I'm porting a set of LT1 heads myself and came across a topic that said not to match the exhaust port with the gasket, but I've already done it.. I didn't make any holes or anything, I'm talking strictly from a performance stand point. I heard that if you make the ports too big you lose power because the velocity of the exhaust gasses will be too slow and there isn't enough back pressure. I matched my exhaust port to almost the same size as a felpro 1406 gasket. The port still isn't as big as the 1 3/4" primaries of my AS&M headers, so will I be alright???? Any info would be greatly appreciated
Thanx!!!

 

I think there's a coolant passage that runs right below the exhaust ports.

 

I didn't grind through or make a hole anywhere, I'm strictly talking from a performance stand point.

 

I think they will be fine. I have heard of guys gringing into the water jacket and welding it up on both sides to make the port larger. on a stock casting I don't think there is enough material to make the ports to big.
Just my .02
Kory

 

That's probably on the intake side. They can be as large as you want. And they are probably dealing with larger valves. The exhaust side is suppose to be more sensitive.

 

when I brought my heads I ported to a pro he told me the biggest mistake dyi porters do is reshape the exhaust chambers. He told me there was a reason the ports are D shaped. If gasket match them you would have not only reshaped the port but messed with the short side raduis. I'm not pro and certainly don't know what your porting will do as far as performance but I've learned that porting is something that takes experience and knowledge, not experience or knowledge

I'd say just flow them and see what numbers you get. When I ported a set of heads for the first time, I messed with the exhaust ports and short side radius quite a bit. Still flowed pretty good

 

porting the exhaust port is just as effective in porting the intake...
dont change the shape or raise the roof and your good to go....people say not to gasket match the exhuat port becasue there HAS to a step from the port the the header primary...meaning the port opening has to a little smaller then the header opening...this is so that when the exhaust pulses mover though the exhasut they DO NOT go back into the head. so with the little step there, its just enough to keep those gasses from going back into the chamber during overlap...also POLISHING them makes a BIG difference

 

It is my understanding that LT1 exhaust sides are pretty pathetic anyway. LS1 guys flow exhaust side numbers that are as good or better than a stock LT1 intake port. Given that, I don't imagine you could hurt yourself too bad by porting the hell out of the exhaust side. I don't believe that extra backpressure is good in terms of making power anyway. I would be curious whether or not the walls get too thin (i.e., melting problems) if the exhaust side is ported out to the gasket ? ? ? Anyone ? ? ?

 

I didn't change the shape of the port. The gasket I'm using is a D-shape also. I basically just enlarged it. There is still about a 1/4inch of material on the thinest area, and all the ports are equal to or slightly smaller then the gasket ports. So I think I'm alright that way.

 

Ok I am working on my heads and have made the ports to match the gaskets. However, I have a ramp. Yes I did make the size the same as the gasket but if you look right at it there is a smooth bump as it leads out to the exhaust. The bump is maybe 1/4 inch tall. I felt that would increase the velocity of the gases. And no I did not cut into the water passage. The intake is another story there is just so much to remove. I did make a pin head hole on two intake ports by the push rod slots. No big deal. I have read and done some porting on import heads. The idea is to visualize the air flowing through the ports. I have 12 hours invested and have done 5 ports. Too slow but I take off enough at a time to make sure not to remove too much.

Head porters let me know if I'm right in my assumptions. Note the exhaust port is still D shaped and will be very polished.