[gtofreek]

If you go to CheaperthanDirt.com you can buy old surplus gas masks for about $10-$15. They make great porting masks as they have eye, nose, and mouth protection, and I find they don't fog up like regular safety glasses.

[beertracker]

The attached photos are from a 6x-8 exhaust port. Three of them show the uncut valve guide channel. So to widen this channel how much can I cut and not break through?

Two of the photos show a ¼” drill and 3/8” egg cutter for comparison. What size cutter would you recommend I use for widening this channel?

The 6x throats have very distinct protruding lips just prior to the start of the short turn. Should I cut back the short turn more? The other photos show cuts made to the protruding lips. How do the photos look? Should I cut back more? bt

[beertracker]

two more photos

[gtofreek]

How much are you trying to get the flow up to? Are you using a 1.77" valve, or a 1.66"? As far as the short turn is concerned, start at the bottom of the valve seat, and grind straight down to the short turn. Grind it until it is straight. This will slightly raise the short turn some. Then just round over that sharp lip that your arrows are pointing at in pics #3, and #5. Don't grind that lip down, just round it over so it's not sharp. The air naturally wants to get shoved to the roof, making that edge straight from the seat to the short turn will help guide the air in the way it wants to go. If you grind that short turn down, and really radius it, it will flow more air at really high lifts, but the lower lift numbers will suffer a fair amount. If you're not doing a full blown port job, then don't even worry about channeling around the guide. you will just wind up with a port that flows 90% or more of the intake. Just smooth those casting bumps up throughout the port, fix the short turn, and open up to 1.77" valve, and it will flow 180-190 on the center ports at .550", and 190-200 on the end ports. Unless you're planning on getting the intake to flow over 250[which will take a lot of work], then that's all you really need to do. Don't worry about the bump in the exhaust throat, next to the intake seat. Just smooth off the edges, and leave it alone. You can grind that completely out, and it won't change the flow a bit, just make it thinner, and more likely to break.

[steve25]

You do not want to widen that channel, just Bullet nose the valve guide, you will drop off low lift velocity and flow plus waste grinding effort!

[Blued and Painted]

post 42 pic 3. Yes cut that lip off and make a small radius into the turn.

[steve25]

Flow numbers @ 28" for stock 6X center port, and then after a 2 minute rework of blending off the lip left by the throat cutter.

.050". 20.6. 21.7

.100". 43. 45.2

.200". 93. 93.9

.300". 125. 127

.400". 135.7. 141

.450". 138.7. 143.7

.500". 140.2. 149

.550". 141.7. 151

.600". 141.7. 152



Do not blend off this transistion of the port shown in this photo!

How much of a Intake flow increase are you shooting for?

[beertracker]

I am trying to duplicate Jim Hand's flow results from his book. bt

Given 6x ported head, 1.66” exhaust valve the goal is
.050” .100” .200 .300 .400 .500
26 cfm 57 109 139 180 202

Here are the ported 2.11" intake numbers I am shooting for. Again from Jim Hand's book

.050" .100 .200 .300 .400 .500
43 cfm 81 155 203 234 245

It will be a while before I get to working on the intake side.

[gtofreek]

That exhaust flow will support 250 CFM intake port. You're not going to get 250 without a ton of work, and if not done correctly, you won't get over 230. So just cleaning those exhaust ports up and lightly radiusing the short turn, you will have more than enough exhaust flow to support the intake. Like Steve said, don't grind away the bulge next to the intake port. Plus, if that's at 28" of flow, then I think it will be pretty hard to get 200 CFM from a 1.66" valve. A 1.77" valves allows for a valve job that will easily get 200 CFM.

[beertracker]

See post 43 pic 2. See where the red arrows are pointing. I think this is the protruding lip that Jim Hand speaks of in his book. He states to remove this completely. So are the arrows pointing to the lip Jim speaks of? Should I remove this lip? Or am I mis-reading something?

His book photos are not clear on this.

Jim Hand quote:
"The 6x throats have very distinct protruding lips just prior to the start of the short turn. Remove the entire lip so that the throat is basically straight down from the seat to the turn/guide area."
end quote.

Pontiac put the circular lip in to provide a pressure drop and velocity increased based on Bernoulli's Equation.

The driver side head already has the lip removed. So if it's ruined let me know.

[beertracker]

Originally Posted by gtofreek

That exhaust flow will support 250 CFM intake port. You're not going to get 250 without a ton of work, and if not done correctly, you won't get over 230. So just cleaning those exhaust ports up and lightly radiusing the short turn, you will have more than enough exhaust flow to support the intake. Like Steve said, don't grind away the bulge next to the intake port. Plus, if that's at 28" of flow, then I think it will be pretty hard to get 200 CFM from a 1.66" valve. A 1.77" valves allows for a valve job that will easily get 200 CFM.

The exhaust and intake numbers were checked at 15" on a modified Super Flow 110 Flow Bench and the flow values were converted to 28".

bt

[beertracker]

Originally Posted by steve25

Flow numbers @ 28" for stock 6X center port, and then after a 2 minute rework of blending off the lip left by the throat cutter.

.050". 20.6. 21.7

.100". 43. 45.2

.200". 93. 93.9

.300". 125. 127

.400". 135.7. 141

.450". 138.7. 143.7

.500". 140.2. 149

.550". 141.7. 151

.600". 141.7. 152



Do not blend off this transistion of the port shown in this photo!

How much of a Intake flow increase are you shooting for?

Steve:

Do you mean do not grind off this transistion of the port shown in this photo? I can't make out from the photo what is being pointed to.

bt

[steve25]

All Pontiac production Exh ports have what I call the main throat , and a sub throat.
The sub throat area is the main restriction at lifts above .400" and the factory it would seem did this for a reason!
They where concerned about having good low lift Exh flow during the important blow down period and instead of increasing production cost by applying a two angle valve seat and or back cutting the valve itself they got extra low lift Exh velocity by just stopping the depth of the main throat cut and having the cast shaped in place to leave that kick over on the Intake port side of the Exh valve.

This to a good extent has the same effect as a multi angle Exh seat would in terms of low lift flow while keeping that nice big long life seat width that the heads have shock.

The stock main throat area in these X series heads averages 1.855" sq in, the sub throat area is 1.41" sq in which is a 23 % reduction in area

Percentage wise the main throat is a great 92% and the sub throat 81% which is 4% off from the point of being very effective!
This points out the good news that it does not take a ton of rework to pick up 25 to 30 cfm out to the Exh flange.

Here's a quick drawing of what to blend off and what to leave as looking in the Exh runner from the flange.
The next drawings are the dimensions of the sub throat once the remains of the factory throat cutter are taken off, and then later once the port is reworked more to provide these flow numbers below.

These flow numbers are for 1 hours worth of rework with a 1.66" valve that has been back cut with a 30 degree angle with no full Bowl blend done yet, and all still just ruff ground/ no polish and no gasket match at the flange.

.050". 26.2

.100". 52.6

.200". 105.8


.300". 139.6

.400". 160.4

.450". 166.4

.500". 171.8.

.500". 176.8

.600". 180.7

.650". 181.7

.700". 184.7

Note that at .450" lift this port is already flowing as much as a stock 1971 cast number 96 head with its 1.77" Exh valve!

These next flow numbers are for this same port with the reworked second throat area of 1.494" along with these changes.

1.77" valve with a valve job consisting of a .040" wide 30 degree top cut.
Main 45 degree seat .060" wide.
60 degree bottom cut , .100" wide.
Short turn layed back some 1/16" and polished to blend in.

Note that the short turn width in this test is still under sized so the Exh port displayed problems of pumping issues from between .500" to .650" lift that where hampering the flow numbers!

This was latter corrected with a full bowl blend and a gasket match on the roof of the port at the flange.
This shows you why not having af flow bench can kill ya!

.050". 32.9

.100". 67.3

.200". 127

.300". 157.5

.400". 172.3

.450". 179.3

.500". 185.7

.550". 191.6

.600". 193.6

.650". 207.5

.700". 211.4

Here's the flow gain for that same port with a 1 3/4" tube on its flange.

.200". 130

.300". 163.4

.400". 180.3

.450". 202.9

.500". 209.4

.550". 213.3

.600". 216

.650". 222.5

.700". 223.8
Nice gain for just a tube, no less a good scavenging Collector on a header, no?

[steve25]

If your porting for 245 Intake cfm and your going to run Headers then I would not rework the Exh side for more than 175 cfm especially if you already have a duel pattern Cam.

[steve25]

The one good thing about reworking cast iron is that you can grind with stones, and with stones you can shape them by running them on other stones to use as combination templates and grinders.
Here are shots of 3 of the common size stones I use in reworking 1.66" Exh valve heads to flow anywhere from 180 to up to 210 cfm@28".

Once you rework the valve bowl to a given throat size the shapes used are much more important to achieving a given level of flow then size!
In other words the right curves allow for better usage of the given amount of port area the valve bowl and Exh runner has.

[steve25]

Here's the stone combination I use for the center Exh ports along with the same 1.456" throat template.
Note that the sub throat is still in place.
The short turn is ground out wider on the center Exh ports by means of using the smaller stone, and note how leaving the sub throat in place, but blending it into the short turn Funnels the flow into place and around the short turn.

[Blued and Painted]

for the heavy lifting in the intake bowl (6x), do you use bowl cutters mounted on a guide spud.

[gtofreek]

For "bowl hogging" we use a blade cutter mounted in a cutter body, that spins on a "pilot" in the valve guide. You have to be careful how much you remove though, as you might break though, or make very thin.

[steve25]

Yes I do .
I have many valve seat incert cutters that I have modified to common sizes I use .

[Blued and Painted]

I would think a bowl cutter would give a more consistent starting point vs free hand. Pic's ?