19 replies to this topic

[TopCatCustom]

Looked into carbon pushrods, but there seems to be a very mixed feeling about them. I noticed Minispares do both performance ones and alloy ones- no weights quoted but does anyone have any experience of them, or any other lighter types to consider?

I'm obviously looking for a lighter valve train if anyone fancies chipping in to the convo with ideas!

[jamie@thefatgarage]

I must admit to being skeptical about the benefits. Or at least benefit in terms of actual hp/£. If you do get them I'd be very interested in seeing before and after dyno figures.

[rusty789]

Surely Titanium would be a good option?

[AndyMiniMad.]

I would not think the gains from lightened push rods would be worth the £££ss. If of course your engine has already been lightened to the max, then i guess every little bit helps.

[TopCatCustom]

I must admit to being skeptical about the benefits. Or at least benefit in terms of actual hp/£. If you do get them I'd be very interested in seeing before and after dyno figures.

From reading other stuff online the weight they save could help towards another 500rpm... could be BS of course but I don't doubt there is some difference

Surely Titanium would be a good option?

Funnily enough I was just thinking that whilst driving after creating this post.....

I would not think the gains from lightened push rods would be worth the £££ss. If of course your engine has already been lightened to the max, then i guess every little bit helps.

It's more about lightening the valvetrain and moving parts than saving weight on the car. I'm sure I read somewhere that weight savings in rotating assemblies in the engine (and associated parts) is worth **x the amount of weight saved on static parts i.e. dead weight on the car itself, but I cant remember the figure.

[Dan]

The main benefit of tubular push rods is not weight, it's rigidity which gives greater control of the valve train.

[AndyMiniMad.]

I must admit to being skeptical about the benefits. Or at least benefit in terms of actual hp/£. If you do get them I'd be very interested in seeing before and after dyno figures.

From reading other stuff online the weight they save could help towards another 500rpm... could be BS of course but I don't doubt there is some difference

Surely Titanium would be a good option?

Funnily enough I was just thinking that whilst driving after creating this post.....

I would not think the gains from lightened push rods would be worth the £££ss. If of course your engine has already been lightened to the max, then i guess every little bit helps.

It's more about lightening the valvetrain and moving parts than saving weight on the car. I'm sure I read somewhere that weight savings in rotating assemblies in the engine (and associated parts) is worth **x the amount of weight saved on static parts i.e. dead weight on the car itself, but I cant remember the figure.

Yeah lightening the rotating stuff is the way to go, but remember the push rods are opening the valves against the presure of the valve springs. are your springs matched to your engine spec and cam profile? If you can lighten the load on the springs without risking valve bounce them im sure the gains will be better than lightened push rods. But as I said, if you have already maxed your engine lightness then why not go for carbon rods.

[Wil_h]

I would not think the gains from lightened push rods would be worth the £££ss. If of course your engine has already been lightened to the max, then i guess every little bit helps.

It's more about lightening the valvetrain and moving parts than saving weight on the car. I'm sure I read somewhere that weight savings in rotating assemblies in the engine (and associated parts) is worth **x the amount of weight saved on static parts i.e. dead weight on the car itself, but I cant remember the figure.

Yes this is true, but a pushrod is not a rotating part.

Just putting in lighter pushrods will not increase rpm even by 1. Max rpm is governed by head/cam/induction, the mechanicals of the engine then have to be built to cope with achievable rpm. Of course a badly balanced engine may limit rpm, but I consider balancing a requirement for your engine to cope with high rpm.

The MS pushrods have a good press and can be ordered any length.

I have personally never used anything other than standard pushrods.

[mini13]

Titanium is very bad for pushrods, apparently its quite springy,

[Sprocket]

light weight push rods are only worth while when complimenting titanium spring caps ank valve keepers, alloy rockers and lightened followers. it is more to do with keeping the follower on the cam without the excessive poundage on the valve springs, and, the faster accelerating ramps of some race cams.

[AndyMiniMad.]

light weight push rods are only worth while when complimenting titanium spring caps ank valve keepers, alloy rockers and lightened followers. it is more to do with keeping the follower on the cam without the excessive poundage on the valve springs, and, the faster accelerating ramps of some race cams.

Yep, Thats what I meant!!! Sprocket puts it way better than I could though!!

[Dan]

Just putting in lighter pushrods will not increase rpm even by 1.

Not increase RPM no but will increase red line in theory. Lighter is better, lighter pushrods have less innertia so can accelerate quicker for the same energy input. So they change direction faster so they in theory allow the valves to move faster, allowing higher RPM before they become a limiting factor. As suggested though weight savings in the valve train are not worth the same as saving in the rotating parts. The gains are so slight however that they are far outweighed by all the slack and lost travel in the overhead valve system. That's the real limit for an overhead valve engine and is why Desmodromic valves are better. So the increase in rigidity of the rod is more of a benefit than the loss of weight because it reduces the lost travel.

[Cooperman]

As already stated, the issue is the inertia of the valve opening system. That includes everything from the cam followers to the valves themselves.
I built a 970 'S' which needed to rev to over 8500 and the biggest source of inertia was the rocker shaft. In the end I lightened an original Cooper 'S' rockers by grinding and polishing, shortened the length of the cam followers by taking 2.5 mm off the top (i.e. the open end), and used valve springs which were not too high a rate after speaking with Kent's Tech. Support (can't find a record of the part number though). Cam was a 286, C.R. was 11:1, carbs were twin HS4. It had a custom-built Aldon distributor.
With that done it was fine at just over 8000, but on the rollers max power was 88 bhp at 6700, so there was no real need to rev it to much over about 7000, so it was fine. Had it not been, I would have lightened the valve stems and considered lighter push rods, probably aluminium tubular ones.

[TopCatCustom]

All good points thanks, and I hadn't taken titanium's "springy" nature into consideration!

The long and short is- the lighter everything in the valve train is, the faster you can rev it whilst keeping everything in contact and operating properly. However there is little point beyond 7k or so unless using a 300° or so cam that needs the revs.

Agreed?

[Cooperman]

All good points thanks, and I hadn't taken titanium's "springy" nature into consideration!

The long and short is- the lighter everything in the valve train is, the faster you can rev it whilst keeping everything in contact and operating properly. However there is little point beyond 7k or so unless using a 300° or so cam that needs the revs.

Agreed?

Yes, that sums it up nicely.
Lighten the rockers by machining away excess width, not depth, and polish them to avoid any stress-raising points. That makes a big difference.