731 head for NA eta?

[kickinindian]

i would not consider it cobbling together parts i know the rod ratio is not ideal, and the crank cutting is iffy but its alot cheaper than buying custom pistons and what not.

im pretty much copying this build

http://maxbimmer.com/forums/showthread.php?t=149292

[digger]

i would not consider it cobbling together parts i know the rod ratio is not ideal, and the crank cutting is iffy but its alot cheaper than buying custom pistons and what not.

im pretty much copying this build
http://maxbimmer.com/forums/showthread.php?t=149292

i don't think they referred to cobbling bits together with 2.8L stroker it is a proven swap that works pretty well when executed properly.....

[kickinindian]

i don't think they referred to cobbling bits together with 2.8L stroker it is a proven swap that works pretty well when executed properly.....

I was referring to skifrees post up above

[jeffnhiscars]

I have an inbound 731 w 323 intake (among other bits and pieces) and since I've PMed with a couple of you regarding my options I figured it was time to weigh in a 731 specific thread to limit the variables.

keep in mind that this is for the Time Capsule...bone stock (except for sssquid chip), 126k well documented (thus healthy) 87 ETA w a 2.93S. My inclination at the moment is to do the motronic update later after one sourced everything and can perform that phase in reasonably short shift.

I know it's all about breathing and balance so I know going in that is not going to get every drop of potential from the get go, but I'm fine with that since I hope to be able to measure (or at least rate) each step for 731 posterity.
Phase 1 will be your basic head refresh. Beyond that my understanding is that the 731 & 885 both have 36mm exhausts, but the 731 has 40 vs 42mm intake, so I'm leaning toward using i valves, of course double valve springs and keep the 323 cam since I haven't read anything that says the 885 cam is much better.

I also am thinking to use the 323 intake which is not quite as open as the 885 but then I've read that the 885 intake has way more flow than I need and that too much is as bad as not enough. Will be interesting to see. Afterthought is to port match the intakes to an i just so I don't have to pull the head if I decide to an intakes later. I'm not seeing that as a problem with the 323 intake.

It's also been suggested that I do some port polish etc which I'm fine with if I was satisfied that it would be done right. We've all learned the hard way that this is as much art as science.

I'll have the i TB as well so as long as I can install and connect it that may be part of phase I. Again this will be on ETA electrics so I think an i afm won't work for now.

Anyway, these are my thoughts. Open to input and opinions and general BS :)

[digger]

731 came with the 34mm exhaust valve, nicely ported head with 42/36 valves..... id get the head ported when you get it refreshed as you may need new seats, guides etc and it makes more sense to do it all at once. if you were in oz youd just send it to rama to sort out.

[jeffnhiscars]

If I was in Oz I'd send it myself to Rama :)

are the guides the same or are they specific to the head or valves

[2mAn]

I'd spend good money on that head with a solid porting job by people who know what they are doing. Bigger valves, and a performance cam and you will be happy for a long time...

[jeffnhiscars]

I'd spend good money on that head with a solid porting job by people who know what they are doing. Bigger valves, and a performance cam and you will be happy for a long time...

this is where it becomes fun. Lots of options and I don't think there is a "standard" since I suspect very few people do exactly the same thing as the last guy. Valves yes. Porting yes. Again, think spirited DD not track.

Cam- I've read (and I know reading can be bad for your health) that the 731 cam has its strengths and weaknesses. I've read diggers measurements on different cams and tbh much of that data is above my pay grade. I'll go back to my preference for practicality vs all out thermonuclear war ($$$) and ask if it's really worth spending money on another cam ?

Porting - the bottom line on this is finding someone "who knows what they are doing". Easier said than done unless I want to ship the head to Oz :)

Part of me has no hesitation to get a die grinder and have at it and part of me knows better. Just enough, in just the right places & equal in all cylinders. digger mentioned throat, short side, streamline guide etc. I hVe a great machinist I trust to enlarge seat, deck etc but have no clue at to whether he knows how to improve a 731 so any suggestions on how to select and instruct a shop would be appreciated. Keep in mind I'm in nascar heaven and there are tons of guys doing this around here. I just doubt if they would know a 731 if it fell on them.

Intake- most of the guys working w 731s are down under (or at least not in NA) where it seems 885 bits are in limited supply. I know the 885 intake is bigger but that's not always better. So to my mind this is a toss up (balance again vs max size). I'm inclined to use the intake that was designed to work with the head since a) I have it and b) much of the r&d on the 731 would likely have been done with a 323 intake

[nando]

Don't port the 323i intake. As it turns out, the 885 intake ports are almost a perfect match for the 731 head. so either use the intake as is, or use an 885 intake as it's really already "ported" for a 731 head. I wouldn't say the 885 intake flows too much either, as stock manifolds go it's not bad but it definitely has limitations. between the two I'd just go with the 885, especially since you'll have more displacement than the 323i and bigger intake valves/ported head.

as far as a cam, I'd say yes it's probably worth it. What compression ratio are you targeting? I don't know if the 284/272 is still recommended but it might suit your engine well. Mind valve clearance at TDC, of course..

[jeffnhiscars]

Don't port the 323i intake. As it turns out, the 885 intake ports are almost a perfect match for the 731 head. so either use the intake as is, or use an 885 intake as it's really already "ported" for a 731 head. I wouldn't say the 885 intake flows too much either, as stock manifolds go it's not bad but it definitely has limitations. between the two I'd just go with the 885, especially since you'll have more displacement than the 323i and bigger intake valves/ported head.

as far as a cam, I'd say yes it's probably worth it. What compression ratio are you targeting? I don't know if the 284/272 is still recommended but it might suit your engine well. Mind valve clearance at TDC, of course..

I wasn't planning to do any iwork on the intake mani other than possibly port matching if needed. the 323 intake is coming with the 731 and Since i don't have a spare 885 intake laying around (not that they are hard to find) I figured I'd work with the 323 for now for 2 reasons....1) It's not hard to swap it out later without removing the head and b) remember phase 1 will be w stock ecu, injectors etc so I'm not likely to get much benefit from an 885 intake right now.

As for CR I'm not wise enough to have a specific number in mind. given that I am not changing Pistons and that I opted for the 731 over an 885 I think that's all the CR decisions I can make without changing the scope of the project...it is what it is..I believe 9.5:1 is the consensus.

Given that, am I really going to see $500 in gain over the 731 cam which I understand is a 260 ?

[jeffnhiscars]

Context is DD (not mine), auto trans and maybe 6k/yr. goal is. cost effective fun project for an e30'addict, without blowing my brains out.

My gut tells me a dual exhaust should come before a cam if I had to choose (I don't but then what's the fun if all you do it throw $$$ at it)

[nando]

yeah, don't even port match it. like I said, the 885 intake is basically port matched to the 731 head out of the box. I'd just run the 323i intake for now and swap it out later.

At 9.5:1 I think a 272 would be a better bet. the 323i cam will probably work fine but it will be a lot harder to change this later.. exhaust can always be done, but swapping cams requires pulling the head!

[jeffnhiscars]

yeah, don't even port match it. like I said, the 885 intake is basically port matched to the 731 head out of the box. I'd just run the 323i intake for now and swap it out later.

At 9.5:1 I think a 272 would be a better bet. the 323i cam will probably work fine but it will be a lot harder to change this later.. exhaust can always be done, but swapping cams requires pulling the head!

Those are my thoughts as well about doing the head once. I'm not sure if it's 9.5:1 but that's easy enough to check. The only cam prices I'm aware of is $500 +\- for a shrink (actually Schrick although you may need a shrink if you spend $500 for a cam)which is overkill or $225ish for stock. What's a 272 going to cost, will it run ok short term on ETA electrics and if it turns out to be 9-9.3:1 would you still think the 272 is worth the cost ?

[whodwho]

yeah, don't even port match it. like I said, the 885 intake is basically port matched to the 731 head out of the box.
...

I wouldn't say it is that close, and stepped the wrong way for a beneficial anti-reversion step 8^)

[nando]

the shape of the 885 intake matches the inlet of the 731 head. what you're comparing there is the intake ports. the 885 intake port is smaller than the 885 head inlet. I believe the 885 intake port is still a bit smaller than the 731 inlet - somebody posted measurements / casts of them on E30tech several years ago.