[AMX guy]

I'm doing a pretty much stock restoration on my '66 Tri power GTO but I wouldn't be opposed to a little larger diameter pipe if it will not cause fitting issues.

Was stock size 2" or 2 1/4" ? I assume 2 1/2" would be tough to fit in a stock style system ?

I see some systems with resonators and some without, both are stock style. did they have resonators in '66 ?

[b-man]

Go with a 2-1/2" system if you don't care about originality.

The 2-1/2" size is the most common and relatively inexpensive.

The factory log exhaust manifolds will work fine if you buy the PYPES headpipes that are made specifically for this application.

PYPES mandrel bent 2-1/2" stainless steel headpipes (p/n DGA10S-1 & DGA10S-2).

[AMX guy]

I'd rather buy one of the pre bent systems, I've had very good luck with them. but I haven't seen one in 2 1/2 " . no clearance issues with 2 1/2 " ? I know it sounds a lot better but I don't want bumping on stuff ..

Aren't the Pypes systems kind of a do it yourself weld kit ?

I'd just take it to a shop and have a custom system put on but I have to do a cam break in first so a pre bent kit is nice to have .

[b-man]

I have installed pre-bent 2-1/2" systems on several early A-body Pontiacs in my driveway or garage and have simply clamped them together without any welding. Simply pick your mufflers from the multitude of offerings and buy whichever brand of exhaust system you prefer.

I just recently put a mandrel-bent 2-1/2" Flowmaster aluminized steel H-pipe system on my '64 Le Mans convertible using the PYPES headpipes pictured using 20" long 17749 Walker Dynomax Super Turbo mufflers. No welding, just a quick trip to the local muffler shop to have a couple of the pipes expanded so I could slip the headpipe connections to the rest of the system together.

No clearance issues, everything fits rather nicely under the car and clears everything just fine. There's no difference chassis-wise between a '64 and a '67, they're both built on essentially the same exact chassis and floor pan.

I pulled out the old 2" system and took this picture for the sake of comparison. You can easily visualize how much better the 2-1/2" mandrel bent system will flow. The headpipes were trimmed down quite a bit while fitting everything up under the car.

[400 4spd.]

'66 automatic transmission cars had resonators.

[gtospieg]

I used the 2 1/2" Pypes system with X pipe(67GTO) and no fitment issues. Start from the rear and work your way forward.

[importsmasher]

Originally Posted by 400 4spd.

'66 automatic transmission cars had resonators.

My 66 4 speed car came with resonators.....

Importsmasher

[Jack P.]

Inline tube has some nice kits and some choices in size. you can also pick and chose the pieces you want and build a system.

[Jeff Hamlin]

Originally Posted by importsmasher

My 66 4 speed car came with resonators.....

Importsmasher

I recall reading something about only on AT,
but the Parts Book page gives no indication on this.

It just list 66 T/8

[fyrffytr1]

I also have the Pypes 2 1/2 system with the X crossover in my 67 with automatic transmission. No problems at all.

[60sstuff]

All 1966 GTO (manual shift and Automatic) came with the resonators.

1967 automatics also came with the resonators, but 67 manual shift did not.

I recently installed the complete Gardner Exhaust System on my 66, but used a pair of NOS resonators instead of the Gardner version.

The top resonator is NOS OEM, and the bottom is the Gardner exhaust version resonator.

Chris.

[400 4spd.]

Originally Posted by 60sstuff

All 1966 GTO (manual shift and Automatic) came with the resonators.

1967 automatics also came with the resonators, but 67 manual shift did not........................

Chris.

My apologies, I thought that applied to '66 as well.

[60sstuff]

Originally Posted by 400 4spd.

My apologies, I thought that applied to '66 as well.

All Good 400 4spd.

I’m always getting new/great information off this Board !

Good Day.

Chris.

PS, how were you able to be on here for 48 years?

[GT182]

I have a 2 1/2" exhaust system on my 66, with an H-pipe and Cherry Bombs for mufflers. Gives it a nice rumble without being offensive. Wind it up and let off the gas and you get a little popping sound out if them. Lots of the guys around here like the sound better than the Flow Masters they have on their cars.

I've ridden in a 65 2+2 that had the Pypes system under it and it was so loud going down the road you couldn't hear the other person with you, or hear yourself think. And he was just driving normally... not horsing around at all.

[67Twistytee]

Is there a good resonator option for the Pypes 2 1/2” set-up? I have it with the x-Pypes feeding into dual magnaflows. Sounds great but I’m getting some of that 2k drone the V8s are noted for, at least on the automatics.

[GT182]

I too get the droning noise but it's not all that bad. My first 66 GTO back in 1970 didn't have it, but I believe that was due to using plain 'ol stock mufflers. It had no resonators. Probably the because it had both tail pipes replaced, or it didn't come with them. The one I have no didn't have the droning noise either as it also had stock type mufflers and no resonators. All were side by side.... not staggered.

I have heard that if you stagger the non stock mufflers a bit then there's no drone from the exhaust. How true that is I don't know.