Advice please

[benno440]

Gents,

I got a customer/friend he has a VC valiant that is street/strip car. It has a 318 (mild) in it at the moment and he is building a 360 (mild drag motor) for it. currently it runs 14 sec quarters flat. running the 904 auto (is that correct?)
He wants me to build him a set of tuned length stainless headers for it and a full exhaust system with dynomax ultra flo's and also cutouts just past the headers.

he wants these to run well on the 318 but also work for the 360 once it is built.

it is currently also running a edelbrock rpm intake and 600cfm edelbrock, but he is keen to change intake and carb, he mainly wants to see what he can get out of the 318 before he puts the 360 in.

My questions are:

What size tubes would work best for the headers to make the 318 open up and breath and then work awesome for the 360 once it is built. the build is more focused for the 360 but that motor wont be ready for another year or so and wants a good system for the 318 now, he is dead set on a tuned length of stainless headers so this has to work.

and what size exhaust system? I was thinking around 1 7/8 for headers and a 2.5 or 3" exhaust???

Also he was thinking about getting a set of edelbrock heads for the 318 and then later using them on the 360 is this doable? he wants good compression, but does not know anything about the 318, but surely it is not stock as it revs upto 6500rpm and runs a 14 flat in a 3500lb car on street tyres and a non lock diff.

let me know what you think?

 

[Meep-Meep]

Primary header tube size should be roughly 1/8" larger than the exhaust valve size. And there is no one ideal primary tube size between the 318 and 360 - if one wants to split hairs. As long as you will be building a set of headers might as well build a set of stepped headers and really get the most out of the part. Issue is figuring the exact location of the step to relieve the pressure at a specific point along the primary tube at a given RPM. I believe there is a 1000 RPM window where you have the sweet spot where the exhaust pulse is in sync to help scavenge the cylinder. It's a fascinating subject.

2.5" pipe all the way out should be good enough for a 360. I'm running 3" on a 440 and 426W and the 440 ran high 12's through the Flowmasters.

 

[benno440]

hmmm, thanks meep, I am guessing 1 3/4 header and 2.5 exhaust. I was going to do the step in the headers just don't know what size and how far down, is there a way to work that out?

 

[rumblefish360]

I'm not sure about where (how far) the step should take place. When I read up on this subject at various header company sites, they all seem to have a different perspective on the issue. I did not that none of them stepped up in pipe size very quickly or half way down the pipe length.

If I had to guess, I think at approx. 8 to 10 inches in length was the approx. Average length before the pipe stepped up. I think it is a engine to engine spec that would change.

I also left a lengthy reply (so grab your smokes and a drink) on your mirror thread here ---> http://www.forbbodiesonly.com/moparforum/showthread.php?77497-racers-need-some-advice-please

 

[Meep-Meep]

Benno, it's all right here:
http://www.amazon.com/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099

I have an older version of this book and the amount of information and methods of how they achieved the results are staggering.