp) justa rapid spike downward like it was missing fuel or air.

The rapid drop with no plataue (sp) is what confuses me. I put in a new fuel filter today and cleaned the dirty element in the MAM. I'am going to check fuel delivery first via checking the injectors. Then I'll address the air by getting a new MAM, TB and hopefully porting the lower. Then the stock ignition will be addressed.

What other things could cause such a rapid HP decline at high RPM's? I would think a need for more air would still plataue (sp) prior to falling off would that be correct?

[fiveohpatrol]

Originally Posted by Fox-4-Cobra

The AFR was 13.9 according to the print off.

bingo, there's your problem. When it starts to go that lean, it will NOT rev where it needs to.
Can you post up the hp/AF curve?

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