Racing camshafts

[hasa]

Does someone have here experiences about M20 racing camshafts. I'd classify anything that goes beyond Schrick 304 as "racing".

Motivation for the question is that I'd like to replace my Schrick 304 by something that delivers more in the 5000-7500 range in a 84mm stroke engine. RHD roller cam setup is of course the ultimate solution, but how about Cat Cams, dBilas or similar?

[digger]

what are the detail specs of your engine and what does the actual power curve look like?

If a schrick 304 isn't running easily to 7500 there is it is reasonably likely something else in the system that's not spec'd appropriately for that rpm.
for example with a 288 cam in a 2.8-3L will peak around 7000 with a RHD ITB setup

[hasa]

Yes my current setup has restrictive parts, you are right. 40mm id/ 45mm od headers secondaries are first suspect. Stock 885 head and 2.5” single exhaust after that.

But I’d still hear, if anyone here has used those hotter cams.

[digger]

Not sure what info you are looking for but finding good valve springs and getting rockers to live is the issue that I know people in these parts had with big catcams they used

[moatilliatta]

I think metric mechanic now has their steel rockers released.

[digger]

They have m30 ones not sure about m20 though.
catcams do a steel rocker but pretty spendy

[hasa]

So you say that it does not work with std rockers to go beyond Schrick 304? I can understand that, if the acceleration forces just become too high no matter which valve springs are there.

My experiences with racing engines have always emphasized that the springs must be stiff enough so that valve float does not occur. Whenever the springs cannot control the valvetrain movements, many different evil things happen. Of course the spring stiffness may be too much for the components too.

Cat Cams seems to suggest their 115kg springs to all the hottest cams
dBilas promotes their "120kp" springs to all applications that require spring upgrade

PPF on Sweden seem to sell some insane springs for the turbo applications

http://server.pure-pf.com/webshop2/en/valve-spring-kits-bmw/314-m20-valve-spring-kit-stage-3.html

[digger]

The OE rockers will physically work unless the cam is stated as not being compatible.I was referring to the HD rockers may not as the pad is different on some earlier versions. they may have addressed this but pad quality seems questionable.

One issue is good quality springs without them going soft. PAC sell a beehive spring and retainer iirc that’s compatible, it’s from a ford 2v modular engine.

With stuffer sorings then you rockers that can withstand the higher loads and surface speeds that are required.

you can run what the cam companies recommend but it’s worth looking at alternatives

[TobyB]

Whenever the springs cannot control the valvetrain movements, many different evil things happen.

I usually only experience one evil thing- on throttle lift- off, an intake rocker breaks.

Yes, the stock rockers with the right springs will go to 7500 and sit there all day. IF they don't have
voids in them, and that's getting to be hard to prove (got x-ray?)

Yes, some cams are too aggressive for any rocker- as hasa implies, it's not the acceleration,
it's the deceleration that's the problem. If the lobe isn't too steep for the lash pad,
and doesn't drop away like a cliff, it can be made to work.
'How long will it last?' is always a valid question, too, as high spring pressures
put a lot of load on the lobes and pads.

One thing you do not discuss is intake- 40mm itbs would be the minimum for 7500,
and much above that, bigger would be better.

t

[digger]

I usually only experience one evil thing- on throttle lift- off, an intake rocker breaks.

Yes, the stock rockers with the right springs will go to 7500 and sit there all day. IF they don't have
voids in them, and that's getting to be hard to prove (got x-ray?)

Yes, some cams are too aggressive for any rocker- as hasa implies, it's not the acceleration,
it's the deceleration that's the problem. If the lobe isn't too steep for the lash pad,
and doesn't drop away like a cliff, it can be made to work.
'How long will it last?' is always a valid question, too, as high spring pressures
put a lot of load on the lobes and pads.

One thing you do not discuss is intake- 40mm itbs would be the minimum for 7500,
and much above that, bigger would be better.

t

I think in another thread he may have jenvey 45 throttles for some time already and now a ported head to go in at the same time as the cam.

[hasa]

My particular engine combo is

84 crank
11.5cr forged bottom
195cfm ported AMC head
dbilas+jenvey 45mm intake side
semi-long generic headers

I consider purchasing dBilas 312 or anything similar from Cat Cams. I'll first check how much I have room for valve opening at TDC. I did it some time ago, but can't recall.

[Maximumtune30]

A shop in Finland called Vp-motorsport sells steel rockers for the m20, 500€ for a 12x set. I'm not sure if they will ship them to you though.

Another shop called Futurez sells steel rockers made by ENEM 535€ for 12x set, but they only sell them if you buy a enem cam from them, i don't think they sell them seperately.

[digger]

i've got sample of the Enem ones and they dont look very good from pad geometric profile (will produce difference valve lift though haven't measured to quantify) and surface finish, they pale in comparison to the catcams sample i have but costs is alot different so.....

[AWDBOB]

I have a spare set of these I could be convinced to let go of if you're on the hunt, hasa.

https://www.pureperformancemotorsport.com/bmw-m20-billet-7075-t6-custom-rocker-arms.html

[hasa]

I have a spare set of these I could be convinced to let go of if you're on the hunt, hasa.

https://www.pureperformancemotorspor...cker-arms.html

Thanks for the offer, but I'll try to get along with the OEM rockers.

I've understood that these HD rockers are all (except RHD) targeted for the turbo scene, where exhaust backpressure sets unique requirements for the rocker strength. I may be wrong... but anyway.