Renault Engine Building tips

[MRN I J]

Got a quote from our machineshop for x flow roller rockers for 15 sets, just finalising & will post price shortly, to get a larger ratio rocker in we might have to make the 5 supports & move the inlet rocker shaft back towards the plug tubes, modifying the rocker to avoid the plug tube, exhaust side is easy & rocker shaft would remain in the same place.

will possibly make roller rockers for wedge head aswell which are quite easy to get to work with more ratio.

[gideon]

One of our members in Australia, Willa, had two sets of roller rockers made for the wedge head in 2019

http://www.lotuseuropa.org/LotusForum/index.php?topic=1053.msg36061#msg36061

I just thought I'd cross reference this in case there's any chance of sharing design information or anything like that.

[Ultimaguy476]

I am wondering what the advantage is to changing the rocker ratio instead of changing the cam grind? 
It seems a tradeoff:
-With higher rocker ratio, the push rods and lifters move less.  Does this translate into something good, like higher achievable rev limits?
-Higher rocker ratio would put more pressure on the rockers and shaft.

In the end, the idea is to get more movement out of the valve.  Seems that changing the cam grind achieves this.

What am I missing?

[Bainford]

I am wondering what the advantage is to changing the rocker ratio instead of changing the cam grind? 
It seems a tradeoff:
-With higher rocker ratio, the push rods and lifters move less.  Does this translate into something good, like higher achievable rev limits?
-Higher rocker ratio would put more pressure on the rockers and shaft.

In the end, the idea is to get more movement out of the valve.  Seems that changing the cam grind achieves this.

What am I missing?

With either method, there will be increased mechanical losses. I expect that the problem with just fattening the cam lobe is the interface dynamics between the lobe and the follower. At some point, any small increase in ramp angle and height of the lobe will have a significant increase in shear stress of the lubrication film separating the two. These stresses will increase as well with a greater rocker ratio, but less dramatically so than by a big, hairy re-grind. And, as you mentioned, less overall travel of the reciprocating valve train components will enhance valve train stability at speed.

[MRN I J]

Only original cams to regrind unless we put in an order for 50 or 100 chilled cast blanks from India which is the best place to get cam blanks made.
As Bainford states there are limits on cam dynamics whatever blank you use, you can lessen the problems by increasing the diameter of the cam follower when the new blanks are made, read Bell's Four Stroke Performance Tuning book for more info.
Roller rockers with more ratio are an easy solution (wont say cheap) the friction would be less than the std rockers which puts huge strain on the valves & guides.

[Ultimaguy476]

MRN...I believe you meant the diameter of the cam lobe, not follower?

I agree that a larger cam lobe is preferable, although I'm not sure I am following the reasoning that says that higher ratio rockers is better than a more aggressive cam, assuming that the cam lobes are reasonable size.

I got no interest when I posted about getting a group buy of cams.  I was hoping that we could either get them with unground lobes to be ground to preferrence or get them with different profiles as not everyone wants the same profile. 

CATCAMS sells 6 different cam profiles....unfortunately we would have to give up offspring to afford them at $550/ea.

I am currrently getting just under .500 valve lift with my current roller rockers and reground cam.

[MRN I J]

MRN...I believe you meant the diameter of the cam lobe, not follower?

I agree that a larger cam lobe is preferable, although I'm not sure I am following the reasoning that says that higher ratio rockers is better than a more aggressive cam, assuming that the cam lobes are reasonable size.

I got no interest when I posted about getting a group buy of cams.  I was hoping that we could either get them with unground lobes to be ground to preferrence or get them with different profiles as not everyone wants the same profile. 

CATCAMS sells 6 different cam profiles....unfortunately we would have to give up offspring to afford them at $550/ea.

I am currrently getting just under .500 valve lift with my current roller rockers and reground cam.

there is a direct relationship between cam lobe height / cam base circle & follower diameter.
Are CATCAMS grinding on new blanks

[MRN I J]

looks like they are grinding on steel billets only, not chilled cast blanks as metalurgically correct. I'll get a price in chilled cast blanks

[Ultimaguy476]

I would love a good blank so I can get full size lobes again.  Keep me posted.

BTW...any news on the roller rockers?

[GavinT]

I think some of the appeal re higher ratio rockers has to do with convenience and marketing, too.
It's a lot easier to install a new set of rockers than take the whole engine apart to change the cam. Higher ratio rockers effectively increase valve acceleration for a similar pseudo overlap gain. I don't know how these high ratio kits handle the geometry changes.

But stock ratio roller rockers also come with a few quirks. They rigidly maintain a static dimension between rocker fulcrum & valve stem whereas a stock rocker changes as it moves through it's arc. I'd want a cam that takes the differences into account.
Also, a roller rocker introduces an additional potential point of failure - the roller tip.

There's no doubt roller rockers add some bling . . expensive and unseen but other than that?
That's a lot of dollars for zero HP.

I see them more as an enabling mod.
Given they reduce side loading of the valve stem, perhaps the obvious next step for a racer is to move to 7mm valve stems, titanium valve retainers and remove any valve guide remaining in the port.
Anyone cross drilled their lifters?

[Richard48Y]

As it is so very pertinent to my current build I am bringing this back from the dead.

In my recent searches new original TS rockers are extinct, I have not been able to find a source anywhere at any price.
That leaves reproductions and if you are going to that much effort they may as well be roller tip.
Lots of CNC shops around but few foundries or shops that want to use castings.
I see that I commented on this thread in the past, it is one of the threads I could not find using search.
The thread drifted hard into cylinders and the roller rockers were left unresolved.
I am currently pursuing a couple of leads for them.
This thread shows that one of those is the company that did them for Ultima Guy.
A couple more are in the UK, they may have more Renault customers there?
If all else fails I know a shop that would probably do them, but as noted the good alloy is being difficult to source at a decent price.
Any metallurgist here to offer an alternative and heat treat?

Is the offer of loan for reverse engineering still open?
I still have a couple of CAD programs on the PC.
These should not be too difficult as it seems they are largely strait lines.
For my own use I would retain the original ratio but if most of the program may remain intact an alternate version should not be difficult.

[Richard48Y]

Spoke with Rockers Unlimited.
They are not keen on making more.
I have asked if they would sell me the CAD files.
Should have an answer tomorrow.

[Richard48Y]

No luck at Rockers Unlimited, they are backed up with work and no longer have the CAD files.
There are two more companies I am trying to get quotes from.
One in the UK and another in the US.
Last resort may be to make them myself with help from a machinist I sometimes work for.
Question becomes is 7075 really necessary or can we find another alloy?

[Richard48Y]

Roller rockers may be moving forward again.
I've submitted some pics to a willing company.
Waiting for a rough quote and minimum quantity.

[Richard48Y]

  Ugh, $10K tooling cost for a die cast version.
I am sure they would be great but I've asked for a quote on CNC milled aluminum, reasoning that fixtures would be less expensive.