59 550 heads w/1.60 exh & 1.94 valve increase size ???

[Al R.]

Machine shop recommended stepping up to the larger valve size of 1.60 for the exhaust and 1.94 on the intake on my old 550 heads for my 283-290HP FI car. I'm also replacing the valves and seats as well as the guides and have posi-seals installed on the valves , due to excessive wear. Also going for screw-in rocker studs, as 1-2 on each head have pulled out slightly. Hardened seats will also be installed. Machine shop owner is also going to pocket port the heads under the valves. SS swirl valves will be used. Question is--- will there be any measurable HP or torque gains going with the larger swirl type valves over the stock valves. The valves are going to be replaced anyway. 1 other ?-- is there any advantage to using 1.6 ratio rockers? 10.5 CR pistons with the correct 290 FI cam bored .030 over 3.70 ratio rear. Want to keep the 550 heads for originality. TIA

[Jim L.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Others will have opinions about the 1.6 rockers and larger valves. My opinion is that you are seriously jeopardizing the heads by machining them for hardened seats, a procedure for which there is little demonstrated need.

[Michael H.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Others will have opinions about the 1.6 rockers and larger valves. My opinion is that you are seriously jeopardizing the heads by machining them for hardened seats, a procedure for which there is little demonstrated need.

I agree, and there wouldn't be enough of a difference to make it worth going to larger valves.

Rocker arms with a 1.6 ratio will require a different valve lash. Again, more trouble than it's worth.

As Jim mentioned, no real gain will be felt because of those modifications.

[Don H.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

I agree, no need for the hardened seats unless it is a daily driver and you are going to put MANY miles on it using no lead fuel. I know of a 427 / 435 that had a head ruined doing it. Good luck, Don H.

[Al R.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Thanks everyone, I guess I'll stay with the 1.5s. 1 thing maybe someone can answer-- the valves in some locations were lower in the head which the shop owner said was due to the valves beating down on the seats. Does this sound legit? or is it something to get more money or is it the valves have been ground too many times in the past, causing them to sit lower on the seats?

[Tom P.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Thanks everyone, I guess I'll stay with the 1.5s. 1 thing maybe someone can answer-- the valves in some locations were lower in the head which the shop owner said was due to the valves beating down on the seats. Does this sound legit? or is it something to get more money or is it the valves have been ground too many times in the past, causing them to sit lower on the seats?

What others have said about NOT installing hardened seats is correct (if the cutter goes into the water jacket, the head is junk). I'm not going to say that there is no benefit to adding hardened seats, BUUUUUUUUUUUUT, for those heads, and the application, it just is NOT the best thing to do. With the introduction of unleaded gas around 1971, GM began to induction harden exhaust seats for the purpose of reducing wearing down of the valve seat because of a lack of the protection provided by the leadtetraethyl. Well after all these years of experience in automotive engines that are not constantly subjected to severe heavy duty use (such as heavy duty truck engines), there just has not been significant wear which really justifies installing hardened seats.
Back in the early days of unleaded gas, there may have been a legitimate concern about valve seat wear/recession. But the scare resulting from that concern just has not proven valid.
Regarding valve seat recession in your heads, yes, it certainly could have occured to some extent. I can't speak to that because I don't have your heads in my hands to personally inspect them.
Next, your heads were originally cast and machined for 1.72/1.5 valves. You probably would be OK to open up the exhaust seats to accept 1.6 valves, but cutting the intake seats to accept 1.94 valves may be asking for trouble because that much of a cut could end up in the water jacket. IF THEY WERE MY HEADS, I would maybe consider going to a 1.84 intake valve (such as used in some 305 heads) and I think you would be more than safe--------------------------but I would not even consider going to the 1.94 valves.
As far as screw-in studs and guide plates are concerned, everyone of my SB heads get them. I think that is a very worth while upgrade.
A LIGHT cleaning up of the casting surfaces of the bowls and intake runners and port matching the intake ports would also be rather beneficial.

[Al R.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Thanks Tom, I will give the shop owner this info on the intake valves and have him re-look at the seats, with me present!. Al

[Duke W.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

I can't imagine that the guy actually ever did what he recommended on a set of small port heads. Chances are you will end up with two scrapped heads. I would seriously question other "advice" he offers, too.

Sticking with the OE 1.5" exhaust and enlarging the inlet seat for a 1.84" inlet valve is a safe proposition. 21-2N stainless exhaust valves are a good idea but stainless inlets are way overkill. "Swirl polished " valves really won't add much. The improvement in top end power and rev range is 99 percent pocket porting/port matching/chamber relieving. If done right the engine will make useable power to at least 7000.

If you want broader torque bandwidth have Crane grind you a "cheater Duntov" with POMLs of 110/118. The reduced overlap will also tame the idle a bit. Use Sealed Power VS677 valve springs installed at .090" above coil bind.

The Duntov cam has very harsh dynamics just above the tops of the clearance ramps on both sides. (The lobe is symmetrical) so it will tend to pound in valve seats unless the lash is set tight. It's one reason why I don't like the Duntov cam, but the LT-1 cam is probably too big for a short stroke 283. All other OE cams going back to 1957 have asymmetrical lobes with gentler closing than opening, so they are easier on the valve seats.

Lastly, unless you install some decent connecting rods figure the thing will blow up after a few thousand miles.

Duke

[Joe L.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

Thanks everyone, I guess I'll stay with the 1.5s. 1 thing maybe someone can answer-- the valves in some locations were lower in the head which the shop owner said was due to the valves beating down on the seats. Does this sound legit? or is it something to get more money or is it the valves have been ground too many times in the past, causing them to sit lower on the seats?

Al------



Most likely, it's the fact that the valves have been ground a number of times previously. Every time this happens, the valves seats get a little lower.

I also do not recommend going with hardened seats or larger valves. This head casting was never manufactured with larger valve size than the size you have. That means that you have no reason to believe that larger valves can safely be installed in these heads. Of course, it MIGHT be possible to install them but, for me, it would be too great of a risk. Plus, any "gain" you got out of it would be negligible.

[Joe L.]

Re: 59 550 heads w/1.60 exh & 1.94 valve increase size ???

What others have said about NOT installing hardened seats is correct (if the cutter goes into the water jacket, the head is junk).

Tom and Al-------



Even worse, the cutter doesn't get into the water jacket but the base of the pocket gets so thin that it "breaks out" when the hardened seat is driven in. Then, everyone thinks everything is just fine (until the head is put into service, of course).