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

[neverwouldof]

So i dynoed the Cobra today and didn't come out as expected.... Here is the link to the car i bought from NJ ...

FS: 427 SO Contemporary Cobra in NJ


Now i have questions on how much HP can it lose if running lean and not tuned well. I was told it was tuned and $400 was spent before i had it shipped down to me. 603hp at crank should result in at least 510 to wheels. taking 15% calculations. By the way, John McMahon was not the seller he only posted it for the seller. Whats your thoughts?


Click below to see jpeg of Dyno sheet from today...

http://photos.yahoo.com/northfloridarealtor

[Tom Wells]

Hey nwo,

Forget the numbers! Come join us at the Reptile Roundup:

http://www.firstcoastcobraclub.com/viewtopic.php?t=19

You can do two days on the track at Sebring and then decide if you need more power

Tom

[neverwouldof]

Originally Posted by Tom Wells

Hey nwo,

Forget the numbers! Come join us at the Reptile Roundup:

http://www.firstcoastcobraclub.com/viewtopic.php?t=19

You can do two days on the track at Sebring and then decide if you need more power

Tom

Ya that sounds good and i've had my eye on it but no way of transporting it down yet.... still looking into it though. The numbers aren't the issue, it is what i was told i was buying is the issue... hopefully it's out of tune and can be made right. We'll see but thanks for the invite.

Keith

[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.

[mikiec]

Transport??? Just get in and drive it there.

Mike

[neverwouldof]

Originally Posted by mikiec

Transport??? Just get in and drive it there.

Mike

Lol... no top (still waiting on seller to send me frame for convertible, not sure that will ever happen) and this is sunny florida ( weather man says 40% chance of rain every day of the year! 100% lately though).

[SCOBRAC]

There really isn't enough data to tell the story. We need to see the barometric pressure temp, and fuel data A/F ratio etc. Has the dyno been calibrated, what fuel was used? What carburation was used in the initial dyno run. Was it the same as your run?

The thing that strikes me about your car is the 2.88 diff. I think it had an effect on your rwh. I'm not a dyno guy but it seems like Powersurge hit it on the head when he referenced the 2-3 pulls. Your car (compared to say my car with a 3.54 ratio) is always in 2nd starting out.

Those are respectable 427 numbers. Remember maximum horsepower and maximum drivability are very different things. A little detuning is not a bad thing.

[CJ428CJ]

The Richmond 5 spd is 1:1 in 5th gear not 4th gear. You'd want to run it on the dyno in 5th gear. You'll have more transmission losses in anything other than 5th but I'm not sure how much.

Chris

[Power Surge]

Originally Posted by CJ428CJ

The Richmond 5 spd is 1:1 in 5th gear not 4th gear. You'd want to run it on the dyno in 5th gear. You'll have more transmission losses in anything other than 5th but I'm not sure how much.

Chris

There you go, that will drop the numbers some.

[gman]

1.24:1 4thgear ratio in richmond 5 speed. can you calculate the real hp with this number?

[Anthony]

Originally Posted by gman

1.24:1 4thgear ratio in richmond 5 speed. can you calculate the real hp with this number?

I would think the dyno can calculate torque / Hp in any gear, since the dyno always knows engine RPM's vs rear wheel speed, thus knowing overall gearing, whether you're in 3rd, 4th, or 5th. I would guess that anything other than 1:1 in the tranny will probably lose more HP through the tranny, and I also think you don't want the car geared down too low such that it will spin the rear wheels on the dyno.

[neverwouldof]

Originally Posted by CJ428CJ

The Richmond 5 spd is 1:1 in 5th gear not 4th gear. You'd want to run it on the dyno in 5th gear. You'll have more transmission losses in anything other than 5th but I'm not sure how much.

Chris

So your saying run the dyno in 5th gear up to 7000rpm..... that would produce near 180mph. Not so sure about that especially until i get it into a shop and get it looked at. Don't nead a dead engine on my hands.

[neverwouldof]

Whats the gearing on a TKO 500 in fifth gear then?

[DC COBRA]

Man I wished my cobra only loss 18%, I would be pretty ecstatted about that. Mine dynoed 612 at flywheel, but only 442 at rear wheels. Man that is a 28% loss, almost shameful. Got all the goodies to like very unrestricted exhaust, 3.73 gears (they say that makes no difference on dyno figures), Mcleoud double disc clutch(no slippage there), and the good old IRS(BMW). Although nothing to be ashamed of, forget the numbers, this b**ch is fast, fast, fast.

DON

[neverwouldof]

How do these little honda civic 4-bangers dyno out at 500-600hp at the wheels? Nitrous and charging i know but i can't imaging how all the other drive line parts hold up. Guess the engines don't last too long either....

[kris-kincaid]

The IRS diffs in these cars are really lossy when compared to a standard live axle. BTW neverwouldof, thats a nice car you have!