Dual Exhaust for my 86 GP
 

My all original GP needs an exhaust and I was wondering if anyone has upgraded theirs to a dual system. This is a V8 car and seriously need some help to breath. Doesn't look like anyone makes a system for them. Do you think using a high performance cat and then duals back with high flow mufflers would be OK or should I go for true duals to get the required benefit to really help this car breath. If I did true duals I would still want to use cats to keep things legal.

search exhaust forum for discussion.

I already did that and never found anything that applied.

A little more info on the car/motor and your goals would help us, help you.

Sorry about that. The car is all stock with the 305 V8 and 4 bbl carb. I have kept the car in excellent original condition since new and as you know with these cars the performance was non existant. Since I need to replace the exhaust I figured something better than stock would make it run a little better.

I used the system from Pypes in my 78 GP with a 400 and they it very well. They has a number of different now pipes if are using manifolds or shorty headers combined with your engine.

A set of small tube headers would be a bonus and cheap since your are talking sbc.

I would not waste time/money on true dauls,you don't need them.Plus then you need a different crossmember,etc.

I have a 83 wagon,warmed over 350, with Edelbrock headers that still use a air pump,3" single pipe with Monte SS "high flow" cat,the back half is a Grand National style that splits after the cat to dual mufflers and pipes.Sound good and runs great.I think it would be overkill for you.

My old 79 Grand Prix,stock 301,was upgraded with just a bigger single.I went to a muffler shop,had the them run a singe 2 1/5 pipe from the y after the manifold back,no cat and a big Dynomax muffler.He used the "right side" of a Monte SS exhaust as a guide. The car also sounded and ran better for cheap.

It's only a 305 ,don't get carried away.

it probably wouldn't hurt to replace the cat with a new high flow one. that would be the first step i think. you can either get a single in/out cat, or a single in/dual out cat. or use a crossflow muffler, like those found on firebirds/camaros, which will have the look of duals, and will sound better, especially if you use a chambered muffler like a flowmaster. and using the single in/out cat with a crossflow would be cheaper also

Thanks everyone for the discussion. There are several good ideas here. I will seek out a good shop and see what I can work out.

FWIW the head pipes off of a 73 G body with the engine of choice are really close to fitting in these cars. I put the front 1/2 of the system from the cutlass I took the W-30 from when I installed it in the 81 G/P with a TH400.

Mike

How did you make out with the exhaust?? When my 2+2's
orig pipes needed replacing I went with the GM factory 442 duals from the cat back. Went in perfectly! Dave K.

Dynomax sells a complete dual cat back replacement exhaust set up that replicates the Monte Carlo SS. I even find it on ebay at times. Jegs and Summit sell exhaust kits for these cars but will require a new crossmember that they also sell.

You may find more good info at www.maliburacing.com

I bought pypes exhaust and am completely dissatisfied.

You can modify the original crossmember for true duals if you can weld.

MIke

The Monte SS tails goes straight out back, not stock looking for the GP. Dave K.