[gtofreek]

More pics. All stripped down and ready for SS steel shot blasting.

[steve25]

Hey Paul, what's the casting date on those 670s?
Those are only the third set I have seen with those big cast numbers in the Intake bowls!

[Nicks67GTO]

Paul, why did you decide to angle mill? I was always under the impression that was a SBC thing and wasn't necessary on a Pontiac? Is there an advantage to angle milling?

[gtofreek]

Originally Posted by steve25

Hey Paul, what's the casting date on those 670s?
Those are only the third set I have seen with those big cast numbers in the Intake bowls!

I'll have to check. Those aren't numbers. Those are just the spots where the mold braces were.

[gtofreek]

Originally Posted by Nicks67GTO

Paul, why did you decide to angle mill? I was always under the impression that was a SBC thing and wasn't necessary on a Pontiac? Is there an advantage to angle milling?

It had nothing to do with SB Chevy's. I angle milled it because I want the sparkplug closer to the piston, so the chamber is shallower, and give the engine less tendency to detonate. Most people think detonation occurs from a hot spot in the chamber. But it doesn't. Hot spots cause pre-ignition which happens during the intake stroke, when the piston is near BDC. If a hot spot lights off the in coming fuel, it starts burning, and as the piston starts back up the cylinder and try's to compress that burning mixture, the pressure that develops is so high, it will melt and blow a hole right through the top of the piston. Pre-ignition destroys an engine in milliseconds.

Detonation occurs when the sparkplug fires the mixture, but the mixture doesn't get completely burned before max cylinder pressure occurs, Then, what ever air/fuel is left over, detonates from the pressure. Engines can survive detonation for quite some time. Engines don't survive pre-ignition. So by getting the sparkplug closer to the piston, and making the chamber shallower, should get the fuel burned quicker[less area to complete the burn in] so there is none, to very little unburned fuel left to detonate. By angle milling these, I got the sparkplug .080" closer to the piston.

[Nicks67GTO]

Originally Posted by gtofreek

It had nothing to do with SB Chevy's. I angle milled it because I want the sparkplug closer to the piston, so the chamber is shallower, and give the engine less tendency to detonate. Most people think detonation occurs from a hot spot in the chamber. But it doesn't. Hot spots cause pre-ignition which happens during the intake stroke, when the piston is near BDC. If a hot spot lights off the in coming fuel, it starts burning, and as the piston starts back up the cylinder and try's to compress that burning mixture, the pressure that develops is so high, it will melt and blow a hole right through the top of the piston. Pre-ignition destroys an engine in milliseconds.

Detonation occurs when the sparkplug fires the mixture, but the mixture doesn't get completely burned before max cylinder pressure occurs, Then, what ever air/fuel is left over, detonates from the pressure. Engines can survive detonation for quite some time. Engines don't survive pre-ignition. So by getting the sparkplug closer to the piston, and making the chamber shallower, should get the fuel burned quicker[less area to complete the burn in] so there is none, to very little unburned fuel left to detonate. By angle milling these, I got the sparkplug .080" closer to the piston.

Makes sense. Thanks!

[gtofreek]

Well, we re-calibrated our flow bench because we have been noticing that it has been reading lower than other SF 600 benchs for quite sometime. We finally knew something was wrong when i flowed some SS heads for a guy in Sweden that we have been helping out. The last time he was here, I flowed it and it would only do 307-308 CFM no matter what we did. When he left and took the heads back to Sweden, he flowed them on his bench, and they flowed 323. He worked on them and gt them flowing 337! He was very happy, as this is by far the most he has ever had them flowing. So he comes back to the states[his buddy lives in Phoenix, and they have a racecar there], and brings the heads back as he wants confirm the improvement he made on them. Well they still only flowed 307 on our bench.

So that brings us to today. We have been going round and around trying to find if there was something wrong with our bench. We could find nothing wrong with it. Today a friend of ours from Wisconsin was in town, and he specializes in airflow dynamics, and flowbenchs. He couldn't find anything wrong either, except that when he flowed some calibrated flow plates, our bench came up short. He re-calibrated it using those square edge orifice plates, and made us a new flow range spec sheet. Turns out our bench was a fair amount low, because the flow range sheet I have been calculating all the flow with was done at 25" of water, and not 28" plus it was calibrated with a plate that was not a square edge orifice.

With our old flow range spec sheet I was calculating all the flow off of 297 CFM being 100% of flow range 4. In reality, at 25" water, it flowed 311.1 CFM. So using these new specs, my head actually flows a lot better than I thought. Here are some new numbers based off of this new calibration.

.250" = 193.8 cfm
.300" = 230.2
.350" = 258.8
.400" = 278.1
.450" = 286.8

I need to bring my last flow sheet home so I can recalculate all the lift points to .800". Because I had 280 something at .800" before, which should put me well into the mid to upper 290's. I'm getting excited to start grinding on them again.

Originally Posted by gtofreek

Worked on the head some more today. I ground the guide leader out, and now it is at 176 CC's. I also re-did the valve job with a different cutter that accents this flat floor chamber a little better. Here is the new flow numbers.

_Lift_____CFM

.100"____71
.150"____105.4
.200"____146
.250"____185
.300"____219.8
.350"____247.1
.400"____265.5
.450"____273.8
.500"____282.5 with use of a flowball, carefully placed in top divider radius, just above the short turn. It still turns over around .475" lift.

[gtospieg]

I just found this thread and read thru the entire thing ...wow...the level of work and attention to detail are nothing short of phenomenal...can't wait to see the final results!

[gtofreek]

Thank you!

[gtofreek]

OK, I re-calculated my flow sheet with the new calibration on the flow bench. Here is what it does. This was on my test head.

.100" = 77 CFM
.150" = 111.4
.200" = 153.8
.250" = 195.3
.300" = 230.7
.350" = 258
.400" = 277.5
.450" = 272.2
.500" = 274.4
.550" = 274.4
.600" = 276
.650" = 279.1
.700" = 282.8
.750" = 284.7
.800" = 285.9

[vidguy]

Great stuff. I didn't know you had your own flow bench. I really enjoy your documenting the machining..

[gtofreek]

We have pretty much everything except crank and cam grinders. We even have a custom carburetor shop. Jeff specializes in Holleys, and is one of the best in the country. His carburetors run like electronic fuel injection, only more responsive!

[steve25]

Be sure to check the level site on the Manometer Paul, as wood and concrete floors can settle and throw the level off.
I had this happen to mine for a day and when chasing voltage / motor and mechanical things when it was just the my wood floor shifted, lol!

Are you flow testing with a Manifold Paul, as it can really change things, and have you converted over to a 45 degree seat or not?

[steve25]

Paul if you make a teardrop shape like this out of clay type Epoxy and sit it on the Intake runner floor up close to the common wall and about 1\2" to 3/4" in from the flange , and with the pionted end towards the flange you can slow down the high lift high speed air stream on the floor and delay the tumble fully, or reduce and delay it up to a higher lift and hence gain cfm.

I mold it with a thick old Guitar string in it to pin down where it needs to be during a flow test and the string does not effect the flow test, but some bailing or Mechanics wire works also.

What are the angles on the valve job that you have going on?

[gtofreek]

Manometer is level. Sitting on concrete floor. I'm flowing with intake once I get heads how I want them. I flowed it with the unported intake before and it barely hurt the flow. So then I can port it to get head flow back.

[steve25]

Paul you can also little by little grind away some of the bottom cut at the short turn, starting on the common wall side and moving over to the center of the short turn.
Go slow as this needs to be done parallel to the 14 degree valve inclination angle.

The push rod will side does not pass as much air, as velocity probing will confirm so leave that for latter.

Make the floor as wide and flat as you can starting from the end of the push rod pinch point.

Steps taken to make the air flow velocity equal left and right across the short turn will help

If you can shuffle the head over on the flow bench adapter to get that port away from the side of the adapter the tumble will slow down and kick in at a higher lift point, or stop completely , this indicates what the issue is.

The greater air mass coming down the common wall and out the chamber finds that close fitting cylinder wall a restriction and then in turn heads for a area of lesser restriction, that being the center of the bore!

That fight of all that common wall flow trying to merge with the push rod side flow creates the tumble.
Also make sure your grinding on the floor has left it pointing towards the spark plug , not the chamber wall to the side of the chamber as it is cast stock.

How is your valveside to chamber wall clearance per inch of lift?

[Tom Vaught]

Paul, your mail box is full! I have a pm ready to send you.

Tom V.

[gtofreek]

Emptied.

[gtospieg]

anything new to report on this awesome engine build?...

[gtofreek]

Yes, when I get a chance here in the next couple days.