Mike,
If you decide to go with the headers (as I would), do NOT try to control
heat from them by wrapping them -- that will almost inevitably cause them
to rust thorough pretty soon. If you get them ceramic coated, that would
delay the rust, but I still would not wrap them. Nor will ceramic coating
help much with the heat (still worth doing for longevity). The best
solution for the heat is to cut away the inner 1/3 of the wheel well liners
(especially on the right side) to let it escaped. If your engine hatch
cover is well sealed and insulated, you probably won't notice additional
heat; but, you'll probably find them a little nosier than the manifold was
before it cracked.
JMHO,
Ken H.
On Sun, May 24, 2020 at 6:36 PM Mike Kelley via Gmclist <
> Thanks guys (Rich M., John L., and, Jim H.):
> I appreciate your responses and your advice!
> Now time to do a bit of research to make this difficult decision!
> Mike/The Corvair a holic
>
> Sent from my iPhone
>
> > On May 24, 2020, at 5:21 PM, James Hupy via Gmclist <
> >
> > I have had Doug Thorley Ceramic Coated Headers on my 403 in my 78 Royale
> > since at least September, 2008. Mileage then was 89,758. Mileage now,
> over
> > 140,000 in 2020. So, judge for yourselves if the headers will hold up or
> > not. I have not replaced the graphite exhaust gaskets, nor do I have any
> > exhaust leaks. Don't know if his headers are still made of the same
> > material and the same thickness as mine are or not. They are a quality
> > product.
> > I have replaced numerous cast iron exhaust manifolds in that same time
> > frame on both right and left sides, and on 403 as well as 455 engines,
> due
> > to cracked castings. So, I kinda lean towards headers a bit. They will
> > cause your engine to run a bit lean, due to improved scavenging,
> although
> > that effect is minimal below 2500 rpm. A good CO exhaust check is a good
> > idea after your install. Maybe, a slight rejecting may be necessary, or
> > install a throttle body fuel injection system like the Howell system
> which
> > is infinitely tunable for changes like porting, headers, port matching,
> > shaved heads, aftermarket cams, pistons, etc.
> > Jim Hupy
> > Salem, Oregon
> >
> > On Sun, May 24, 2020, 2:50 PM Mike Kelley via Gmclist <
> >
> >> Hi fellow GMCers:
> >> Mine is a 76 Eleganza II 455 w/ 3:21 final drive. I have cracked
> >> manifolds on my Dick Patterson rebuilt engine (about 80,000 miles in
> >> rebuild and 225,000 miles on coach).
> >> Looking for advise as to which way to go. I have access to a set of used
> >> manifolds at $400.00. I also have access to a new set of Thorley
> headers
> >> at $250.00. I know I will need add’l exhaust work if I go w/ headers.
> I
> >> am told to plan on insulating them if I go w/ headers due to excess
> heat in
> >> engine bay but have no idea what this may cost. Have also been told
> >> ceramic coating may be advisable but am not sure if that would solve the
> >> heat problem. I am not a mechanic so will be paying for the
> installation
> >> portion also.
> >> Ok - my GMC friends - advise as to the best way to go and why and
> approx $
> >> cost.
> >> Thanks,
> >> Mike/The Corvair a holic
> >>
> >> Sent from my iPhone
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