Proud Cobra Owner - SP01862

[wkooiman]

If the Holley Street Avenger was brand new, it should have worked fine right out of the box. There are differences between each carburetor model, of course, but they are not so great to cause the engine to run like crap. You likely have a different problem.

And if you really made 470HP with a 750CFM, and you switched to a more radical camshaft, you are going the wrong way by using a 650CFM carburetor.

You need local help from someone that knows what he is doing. Carburetor tuning isn't difficult, but it is a dying art.

My favorite carburetors are from Quick Fuel Technology. They build excellent carburetors based on Holleys. Another good choice is the Holley HP series. I'm suggesting this over the others because you said you have a more radical camshaft. They carburetor and camshaft need to work together.

My favorite carburetor tuning website is this: Carburetor Tuning the Scientific Way

There is a section near the bottom where he explains how to tune using an O2 sensor and a vacuum gauge. I did this on my car (non Cobra), and it made tuning a piece of cake. The O2 sensor eliminates the guesswork.

[DriftingCloud]

Originally Posted by wkooiman

If the Holley Street Avenger was brand new, it should have worked fine right out of the box. There are differences between each carburetor model, of course, but they are not so great to cause the engine to run like crap. You likely have a different problem.

wkooiman,

It was brand new, and the shop who choose it was the same shop who chose the Trickflow Stage 3 cam. I couldn't agree with you more about the cam and carb needing to work together. Given everything else was better (not perfect, but better) prior to the cam and carb switch, it's not a stretch to say the carb choice was very poor, especially going in the direction of a more aggressive cam.

I do need to look into the fuel pressure more. I know that.

Originally Posted by wkooiman

And if you really made 470HP with a 750CFM, and you switched to a more radical camshaft, you are going the wrong way by using a 650CFM carburetor.

Dyno from the time of the original build is attached. The car was not dynoed again after the new cam.

Originally Posted by wkooiman

You need local help from someone that knows what he is doing. Carburetor tuning isn't difficult, but it is a dying art.

I'd love that, but haven't found it yet. And that's not for lack of looking. The second "expert" I worked with was careless with his lift arms and cracked the fiberglass slightly under each exhaust outlet. *#^&@#?<%!!! With help like this, I know I'm better off on my own, even if that's groping in the dark much more slowly.

I'm really more interested in finding someone to work WITH so I can learn more rather than have someone just do it for me so it forever remains a mystery. I hate it when I ask questions and people get defensive. I kind of feel like if you can't explain your idea/plan, it might not be such a good one.

Originally Posted by wkooiman

My favorite carburetors are from Quick Fuel Technology. They build excellent carburetors based on Holleys. Another good choice is the Holley HP series.

I only have some limited experience with Holley and Demon (Barry Grant). I know a lot of others share your appreciation of Quick Fuel, though.

Originally Posted by wkooiman

My favorite carburetor tuning website is this: Carburetor Tuning the Scientific Way

There is a section near the bottom where he explains how to tune using an O2 sensor and a vacuum gauge. I did this on my car (non Cobra), and it made tuning a piece of cake. The O2 sensor eliminates the guesswork.

I'm still digesting the link, but I appreciate you sending it! That's exactly the kind of educational stuff I've been reading up on lately. I wasn't aware of that site, so thanks!