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.

i modifiy and bevel/notch top of the liner (above ring travel)and that helps to unshroud the inlet valve , exhaust has plenty of clearence!

and last but not least( on pre-HE ,if you just cut/mill .050 off the head surface it puts the valves .050 deeper into the cylinder bore, (lets not forget we are trying to fill the cylinder not so much the chamber).

this fact was tested by Jaguar 50yrs ago and it dyno’d 10/12HP more at same RPMs.

sometimes i forget some of the mods i have in my V12(must be getting old,but remember at night half asleep)! yes many mods done!!

almost forgot,DUH, my V12 uses 3MM oversize SS valves , bought and recommended from Grp44 ,LANKY chief engine builder for 44!
i believe he knew something about Jag V12s???

thought!! if valves are .050 deeper in bore could that be like MORE EFFECTIVE lift.??

Not really because the seat is deeper and the ‘curtain’ around the opening valve is unchanged.

multi angle valve seat can correct some of that theory, a good flow test by JAGUAR showed little effect, but in practical use(reality) they came up with more power!

and in todays world of port /seat/ valve shape of computer FLOW dynamics it could be done!

and i have said for yrs, just forcefeed the bitch and be done with all flow restrictions!

better to force the air in ,than suck it in!

thanks Pete for helping memory,!

as said 3MM oversize valves , on pre-he outside inlet seat diameter is very close to 3mm, as you may know the throat area is smaller , so being a fully equipped engine machine shop, i carefully opened up the seats to a nice tapered shape of throat 3mm more and of course ported and smoothed all rough edges!

at this point the actual curtain area would be larger diameter that would help increase air flow.
finished off with some proper multi angle seats, and flowed in to bowl and port, actually change some of the port angle to help increase SWIRL,(hoping it would help chamber turbulence also).

altho exhaust seat was not quite 3MM, so i reduced valve diameter by 1mm and refinished valve face smooth flowed into the throat and port, gave some thought for raising the exh. port but to much work for match to ex manifold!

also increased inlet plenums and runner internally, by having them EXTRUDE ABRASIVE HONING, came out beautiful smooth and took out all the humps and bumps of bolt intrusion castings and remove injector bumps!
i measured before and after inside was all the way thru about an 1/8"larger of each side , but most impressive was the plenum into runner shape funnel nice!
the compression was increased about .2 tenths, guess to 9.2/1, from milling the head lower!

Of course that could help but you asked about 50 thou off the head.

2mm off the head surface lowers the valves and seats down into the bore ,exposing much more flow into the cylinder, careful shaping will help the overall flow!
i thought about the chain getting looser, but jag must have taken that into design, factory tensioner takes up the slack very well, and close examination seems to better the chain tracking actually making it more use able! been 25yrs and still no problems, had to alter cam timing one notch on both cams!
it was interesting to say the least, but i have never been one to NOT try something different!

almost forgot,Duh, also had
the flat head surface Ceramic thermal barrier coated, to keep chamber temperatures in the chamber to do expansion work, NOT to have more heat get into the head coolant ,( V12 has a nasty habit of overheating)!

i went over a lot of my ideas with Lanky 44, he said if some of that was available when 44 was building engines they may have used them!
i have many more mods but this was my way of thinking 30yrs ago!

OH OH! to elaborate more on how much money i spent with those heads!
along with the head surface coating, i also had them coat the exhaust seat and port,(i’m betting you know wher i’m going), along with coated ex.valve top and under part(not the guide tho). something many dont know about the dropped seat issues, is caused by the long length of the exh. port transfering heat into the head coolant ,so coat it and keep that spent heat going out, (especially if turbocharged).
ported the exhaust manifolds and coated them inside and out! pic.


OK over and out!!
thanks for listening
Darn hold on, most important, Gold coated the piston tops(higher temp resistant).
WHY to keep combustion heat from melting a piston, and insulating heat into under piston oil splash and causing high oil temps!

for Kirby, i dont come up with theories ,i do make it a reality, with some pix!jag%20engine%20inside%20002 jag%20engine%20inside%20005 .

notice NO wear on cam lobes , about 5000miles at that time!


and for the young guns, pic of the timing chain and asscociated parts!

2.5in, is the maximum you can run over the axle without hitting on bump or rebound

In 1976 when the XJS 5.3 (327ci.) was released, it made comparable HP to the Chev 350.
You must compare apples with apples.


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