Original GM Issue Sidepipe Design:65-67

[Joe C.]

Does anyone here have any information on how the inner tubes were constructed and configured. I understand that they were of rather thin gauge steel (18ga?) and the longitudinal seam was rolled, not welded............is this correct? Was the inner tube diameter 1 3/4" or 1 7/8"? Also, what was the configuration of the perforations in the inner tube. Were they plain, round, drilled holes like old fashioned Thrush/Hollywood/glasspacks? Were they an odd shape, with an internal scoop projecting into the inner tube, further restricting it? Were they triangular in shape? Rectangular with the long axis perpendicular to the flow?
Thanks in advance.

Joe

[Jon #40768]

Re: Original GM Issue Sidepipe Design:65-67

I have not looked up the spout of my pipes in many tears, but I do not remember any inner pipes. The pipes are straight through with 8 sets of crimps. There are 4 crimps around the diameter. I know these are factory pipes as I bought them from GM about 23 years ago. I cant say that they are exact as what the car came with.
Jon

[John H.]

Re: Original GM Issue Sidepipe Design:65-67

They're a double-wall (double-pipe) design; the inner pipe is 1-7/8" diameter and is perforated, and those perforations form attenuation chambers inbetween the crimps in the larger-O.D. outer pipe. The perforations also cause disruption of laminar flow along the I.D. of the inner 1-7/8" pipe, effectively reducing its I.D. even further. I don't recall the exact configuration of the inner pipe perforations, but I do recall the SAE paper written by a powertrain engineer at GM Research years ago that predicted (and validated) the power loss vs. the standard 2-1/2" under-car exhaust system. Sidepipes were NOT an Engineering-driven option; they were driven by Marketing and Styling.

[Duke W.]

Re: Original GM Issue Sidepipe Design:65-67

John - any indication of the percent power loss at high revs on a SHP SB?

Duke

[Bill W.]

Re: Original GM Issue Sidepipe Design:65-67

John do you have any information on the date or first vin # side pipes were used on (production)? Who was the designer ? my 65 #17346...5/12/65 ..has them...Bill

[Wayne K.]

Re: Original GM Issue Sidepipe Design:65-67

Duke,

I have no documentation but I do remember from a past post on this issue and I recall something like 10%.

Wayne

[John H.]

Re: Original GM Issue Sidepipe Design:65-67

Bill -

I'm not familiar with that one, but I believe someone posted a week or two back that sidepipes on a '65 prior to around #9,000 could be suspect.

[George J.]

Re: Original GM Issue Sidepipe Design:65-67

Duke, John, et al,

When running my '65 fi engine on the dyno after a rebuild using the stock pistons (10.2:1 measured comp ratio) and cam and the shops large diameter ( probably 3") exhaust they recorded a peak hp of 333. Bolting up the side exhaust with no tuning it generated 294 hp. So, a 10% reduction seems plausible.
My '65 original came with them according to the information we gathered at a Mich Chapter tech session regarding the cut outs on the bird cage. It is serial no. 14713, an early April car.

George

[Bill Stephenson]

Re: Original GM Issue Sidepipe Design:65-67

-------George,,,Its a rare 65 fuelie that was delivered new with sidepipes. You should treasure that one............Bill S

[George J.]

Re: Original GM Issue Sidepipe Design:65-67

Bill,

Thanks. It was in fantastic shape when I bought it. Now it is well used. I wanted to drive one of the best '60's sports cars made.

George