[Stan Weiss]

Originally Posted by steve25

My recent flow bench test of last fall show ( moving a head around on a Bore adapter) that your better off even with the Bore size of a .060" over 350 motor to either run only a 1.96" Intake valve, or a 2.11" valve with limited lift if your running a pre 1970 head casting.

The deeper chambers of the post 1970 heads will not cut into the added flow numbers of running a 2.11" valve at a lift of up to .450" if I recall my numbers right.

If your 350 build needs to drop some compression then adding the needed Intake valve chamfer to the top of each Bore is a good help!

Steve,
How much difference is there in unported heads between the1.96" intake valve and the 2.11" intake valve? How much could the 1.96" valve head be helped with a 2.02" intake valve and matching bowl work?

Stan

[steve25]

I will get back to you on Monday morning Stan with that info as I will be away from home until Sunday evening.

[Jay S]

Steve I look forward to the answer to Stan’s question as well. When you get back.


An old quote from Speedtalk....probably referring to a race engine. Most of us would do the chamfer if the gains were 1/4 of this...


“On some engines, when the intake valve over hangs the bore, the correct chamfer can make up to a 50 HP differance in the engines output. “


JOE SHERMAN RACING ENGINE



I had not really considered it before, but It is curious why Pontiac bore chamfered in the exhaust only on some later 350s. Emissions??? Doesn’t seem like it would have been for power?

The bore chamfers on the 350 appear to go out close to the the head gasket sealing area, the same it’s bigger brothers. The 3.875 bore makes the chamfer get bigger from the small bore. I have a 400 with the intake chamfers and a 350 double chamfer engine here, I will try cc’ing the chamfers.

[77 TRASHCAN]

I had not really considered it before, but It is curious why Pontiac bore chamfered in the exhaust only on some later 350s. Emissions??? Doesn’t seem like it would have been for power?

I wonder if any of the auto makers devised a way to check air flow through an engine, with the cylinder head on the engine??? I think Smokey Yunck had such a machine, or way of doing such. Makes me wonder if having the intake valve closer to the cylinder promoted bteer port velocity....just wondering...

[steve25]

Jay, you don't need to rig up a way to CC the chamfers ( big PIA!) just get some clay , mold it into the chamfer area that has been oiled up, then remove it and drop it in your CC burette and read the change in level.

For those of you who want to CC stuff and get a in the ball park reading but do not have a reall Burette, just get a glass kitchen type measuring cup because on one of there sides they are graduated in ML ( millleters ) which is the same a CCs.

[455-4+1]

Probably a little off topic, but related all the same.
Obviously the chamfer adds to the clearance volume, which when related to the swept volume, lowers static compression ratio.
When VE approaches (or exceeds) 100% via inertia tuning, is this added volume an advantage, (like in a boosted application) and at what point does the crossover between lost static compression, and added available volume for higher than atmospheric cylinder filling occur?
(realising fully that 100% VE in street engine is a very big ask 😉

[steve25]

Ok Stan and all you folks, here's the info you where looking for , and maybe some you folks did not want you hear also!

The first flow numbers here are durived from a 1968 casting number 15 with a casting date of K 027.

This flow test was done with its stock 1.96" Intake valve in good condition and a freshened up 30 degree seat who's OD was still way under max coming in at 1.89".

The second flow test was this same port in the same head, but fitted with a 2.02" Chevy Intake valve with a 45 degree seat, its seat OD came out to 1.95".

This 2.02" valve was a stock GM valve in good condition with NO stem undercut down to 5/16" from the stock 11/32".

Both set up's average out to each valve being under utilized by about 2 % in regards to seat OD.

Flow numbers are at a 28" depression and temperature corrected.

1.96" valve / 30 degree seat.
.050". .100". .200". .300". .400". .450". .500". .550". .600".
40.4. 75.8. 142.2. 183.2. 185.7. 188.2. 189.5. 190
2.02" valve/ 45 degree seat.
33.9. 67. 135.3. 183. 185. 188.8. 191.3

There's a total flow loss with the 2.02" valve of 20.9 cfm which would show up as a 3.85 HP loss per cylinder on a running motor.

Now on to the bad news!

Since this whole string of post was started in regards to a 350 cid motor that likely has a 3.910" Bore , here are my findings after checking the max width of the chambers of 4 different stock factory head castings I have on hand.

I checked all 4 chambers in each head.

Casting # 15 - 6X-4. - #62. - 6X-8
---- k027. - F115. - I038. - H246
4.290". - 4.217". - 4.310". - 4.215"
4.296". - 4.225". - 4.312". - 4.215"
4.298". - 4.200". - 4.312". - 4.213"
4.308". - 4.200". - 4.314". - 4.215"

It's very plainly obvious that from these numbers there is no stock block Pontiac that would not benefit from both intake and Exh valve chamfers in the tops of the Bores, especially all the motors with under a 4.120" Bore!

Yesterday I made up a Bore adapter to go down to a 3.920" Bore size on my flow bench and later today I will do a retest of the above, plus flow test one of those stock 6x heads to show the flow reduction produced by not having chamfers at the top of the Bores!

[slowbird]

Fwiw we ran 16 heads on a stock 73 350 short block with a cam that had .454 lift. Ran pretty good until the stock cast pistons let go.

[steve25]

In which way did they give up, broken ring lands?

[slowbird]

Originally Posted by steve25

In which way did they give up, broken ring lands?

Yes. The short block had 120k miles on it, we got a little aggressive with the timing at the track and they just didn't like it lol

[steve25]

Yup, I found that out with a 389 I had when I mis- set the base timing up to 44 degree's
Live & learn & spend $, lol!

[Jay S]

Thanks for info Steve! Appears the next valve size up worth doing in a 350 that would be common size is a 2.05. Not a 2.02.

Seeing those numbers I will go measure the width of the bore chamfers on the 350 and see how they match up to the heads you listed.

I did cc the bore chamfers the other day on a 350 with both the e and I chamfers. They were not as big as I remember. Maybe they do not go out as far as the 400s and 455s.
Exhaust chamfer =.8 cc,
Intake chamfer = 1.4 cc
Total = 2.2 cc
The engine had a chamfer at the top of the bored on the full circumference also. I didn’t check it. But it looked like it would push the total volume from 2.2 cc to 3 cc. I will measure what that bore chamfer takes the bores out to. That circumference chamfer is probably helping out too.

In regard to 455-4+1 post, it does not appear there is enough volume in the bore chamfers to ever see a drop or gain in power even when the inertia effect on the VE. At least it doesn’t to me. The cam and the attributes of the heads/engine are players in the net gains or losses in inertia cylinder fill. It would be difficult to determine where net gains turn to net losses is from drops in compression.

Calculating out the V/P index for an engine and finding where the engines V/P curve has the most acceleration is good starting place for finding where gains/losses crossover.

[steve25]

It's worth doing only if it's a 30 degree seat, yes!

[Stan Weiss]

Originally Posted by steve25

Ok Stan and all you folks, here's the info you where looking for , and maybe some you folks did not want you hear also!

The first flow numbers here are durived from a 1968 casting number 15 with a casting date of K 027.

This flow test was done with its stock 1.96" Intake valve in good condition and a freshened up 30 degree seat who's OD was still way under max coming in at 1.89".

The second flow test was this same port in the same head, but fitted with a 2.02" Chevy Intake valve with a 45 degree seat, its seat OD came out to 1.95".

This 2.02" valve was a stock GM valve in good condition with NO stem undercut down to 5/16" from the stock 11/32".

Both set up's average out to each valve being under utilized by about 2 % in regards to seat OD.

Flow numbers are at a 28" depression and temperature corrected.

1.96" valve / 30 degree seat.
.050". .100". .200". .300". .400". .450". .500". .550". .600".
40.4. 75.8. 142.2. 183.2. 185.7. 188.2. 189.5. 190
2.02" valve/ 45 degree seat.
33.9. 67. 135.3. 183. 185. 188.8. 191.3

There's a total flow loss with the 2.02" valve of 20.9 cfm which would show up as a 3.85 HP loss per cylinder on a running motor.

Now on to the bad news!

Since this whole string of post was started in regards to a 350 cid motor that likely has a 3.910" Bore , here are my findings after checking the max width of the chambers of 4 different stock factory head castings I have on hand.

I checked all 4 chambers in each head.

Casting # 15 - 6X-4. - #62. - 6X-8
---- k027. - F115. - I038. - H246
4.290". - 4.217". - 4.310". - 4.215"
4.296". - 4.225". - 4.312". - 4.215"
4.298". - 4.200". - 4.312". - 4.213"
4.308". - 4.200". - 4.314". - 4.215"

It's very plainly obvious that from these numbers there is no stock block Pontiac that would not benefit from both intake and Exh valve chamfers in the tops of the Bores, especially all the motors with under a 4.120" Bore!

Yesterday I made up a Bore adapter to go down to a 3.920" Bore size on my flow bench and later today I will do a retest of the above, plus flow test one of those stock 6x heads to show the flow reduction produced by not having chamfers at the top of the Bores!

Steve,
Thanks for al that great information. Was that great a difference between valve size and seat OD normal on Pontiac heads?

Stan

[slowbird]

Originally Posted by steve25

It's worth doing only if it's a 30 degree seat, yes!

Why??

[steve25]

Yes Stan.
I have never seen any manufacturer max out the OD, which is due to production tolerance's and the variations that can go along with it

[steve25]

Jay, thanks for that info!

Slowbird, I will attempt to answer your question in the morning as there's a lot of sides to that.

[steve25]

Sorry folks that I have not posted back results of flow test with a 350 type 3.910" Bore with valve notches and without , but I am having a hard time finding something to use as a Bore sleve to accurately get my 4.00" flow bench adapter down to that needed 3.910" test size.

I will try again to resolve that tonight.

[steve25]

Slowbird, the answer to that "why " question for me greatly hinges on the chamber shape in the head we are talking about and the total amount of valve lift to be run.

If you just look at the total added up amount of Intake airflow up to .550" lift that a 30 degree seat valve can produce it will always exceed the airflow of a 45 degree seat by 10 to 15 CFM, and even when you add a 30 degree back cut to the back side of a 45 degree seat valve, it will still fall short of what a 30 seat valve can produce.

The other big plus for a street motor using a 30 degree seat Intake valve is that the seats last far far longer without pounding out, which is a big plus with unleaded fuel!

The only small down side to this is the need for a tad more spring seat pressure to maintain control of the valve since a 30 degree seat can not seal up by wedging force like a 45 seat ,just clamping force.

[slowbird]

Originally Posted by steve25

Slowbird, the answer to that "why " question for me greatly hinges on the chamber shape in the head we are talking about and the total amount of valve lift to be run.

If you just look at the total added up amount of Intake airflow up to .550" lift that a 30 degree seat valve can produce it will always exceed the airflow of a 45 degree seat by 10 to 15 CFM, and even when you add a 30 degree back cut to the back side of a 45 degree seat valve, it will still fall short of what a 30 seat valve can produce.

The other big plus for a street motor using a 30 degree seat Intake valve is that the seats last far far longer without pounding out, which is a big plus with unleaded fuel!

The only small down side to this is the need for a tad more spring seat pressure to maintain control of the valve since a 30 degree seat can not seal up by wedging force like a 45 seat ,just clamping force.

Flow isn't everything though. Years ago we had ported 62 heads flowed 230ish. Had some issues that required us to install new valvess. We went with a 2.125 valve and 45° seats. Hurting lower lift flow and help upper lift. Cam had .550lift. Car picked up about .05 and about 1mph in 1/8.