21 replies to this topic

[Ethel]

Race engine building is all about trying to find improvements that give you the edge over the competition, a lighter valve train means you can run higher revs with less valve spring pressure.

CF is stronger by weight, not dimension, over steel; the rods need to be thicker to be at least as strong. A pushrod is a relatively big part that reciprocates the valve as far from the fulcrum as is possible, it's an ideal candidate for weight reduction. All the more so if you can improve its rigidity into the bargain.

 

Minispares stopped flogging 'em, apparently because of excess failures, but that's no indicator of the cause of the failures. They still offer thicker rods, also in alloy for weight reduction.

[tiger99]

Alloy is going to be not very good either. One fatigue cycle for every two engine revs.....

 

The problem with carbon is probably not going to be strength, but stiffness. Think fishing rod! That is why the steel rods can't be thinner, under compression all thin things buckle. But a tube is stiffer than a rod of the same mass, so how about hollow steel rods? The stiffness, if I remember correctly, is proportional to R⁴-r⁴, while the mass is proportional to R²-r² where R is the outer diameter and r the inner, so boring a hole down the middle of a standard piece of rod of half its diameter removes 25% of its mass, and only reduces stiffness (and rotational moment of inertia, not important here as the rods don't spin) by 6.25%. Work out for yourselves how big R has to be to get standard stiffness with r adjusted to get half the mass. But you can't go too far and make the wall thickness too small, like a 3 inch tube made from 1 thou sheet, which would just crumple.

 

I don't see any other real problem with carbon composite, as long as the ends, which I assume have to be steel, are fitted in a suitable way. That is the fundamental problem with most composites, and I suspect will be why they ultimately fail, provided that they are not rubbing.

 

But, I would suggest that if you need so much reduction in valve train mass, you should first do all the obvious things like fitting titanium valve collets and spring retainers, and gas flowing the valves properly, which reduces head mass, as well as attending to the rockers as Cooperman has already suggested. Are titanium rockers possible? But then the next logical step is an overhead cam. BMW bike cylinder head conversion....

 

And there lies an interesting question, if you are going to the trouble and expense of making a completely new head, like the several 7 port and 8 port varieties on the market, why not go all the way and make it overhead cam? Why waste money tackling half the problem? Just curious.....

 

I will be interested to hear how these rods do perform, after a few tens of thousands of miles.

[Cooperman]

Alloy is going to be not very good either. One fatigue cycle for every two engine revs.....

 

The problem with carbon is probably not going to be strength, but stiffness. Think fishing rod! That is why the steel rods can't be thinner, under compression all thin things buckle. But a tube is stiffer than a rod of the same mass, so how about hollow steel rods? The stiffness, if I remember correctly, is proportional to R⁴-r⁴, while the mass is proportional to R²-r² where R is the outer diameter and r the inner, so boring a hole down the middle of a standard piece of rod of half its diameter removes 25% of its mass, and only reduces stiffness (and rotational moment of inertia, not important here as the rods don't spin) by 6.25%. Work out for yourselves how big R has to be to get standard stiffness with r adjusted to get half the mass. But you can't go too far and make the wall thickness too small, like a 3 inch tube made from 1 thou sheet, which would just crumple.

 

I don't see any other real problem with carbon composite, as long as the ends, which I assume have to be steel, are fitted in a suitable way. That is the fundamental problem with most composites, and I suspect will be why they ultimately fail, provided that they are not rubbing.

 

But, I would suggest that if you need so much reduction in valve train mass, you should first do all the obvious things like fitting titanium valve collets and spring retainers, and gas flowing the valves properly, which reduces head mass, as well as attending to the rockers as Cooperman has already suggested. Are titanium rockers possible? But then the next logical step is an overhead cam. BMW bike cylinder head conversion....

 

And there lies an interesting question, if you are going to the trouble and expense of making a completely new head, like the several 7 port and 8 port varieties on the market, why not go all the way and make it overhead cam? Why waste money tackling half the problem? Just curious.....

 

I will be interested to hear how these rods do perform, after a few tens of thousands of miles.

Since the application is really only for racing cars it may be that an OHC conversion is not allowed under the regulations.

There really is no point in fitting CF or even tubular rods in a road car as you are never desperate for another couple of hundred revs or so or have a need to reduce the valve spring poundage slightly. A properly built road engine should do thousands of miles anyway with a standard valve train.

I have used the original rocker shaft from a Cooper 'S' and lightened/polished it to get valve train mass down for a 970 'S' rally car running a 286 cam. We lightened the cam followers as well and used VS2 valve springs (from memory) to be able to use 8000 rpm without getting valve-bounce. That worked, but even then the car was not as quick as a 1040 cc Hillman Imp!

I guess tubular titanium push rods would work in a race engine and investigation of fatigue life would indicate after how many races they would need to be changed. If you are paying over £20,000 for a Mini race engine, then replacing the push rods every season is not an issue.

[MIGLIACARS]

 

Alloy is going to be not very good either. One fatigue cycle for every two engine revs.....

 

The problem with carbon is probably not going to be strength, but stiffness. Think fishing rod! That is why the steel rods can't be thinner, under compression all thin things buckle. But a tube is stiffer than a rod of the same mass, so how about hollow steel rods? The stiffness, if I remember correctly, is proportional to R⁴-r⁴, while the mass is proportional to R²-r² where R is the outer diameter and r the inner, so boring a hole down the middle of a standard piece of rod of half its diameter removes 25% of its mass, and only reduces stiffness (and rotational moment of inertia, not important here as the rods don't spin) by 6.25%. Work out for yourselves how big R has to be to get standard stiffness with r adjusted to get half the mass. But you can't go too far and make the wall thickness too small, like a 3 inch tube made from 1 thou sheet, which would just crumple.

 

I don't see any other real problem with carbon composite, as long as the ends, which I assume have to be steel, are fitted in a suitable way. That is the fundamental problem with most composites, and I suspect will be why they ultimately fail, provided that they are not rubbing.

 

But, I would suggest that if you need so much reduction in valve train mass, you should first do all the obvious things like fitting titanium valve collets and spring retainers, and gas flowing the valves properly, which reduces head mass, as well as attending to the rockers as Cooperman has already suggested. Are titanium rockers possible? But then the next logical step is an overhead cam. BMW bike cylinder head conversion....

 

And there lies an interesting question, if you are going to the trouble and expense of making a completely new head, like the several 7 port and 8 port varieties on the market, why not go all the way and make it overhead cam? Why waste money tackling half the problem? Just curious.....

 

I will be interested to hear how these rods do perform, after a few tens of thousands of miles.

Since the application is really only for racing cars it may be that an OHC conversion is not allowed under the regulations.

There really is no point in fitting CF or even tubular rods in a road car as you are never desperate for another couple of hundred revs or so or have a need to reduce the valve spring poundage slightly. A properly built road engine should do thousands of miles anyway with a standard valve train.

I have used the original rocker shaft from a Cooper 'S' and lightened/polished it to get valve train mass down for a 970 'S' rally car running a 286 cam. We lightened the cam followers as well and used VS2 valve springs (from memory) to be able to use 8000 rpm without getting valve-bounce. That worked, but even then the car was not as quick as a 1040 cc Hillman Imp!

I guess tubular titanium push rods would work in a race engine and investigation of fatigue life would indicate after how many races they would need to be changed. If you are paying over £20,000 for a Mini race engine, then replacing the push rods every season is not an issue.

 

I like the way you think.

[MINI MAD RKH]

 

I guess tubular titanium push rods would work in a race engine and investigation of fatigue life would indicate after how many races they would need to be changed. If you are paying over £20,000 for a Mini race engine, then replacing the push rods every season is not an issue.

 

 

Crikey, are Mini race engines really that expensive?? 

[Cooperman]

A full-on Group 2 Historic race engine to FIA regulations and complete with gearbox cost around £23000 and will last one season without major re-work (hopefully) Power output is guaranteed at c.130 bhp (from memory) and without that sort of engine you won't have a chance of winning. That is a Cooper 'S' basic block with a specially made forged crank (new). Everything is optimised and absolutely top quality with a huge number of hours taken to do a very thorough build. The labour alone will be over 100 hours, or so I was told, so there are several thousands of pounds of labour.

[[email protected]]

 

Mini Sport use to sell them years ago about 1999-2000

Nearly as old as this thread then

 

hahaha