Fe 427 hp?

[Rawkkrawler]

Curious...

I just had my Cobra Dyno'd yesterday. Came in at 326HP / 365TQ at the wheels, seemed low to me.

67 FE 427
Mild Cam
Comp Cam Shaft Rockers
Edlebrock Aluminum RPM Heads
Offy Dual 4 intake (low rise)
Dual Edlebrock carbs (500's I think)
Tremec 3550 Tranny
Corvette IRS (C4)
Not sure about the gears
MSD Ignition (6AL2, Pro Billet, Blaster SS)

Timing was set at 22 initial

Is this about normal for a fairly stock motor?

Any tuning ideas to squeeze a couple more horsepower out of it?

Thanks!

[blykins]

That's not out of the ordinary for a rear wheel dyno. Cobras suck a lot of power due to the restrictive exhaust and the driveline losses.

It's not uncommon to lose 100-125hp from the flywheel to the rear wheels.

[blykins]

Forgot to answer your second question....

That intake is probably the bottleneck for your power. An intake and cam swap would probably liven the thing up quite a bit.

[Silverback51]

What brand of dyno was it? The Mustang Dyno usually reads 15 to 20% lower than some of the other major brands, like DynoJet.

[patrickt]

Originally Posted by blykins

That intake is probably the bottleneck for your power. An intake and cam swap would probably liven the thing up quite a bit.

... and this time you're going to recommend a Blue Thunder intake and classic solid flat tappet cam, right?

[blykins]

1 out of 2 an't bad....

[Dwight]

typical Cobra loses 20% but with you IRS maybe a 25%.

20% loss, your motor would be a little over 400 flywheel, 25% about 445.

a 427 RACE motor, back in the day, made about 525 flywheel.

I would think you could get 475 - 500 and still keep it streetable.

A couple of my buddies have Keith Craft FE strokers. One a 427 stroked to 487 making 618 flywheel hp. The other is a 428 stroked to 461 making 601.
Both are very streetable and fast.

Keith can CNC your heads and pick a cam for your street motor. If your short block is good let Keith do your heads and buy a cam from him.

Dwight

[Ibr8k4vetts]

Originally Posted by blykins

That's not out of the ordinary for a rear wheel dyno. Cobras suck a lot of power due to the restrictive exhaust and the driveline losses.

It's not uncommon to lose 100-125hp from the flywheel to the rear wheels.

restrictive exhaust, I don't understand that term Can you please tell me how almost straight pipes are restrictive? I'm NOT trying to be a smart azz, I just don't understand.

[cobred]

The side pipes look huge on the outside but its on the inside that counts. My 1st set had 2" pipes with a baffle so I had 4 2" primaries going into a 2" pipe, very restrictive. Then I went to a set with 2.250 glass packs and now have 3" glass packs. I did other work so I cant tell how much the pipe changes added.

[67FEfastback]

Originally Posted by Rawkkrawler

Curious...

I just had my Cobra Dyno'd yesterday. Came in at 326HP / 365TQ at the wheels, seemed low to me.



Is this about normal for a fairly stock motor?

Any tuning ideas to squeeze a couple more horsepower out of it?

Thanks!

Sounds about right, for your set up, on a mustang dyno.

How does the car run, with your current set up? Seat of the pants feel?

Ultimately dyno numbers are just for bragging.

Does the motor have forged or cast pistons? Con rods? How many miles on it?
What type of driving do you do? Cruising? Pub burns? Racing?
All questions, you need to ask before making changes.

[blykins]

Originally Posted by Ibr8k4vetts

restrictive exhaust, I don't understand that term Can you please tell me how almost straight pipes are restrictive? I'm NOT trying to be a smart azz, I just don't understand.

If you look at most Cobra exhaust systems, you'll see that:

1. The headers go into sidepipes. It's a very sharp 90° bend in that area. Also, the headers don't have collectors, but the sidepipes do...essentially after that sharp 90.

2. Most Cobra sidepipe mufflers are tiny inside. They're about 4" on the OD, but you probably couldn't roll a golf ball through most of them. Very restrictive for the engines that are making 450-600hp.

I think it was Ernie (Excaliber) that said this...but he had his car rear wheel dyno'd. He made one pull, then pulled the sidepipes off and made another pull. It gained approximately 100hp.

[Dwight]

this is what you find inside most Cobra sidepipes.



and this is the fiberglass that is used

[Excaliber]

When my original side oiler was dynoed (out of the car) adding the side pipes resulted in a 97 horse power loss. These are 4" round pipes with the typical restrictive stuff inside.

Of course the more power and the higher the rpm at which that power is made will have a big impact on how much you loose on any given engine. If the cam and intake are the "bottle neck" then side pipes will be less of an issue. With lower rpm your not flowing as much air so there again, side pipes will be less of an issue.

My engine was making power in the 7,000 rpm range, the "bottle neck" WAS the side pipes. So in my case it was a rather dramatic loss of power. It would be perhaps half of that if the motor couldn't breathe well from an intake bottle neck.

Of course on top of the side pipe loss you also have to add drive line and accessories power loss when your dyno the rear wheels with a car, not a bare engine. Add another 20% or so loss on top of the side pipes. End result can be a very discouraging horse power number, but it's all relative.

[Rawkkrawler]

Thanks everyone! I feel better about the numbers.

I have, however, encountered a new issue....severe backfire during deceleration. Just when I thought the complete MSD ignition swap smoothed everything out. I have read several posts and everything points to a header leak. I did initially want to blame the ignition but it most likely is fine. I pulled plugs this morning (their new with 100 miles) and found most a light brown color. Number 3, 5, and 6 look brand new out of the box. Is this an issue? My initial timing is at 20 degrees.

To answer some questions asked earlier in the post, I don't plan to race, just want a smooth big block that I can cruise around in.

[blykins]

Backfiring out the exhaust?

I would check the header gaskets and sidepipe/header gaskets if there are any...

[Rawkkrawler]

Thanks Brent..

Should I be concerned with the different color plugs? Some seem to be a nice tan/brown with 3 being as white as new. With 2X4 carbs, I would think I'd get a consistent burn. Would the different plug color point to the leaky header pipe? My guess is no.

[blykins]

If you could post some pictures, it would help.

Dual carbs are much harder to keep in tune than a single carb setup.

[lovehamr]

The Ebok carbs aren't gonna help in that area either.

[Excaliber]

MSD ignition, because it fires with Mulitple Spark (discharge), not just one spark, at lower rpm makes reading plugs tougher than the old school single spark ignition systems did. Generally speaking it keeps the plugs pretty darn clean.

Yup, exhaust is sucking in air somewhere causing a secondary burn in the exhaust system when decellerating.

[Rawkkrawler]

Narrowing it down I hope, at least I'm able to find a constant symptom. When I let off the gas, at any RPM and clutch out, I get the light popping (I'm going to go with the experts and swap the header gaskets) put when I ease back into the gas I get the stutter. It just last a second but again, it happens at any RPM immediately after I decelerate then get back into it. Note: If I'm running through the gears hard, no issue, powerful as expected. It just happens when I let off (clutch out) and ease back in (cruising). It's a small hiccup that seems carb related. The Mustang Dyno sowed a fuel ratio of 13-14 from 3500-6000 RPM. Edlebrock idle screws are about 2 turns out (smells rich at idle).

Thanks again!!

Mike