what is shape and dimensions of exhaust ports on stock heads 81 350

[dirtypants]

what is the shape (square, round, D, oval ??) and dimensions of the exhaust ports on stock heads for 81 350ci and...
has anyone used Remflex exhaust manifold gaskets..for aftermarket headers,..which Remflex part #..happy with em or not? If you used Fel Pro..or other, same questions..which part #, happy or not?
Thanks
Nick

 

[toobroketoretire]

what is the shape (square, round, D, oval ??) and dimensions of the exhaust ports on stock heads for 81 350ci and...
has anyone used Remflex exhaust manifold gaskets..for aftermarket headers,..which Remflex part #..happy with em or not? If you used Fel Pro..or other, same questions..which part #, happy or not?
Thanks
Nick

You should NEVER use gaskets for exhaust manifolds or headers because gaskets will eventually fail. Just bolt them on metal-to-metal.

 

[dirtypants]

You should NEVER use gaskets for exhaust manifolds or headers because gaskets will eventually fail. Just bolt them on metal-to-metal.

\
never say never

Nick

 

[SVO]

Your exhaust port shape should be kinda square-ish.

If you are talking about factory cast iron exhaust manifolds like this: More Information for DORMAN 674501

from the factory, there was no gasket installed between the head and the manifold but FelPro and others makes a gasket that can be used with the cast iron manifold. With use, you can get warpping of the manifold, hence FelPro and others offering a gasket that can be retro fitted.

Not that famiilar with what the stock manifolds for a '81 are but understand that they are a stainless shorty header style, which uses a gasket between the header flange and the head. Believe Tom Bryant laid all that out in a earlier post.

If you are talking about aftermarket exhaust headers, like the Hooker or Hedman brand, then you need a header gasket to go between the header flange and the head. Mr. Gasket is the usual go to brand for header gaskets. The Mr. Gasket gasket is a thick hi temp garlock type material which is needed to seal the header flange to the head. With aftermarket headers, you will never get a seal without using a header gasket.

Am not familiar with the Remflex brand, so cannot comment on them.

So yes, never say never.

 

[dirtypants]

thanks all so far..Can anyone post the shape and dimensions of exhaust ports on a stock, original head on 81 small block?
And..what else can I look for, on exterior of heads..to see if original, or a later install of a diff type. Exhaust port size and dimension may be one thing, and I will see em soon when I remove the exh manifolds..so please let me know what to look for.
Thanks
Nick

 

[toobroketoretire]

About 1-1/4" square with rounded corners. But it's best to NEVER use gaskets because gaskets will eventually fail whereas metal-to-metal never fails. If your heads had gaskets at one time make darned sure every bit of the old gasket material has been scraped or sanded off and likewise for the manifolds/headers. Everything MUST be cleaned to bare metal before bolting back together.

 

[SVO]

O.K. Nick, time for a little homework.

Grab a pad of paper & pencil, and let's go under the hood of your car. For starters, on the passenger side of the car, at the front of the head is a machined pad. On that pad is two sets of numbers - one is the last eight digits of the VIN number of your car starting with a "S" or "B", the second number is the production date & engine code. For your '81, the engine code should be either a "ZDA" or "ZDC". If one of these engine codes matches the stamping on the block, then we know we are dealing with the original motor in your car.

Next, remove one of the valve covers and look for a 6 digit casting number in the valve rocker area. Casting number for the stock head for your car should be "462624". There should also be another 4 digit number starting with a letter and 3 numbers, this is the casting date for you head. If you see the number "462624", then you know you have the stock heads for your car. Any other number may mean you have some other non original heads on your engine.

If you go back to the Dorman link that I posted and open it, you will see a picture of a cast iron ramhorn exhaust manifold. At the upper right hand corner of the picture is a arrow. Click the arrow and it should open a picture showing the back side of the exhaust manifold- that is what the stock exhaust ports in your head should look like.

If you want dimensions for your head, find a copy of "Corvette By The Numbers" (http://www.parts123.com/corvettecentral/dyndetail.pta?catalog=0000050g&ukey=15556). In the head section it has drawings showing the dimension of the intake & exhaust ports.

Cheers,

Bob

 

[KANE]

Quick sidebar...

Not exactly on the topic, but may be of interest... since we are talking about heads.

If you wanted to see what the spark map looked like for either an 81 or 82, look up the SA table for the 85 and 86 iron head Vettes. This is worthy to share because no one seems to have a copy of the SA tables saved from the PROMs of the 81 and 82s.

The 85 and 86 iron head cars used the same head as the 81 and 82 if I remember correctly. Heads determine a great majority of what the SA table looks like.

Might be interesting to see where, when, and how much spark they have across RPM and KPA.

 

[Tom Bryant]

A stock cast iron manifold is milled flat on the mating surface and, unless it's damaged, it should never need a gasket. The '81 manifolds don't have a flat mating surface. In fact it is sort of rounded and rough. There is no way it will ever seal without a gasket. As for aftermarket headers, some are a lot better than others. A header with separate flanges for the end pipes with at least 3/8' thick flanges that are smooth and flat will have a good chance of sealing without a gasket. Can't say for sure. I've never tried it. One piece flanges will grow with heat and actually the section between the end ports and the center pair of ports will bow if it gets hot enough, such as during a long run on the highway. Cheaper headers with thinner flanges will be hard to keep from leaking even with a good quality copper gasket. I prefer to use ARP header studs instead of bolts. They are fine thread and seem to do a better job of clamping. I put a ton of miles on my daily driver '67 427 coupe with Doug's side pipe headers and never had a flange leak or gasket blow out.

Pictures are '81 manifolds. One shows the amount of access weld in the port area and after it was removed. This is about the same shape as the port in the head.

Tom