2.7i 731 head build

[digger]

so what makes the 731 a worthwhile upgrade? if they have smaller ports then surely the laws of physics would say that the 885 would make more power cos it can shift more air?

sorry to be a drag. just interested in what must be a good upgrade some reason. need to make sure i choose the right head for my build.

the problem is with most peoples understanding of the laws of physics. One of the biggest is bigger is better which doesn't always work out in a transient system (not steady state flow)
A stock 885 flows enough for 260hp but the engine only makes 170 because of the way the rest of system (intake, exhaust, etc) functions. The more flow the more "HP Potential" but not always "more HP". So the fact the 885 flow more is because of the size then it is not usually that efficient unless of course it is a huge bottleneck in the first place. The smaller port of the 731 allows more freedom in shape altering by material removal (885 really needs material added which is harder) and they can be made to flow the same as a stock 885 with a smaller volume (i.e. average cross section) which means more velocity for the same flow. There are a few other reasons one might choosie a modified 731 over a stock 885 but i wont go into it now.

Note i am talking about a modified 731 not a stock one.........a stock 731 is only an upgrade to a stock 200

[e30leigh]

the problem is with most peoples understanding of the laws of physics. One of the biggest is bigger is better which doesn't always work out in a transient system (not steady state flow)
A stock 885 flows enough for 260hp but the engine only makes 170 because of the way the rest of system (intake, exhaust, etc) functions. The more flow the more "HP Potential" but not always "more HP". So the fact the 885 flow more is because of the size then it is not usually that efficient unless of course it is a huge bottleneck in the first place. The smaller port of the 731 allows more freedom in shape altering by material removal (885 really needs material added which is harder) and they can be made to flow the same as a stock 885 with a smaller volume (i.e. average cross section) which means more velocity for the same flow. There are a few other reasons one might choosie a modified 731 over a stock 885 but i wont go into it now.

Note i am talking about a modified 731 not a stock one.........a stock 731 is only an upgrade to a stock 200

that is all very interesting. i ask as i mainly wanted to know what head to use on my turbo build. im tempted to go the way of 885. was i dont want to spend much port and flowing the head out. and also im afraid that under boost the 731 is going to hold everything back too much.

from what ive been reading stock vs stock. there is no comparison for the 885's larger ports?
but given work and dollars spent. the 731 is very capable or better due to the higher velocity and flow rates that better match the abilities of the rest of the motor.

[digger]

that is all very interesting. i ask as i mainly wanted to know what head to use on my turbo build. im tempted to go the way of 885. was i dont want to spend much port and flowing the head out. and also im afraid that under boost the 731 is going to hold everything back too much.

from what ive been reading stock vs stock. there is no comparison for the 885's larger ports?
but given work and dollars spent. the 731 is very capable or better due to the higher velocity and flow rates that better match the abilities of the rest of the motor.

just use an 885

[e30leigh]

pretty much what ive decided lol. thanks for the insight

[Wanganstyle]

I have had several conversations with Mark about his chip. It was tuned with a 2.7 731 head combo. The best way to get in touch with Mark is to give him a call. He is very helpful and we have even talked about doing a group buy for r3v members.

I have no need or desire for mrkd products. Anyone can map a m20 with commonly avail chips and tuner pro software. You can diy if you understand electronic mapping- It's not very high tech, I could drop my car off at MCE tuning and have them mapped it for power on the dyno with my local crap 91 octane for similar cost to sending dough to Canada. MCE is local to me and is the official NorCal spec e30 dyno.

[2mAn]

im really close to biting the bullet and buying this 731 head. the head has been decked and re-surfaced, 3 angle valve job, polished cam journals, and new valve stem seals, adjusted valve lash. he spent more than the $350 he is asking and he will include 19# injectors and an "I" manifold

[e30leigh]

dddooooo it!

[MrNatural]

2.7i 731 head build

im really close to biting the bullet and buying this 731 head. the head has been decked and re-surfaced, 3 angle valve job, polished cam journals, and new valve stem seals, adjusted valve lash. he spent more than the $350 he is asking and he will include 19# injectors and an "I" manifold

Swap over to motronic 1.3 and you'll love it!

[2mAn]

Im trying to decide between that or just getting the MarkD chip. I hate wiring, but Ive read somewhere that the 87 IS harness is plug n play

sorry for the thread jack

[cheapshot]

I have no need or desire for mrkd products. Anyone can map a m20 with commonly avail chips and tuner pro software. You can diy if you understand electronic mapping- It's not very high tech, I could drop my car off at MCE tuning and have them mapped it for power on the dyno with my local crap 91 octane for similar cost to sending dough to Canada. MCE is local to me and is the official NorCal spec e30 dyno.

I'm told the chip for the 027 dme is getting very hard to source. Also, not anyone can map their own ecu because of the lack of understanding electronic mapping, which would include me. Not all of us have access to a shop that has these capabilities. Mark has been a valuable asset to this community and I hope it continues to support him. Best of luck to you.

[Wanganstyle]

No luck required. My built m20 is already mapped custom for Cali 91. No mark d needed here; Cali crap gas needs Cali tuning.

My m20 did a track day and dyno'ed double the passes on the same dyno that the ryangmw s54 tuned by RGMW blew up on.

then I drove it home after taking it drifting all afternoon.

[iXe<30]

sorry but whaat is all this doing to your gas mileage jw

[red325ix]

Any updates on the build cheapshot?

Also.....Do you know what the new rev limit is with the MarkD chip that is designed for this swap using the 027 DME?