Exhaust & intake manifolds

Kevin - Illinois

Kevin - Illinois

Senior Member
I often read about machining manifolds and I don't have any experience in machining. I was wondering if someone could explain how the exhaust / intake manifolds are machined for an exact fit. Does the machinist work the faces of each manifold where they bolt together or does he work the actual ports of each manifold?
 
They are bolted together, then the ports are resurfaced into a straight plane. There are different methods with the crudest (in my mind) being what looks like a belt sander.
 
Kevin: I've had several intake/exhaust manifolds resurfaced in the past. We have a nearby NAPA shop with a horizontal grinding table. The guy will run the intake/exhaust as a unit until it cleans up, (is all shiny). Costs about $35.00. Number 4 or number 1 will warp and blow manifold gaskets. I never separate the exhaust from the intake when I take it in for resurfacing. Depending on how much will need to come off to get it straight, you may need to grind down the gland rings for clearance when you intall back on your engine. Be sure it's not hanging up on the gland rings when you put it back on your car. Good luck.
 
There are two types of machining the manifolds. The first is as has been described, making the gasket surfaces identical for a good seal. The second operation is enlarge the intake port (the port that the carburetor was bolted to) to slightly over 1 1/4" (1.250).
This enlargement to Mod. "B" specs gives a slight increase in HP and is very easy for a machinist to do. But it must be very securely held in place while drilling.
Terry
 
Had a friend with a Packard Caribbean, complete restoration, beautiful car. After 200 miles of a complete engine rebuild it sounded very trashy. I pulled off the manifold and found that they resurfaced both intake and exhaust surfaces seperatly and when bolted together there was almost 30 thousants between surfaces. I took it back to the NAPA shop and they looked at it and did the work again for free. 200 mile old gaskets were replace and she sounded like a new car. Iceman
 
Something else to consider, the manifold can warp in another way. With the added weight of the exhaust clamped onto the downturn area by the #4 port, it can “droop”. Take a straight edge across all 4 holes. I have seen them warped as bad as ¼”. This problem was addressed by Ford in 31 and is why those manifolds had the added material in the downturn area.
Vince Falters, Ford Garage site has a nice article about this. I would check the alignment before you spend any money on an old manifold.
http://www.fordgarage.com/pages/exmancompare.htm
 
If buying a new IN & EX manifold, good idea to verify with the vendor if IN & EX are made by the same manufacturer -- vendor said YES & that no machining needed to be done.

He was correct -- they fitted perfectly with no sag.

Bought & installed new gland rings which fitted tightly in both block & manifold grooves thus preventing mainfold sagging at the rear, caused by weight of exhaust pipe & muffler.

A tight fitting IN & EX manifold can be more important than some may imagine for quick starting, proper fuel/air mixture, & overall performance.
 
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