exhaust tube size

[Moparmatt72]

Recap on my set up 440 +.060 (with some to spare) stealth ported heads with 1.7 roller rockers, isky 292 509 cam, ported m1 with a 850dp, hooker sc 2" prim 3.5" collectors. My question it will be pretty much mostly track car will going 3.5" exhaust hurt with a 3" cross over h pipe? I noticed most or you have 3" do you loose that much with going .5 " bigger.

 

[383man]

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I use 2" TTI headers with a 3" X-pipe exh system out to my rear bumper and I use Ultra-Flow mufflers. It seems to work fine for me as I have never uncapped the car so I dont know if it would go faster uncapped or with 3.5 pipes but I am very happy with the 3" system. Ron

 

[Cranky]

Imo, your 3" is more than adequate for the combination you have. Also, did you 'engineer' your headers? Might do some reading to get an idea what's happening in the exhaust system... http://www.kengineering.info/header design article.htm

 

[Moparmatt72]

Very interesting read thanks cranky and no they are off the shelf. That's why I was wondering about going bigger so I wouldn't need to uncork them. I was just wondering I know it would sound more aggressive but with 588" lift and a 109 overlap it's ggoing to sound sweet anyways.

 

[Meep-Meep]

A rule of thumb is to size the primary tubes 1/8" larger than the exhaust valve. What this does is take the boundary layer into effect so you end up with an effective ID of the actual valve size. 1.74" valve should do nicely with a 1-7/8" tube. A 1.81" valve like I have seems to do well with a 2" ID. My exhaust set up is similar to 383man's but I have a lot less motor and I too have never uncapped my car at the track.

 

[Moparmatt72]

Well the stealthy do come with 1.81 exhaust so the 2" prim work well had them on my 906 heads with bigger valves done. Ill stick with the 3" size with the same size cross over and run it that way. Was just curious if it would hurt performance that much. With a lot bigger motor or force induction would flow it no prob at 3.5".