m20 cam profiles and rockers

[digger]

these were posted before but dissapeared somewhere so thought i should repost

The cams measured were:

1) Schrick 288
2) MM Rally
3) M20B25 K (measured two which were identical)
4) M20B20 L
5) M20B23 (1/1984 car, may be a different cam for 1985 models)













here is a comparison between HD rockers and stock bmw ones.

it appears the HD are designed to suit reground cams as the pad has been offset slighty





I've not yet compared valve motion between the two different rockers properly but on one cam i've had for a few years collecting dust (catcam 296) the lift is drastically increased with the HD from 12.3mm to 13.0mm. unfortunately this cam is a rather aggressive cam and the end of the pad would dig into the cam and cause it to shit itself rather quickly, if only the pad was longer at both ends this might offer a bigger effective rocker ratio. i believe the billet rocker have longer pads for this reason but i dont know if the pads are also offset.





http://www.e30tech.com/forum/showthread.php?t=116816 ref post #17 for real world results


i expect on a more mild cam the HD rockers might add more area under the curve without the pad running off its end.

[digger]

some might be interested in this. read it on the catcams website

http://www.catcams.com/tabid/432/default.aspx?tabfile_ID=37

catcams now have steel m20 billet rockers coated feet. longer feet to so dont have the same limits on velocity so you should be able to get more lift without excessive duration compared to the standard rockers if you get a custom cam. one of the guys over there said 290 duration you can have 12.5mm easily, compared to 11.5mm from Schrick 288

they will work with existing cams

id be all over this if i didnt have the RHD roller ones already.

i think these are quite a bit cheaper than VAC billet alloy and the shitty PPM knockoffs but will be quite a bit more $$$ than cast ones. i think they are 120 each but not seen it listed officially

[The Red Baron]

This is awesome, I'm actually currently looking for new rockers to go with my 280/274 cam, and VAC heavy duty valve springs and retainers.

These are the springs https://store.vacmotorsports.com/mob...-m20-p972.aspx

With the cam and spring combo, obviously I'm hesitant to use the oem rockers that have 90k on them. I'm interested in your mentioned roller option, can you provide more information on those, or something you'd recommend to use with this profile?

[digger]

the RHD roller kit utilizes a dedicated kind of lobe to work with the roller so it isn't compatible with regular m20 grinds. unless you are looking to push the envelope then probably overkill for most given the cost. i dont know if there has been enough interest to do more batches of rockers and cams youd have to email Rama.

http://racehead.com.au/products-page/engine-components/bmw-m20-roller-cam-conversion-kit/

280/274 is such a mild cam OE rockers would be fine, i like the MM peened and inspected rockers , OE quality with some improvements. if i was looking at bigger than 288 with an agressive profile like some of the catcams lobes on a lower budget or if RHD weren't available then i would look at the catcams rockers with a custom grind to try and maximize the lobe area using a more aggressive profile

[zaq123]

I wonder how much does the pad height change the rocker ratio? lower pad = higher eccentric to maintain the same clearance, I think..
Do you think the same idea applies (pic)?

[wilholl]

So, am I correct in reading the graphs, that it looks like the Euro 2.3L cam is very close to the standard 2.5L cam?

If so, I think I will just toss the 2.3L Euro cam I have buried in the garage.

[digger]

I wonder how much does the pad height change the rocker ratio? lower pad = higher eccentric to maintain the same clearance, I think..
Do you think the same idea applies (pic)?

i think i still have the bits lying around if i get a chance i will try dig them out over the weekend and compare the lift profile of stock b25 with OE rockers and the IE ones to see how much the profile changes.

it would probably be the same as the pic, the arc is the same but the position at 0 lift is different so at max lift the rocker has different relationship to the head so it can change things. the same as the the tip height of the valve can change geometry a bit to

[digger]

So, am I correct in reading the graphs, that it looks like the Euro 2.3L cam is very close to the standard 2.5L cam?

If so, I think I will just toss the 2.3L Euro cam I have buried in the garage.

They are "similar" but don't believe what people tell you that it is better for performance because it has more duration, that it is only half correct, it is slightly inferior IMO.
If I had both in front of me id use the b25 every day of the week. but I would not buy a stock b25 cam if I had a good b23 one lying around. if you use the b23 cam run the clearances a little looser than factory recommended.

[digger]

I wonder how much does the pad height change the rocker ratio? lower pad = higher eccentric to maintain the same clearance, I think..
Do you think the same idea applies (pic)?

so IE HD rockers increase peak valve lift of stock cam by approx 0.40 mm or 4% the HD rockers i had still had the lobe coming very close to running off the pad

[zaq123]

so IE HD rockers increase peak valve lift of stock cam by approx 0.40 mm or 4% the HD rockers i had still had the lobe coming very close to running off the pad

running off the stock cam? 0.4mm is a lot. What lash was installed for the measurement? Did you use OEM springs? I don't have good OEM rocker. Otherwise I would try to find out the following:
1. given the same lash(0mm,0.25, whatever, as long as the same for both rockers and on the same cam), HD vs OEM....does the cam pad ramp on both provides the same valve oped duration or it's different?
Also if you compare assembled OEM and HD rocker with the same lash setting: Does eccentric position with HD rocker provides for more ascending eccentric ramp towards the full lift vs the eccentric position on OEM?

[zaq123]

for example: at the same lash at TDC(point at a for HD and point a1 for OEM): b-a=c is the ramp at full lift for HD rocker, b1-a1=c1 for OEM. Is it possible that C ramp is greater than C1 ramp?

[digger]

i used inner springs only so you will lose some lift due to deflection withe double springs but it is the same for both rockers. i plot with zero clearance and offset a curve 0.25mm to account for clearance

it looks to me like the centre point of the pad radius is probably the same on both rockers but the radius on HD is slighty larger (using a radius gauge OE is 32mm and the HD just under 34mm) so the arc is offset like two concentric arcs. this means the HD work better on the smaller base circle of a regrind as the eccnetric doesnt run out of adjustment.

the change results in a change in duration of about 4-5* at seat but would be more change at higher lift points and the lift increase is about 0.4mm perhaps a little more.

so if you are in SPECe30 and use OE rockers you are probably losing a couple of hp compared to others

[zaq123]

i used inner springs only so you will lose some lift due to deflection withe double springs but it is the same for both rockers. i plot with zero clearance and offset a curve 0.25mm to account for clearance

it looks to me like the centre point of the pad radius is probably the same on both rockers but the radius on HD is slighty larger (using a radius gauge OE is 32mm and the HD just under 34mm) so the arc is offset like two concentric arcs. this means the HD work better on the smaller base circle of a regrind as the eccnetric doesnt run out of adjustment.

the change results in a change in duration of about 4-5* at seat but would be more change at higher lift points and the lift increase is about 0.4mm perhaps a little more.

so if you are in SPECe30 and use OE rockers you are probably losing a couple of hp compared to others

What do you think about my post regarding eccenrics? To dial proper lash with HD rockers, eccentric will be pushed in closer to point A on the pic vs. A1 on oem rocker. When at full lift, A moves to B and the change in eccentric's radius is greater vs OEM A1 to B1 resulting in probably greater lift.

[jeffnhiscars]

There's a variable that I think could skew the math here. The distance between the eccentric bolt hole and the edge of the rocker tang varies greatly from rocker to rocker. Less so on OE but the range on the new Febis I had was so extreme I sent them back.

Either way the hole locatoion is not consistent

[zaq123]

What do you think about my post regarding eccenrics? To dial proper lash with HD rockers, eccentric will be pushed in closer to point A on the pic vs. A1 on oem rocker. When at full lift, A moves to B and the change in eccentric's radius is greater vs OEM A1 to B1 resulting in probably greater lift.

Also it looks like cam pad on HD rockers is 2.5 mm longer (about 1.25mm in each direction). Should help with the "run off the cam" vs oem.