Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

[Victor S.]

Hi All -

I'm trying to determine the correct factory front pipe and rear muffler arched clamps for the 74 454 2 1/2" original exhaust. I know it was a guillotine style flat bottom clamp - but there are a lot of variations in these clamps, especially on the sides. AIM part diagrams are not that detailed - and its hard to tell from the judging guide as pics are not that clear. My exhaust had been replaced - but I now have the complete original 74 BB exhaust system from front to back but I'm struggling to find what these four clamps look like. It appears that the fronts were different than the rear muffler bracket clamps - at least that is what the AIM shows. Any help would be much appreciated. Thank You -

Vic

[Patrick H.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

This enlarged picture from the Judging Guide suggests that the clamps have slightly rounded bottoms, and have a "bulge" for each end of the U. The only place I found clamps at all like this for my 72 was at Camaro Central:

https://www.camarocentral.com/Exhaust_Pipe_Muffler_Clamp_2_Inch_OE_Style_p/fue-380a.htm

They carry 2-1/4 but not 2-1/2 inch clamps like this.
However, the key is that you may have to look at non-Corvette sources for the correct clamps.

Oh, and Gardner Exhaust might have them, but they ONLY sell them with a complete exhaust system. You cannot buy the clamps separately. I asked and tried.

You might be able to make a 2-1/2 work, but...
Else Bosal makes the 250-265, which is as close as I've otherwise seen. However, it still has differences from original.

[Tom R.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Victor
I'll add to what Patrick has posted. After we published the 3/4 and 5/7 manuals, I took another look at exhaust systems, especially 75 and up. While exhaust system configurations changed dramatically in 75, due to increased heat from exhaust emission control, including the catalytic converter, I concluded some clamps from pre-75 continued to be used.

As you both note, clamp configuration has many variations but what remained constant was the use of those flanged nuts...not regular nuts with lock washers! Patrick's photo, as you probably figured out, is a clip of the image in the 3/4 manual. The first photo shows a 74 L82 exhaust clamp.

74 L82 exhaust clamp. Unfortunately, it does not show the strap across the top of the pipe.

exhaust_clamp_L82_74.jpg

Here's a clamp I've concluded is used from 75-82, and perhaps earlier. Note the flat strap

DSC05379.jpg

And here's the flat strap and its signature K embossment at the top of the strap.

DSC05380.jpg

I believe what we can conclude here, is the configuration of the lower clamp, open sides and flat bottom and flange nuts. What I can't confirm is whether in 74, the U bolt was a flat strap or rounded, as shown in the Camaro Central image.

[Victor S.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Thanks guys - that's a big help - very much appreciated/V

[Robert R.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Vic,
Here’s a pic of the original front clamp and u-bolt on my 454, M40 ‘74. You can see that the u-bolt is flattened at the top and the clamp is similar to the one that Camaro central sells.
Bob

IMG_2336.jpg

[Tom R.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

And the nuts are flanged! Good work.

I should add that the flat strap clamp was used on all 2 1/2 inch pipes through 82. So, as shown, not only 454s in 74, but L82s as well. What's interesting is that in 75, a header Y-pipe routed to a 2 1/2 collector pipe, or what was called an extension pipe where it bolted to the cat converter (they secured the pipe at the front while securing a heat shield at the top of the pipe (it routed under the passenger seat). The strap clamp was used on both ends. L82s used the 2 1/2" pipe in a rear pipe Y configuration, exiting the cat until it got to each muffler. Here the strap clamp was used. Where the muffler was hung from the frame at the tip used 2 1/4 clamps. L48s also used the strap clamp at the extension pipe, but exiting the cat, the 2 1/4 clamps were used. This was consistent from 75 thru 82. owners with 75-77 that use the TIMJG will see that the exhaust section reflects 74 usage. It's been rewritten but not published to reflect what I noted here.

Would be interesting to learn if the strap clamp was used earlier than 74, like in 73...give Jimmy P something to do! LOL

[Mark E.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

This enlarged picture from the Judging Guide suggests that the clamps have slightly rounded bottoms, and have a "bulge" for each end of the U. The only place I found clamps at all like this for my 72 was at Camaro Central:

https://www.camarocentral.com/Exhaust_Pipe_Muffler_Clamp_2_Inch_OE_Style_p/fue-380a.htm

They carry 2-1/4 but not 2-1/2 inch clamps like this.
However, the key is that you may have to look at non-Corvette sources for the correct clamps.

Oh, and Gardner Exhaust might have them, but they ONLY sell them with a complete exhaust system. You cannot buy the clamps separately. I asked and tried.

You might be able to make a 2-1/2 work, but...
Else Bosal makes the 250-265, which is as close as I've otherwise seen. However, it still has differences from original.

This JG photo doesn't show bonding straps. Did 1974 not have these? Or maybe this is a non-radio car?

[Patrick H.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

This JG photo doesn't show bonding straps. Did 1974 not have these? Or maybe this is a non-radio car?

I assume you mean grounding straps, which were gone after 1970.

[Mark E.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

I assume you mean grounding straps, which were gone after 1970.

Interesting. I wonder why Chevy discontinued the straps. Discovered they weren't necessary?

I call them bonding straps. Bonding equalizes potential and prevents static charge (in this case, with the exhaust). Grounding completes a circuit.

[Patrick H.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Victor
I'll add to what Patrick has posted. After we published the 3/4 and 5/7 manuals, I took another look at exhaust systems, especially 75 and up. While exhaust system configurations changed dramatically in 75, due to increased heat from exhaust emission control, including the catalytic converter, I concluded some clamps from pre-75 continued to be used.

As you both note, clamp configuration has many variations but what remained constant was the use of those flanged nuts...not regular nuts with lock washers! Patrick's photo, as you probably figured out, is a clip of the image in the 3/4 manual. The first photo shows a 74 L82 exhaust clamp.

74 L82 exhaust clamp. Unfortunately, it does not show the strap across the top of the pipe.



Here's a clamp I've concluded is used from 75-82, and perhaps earlier. Note the flat strap



And here's the flat strap and its signature K embossment at the top of the strap.



I believe what we can conclude here, is the configuration of the lower clamp, open sides and flat bottom and flange nuts. What I can't confirm is whether in 74, the U bolt was a flat strap or rounded, as shown in the Camaro Central image.

You'll have to get a reproduction K-stamped flat strap clamp, and then find a proper "bottom" for a 2-1/2 configuration.
I'm not sure if anyone makes a K flat strap in 2-1/2, or only in 2-inch configuration.

[Patrick H.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

I call them bonding straps.

Call them what you want, but GM and the rest of the world call them ground straps.

[Victor S.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Thanks all - I really appreciate all the help. One more question - on the 74 BB cars would these front clamps have been the same at the muffler hanger on the rear of the car OR like what Tom posted above for the 74 L82 - as the bottom lower side of the clamp looks slightly different than what Bob posted.

[Robert R.]

IMG_2339.jpg

[Tom R.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

Thanks all - I really appreciate all the help. One more question - on the 74 BB cars would these front clamps have been the same at the muffler hanger on the rear of the car OR like what Tom posted above for the 74 L82 - as the bottom lower side of the clamp looks slightly different than what Bob posted.

No! those clamps were smaller and accommodating the muffler tip pipe...what size was it? Probably 2 1/4 inch. Robert can measure his and I'll bet its the smaller size. As well as a different configuration.

[Robert R.]

Re: Need Pic Showing Original Front and Rear Factory Exhaust Clamps - 74 454 - 2.5"

No! those clamps were smaller and accommodating the muffler tip pipe...what size was it? Probably 2 1/4 inch. Robert can measure his and I'll bet it’s the smaller size. As well as a different configuration.

Unfortunately, the only mufflers I have for my cars are NOS, but they all measure 2 1/4”. The outlet tips for the big block and small block mufflers are identical.

Tom, i believe the L82 muffler clamp that you show in your June 12, 4:33AM post shows an original clamp. It is the same style that is shown in my above post of the Hemmings ad.