C2 Tread and Exhaust Question

[Patrick F. McInerney]

The only reference I find for tread dimensions on my '64 is in the owners manual. It lists 56.3" front and 57.0" rear. Is tread measured from center to center of the tire tread? I want to use this dimension to position the rear torque arms on the chassis before proceeding to toe and camber adjustments.

On the exhaust system for the 365 SHP engine is the heat riser valve used and, then, only on the right side?

Thanks again to all of you for your excellent help.

Pat McInerney

[Michael W.]

Re: C2 Tread and Exhaust Question

Can't help on the exhaust question, but the tread dimension is essentially non-adjustable and I suppose provided for reference purposes only. The overall width of the differential, half shafts, wheel spindles etc and their assembly locations will determine the width of the track, but none of these elements are adjustable in any way.

One could argue that altering the camber angle will change the tread dimension to a large degree and altering the toe-in to a lesser degree, but in the effort to achieve the correct tread, the alignment angles may not be correct.

You may just want to ensure you have the correct wheel alignment and let it go at that.

[Michael W.]

Re: C2 Tread and Exhaust Question

Can't help on the exhaust question, but the tread dimension is essentially non-adjustable and I suppose provided for reference purposes only. The overall width of the differential, half shafts, wheel spindles etc and their assembly locations will determine the width of the track, but none of these elements are adjustable in any way.

One could argue that altering the camber angle will change the tread dimension to a large degree and altering the toe-in to a lesser degree, but in the effort to achieve the correct tread, the alignment angles may not be correct.

You may just want to ensure you have the correct wheel alignment and let it go at that.

[Joe L.]

Re: C2 Tread and Exhaust Question

Pat-----

Yes, tread width is measured from the center of the wheel (or, more conveniently, center of the tire tread).

For L-76 engines a heat riser was used and it is used only on the right side. The only C2 without a heat riser valve was the L-84 FI. All Corvette engines with heat risers use them on the right side only.

[Joe L.]

Re: C2 Tread and Exhaust Question

Pat-----

Yes, tread width is measured from the center of the wheel (or, more conveniently, center of the tire tread).

For L-76 engines a heat riser was used and it is used only on the right side. The only C2 without a heat riser valve was the L-84 FI. All Corvette engines with heat risers use them on the right side only.

[Duke W.]

Re: C2 Tread and Exhaust Question

I'll assume those tread dimensions (center of tire tread to center of tire tread) are accurate to within 0.1 inch of design nominal, but don't include production variance and are not accurate enough to use for toe measurements. Also these nominal dimensions are
only valid if you have the OEM or equal offset wheels. Tread dimension change is double the change in wheel offset. Tread dimension also changes with camber. 1965 and '66 models have slightly higher specified tread dimensions because the wheel mounting plane is a bit more outboard from the centerline compared to drum brake models. The tread changed again in '67 with the change in wheel offset.

As far as setting the toe is concerned, you want it equally divided between both wheels, and the only way to do this, short of a modern alignment rack, is to determine the true centerline of the frame, then string it with a plumbob or two and measure the toe of each wheel relative to true center with the rear trailing arms at normal ride height - the nominal "D" dimension. This is fairly easy to do with the body off - a bit tougher with the body on, but a typical four post drive on lift should make it much easier with the body on. Get out your surveying instruments.

The 365 HP engine does use a heat riser, and as do all other carbureted Corvette engines, and there is one valve on the RH side. When cold the valve is closed forcing the right bank exhaust through the manifold crossover, which heats the base of the inlet manifold plenum and helps evaporate the liquid fuel for better distribution and a leaner cold mixture. The valves are problematic being as how they tend to stick. If you don't plan on driving the car in winter weather I would suggest using the FI spacer that has no valve, or you could remove the valve plate leaving the exterior untouched if you are going to have the car judged.

The heat riser on my SWC caused the RH muffler to rot out in '68. At that point I wired it open, and later replaced it with the FI spacer. There was no effect on cold operation as far as I could tell, but the one time I tried blocking off the heat riser passage with stainless steel shims, it would stumble on first gear takeoff until the engine had been running for at least 20 minutes, so I removed them after about a week.

Duke

[Duke W.]

Re: C2 Tread and Exhaust Question

I'll assume those tread dimensions (center of tire tread to center of tire tread) are accurate to within 0.1 inch of design nominal, but don't include production variance and are not accurate enough to use for toe measurements. Also these nominal dimensions are
only valid if you have the OEM or equal offset wheels. Tread dimension change is double the change in wheel offset. Tread dimension also changes with camber. 1965 and '66 models have slightly higher specified tread dimensions because the wheel mounting plane is a bit more outboard from the centerline compared to drum brake models. The tread changed again in '67 with the change in wheel offset.

As far as setting the toe is concerned, you want it equally divided between both wheels, and the only way to do this, short of a modern alignment rack, is to determine the true centerline of the frame, then string it with a plumbob or two and measure the toe of each wheel relative to true center with the rear trailing arms at normal ride height - the nominal "D" dimension. This is fairly easy to do with the body off - a bit tougher with the body on, but a typical four post drive on lift should make it much easier with the body on. Get out your surveying instruments.

The 365 HP engine does use a heat riser, and as do all other carbureted Corvette engines, and there is one valve on the RH side. When cold the valve is closed forcing the right bank exhaust through the manifold crossover, which heats the base of the inlet manifold plenum and helps evaporate the liquid fuel for better distribution and a leaner cold mixture. The valves are problematic being as how they tend to stick. If you don't plan on driving the car in winter weather I would suggest using the FI spacer that has no valve, or you could remove the valve plate leaving the exterior untouched if you are going to have the car judged.

The heat riser on my SWC caused the RH muffler to rot out in '68. At that point I wired it open, and later replaced it with the FI spacer. There was no effect on cold operation as far as I could tell, but the one time I tried blocking off the heat riser passage with stainless steel shims, it would stumble on first gear takeoff until the engine had been running for at least 20 minutes, so I removed them after about a week.

Duke