I have a 1966 convertible with a 289-It is just a nice driver-trying to get a couple more horsepower out of it and I need to replace the rusting exhaust system with something new.

I just bought a pair of tri y headers-I have the lower bracket for the power sterring in place......Eventually I am going to add a 4v carb and a new intake...I was wondering what size exhaust pipesI should use? 2 1/4, 2 1/2, 3 ...I am probably going with flowmaster 40s and "H" pipe.......The exhaust also has the GT trumpet tips on the end.

Thanks in advance Scott

 

3 inches would be to big IMO. When my 68 was a 302 it was 2 1/2 pipe with flowmasters and it was a great setup. I think you'd be fine with either 2 1/4 or 2 1/2.

 

2 1/4 or 2 1/2, 2 1/4 will be plenty though and a bit quieter

 

2 1/4" is plenty. and IMO you dont need the h pipe. but i know for a fact a few others will disagree.

 

I would use an X-pipe over an H pipe. It will improve exhaust gas scavenging. In addition,"straight through"mufflers will outperform chambered mufflers. Magnaflow is a good choice.

 

2-1/4" is perfect for even a mild 289 build. Look at the chart here: http://www.flowmastermufflers.com/faq.html

H-pipes help balance exhaust pressure between cylinder banks, improving exhaust efficiency. They also help mellow out a normally raspy exhaust note. You don't absolutely need one, but I'd very, very strongly recommend it. It's just a simple straight tube welded in between the two banks (as close to the collectors as is reasonably possible), so it's not an expensive add-on, and it'll be worth 5-15hp.

I wouldn't be worrying too much about optimal muffler flow charactaristics; you're not going to be making enough power for it to matter anywhere but a dyno. Get mufflers because you like the way they sound.

 

While I agree that the gain may be minimal, I never liked the idea of leaving HP on the table. Especially since most people tend to do modifications in the future that will increase power.

 

Magna flows sound perfect. the Flowmasters area little loud.

 

Thanks for all the advise-I think I got a game plan now........Scott

 

I went with the JBA on summit racing - got the H-pipe, 2 1/2" all the way back with the tips welded on the end to exit through the rear valence (it tucked up nicely under the TCP sub-frame kit that I have - about 1/4" clearance above and below). This sounds great and performs well. If you have a chance, go to the JBA website and check out the wave file