KF9BD

Have searched but can't find the diameter of the 99 stock exhaust manifold exit port where the manifold bolts up to the pipe leading to the stock cats. Anyone know? I have looked at pictures (ls1howto.com) and the diameter appears to be larger than the 2.5" mid pipe/exhaust pipe.

Also, does anyone know the diameter of the pipe that bolts to the exhaust manifold? Picture of this pipe look larger that 2.5" also.

Thanks

Jack Behrle

I have a pair of 99 take offs on the shelf in the garage. They measure 2.5" inside diameter.

KF9BD

Great. Thanks for the response.

Which of the following do you think would be better from a sound and performance perspective:

1. 3" pipes to include x-pipe and cats from the stock manifolds to TI cat-back.

2. 2.5" pipes to include x-pipe and cats from the stock manifolds to TI cat-back.

My effort is directed towards an exhaust system that will be very close to the stock in sound, yet provide an importment in flow sufficient to support 400 rwhp.

I am not considering headers because of the increased noise transmission.

Jack Behrle

I went with Kooks 1.75 LTs back to stock cats and muffllers. Not a large change in sound but great performance improvement.
Also, I kept all the o2 sensors in place so no codes or other hassles.

KF9BD

You didn't pickup much more valve train noise with the headers? Interesting....whats is you rwhp $ rwtq?

Scubanme

97 to 99 exhaust manifolds are a bad design. They have almost no seperate tubes to speak of. If you really want to retain stock manifold
reliablity and ease of maintenance, then go with 2001 or newer exhaust manifolds. You will also need the H-pipe setup, but you can run your cat-backs. I would get a whole exhaust system from a Z06 and you will have that little extra exhaust tone that sounds great and stock reliabilty.

KF9BD

I have heard that the 2001 and up exhaust manifolds were better. Do you believe the 2001 and up h-pipe is better than an after market (magnaflow or Random Tech) x-pipe?

Also, any comments on my previous question concerning pipe diameter?

Thanks

Jack Behrle

370hp/350torque after a tune

Jack Behrle

Very, very slight noise...almost like a sewing machine. If you did not know there was a cam installed, you would never notice the sounds.

KF9BD

Very good gains.

Thanks, Jack.