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mismatched diameter exhaust manifold

P pauleric
I have an exhaust coming from Vintage Speed built with 1 5/8" diameter tube. It is designed to work with a heater box. I called CIP1 to ask if they had a heater box with 1 5/8" diameter tubing. The answer was yes. I should have asked if they had a cheap heater box with 1 5/8" tube. The CSP boxes run close to $750 for the pair. Berg isnt much different. The person I spoke with claimed alot of people he knows run the mismatched 1-1/2" heater boxes with 1-5/8" exhaust. That there isnt much of a difference and it really will not matter wither way.

With the particular exhaust I bought I would end up with No. 1 and No. 3 cylinders blowing through 1 1/2" dia. tube and No. 2, No. 4 blowing through 1-5/8".

Any thoughts on running this way? Doesnt smell right to me.
1956 Thunder Ranch(Speedster)
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P pauleric
I have an exhaust coming from Vintage Speed built with 1 5/8" diameter tube. It is designed to work with a heater box. I called CIP1 to ask if they had a heater box with 1 5/8" diameter tubing. The answer was yes. I should have asked if they had a cheap heater box with 1 5/8" tube. The CSP boxes run close to $750 for the pair. Berg isnt much different. The person I spoke with claimed alot of people he knows run the mismatched 1-1/2" heater boxes with 1-5/8" exhaust. That there isnt much of a difference and it really will not matter wither way.

With the particular exhaust I bought I would end up with No. 1 and No. 3 cylinders blowing through 1 1/2" dia. tube and No. 2, No. 4 blowing through 1-5/8".

Any thoughts on running this way? Doesnt smell right to me.
Lane AndersonLane AndersonMt. Pleasant, SC Supporting Member
I have A1 Sidewinder heater boxes that are the same size as my exhaust. I think they are both 1 5/8" but they could be 1 1/2" (don't remember). They are flanged to fit the A1 header. I think the whole exhaust system, muffler included, retailed for <$1000. Check with Carey Hines as he's the one who provided mine. I don't know if your header will work with flanged heater boxes, or if it requires the usual slip-fit. Carey may be able to answer you there. All that said, the CSP boxes are probably about the best quality you can get, but their exhaust and brake stuff sure is pricey.
Gordon NicholsGordon NicholsMassachusetts 1993 CMC Supporting Member
For what it's worth department.

It'll probably idle fine, but up above 4,000 rpm it might never run as smooth as if they were all the same size and balanced.

Larry might have some insight on this, too, but it would seem to me that, under power loads you might notice the roughness.

But then.....1/8" difference sure isn't a whole lot, is it?

This all goes into the "It Depends" department: If you're not going racing with it and don't expect to spend long periods of time well over 4 grand rpm, you'll probably never notice the difference (as Justin doesn't).
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