What is the exact position of the holes for the tail pipe?

[Hans R.]

I have a -66 Coupe 300 HP with Powerglide. The rear panels under the bumpers do not have any holes for the exhaust pipes, so it appears that the car had sidepipes earlier. According to the books, a -66 with the base engine and powerglide did not ever come with sidepipes from the factory. Now I have bought a new under the car exhaust system and need to route the tail pipes thru the rear panels. Does anyone have the exact measurements where the holes should be located in the panels? Or is there some documentation out there that gives this information? It is a little tricky to make the holes just from looking at pictures.

[Tom H.]

Re: What is the exact position of the holes for the tail pipe?

I cannot answer your question as to the exact position of the holes. I would purchase a panel that has the holes already in place. They are available from most suppliers. Roughly a 240.00 - 250.00 item new. If your existing panel is a true GM panel that has never had holes, I'd sure never put holes in it. You might look closely at the panel to see if it may have originally had the holes that have been filled in.

[Hans R.]

Re: What is the exact position of the holes for the tail pipe?

I cannot answer your question as to the exact position of the holes. I would purchase a panel that has the holes already in place. They are available from most suppliers. Roughly a 240.00 - 250.00 item new. If your existing panel is a true GM panel that has never had holes, I'd sure never put holes in it. You might look closely at the panel to see if it may have originally had the holes that have been filled in.

Thanks Tom. No, there is no sign of filled in holes. I'm pretty sure the panels has been replaced on the car by some guy who installed non-original sidepies. (The same guy that have installed -67 louvers on this -66 model). So the panels are not the original ones that came with my car. But I guess the panels could still have been bought from GM.
I need to have the car ready within 2 weeks and it will take some time to get new panels and painted here in Sweden. So I need to go ahead and make holes in the existing panels. Sorry.

[Wayne M.]

Re: What is the exact position of the holes for the tail pipe?

..... According to the books, a -66 with the base engine and powerglide did not ever come with sidepipes from the factory. Now I have bought a new under the car exhaust system and need to route the tail pipes thru the rear panels. Does anyone have the exact measurements where the holes should be located in the panels? ....

Hans --- I'll echo Tom H. and say that it would be a shame to cut holes in an otherwise intact exhaust valence panel.

However, in 1966 and 1967, side exhaust (N14) was available on ALL engine/transmission combinations. It was 1965 that required a 4-speed trans AND an optional engine (because of the 2_1/2" exhaust manifold dump) for both N14 and N11.

One more reason to be doubly certain that your car did not originally come with side exhaust before modifying.

[Douglas L.]

Re: What is the exact position of the holes for the tail pipe?

Hey Hans,

Before you start on the rear panel, have you removed the side exhausts yet?

If you have, are the metal and fiberglass rocker mounting tabs cut? It's not easy to fix cut tabs.

If your car was not side exhaust from the factory, you should see evidence on the rear of the frame where the original exhaust hangers were mounted. You should also see evidence of grounding straps(threaded screw holes) being used at the middle frame crossmember. If no grounding straps, screw holes show no evidence of threads. In addition, you can check the triangular splash panels just rear of the front tires. If they have a rubber sealing strip mounted rear edge of them, that means under car exhaust. If not, that means side exhaust. Check for staple holes if the rubber sealing strip is missing.

As far as cutting the panel, like previous comments, if it's original, I wouldn't do it. If it's repro, no problem.

Good luck

[Hans R.]

Re: What is the exact position of the holes for the tail pipe?

Hans --- I'll echo Tom H. and say that it would be a shame to cut holes in an otherwise intact exhaust valence panel.

However, in 1966 and 1967, side exhaust (N14) was available on ALL engine/transmission combinations. It was 1965 that required a 4-speed trans AND an optional engine (because of the 2_1/2" exhaust manifold dump) for both N14 and N11.

One more reason to be doubly certain that your car did not originally come with side exhaust before modifying.

Hi Wayne,

Interesting, I've trusted the info in 1966 Technical Information Manual to be true in this matter. It says (page 116) that base engine with Powerglide and 2 inch exhaust system was not available with side-mounted exhaust and it will give a total deduction if so equipped.
Where have you found the info that N14 was available for all combinations?

[Hans R.]

Re: What is the exact position of the holes for the tail pipe?

Hey Hans,

Before you start on the rear panel, have you removed the side exhausts yet?

If you have, are the metal and fiberglass rocker mounting tabs cut? It's not easy to fix cut tabs.

If your car was not side exhaust from the factory, you should see evidence on the rear of the frame where the original exhaust hangers were mounted. You should also see evidence of grounding straps(threaded screw holes) being used at the middle frame crossmember. If no grounding straps, screw holes show no evidence of threads. In addition, you can check the triangular splash panels just rear of the front tires. If they have a rubber sealing strip mounted rear edge of them, that means under car exhaust. If not, that means side exhaust. Check for staple holes if the rubber sealing strip is missing.

As far as cutting the panel, like previous comments, if it's original, I wouldn't do it. If it's repro, no problem.

Good luck

Hi Douglas,

The car has a customized under the car exhaust since I bought it in 1981. It exits under the rear panel.
It also have the standard rocker molding.

1. I'm not sure I know where to look for the fiberglass and metal rocker mounting tabs, can you explain? I took pictures (enclosed) under front ands rear fender. Do you see something there?

I donot have the splash shields.

2. What should I look for in the rear of the frame where the original exhaust hangers were mounted?

3. I see no evidence of threads in the screw holes for the grounding strap! Could this be a evidence on it's own that the car came with sidepipes?

4. One thing that lead me to believe it had a non-original side-exhaust system mounted at one time is the residue of a bracket on the frame under the front fender, please see enclosed picture.

If any of this indicates that my car came with sidepies, I will try to get a reproduction rear panel with holes. And keep the current panel for a future decision to install "original" side pipes.

Thanks in advance your interest in my case.

[Rich P.]

Re: What is the exact position of the holes for the tail pipe?

Hans,

I restored a 67 300 HP Powerglide car with factory side pipesin 1989. My customer bought the car in 71 for 1200.00. He had the tank sticker and when I restored it I was the first one to take it apart and IT WAS REAL, rocker cut outs, no side moulding tabs, no marks on the muffler hanger locations, front fender cut outs, rear wheel well cut outs and no threads in the holes for the center pipe. Plus it had all factory hardware attaching it so it could be possible.

Rich

[Douglas L.]

Re: What is the exact position of the holes for the tail pipe?

Hans,

Take a look at the picture below. You see the green tabs sticking down under the passenger door. Also, you see the fiberglass tabs at each end of where the rocker panel fits.

If your car is a true side exhaust car, no evidence of the green metal tabs will be there and the fiberglass tabs will have been cut off even with the other fiberglass.

[Stuart F.]

Re: What is the exact position of the holes for the tail pipe?

Just another thought on the problem; when/if you cut holes in rear panel, how will you mount bezels? As I recall, there are tabs on the panels for clip nuts.

Stu Fox

[Patrick H.]

Re: What is the exact position of the holes for the tail pipe?

Just another thought on the problem; when/if you cut holes in rear panel, how will you mount bezels? As I recall, there are tabs on the panels for clip nuts.

Stu Fox

Exactly.
You need to replace the whole panel, which is actually very easy to do. The hardest part is having the paint matched.
Original panels with holes, tabs, etc are quite common at swap meets.

And, if you have an uncut original panel, it's worth some $.

Patrick

[Duke W.]

Re: What is the exact position of the holes for the tail pipe?

The rear valence panels for under-the-car and sidepipe exhausts are completely different molded parts. The under-the-car version has cylindrical flanges on the inside of the panel surrounding the tailpipe openings that the the bezels are fastened to. The sidepipe panel is molded without the flanges or holes.

Cutting holes in a sidepipe rear valence will not allow you to mount the bezels. You'll just end up wrecking a good panel.

Just leave the panel off until you can obtain and finish a proper panel for under-the-car exhaust. Your sidepipe panel still has value for those who convert to sidepipes or need a new panel for whatever reason. If you cut holes in it, it may be next to worthless!

Duke

[Tom H.]

Re: What is the exact position of the holes for the tail pipe?

Hans !

Unless I have missed it, I don't believe we have discussed if your car is an AO Smith body car or St. Louis. Of course the AO Smith version would rule out the possibility of factory installed side exhaust.

[John H.]

Re: What is the exact position of the holes for the tail pipe?

Hi Wayne,

Interesting, I've trusted the info in 1966 Technical Information Manual to be true in this matter. It says (page 116) that base engine with Powerglide and 2 inch exhaust system was not available with side-mounted exhaust and it will give a total deduction if so equipped.

That's incorrect. All '66 small-block engines had 2" outlets on the exhaust manifolds, regardless whether they had 2" pipes and mufflers, 2-1/2" pipes and mufflers, or optional sidepipes. There were no ordering restrictions on the N14 side exhausts in '66-'67.

[Hans R.]

Re: What is the exact position of the holes for the tail pipe?

Thanks to you all, Tom, Wayne, Douglas, Rich, Stuart, Patrick, Duke and John.
It's fantastic to sit here overseas and still have all the knowledge from you
US guys available at my finger-tips.
To sum things up:
There are no threads in the holes for grounding straps at the middle frame crossmember
It's a St. Louis body car
There are no signs of any green metal tabs for the rocker panels
The fiberglass tabs at both ends of rockerpanels are cut
There are no holes in the rear valence panels
So it appears that my car came with side-pipes.
As I bought a new complete under-the-car exhaust system I will go ahead and install that.
But I will not cut any holes in the existing rear valence panels. I will put them aside for
a possible future installation of side-pipes.
I will order a repro rear valence panels with holes
Thanks a million for all your input on this case.