m20 cam profiles and rockers

[RiB]

Hi . I have a question related to these camshafts . Is there a difference in the lift size between a non facelift and a facelift model ?
Long story short i am doing an M20B20 stroked to M20B24 + Turbo 400bhp marc but i don`t know what camshaft to use .

Some people say B25 camshaft is good, some people say the B23 camshaft is the most "brutal" but comparing the diagrams, even the B20 camshaft performs good if not even better when it comes to Intake or Exhaust valves .
Any response is welcome !

[digger]

ok fair enough

[agisthos]

Normally you get a cam card telling you the specifics of the cam so it can be installed correctl especially if it's s custom one. Who did the custom ?

This is my problem. No one knows!! I got the car from a 2nd dealer in 2005, who told me it had a mild cam and head work done.

It was lumpy. Not too bad for daily driving, just right.

So now with the engine rebuild.... the block and crank are fine, and I can get new 323i pistons for $400. But the head was previously welded right across the middle and is corroded.

So I told the engine builder I want whatever new head to be done exactly like the old one, as it was great. But in order to figure out what was done he wants stock measurements to compare the current one to.

I thought it was a schrick cam (or equivalent copy), something that would have a part number on it. But no, nothing!! Its blank.

[digger]

Normally you get a cam card telling you the specifics of the cam so it can be installed correctl especially if it's s custom one. Who did the custom ?

[agisthos]

original post fixed.
if its a custom cam why do you care what the stock cam is? what does the cam card say?

Thanx

Cam card? er.... I don't think there is one?

The engine builder wanted to know what the specs of an original 323i 731 head are - cam lift, lobe lift, valve lift, rocker ratio e.t.c so he can compare to what is in there now.

[digger]

original post fixed.
if its a custom cam why do you care what the stock cam is? what does the cam card say?

[agisthos]

Digger it would be really helpful if you could repost the original images, they have expired.

It seems my cam is a custom grind that has no part number whatsoever, and my engine builder wants to know what the stock cam measurements are supposed to be (for the M20B23).

[digger]

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.

when andrew was still at IE he said they made the change to longer pads but some people could still get old stock if they buy elsewhere

[digger]

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

if you put a bunch of rockers onto a rocker shaft and slide some precision 6mm rod through the eccentric holes they all line up with OE ones. the distance to the edge is irrelevant from a geometry point of view

[digger]

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.

yes depending on what the angular position of the eccentric is then the true centre of the eccentric moves changing the effective ratio. so if you run different length valves or different base circle cam then the effect is similar to. its actually really complicated geometry not simple like a cam on bucket

[zaq123]

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

HD rockers look pretty consistent and in line with BMW oem rockers (shaft to eccentric hole alignment is the same). I was considering returning HD cams as they give too much lift for my oem springs. My 10:1 build could benefit from ow duration hight lift cam (276, 11.5mm) but with these HD rockers, valve lift is close to 12mm. Freaking a lot for oem springs, I suspect.

[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.

[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]

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.

[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