Double hump heads

[Chuck R.]

I'm going to look at a set of 327 heads for sale from a semi retired performance car nut. I'm told the Guy is a straight shooter but, you all know how most of those storys wind up.

What's got my attention is that he claims these are double hump heads with 2.02 valves.

Since I don't have squat for information on early 60s heads, what should I be looking at for numbers and give aways?

Appreciate any and all tips.

Chuck

[Mike M.]

Re: Double hump heads

you need to look up the casting # of the heads you need for your vet as well as the casting dates and see if the heads being sold are appropriate for your vet.you can barely get a finger nail between the intake and exhaust valves of a 202 equipped small block chevy head. mike

[Chuck R.]

Re: High Mike

Well actually, I'm keeping my original and complete 327 under the bench for the next owner when that time comes.

I'm actually contemplating putting these heads on a 350 I'm building up.

I'm more curious as to these head's pedegree in case the fella trys blowing smoke up my hinney.

Chuck

[Duke W.]

Re: Double hump heads

The first "double hump" heads were 3782461,which were used on the '61 315FI engine with 1.94"/1.50" valves. The 2.02"/1.60" valves were first cut into these heads heads in '65 for SHP/FI engines, and if they were originally built with the larger valves, there will be a radius cut on the chamber centered on the inlet valve axis. The 461 castings were replaced with 3890462 castings for 1967 and 3917291/2 in '68, and several later casting numbers have similar port layout with both 1.94"/1.50" and the larger valves.

Determine the casting number/date which is on the floor of the rocker box. If they are 461s look to see if there is an "X" on the bottom side, under the water outlet. These have a little more inlet port volume, and are excellent performance vintage heads, regardless of valve size.

You should also look to see if the ports have been hand worked, ask whether the valves have been reseated or had the valve guides rebuilt and determine whether they have been surfaced. An original surface should have linear tooling marks ("broach marks") similar to block decks and radial tool marks if they have been surfaced.

I prefer the smaller 1.94/1.50 valves. With the larger valves the heads have a tendency to crack between the seats, so check that area carefully.

Duke

[Chuck R.]

Re: Excellent!

That's what I'm after!

Thanks to you both for the quick hits.

Chuck

[Mike M.]

Re: Double hump heads

duke: i think the 202 exh valve first showed up on the 64 365'd snf 375'd. mike

[Joe L.]

Re: Double hump heads

Mike and Duke----

Yes, 1964 was the first year for the 2.02"/1.60" valve size small block heads for L-76 and L-84 applications.

[Duke W.]

Re: Double hump heads

Of course! I actually know that, but I don't think it's the first time I've screwed it up.

Duke

[Jason B.]

Re: Double hump heads

I've read mention to checking the clearance between the 2.02" and 1.60" valves (very small) and checking for an "X" on the engine side of the head below the water jacket, but my question is this. Is there ANY way to see if the 461 heads have the 2.02/1.60 valves with the heads installed on the engine?

Thanks in advance for the information.

Jason B.

[Duke W.]

Re: Double hump heads

A flexible tube bore scope inserted into the spark plug hole so you can look at the valve heads.

Duke

[Chuck R.]

Re: What's the performance trade off?

This cat's really got me going now!

I picked up the heads which were in fact 461s, with the following observations

His handy little pocket books show these heads as being applied to both 302 & 327 applications from 1962 through 1969.
They had screwed in rocker studs. Was this common for 461s?
They didn't have the infamous X
The valve train was M.I.A.
Date codes were J 1 3

He actually just gave me the heads so that I could have them checked out and if they panned out I could pay him later.

PLUS, he offered me a pair of freshly re-built 327 heads with the 1.94/1.50 valve train.

What would I be trading off performance wise if I went with the smaller valved heads vs the 2.02s as a general rule of thumb?

He's quite the guy, he has a mint 62 two door, four speed Bel Air with the split bench seats an crazy S bent floor shifter. Nice car!

Hmm I wonder if he'll let that super T-10 go he has under his bench cheap? Have to work on him on that one

Chuck

[Duke W.]

Re: What's the performance trade off?

I don't know what "pocket book" he was using, but 461s were first used on the '61 283 FI engines (both 275 and 315 HP), and for 300 and above HP engines in '62-'65 and the 250 HP engines in '65. I don't think they were used in production after this, and no 302s were built in this era. Also 461s were never built with screw in rocker studs.

The casting date is October 1, 1963, so they were originally installed on a '64 engine.

According to my simulations the different valve sizes equates to about a 2 percent difference in top end power. For street engines, I don't recommend increasing the valve sizes. I don't think the reliability tradeoff is worth the additional top end power, but for a racing engine I would open them up. If you do you must make the radius cut in the chamber to unshroud the inlet valve, or they may flow worse.

I don't have any comparative flow for the 461 versus 461X, so I can't quantify the difference in potential power.

The "freshly rebuilt 327 heads" could also be 461s, but are probably 462s if they are post-'65 or 291 or 292 is they are off a '68 327.

Duke

[Chuck R.]

Re: Ok

Sounds like then that there isn't much of an advantage of the 2.02s over the 1.94s as I'm only a weekend warrior and not going to be pounding it.

Think I'll pickup the re-built heads, throw the 461s on the open market and call it a day.

Thanks for your feed back Duke, I have a better comfort level over which way I want to go now.

Chuck