Hello everybody. Im new to this forum and this is my first post. I need some help here. Me and my dad bought a 400 sbc from an engine builder, it has 12:1 compression piston, steel crank destroked with a 350 crank. Good cam, and a holley 750 double pumper carb. We have set the timing (to what we think is right) but the car takes of hard for 15 feet then it falls on its face, its like it goes to half throttle. It wont continue to pull hard, it barely will spin the tires with a 400-450 hp motor?? I need help PLEASE!! Thank you in advance.

 

Welcome to the forum.

Need more information to make any judgements about your problem. Is the engine carburated? Automatic transmission or manual? Are you sure you're getting fuel in sufficient quantity to the engine? What type of ignition system does it have? What heads does the engine have? What is the combustion chamber volume?

Did the engine builder dyno the engine? Have you asked the engine builder about this problem?

 

The engine is a carb engine, it has a holley 750 double pumper so i know the fuel is getting to the engine. It has a turbo 350 auto tranny, and the heads didnt come with a spec sheet so i can answer that question.

 

You are probably over carbureted for that size engine. If you're talking about falling flat under a full throttle condition, then you're either getting too much gas or not enough gas. With that carburetor, I suspect it's too much.

One thing you might try is cutting down on the pump stroke to reduce the shot of gas that goes the engine.

A Holley carburetor needs to be tuned for each individual engine which is why I asked if the engine was dynoed previously.