Dynoed my 427so Cobra today.... interesting to say the least!

[Power Surge]

Doesn't seem too far off, hp wise. Most 427s chassis dyno in the 390hp range. The torque is kinda low though, for that displacement. Your dyno graph looks more like a stroked Windsor.

Your A/F is kind of whacky, but not too bad. It's a little rich in the mid range, and goes a tad lean at 6k, but it's not so far off that you'd be missing a bunch of hp. I think the dual quads are giving you the crazy A/F lines.

Just for comparison sake, I just finished up dynoing a car with a similar setup. It's a 468 inch 427, alloy heads, with a single carb. The motor "supposedly" dynoed 560 on an engine dyno. On the chassis dyno, it made 398hp/450tq. That was after I tuned it tho, as the carb needed jetting and the dist was messed up only giving about 28 degrees of advance.

[neverwouldof]

Originally Posted by Power Surge

Doesn't seem too far off, hp wise. Most 427s chassis dyno in the 390hp range. The torque is kinda low though, for that displacement. Your dyno graph looks more like a stroked Windsor.

Your A/F is kind of whacky, but not too bad. It's a little rich in the mid range, and goes a tad lean at 6k, but it's not so far off that you'd be missing a bunch of hp. I think the dual quads are giving you the crazy A/F lines.

Just for comparison sake, I just finished up dynoing a car with a similar setup. It's a 468 inch 427, alloy heads, with a single carb. The motor "supposedly" dynoed 560 on an engine dyno. On the chassis dyno, it made 398hp/450tq. That was after I tuned it tho, as the carb needed jetting and the dist was messed up only giving about 28 degrees of advance.

Maybe i'm expecting to much.... but how does a 427 go from 603hp at crank to 394 whp when there is hardly any backpressure in a cobra. From all the other threds i read 15% was the going rate. The Dyno shop guy says he usually see's closer to 12's. Viper in there 505 crank and 424 whp with muffler system untouched..... it's crazy i tell ya. Only thing i can figure is the air/fuel getting to engine. If you looked at engine build up... it has some nice pieces!

[Power Surge]

Originally Posted by neverwouldof

Maybe i'm expecting to much.... but how does a 427 go from 603hp at crank to 394 whp when there is hardly any backpressure in a cobra. From all the other threds i read 15% was the going rate. The Dyno shop guy says he usually see's closer to 12's. Viper in there 505 crank and 424 whp with muffler system untouched..... it's crazy i tell ya. Only thing i can figure is the air/fuel getting to engine. If you looked at engine build up... it has some nice pieces!

Two things kill the engine to wheel hp in a Cobra... exhaust, and IRS. The IRS soaks up a ton of power, especially if it's the Jag setup with no upper control arms. The other thing is the Cobra exhaust. Most Cobra side exhaust setups zap a good 70-100hp from a motor. Your motor was dynoed at 603hp, but that was with real tuned long tube header, not Cobra side exhaust. The problem with improving the Cobra side exhaust, is the mufflers that hurt the power the least, are loud as hell.

But even with 18% loss (which is what I use for most Cobras), you're still missing some power. You should have your timing checked, and make sure you're getting enough advance. That was the issue with the car I had here. Fixed the dist issue and it picked up another 25rwhp. You might also consider switching to a nice 1x4 intake and carb.

[neverwouldof]

Power surge.... thanks for your input! i am going to take over to a recommended engine performance shop that works on FE's when they have an open spot. Hopefully they'll tell me some good news. The dyno shop said if any of there rice rockets had air/fuel ratio's that lean they would go BOOM!

[Power Surge]

Originally Posted by neverwouldof

Power surge.... thanks for your input! i am going to take over to a recommended engine performance shop that works on FE's when they have an open spot. Hopefully they'll tell me some good news. The dyno shop said if any of there rice rockets had air/fuel ratio's that lean they would go BOOM!

Optimum A/F for a naturally asperated pump gas motor is in the 12.8-13.2 range. Any higher than that is too lean. For forced induction or nitrous, it's 11.8-12.2. That might be what they are used to. Little turbo motors.

One more thing... what trans do you have, and what gear did they pull the car in? You want to have the car pulled in 4th (that's 1:1 on both a toploader and 5 speed). If they pulled the car in 3rd or 2nd (common in some shops), you will have much lower numbers.

[neverwouldof]

Originally Posted by Power Surge

Optimum A/F for a naturally asperated pump gas motor is in the 12.8-13.2 range. Any higher than that is too lean. For forced induction or nitrous, it's 11.8-12.2. That might be what they are used to. Little turbo motors.

One more thing... what trans do you have, and what gear did they pull the car in? You want to have the car pulled in 4th (that's 1:1 on both a toploader and 5 speed). If they pulled the car in 3rd or 2nd (common in some shops), you will have much lower numbers.

They pulled it in 4th gear up to 7000rpm. It's a 5 gear setup from Richmond. It hit 140mph at 6800rpm in 4th gear. Thats what they showed me....

Keith

[avanti-176]

Also remember ...different dynos say different things.
But it does sound like something is a little off. I would agree with power surge and start with the timing. Pay attention to power surge I have read an awful lot of his posts....he knows his stuff.

Good luck,
Dan

[undy]

Originally Posted by neverwouldof

They pulled it in 4th gear up to 7000rpm. It's a 5 gear setup from Richmond. It hit 140mph at 6800rpm in 4th gear. Thats what they showed me....

Keith

...a litlle insight on Richmond 5 speeds... 5th gear is the 1-1 ratio, 4th being similar to 3rd in a standard 4 speed. As Sal said the low gear pull will make smaller numbers. Also.. I'd be a little leary of a shop that didn't know what gear to use, IMHO.

The Richmond 6 spd is Richmond's only over drive tranny. Their 5 speed is a spin-off from the old Doug Nash 5 speed.

Dave