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

[Fox-4-Cobra]

I got the SCT tune and Dyno today. The engine died/choked off at 5200 RPM. The Dyno showed 246 HP @ 5100 and 297.5 TQ @ 3800.

The combo consist of a 331 SB (9.75 CR) GT-40 Irons (3 Angle Valve Job, Surfaced) 1.7 RR's, E-Cam, Shorty's, ORH and Flows. The rest is all factory as it came on the car (1994 Cobra).

I knew the stock TB, Mass Air Meter and Cobra intake would choke it some. I thought it would peak at 5500 and make another 30 RWHP. The wife and I are expecting so I wont be getting heads anytime soon.

Anybody have an opinion on what a larger Mass Air Meter and Throttle Body will do for the numbers? I know I'll have to get it retuned, to bad I did not get those parts before the tune although drivability was horrible. Happy with the TQ just want a little more HP. Anything I can do that wont affect the chip & tune to get a little more out of it?

[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?

[red82gt]

First off, what type of dyno (mustang, dynojet, etc..)? Next thing, what does the A/F do when the power falls off? Also, how much timing are you runnning?

[Fox-4-Cobra]

It was a Dyno Jet, total timing was at 28, the AFR dropped slightly. I'am going to get a new MAM and TB and hope it frees up some power when it's retuned. I know full potential will not be achieved with the GT-40 Irons, cant afford new ones right now though.

Does anybody have an estimate on how lean it will get with a 73 mm MAM and an aftermarket 65 mm TB. Once I get those on I will not be able to get it tuned for several weeks.

Thanks For The Help!

[red82gt]

Any particular reason why you were only running 28* of total timing? With non-p GT-40's you'll need more timing, with my old combo it was best with 34* of total timing. On back to back runs, I gained 1.5mph going from 30* total to 32*, then another mph going up to 34*.

[Dark_5.0]

Afetr re-reading this thread it sounds to me like your clutch is slipping.

Bet you a dollar.

[Gearhead999]

Agree on the low degree of advance. 5150 rpm is where the torque and the hp meet.
Sounds like it needs more timing.

[Fox-4-Cobra]

I will advance total timing to 32. I hope the clutch is not slipping we just put it in

I changed the cap, plug and coil wires, fuel filter (dirty appeared to be from Ford on a 100K chasis). I was dumb not to look into that before putting it back together. Adding a new MAM and TB this week. I will then get it back to the Dyno late next week and let everybody know how she does. It already feels stronger except it no longer wants to idle when the chip is flipped to the street tune

I appreciate the reply's it really helps me in tracking down cause(s). Everything will be addressed and I will be looking into the clutch slipage.

Thanks

[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?

[fiveohpatrol]

oh yeah, PM me if you'd be interested in purchasing a used pro-M 80mm MAM calibrated for 24lb injectors, for cheap