Hey cylinder head flow studs... just wondering...?

[rapidride2]

Working on a set of ported factory GM 781 oval port heads but this question lies with most any cylinder head.

I need to replace the intake seats. Are there any issues leaving the intake valve seats a little high/proud (by about .020)

Thinking it may reduce reversion.. Anyone have any thoughts based on real world experiences?

Negligible power loss? or negligible power gains ?

Thanks.

[KnightEngines]

That will really screw up pressure recovery.
If anything you want to sink the seats.

[mag2555]

Besides the issue posted above how deep will the new seats be?

You need to determine where the minimum throat diameter is now and make sure that once the new seats are installed that your current ID is still maintained.

[Ken_Parkman]

I did that on my EMC engine way back in 04. I did not have the resources to do a delta test or compete with the really big boys, but the engine actually scored quite well I thought. The valve job was very unique and it did substantially kill low lift reverse flow on the flowbench. At low lift the flow was somewhat like a diode, and I do believe that is why the engine exhibited very good low rpm characteristics. The torque was 1.12 ft-lbs per inch at 2500 rpm on a 613 hp 409 AMC. The way the scoring worked put a premium in rpm range with the scoring band 2500 to 6500 rpm; I'm not sure what application other than the EMC wants that. The engine scored at the top of the off-brand marques and amateur builders but was not competitive with the geniuses like Kasse.

[rebelrouser]

I did that on my EMC engine way back in 04. I did not have the resources to do a delta test or compete with the really big boys, but the engine actually scored quite well I thought. The valve job was very unique and it did substantially kill low lift reverse flow on the flowbench. At low lift the flow was somewhat like a diode, and I do believe that is why the engine exhibited very good low rpm characteristics. The torque was 1.12 ft-lbs per inch at 2500 rpm on a 613 hp 409 AMC. The way the scoring worked put a premium in rpm range with the scoring band 2500 to 6500 rpm; I'm not sure what application other than the EMC wants that. The engine scored at the top of the off-brand marques and amateur builders but was not competitive with the geniuses like Kasse.

Just curious, If I remember right the AMC engines had 30 degree intake valve seats. Your heads were 30 or 45 degree?

[Ken_Parkman]

The seats were 45, but there was substantial weirdness in the valve job on the EMC engine. Features intentionally added so the make the reverse flow work against itself, with the raised intake seats being one. I would not do that level of weirdness in a normal application.

30 degree intake seats are stock, and they do a wonderful job of flowing at low lift and backwards. This I have tracked in operation, and as soon as you add any kind of performance cam I get rid of the 30's to kill some low lift flow.

[BobbyB]

The seats were 45, but there was substantial weirdness in the valve job on the EMC engine. Features intentionally added so the make the reverse flow work against itself, with the raised intake seats being one. I would not do that level of weirdness in a normal application.

30 degree intake seats are stock, and they do a wonderful job of flowing at low lift and backwards. This I have tracked in operation, and as soon as you add any kind of performance cam I get rid of the 30's to kill some low lift flow.

Do you believe that killing low lift flow is a good thing for most street/strip engines?

[Ken_Parkman]

For the most part yes. Depends on the cam and application. My opinion is with a shorter duration cam it makes less difference. I remember one engine which ended up with 45 degrees seats on one head and 30s on the other. The difference in reversion was glaringly obvious.

[BobbyB]

For the most part yes. Depends on the cam and application. My opinion is with a shorter duration cam it makes less difference. I remember one engine which ended up with 45 degrees seats on one head and 30s on the other. The difference in reversion was glaringly obvious.

Any tricks you can share that a novice can use to get low lift flow without much reversion?
Do you do just flow test the intake in both directions to check progress?

[Ken_Parkman]

To kill low lift flow? Seat angle is the immediate big thing. Do a drawing of actual flow area at a couple lift points and then change the seat angle and see what happens to the flow area. Big changes.

[NewbVetteGuy]

For the most part yes. Depends on the cam and application. My opinion is with a shorter duration cam it makes less difference. I remember one engine which ended up with 45 degrees seats on one head and 30s on the other. The difference in reversion was glaringly obvious.

Any tricks you can share that a novice can use to get low lift flow without much reversion?

There's a TON of very related information in this 39 page ST thread: viewtopic.php?f=1&t=53485


Adam

[Stan Weiss]

To kill low lift flow? Seat angle is the immediate big thing. Do a drawing of actual flow area at a couple lift points and then change the seat angle and see what happens to the flow area. Big changes.

What I get for a 2.02" intake valve with 30, 45 and 55 seat angles.

Stan


_________________Flow_Test_1_Data

In._Valve____________Ex._Valve___________
Seat_Angle_______30__Seat_Angle_______42_
Seat_Width____0.045__Seat_Width____0.065_

________
Actual__Effective_
Valve___Valve_____
Lift_InchArea_In.__
0_______0_________
50______0.267_____
100_____0.54______
150_____0.83______
200_____1.131_____
250_____1.436_____
300_____1.744_____
350_____1.795_____


_________________Flow_Test_2_Data

In._Valve____________Ex._Valve___________
Seat_Angle_______45__Seat_Angle_______42_
Seat_Width____0.045__Seat_Width____0.065_

________
Actual__Effective_
Valve___Valve_____
Lift_InchArea_In.__
0_______0_________
50______0.22______
100_____0.47______
150_____0.764_____
200_____1.069_____
250_____1.377_____
300_____1.687_____
350_____1.795_____

_________________Flow_Test_3_Data

In._Valve____________Ex._Valve___________
Seat_Angle_______55__Seat_Angle_______42_
Seat_Width____0.045__Seat_Width____0.065_

________
Actual__Effective_
Valve___Valve_____
Lift_InchArea_In.__
0_______0_________
50______0.179_____
100_____0.427_____
150_____0.727_____
200_____1.035_____
250_____1.345_____
300_____1.656_____
350_____1.795_____

[Ken_Parkman]

Stans calculation shows a 13% drop in flow area @ .100" lift by changing from 30 to 45 degree seats. I've gotten a little higher % reduction in flow than that but similar on a good back to back on the same heads with the same valve size.

Can you imagine the flow only guys with a 15% reduction in flow? They would have a heart attack. The example I'm quoting had more cylinder head work than the valve job, but the heads went back on the car with absolutely no other changes and it went 6 tenths faster, somewhere around 80 hp.

[RevTheory]

I'm giving serious thought to 2.05 valves with 50* seats if my DART seats are jacked up on the 2.02s they currently have (32*-45*-60*-70*, 91.5% throat.) Hopefully I'll know where they stand soon and go from there. I'm guessing current velocity profile is the key, yes? Sort of, sometimes?

[af2]

Can you imagine the flow only guys with a 15% reduction in flow? They would have a heart attack. The example I'm quoting had more cylinder head work than the valve job, but the heads went back on the car with absolutely no other changes and it went 6 tenths faster, somewhere around 80 hp.

Yep 5000 cfm means nothing on a 355!