Bigger valves, any downsides?

[PackardV8]

Sort-of-on-topic, as it asks about the effect of increasing intake valve diameter.

1. Yes, an area of the circumference of the valve can be too close to the cylinder wall, i.e. "shrouded" and thus flow in that area is not optimum. However, when increasing intake valve diameter, is the increase in total area usually greater than the increase in shrouded area? Isn't the area of greatest flow always toward the center of the cylinder in most cases? So the greater increase in effective area mitigates the slightly greater shrouded area?

2. Does anyone here have a link to a discussion where increasing the valve diameter, thus increasing the shrouding effect, actually resulted in a reduction in CFM? If so, can we be certain it was shrouding and not, as previously mentioned, just the increase in diameter reducing velocity?

3. I can see how the above might be true in old-school wedge chambered OH2V designs, where the chambers are deep and the valves shrouded as much by the chamber as by the cylinder wall. Increasing the valve diameter moves a larger percentage of the discharge area closer to the chamber wall. T/F ?

4. Obsolete OH2V heads can be milled .060" -.125". Anyone seen any data/discussion on the effect of maximum milling of the head surface reducing the depth of the old-school chambers and thus reducing the effect of the deep chamber shrouding? We can't get to where the LS is, but would it help?


6. OTOH, the '58-64 Chevrolet W-series and '58-64 MEL valves weren't shrouded by the chamber and they weren't the answer.


7. Trying to find a photo and a name, but fifty years ago in OZ, I saw a special builder using a flat four aircraft engine with his own design swinging poppet valve. Picture a valve with the stem bent ninety degrees and put on a trunion, so when it swings open, it's completely out of the air flow. Since the engine was air cooled there was no worries about more bolt holes in the head and the bent valve probably was only livable at low RPM, but he got some really great VE and won many local races with it. (Old OZ guys, help us here!)

[pdq67]

I want to comment on two things here..

First, the old "W"/"MEL", engine heads!

They would have worked GREAT if their ports would have been, "stood-up", so that they had a better angel and not the poor port angles they had. This is proven by the '63, 427", Z-11 , "W", engine's intake manifold revamping. They just didn't continue the revamp into the head ports on both valves.

And second.

I would love to see a SBC and BBC head made like the old Jeep Mail Truck, "Tornado", "SOHC", hemi-headed 6-banger engine!

BUT MODERNIZED!!

Try this link?

http://wildaboutcarsonline.com/members/ ... ix_1-4.pdf

I think if I read my research right on this old engine that the last ones made down in South America were made with 12-lobe cams so they were, as I call it, "modernized', to a point before being scrapped... They probably used, "knife and fork", rockers to keep the head a TRUE hemi???

pdq67

[PackardV8]

They would have worked GREAT if their ports would have been, "stood-up"

Stood-up ports are easy. Fitting them under a hood, not so much.

I would love to see a SBC and BBC head made like the old Jeep Mail Truck, "Tornado", "SOHC", hemi-headed 6-banger engine! BUT MODERNIZED!!

The best argument against the single cam hemi would have been it was out there in the public domain for for more than a hundred years and few others had bothered to use it. Kaiser was a small bankrupt company, having to buy Continental flatheads and by 1962 it was the last flathead in the market and no one wanted them, so Kaiser was desperate for an overhead valve engine. They claimed it as "having the lowest specific fuel consumption of all production gasoline engines on the market."

Ford spent the bucks to try a single OHCV8, but the single cam hemi wasn't their better idea. It was dropped as a technological dead end.


Ironically, it took the Japanese to perfect the design and millions of hemi and semi-hemi SOHC fours and sixes have worked wonderfully well.

[Walter R. Malik]

Ford spent the bucks to try a single OHCV8, but the single cam hemi wasn't their better idea. It was dropped as a technological dead end.


Ironically, it took the Japanese to perfect the design and millions of hemi and semi-hemi SOHC fours and sixes have worked wonderfully well.

In just the last few years Ford had a "Raptor" single overhead cam gasoline V-8 truck engine of 6.2L which was a great engine but, Ford didn't make any money selling it so, it got dropped.

[GerryP]

In just the last few years Ford had a "Raptor" single overhead cam gasoline V-8 truck engine of 6.2L which was a great engine but, Ford didn't make any money selling it so, it got dropped.

The exact same 6.2 gasser lives on in the F-series Super Duty since around 2011. You can get a new one today. Awsome engine.

[gmrocket]

The valve controls how big the "hole" can be.....

Are you sure?

The flow is determined by the size of the hole.
The valve just blocks the hole.
You can make the hole bigger so it just closes with the edge of the valve.
You can keep the hole the same size and use a 1 mm bigger valve.


Now from a wannabe machinists point of view, the whole purpose of a valve 1 mm bigger is to fit a worn seat?
If you try a bigger valve in a stock seat, too much valve lash.If the seat is worn you can cut it down to fit.Still the same throat dia. though?

So really........it's a bit like those sales and marketing things, you get what you pay for..................because you're buying bigger valves.
But you don't really because you can work the heads to use the original valves for more flow.


Well...............fitting bigger valves....it's so easy, you just swap them out at home and lap them in????
Or did I miss something?

Ya your missing it. Maybe if there was a forum for beginner questions, that would make sense.

[groberts101]

Ideally, depending on where the choke is located, you increase compression to reduce some of the downsides of the bigger valve/s too. My learning curve has been that valve/s size and shape is slightly more important at low/mid lifts, and changes towards the seat profile and hole/throat sizing at higher lift/airflow ranges.

Another thing to think about. Bigger holes/throats(volume) and gentler or laid back SSR approach angles also allow more latitude for valve/s underhead angle designs. Worried about preserving seat velocity profiles at lower lifts(which all unto itself can also help reduce reversion) with your fast action high lift cam? Install a tulip style valve with larger backside radius.

[pdq67]

They would have worked GREAT if their ports would have been, "stood-up"

Stood-up ports are easy. Fitting them under a hood, not so much.

I would love to see a SBC and BBC head made like the old Jeep Mail Truck, "Tornado", "SOHC", hemi-headed 6-banger engine! BUT MODERNIZED!!

The best argument against the single cam hemi would have been it was out there in the public domain for for more than a hundred years and few others had bothered to use it. Kaiser was a small bankrupt company, having to buy Continental flatheads and by 1962 it was the last flathead in the market and no one wanted them, so Kaiser was desperate for an overhead valve engine. They claimed it as "having the lowest specific fuel consumption of all production gasoline engines on the market."

Ford spent the bucks to try a single OHCV8, but the single cam hemi wasn't their better idea. It was dropped as a technological dead end.


Ironically, it took the Japanese to perfect the design and millions of hemi and semi-hemi SOHC fours and sixes have worked wonderfully well.

Jack,

I beg to differ here!!

Imho, Ford's cammer 427 was awesome! 6' timing chain and all!

What, the suckers would do 9,000 rpm and produce like 600+ Hp if not mistaken. AND i THINK(?), from the factory... Shades of talking about a Z-28 SBC on Steroids!!

I just got off my Throne where I was reading about the LS- engine conversion using a modified small block Ford type Hemi-Head and was thinking about how to make a, "ball-stud", design REAL hemi-head for a 1st Gen. SBC engine and not just a twisted wedge chambered so-called hemi-head...

And this is where this comes in here!!

I really would REALLY like it if somebody would PLEASE post up pictures of the 12 lobe OHC set-up for the last of the Jeep Tornado 6-banger engines. If this does indeed exist??

I would love to see Pete Aardema redesign the Mail Jeep engines SOHC design so that it would bolt on to a 1st Gen. SBC head...

pdq67

[pdq67]

Jack,

If you would then please hunt up info on this...

" I would really would REALLY like it if somebody would PLEASE post up pictures of the 12 lobe OHC set-up for the last of the Jeep Tornado 6-banger mail truck engines. If this does indeed exist??"..

Thanks in advance..

pdq67

[Casper393W]

The Ford 6.2 engine can make serious power! The problem is the aftermarket hasn't bought into it yet because it is a truck engine.... I have seen a stroked version making near 800hp on motor alone!

You can take a stock head casting and get right at 400 cfm out of them! That should tell you what can be done.

Andy

[n2xlr8n]

The Ford 6.2 engine can make serious power! The problem is the aftermarket hasn't bought into it yet because it is a truck engine.... I have seen a stroked version making near 800hp on motor alone!

You can take a stock head casting and get right at 400 cfm out of them! That should tell you what can be done.

Andy

Yep. There is bone stock bottom end and valvetrain 6.2 on our Raptor forum making 720whp with about 16 psi of boost on 93.

My 2011 makes 492 atw on 93 with about 7 psi. My wife looked at me during her first ride offroad and said "This is far too quick for a 4wd truck"

[PackardV8]

My wife looked at me during her first ride offroad and said "This is far too quick for a 4wd truck".

Then then 'Bama gals have changed in many ways since I was born 'n raised there.

[Newold1]

Jesus,
you guys can really digress!

OP, what engine? What head? what size existing valves and what are you trying to achieve?

Those alone make such a varied difference what you are asking is like How blue is the sky?! Stop trying to generalize!

[n2xlr8n]

My wife looked at me during her first ride offroad and said "This is far too quick for a 4wd truck".

Then then 'Bama gals have changed in many ways since I was born 'n raised there.

You know better than that, Jack. She's a hotrodder.

Sorry for the OT, fellas.

[Ken_Parkman]

Sorry to continue the digression, but here you go PDQ