The company I worked for has a dealer account set up with extrude hone. I remember about 10yrs ago we sent out some cast iron 302 heads for extrude honing, the results were awesome, the intake and exhaust ports were mirror finished.

I know its very expensive to do, but what do you guys think about using this service for the M70 heads? How much of a difference it this from port/polishing the heads?

I don't have any plans to do this right now, but I would like to read other owners opinions. I had a friend who raced mustang with me, get his heads ported and polished, but what happened was the head was opened so much that it made one of the water (coolant) jackets weak and he had coolant in the combustion chamber.

I was trying to find a picture of the M70 head cut in half, I forgot who had it, but I wonder what type of HP would be gained with extrude honing the heads and intake.

Mwrench has the pics I think..........the M70 heads suck bigtime (especially the ex ports) and no real gains to be had (not much meat to work with) ..........thats why FI is the best option...

yeah I kind of figured. I will have to check his site for picture.

Here is a cutaway pic of the M70 head and I was going to have mine done like what you are talking about but Birdsauto already did this across the pond to gain fifty horsepower with just bolting it back on to stock. PumpedTSI is right the heads flow sucks but that honing would majorly help anyways, also the ridge for the valve guide is on the intake side too from what I can see when I had my intakes off.

http://img505.imageshack.us/img505/308/v12headcutaway069go2.png (http://imageshack.us)

Mwrench has several cut outs, on his sight, Pumpeds right, You gotta Force the air through the heads, Can't wait for my car to whistle one day, I'd be happy with a Stage 1.....

Are you serious that by doing the extrude hone process that you would net 50 HP, can you imagine, add schrick cams and then a wokke chips....maybe close to CSI power band? Oh forgot the intakes, extrude hone them also.....wow that is way cool, then add a F/I set up, CRAZY!

The 50HP will be achieved by doing all those mods +, Not just the Extrude process, The Extruding gives you almost squat, All the mods together gets you a littles somewhere, I should of sent the block out while the heads were off.

Here is a cutaway pic of the M70 head and I was going to have mine done like what you are talking about but Birdsauto already did this across the pond to gain fifty horsepower with just bolting it back on to stock. PumpedTSI is right the heads flow sucks but that honing would majorly help anyways, also the ridge for the valve guide is on the intake side too from what I can see when I had my intakes off.

http://img505.imageshack.us/img505/308/v12headcutaway069go2.png (http://imageshack.us)

I would have to see this gain to believe it, with 8.8:1 compression, I don't care what was done to the exhaust port, you will not get 50 HP gain, Without any other changes to the engine, you might be able to "squeeze" 5 HP with head mods. This isn't rocket science, the exhaust ports just don't flow and there is not enough meat to allow any serious port work. The exhaust port would have to be raised at least 25-35mm before any real improvement could be made. Obviously that can't be done!

Got to my website and look at ALL of the pictures, the valve guide is only one area that could use a little help but that doesn't do anything for flow, it is the port design that is bad. I wish BMW had done the head like the M30 engine (of course would have rather seen a 4 valve head!!!) and gotten the exhaust port as well as they did the intake.

Last comment, if it was really as easy as port work to get 50 HP, EVERYONE would have done it and would still be doing it!!

http://www.mwrench.com/Whitepapers/V-12%20head/

Well Ed,

Can't wait for the day someone comes out with a 760 engine conversion for the E31, I did see the 5.0 V8 conversion from a M5.

Ed

Have you been able to do any research on the 760 engine, I don't know anything about, if you have do you think it could work?

They were considering that mod at coastmoterworks before the M5 conversion, The torque specs on the 760 are low, Our engines have better torque, May be with a serious port & Polish and just go all out on the heads would be a start though, That would be nice though, New BMW engine in a older car with power that matches the looks.

Ed

Have you been able to do any research on the 760 engine, I don't know anything about, if you have do you think it could work?

I haven't done much except measure the engine and give it a good visual inspection. The 760 engine is about 2-3 inches longer and it taller by a couple. It is a BIG engine!!

Mechanically it would fit but probably would have to be a automatic trans. The engine and trans are so closely linked together AND this engine is a direct injection engine (fuel is injected directly into the combustion chambers) variable valve lift and duration (call it super VANOS!) which is all controlled electronically with system interdependence. It would be extreme difficult to hack into this system without some factory support or complete knowledge. You just can't wire in a "Megasquirt" system and turn the key.

Could it be done?? SURE! but at what cost, the conversion could well run 10 times the value of the vehicle. If you are a VERY wealthy person with nothing better to spend money on------

If you want a high HP E31 there are much better alternatives, even some V-12s BUT it may not be emissions legal in some States.

That M5 V-8 E31 is an auto box!!! And they were worried about low torque of the 760??!! I don't know where they got their numbers, 438 HP and 444 lb/ft torque is low???

just picking your brain Ed, thanks for the input.

Has anyone read that article about the Hartge 3 series with the V10?

If I remember, it was in "Bimmer" about 2/3 monts ago. $100,000 plus and your dreams can come true...

MWrench, You have a point that it is not just an exhaust porting but rather what they call a head conversion at BirdsAuto.com. I asked exactly how they did it, like port and polish or whole new head, but I got no response.

If someone would like a 760 engine to look forward to here you go:

I just got news from a tuner who can rework the N73B60 motor to a 6.9L displacement. The cost however is not available at the moment as this is in R&D phase (Turbo implementation). Here are some initial details (I am salivating):

AXA - 6.9 liter
Power ratio 112 hp / liter
Bore 90
Stroke 90
Displacement 6871
Intake valve 36.0 / 5.92
Exhaust valve 30.5 / 5.90
Compression ratio 11.0 / 1
Int cams 284 dur
Exh cams 276 dur
NA HP 772 @ 7600
NA Torque 703 @ 5200
Turbo HP w/ 12psi approx 1,003
Turbo HP w/14psi approx 1,205

Sorry to keep quoting you Ahmed303 but I can't help it, I WANT THAT MOTOR IN MY CAR.

703Lbs of Torque?

Its a lot right!

Plenty enough, Might be to much for connecting parts behind the engine.

And even strut mount welds. Have seen that before.:(