[er455]

Thanks Tom , so my downpipe now starts off 5” right off the turbo for only 4” then I have it reduced down to 3.5” for about 4 feet to get under the car where it goes from 3.5” to dual 2.5” merge pipe all the way out the back . Was thinking about going from 5” off the turbo to a 4” for about 4’ to get under the car then go from 4” to a dual 3” merge pipe all the back..

[Tom Vaught]

Originally Posted by er455

Thanks Tom ,

Was thinking about going from 5” off the turbo to a 4” for about 4’ to get under the car then go from 4” to a dual 3” merge pipe all the back..

You are welcome. Like I said 5" off the turbo for 10-12" is fine then reduce to the 4" downward to under the car, etc.

Tom V.

[er455]

Originally Posted by 73 TRANSAM

On my setup, I have a 5" downpipe about 2 feet then neck down to 4". Then I'm going to do a two 3" pipe to the muffler. This is with a PT91.5 G trim single.

How does it sound? Any pics ?

[70 bird]

Here is a video my buddy shot about 9 years ago. 5in to 4in until just past the transmission. then it splits into 2- 3in pipes into 3in dynomax ultraflows. then 3in over the axle and out the back. Probably about 80lbs of pipes! lol. Its almost too quiet but its what I wanted, a sleeper.

https://www.youtube.com/watch?v=Osf-qINumqY

[n2ogpsj462]

I've got about 3ft of 5" reduced to 4 as it turns parallel to the ground then split 3". I utilized my existing 3" x pipe. Just trimmed down the drivers side entrance and welded it up. I recall reading way back when doing this that you needed as much 5" off the housing as possible before reducing but since then I've seen many setups that didn't follow that and run well.
I'm sure Tom has the actual answer to that

[Tom Vaught]

Originally Posted by n2ogpsj462

I've got about 3ft of 5" reduced to 4 as it turns parallel to the ground then split 3". I utilized my existing 3" x pipe. Just trimmed down the drivers side entrance and welded it up. I recall reading way back when doing this that you needed as much 5" off the housing as possible before reducing but since then I've seen many setups that didn't follow that and run well.
I'm sure Tom has the actual answer to that

The reality is n2ogpsj462 that the vehicle package has a big effect on what you can actually run with the large (say 5" tubing) before you have to make the downturn to go under the dash area.

If you have a remote filter set-up you might be able to make the 90 degree turn with 5" and go a few inches more before having to make the second turn sending the exhaust towards the rear of the vehicle.

If you can't package the 5" turn and a bit of 5" downpipe (in the space) you might as well just reduce to 4" before the downturn and plumb it that way as far as you can.

Again "Package" defines most turbo plumbing in today's world.

Tom V.

[Jack P.]

Is the serpentine belt system from a kit or made to fit using different pieces?

[er455]

Originally Posted by Jack P.

Is the serpentine belt system from a kit or made to fit using different pieces?

Separate pieces crank pulley is off a 5.0 mustang that machines out slightly to fit the Pontiac balancer and the rest is from a Buick grand national ...

[Jack P.]

May I ask what years Mustang pulley will work and does the Buick alt. and P.S. brackets bolt right up to the Pontiac engine. I would like to do it without A/C. Other people on this forum may like to do one both ways.

[er455]

Originally Posted by Jack P.

May I ask what years Mustang pulley will work and does the Buick alt. and P.S. brackets bolt right up to the Pontiac engine. I would like to do it without A/C. Other people on this forum may like to do one both ways.

I got the crank pulley off a late 80, 5.0 and the rest ac, alt, and power steering pump is all from a grand national with a customer one off adaptor plate to bolt the grand national accessory bracket to a Pontiac head