More Valve Lift

I have concluded that the primary reason that modern American V8’s develop sooooo much more power than our aging V12’s is… valve lift. A Chevy LS has more than .600" valve lift, partly accomplished with rockers with a 1.6:1 ratio or better. A Ford Coyote has more than .500" lift on four valves/cyl, accomplished without rockers, it’s all in the overhead cams. By comparison, the .375" of lift our 2-valve V12 has looks pretty weak, and is almost certainly the power limitation.

Here’s the idea I propose: Regrind the OEM camshafts for a 1/4" smaller base circle. This will probably require a tad more duration. Replace the valves with valves with stems 1/8" longer. Replace the valve springs with springs that are 1/8" longer.


Presto, change-o, we have .500" lift. On a pre-H.E., instant tire burner. On an H.E., somebody will probably need to figure out how to get the pocketed exhaust valve to work well with the additional lift. I presume some massaging of that pocket would be in order, which in turn will probably reduce the compression ratio a bit. Probably can compensate with a hair more timing advance.

Also need to ensure that the valves don’t get involved with the pistons, without reducing the lift!

Note that the tappets would end up sticking out of the tappet block by 1/8". I kinda doubt if that’s a problem.

All this would seem simple enough to accomplish if suitable valves and springs can be found for reasonable prices. I’d be willing to bet such parts exist somewhere on some commonly-available junkyard engine or another. I have no idea how to find them, though.

BTW, we’ve had discussions on whether the exhaust systems on our Jaguars are limiting, with Roger Bywater assuring us they are not. Perhaps worth noting, though, that the exhaust systems on modern American V8 Mustangs and Camaros are typically 3" dia., and that’s per bank, dual exhaust with an X-pipe. I don’t think Ford or Chevy would pay the premium for such large pipes if they didn’t accomplish anything.

I like it, 3" over the axle maybe, guess Ron can offer.

Kirby you maybe a little optomistic , i think me and you went over the poor breathing of the V12 engine, 5yrs ago,and my final post was that all poppet valve 4 cycle engines is the valve will always be the biggest obstruction in the intake path!
that said getting a useful .500 in. lift would be more than your description, and the cost of some precise machine work!

and as i said back then using forced induction always reduces the negative effects of a restricted air flow path!
like 1 BAR(14.7psi) of inlet manifold pressure theory, says a 100% increase in power, OK maybe not quite but a big increase in torque! i think we went round about torque is king for a street car!

Im not able to forecast the longevity of a camshaft with the circumference lessened by as much. lot of twister action. Too long for the cam, probably needs a different starting metallic starting point. Maybe a camshaft supplier, then it only the carriers etc to deal with.:grinning:

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I think your thinking is correct - that is, that more lift has been shown to be an advantage with this engine. At least with larger inlet and exhaust valves in the PreHE.

However, using a reground existing cam will not work. Or not for long. The reason being, that the reduced radius on the nose of the cam will break through the oil film on the tappet and cause considerable wear. This is why the Gp C engine resorted to increased base circle larger radius nose. It’s a bit more complex than that. You’d need stiffer springs to control the deceleration. And at low rpm, the stiffer springs and smaller radius of the cam nose produce oil film problems. This demands a thicker tappet block or at least a spacer plate.

The second issue is the velocity of the lifting valve ends up being directly proportional to the tappet diameter. You need to give the cam more time to move the valve into position. You can’t do this with the smaller cam, so you end up with bigger base circles to go with the higher lift. And that ends up needing larger diameter tappets. Mathematically it ends up being directly proportional … but still leading to new tappet blocks.

Modern technology might offer solutions. Diamond Like Carbon (DLC) coatings, better lubrication. ?

If people haven’t found out yet, Alan Scott’s new book is out - on the development of the Gp C race cars. In this he details his work to make the 2 valve out perform the 4 valve in all but the most extreme circumstances. (And a fair bit of disbelief that it was possible).

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Because of the pocketed exhaust valve of the HE you cannot fit a larger Intake valve, which is more important than an increase in exhaust size.

I’m not as convinced that bigger valves are that helpful. The problem is that they can end up closer to the cylinder walls. Basically, there’s a bigger valve head in the way of the flow. I suspect increased lift is a better way to go, at least up to a point.

Yes. I’d agree with that. The larger valves tend to go with wider bores otherwise there’d be extreme shadowing around the side of the valve near the cylinder wall.