Valve angles

[SchmidtMotorWorks]

It seems that smaller valve angles are key to high performance however few engines have valve angles less than 10 degrees. I wonder what dissadvantages arrise from angles less than 10 degrees.

Some guesses are:
Valve pocket to ring groove interference.
Centralized combustion volume.

Does anyone know of any high performance engines with vertical valves? I think some old Jaguar engines had vertical valves.

[beth]

The cylinder head has to be lots taller and the valves longer.

[bobqzzi]

If the valve is vertical and of maximum size, wouldn't cylinder wall shrouding be a factor?

[Engineguy]

Some guesses are:
Valve pocket to ring groove interference.

That depends on the rotation point that you unwind the valve angle about. If your rotation point is to the right of point A, yes, the widest part of the valve pocket gets deeper and threatens the ring groove... but if the rotation point is at or to the left of point A the pocket tends toward disappearance.

18° shown

[Engineguy]

The cylinder head has to be lots taller and the valves longer.

A valve of 5.45" length, rotated from 18° to vertical only adds 0.27" to head height.

I don't see any reason the valves need to be longer.

The LS7 valve angle is 12° (compared to LS6 at 15°), and looking at cross-section drawings I don't see any obstacles, be they in port location or pushrod/rocker packaging, to going all the way... that's not to say it is certain there is an advantage left to doing so. I think the greatest part of the benefit has been in going from the horrid 23° to less than half that, but I can see where a few more degrees might still help.

[SWB]

Remember too that the more vertical the valve the smaller the effective size can be made. If you stand them up 90* to the deck then you're stuck with a certain size which can be made to flow effectively. By canting them off in one or better yet, two directions, you can design a much more effective and flow supportive geometry for them to work within. Therefore I think somewhere around 12 degrees one way and whatever (4-5) the other is what is nearly optimal from a total flow standpoint. It's just one big compromise all around, so when you see a lot of the same thing, it's probably because everyone has settled within that range. I don't think the people designing these top level racing heads are idiots or ignoramuses.

SWB

[Engineguy]

Remember too that the more vertical the valve the smaller the effective size can be made. If you stand them up 90* to the deck then you're stuck with a certain size which can be made to flow effectively. By canting them off in one or better yet, two directions, you can design a much more effective and flow supportive geometry for them to work within. Therefore I think somewhere around 12 degrees one way and whatever (4-5) the other is what is nearly optimal from a total flow standpoint. It's just one big compromise all around, so when you see a lot of the same thing, it's probably because everyone has settled within that range. I don't think the people designing these top level racing heads are idiots or ignoramuses.
SWB

The major angle of a 2-valve wedge head neither allows larger valves or unshrouds the valve from the bore... it's not even close to the cylinder wall on that side. I'm not calling anyone an idiot... it is in fact their trend (23 > 18 > 15 > 12) that causes the speculation about the possibilities of even lesser angle.

Side cant (angle between valve stems) does to a small degree allow both slightly larger valves and unshrouding from the cylinder wall, but of course there are downsides if taken too far (too hemi).

Even most serious racing heads made for 2-valve production-based engines make concessions to existing architecture (cam location and pushrod angles, in and ex manifold flange general location, rocker simplicity). It's not being a heretic to question the status quo bestowed on us by the cylinder head gods... it's how progress is made.

[SchmidtMotorWorks]

I don't think the people designing these top level racing heads are idiots or ignoramuses.

Agreed, but Miller, Offenhauser, Drake, Goosen made good power with 36 degree valve angles. I just haven't seen anything in lower range that we can point to and say, "yep that doesn't work well because ABC".

[SchmidtMotorWorks]

That depends on the rotation point that you unwind the valve angle about.

Engine Guy, when I mentioned valve pocket to ring groove problems, I was thinking of hemi heads, I should have been more clear.

[hydra]

It is my observation that state of the art NA engines, whether wedge, hemi, or 4V, have the valves inclined in the 10-15 degree range, which leads me to believe that the ideal port/cylinder axis inclination is around 45 degrees...

[Ron E]

Another benefit of the continued reduction in valve angles is, the long-side vs short-side geometry from bowl to chamber becomes less different. Fuel-dispersion can be (not an automatic result, but "can be") improved with reduced valve angles.

[MadBill]

The last 'clean screen' pure race pushrod V-8 I'm aware of was the '94 Indy Penske/M-B. Wonder what their combustion chamber looked like?

BTW, at the time it was touted as a major miracle that M-B signed on in Novemeber '93 yet finshed 1-2-3 at Indy only 6 months later. It wasn't actaully that big a deal, since GM had just pulled out that summer, having previously bankrolled and co-developed everything except the logo on the rocker covers...
http://www.motorsport.com/news/article. ... S=CHAMPCAR

[Ron E]

MadBill, do you mean that Ilmore 2V? It's a slightly twisted hemi. Each side of the chamber is scalloped around it's valve. It has a slight figure 8 form. Valve angle looks to be about 15 degrees (both). Straight round intake ports, but they do transition into a wider floor at the gentle short-turn. It's , I believe" a 72 degree (banks) motor, and even with the narrow banks the intake ports are almost vertical. Bank-angle, Cam placement and valve train result in intake and exhaust rockers very close to the same length.

It's all laid out in a book on Ilmor. I have it....somewhere. I'll find and get you the name and publisher. It gives the story, along with the many "snags" they ran into, before and after on this, and some others. That motor is a work of art!

[beth]

The cylinder head has to be lots taller and the valves longer.

A valve of 5.45" length, rotated from 18° to vertical only adds 0.27" to head height.

I don't see any reason the valves need to be longer.

Yes, you can change the angle without changing valve length. But if the port is going to work, it has to be lots higher or the turn angle is too sharp. The higher port and straighter section before the seat required with this design are what make the head and valve longer.

[Gary Blair]

From a Ford perspective the Cleveland is 9.5 X 3.5

The 429/460 is 9.5 X 5.0

The Yates SB and BB are 7.5 X 0.00

All of these heads work very well with shallow valve inclines.

The Yates is rotated 23 degrees and has much less shrouding than a conventional inline wedge.

Some NHRA Pro Stock heads may be quite shallow.