M103 Rocker Arm Ratio?
 

This is a wierd one,,, Anybody have any clue what the rocker arm ratio is on an 86 300E M103 engine??
Thanks!
Adam

bump_____

Anyone?

Tell the truth... I'm not sure what that means.
Does this sheet help?

Pretty sure M.B.Doc or Gilly will know. ;)

A264172
What it means is this, I'll just use a Chevy for this.
One end of the rocker arm is moved by a pushrod, which in turn is actuated by a hydraulic lifter, which is actuated by a lobe on the camshaft.
The other end of the rocker arm actuates the valve.
This is not a 1:1 ratio.
For instance on a small block Chevrolet, this ratio would be 1 : 1.50.
I.e. for every 0.100" lift at the camshaft, you would have 0.150" of lift at the valve.
For more detailed information ( or if you really care ), you'll have to pay me. :D

Interesting... luckily I don't have a Chevy ;)
Maybe when I find a cheap valve spring compressor that will work well on my M103... and attempt the seals, sometime in the future. I'll get back to you on that.

Adam,
Is that a preformance mod you are attempting?
Manny ain't talkin :D

I've never seen a published rocker arm ratio for M102/3, but by looking at cross section drawings of the engine I would surmise that it is essentially 1:1, which is maybe why it is not mentioned in any specification lists.

Rocker arm ratios are not constant, but vary with valve lift. For example, everyone "knows" that vintage Chevrolet small blocks are 1.5:1. Not true! I've measured the rocker arm ratio on my '63 Corvette with mechanical lifters and it is 1.37:1 at the lash point and 1.44:1 at maximum lift with a cam lobe height of about .300".

Duke

Hi Guys!

First off A264172, You Rock!! With those numbers I will be able to calculate rocker arm ratio, which I will do later. THANKS A LOT!!

Manny and Duke2.6,
Your right on, those are the numbers I need. Although the ratio looks close, I don't believe it's 1:1. I may be wrong though, I'm no math wiz. My performance machine shop guy is helping me with the valvetrain geometry and the "new"cam.

Everyone,
Not to brag,,,,, Well, maybe just a little.. Wait until I unleash the final build on this M103 Turbo. This project started off as a chepo junkyard turbo $1000 dollar thing. I"m now at the $10,000 mark on this project and it just keeps going up. Some people may say I'm crazy spending money and time suping up an old 300E. They maybe right, but in the meantime I am lerning a lot about building performance engines and will be able to knock the pants off of those honda civics with my 4-door sleeper. Just wait... :D :D :D :D :D

Thanks Again!
Adam

I don't see at all how knowing this will help. The cam is "here", the valve stem is "there". Unless someone is going to custom-make you a set of rocker arm brackets which will alter the geometry, how is knowing the ratio going to be a benefit? All you'd need to know (besides knowing a mathmetician) is the distance from the center of the rocker shaft to the center of the valve stem, and from the rocker shaft to the center of the camshaft core.

Gilly

Hi Gilly,
Actually the altered cam is "?" in relation to the custom valve stem length, the new valve seat height, the new spring seat pressure and the new valve retainers and locks. As you can see I have some dimensions here that will need to be known to order my custom pistons and hydraulic lifter shims. I may go with solid/adjustable valve lash if the geometry is way too off, (it shouldn’t be) or if there is an intake or exhaust reversion problem at high rpm. As you said "All you'd need to know (besides knowing a mathematician) is the distance from the center of the rocker shaft to the center of the valve stem." That is correct and all I need for completing the calculations. I wanted to get the original dimensions so we don’t have to spend the time measuring the old rockers. Besides, I would rather not guess on a project like this.
Regards,
Adam

I wonder if it'd be in a M103 intro book. I also wonder if this would be in WIS somewhere obscure, probably Gp 5 or 1?

Gilly

Hi Gilly,
Thanks for the help, What is WIS and where could I get an intro book?
Thanks!
Adam

WIS is available online. I don't have the website address, but anyone can buy a subscription.

If you do a search, it has been mentioned many times.

WIS is workstation information system, yes you can "rent" it online, I think the website is mbtekinfo.com, something like that. Anyone?
If you want a book, going to just have to find one, try books4cars.com.

Gilly

Why not just install an EATON supercharger in the stock engine?
That would be MUCH cheaper, and greater performance gains.