I’m in the process of installing a new 383 engine in my 91corvette and ran into a problem with the manifold. The heads are 1205 size and the stock base seems a little small, not much meat to enlarge it to 2” height so while waiting for the 1205gasket bought an Edelbrock already ported manifold that accepts the 1205. The runner side ports are 42mm/1.65” in diameter. I also bought a set of Edelbrock runners not modified and the plan is to port match them to As&m gaskets. Until the gaskets arrive(will take a bit longer and I need to solve things faster) I want to laser cut a set, of runner gaskets, by scanning the stock ones adding more meat and compare to pictures of as&m, or if anyone has a set and can scan them, would be great.
The concern is I’ve heard these large runners are much more difficult to install, if the stock was already difficult now this is at the next level . The miniram would’ve been nice but still some challenges there and might catch attention at the DOT inspection as the car needs to look stock, I don’t know what they look for.
Now the question, did anyone manage to install the upper plenum without taking the valve covers on? As for the As&m I understand you need to loosen the runners to put the valve covers on and with Edelbrock you need to take the valve covers off to tighten the runners.

 

I am in for pics of the AS&M gaskets when you receive them as I have Edelbrock runners to toss on also.

 

Actually I've ordered TPIS gaskets and will probably take a long time until I get them. Here is a scanned piece of paper pressed against the upper plenum ports to copy the contour. In case you have them uninstalled, If you have the time and patience to copy the ports of the Edelbrock, that would help me a lot, until my set arrives here in Romania. The pictures I have online of TPIS and Edelbrock don't seem to match the bolt pattern of my stock manifold. Even the Felpro gasket for the GM TPI intake has the air ports a bit off, like 1 mm.


this is a picture from the internet and the outline of PS (right) upper plenum stock ports

 

I was under the impression TPIS was no longer in business.

Edelbrock sells gaskets, only for the lower though which is odd.

 

It may take some time for them to respond. I got the 58mm TB from them last summer after a few months of waiting.
The base and runners are discontinued and probably that's why they don't sell those gaskets. Possibly they have some left in stock.

 

I did a test on my home cnc with oscillating blade cutter and this is how it turned out:


this is the 58mm TB, but I’ll go initially with the stock TB.

I haven’t got the manifold and runners yet

 

The eldelbrock runners have an egr port on the passenger side for older TPI intakes. I have the cold start injector delete but I need to block the passenger side and not sure if I can block it using a gasket with aluminum insert or it needs a more reliable way to plug it. That portion would be exposed to manifold vacuum but also high temperature exhaust back pressure

ps, I’ve finished designing the edelbrock runners gaskets and cut the two upper ones.

 

porting the upper plenum with a vfd cnc spindle





PS
I’ve installed them on the car and they fit very well. the gasket material is very nice quality 1.5mm thick.
For the lower manifold I’ve made them out of aluminum insert gasket, also 1.5mm. The aluminum foil is actually perforated but the leak through the gasket must be extremely slow to make any difference. Whereas the fist material is relatively easy to cut with the tungsten knife OTK the laminated one is much more difficult and I could only make one util it destroyed the tungsten knife. I’ve continued using the endmill (new g codes)…Super easy to cut but they require a lot of effort to trim the expanded edges. Probably the normal gasket for would’ve worked because the pressure is low. If you buy thinner paper gaskets it might not be a good idea, but these 1.5mm are pretty strong.