The Road to Drag Week 2014 - May 11

[jayb]

I seen a couple on youtube  heres one Jay  https://www.youtube.com/watch?v=yVwzXeAtEHg

Thanks Dave, that is one of Bill Conley's videos.  Probably one of my heads, too LOL!  I've seen most of those.  I thought Doug meant he saw one where the valve head was moving around, so it would have had to have been taken on a spintron machine, looking up into the bore towards the combustion chamber.  Something like that would be very interesting to see...

[sumfoo1]

damn i want a cammer so bad....

[cjshaker]

Jay, I'll see if I can locate them. They were not Bills videos, I'm familiar with them. And yes, one was of the spring assembly, but the other was from inside the chamber, level with the valve. A hole was drilled in the head to get the proper angle. Unfortunately I didn't bookmark them, and I ran across the videos while studying valvetrain stability, since that's where most engine failures stem from.

I believe the problem is pretty universal in high performance engines. Just not previously verified due to lack of technology to confirm the issue. I'm sure that small stem valves make it worse, as would cut down valve guides to aid flow, so it's just a factor one has to live with and account for when determining clearances. My own theory is that coil springs by nature dont apply an even force around the circumference of the base or top. You can see this when you squeeze a lighter spring between your fingers. It wants to 'squeeze' out in one direction...a byproduct of its coils. Add a rocker applying uneven pressure as it sweeps across it's arc of travel and it just compounds the issue. The only way I've seen to control the problem is to go with slide valve or air actuator technology, and that's reserved for F1 stuff.

[jayb]

Thanks Doug, I appreciate you checking into that.  FWIW the SOHC may be more prone to that problem than other engines, because percentage wise less of the guide resides in the main head area, and more protrudes into the port.  On my engine of course the aluminum support in the port for the guide has been reduced in size, and the OD of the guide itself has been tapered as it gets close to the end, so all this would work against stability of the end of the valve in a dynamic situation.  Maybe this is the explanation for the valve to piston contact I saw on the previous incarnation of the engine...

[TomP]

All this stuff makes me want a Cammer less, not more! It sounds like they are overly complicated and have real limitations to cam size. The fact Jay is making as much power as he does is amazing.

[jayb]

Tom, you are spot-on about the limitations of the SOHC.  The biggest one is that the cam lobes have to rotate directly under the rocker arms.  This limits the size of the lobes if you keep the stock base circle on the cams, and as soon as you decrease the base circle size to get more lift, you end up adding valvetrain instability.  It is a real conundrum with those engines.  For a while I was working on a high ratio rocker for the SOHC; that project has been back-burnered for now, but hopefully I will get back to it at some point.

The hemispherical combustion chamber is also a limitation; a more modern chamber would provide more power and allow a lighter piston.  Again, I have plans to modify a set of Robert Pond's heads to put a smaller chamber in, and in fact I've already done the chamber design to reduce the volume by 20 ccs without any major impact on port flow.  But again, I haven't had the time to pursue this yet.

On the plus side of the ledger, though, there is no other FE port arrangement that is anywhere close to the SOHC for flow.  I've worked with the engineers at Comp Cams on some of their standard and a couple of "special" cam profiles, and they have been amazed that my big SOHC makes over 900 HP with a .720" lift cam.  They basically said they don't know of any other engine that can do that.  In the end, though, with the ability to run lifts in excess of 1.0", you can make more power with a pushrod motor like a 385 Ford or a big block Chev. 

What is needed is an all-new FE wedge head design, to allow us FE guys to compete with some of those other engines...

[Drew Pojedinec]

Been thinking that forever....
canted valve with obviously different rocker system that would allow such a thing.  We have to get jon kaase interested in FE's

[machoneman]

Kaase already did:

http://www.jonkaaseracingengines.com/component/content/article/231-kaase-p-38-heads.html

The P38 heads need to be scaled up for an FE with attendant changes. His P51 heads are somewhat similar (BBF) but are essentially a copy of std. BBF heads with changes. The SBF based P38 heads are truly a new design, with side-canted valves unlike the poly-angle Boss 302/Cleveland 351 heads. Note too that only a new valve cover is needed. However I don't think a scaled up FE head could get away with only a new cover if one wanted to use traditional FE intakes. Jay's re-incarnation of the adapter though would allow a lot more leeway in designing either a side-cant head or a poly-angle head.  JMO 

Btw, the C-460 head as well offers ideas on a new FE head

http://www.mbellc.com/index.php/component/virtuemart/component/virtuemart/?page=shop.product_details&flypage=flypage.tpl&product_id=42

[turbohunter]

The hemispherical combustion chamber is also a limitation

Wow, my little pea brain is reeling over that statement.
As a child of the 60s there is "supposed" to nothing better than hemi heads.
I love this forum. Thanks for all the brain stretchers guys.

[Drew Pojedinec]

Think about the hemi chamber and how a piston must meet it in order to get high compression.
now think about how the flame will move vs with a really nice closed chamber.
Plus to make such a big dome in a piston makes it heavy.

but otherwise, yeah, stuff massive air into hemi chamber..... but at a cost, it aint 1964.

[turbohunter]

but at a cost, it aint 1964.

Which brings us back to SOHC motors

[Drew Pojedinec]

I meant "of course it aint 1964"
I don't sleep enough to have proper grammer

I'm sure Jay and other SOHC officianado's are using a LOT of modern technology to avoid detonation and making the chamber as efficient as possible, but if they could get the same air slammed in with Barry's new head and a super light flattop, I'm sure they would.

Course I'll let those SOHC experts talk further.... I'm just a diesel mechanic, that lives on top of two v16 engines and thinks about stuff like fuel movement in combustion chambers.

[Barry_R]

Couple things.

First is that I use the exact same process for assembling the backing plate to the long block & heads - same sealant, sam bolt strategy.  Almost eerie - but its really the only way to do it.  These things tend to leak pretty good around the lower side of the cylinder head/front cover interface if you don't glue 'em up a bit.  I think they can hold a fair amount of oil there based on the casting shapes. 

And you really need to remember to keep that one bolt installed when you're ready to move ahead with the cover.  You know which one - - it's the one that you cannot see when the cover's installed - - the one that goes into water - - the one that'll fill the oil pan right up if you forgot it.  Not that I ever did that....

As for valve clearance issues - I can pretty much promise that they move around a fair amount.  I've tried big exhaust valves in a 390 where I mounted the head, verified radial clearance to the bore through the valve's travel to be plenty adequate.  And then found that every valve had "self notched" the side of the bore after running for a while.  These were 11/32 stems too - not real skinny, and they moved at least .030 - probably more.

[LuxurySportCoupe]

Think about the hemi chamber and how a piston must meet it in order to get high compression.
now think about how the flame will move vs with a really nice closed chamber.
Plus to make such a big dome in a piston makes it heavy.

but otherwise, yeah, stuff massive air into hemi chamber..... but at a cost, it aint 1964.

What about a nice flattop or small dish in a SOHC package? I think that would lend itself perfectly to a boost friendly compression ratio, coupled with all that head flow would make a sweet package. I just really would love to see a turbocharged SOHC, I can always dream right? lol.

[jayb]

Funny you should mention that, I have a turbocharged SOHC in the works, that uses basically a flat top piston to get 8.75:1 compression ratio.  Unfortunately, the engine has been "in the works" for five years.  I need to get around to finishing that one...