620 L20 exhaust manifold

[superbee620]

I’m trying to put a 78 L20 engine in my 73 620 . My question is I’d like to use my exhaust manifold off the 73 which is square port but the head is round exhaust port. Will this work ? and if so should I use a square port gasket or round port gasket ? Thanks 

Edited September 11, 2019 by superbee620
I found the info finally when I googled it . It was on the ratsun site lol

[H20doctor]

wont work ... your exhaust manifold has to mach the block ... round to round , square to square

[bilzbobaggins]

I thought the "rule" was you could use a square manifold on a round port head, but not the other way around?  It isnt optimal but workable?

Edited September 11, 2019 by bilzbobaggins

[ValveFloater]

Use the gasket that matches the head not the exhaust. It works fine, just keep an eye out for leaks and readjust as needed. Many people will tell you you can not run it like that but as long as it doesn't leak you dont risk burning a valve. 

[banzai510(hainz)]

datzenmike will know

[datzenmike]

Yes, it's do-able. I think I would run the square port gasket as it has a metal ring around the edge that will be fully crushed against the head for a good seal. A round ring will fall inside the square opening in the corners and the square manifold will only be pinched against the 'paper' gasket.

[superbee620]

Thanks guys I appreciate the advice. Used square gasket .Putting engine in tomorrow . 

Fingers crossed

Edited September 13, 2019 by superbee620

[Rays74]

Be aware as well that the square manifold will have likely come from either an L16 or L18 and may end up pointing the downpipe at the bellhousing since the L20B is a touch taller.

It's workable but just know 😉

[ValveFloater]

Simply put, the round gasket has more surface area than the square. 

[datzenmike]

The metal 'fire' ? rings protect the softer gasket material edges, but mostly it crushes for a good seal. If you put a round gasket up against the square exhaust manifold you'll see that the square shape doesn't clamp onto the metal ring and seal properly, only a round manifold would. I daresay both will work initially, but the square gasket would be the best seal.

[ValveFloater]

Thanks Mike, makes sense.

[superbee620]

If anyone was wondering. I used the square gasket and have been driving it for 7 months with no problems. Thanks everyone 

[banzai510(hainz)]

Thanks for letting us know