Lets talk CAMS! :D

[Jacko]

Chaps, i'm going to get a cam for the2.7 before i install it (i know i know, should have done this by now but life it busy and cars have to take a back seat )

The engine is just a std ETA bottom end (not decked) with a 325 head (can't remember the name of it now) and i want some more beans for when i go to spa and the ring in the summer. I need to beat my previous best of 9:31 (never going to happy but we can try)

Soooooo, what cam can i get away with this engine? Also, i fancy whipping the head off while i'm at it and getting it ported - any ideas what i need to be saying to my engineer when it comes to improving the power? I've just dropped off my flywheel and injectors to be worked on and the car is going away for a bit of work to the engine bay and want to keep the pace up although they will be famous last words i'm sure. I was thinking CAT cam rather than schrick (keep the cost down) how do i know if the values will clear the pistons at TDC?

Thanks
Jacko.

[e21-Mark]

I've got a 288 degree Schrick but am pretty sure Cat do a simillar profile. As for flowing, I don't think there are any real gains to be had so save your beans.

[Jacko]

Yeah i think CAT do a similar profile to that, any issue with valves touching pistons? Would i not see any gain with installing the cam...i know its not going to be mega but every little helps or is it the head work where i'd not see any gain?

Regards
Jacko.

[e21-Mark]

I definately felt the increase in performance from the cam. Acceleration felt a bit more urgent from 3000 rpm onward and the torque seems to peak a little earlier in the rev band. I read / was told that there was little or nothing to be gained from flow work on the m20 head. You could consider slightly enlarging the holes in the oil spray bar to increase flow to the cam & followers? I've had no piston & valve collision problems either.

[Jacko]

What block and head are you running and have either of them been skimmed? I know my deck hasn't been played with but i know its what a lot of people do to raise the compression. I'm not sure i really want to start taking meat off the block though. I want as much power as i can get without blowing the bank. No point spending thousands on this engine when i can fit a 3.0 engine for around £1000 so it doesn't make sense.

[e21-Mark]

Yes, the block has been decked to raise compression.

[Jacko]

Is it worth me getting the deck skimmed do you think? How much of a gain would this give over it not being decked?

[e21-Mark]

I don't honestly know? If you google m20 2.7 build the wikipedia link describes 2 ways of building a 2.7 and says the best route is to deck the block and bring the compression up. Mind you, I know of several builds where this wasn't done and they still have a strong, powerful engine. Check e30 zone for the build threads too.

[gerrit323]

I use the split duration dbilas cam 282/272 .. not a standard 2.7 .. completely reworked (in process)

[Jacko]

Is it worth me getting the deck decked? How much of a gain will i see?

[e21-Mark]

All the info is here. Getting the block decked is to increase compression as the eta engine was designed to be a hi-torque, slow revving engine.

http://en.wikipedia.org/wiki/BMW_M20#Re ... _Eta_based

[Jacko]

Yeah i understand its a low comp engine and i understand that skimming the deck will raise compression. My question is really how much difference will it make? Power and delivery wise...

[e21-Mark]

If you're going to the time, effort & expense of a cam swap I would get it done. I can't give you figures but you need to optimize the sat up and you might struggle to time it all up without decking the block too.

[Duracel79]

If you've got ETA pistons DON'T deck the block otherwise the pistons will poke out the top of the block. Decking is required when using the 325i pistons on 130mm rods and 81mm crank.

Its always best to build an engine with plastercine first, turn over by hand to check all the clearances for cam/valve lift.

Ben

[e21-Mark]

Sorry - assumed it was a 2.5 we were talking about. As Ben says, no need with Eta.