50 degree valve seats in modern hot street builds: is it finally time?

[Warp Speed]

Warpspeed, did you miss my question about post race valve lash numbers ?? Mark H.

No, I got it..........

[DrillDawg]

To Frankshaft......I seen that, sorry to pick on you, but if enough people would call the sheriff instead of trying to handle it on their own even a good guy could get in trouble.

[pamotorman]

http://www.enginelabs.com/features/valv ... rk-engine/ here is a write up

[CGT]

Why "mitigate" one of the benefits of the steeper seats? High lift flow improvement is not the reason for steep seats helping HP. IMO the low lift (or very low lift) curtain area change is more responsible than any gains at high lift.

Certainly is a nice side effect isn't it?

[user-30563]

So has anyone actually 45º a set of heads, pulled them off and 50º them and seen the results?

Or is it a can of worms that there is no real answer because you would need to change cams and maybe something else? So all we really have is theory..

Is this fair, or is there documented proof?

[Carnut1]

I have had a few conversations with DV on the subject. What he did was take an old 18 degree edelbrock head, port a decent intake runner and designed replacable seats to install and then we flow tested and analized through his iop program. He decided to make a trick less than 40 degree seat, a 45 degree seat, and a 55 degree seat. The results were very interesting. Thanks, Charlie

[NewbVetteGuy]

Yes, makes one think: "As steep and narrow as metallurgy will support for the race distance."

Why do you think a narrower seat is preferred?

Rick

Just that while the angle and width both contribute to contact pressure, a narrower seat works to mitigate the reduced curtain area of a steeper angle.

Bill,

Is there a calculation that takes into effect things like seat angle, width, close pressure, etc.. to estimate contact pressure or is it just a rule-of-thumb kinda deal that you keep in the back of your mind?


Adam

[NewbVetteGuy]

An amazing conversation so far, I still have a few questions:


Longevity: What are the primary factors that can increase / decrease longevity when going with steeper valve angles like this? (And is each one a major factor or a minor factor?)

• *spring closed pressure
  *seat width
  *exhaust close velocity (aggressiveness of the exhaust lobe close & rocker ratio- especially from 0.050 - 0.006 / 0.006 to close???)
  *seat materials/ metallurgy

Assuming that you make some reasonable trade-offs focused on longevity with a 50 degree seat angle, what's a reasonable, street miles lifetime expectation?


Moving to a 50 degree seat @ Rebuild Time:
Are there any major considerations / concerns when moving to a 50 degree seat @ rebuild time?
If I wanted to have my set of off-the-shelf Profiler heads rebuilt, can the stock steel seats just be reground with a new set of angles and have either new valves or reground valves installed?

-I've picked up whispers and rumors that I don't fully understand that this might not be super straight forward and might make the valve recessed too much in the head?!?



Anyone have a before and after set of dyno sheets, that starts at a reasonably low RPM, and shows a before and after with a typical 45 degree seat angle setup and a typical 50 degree seat angle setup? (The HotRod article got close but didn't show any lower RPM data)




Adam

[NewbVetteGuy]

So has anyone actually 45º a set of heads, pulled them off and 50º them and seen the results?

THIS!

The Hotrod article linked to below, does what you're asking, but the dyno results were only posted from 3,500 RPM and up. I'm curious what the torque looks like below this point.

What's the torque difference like at typical street TC stall speeds? (2,500-3,000 RPM) --If it's improved here, then the performance benefits are even more applicable to street builds, IMHO.

What's the torque look like at highway cruise? -Again, if the torque is improved even down this low, the combo of extra torque at highway cruise RPM and less reversion should mean more MPG, too and again, even more beneficial for modern street builds where fuel economy may determine how often you choose to/ can afford to, drive it.


The 50 degree seat angles have a reputation for hurting at low lift (and in some internet lore, low RPMs) and helping at high lift and high RPMs. I'm VERY interested in what happens to lower RPM torque when moving from 45-50.



Adam

[NewbVetteGuy]

You will get different theory's on this, Gary Theory, on the intake your reducing reversion while taking advantage of more aggressive lobe profiles or longer lobes with more area. On the ex you don't dump compression pressure on opening and your reducing reversion at overlap.

Related (ish) Question: Will the steeper valve angle on the exhaust cause a less intense pressure wave in the exhaust? -I thought that the high-pressure blast into the exhaust right when the exhaust valve first opens is one of the more important factors in getting strong exhaust wave action; so I'm wondering out loud if this could be a bad thing with a tuned exhaust length.

If a lower valve angle in the exhaust means a more intense wave and better scavenging, I'd think you'd want to leave the exhaust valve alone with a tuned exhaust length and use other Anti-Reversion techniques there.



Adam

[NewbVetteGuy]

Keep in mind that if your port work and cam are optimized for a 45* seat just switching to a 50* could loose power, you always run that risk when changing something on a combo.
I would focus on the one you are going to run.

Gary, can you elaborate on this? (I think I'm too dumb to understand what you mean by it without further explanation.)

What aspect of a cam should change when going with a 50 degree seat vs a 45 degree seat?
-You wouldn't change the timing of any of the valve events, would you?


My understanding: The change that is occurring from an airflow perspective of going with a 50 degree seat is that you're decreasing the flow across the bottom of your lift curve, in exchange for more flow (and velocity as the CSA doesn't change) higher up in your lift curve; you make the cam behave like a smaller duration cam at overlap and low lifts, and behave like one that has even more lift at higher lifts.

I could see scenarios where you would NOT come out ahead at that game (you lose more than you gain), but with fast lobes, decent rocker ratios, and a good amount of valve lift-you're starting from a cam that's most likely to see more gain than loss, right? <-I'm trying to pre-set the parameters in which I think that you'd gain more than you'd lose.


Adam

[Frankshaft]

To answer above, you could change cams to compliment the 50 degree seat more. For a "street" car, you could get away with a more radical cam as far as overlap/duration wise, without losing the "bottom end" drivability. The engine would see the steep seat as less overlap, or have the same effect. At Least that's how it feels to the driver. With no loss and a gain in mid and top end. It " comes on the cam" sooner. Trying to describe it how most can understand it. It's doesn't need to be so complicated.

It makes more tq starting sooner, and it makes more mid/ peak because the extra airflow thru same cross section, assuming that wasn't charged, increases velocity and fills cylinder more at that point, and, because it flows more, and it improves other Dynamics at play, other than flow, makes more Horsepower. Win win win.

Without quoting above, a 50 degree seat has exactly the opposite effect as most think. Same with a " low lift flow" enhancing valve job. And, the reason a "low lift flow" enhancing valve job is not good for the opposite effect it has to how the engine reacts to it, because the "shape" of it kills high rpm Dynamics.

[CGT]

(and velocity as the CSA doesn't change)

The window CSA with the steeper valve seat will now be smaller even at higher lifts. So..even the same flow as the shallower seat is now at a higher window DC. Smaller, faster window with less reversion, both times in the cycle when the piston is going the wrong way....IVO BTDC and IVC ABDC as well.

[HDBD]

Besides longevity what is the downside.

[NewbVetteGuy]

(and velocity as the CSA doesn't change)

The window CSA with the steeper valve seat will now be smaller even at higher lifts. So..even the same flow as the shallower seat is now at a higher window DC. Smaller, faster window with less reversion, both times in the cycle when the piston is going the wrong way....IVO BTDC and IVC ABDC.

I need to go back and learn a few basic things before I think I can understand this statement fully, but I think I get the basics.

-The steeper the valve angle, the narrower the space that the air has to travel between the valve seat and the valve -so the angle DOES change the cross sectional area of the air going past the valve, and therefore increases the air's velocity going into the chamber. (Did I get that right?)

-I keep thinking of the pinch point along the head's intake tract as the "min CSA" point of the entire airflow path and forget about the valve curtain area. I need to go back and understand at what points the "bottleneck" moves from the valve curtain area to the pinch point of the intake tract. I've been avoiding understanding it in too much detail but I think it's time to go back and do my homework...



Adam