m20b29 cam question

[mrlucretius]

Hello,

I am getting a motor built, a 2.9L m20. I believe that is the 84x85mm crank / bore with the standard 2.5i head. The head has a decent port and polish, +1mm intake valve, it will have long tube exhaust header and custom exhaust, with dbilas ITBs.

Question about the cam: will this thing be suitable as a daily driver? As in, will it idle, will it have a smooth power band, will it pass emissions (with a temporary cat installed)? I will have an MSPNP and a proper tune.

Thoughts, comments, suggestions?

Cam specs:

296 inlet
296 exhaust
258 inlet / exhaust
106 lobe center
12mm lift
3.6mm lift at tdc
42/74 - 74/42 IO/IC - EO/EC
2mm clearance to
122kp valve spring hardness
37mm fitted length

I think it is very similar to this cam, except with slightly less lift:

EDIT: I had the wrong link. This is the correct link to the 296 Dbilas cam:

http://www.dbilas-shop.com/Products/Performance-camshafts/BMW/2-0-2-7-6-Zyl-12V-M20/New-camshafts/BMW-2-0-2-7-6-Cyl-12V-M20-Performance-camshaft::4924.html

Thanks!

[SkiFree]

If this is a street car that cam is pretty dang aggressive, but so is your engine-spec. (+1mm valves, 45mm ITB's).

-I don't know smog laws in your specific area, but I'm guessing passing may be a challenge.

-As for idling.... a mild idle is going to be a challenge, but I've seen dyno tuners do some amazing things.


My two cents, for a street engine I would have gone less aggressive with a 2.9L build (40mm RHD ITB's, standard valve diameters, 284/280 cam). That being said, if you have a guy doing this for you or someone that swears they know what they are doing, then see where it goes?

[mrlucretius]

Hey,

Thanks for your input. I am in Boulder County Colorado. Emissions limits:

Year CO HC NOx
1989 20.0 2.0 4.0

The thing is, this guy has all these parts collecting dust including the cam. He was going to put it in his stripped e30 racecar, but instead decided to stuff an S54 in there instead.

He thinks it should be fine to daily drive, so does the well regarded engine builder he is working with. I am just a little nervous after receiving the cam spec...

Why do you suggest smaller ITBs? What effect would the larger ITBs have for a given engine build?

Also, what kind of crank / wheel HP do you think your suggested cam / build might make?

I am willing to get a different cam if it would be no fun to daily drive / idle / etc issues. ITBs are already purchased...

I guess I can always swap the cam out to a milder version without too much pain...

[mrlucretius]

Well to answer my question about ITBs:

http://racehead.com.au/designing-performance/what-size-itb-should-i-use/

[SkiFree]

What pistons are being used and what is the estimated compression ratio?

[ForcedFirebird]

It will work "ok" if you have a lot of compression, otherwise you will have no idle vacuum, probably have to idle around 1000-1100, and have no power until just before your shift. Overlap may be an issue for passing a sniffer, but a good tuner can do a temp sniffer tune for you. Not sure if your locals will be weary of an aftermarket ECU, but the Motronic will be fun to tune that...

[downforce22]

we're you looking to turbo your m20? Stock cam is good for turbo.

[mrlucretius]

No plans for a turbo setup.

Should run at 10:1 compression with the pistons he has.

[digger]

you can daily drive any cam you want, it is a question of how fun is it going to be when 99% of the time you'll be at low to medium rpm and light throttle to medium throttle in traffic. Thats a pretty wild cam for a 2.9L and daily driver. if it is a street car thats driven on weekends only or at track days then sure it will be manageable IMO with some compromises as long as it is with itb and a standalone ecu. i doubt you'll ever pass emissions without some trickery.

just as important if not more important with the iTB is the runner length, short runners kill the midrange

[mrlucretius]

So I expressed my concerns and my engine builder is think a Shrick 288 camshaft may be much better for my needs? Thoughts?

[ForcedFirebird]

10:1 isn't a very aggressive CR for that duration/lap. We have gotten some pretty wild combinations to pass a sniffer, but they always had matching compression/cam. More overlap/duration moves the power band up (pumping loss via reversion) and less overlap/duration moves the band down but also increases TQ since the trapped mass is higher/more dense (increasing dynamic CR). More CR usually means more TQ/low range power all else being equal.

I have some really nice software (Dynomation) that calculates trapped mass at any given crank angle, but haven't taken the time to get all the m20 info into it to be completely accurate. The software is linked with Comp Cams lobe profiles and we use it to design cams for the domestic market.

just as important if not more important with the iTB is the runner length, short runners kill the midrange

I lost a bunch of dyno runs/winpep when the dyno PC HDD gave up the ghost, but IIRC removing the spacers on the ITB's (shortening the runners) made the peak greater than the full length, but it was very sharp and much lower RPM than the long runners. Peak power was greater, but area under the curve suffered severely. Maybe these particular files made it to the SD card, will have to look if I ever get a free moment.

[mrlucretius]

Well, I have officially pulled the trigger on this build... Thanks for all the feedback. I will keep you all posted as to the results.

[digger]

So I expressed my concerns and my engine builder is think a Shrick 288 camshaft may be much better for my needs? Thoughts?

should be a better choice for a DD

[mrlucretius]

10:1 isn't a very aggressive CR for that duration/lap. We have gotten some pretty wild combinations to pass a sniffer, but they always had matching compression/cam.

Can you explain this some more? What do you mean by "matching"?

[zaq123]

should be a better choice for a DD

what's LSA for 288 cam?

PS. found it, 110