I've got some 3927186 double hump heads. I need to get rid of the stock 2 piece valves, and get some 1 piece stainless valves. I'm wondering if it's worth going 2.02 or not. I currently have 1.5"/1.94" valves with hardened exhaust seats. The one thing I am concerned about is porting. If I put 2.02's in, I will need to port the heads more, I'm wondering how easy it is to hit a water jacket when porting out just below where the valve seats. Is this called the throat? If you do happen to hit a water jacket, is it possible to repair it? Thanks, Scott

If you go the 2.02 valves make sure to unshroud the intake area. The exhaust needs to go to 1.6 which is equally or maybe more important. There's all kinds of tricks for work in the chamber and porting. I'd ask someone that's messed with 461s and the like for a long time.

going to larger valves has an added benefit on older high mileage heads,if they have been reworked several times over the years the valves will have sunk into the combustion chambers and increased the compression ratio possibly risking detonation.installing larger valves will require cutting larger seats, therefore you get fresh seat material to work with that is like when the heads were brand new.also,this can help the combustion process if you run dome top pistons because the dome won't be blocking the spark plug/combustion mixture interface since the valves will be pulled further back out of the combustion chamber.(more room).

Originally posted by bowtie455:
going to larger valves has an added benefit on older high mileage heads,if they have been reworked several times over the years the valves will have sunk into the combustion chambers and increased the compression ratio possibly risking detonation.installing larger valves will require cutting larger seats, therefore you get fresh seat material to work with that is like when the heads were brand new.also,this can help the combustion process if you run dome top pistons because the dome won't be blocking the spark plug/combustion mixture interface since the valves will be pulled further back out of the combustion chamber.(more room). =
Ummm Huh?? :confused:
Methinks you need to reconsider this except for the fresh seat material part :D

sorry,my bad due to sleep deprivation and overmedication.thanks for the correction Wolfplace. graemlins/boring.gif = graemlins/clonk.gif

So has anyone on board ported the hell outta stock heads? I'd like to put the bigger valves in, like you guys said, it will pull my valves back up outta the heads and give me consistant compression/valve train geometry, + more power as long as I can port the heads out more.

It's not a good idea to ruin a perfectly good set of heads by "porting the hell outta" them.

The purpose of porting is to inprove the flow characteristics of the port; not to remove material for the sake of removing material.

If you put larger valves in a set of heads, typically you need to open up the throat, right behind the seat. It wants to be about 85% of the valve diameter; no larger. If it's larger, the air doesn't follow the contour of the valve as well, and instead rushes down the port and smashes in to the back of the valve around the edges, instead of flowing near the center and following the shape of the valve as it "tulips" outward.

Larger is not always better.

Undercut-stem valves are often more effective at improving port flow, than larger valves of the same design.

Yes I run 186s alot. I have a set of them on my daily driver.

I know I don't wan't the port to be "just plain bigger", I wan't it to flow better! Since I currently have done a nice job of porting them, if I put 2.02" valves in, I will need to take another .040" worth of meat around the entire circumference of the throat, that's just under a 1/20th of an inch. That would make the the throat proportionally the same comparing valve size. The actual runner and bowl I would leave alone, because with the way they are they arent a restriction.

David Vizard's book on cylinder heads will walk you through all the steps needed on your heads, buy it. Bob

I have a set of 461s that are pretty much what you are looking for. They do not have accessory holes though so you have to work around that. They are supposed to flow in the 220-240 range. He says 240 but I'm saying at least 220.