72 Corvette - Restoration Updates

[johng]

Was your ebay seller fsmoto_auto? I bought mine from them 3 years ago and whilst it's a sightly different design to yours it's working just fine. My inlet was also smaller than my existing hose, so I wrapped some self amalgamating tape around it to build it up. It hasn't leaked yet.

 

[TimP]

I bought mine from chr_racing but I know the company you mention and I think they might well sell the same products - they certainly look very similar. Glad to hear yours is working well. The one I bought looks nicely made and difficult to beat at that price. I hope it lasts as well as yours has.

 

[TimP]

Having got a radiator installed the only thing stopping some longer engine runs was some sort of exhaust system - for the short runs I did just to find out if the engine would run, the exhaust finished at the manifold outlet. Not the safest of situations and a tad noisy - unless I was prepared (which I wasn't) to give my neighbours some serious aural grief I needed to fit some mufflers. In theory this should have been straightforward, if expensive. I had sourced two sets of mufflers - a stock (1969) pair in very good condition and also a couple of Flowmasters, also in perfectly usable condition.

The problem was that, at some point in the past a previous owner had modified the engine downpipes to 2.5" (I think the stock ones are 2"), but all the mufflers I had were 2" inlets and outlets. I haven't been able to find a couple of good 2.5" mufflers so I decided to fabricate my own set of intermediate pipes, managing the discrepancy on sizes as I went along. I thought this would be reasonably straightforward. Stupid boy.

First task was to buy some exhaust tubing and then work out where the bends and angles needed to be in order to get the pipes as high off the ground as possible. The downpipes are unequal length and finish just in (driver side) or in front (passenger side) of the gearbox crossmember. I used a 30 degree standard bend in 2.5" tube to get the exhaust through the two holes in the cross member and with a little shortening of the driver's side bend they end at the same point. The front end is swaged so it fits over the downpipes and can be clamped in position to the exhaust mounting arcs that are attached to the crossmember.

The next bend, to bring the pipe along the underside of the car, was quite shallow and couldn't be bought off the shelf but I found a seller on eBay that would bend the tube to order. The angle was estimated using a 'tool' made from a steel ruler, a square and a clamp.....

The bend for this part was found to be 15 degrees so these were fitted on to the end of the stubs emanating from the cross member. The the long straight run was added to this.


The pipe then takes a path towards the centre of the car, goes under the strut mount carrier and then bends outwards and slightly upwards to the muffler inlet, ending up with a couple of pipes that look like this... one nearly finished and one with tack welds holding it together. The 2.5" to 2" reducers have also been fitted here. If at some point I want to go for 2.5" mufflers I can just cut these off and weld on an extension in their place.


In terms of welding these sections together I decided to go for a strong join with a sleeve rather than just a butt weld. It's plug/puddle welded at three points around the tube and then welded along the join.


There was a lot of trial and error in this - it took a lot of experimentation to get this right.


Thinking it was best to have these exhausts firmly mounted I fabricated a small bracket that fits on the spring bolt that comes out of the bottom of the leaf spring.


..and then used a standard rubber mounting isolator to attach the two exhausts.

After welding two kinked rods on to the exhaust pipes this bracket holds everything nicely in place.


Continued on the next page - I've overrun the attachments limit......

 

[TimP]

I have used mild steel for the exhaust. I previously had a Plymouth Satellite on which someone had fitted a stainless exhaust and it didn't sound the way I wanted to. Maybe that was for other reasons but also thought mild steel would be easier to work with as well. To give some (probably flimsy) chance at keeping the rust at bay I tidied up the complete system with some VHT paint.



It looks ok and sounds just like I wanted it to - quite mellow and not too loud. It's tucked up quite nicely and I don't think it should be at risk of grounding although I haven't taken the car off the chocks yet to find out - there are one or two other little jobs to finish off prior to doing that. The new exhaust is clamped in place at each end using stainless steel clamps. The square embellishers/tips haven't been fitted yet but I shall do some more testing before those get fitted.

I will soon be able to get the car out of the garage and do some extended engine runs. I have nearly finished the power brake and master cylinder installation. It's getting close to a road test.

Happy New Year everybody and best wishes for 2026!

 

[johng]

Great work Tim, looks like it will be ready for a road test just as they salt the roads!

 

[teamzr1]

Have you considered heat wrapping the pipes to reduce heating up the floor pan ?

Also, I notice pipe reducers and types of bends will reduce exhaust flow and add more back pressure to engine

 

[TimP]

Great work Tim, looks like it will be ready for a road test just as they salt the roads!

Thanks! Hadn't thought of that - it's a distinct possibility bearing in mind the latest forecasts. I'll just have to be patient ......

 

[TimP]

Have you considered heat wrapping the pipes to reduce heating up the floor pan ?

Also, I notice pipe reducers and types of bends will reduce exhaust flow and add more back pressure to engine

View attachment 32318

Yes - interesting you should say that. I have wrapped the exhaust downpipes - you can just see this on the drivers side at the bottom right of your picture. I have insulated the inside of the passenger compartment but you are right, preventing the heat getting to the floor pan in the first place would be a better idea. I think I will see how this works in practice (and make sure it is fully leak proof) and might do what you suggest the next time I need to remove the exhaust.

Hopefully the reducers will be a short term measure. I was wondering if I could modify the Flowmaster's to take a 2.5" pipe in and out or perhaps just bite the bullet and buy new mufflers of the right size. Outright performance is not my intention - think Captain Slow, as far as my driving is concerned. Presumably a pressure wave would bounce off the reducer going back in the direction of the engine which may effect scavenging at the upper end but I'm not sure it's going to make much difference to a car in a light state of tune, like mine. Having said that I'm way out of my depth on this so I would listen to more informed comment. What's your view on what it might do or what I should look out for?

 

[teamzr1]

As to heat reduction/reflection
If you have not used like this as example, this comes in sheets and have a sticky backing that works at high temps
Very thin and could be placed on the underside of the floor pan above the exhaust system and also can be wrapped around the pipes
Also helps reduce sounds


Where performance is an issue as you know the smallest diameter of the exhaust dictates the total flow volume for the whole exhaust length
With reduced flow and increased back pressure, that also reduces exhaust pulses to pull the exhaust out of the cylinders when exhaust valve opens
That means when that valve closes not all the exhaust has been removed so next time the cylinder fires it is not a clean charge
so not a good burn, which reduces how efficient the air and fuel since dirty exhaust is still in cylinder volume
That reduces performance and fuel mileage

The 2.5" to 2" reducers really hurt the flow and would be better if the mufflers had an inlet and outlet of 2 1/2 inches

Consider like I have, and other newer Corvettes uses 3 inches with no reductions
On the nutty side, I made my exhaust 3 inches from collector with mufflers have 3" in and outlets through muffler tips.

Shown in race mode but for street, 3 inch pipes are installed to tips at the ass end
and the X-pipe design assured no reduction of flow and increases the exhaust pulses to pull exhaust out of cylinders

 

[Roscobbc]

If your storage/garage location is affected in winter by condensation and moisture.......the two things that will be adversely affected will be braking components (so calipers, master cylinder, perhaps brake lines) and any part of a mild steel exhaust exhaust system 'wrapped' in heat resistant bandage material. If the car isn't used on a regular basis the 'wrap' may absorb any water or condensation and speed-up the normal rusting process of steel. Headers seem even worse affected and stainless steel pipework can suffer heat induced embrittlement and failure of welds. There are sheet aluminised reflective solutions out there......simply look under any modern cars exhaust system to see how current OEM's deal this heat issues.

 

[TimP]

As to heat reduction/reflection
If you have not used like this as example, this comes in sheets and have a sticky backing that works at high temps
Very thin and could be placed on the underside of the floor pan above the exhaust system and also can be wrapped around the pipes
Also helps reduce sounds
View attachment 32319

Where performance is an issue as you know the smallest diameter of the exhaust dictates the total flow volume for the whole exhaust length
With reduced flow and increased back pressure, that also reduces exhaust pulses to pull the exhaust out of the cylinders when exhaust valve opens
That means when that valve closes not all the exhaust has been removed so next time the cylinder fires it is not a clean charge
so not a good burn, which reduces how efficient the air and fuel since dirty exhaust is still in cylinder volume
That reduces performance and fuel mileage

The 2.5" to 2" reducers really hurt the flow and would be better if the mufflers had an inlet and outlet of 2 1/2 inches

Consider like I have, and other newer Corvettes uses 3 inches with no reductions
On the nutty side, I made my exhaust 3 inches from collector with mufflers have 3" in and outlets through muffler tips.

Shown in race mode but for street, 3 inch pipes are installed to tips at the ass end
and the X-pipe design assured no reduction of flow and increases the exhaust pulses to pull exhaust out of cylinders

View attachment 32320

That installation looks very neat. As regards the reducers I will have a look and see if I can find something more suitable.

 

[TimP]

If your storage/garage location is affected in winter by condensation and moisture.......the two things that will be adversely affected will be braking components (so calipers, master cylinder, perhaps brake lines) and any part of a mild steel exhaust exhaust system 'wrapped' in heat resistant bandage material. If the car isn't used on a regular basis the 'wrap' may absorb any water or condensation and speed-up the normal rusting process of steel. Headers seem even worse affected and stainless steel pipework can suffer heat induced embrittlement and failure of welds. There are sheet aluminised reflective solutions out there......simply look under any modern cars exhaust system to see how current OEM's deal this heat issues.

It'a a good point about the wrap. From a damp point of view my garage, following some upgrades last year, isn't too bad. However, I think the suggestions regarding self adhesive foil (which I have used elsewhere above the transmission tunnel, or aluminium heat deflectors both make a lot of sense - I will investigate.

 

[TimP]

I ran the engine for a while today, outside of the garage. From my perspective, it's sounds great. Oil pressure seems good (cold start at about 2000rpm) and having the car off the chocks I can confirm that there is plenty of ground clearance, though I might swivel the clamps round a bit. Makes a lot of smoke though - I forgot to clean out all the grease they use in the mandrel forming/bending process for the exhaust tubes.... Doesn't half smell.

 

[teamzr1]

If your storage/garage location is affected in winter by condensation and moisture.......the two things that will be adversely affected will be braking components (so calipers, master cylinder, perhaps brake lines) and any part of a mild steel exhaust exhaust system 'wrapped' in heat resistant bandage material. If the car isn't used on a regular basis the 'wrap' may absorb any water or condensation and speed-up the normal rusting process of steel. Headers seem even worse affected and stainless steel pipework can suffer heat induced embrittlement and failure of welds. There are sheet aluminised reflective solutions out there......simply look under any modern cars exhaust system to see how current OEM's deal this heat issues.

My viewpoint in seeing lots of headers going bad with Corvettes I custom tuned
If made of stainless steel, no wrap is needed as it they do not output as much heat

If made of mild steel, lots of problems can happen, worse when external heat wrapping
That is due to the pipe is thinner than the welds
When trapping the heat with wraps, the 2 metals are different thickness and contract and expand differently
Being the weld is thicker, they will crack away from the thinner pipe
This can be a bitch with vehicles that have O2 sensors as air is pulled into thin cracks you cannot see
which causes the O2s to incorrectly report the AFR causing an ECM or PCM to incorrectly command fuel injectors
Other than performance issues from that can cause engine to fail SMOG testing and unless using a smoker
cannot find where the leaks' are

Here is just a few I personally say as to damage of using heat wraps
Best is to use the heat sheets I posted, not to the exhaust but to areas wanting to deflect that exhaust system heat

If your storage/garage location is affected in winter by condensation and moisture.......the two things that will be adversely affected will be braking components (so calipers, master cylinder, perhaps brake lines) and any part of a mild steel exhaust exhaust system 'wrapped' in heat resistant bandage material. If the car isn't used on a regular basis the 'wrap' may absorb any water or condensation and speed-up the normal rusting process of steel. Headers seem even worse affected and stainless steel pipework can suffer heat induced embrittlement and failure of welds. There are sheet aluminised reflective solutions out there......simply look under any modern cars exhaust system to see how current OEM's deal this heat issues.

 

[teamzr1]