[blykins]

Rear wheel dynos and Cobras just don't mix.

The exhaust is very restrictive on most of these cars, plus you have regular driveline losses.

Your "breaking up" at 5800 is more than likely a valve spring issue....you're probably seeing a little valve float. Most hydraulic camshafts aren't made to turn lots of rpms, unless the engine was setup that way from the get-go.

As a general note from a builder, it's very difficult to dyno an engine, then ship it across the country to a different climate, where the customer sticks it in a car with a tiny air cleaner, and have the A/F ratio be exactly where it needs to be. We can only do so much on an engine dyno. You can generally assume that there will need to be some minor tuning involved. I will dyno the engine with the distributor/carburetor that the customer will have, so it will be as close as I can get it here.

Also, MSD boxes will vary. Most guys don't know this, but you can dyno an engine with one box, then send it to the customer who has another box, and the timing can be off. It always needs to be verified.

Someone mentioned the throttle linkage....that's an easy and important thing to check. Have someone push the gas pedal to the floor while you look down the carb. Both butterflies should be in the vertical position if it's a mechanical secondary carb. Even installation/dyno shops can screw this one up....

From what I've seen, Cobras will lose anywhere from 100-125 hp going from an engine dyno to a chassis dyno. Lots of variables there and the main point is that you use a dyno for incremental testing. You can't expect every dyno to repeat to the same number.