731 question: b20 cam vs. b23 cam

[E30 Wagen]

If I wanted to make a lot of power I would have simply built a proper 2.7 with a 885 head. I went with a 731 because it's just easier to bolt on a stock eta block without needing to change the pistons, plus I like the "euro" factor of it. I'm just getting my feet wet with this whole 2.7 thing so I'd rather do what I can with what I have before spending big money on a new cam, pistons, head work, etc. I have a complete spare 885 head that I can steal parts from. I got it from a junkyard, so I just hope everything is useable. I know some have run a b25 cam in a modified eta head with good results, so if it will help my 731 breath a little better then why not?

[digger]

my point was whichever OEM "i" cam you use doesnt really matter much and you're probably over thinking it a bit, as neither will be a "screamer". i wasnt actually suggesting you do a ported head etc but that this would be required if you wanted to make noticeably more hp than a b25.

[Hooffenstein HD]

my point was whichever OEM "i" cam you use doesnt really matter much and you're probably over thinking it a bit, as neither will be a "screamer". i wasnt actually suggesting you do a ported head etc but that this would be required if you wanted to make noticeably more hp than a b25.

As digger said, The basic 2.7i don't really scream that hard. The B25 is a fairly well designed engine and do seem to have a higher, more revvy power band. This could partly be due to the 2.7's shorter rods but more than likely mostly in the head.
The 2.7i's do torque like a mofo and should throw down a similar peak hp but not more than a B25 unless you work the seats, bowls and SSR and use an aftermarket cam.


I'd ask the machine shop how much they'd charge to install your 42mm valves from the 885. That's going to make more difference than any of the OE cams would. It would flow more at low, or high lift. I think Rama got a 30% increase in flow from 42mm valves in the 731 head with a 45/65 seat cut and the bottom cut blended in.

EDIT: There's a great thread on the M20 engine over on speedtalk.

[digger]

when doing bigger valves, its the complementing valve job, throat, backcut valves, shortside and bowl work that does the trick. rama is the man for the 731, he can easily do a head that flows better than an 885 with a smaller port

[jeffnhiscars]

This is actually the thread I was hoping to find since I just found out my b23 cam is not at its peak.

I'm hearing that a b25 is an ok substitute but given the +2 valves and port work I'm doing a 272 would perform notably better albeit at higher cost ?

I'm not sure how reliable these letters are but there's a "B" on the cam as well as the numbers "358".

[digger]

a 272 probably makes the most sense given where all this is headed

[jeffnhiscars]

a 272 probably makes the most sense given where all this is headed

Somehow I knew you were going to say that lol.

Would a 272 force me to upgrade the externals to avoid fuel starvation and what about drivability and a lumpy idle ?

[digger]

the thing about making changes here there and everywhere is the tune, i dont recall what ecu/fuel system you're going to use (M1.3?)but with a good chip will drive fine. it might be a bit lumpier but if the engine and electrics are working well its not bad.

[jeffnhiscars]

the thing about making changes here there and everywhere is the tune, i dont recall what ecu/fuel system you're going to use (M1.3?)but with a good chip will drive fine. it might be a bit lumpier but if the engine and electrics are working well its not bad.

Here there and everywhere being the operative words which is why I'm trying to stick with modest and fairly well tried and proven changes.

A couple of things are pointing me towards a b25 cam. First is that the base plan was to do this in bite size stages to minimize down time and to preserve drivability. This means head first and b25 bolt ons after and I think a 272 would demand more than just a head swap to meet that goal.

Second is that this is a DD auto trans which will never see high revs which, to my understanding is where much of the gains from a 272 would be.

Third is that a number of people have said a stock 731 on a stock ETA block is a blast and I'm already beyond that. Has to be a line somewhere.

Finally, I can buy a brand new b25 cam for $130 which is a suitable replacement for the worn b23. Sure it's a febi not a Shrick but I don't doubt it will do the job for some time. Throw in new stock rockers and it's virtually a brand new head and Bob's your uncle

At least that's my theory for tonight :)

[5Toes]

also have you considered using delta cams in tacoma or similar to get an original 885 cam reground. its affordable and they dont have to add material at all, just change the shape of the lobes.

[jeffnhiscars]

also have you considered using delta cams in tacoma or similar to get an original 885 cam reground. its affordable and they dont have to add material at all, just change the shape of the lobes.

We did dicuss a re grind and I'm not sure what the advantages are VS new. Will it actually be cheaper esp if I have to ship it and can you change the profile ?

FYI this is a b23 cam and I'm sure there is someplace closer if I went that route.

[digger]

you can regrind to more duration by changing the base circle, sometimes this requires new eccentrics sometimes not, but if you use the HD rockers these will probably work out of the box as they appear to have an offset pad.

iirc delta cams grind the MM cams, they are welded though

[jeffnhiscars]

you can regrind to more duration by changing the base circle, sometimes this requires new eccentrics sometimes not, but if you use the HD rockers these will probably work out of the box as they appear to have an offset pad.

iirc delta cams grind the MM cams, they are welded though

Sounds more complicated than I am prepared to deal with and if we start to talk about HD rockers I'm going to start talking about mission creep and how a project can get out of control :)