Manifold

[kcav8or]

I'm replacing the exhaust pipe and manifold on my '31 Model A. I thought someone might be able to explain something. Why is the intake manifold nestled so tightly inside the exhaust manifold? I can see a lot of problems with that approach, but what's the advantage? Does it preheat the intake air?

[colin1928]

Yes heat for the inlet

[kcav8or]

I know that modern engines don't take that approach. So what do they do instead? What problem does preheating address?

[1967 Ford]

There is better atomization of the air/ fuel mix with preheating (particularly when the engine is cold.
In the 70's-80's cars had Thermatic Air Cleaners with that heat stove on the exhaust manifold that piped hot air into the air cleaner when cold to reduce Hydrocarbon emissions. I think a lot of newer cars still have something similar.

[kcav8or]

How can I prevent the new manifold from looking like the old one? Has anybody used the high temperature manifold paint I've seen on the parts sites? Does it work well?

[Patrick L.]

Sponsored Links (Register now to hide all advertisements)

New coated/painted manifolds are available.

[Tom Wesenberg]

I used and like VHT New Cast, which sprays on and keeps the manifold looking like new cast iron. It stays nice for about 3 years for me, then needs to be redone.

[Mitch//pa]

i bought the new ceramic coated manifold from snyders... for the few dollars difference its was a no brainer for me....even after i purchased the regular one and never used it, i will sell it and move on. why paint it when these are available

[Christoph]

My manifold looked BAD too.
I had my old manifold ceramic-coated, about 3 years ago.
Still nice and shiny
Nobody knows why its still "better than new" (well - you know now)


BTW
i had the intake ceramic-coated and
i had both halfes of the carb ceramic-coated too
Best i could doo

[MBI Houston]

How difficult is it to replace a manifold for a novice mechanic? Les Andrews books don't talk about this task.

[cp5491r]

Pretty easy but there are some caveats. See some thread on this site.
One item is to make sure the intake and exhaust manifolds, when mated, are level to each other. Mine fit fine but others may need machining to allow for a good fit with the gaskets. A second thing- use a torque wrench when bolting on and go slow going from one stud to the next until all are torqued to maybe 45 lbs. The cast iron ears can snap off easily.

[tbirdtbird]

Old one was painted with crappy paint and crappy prep. Get all that paint off there with paint stripper, then wire wheel it down to nice clean cast iron. Use phosphoric acid generously with a steel wool pad (plain steel wool, not Brillo which has soap in it) to scrub the phos in deep, wipe off with clean white rag, change rag, repeat until no discoloration comes off on the rag, wipe dry ( do NOT rinse), sun dry or play a propane flame or heat gun over it GENTLY until it is dry. It will turn a nice gray battleship color. Use a scotchbrite pad gently to get off any remaining tiny bits of your rags. The metal is now properly prepared for painting in the best known manner. Use a good quality engine green enamel from one of the suppliers like Brattons. You may need 2 coats, NO more. Do not use any primer on the metal, just go straight to the engine green.

I have prepped all my metal parts with this method for about 30 yrs. I did the manifold on my Deluxe more than 20 yrs ago. It still looks like the day I did it. Same for the body of the car....looks like day 1, no rust leaking thru anywhere. And the car was in the humid Northeast for 15 of those years.

There is a thread on here now about using phosphoric acid, search it. This method was documented at least as far back as the '40s, get an old copy of the Metals Handbook and look it up. No restoration or metal work goes out of this shop without this process.

[SSsssteamer]

Originally Posted by kcav8or

I'm replacing the exhaust pipe and manifold on my '31 Model A. I thought someone might be able to explain something. Why is the intake manifold nestled so tightly inside the exhaust manifold? I can see a lot of problems with that approach, but what's the advantage? Does it preheat the intake air?

Preheating the intake helps prevent the intake manifold/carb from icing up. The terrible gas that was available in the 1920's and early 1930's needed the extra heat for aiding in its complete combustion. The old gas available at the time was just a bit better than stove oil. Stove oil was often used in the early vehicles as an alternative fuel. A separate small tank for starting up on gasoline was needed. Start the engine on gasoline and then when it was warmed up, switch it over to the stove oil. Upon shutting down for the day, it was wise to switch back over to gasoline to the carburetor so that the next morning the engine could be started up with a carburetor full of gasoline. Back in the early 1960's we had a model A doodle bug tractor that I always ran on stove oil. Stove oil at the time was only about 12 cents a gallon and we had a full tank of it along side our home to draw from. Gasoline at the time cost about 35 cents a gallon. I got more power out of gasoline than I got out of stove oil, but stove oil was only about a third of the price of gas.

[kcav8or]

I bought my manifold from Snyder's. Wish I would have seen the coated one, but somehow I missed it.

[Purdy Swoft]

I cleaned up rusty exhaust manifolds with the wire brush on my bench grinder and sprayed them with Cast Blast from Snyders. Its been holding up good on my roadster for the past eight years. It can't be as good as a new ceramic coated manifold but its getting the job done .

[Duffy1]

I had my manifolds surfaced flat. I tighten until I see the gasket start to compress . In my case it was at 20 ft-lbs. Heated manifold to 325 degrees F and coated with POR 15 HIGH TEMP COATING .

[hardtimes]

Originally Posted by kcav8or

I bought my manifold from Snyder's. Wish I would have seen the coated one, but somehow I missed it.

Since you have paid for a new manifold, it may be cost effective to look for a ceramacoat business in your area. This is a wonderful and worthwhile process that LASTS. There is another little known benefit that can be had also. Tell your ceramacoat guy to also ensure that the INSIDE of the manifold is also coated. About 10 years ago, I had a header pipe setup on my B engine coated in and out. The idea of coating inside also, is so that heat is hurried along thru the system, which improves efficiency which improves performance. On the intake side, fuel mixing and delivery is also done in a somewhat better fashion, i.e.- kinda like the idea of why smoothing/porting is done, IMO.

[1crosscut]

I too like the Cast Blast. Very good stuff. Just don't cure it in the oven in your house. I was just glad that my wife was off on a business trip for a couple of days. By the time she got back all was good again. I use my gas grill now.

[Purdy Swoft]

Mine got heat cured on the engine after I installed it. It was a little while after spraying on two coats before it got run. It doesn't seem to have caused a problem.

[kcav8or]

Where do you find phosphoric acid? I suppose I could use the same cheap soda trick that I used on my chrome horn. Soda contains H3PO4, but probably at a much weaker concentration than would be best for this job.