Reduced low lift flow from porting...

[BradH]

I put whatever top cut the chamber can take.

This is the core of my arguments about a lot of stuff that gets tossed around in forums.

Not all heads and/or combinations are suitable candidates to try and implement the latest trends being used on the newest, most advanced castings currently available.

And that point is often not talked about.

I agree. What kills me is guys read that you need "this" or "that" seat and end up putting the wrong top cut on it and killing the head.

One of the reasons I asked my question was that I remembered where Darin Morgan commented that certain seat angle & top angle combinations only worked well if the chamber allowed for a particular length of the transition from the ID of top cut into the chamber (pressure recovery implications, possibly?). So when you showed a "traditional" 23* chamber w/ a 40* top cut, I was looking for that transition as an example. Honestly, I can't tell if it works for your head because it's a good match for the chamber as cast, or if there was specific work you did to the chamber to make it work.

[CamKing]

Honestly, who uses .500 lift these days, except for maybe for the tow rig??!
And I'm being serious!

There are many circle track classes that are limited to .500" lift. Also some that are limited to .390"/.410", .425", .450", and .550".
Some run hydraulic flat tappets, some run mechanical flat tappets.
For most, the only improvement you can make to the heads, is in the valve job.

[Stan Weiss]

I think like many things low lift is a relative term. Maybe it should be referenced as a percentage of max cam lift? The OP talks about picking up from .400" which could be fine for him but probable not for that Pontiac with .420" max lift.

Stan

I obviously can't tell you exactly what our heads flow, but it's not uncommon to see a Cup head go 440+cfm. Not sure what you are referring to as far as TDC?

Jay,
You take the intake valve lift @ TDC and see what the head has for flow at that lift.

Stan

What is learned by this and how is it applied?

Jay,
For me lift at TDC is a way to help quantify what low lift is for a given combination. Remember that there are people here who built a great variety / different types of engine and some could be running less than half the valve lift you are.

Stan

[HDBD]

There is a place for a 15 deg top angle. I learned about the benefits from Roger Helgesen aka Dr Air. Smart man, good teacher.

[Warp Speed]

I think like many things low lift is a relative term. Maybe it should be referenced as a percentage of max cam lift? The OP talks about picking up from .400" which could be fine for him but probable not for that Pontiac with .420" max lift.

Stan

Jay,
You take the intake valve lift @ TDC and see what the head has for flow at that lift.

Stan

What is learned by this and how is it applied?

Jay,
For me lift at TDC is a way to help quantify what low lift is for a given combination. Remember that there are people here who built a great variety / different types of engine and some could be running less than half the valve lift you are.

Stan

Very true, but what does the flow at tdc really have to do with?
So the lift during overlap, at tdc, is what defines the low lift flow point?
Why not 10* btdc?
Why not 5* btdc?
Or these same values atdc?
I feel people put too much concern in overlap itself. To me it is just kind of a necessary evil.
I know some like DV use it as a basis for cam selection but......?

[ClassAct]

I put whatever top cut the chamber can take.

This is the core of my arguments about a lot of stuff that gets tossed around in forums.

Not all heads and/or combinations are suitable candidates to try and implement the latest trends being used on the newest, most advanced castings currently available.

And that point is often not talked about.

Ok, I'm going to say something that will probably get me publically stoned (and not in the hippie sense of the term) but here goes.

I do all my SBM and BBM stuff with a 50 degree seat. I've never done a 50 on a Pontiac, because I can't find a willing stooge to let me have at it. Can you blame them? Anyway, I've done lots of 45 degree Pontiac seats. I don't do any 30's any more. I have a 400 coming in this winter and it will get a 45.

I've always heard about "sinking" the valve and how it's a killer. It is. BUT, if you need to get a top cut in there, you aren't really sinking the valve. A top cut, done correctly is always a power maker, even if you are "sinking" the valve.

I learned this in 1995 when I didn't even have a flow bench. I was working with a buddy and I did all the short block crap and he was doing the heads. I watched him cut a valve job one night after work and he was taught that sinking a valve was worse than defiling the Virgin Mary. Once the seat was in, he was done. And I knew his mentor. And that's how he did it.

After a long discussion, I said lets rent some flow bench time, a third party flow bench (not his mentors bench as I didn't want that influence there) and he could do one head, and I'd do the other.

Just so happened it was a SBM we were doing for a local circle burner on dirt. It's been so I long, I now no longer remember the top cut, but I chose my own cutter (not something they already had on the shelf) and it didn't have a 35 top cut. Could have been 38 but I think it was a 40. I also had to use a cutter on the chamber to blend the top cut back into the chamber.

At the test, everyone who looked at the heads said I was going through the looking glass to the rabbit hole of stupid. When we left, I was the one smiling. My head made more flow everywhere, had significantly less turbulence all through the lift curve, the port was significantly more quiet (bad English but it's due to my limited education) and, it was the first time I'd seen a port flowed backwards. My head killed his head in reverse flow. After almost 25 years, I think I was 40-50 CFM LESS in reverse flow. That's big for those heads.

I always get a top cut. Even if it sinks the valves. I'd like to hear Warp and DV and get their thoughts on "sinking" valves to get a top cut.

[CamKing]

BTW, I think the people that have seen power gains by reducing what they call "Low Lift Flow", are only seeing the gains, because the cam they're running has too much duration for their application, so by killing the flow, at the lower lifts, it's band-aiding the fact that the cam is spending too much time at those lifts(too much duration).

[GARY C]

I obviously can't tell you exactly what our heads flow, but it's not uncommon to see a Cup head go 440+cfm. Not sure what you are referring to as far as TDC?

Jay,
You take the intake valve lift @ TDC and see what the head has for flow at that lift.

Stan

What is learned by this and how is it applied?

I would just be interested to see a comparison of flow at TDC on different engines as opposed to commonly used low lift flow # from a bench only as it would be the best reference point to look at it on an actually engine.

The numbers would not have to be from a current head, even one from 5 or ten years ago would be interesting.

[GARY C]

BTW, I think the people that have seen power gains by reducing what they call "Low Lift Flow", are only seeing the gains, because the cam they're running has too much duration for their application, so by killing the flow, at the lower lifts, it's band-aiding the fact that the cam is spending too much time at those lifts(too much duration).

Yes, thats why I would like to see it referenced as flow at tdc as it seems that would be more indicative of what the engine is seeing and take the flow bench out of it.

I understand the need to start int early to reach peak sooner, it just seems like there would be more to learn if people could look more at what the head is doing on the engine and not just on a bench... I could be wrong.

[Warp Speed]

Everything is a compromise, but a top cut (or cuts) are or the utmost importance to any valve job imo. Some more than others.
Some combinations need to be sunk a little for things to be proper, and for gains to be realized with steeper seat angles. That is a big fear in many, and has been for decades.
I prefer, if at all possible, to not have the chamber dictate the valve job. Kinda like the tail wagging the dog. Lol
If it needs a "little" sinking, so be it. If it would need tons..........find a different head. Lol
How about the exhaust side?!?

[Warp Speed]

BTW, I think the people that have seen power gains by reducing what they call "Low Lift Flow", are only seeing the gains, because the cam they're running has too much duration for their application, so by killing the flow, at the lower lifts, it's band-aiding the fact that the cam is spending too much time at those lifts(too much duration).

This can be true, but we are also limited to acceleration by the valve spring and the rest of the system. If we all ran air springs, the events would be totally different!
But that is just one of the many aspects of steaper valve angles.

[ClassAct]

BTW, I think the people that have seen power gains by reducing what they call "Low Lift Flow", are only seeing the gains, because the cam they're running has too much duration for their application, so by killing the flow, at the lower lifts, it's band-aiding the fact that the cam is spending too much time at those lifts(too much duration).

I always order the cam after the flow bench and porting work is done. If the cam is too big, that would be on the cam grinder. I haven't bought an off the shelf cam since 1985 or something, unless it's for a customer who throws a temper tantrum about getting a bespoke cam.

[Stan Weiss]

I think like many things low lift is a relative term. Maybe it should be referenced as a percentage of max cam lift? The OP talks about picking up from .400" which could be fine for him but probable not for that Pontiac with .420" max lift.

Stan

What is learned by this and how is it applied?

Jay,
For me lift at TDC is a way to help quantify what low lift is for a given combination. Remember that there are people here who built a great variety / different types of engine and some could be running less than half the valve lift you are.

Stan

Very true, but what does the flow at tdc really have to do with?
So the lift during overlap, at tdc, is what defines the low lift flow point?
Why not 10* btdc?
Why not 5* btdc?
Or these same values atdc?
I feel people put too much concern in overlap itself. To me it is just kind of a necessary evil.
I know some like DV use it as a basis for cam selection but......?

Jay,
TDC is just a reference point and you can choice what ever one you like.

I picked TDC because it is a transition point / the piston is no going up and the piston is not going down and is seating there with zero velocity.

How in the world did overlap and DV come into this discussion?

Stan

[GARY C]

I put whatever top cut the chamber can take.

This is the core of my arguments about a lot of stuff that gets tossed around in forums.

Not all heads and/or combinations are suitable candidates to try and implement the latest trends being used on the newest, most advanced castings currently available.

And that point is often not talked about.

Ok, I'm going to say something that will probably get me publically stoned (and not in the hippie sense of the term) but here goes.

I do all my SBM and BBM stuff with a 50 degree seat. I've never done a 50 on a Pontiac, because I can't find a willing stooge to let me have at it. Can you blame them? Anyway, I've done lots of 45 degree Pontiac seats. I don't do any 30's any more. I have a 400 coming in this winter and it will get a 45.

I've always heard about "sinking" the valve and how it's a killer. It is. BUT, if you need to get a top cut in there, you aren't really sinking the valve. A top cut, done correctly is always a power maker, even if you are "sinking" the valve.

I learned this in 1995 when I didn't even have a flow bench. I was working with a buddy and I did all the short block crap and he was doing the heads. I watched him cut a valve job one night after work and he was taught that sinking a valve was worse than defiling the Virgin Mary. Once the seat was in, he was done. And I knew his mentor. And that's how he did it.

After a long discussion, I said lets rent some flow bench time, a third party flow bench (not his mentors bench as I didn't want that influence there) and he could do one head, and I'd do the other.

Just so happened it was a SBM we were doing for a local circle burner on dirt. It's been so I long, I now no longer remember the top cut, but I chose my own cutter (not something they already had on the shelf) and it didn't have a 35 top cut. Could have been 38 but I think it was a 40. I also had to use a cutter on the chamber to blend the top cut back into the chamber.

At the test, everyone who looked at the heads said I was going through the looking glass to the rabbit hole of stupid. When we left, I was the one smiling. My head made more flow everywhere, had significantly less turbulence all through the lift curve, the port was significantly more quiet (bad English but it's due to my limited education) and, it was the first time I'd seen a port flowed backwards. My head killed his head in reverse flow. After almost 25 years, I think I was 40-50 CFM LESS in reverse flow. That's big for those heads.

I always get a top cut. Even if it sinks the valves. I'd like to hear Warp and DV and get their thoughts on "sinking" valves to get a top cut.

Yes the Pontiac 400 would be an interesting one for back to back test and a few cam sizes due to the bigger valves. I think you would have to sink the valves to get a decent top cut on the flat chamber roof but I don't know that thats bad..

[GARY C]

Jay,
For me lift at TDC is a way to help quantify what low lift is for a given combination. Remember that there are people here who built a great variety / different types of engine and some could be running less than half the valve lift you are.

Stan

Very true, but what does the flow at tdc really have to do with?
So the lift during overlap, at tdc, is what defines the low lift flow point?
Why not 10* btdc?
Why not 5* btdc?
Or these same values atdc?
I feel people put too much concern in overlap itself. To me it is just kind of a necessary evil.
I know some like DV use it as a basis for cam selection but......?

Jay,
TDC is just a reference point and you can choice what ever one you like.

I picked TDC because it is a transition point / the piston is no going up and the piston is not going down and is seating there with zero velocity.

How in the world did overlap and DV come into this discussion?

Stan

Yes that and some cam mnf list lift at TDC in the general specs so it just seems like a good starting point as a different way to look at it.