[BigBlockBigTire69]

Got a 555 BBC Pump gas motor 11:1. Alot of cam. Car is street/strip. Shifting at 7,000. Makes 850hp. What size header and what size tubing. Was thinking 2 1/4 header into a 3.5" collector and 3.5" exhaust thru a set of delta force race mufflers from flowmaster dumped at the rear axle. Is 3.5" enough for this combo. I would go with 4" but I don't want to sacrifice midrange power and torque unless it really needs 4" exhaust.

 

[Lew540]

I would go 2 1/8 this way everything fits and not worth loss of any or minor HP. Lemons are the best. Run 3.5 inch collector and exhaust out the back and I mean out the back. Under the car it will drone and smell and you will hate it. If you are tubbed and limited on room at least have them shoot out the side. I have 3.5 inch all the way out the back to the bumper. Go with a Borla XR1 muffler or a muffler with a straight through design. You could probably get by with 3 inch over the axle if there are fitment issues. Make sure you have a mandrel bend and try to fit an X or H Pipe in there. A lot of times it is not worth the 5-10 hp to go through fitment or drone hassles.

 

[GR8WHITE]

Lemons all the way. I would stay 2 1/8". They built me stepped headers 2 1/8 - 2 1/4" (no extra charge) but know that a 2 1/4" requires a 4" collector. I welded on a reducer to 3.5" so I can run 3.5" for now on the motor to get the car sorted out. Then switch to 4" when I bolt the vortech blower on and let her eat!

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[bracketchev1221]

I think you could get away with a 2 1/8" tube header. My 565 was dynoed on a 2 1/8" header and made 980 hp. Not sure if there was any gain in the car with 2 1/4" headers with a 4" collector. IF there was it was not a whole lot.

 

[BigBlockBigTire69]

I think you could get away with a 2 1/8" tube header. My 565 was dynoed on a 2 1/8" header and made 980 hp. Not sure if there was any gain in the car with 2 1/4" headers with a 4" collector. IF there was it was not a whole lot.

Would hope my new 555 combo makes somewhat close to that much hp I decided to go 14.5:1 compression and made some other changes , what's the setup on your 565??

 

[bracketchev1221]

Would hope my new 555 combo makes somewhat close to that much hp I decided to go 14.5:1 compression and made some other changes , what's the setup on your 565??

The 565 was a Je piston 15:1 gas ported piston with .043/.043/3/16 low tension rings. Same heads off the 548, the cam was increased from .788/.765 275/282 to .814/.798 282/290. I also changed the rod from 6.385 to 6.535. Those were the major changes. So 17 inches bigger it made 70 hp more.

 

[Lew540]

Remember keep a balance of what makes sense and easy to install/servicability versus a total nightmare and only get 5-10 hp at 7,000 rpm.

 

[bracketchev1221]

Remember keep a balance of what makes sense and easy to install/servicability versus a total nightmare and only get 5-10 hp at 7,000 rpm.

Exactly. If you can get 2 1/8” headers in and get to all the plugs and filter you’re miles ahead of 2 1/4” that are a nightmare. I had mine custom built to the car in 2003. They were the best investment and made in 5 pieces so they went in and out easily