Correct type center exhaust clamp for 1970

[Rich D.]

Hi, folks. Can anybody show/tell me what the correct exhaust clamp for the under-transmission joint looks like on 1970? Thanks in advance.

[Joe L.]

Re: Correct type center exhaust clamp for 1970

Hi, folks. Can anybody show/tell me what the correct exhaust clamp for the under-transmission joint looks like on 1970? Thanks in advance.

Rich-----


Are you talking about the "ox bow" bracket (which GM refers to as a CLAMP) or do you mean the u-bolt assembly? If you mean the u-bolt assembly, the attached pictures depict a TYPICAL clamp, not necessarily correct in every nuance of detail. Note that the u-bolt has a flattened upper section. Not all originals had this flattened section but if I were you, I would assume that yours did-----I like the extra contact and stability provided by the flattened u-bolt section.

[Rich D.]

Re: Correct type center exhaust clamp for 1970

Rich-----


Are you talking about the "ox bow" bracket (which GM refers to as a CLAMP) or do you mean the u-bolt assembly? If you mean the u-bolt assembly, the attached pictures depict a TYPICAL clamp, not necessarily correct in every nuance of detail. Note that the u-bolt has a flattened upper section. Not all originals had this flattened section but if I were you, I would assume that yours did-----I like the extra contact and stability provided by the flattened u-bolt section.

Hi, Joe. Thanks for the quick response. I did mean the actual clamp as per your photo, not the "ox bow" hanger. Your pictures answer my first question, but raise a second one: According to the '70 AIM, a different type of clamp is used on the muffler-to-exhaust-connection. On my car, the clamps holding the tips to the mufflers look like your photos. But if these are correct for the center joint, what do the exhaust tip clamps look like??

I should mention that the exhaust system on my car is positively not the original. Its the second one I've installed since I bought the car (15 years ago). When I bought it, the car had a very ratty 1969-style side exhaust system, so I've no reference point to start with.

Thanks again.

[Joe L.]

Re: Correct type center exhaust clamp for 1970

Hi, Joe. Thanks for the quick response. I did mean the actual clamp as per your photo, not the "ox bow" hanger. Your pictures answer my first question, but raise a second one: According to the '70 AIM, a different type of clamp is used on the muffler-to-exhaust-connection. On my car, the clamps holding the tips to the mufflers look like your photos. But if these are correct for the center joint, what do the exhaust tip clamps look like??

I should mention that the exhaust system on my car is positively not the original. Its the second one I've installed since I bought the car (15 years ago). When I bought it, the car had a very ratty 1969-style side exhaust system, so I've no reference point to start with.

Thanks again.

Rich------


The clamp for the exhaust tips-to-muffler was the "open" style clamp rather than the "guillotine" style I pictured for the center connection. They had small "extensions" on each side which are hard to describe. I think you may be able to find photos in the catalogs of various reproduction sources. These clamps were all 2" size and had the flattened u-bolt.

As far as the connection from the rear pipe to the muffler extension, there was no such connection point used in PRODUCTION---the rear pipe extended all the way to the muffler and was welded to it at that point. So, only this configuration with "no clamp" is correct. If you use SERVICE style mufflers with forward extensions, I suppose you can use just about any clamp you want. I would use the guillotine style as pictured previously.

[Chuck S.]

Re: Correct type center exhaust clamp for 1970

...The clamp for the exhaust tips-to-muffler was the "open" style clamp rather than the "guillotine" style I pictured for the center connection. They had small "extensions" on each side which are hard to describe...

The Fourth Edition 70-72 TIM&JG has sketches of the respective clamps on page 100, but the "open style" drawing bears little resemblance to the actual clamp. You can buy a clamp that looks like that at Megalomart (I've done it), but it won't have the flattened U-bolt.

What Joe is trying to describe is like "tabs" that are formed to close the "open" sides of the clamp at the very bottom. Think of the bottom of the clamp as being rounded on all bent edges with bent side tabs extending up maybe 3/8" on the open sides. The wide faces extend up to a circular cutout that fits the exhaust tip. The U-bolt is also flattened as Joe described the underbody clamp U-bolt.

Paragon has reproduced this clamp, and it is very close in configuration to the originals. Unfortunately, like most repro parts, it is recognizable as a repro; one identifiable fault is lack of the fabricator's letter stamp. Paragon's will fare better in judging than the one from Megalomart IMO.

[Robert C.]

Re: Correct type center exhaust clamp for 1970

The center clamp, "guillotine" style that Joe pictured is the correct configuration. The originals had a 4 digit part # on the body and the letter "K" raised on the flat top. Paragon's two types are pictured in their catalog and are the only correct stye clamps.

[Terry M.]

Re: Correct type center exhaust clamp for 1970

You might want to consider whether the subject car has 2.5-inch exhaust (BB & LT1) or 2-inch (all the rest). That may or may not make a difference. When was the last time any of us saw an original 2-inch 1970 exhaust system? While we are on that how about the M40 system? The ox-bow hanger was different, could the clamps have been different as well?

[Pat M.]

Re: Correct type center exhaust clamp for 1970

When was the last time any of us saw an original 2-inch 1970 exhaust system?

Terry - you saw my original 70 2-inch exhaust pipes in Kissimmee last January, remember?

[Joe L.]

Re: Correct type center exhaust clamp for 1970

You might want to consider whether the subject car has 2.5-inch exhaust (BB & LT1) or 2-inch (all the rest). That may or may not make a difference. When was the last time any of us saw an original 2-inch 1970 exhaust system? While we are on that how about the M40 system? The ox-bow hanger was different, could the clamps have been different as well?

Terry-----


If one looks under ANY 1969, they should see a 2" exhaust system if it's as originally configured. Even if they look under an L-88 or ZL-1 (not my "ZL-1", though). I realize, of course, that the question here involves a 1970. As you mention, 1970 base engine or L-46 should have 2" exhaust, just like all 1969's.

[Terry M.]

Re: Correct type center exhaust clamp for 1970

Pat,
I am going to have to dig out those pictures. Will you be in St. Charles?

Joe,
Yep, but original exhaust systems in either size are not common -- the year not withstanding. I'm sure there are more in the arid climates out west or at altitude than anywhere else. Those of us in the Midwest don't see them much these days.

Does your original system have the same style clamps Joe?

[Joe L.]

Re: Correct type center exhaust clamp for 1970

Pat,
I am going to have to dig out those pictures. Will you be in St. Charles?

Joe,
Yep, but original exhaust systems in either size are not common -- the year not withstanding. I'm sure there are more in the arid climates out west or at altitude than anywhere else. Those of us in the Midwest don't see them much these days.

Does your original system have the same style clamps Joe?

Terry-----


Yes, it did have. However, I changed the system many years ago to full 2" stainless steel.

[Chuck S.]

Re: Correct type center exhaust clamp for 1970

...Does your original system have the same style clamps Joe?

Which clamps are we discussing, Terry, the underbody clamps or the exhaust tip clamps?

As for the exhaust tip clamps, you and I were standing at the rear of the Sal Carbone's LT1 at Marlborough, and I noted that the RH exhaust tip clamp appeared the exact same configuration as the clamps I found on the 2" exhaust of my base engine.

Aren't the exhaust tips the same?...I would then expect the clamps to be the same. I admit the flattened U-bolts on my clamps looked like they were oversized for the tips, but they seemed to work fine.

[Robert C.]

Re: Correct type center exhaust clamp for 1970

All the rear exhaust clamps are 2" no matter what. The center one's are 2" or 21/2" depending on the engine option. I always thought that was a bit constricting for the 70-72 LT-1s and BB's.

[Chuck S.]

Re: Correct type center exhaust clamp for 1970

All the rear exhaust clamps are 2" no matter what. The center one's are 2" or 21/2" depending on the engine option. I always thought that was a bit constricting for the 70-72 LT-1s and BB's.

Intuitively, it would seem that way, but fluid dynamics calculations would show that reducing the diameter at the very end of the system, or over any short distance of the total system length, would have minimal effect on system pressure losses (increased back pressure on the engine).

Back pressure created by the exhaust system is dependent on the friction coefficient of the pipe interior wall, the flow velocity, and the distance the flow travels. There are also turbulence losses due the baffling in the mufflers, but that is pretty much the same regardless of the muffler inlet and outlet diameters.

When the 2.5" exhaust system "necks" down to a smaller diameter at the very end, this increases the local flow velocity and therefore the pressure losses in that short distance. However, this increased pressure loss occurs over a very short length of the total system...the effect on total cumulative back pressure is minimal. If the pipe diameter is 2" over the entire length of the exhaust system, the pressure loss (back pressure increase) becomes measurable for larger displacement engines and/or higher volumes of flow.

NASCAR exhaust restrictor plates are operating in another fluid flow regime...not the same.

[Pat M.]

Re: Correct type center exhaust clamp for 1970

Pat,
I am going to have to dig out those pictures. Will you be in St. Charles?

Terry - here's some pictures to remind you. You said something like, "yeah, they're original, although they're covered with some kinda ... (gunk, crap, etc.)."
It's paint by the way.
And yes, I will be in St. Charles, and I'm really looking forward to it.