[25stevem]

Today while finishing porting work on a set of 389 heads( 17 degree inclination angle ) it dawned on me why these early heads have faster port velocity for any given level of air flow or port area then the latter 14 degree heads.

These. Early heads due to there valve inclination angle and having the chamber much further over towards the exh port side of the head have a .440” longer intake port and by the same token they have a .440” shorter exh runner.

Just passing on a kinda slap on the forehead moment.

[b-man]

Isn’t it 20 vs 14 degrees?

Interesting data nonetheless.

[ANDYA]

Steve, could you give some specifics on the heads you are porting ? What size engine they are going on and what is the intended performance. How much you were able to get them to flow. I have a set of #77 heads that I want to use with a 65 421 block. Looking to make some good power using all GM 1965 stuff.

[25stevem]

ANDYA here is the info for you.
These heads I just finished are for a 389, but could be used for a 421, or even a 326.

These heads are a 1958 casting with 1.88” and 1.60” valves.
Here are the stock and ported flow numbers for intake and exh.
I stepped up to a 1.92” intake, but used the stock 1.60” size exh valve.

Flow is at 28”
Intake
.050”. 33.4/////38.8
.100”. 70.2/////71
.150”. 104.8/////110.4
.200”. 133.2/////139.8
.250”. 150.3////161.5
.300”. 155/////183.4
.350”. 158.7/////196.9
.400. 159.7/////203.8

Exh
Center exh port.
No back cut has yet been applied to the valve so the the low lift flow numbers up to .250” will still go up.

.050”. 23.3/////27
.100”. 50./////51.7
.150”. 74/////75.8
.200”. 95.4/////101.7
.250”. 113.2/////125.6
.300”. 125.2/////143
.350”. 130.2////159.4
.400”. 133.7/////166.2
.450”. 134.4////170.2
.500”///////////////////173
.550”///////////////////175

Your #77 heads can be ported up far more since there is no limiting oil passage on the roof like these heads to feed the oil to the rocker studs.

The intake side of your heads can safely go 240 cfm ( I have ported them to 250) and since your 77 heads exh valve is 1.66” then exh side will go a good bunch higher then what I posted here.

I have not checked the stock intake and ported CCs, but will do that over the weekend and make a up date post to follow this.

[Stan Weiss]

Originally Posted by 25stevem

Today while finishing porting work on a set of 389 heads( 17 degree inclination angle ) it dawned on me why these early heads have faster port velocity for any given level of air flow or port area then the latter 14 degree heads.

These. Early heads due to there valve inclination angle and having the chamber much further over towards the exh port side of the head have a .440” longer intake port and by the same token they have a .440” shorter exh runner.

Just passing on a kinda slap on the forehead moment.

Steve,
I don't understand what you are saying here. CFM, CSA, and velocity are linked together. If I know any 2 I can calculate the 3rd one.

Stan

[25stevem]

Stan, I guess what a really was saying is that these longer intake runners change the tuned length to favor lower rpm power even if for example these early heads where to have the same minimum port area as a 14 degree head.

[25stevem]

Here’s a picture representing the length difference.

[ANDYA]

Thanks for the reply Steve. It looks like you can get the #77 heads to flow some decent numbers. That’s good news for me. Like I mentioned,, I want to build a 440 cid combo based on a 421 block and #77 heads to go into a 65 GTO. Induction is going to be one of the new repro bathtub manifolds so the idea is to put out some impressive power for the parts being used.

[25stevem]

Sounds like a nice build that will be fun to stuff you foot into!

I had time to CC these heads .
These ported heads are 178 CCs where as a stock one is 156.5.

Not too shabby.
The ported heads picked up 22% more flow for a 13% gain in port volume.

[77 TRASHCAN]

No wonder the earlier 389 and 421's ran as well as they did, in stock form!!!

['ol Pinion head]

SteveM, since speaking closed chamber heads (realize early ones) let me get off in the weeds a little. what do you think of having the open chamber mod performed on '670's versus lowering compression through use of dished pistons?

[25stevem]

It would very much depend on if the head was to be run stock or ported up to about 245 cfm or greater.

If stock then go with the dish.
If ported then the chamber needs to be made into something like the 68 and up chambers to unshroud the intake valve.

How much of a open chamber you need to go for hinges on how much flow your going for and at what lift you want that peak flow to take place at.

One reason why these 670 heads burn so dirty and tend to detonate is the very near 90 degree angle that the chamber wall meets the chamber floor at on the plug side.

Fuel that de-atomizes ( wet flow ) gets packed into that tight angle and then it either burns late ( makes no added power) , or detonates ( and reduces power) or just plain gets drawn out the exh.

If this chamber to floor meeting point is reworked into a 5/16” radius or better yet 3/8s then more power is made since you will then be burning that fuel and reap the added benefit of far less tendency for detonation to take place .
It’s a win win deal.

The sides of the chambers where they meet the floor is the ideal radius, but unfortunately that’s only well less then 50% of the perimeter of the chamber around the floor.

If you had a 455 and a 72 CC head and needed to get the chambers up to like 88 CCs you could improve on the efficiency of these chambers greatly on the process of making them bigger.

On a side note the 670 heads and there low port angle ( not inclination angle ) can be reworked kinda easy to flow 230 cfm just by doing a certain valve job to them and also doing a light bowl bend to them.

[25stevem]

ANDYA here’s more info for you.
Here are stock flow numbers for your 77 casting, and fully ported flow numbers for a 1965 76 casting fitted with a 1.94” valve.

This valve started as a 1.96” Pontiac intake valve with a 30 degree seat and was cut back to 1.94” and then had the 30 degree recut to a width of .075”.

This 76 casting is the same as your 77, but for a slightly deeper chamber.
.100”. 62/////61
.200”. 114.3/////128.7
.300”. 160/////195.7
.400”. 169.4////225.4
.450”. 174/////237
.500”. 176.8/////240
.550”. 177.7/////249.2
.600”/////////////////250.3

Just well thought out bowl porting work on these heads when fitted with a as above reworked 1.96” / 1.94” valve will get you 195 to 197 cfm at between .400” and .450” lift depending on what the heads have core shift / casting wise.

Note that piston notches will need to be checked when running a 1.94” valve depending on your valve lift.
If your running a dished piston to lower compression there may be no issue, but you should still confirm that.

[ANDYA]

Steve, thank you for the added information. As was posted by ol pinion head I’ve also thought about opening up the cumbustion chamber and running a flat top position. Need to keep this engine pump gas friendly and still make the power. The key to this build is going to be tricked up heads.