Down pipe, size does matter!

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Oct 21, 2012 | 05:41 PM

Zorro O

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Racer

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From: Lynnwood WA

Down pipe, size does matter!

Ok, here's the deal. A few weeks ago I bought some Pypes down pipes from Summit. After they finally arrived I compared them to my 86 C4 exhaust manifolds and found the bolt pattern does not match. These down pipes were sold as 86 C4 specific, yet when I measure the center to center distance between bolts, my 86 shows 3.250" and the Pypes down pipes show 3.750", A half inch difference! I called Summit and they say, they called Pypes, and were told GM made two different bolt patterns for 86 C4. And that they (Pypes) only make the 3.750" ones, and that I should just extend the holes as it will not weaken the flange. I have been in contact with two forum members, they both have 3.250". The idea of "just" elongating the six slots in 3/8" steel plate, does not seem reasonable. Also considering how slow GM has been to change any design, they don't have to, on the Corvette, this just doesn't seem to pass the smell test. I like Summit, and if Pypes is lying to them, I think they should know. If on the other hand Pypes is telling the truth, then Summit should note this anomaly on the order form. Anybody have exhaust flanges with bolt centers of 3.750"?

Zorro

Oct 21, 2012 | 09:40 PM

GREGGPENN

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From: Overland Park Kansas

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Because I haven't heard of any difference in ex manifolds (during ~ 10yrs on the forum), I'm going to say they're all the same.

For L98's.

LT1's are bigger and seem more likely to be what Summit/Pypes are talking about.

Consider this an uneducated guess.

Last edited by GREGGPENN; Oct 21, 2012 at 09:42 PM.

Oct 21, 2012 | 10:26 PM

Zorro O

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Racer

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From: Lynnwood WA

Quote:

Originally Posted by GREGGPENN

Summit just changed their ad. Funny about the timing.

Zorro

Oct 22, 2012 | 01:17 AM

GREGGPENN

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From: Overland Park Kansas

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LOL

If it looks like BS and smells like BS......

Oct 22, 2012 | 05:21 AM

blackozvet

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From: Adelaide South Australia

Summit have done this to me more than once !!
when i complained about an incorrect description after i recieved one of what was supposed to be a pair, they changed the description, then accused me of lying !
but their prices and shipping are so good . . . .

Oct 22, 2012 | 08:59 AM

GREGGPENN

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From: Overland Park Kansas

2020 Corvette of the Year Finalist (appearance mods)

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Quote:

Originally Posted by blackozvet

but their prices and shipping are so good . . . .

Not really. I was able to beat their prices on almost everything for my motor build. Seems like the only thing I ended up buying from them was oversize runner gaskets.

Oct 22, 2012 | 10:20 AM

SuperL98

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From: Mass Mass

Is it possible there might be a communication problem here?

I have a manifold from an 1988 L98 sitting in my shop.

The stud to stud measures 3.25 inches, but if you trace a circle through the studs it looks to be about a 3.75 diameter base circle.

Is everyone (Summit & Pypes) talking about the same measurement?

Oct 22, 2012 | 10:28 AM

383vett

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From: moraga ca

What's a down pipe? Is it the header pipe your talking about or the y-pipe that bolts onto the manifold?

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Oct 22, 2012 | 12:54 PM

Zorro O

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Racer

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From: Lynnwood WA

Quote:

Originally Posted by 383vett

What's a down pipe? Is it the header pipe your talking about or the y-pipe that bolts onto the manifold?

It is the pipe that connects the bottom of the exhaust manifold to the exhaust pipe under the car. It is what I was going to use in place of a Y-pipe, in order to run true dual exhaust.

Zorro

Oct 22, 2012 | 01:20 PM

#10

Zorro O

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From: Lynnwood WA

Quote:

Originally Posted by SuperL98

I was wondering the same thing. It's not easy to describe. But wouldn't you think that before you, manufacture, market, and ship such a basic part, you would check to see if it fit. Or when you find out you have wasted a customers time, with such a basic mistake, you would offer to make it right, rather than suggest the customer remanufacture it at their own expense. Or tell them to send it back for a refund, having wasted a month of the customers time, and leaving them with no alternative source for the part.

Zorro

Oct 22, 2012 | 03:58 PM

#11

383vett

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From: moraga ca

Can you use your old y-pipe, cut it after the connection and use it to start your dual exhaust?

Oct 22, 2012 | 05:08 PM

#12

Zorro O

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Racer

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From: Lynnwood WA

Quote:

Originally Posted by 383vett

Can you use your old y-pipe, cut it after the connection and use it to start your dual exhaust?

I am in the process of putting this C4 motor into my C3. The Y-pipe I have, is too small and rusty. It might be time I start searching the bone yards.

Zorro

Oct 22, 2012 | 05:59 PM

#13

vetteoz

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Quote:

Originally Posted by SuperL98

Is it possible there might be a communication problem here?
The stud to stud measures 3.25 inches, but if you trace a circle through the studs it looks to be about a 3.75 diameter base circle.

In the engineering world circular bolt patterns are usually measured as PCD ( pitch circle diameter ) , not as a bolt to bolt measurement

Same as how wheel stud patterns are listed ; Vette is 4.75" PCD not x.xx" bolt to bolt

Oct 22, 2012 | 06:14 PM

#14

mcm95403

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From: Bangkok, Thailand

It sounds like they used LT-1 flanges. I recently converted my 91 L-98 to LT-1 manifolds and found that the bolt spacing was a little bit wider on the LT-1 manifolds. I used a carbide cutter and a dremel tool to oval the holes. Not fun doing it in the car, but if you have them out of the car it should take all of 10 minutes or so per side.

Oct 22, 2012 | 07:33 PM

#15

Zorro O

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Racer

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From: Lynnwood WA

Quote:

Originally Posted by vetteoz

If I had been asking an engineering department this question, I would have asked about the bolt circle. I was asking people on the Corvette Forum for a number, that they could come up with without having to pull any parts from the car, and find with nothing more sophisticated than a tape measure. And it worked. Of course I could have asked them to pull the exhaust apart, and measure the diameter of the hole in the middle of the manifold=A, then measure the distance from the edge of A to the bolt=B, and then measured the diameter of the bolt=C, and then.
A/2 + B + C/2 = what the tape measure told us already.

Zorro

Oct 22, 2012 | 07:59 PM

#16

Zorro O

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Racer

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From: Lynnwood WA

Quote:

Originally Posted by mcm95403

I think you are right about these being LT-1 parts. As far as it being 10 minutes work. The flanges are .412 thick stainless, and I would need to rework six holes! And because of the O2 bung on one and the welded stops on the other pipe, all 6 of holes would have to be done with the pipe bouncing around on the flange. If I had access to a Bridgeport, it would take an hour. I like your idea of swapping the L98 manifolds for LT-1s. Did you run into any other problems, doing that?

Zorro

Oct 23, 2012 | 06:57 AM

#17

blackozvet

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From: Adelaide South Australia

Quote:

Originally Posted by GREGGPENN

Not really. I was able to beat their prices on almost everything for my motor build. Seems like the only thing I ended up buying from them was oversize runner gaskets.

i was also including their air freight prices to Aust,
but while we are on the subject what places have you found better prices than Summit ?

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