Reduced low lift flow from porting...

[PRH]

I asked this before on one of the 50* seat threads........ never got a response..... I’ll try it again here.......

If you have a head for a particular combo that’s pretty well undersized for both the displacement, and how the motor is being used....... and you put a 45* or 50* seat on it....... and the 50* seat flows less at all lifts up to and including .850 lift......... and the valve never goes beyond .750 lift........ how is this beneficial to making more power?
The motor is starved for flow and area....... I don’t see how changing the seat to 50* and further reducing the flow is going to make more power.

Explain what I’m missing.

[ClassAct]

I asked this before on one of the 50* seat threads........ never got a response..... I’ll try it again here.......

If you have a head for a particular combo that’s pretty well undersized for both the displacement, and how the motor is being used....... and you put a 45* or 50* seat on it....... and the 50* seat flows less at all lifts up to and including .850 lift......... and the valve never goes beyond .750 lift........ how is this beneficial to making more power?
The motor is starved for flow and area....... I don’t see how changing the seat to 50* and further reducing the flow is going to make more power.

Explain what I’m missing.

I'll take a shot at it.

I'll use my current DD 340 as an example. 11:1 CR. Strip Dominator. 255/255 at .050, .620.620 on a 105 LSA installed at 105.

I'm using two different casting. I had both matching castings done, except for a nice little clean up with a paper roll and found a pin hole in 1 freaking bowl. So I had to start over and use a different casting. One is an X head IIRC and the other is a smog head.

Since I have been using other than 45 degree seats since about 2000, I decided to use them on mine. Knowing I've used a 2.08 valve many times with a 45, and knowing that valve is too big to be fed by that little port, and getting enough CSA is nearly impossible with a 2.02 valve, I decided to stay with a 2.02 valve. That way, I can have the shape and bowl percentage of a 50, without trying to feed a 2.08 valve with that shitty port.

I forget the actual flow numbers, but they topped out at about 265 at .550. I guess I could go find the flow sheet but that's pretty damn close. I suspect I could have used a 1.980 intake and been even better off.

Now I forgot the question you asked. Ok, how is losing flow making more power. Because, IMO a flow bench isn't measuring air like the engine sees. I think I flowed these heads as high as 48 inches, and in doing the math, they lost less flow at 45 inches with the 50 than they did with the 45. And the reverse flow numbers were even better with the 50.

I think there are two major mistakes when doing a 50 and not finding power. Three really. One is cam timing. A 50 degree seat should have different timing numbers than a 45. Two is the top cut discussed earlier. Fear of sinking the valve (on any valve job it's bad but no top cut on a 50 or 55 is a killer) keeps guys from getting a good top cut in. And third, along those same lines is using as big a valve as you would with a 45 seat. The 50 doesn't require as much valve size as a 45 and I think some guys lose more "low lift" flow with a 50 than need be, all because the valve is too damn big. A port area limited head doesn't need as big a valve as does a head where you can get the CSA that you really need.

That's the best answer I have. But, like I've said, there is more to flowing a set of heads than just the forward numbers at 28 inches. And in my experience, if you get the 50 degree seat correct, it's better than the 45 everywhere, except maybe in flow numbers at 28 inches.

I have no doubt, with a 45 and a 2.055 valve I could have hit 275, maybe 280 if I was giving it the triple nipple. But everywhere else, the head would have been less. As in how quickly the poet breaks over, and how far it drops and break over. And how much more noise the 45 makes compared to the 50. And obviously, the reverse flow numbers show the 50 far better than a 45. All added up, that's why I chose a 50 whenever I can. If, and it's a big IF, you can get the correct sized valve for the CSA you can get.

Of course, I did a head for that 2.3 Ford or whatever they are with a 50 and it was 20 HP better than the exact same engine with a 45. On the track the 50 would drag the 45. We even switched drivers (my driver was better than the car with the 45) and my driver couldn't make the 45 seat engine run the same, but the other driver was within a tenth of my drivers lap times in the 50 degree car. And we spent an entire test day making both cars better for the other drive. In the end, they both were much faster in the 50 degree seat car. These were some kind of pavement cars and the heads were some CNC Esslinger head that I had to do some porting on to fix. And, I almost forgot, in my experience, a nail head valve is a power killer with a steeper than 45 degree seat.

Hope that helps PRH. It's the best answer my limited education allows.

[PRH]

I don’t think I’m getting the point across about the waaaaay undersized heads.

Think......220cc intake ports flowing about 300 on 14.5:1 540ci.

In this case, we’re dealing with 2 pair of heads.
One set with 45* seats, the other with 50* seats.

The set with the 50* seats was done by an extremely well known engine builder.
The other test head was a head I had here with 45* seats.

They had been put on the motor as an upgrade over another set of heads that had 45* seats.
They had a little mishap with the car, one head comes to me just to make sure there are no issues.
I pull it apart, look it over, take some measurements, notice the steep valve seats.
Aside from the steep seats I see nothing unusual...... and dimensionally its extremely close to another one of that same casting I have in the shop.
So, I flow it.
It flows less at all lifts than the 45* version I have in the shop.

I just don’t see how losing flow throughout the entire lift curve, on a motor that is in real need of additional flow ends up as a plus.

Also, up to this point, the new heads have not gone as quick(or made as much power on the dyno) as the old set of heads that have 45* seats....... which were also done by the same engine builder.

[Carnut1]

Good post Class.

[SpeierRacingHeads]

I've seen some guys blend 10+ right out of a valve job!

[ptuomov]

Very good info and thoughts on this thread.

Somewhat tangentially related, this summer we are planning to do five long blocks for turbo conversion. Need to buy two more good cores before that can start. These are 5L V8s with 4V heads that will redline at 7000 rpm. Since the heads flow almost 300 CFM @ 28” stock, the head is not a limiting factor with 7000 rpm times 620cv/38cid cylinder. For reliability reasons, these will get wide 45-degree seats. However, given that reliability consideration, what else can be done to reduce the reverse flow of intake and exhaust valves? It’s ok or even preferable to sink the valves to the factory wear limit as these heads will run hydraulic bucket lifters and they appear to me most consistent when relatively compressed.

So how to reduce reverse flow, especially at overlap, when one is also looking for extreme reliability?

[travis]

So let me drag this post back down to MY reality for a minute...

148cc port, average CSA 1.85”, 1.94” valve with very little throat after blending in some rough bowl hog work. Peak flow 207cfm at .500” lift. Would you use a 45 or a 50 seat?

Now change to a 2.00” intake valve just to try to get some throat, taking just a tiny bit more out of the fastest parts of the port, would you use a 45 or a 50?

I’ve got a couple of hft cams I want to try just because they are a little different than anything I’ve tried before. One is 278@.006, 220@.050, on a 108. The other is 275@.006, 225@.050, on a 106. Overlap is almost identical. Would you lean towards the 50 seat since both are maybe a little big for the application? What if instead I used a HR 260@.006, 206@.050, .533 lift on a 110 lsa. Would that change your opinion on the seat angle?

[SpeierRacingHeads]

So let me drag this post back down to MY reality for a minute...

148cc port, average CSA 1.85”, 1.94” valve with very little throat after blending in some rough bowl hog work. Peak flow 207cfm at .500” lift. Would you use a 45 or a 50 seat?

Now change to a 2.00” intake valve just to try to get some throat, taking just a tiny bit more out of the fastest parts of the port, would you use a 45 or a 50?

I’ve got a couple of hft cams I want to try just because they are a little different than anything I’ve tried before. One is 278@.006, 220@.050, on a 108. The other is 275@.006, 225@.050, on a 106. Overlap is almost identical. Would you lean towards the 50 seat since both are maybe a little big for the application? What if instead I used a HR 260@.006, 206@.050, .533 lift on a 110 lsa. Would that change your opinion on the seat angle?

Myself it it was here, I would put a 45º on it. I can still get you a 91.5% throat without talking all the bottom cuts away.

[SpeierRacingHeads]

Here is an example. This is a 113 head with a 2.00 valve, 45 degree and a 1.830 throat.
The exhaust is a shelf Sunnen 042, 45 degree.

[ClassAct]

So let me drag this post back down to MY reality for a minute...

148cc port, average CSA 1.85”, 1.94” valve with very little throat after blending in some rough bowl hog work. Peak flow 207cfm at .500” lift. Would you use a 45 or a 50 seat?

Now change to a 2.00” intake valve just to try to get some throat, taking just a tiny bit more out of the fastest parts of the port, would you use a 45 or a 50?

I’ve got a couple of hft cams I want to try just because they are a little different than anything I’ve tried before. One is 278@.006, 220@.050, on a 108. The other is 275@.006, 225@.050, on a 106. Overlap is almost identical. Would you lean towards the 50 seat since both are maybe a little big for the application? What if instead I used a HR 260@.006, 206@.050, .533 lift on a 110 lsa. Would that change your opinion on the seat angle?

Myself it it was here, I would put a 45º on it. I can still get you a 91.5% throat without talking all the bottom cuts away.

I agree with Chad. What you have done is what many do. I personally don't like a 45 seat with a bowl much over 88%. I can't get what I think is appropriate for a valve job on it, with making compromises I don't like.

If you can get a 45 on it at that bowl percentage, go for it. But it's hard to do without making the bottom cuts so narrow the effectively become a radius and then all bets are off.

[ClassAct]

I don’t think I’m getting the point across about the waaaaay undersized heads.

Think......220cc intake ports flowing about 300 on 14.5:1 540ci.

In this case, we’re dealing with 2 pair of heads.
One set with 45* seats, the other with 50* seats.

The set with the 50* seats was done by an extremely well known engine builder.
The other test head was a head I had here with 45* seats.

They had been put on the motor as an upgrade over another set of heads that had 45* seats.
They had a little mishap with the car, one head comes to me just to make sure there are no issues.
I pull it apart, look it over, take some measurements, notice the steep valve seats.
Aside from the steep seats I see nothing unusual...... and dimensionally its extremely close to another one of that same casting I have in the shop.
So, I flow it.
It flows less at all lifts than the 45* version I have in the shop.

I just don’t see how losing flow throughout the entire lift curve, on a motor that is in real need of additional flow ends up as a plus.

Also, up to this point, the new heads have not gone as quick(or made as much power on the dyno) as the old set of heads that have 45* seats....... which were also done by the same engine builder.

Are they both using the same cam? I suspect the 50 degree engine needs more total duration with much less LSA. Off the top of my head, I wouldn't be surprised that the 50 would need an LSA of 109, maybe 110.

Why such small heads on a 540?

[Warp Speed]

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

Ok, I understand now, was just asking for clarification, as I really didn't know where you were going.
The reason I brought overlap into it, is because it seems to be uber important around here, and figured that was what you were referring to. I gave the DV example of how it is sometimes used, both by him and others.
Is that ok?

[travis]

Myself it it was here, I would put a 45º on it. I can still get you a 91.5% throat without talking all the bottom cuts away.

I agree with Chad. What you have done is what many do. I personally don't like a 45 seat with a bowl much over 88%. I can't get what I think is appropriate for a valve job on it, with making compromises I don't like.

If you can get a 45 on it at that bowl percentage, go for it. But it's hard to do without making the bottom cuts so narrow the effectively become a radius and then all bets are off.

The bowl hog wasn’t my doing, they was purchased this way. I don’t know much but I know not to hack the bowls out like was done. The bowl was very rough...that’s the only reason I did what I did.

With as small as the bowls and valves are on these, would the lack of throat really be a problem? I’ve noticed on some others ported stock ford stuff that the bottom cut is usually pretty small.

[PRH]

Why such small heads on a 540?

It’s the only head they can run.

I’m not really looking for suggestions on reworking the combo...... I’m asking “why” the lower flowing 50* heads on a combo like this are supposed to be superior.
Not examples of what happened on some other combo when the seat angles were changed, but specifically what about using steeper than 45* seats would result in the engine making more power, in a combo that has grossly undersized heads, in terms of area and flow...... when utilizing the steep angle results in less flow across the board.

The new 50* heads were done to be a bolt on upgrade by the extremely well known and highly respected engine builder........ to replace the existing heads with 45* seats, also done by the same engine builder.
Discussions about whether or not the current cam was suitable or not were had....... a new cam was not deemed a requirement for the new heads to work.

So far, they have not shown any improvement on the dyno or in the car.

After I flowed them my response was....... well, they don’t flow as good.
But, I keep being told that despite the lesser flow at all lifts...... they are better.

So, my question is.......”why” is that better?

[modok]

"heads too small"
What part of the heads is too small specificaly?
If it's not the valve, then i don't see any reason the steep seat would be better.