'70 Cutlass dual exhaust pipes - suppliers? - ClassicOldsmobile.com


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Old February 13th, 2018, 07:39 AM   #1
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'70 Cutlass dual exhaust pipes - suppliers?

So, Thornton seems to have introduced a new set of headers that fit onto the stock intermediate pipes for a dual exhaust 350. My current long tubes are rusty and a real PITA when it comes to the tension spring and the shifter linkage. I'd like to switch to these new headers and use the stock exhaust pipe routing, but I can't seem to find a supplier of the factory bent intermediate pipes. I've done a search, and the best I can come up with is that the passenger and the driver's side are different pipe sizes on the 350 - 2" vs 2-1/4" - but when I find a supplier of the intermediate pipes, the disqualifier is that I have OAI, which doesn't seem to make a lot of sense. If you have replaced your dual exhaust with the factory style pipes, where did you find your intermediate pipes? Are they the same as the 455? The rest of my exhaust system is excellent - no need to replace anything but the headers and the front pipes. Any help is appreciated!

Last edited by BSiegPaint; February 13th, 2018 at 07:42 AM.
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Old February 13th, 2018, 08:42 AM   #2
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I have no experience with these shorty headers. The outlets APPEAR to be i the stock locations for an SBO, but the ad claims that they accept 2.25" or 2.5" head pipes. The flanges appear to be ball joint and not the stock flare. I'm not convinced that a stock pipe bolts up with no issues.
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Old February 13th, 2018, 09:15 AM   #3
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Quote:
Originally Posted by joe_padavano View Post
I have no experience with these shorty headers. The outlets APPEAR to be i the stock locations for an SBO, but the ad claims that they accept 2.25" or 2.5" head pipes. The flanges appear to be ball joint and not the stock flare. I'm not convinced that a stock pipe bolts up with no issues.
Joe, that’s a perfect point. If stock pipes are 2” on the driver’s side, then these wouldn’t fit onto the stock pipes. So I’m sure this is just a “stock location” fitment, and I’ll need a custom bent pipe to meet up with the muffler(s). That was easy.... thank you
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Old February 14th, 2018, 05:51 AM   #4
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A vendor doesn't know what you have, so, if it makes no sense that it has a no OAI restriction, you can mislead them and buy anyway. Might help to ask why in a separate phone call just to make sure.
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Old February 14th, 2018, 06:52 AM   #5
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A vendor doesn't know what you have, so, if it makes no sense that it has a no OAI restriction, you can mislead them and buy anyway. Might help to ask why in a separate phone call just to make sure.
The Parts Book shows different P/Ns for 1970 350 cars with and without O.A.I. (of course, this likely means W-31 and not a non-W car with a W-25 hood).

Non-O.A.I. is 399546 RH and 403413 LH
O.A.I. is 406218 RH and 406219 LH

Unfortunately, the Parts Book does not detail the differences.
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Old February 14th, 2018, 07:06 AM   #6
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OK, I've figured this out. The 1970 A-body 350 cars all use the same exhaust manifolds, so the front ends of the pipes are the same. The 1970 350 O.A.I. cars (namely, the W-31s and Rallye 350s) use different mufflers than do all other 1970 Cutlii. The exhaust pipe difference must be an expanded aft end where it fits into the muffler. Mystery solved.
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Old February 15th, 2018, 06:42 AM   #7
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What about the Pipes down pipes or ask Thornton what pipes they have fitted to their headers. Nice to see these as nearly ever other make has bolt on shorty headers to stock or stock replacement exhaust. I assumed they were doing a SBO version of that tubular header, not a regular shorty header.

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Old February 15th, 2018, 03:07 PM   #8
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I ordered up a set of these for my 85 442 that currently has crappy long tubes going into a full 2.5" Pypes system (X-Pipe, dual mufflers and tail pipes). I'm planning on junking the beat up leaky long tubes installing some universal Pypes Cats, the Pypes G-body SBC downpipes connected to the Thornton Headers. I'll let everyone how the install goes.

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What about the Pipes down pipes or ask Thornton what pipes they have fitted to their headers. Nice to see these as nearly ever other make has bolt on shorty headers to stock or stock replacement exhaust. I assumed they were doing a SBO version of that tubular header, not a regular shorty header.
I asked Thornton if they'd work with Pypes DGU10S down pipes but got no answer. Pypes lists that # as compatible with SBC powered G-bodys but they also offer the same DP with a 3 bolt flange, seeing as the Pypes are 2 bolt flange as well as the headers being 2 bolt they might work and I'll take my chances. Best case scenario is the headers bolt right up to the down pipes and I just have to do some cutting to fit up to the cats & xpipe. Worst case scenario is cutting the flange off of the down pipes and welding on a new one that is the right size. Cutting and welding flanges is a lot easier than bending exhaust tubing. The Pypes are mandrel bent and you won't find many muffler ships with a mandrel tube bender.

And if you're not concerned about having a Mandrel bent exhaust system any muffler shop should be able to fab up a down pipe. The ball socket on the end of these headers is a pretty universal design and any muffler shop stocks the flared exhaust tube, they just weld that to a bent up section of pipe and slide on the flange with holes in it to bolt up to the header. Shouldn't cost much at all to have fabbed up.

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Old February 15th, 2018, 05:21 PM   #9
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This'll is the down pipes you want to try. The sbc ones probably won't be close, a member modified a sbc G body Y pipe, it needed a lot of modifications. Pretty sure Thornton headers will be based on pre 75 non catalytic converter exhaust manifolds. The DOF10S are the ones to try, read the 13 reviews, multiple 350 owners have used them with success. Get both sets and see which ones will work better.
https://www.summitracing.com/parts/pye-dof10s

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Old February 16th, 2018, 03:57 PM   #10
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I contacted Thornton, and they suggested I contact a place called Never Rust in Pittsburgh, PA - so in other words, they don't have a real answer for the headers they're selling. I checked on the Summit Racing parts and those that used them with the 350 seemed to have excellent reviews, so maybe these are the answer! Thank you
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