Magnum Exhaust Port Dilema

-

72DMag

Well-Known Member
Joined
Oct 21, 2019
Messages
1,169
Reaction score
256
Location
Pittsburgh
Porting a set of R/t cylinder heads and they are going to be used with LA style headers. No big deal and this has been done before. Gasket matched the intake and no problems there. Went to gasket match the exhaust and Holy Cow Batman!! The LA gasket on a magnum head is huge. I would shave off alot of metal (See pics) but not sure if thats a good idea. I pulled up the "How to Build Big Inch Small Block" book that I have and noticed they recommend 1 7/8" headers for a magnum head. Maybe this is why?

So should I just leave the exhaust ports alone on these heads or have others ported them out to match or come close to the size of the LA exhaust gaskets?

20200823_153308.jpg


20200823_153313.jpg


20200823_153318.jpg


20200823_153325.jpg
 
Why don't you go with 302 castings, they have the large exhaust ports??
 
Because I have these already....... lol
Well that makes sense.....but you have a lot of meat to cut. LOL Enlarging the exit won't help if you don't enlarge the whole exhaust path. Sell those and buy some heads with a large exhaust port?? You can get a bare set of 360 heads pretty cheap from any motor machine shop. They might even make a trade??
 
@rumblefish360 Thats what I was thinking to do. If I opened them up to LA size I think I would lose all the velocity of the air. Kinda like what people do wrong on the intake side when they make them too big by porting. My local napa will have the magnum exhaust gaskets in tmrow. So I'm gonna see if that will give me a gasket match area without taking a drastic amount of iron of the head.
 
Well, I’m no head ported but I pay attention...
AND I just slept at a Best Western....
:lol:
But that’s why I pointed you to John, Pittsburghracer. There’s a few other fellows here that do there own work
 
Opening the exhaust ports to the gasket will most likely not gain you anything. Smoothing them out for gas extraction would be much more beneficial.
 
Last edited:
don't do anything the exhaust port is raised for better air flow and fits inside the gasket dont worry about size of port it all ready out flows the la head by 10%
 
I thought the Magnum exhaust port was better than the LA heads? Everything I’ve read and seen says leave the overall outlet shape alone. Don’t many fill in the floor of the LA heads anyways? Find a Magnum exhaust gasket (if one exists) and open it to that maybe. Me I’d leave that area as is and work the guide boss, short side and roof. But someone with more experience will know best
 
I thought the Magnum exhaust port was better than the LA heads? Everything I’ve read and seen says leave the overall outlet shape alone. Don’t many fill in the floor of the LA heads anyways? Find a Magnum exhaust gasket (if one exists) and open it to that maybe. Me I’d leave that area as is and work the guide boss, short side and roof. But someone with more experience will know best

It is. Read post #9. It doesn't have to be as big as the LA because it's raised.
 
It's not like FelPro is an expert on exhaust ports lol
 
Don't touch them!
Those are cheap generic gaskets that are more like the LA port, but wrong for even those.
I did a thread on the mag head 3 months ago, ck it out
 
There ya go! I couldn’t at the time remember who did the porting thread on the Magnum head but here he is.
Porting a set of R/t cylinder heads and they are going to be used with LA style headers. No big deal and this has been done before. Gasket matched the intake and no problems there. Went to gasket match the exhaust and Holy Cow Batman!! The LA gasket on a magnum head is huge. I would shave off alot of metal (See pics) but not sure if thats a good idea. I pulled up the "How to Build Big Inch Small Block" book that I have and noticed they recommend 1 7/8" headers for a magnum head. Maybe this is why?

So should I just leave the exhaust ports alone on these heads or have others ported them out to match or come close to the size of the LA exhaust gaskets?

View attachment 1715583810

View attachment 1715583811

View attachment 1715583812

View attachment 1715583813
 
Porting a set of R/t cylinder heads and they are going to be used with LA style headers. No big deal and this has been done before. Gasket matched the intake and no problems there. Went to gasket match the exhaust and Holy Cow Batman!! The LA gasket on a magnum head is huge. I would shave off alot of metal (See pics) but not sure if thats a good idea. I pulled up the "How to Build Big Inch Small Block" book that I have and noticed they recommend 1 7/8" headers for a magnum head. Maybe this is why?

So should I just leave the exhaust ports alone on these heads or have others ported them out to match or come close to the size of the LA exhaust gaskets?

View attachment 1715583810

View attachment 1715583811

View attachment 1715583812

View attachment 1715583813


Having a smaller exhaust port than the gasket and header opening is no problem. Magnum head exhaust is already better than an LA head as mentioned by others.
 
Porting a set of R/t cylinder heads and they are going to be used with LA style headers. No big deal and this has been done before. Gasket matched the intake and no problems there. Went to gasket match the exhaust and Holy Cow Batman!! The LA gasket on a magnum head is huge. I would shave off alot of metal (See pics) but not sure if thats a good idea. I pulled up the "How to Build Big Inch Small Block" book that I have and noticed they recommend 1 7/8" headers for a magnum head. Maybe this is why?

So should I just leave the exhaust ports alone on these heads or have others ported them out to match or come close to the size of the LA exhaust gaskets?

View attachment 1715583810

View attachment 1715583811

View attachment 1715583812

View attachment 1715583813
Did you just tell me in a PM you sold these locally? Now you're destroying them?
What's wrong with you?
Use a magnum gasket to seal your incorrect headers. You don't have to lie.
You're making those heads worthless if you have no way to see if you're gaining or losing flow. Just go buy speed masters, seriously. No one is going to , as you put it.."trade for aluminum magnum heads".

Screenshot_20200825-174030_Samsung Internet.jpg
 
Last edited:
No, 302 heads have regular 318 port exits. Use magnum exhaust gaskets and don't mess with those Magnum ports.
I've owned 302 castings. They have the same ports as the 360 heads. The blue colored gaskets are 273/318, the other is a 340/360 manifold gasket. It is the main reason I switched to 302 casting on my 318. The exhaust ports are larger.

DSC01769.JPG
DSC01770.JPG
 
Here's food for thought....and I'm not readin all this hogwash to see but I haven't seen anybody talk about the Magnum manifolds. They are much much better flowing....especially the large outlet ones.
 
Here's food for thought....and I'm not readin all this hogwash to see but I haven't seen anybody talk about the Magnum manifolds. They are much much better flowing....especially the large outlet ones.
Any particular year?? The magnum was made for many years. The manifolds I always recommend are the 96/97/98 360 magnum Jeep Grand Cherokee but I don't know which year magnum heads are the best??
 
Any particular year?? The magnum was made for many years. The manifolds I always recommend are the 96/97/98 360 magnum Jeep Grand Cherokee but I don't know which year magnum heads are the best??

Early 90s Dakota R/T have the 2 1/8 openings. And hay.......I thought YOU were the mannyfold guy? lol
 
I've owned 302 castings. They have the same ports as the 360 heads. The blue colored gaskets are 273/318, the other is a 340/360 manifold gasket. It is the main reason I switched to 302 casting on my 318. The exhaust ports are larger.

View attachment 1715584265 View attachment 1715584266
No, they don't. 302 are small like any other 273/318 head. Mayne you mean 308? The gaskets are one size fits all after a certain year for LA. Early stuff they had 2 gaskets. Later on they decided to save a penny..
 
-
Back
Top