School me on the 731 head

[acolella76]

the Ebay mid tubes are not as bad as everyone says, BUT you will need to do some extra work. the head flanges need to be checked for being level to each other and planed as needed. you will most likely need to slightly dimple the pass floorboard right in the corner and you will also need to tweek the X Pipe down a little as it runs close to the point of touching the body.
they also are not a direct bolt-on to your cat/mid pipe. if you can't fab up the joining section from the X-pipe to the cat, you need to budget in some exhaust shop work.

the tubing is not as paper thin as it is made out to be, being that they are stainless you can run a thinner wall than mild. they DO transmit more noise than your stock cast mani so be ready for that.

they run a 1-5/8" primary to a 2" crossover back. a nice size improvementover stock.

you will need to extend your o2 sensor by 2 feet in order to have it work alsoas the bung is farther down stream than stock.

as long as you know the facts about them before hand and you can either mod them yourself of budget for the corrections you will have to make, it is hard to beat them for $168 SHIPPED to your door.

they also have excellent ground clearence BTW. no dragging the down pipes over speed bumps is nice.

I don't plan on running a cat :D

I wasn't planning on the ebay headers to fit perfectly, so I don't mind doing any fab work.

[der affe]

Speaking of headers, would it be frowned upon to go with eBay headers?

Also, are you using stock rocker arms or what? I kinda wanna get new rockers but don't really feel like spending a grand on PPM rocker arms. I could buy a whole damn engine for that much. IE HD's any good?

the Ebay mid tubes are not as bad as everyone says, BUT you will need to do some extra work. the head flanges need to be checked for being level to each other and planed as needed. you will most likely need to slightly dimple the pass floorboard right in the corner and you will also need to tweek the X Pipe down a little as it runs close to the point of touching the body.
they also are not a direct bolt-on to your cat/mid pipe. if you can't fab up the joining section from the X-pipe to the cat, you need to budget in some exhaust shop work.

the tubing is not as paper thin as it is made out to be, being that they are stainless you can run a thinner wall than mild. they DO transmit more noise than your stock cast mani so be ready for that.

they run a 1-5/8" primary to a 2" crossover back. a nice size improvement over stock.

you will need to extend your o2 sensor by 2 feet in order to have it work also as the bung is further down stream than stock.

as long as you know the facts about them before hand and you can either mod them yourself of budget for the corrections you will have to make, it is hard to beat them for $168 SHIPPED to your door.

they also have excellent ground clearence BTW. no dragging the down pipes over speed bumps is nice.

[acolella76]

do you want looks or performance? the tubes are ok (other than being as thin as possible), but the flanges and collectors are not.

IE HD's are generally good, but I've had great luck with Febi rockers up to 7500. I've heard their quality has gone down though...

I know i'm not going to get any real performance gains out of it.. plus i might go boost in the future so they will be replaced.

So i guess either OEM, HD's, or Febi? Sounds good.

[nando]

Speaking of headers, would it be frowned upon to go with eBay headers?

Also, are you using stock rocker arms or what? I kinda wanna get new rockers but don't really feel like spending a grand on PPM rocker arms. I could buy a whole damn engine for that much. IE HD's any good?

do you want looks or performance? the tubes are ok (other than being as thin as possible), but the flanges and collectors are not.

IE HD's are generally good, but I've had great luck with Febi rockers up to 7500. I've heard their quality has gone down though...

[acolella76]

Speaking of headers, would it be frowned upon to go with eBay headers?

Also, are you using stock rocker arms or what? I kinda wanna get new rockers but don't really feel like spending a grand on PPM rocker arms. I could buy a whole damn engine for that much. IE HD's any good?

[ForcedFirebird]

it's almost like there's a "731 flow myth" or something.

the 885 pisses all over the 731 head, end of story. Add in some careful valve seat machining, and the 885 head can flow without turbulence up to 14mm of lift.

Ding ding ding! We have a winner!

Being a head porter, I will have to agree ;)

Now on to headers :P We are gearing up at the shop for a new m20 design, both NA and turbo, will post results when complete :D

[nando]

it's almost like there's a "731 flow myth" or something.

the 885 pisses all over the 731 head, end of story. Add in some careful valve seat machining, and the 885 head can flow without turbulence up to 14mm of lift.

[ForcedFirebird]

Well I am taking the data from the post I linked a different one that you have copied. I was not aware they where in conflict. Therefore lets say on avergae a 731 head flows as good as an 885 one at low valve lifts.

I believe you may have been looking at the graph that represents coefficient of flow vs valve size vs bore diameter, not the actual flow numbers themselves.

[eta]

Well I am taking the data from the post I linked a different one that you have copied. I was not aware they where in conflict. Therefore lets say on avergae a 731 head flows as good as an 885 one at low valve lifts.

[ForcedFirebird]

There are some conflicting posts above.

A 731 head has 40mm inlet valves and 34 mm exhaust valves. A 200 head has the smae valve sizes as well. Both heads have 37 cc combustion chambers. The 731 head can be safely bolted to a 84mm bore block with eta pistons eta conrods and 81mm crack (i.e an eta block). The inlet ports on the 731 head are alot larger than the inlet ports on a 200 head. The exhaust ports on both heads are the same. Given the size and shape difference between 731 and 200 inlet ports porting out the 200 head ports to 731 or 885 shape is a lot of work and will be expensive. Possibly more expensive than a 731 head. The 731 inlet ports are easily shaped to the 885 inlet manifold gasket to take the 2.5i inlet manifold.

The 885 head has 42mm inlet valves and 36mm exhaust valves. It also has 42 cc combustion chambers.

In comparison the 885 head flows a lot more are at 10mm valve lift than the 731 head. The 731 head flows more air at low valve lifts.

http://www.e30zone.net/modules.php?name=Forums&file=viewtopic&t=170822&postdays=0&postorder=asc&start=125

See page 6 for flow data. SI is stock intake. Vertical axis is CFM. He has compared 731 head, 731 with 42mm intake valves and 36 mm exhaust valves, alpina heads and a ported 885 head port3I.

The 885 head is better option for a properly built 2.7i motor using M20B25 pistons 130mm conrods 81 mm crank and a decked block. If you are using an eta block and pistons then the dyno plots I have seen do not show much difference between the 731 head and 885 head on this block.

Your decision to go with 885 head is the best option as you do not need to bother matching the 731 head ports to the 2.5i inlet manifold and you get the same result so less work is a bonus to me.

No one can see that unless they sign up. How do you see that the 731 flow's better anywhere in this graph posted on e30zone?

[ForcedFirebird]

hahaha my friend has a 4.10 in his S50 E30 and never has to use 1st gear again!

How hard was the harness swap would you say?

Harness swap was easy. You have to open the hole a little larger in the firewall, and I swapped to the Motronic 1.3's oil level sensor. The oil pressure switch, I just clipped the wire and soldered a female spade connector on the end (same with the starter wires).

Car ran fine like that, but had no tach. I followed the directions on Strictlyeta.net to get the tach and econoguage to work (still have the eta tach in the car, so it only reads to 5k).

[eta]

There are some conflicting posts above.

A 731 head has 40mm inlet valves and 34 mm exhaust valves. A 200 head has the smae valve sizes as well. Both heads have 37 cc combustion chambers. The 731 head can be safely bolted to a 84mm bore block with eta pistons eta conrods and 81mm crack (i.e an eta block). The inlet ports on the 731 head are alot larger than the inlet ports on a 200 head. The exhaust ports on both heads are the same. Given the size and shape difference between 731 and 200 inlet ports porting out the 200 head ports to 731 or 885 shape is a lot of work and will be expensive. Possibly more expensive than a 731 head. The 731 inlet ports are easily shaped to the 885 inlet manifold gasket to take the 2.5i inlet manifold.

The 885 head has 42mm inlet valves and 36mm exhaust valves. It also has 42 cc combustion chambers.

In comparison the 885 head flows a lot more are at 10mm valve lift than the 731 head. The 731 head flows more air at low valve lifts.

http://www.e30zone.net/modules.php?name=Forums&file=viewtopic&t=170822&postdays=0&postorder=asc&start=125

See page 6 for flow data. SI is stock intake. Vertical axis is CFM. He has compared 731 head, 731 with 42mm intake valves and 36 mm exhaust valves, alpina heads and a ported 885 head port3I.

The 885 head is better option for a properly built 2.7i motor using M20B25 pistons 130mm conrods 81 mm crank and a decked block. If you are using an eta block and pistons then the dyno plots I have seen do not show much difference between the 731 head and 885 head on this block.

Your decision to go with 885 head is the best option as you do not need to bother matching the 731 head ports to the 2.5i inlet manifold and you get the same result so less work is a bonus to me.

[acolella76]

hahaha my friend has a 4.10 in his S50 E30 and never has to use 1st gear again!

How hard was the harness swap would you say?

[ForcedFirebird]

Well damn, that's not too bad! I'm definitely going to have to go with a 3.25 or 3.73 then

Thanks. If you watch the other in-car video of my friend's m50 swap with the same trans and gears, you can see his car isn't much faster, lol. I smoke the local m20b25's already, can;t wait 'till I get some gears. :D Have a 4.10lsd, but drive on the highway too much for that noise, looking for a 3.42 out of a 5 series.

[acolella76]

You won't be disappointed, click the vid link in my signature to see how my 2.7 runs after the 885 head and Motronic 1.3 ecu upgrades. Still has the stock 2.93 rear gears to boot ;)

Well damn, that's not too bad! I'm definitely going to have to go with a 3.25 or 3.73 then

i have a set of euro ETA 525e (11.2:1) pistons that i will be putting up for sale soon alsong with lightened ETA rods that i will be putting up for sale soon.
use those with the 885 head and you end up with a 10.2:1 2.7i stroker and less recipricating weight because of the lightened rods (43 grams lighter per rod).

just throwing that out there as an option.........

If I had the money or time, and didn't want to risk messing up my DD, I would have done that by now! I might be picking up another eta for $300 so maybe I'll do it then :)