ea81 heads

[mountaingoatgruff]

first of all, yes i searched for an answer. no i was not willing to spend hours upon hours of searching through almost-what-i-need when hopefully plenty of you guys can help me here in mere minutes.

 

that said, we're talking about the exhaust diffusers. i seen/heard guys say to cut it out for a bit better flow, but i haven't heard anyone say how much to cut and whether or not one should retain the healthy radius on the end of it.

 

i'm thinking cut at most a 1cm to 1.5cm and leave a radius slightly smaller than the factory cast one.

 

the rest of a mild p&p is pretty straightforward on these heads as far as smoothing the short side radii and leaving other major protrusions. i've just never encountered an exhaust diffuser like this and was wondering how happy i should let the dremel get.

 

thanks:)

[The Beast I Drive]

Im not an expert, but when I look at that separator on the exhaust port I think it wouldnt be a very good idea to cut much off, I think you would get pressure from one side building into the other and disrupting the exhaust flow. That is what that little wall is there to prevent. I dont think taking a little off could hurt though, I just wouldnt get too dremel happy. Again, I am not an expert so this is just my opinion based on what I can see.

-Bill

[Jerry DeMoss]

There really is quite a bit of material that can be taken off safely on the ea81 heads. I have done a few in the past along with the present ea81t build up I am working on now.The main thing I have found is match port the exhaust side to the gasket (not as much needed for n/a) and the intake side as well. The valve pockets are another area for great improvement. The point where the valve seat meets the heads inside the area where the valve sits is a good place to start from. Do a little at a time and do both heads equally while you progress. Another good thing is make sure you are doing so on the larger valve heads. I wouldn't really bother on the smaller ones since they are limited by the valve size. Happy grinding.!

[86BRATMAN]

Actually, an n/a motor will benefit a good deal by port matching the intake and exhaust. The real problem for an ea81 brathing is the intake manifold itself.

[Jerry DeMoss]

Actually, an n/a motor will benefit a good deal by port matching the intake and exhaust. The real problem for an ea81 brathing is the intake manifold itself.

 

Exactly. The reason I stated not as much to the exhaust is cause that is where you loose torque and that is one of the prime benefactors to the n/a motor. I agree there is an awfull lot that can be gained especially on the intake. I hope I didn't come across too harsh.

[mountaingoatgruff]

i am using the large valve heads and while i'm not trying to port for drastic hp gains, i would of course like to get the most for my time and labor.

 

on the intake side all i did was clean up the jointlines and junk of the casting process but mostly i rounded and smoothed the area beneath the valve seat (small side radius' machined spots).

 

on the exhaust side i cleared all the aluminum from the bowl to just barely match the valve seat, took 1cm off the diffusers (which us just where the runners open up inside), drasticly smoothed the whole length of the exhaust port, and simply by way of lots of sanding opened the end bit a hair. of course i also polished the exhaust side and combustion chambers.

 

honestly, all i'm looking for with this car is the best mileage i can possibly get. i'm converting to spfi, did this p&p, i hope to followup with a d/r 5speed and i've been trying to get a buddy of mine to help me with some exhaust work.

 

the answer i was really looking for here is whether i was okay taking a full centimeter off the diffuser. my dad's a mechanic with 30years of exp and he nearly crapped himself when he saw what i did. kinda had me worried is all.

 

thanks as usual, guys!