7m valvetrain weight

[ma71supraturbo]

Saw this posted on celicasupra and thought this would be good info to have in the SM archives...

just receive some goodies for a spare head i try to mod

Brian CROWER parts:
1mm oversized valves and spring/retainers kit


even if they are oversized by 1mm , they are ligther ,1 gramme each vs oem valve


so 24 gr save here and 1mm oversized




spring/retainer kitem vs brian crower set


39 gr for the oem vs 31 for the crower

Cliffs:

BC 1mm oversized valves are ~1gram lighter each (~24 grams lighter for set)
BC springs/retainers are ~8 grams lighter each (~192 grams lighter for the set)

So the 1mm oversized BC valvetrain is ~216 grams lighter than stock

 

[dumbo]

I doubt you'd even notice that on a dyno or anywhere.
Other than the valve size of course.

And technically its not rotating mass, its recipricating.

 

[ma71supraturbo]

I doubt you'd even notice that on a dyno or anywhere.
Other than the valve size of course.

You're pretty much right: assuming the same valves/cams, a lighter valvetrain probably wouldn't appreciably increase power at an existing rpm unless you were already experiencing float. It would slightly decrease the effort required to turn the cams (since less force would be required to accelerate the valves open), but this would be a pretty minor gain in efficiency.

However, it allows you to rev higher which, combined with a better breathing setup (big cams/valves/turbo) would yield more power. And it does this while requiring less spring stiffness than otherwise required -- meaning less wear/tear on the seats/valves.

And technically its not rotating mass, its recipricating.

Quite true -- I just didn't wan't to make changes to his quote, but I guess I'll just snip that last paragraph out for accuracy.

 

[IJ.]

You'll notice it if you get above 8000 and start breaking heavy components, even good lightweight gear suffers at sustained high RPM.

 

[ma71supraturbo]

yeowch! What springs are those?

 

[IJ.]

Ferrea duals

 

[gofastgeorge]

The TODA inner shim set is 30% lighter than stock,
as figured on the parts that count, ie the bucket, retainer, keepers, and shim.
The spring only figures in at half it's weight,
since only half of it is actually going up & down.

And they eliminate the chance of pitching a shim out when using high lift cams with agressive ramps.

 

[dumbo]

I'm assuming the spring rate of those are quite stiffer correct? So the general force(?) to over come that is gonna make more of a difference than the few grams your loosing in valve mass. But with supporting mods I TOTALLY agree.

Thanks, and trust when I finally build a motor I wont be going stock for reasons you stated I can't wait!!!

IJ, that must of made a racket!!

 

[IJ.]

Nope no noise just lost power.

 

[ma71supraturbo]

I'm assuming the spring rate of those are quite stiffer correct? So the general force(?) to over come that is gonna make more of a difference than the few grams your loosing in valve mass.

Not really. Yes, a stiffer spring will require more force to push down -- but it also will push back up (on the cam) with more force. There will be slight frictional losses, of course, but essentially the spring rate change will have negligible parasitic losses.

 

[gofastgeorge]

Sorry, but that is not correct.
At speed, you don't get the pushing back force helping drive the cam.
It is all the springs can do, just to keep the valves from floating.

Try sticking a 1/2" drill on a cam sometime, that has all the springs & valves in place.
You will be lucky to hang onto it, or even having the drill to even come up to speed.

 

[ma71supraturbo]

It is all the springs can do, just to keep the valves from floating.

Lets think about this. The stock valve springs are able to keep the valves from floating for the stock rpm range, no? So any increase over stock spring pressure will simply be applied back to the cam... This force should be the same (minus any frictional losses) as the extra force required to push down on the valves with the stiffer springs.

Try sticking a 1/2" drill on a cam sometime, that has all the springs & valves in place.
You will be lucky to hang onto it, or even having the drill to even come up to speed.

This is true, but that is because the cams are doing work (pushing the valves open). The cam has to do this same work (moving valves) whether the springs are stock or upgraded. The question is whether stiffer springs alone cause more drag on the engine -- and I say theoretically it shouldn't.

 

[dumbo]

I'm not agreeing or disagreeing with either of you, but I don't think the springs have much mechanical advantage to help spin the cam.

 

[3p141592654]

It's really easy, just think of where the energy is going. When the spring is compressed it stores potential energy (1/2kx^2), and when it extends it gives it all back minus frictional losses. If the frictional losses are the same, then stiffer springs will take no more average effort to turn.

In practise, there will be an increase in friction from the higher forces on the lobe, but should be minimal if the cam lobes are not being ground into dust. Also note that we are talking about the net energy integrated over a 360 degree rotation of the cam. Since the cams are bumpy, the instantaneous peak torque loads (positive and negative) will be higher with the stiffer spring.

 

[IJ.]

Tiny valves and not all that much seat pressure even on good springs, my cordless has no trouble spinning a cam.

Be a different matter if we were talking about a roller cam pushrod V8 here.

 

[dumbo]

OK... Just did the HG's on my buddies 90 Toyota pick up(V6) and yes the cams do spin after compressing the springs. So I was wrong, anyways...