Edelbrock 2.055 (30 degree back-cut) testing

[Dale Davies]

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Have you ever done any testing with a 30 degree seat & valve face? I know it's not the best HP setup but I read an article where Dulcich suggests it... He says it improves flow from .100-.400 without hurting flow at higher lift much.... He went on to point out the valve sees that .100-.400 range twice for every one time it sees max lift so gains down low can have a bigger effect than max lift flow... He only suggests doing it on the intake side.... I thought it was an interesting idea... Especially for guys like me who only run 550ish lift cams....

David Vizard discusses valve angles in his videos and his How to Port and Flow Test book. He mentions that Cup Car teams are using 50° to 55° seats. I do not remember if that is for intake, exhaust or both. He also mentions 30° intake seats do flow better especially at low lift, but 30° seats tend to bounce more.
For the Uncle Tony Mission Impossible 318 they are looking at 40° exhaust seats for improved low lift exhaust flow.
In one of his videos, David shows unshrouding valves using "flow balls" used as clearance guides. Port flow is area ruled at low lift. What this means is the flow through the port at low lift is not restricted by the port cross sectional area, but the area between the valve face and the seat. He starts by scribing the cylinder bore or gasket bore on the head deck, as this is do not exceed area for unshrouding. Now depending on the casting thickness, you can undercut the combustion chamber wall by the valve. David starts with a 1/4" ball welded or brazed to a length of welding rod. Lift the valve just enough the ball will pass through the seat area. Then check between the valve margin and casting wall. Where it will not pass, a little grinding is required. Do all cylinders with that, and then go to a 5/16" ball and do the same, working up to 1/2" clearance. Keep wall thickness in mind and do not grind through looking for that 1/2" clearance. DV goes through this on a SBF head but the principals are relevant.
Once you get to .27D of the valve head, the port area becomes the flow control factor. As DV relates, pick the low fruit first and work your way up. So this is the valve seats and the entry and exit 1/2" from the seat. Then generally the area by the valve stem and guide are next. Let the flow go the way it wants to go and you want to enhance flow on the cylinder wall side of the port by grinding on that side and grinding the port roof on the cylinder wall side. This enhances swirl which enhances combustion efficiency.
For the exhaust the quench area needs to be shaped to enhance exhaust flow directly out the exhaust port.

 

[Dale Davies]

I didn't think so. All the exhaust needs to do is get out.

Round off the cylinder side of the margin on the valve. Helps the exhaust get around the edge of the valve and reduces valve temperature, which is always good.

 

[Dale Davies]

It looks good on the flow numbers, but it actually HURTS power in most cases. Exhaust side that is

M

It looks good on the flow numbers, but it actually HURTS power in most cases. Exhaust side that is

Minimal change in exhaust flow, but in a running engine the backcut exhaust valve allows more reversion. When you get your exhaust pulses coming back up the header as a positive pressure or log manifolds, this allows hot exhaust back into the combustion chamber. This hirts the scavenge cycle and hot exhaust increases charge temperature prior to ignition this leads to retarding timing to prevent detonation.

 

[Mean416]

Guys talk about the back cut causing reversion and it actually costing power. I'm not saying they're wrong but I would be interested in seeing a back to back test with no other changes to see what the difference is. I bet most guys that make the claim haven't actually tested this. If anyone can reference something it would be great if you can share.

 

[Dale Davies]

It’s all about the shape. Vizard was big on 30 degree seats.

While you can’t ignore what goes on at .100 lift, the valve spends so little time at those lower lifts that it’s really hard to make big improvements in power focusing on flow down there.

How much flow can you gain when the valve is .100 or .200 off the seat? The curtain area is so small any gains will be small and may affect flow at lifts where the valve spends most of its time.

You also have to consider what the shape of the flow is getting around the valve with a 30 degree seat. Any time you flatten the seat angle, you force the air to head towards the chamber wall rather than into the chamber.

Visualize what the shape of the flow would be like (or draw it out if you like that better) With a 30, 45, 50, 52, 60, 62 or even a 65 degree seat.

The steeper the seat the more vertical the flow pattern around the valve is.

Another consideration DV brings up is dynamics. The 30° intake may flow more at low lift values. The Pontiacs were from when valve lifts rarely passed 0.400". The problems as you point out is the flow cone around the valve and valve bounce. DV relates that Cup Car teams have gone to 50° or 55° seats as the valves wedge into the seat without bounce. The steep seat angle centers the valve in the seat for tight valve seal. Those guys do not miss many tricks as the rules are so restrictive, pretty much more than F1. A 30° seat lets the valve sit where it comes to rest and the guide clearance can let the valve get caught up on one side and leak a bit on the other side. On a sedate grocery getter you would be hard pressed to notice.

 

[Rat Bastid]

Guys talk about the back cut causing reversion and it actually costing power. I'm not saying they're wrong but I would be interested in seeing a back to back test with no other changes to see what the difference is. I bet most guys that make the claim haven't actually tested this. If anyone can reference something it would be great if you can share.

I have tested it. One thing you can see when you have an issue is the intake ports, the intake runners and even in some cases the underside of the air cleaner lid will be sooty.

That is a sure sign of reversion. And it’s a power killer.

The other thing I constantly harp on is flowing both ports in reverse.

If you do something that increases reverse flow you can bet it will be a power loser.

You want the port to flow better forward than it does in reverse. And the further the two are apart, the more power you make.

I flowed all my ports in both directions. Certain back cuts on certain valves made more power. But it is valve specific.

 

[Rat Bastid]

Another consideration DV brings up is dynamics. The 30° intake may flow more at low lift values. The Pontiacs were from when valve lifts rarely passed 0.400". The problems as you point out is the flow cone around the valve and valve bounce. DV relates that Cup Car teams have gone to 50° or 55° seats as the valves wedge into the seat without bounce. The steep seat angle centers the valve in the seat for tight valve seal. Those guys do not miss many tricks as the rules are so restrictive, pretty much more than F1. A 30° seat lets the valve sit where it comes to rest and the guide clearance can let the valve get caught up on one side and leak a bit on the other side. On a sedate grocery getter you would be hard pressed to notice.

I use 50 degree seats on all my street/strip builds. Been doing it for years.

The shape is better than a 45 and far better than a 30.

The 30 degree seat is an example of flow numbers on a flow bench sending you down a loser rabbit hole.

Guys get way too wound up with what is happening at .050, .100 or even .150.

If you know what your valve opening is at TDC you can see they ain’t open very much and the piston is right in the way.

Thats a reason why piston shape and valve notch depth is so important.

 

[Dale Davies]

Guys talk about the back cut causing reversion and it actually costing power. I'm not saying they're wrong but I would be interested in seeing a back to back test with no other changes to see what the difference is. I bet most guys that make the claim haven't actually tested this. If anyone can reference something it would be great if you can share.

Watch David Vizard Powertec 10 Youtube videos. In one or two he references reversion. Combustion chamber face of the valve and not cutting a back cut on the exhaust are mentioned. David also mentions rounding the edge of the valve from the combustion chamber side to the margin to help the exhaust to not get caught on the square corner. This aids in keeping the valve cool. To prevent reversion it is probably a good idea to leave that little lip on the back side of the valve. It may help catching any reversion.

 

[Dale Davies]

I use 50 degree seats on all my street/strip builds. Been doing it for years.

The shape is better than a 45 and far better than a 30.

The 30 degree seat is an example of flow numbers on a flow bench sending you down a loser rabbit hole.

Guys get way too wound up with what is happening at .050, .100 or even .150.

If you know what your valve opening is at TDC you can see they ain’t open very much and the piston is right in the way.

Thats a reason why piston shape and valve notch depth is so important.

DV in his BBC book goes into piston porting. This is relieving the valve pockets in the piston crown while the piston is close to TDC and the cam is on overlap. You are correct. A bit of relieving those valve cutouts goes a long way to keep especially the intake from getting balled up against a 90° wall and fairly sharp edge to the crown.
I wonder what would be the flow change if you had the crank, rod and piston in a cylinder, and just the intake valve in the head. Set the flow bench up to suck on the exhaust port with the crank at say 10° or 15° ATDC where the intake valve and piston come into closest proximity. Perform the test with and unported piston, then relieve the piston and test again. This overlap period in the engine is very important to power developed.

 

[Mean416]

David Vizard is someone I respect. But I don't believe everything that comes out of his mouth as gospel. He's been hustling a bit of snake oil lately.

Taking my statement about reversion a bit further. Reversion, being what it is, also goes back into the intake manifold. You could also argue that the back cut on the intake valve makes reversion easier too. It's not like it just stops at the intake valve.

 

[Dale Davies]

David Vizard is someone I respect. But I don't believe everything that comes out of his mouth as gospel. He's been hustling a bit of snake oil lately.

Taking my statement about reversion a bit further. Reversion, being what it is, also goes back into the intake manifold. You could also argue that the back cut on the intake valve makes reversion easier too. It's not like it just stops at the intake valve.

What is required is pressure wave or pulse tuning. With that we want the exhaust pressure pulse when the exhaust valve opens to do is travel rapidly down the header or exhaust. Log manifolds do not aid this well by virtue of not separating the exhaust ports. When tuning a header and the collector along with a resonator we are trying to get the 3rd or 4th negative pulse traveling back up the header to arrive at the almost closed exhaust valve just prior to the intake valve opening. We want to prevent the positive pressure waves that come back up the exhaust between the negative pressure pulses from getting past the exhaust valve. Granted there will likely be some, but that is what we try to reduce with anti reversion tactics.
Now the negative pulses we eant to let get past the exhaust valve to create negative pressure in the cylinder just prior to and as the intake valve opens. This creates a big pressure difference across the intake valve curtail area as the valve just lifts off its seat. This helps innitiate intake flow into the cylinder even prior to the piston reaching TDC of the exhaust stroke. This getting the intake air mass moving early past the valve and seat helps purge any residual exhaust out the exhaust valve. If the intake and exhaust pressure pulse tuning is correct there should be no or very little reversion.
Regarding what DV teaches, I will listen as a proven resume of about 60 years with clients in Cup Car and F1 proves he knows a thing or two about engines and car setup. He admits he is still learning, but when his knowledge is far advanced from mine, wisdom tells me to be silent and listen.

 

[replicaracer43]

What is required is pressure wave or pulse tuning. With that we want the exhaust pressure pulse when the exhaust valve opens to do is travel rapidly down the header or exhaust. Log manifolds do not aid this well by virtue of not separating the exhaust ports. When tuning a header and the collector along with a resonator we are trying to get the 3rd or 4th negative pulse traveling back up the header to arrive at the almost closed exhaust valve just prior to the intake valve opening. We want to prevent the positive pressure waves that come back up the exhaust between the negative pressure pulses from getting past the exhaust valve. Granted there will likely be some, but that is what we try to reduce with anti reversion tactics.
Now the negative pulses we eant to let get past the exhaust valve to create negative pressure in the cylinder just prior to and as the intake valve opens. This creates a big pressure difference across the intake valve curtail area as the valve just lifts off its seat. This helps innitiate intake flow into the cylinder even prior to the piston reaching TDC of the exhaust stroke. This getting the intake air mass moving early past the valve and seat helps purge any residual exhaust out the exhaust valve. If the intake and exhaust pressure pulse tuning is correct there should be no or very little reversion.
Regarding what DV teaches, I will listen as a proven resume of about 60 years with clients in Cup Car and F1 proves he knows a thing or two about engines and car setup. He admits he is still learning, but when his knowledge is far advanced from mine, wisdom tells me to be silent and listen.

I'm listening to what your saying, and picking up some good info. But my problem is, like you say, his "60 years" of experience. I have looked extensively, and I cannot find any real world proof that he has been involved in anything other than a early 70s ford pinto 4 cylinder, and in the 80s, some obscure European Chrysler 4 cylinder. Maybe it's all top secret. But as soon as he hopped on the UTG bandwagon, my spidey senses went up.

 

[Dale Davies]

I'm listening to what your saying, and picking up some good info. But my problem is, like you say, his "60 years" of experience. I have looked extensively, and I cannot find any real world proof that he has been involved in anything other than a early 70s ford pinto 4 cylinder, and in the 80s, some obscure European Chrysler 4 cylinder. Maybe it's all top secret. But as soon as he hopped on the UTG bandwagon, my spidey senses went up.

Tuning and racing Minis in the Uk for ever ago. How many magazine articles did he write? Much of his work with factories and yop race teams would have at the time been classified.
UTG, Unity Motorsports and DV are in the same area and seem to share some common ground.
You can chose to agree or disagree with them. Like most of us they don't agree all the time.
Bottom line; your car , your dime, do what satisfies you.

 

[replicaracer43]

I'm always skeptical of "story" writers. If he is so bright, and capable, why isn't he doing the r&d head porting, and intake porting on that "save the children" charity 318 build hes promoting? The whole thing seems odd

 

[92b]

It’s all about the shape. Vizard was big on 30 degree seats.

While you can’t ignore what goes on at .100 lift, the valve spends so little time at those lower lifts that it’s really hard to make big improvements in power focusing on flow down there.

How much flow can you gain when the valve is .100 or .200 off the seat? The curtain area is so small any gains will be small and may affect flow at lifts where the valve spends most of its time.

You also have to consider what the shape of the flow is getting around the valve with a 30 degree seat. Any time you flatten the seat angle, you force the air to head towards the chamber wall rather than into the chamber.

Visualize what the shape of the flow would be like (or draw it out if you like that better) With a 30, 45, 50, 52, 60, 62 or even a 65 degree seat.

The steeper the seat the more vertical the flow pattern around the valve is.

Would steeper angles benefit more from a port that has a more straight on approach to the valve from the intake runner? And less so from a stock head where the floor is low and flat and no room for a radius on the short side? See picture

 

[Dale Davies]

Would steeper angles benefit more from a port that has a more straight on approach to the valve from the intake runner? And less so from a stock head where the floor is low and flat and no room for a radius on the short side? See picture

View attachment 1716052053

There are so many variables to take into account. From the Cup car aspect, the steeper valve seat angle wedges the valve tighter into the seat without bounce, providing better valve seal. I would think this is a benefit on engines with high valve lift and aftermarket raised port heads.

 

[Rat Bastid]

Would steeper angles benefit more from a port that has a more straight on approach to the valve from the intake runner? And less so from a stock head where the floor is low and flat and no room for a radius on the short side? See picture

View attachment 1716052053

Yes. I use a 48 degree seat on 23 degree chevy stuff.

The steeper seat has far more to do with flow and the shape of the seat/throat than it does with sealing.

 

[MOPAROFFICIAL]

I’m struggling with my .300 flow number for the first time in years but that’s for another post. While searching for that lift issue I had a few extra minutes before I quit so I did back to back tests with two brand new 2.055 Ferrea intake valves. I’m sure I did this many many years ago but I keep better notes now so I will add this to them. I had always heard it help low to mid numbers and may hurt high lift numbers but this is the gain from .100-.600 lift.

.100——-+6
.200——-+7
.300——-+8
.350——-+7
.400——-+5
.450———+5
.500——-+3
.550———+4
.600——-+4

Gains made by adding 30 degree back cut. Looks about right. Try the engine pro valves if you're ever curious enough to.

 

[Mean416]

What is required is pressure wave or pulse tuning. With that we want the exhaust pressure pulse when the exhaust valve opens to do is travel rapidly down the header or exhaust. Log manifolds do not aid this well by virtue of not separating the exhaust ports. When tuning a header and the collector along with a resonator we are trying to get the 3rd or 4th negative pulse traveling back up the header to arrive at the almost closed exhaust valve just prior to the intake valve opening. We want to prevent the positive pressure waves that come back up the exhaust between the negative pressure pulses from getting past the exhaust valve. Granted there will likely be some, but that is what we try to reduce with anti reversion tactics.
Now the negative pulses we eant to let get past the exhaust valve to create negative pressure in the cylinder just prior to and as the intake valve opens. This creates a big pressure difference across the intake valve curtail area as the valve just lifts off its seat. This helps innitiate intake flow into the cylinder even prior to the piston reaching TDC of the exhaust stroke. This getting the intake air mass moving early past the valve and seat helps purge any residual exhaust out the exhaust valve. If the intake and exhaust pressure pulse tuning is correct there should be no or very little reversion.
Regarding what DV teaches, I will listen as a proven resume of about 60 years with clients in Cup Car and F1 proves he knows a thing or two about engines and car setup. He admits he is still learning, but when his knowledge is far advanced from mine, wisdom tells me to be silent and listen.

Not a thing you said here is addressing my point.

And I actually don't believe he had much if anything to do with F1 engines.

 

[MOPAROFFICIAL]

Yes. I use a 48 degree seat on 23 degree chevy stuff.

The steeper seat has far more to do with flow and the shape of the seat/throat than it does with sealing 'longevity'.

Depending on the heads in general , be it chamber, pocket etc.. some angles are better than others for flow. Long service life is another story for some but that doesn't matter in competition builds so it gets one of those stay in your lane type responses when asked by mainly street usage folks, but 48 is still street friendly and a 39 above it would be nice. The valves are one and done but who cares. they can be had cheap.

 

[Dale Davies]

Not a thing you said here is addressing my point.

And I actually don't believe he had much if anything to do with F1 engines.

Carry on.