M20 Developement - New alternative thoughts?

[Wuddelwu]

Hello from Austria,

as collecting so much M20 Parts that are not useful/wanted in any way, i made some thoughts about and easy, cheap M20 Build out of crap parts, which is easily rebuildable by anyone with unwanted parts.

The goal is to have around 200bhp and 280nm of torque.
So, to start about,some thoughts to introduce some of you into my ideas.

- 2.5 block are getting rarer and more expensive
- Eta, M52B28 etc Cranks are getting more expensive
-130mm rod is not nonsense, but still not the optimium.
-885 heads gettint rarer and more expensive, tend to crack, are often worn whatever, AMC Heads are shit without serious modification


So, i already did some calculations an measurements:

(Sorry, if some of the parts are more of an Euro thing, but i think you will still be able to collect them from ebay or something else. I wrote the estimated prices for the parts behind, thats what i paid/would have to pay in Austria using Ebay etc..

Recipe:

M20B20 Engine Block, stock 80mm bore (100€)
M57D30 88mm Stroke Crankshaft (100€) (I already made it to fit the M20 Cambelt wheel, easy with lathe)
M54B30 or M52B28 135mm rods (because more clearance and significant lighter than M20 shit rods) (80€)
M54B22 Pistons (Need flat pistons for 731 head)(Mill 2mm from the top, cut valve reliefs and they should fit fine) (30€ for 6pcs, unpopular engine) Compression height is 29.7 stock form)
731 head, slightyl reworked ports, 885 Valves in it (100€ + work)
Camshaft ?

I already calculated engine specs and it resulted in 2654ccm displacement, 11,3:1 compression with 1.25mm squish.
I already put the 88mm stroke crankshaft in an B20 Block with Piston and rods and it will fit perfectly with small work on the lower piston bore in the block, despite the small bore size.

So, to come to an end, with some questions:

1. Do you think this will work fine or do i oversee something?
2. Will 885 Valves sit in stock 731 Valve seats? Does anybody have personal experience, not only words from other people?
Plan to help the 731 head is to give it an 3 angle cut, fit 325i valves and work slightly on the port.
If you need new valve seats, are there anywhere new ones avaible for the 885 head?
3. Ho do you think will the engine perform despite being small bore long stroke? Since S54 Engine is Long stroke too, i see no reasons the M20B26,5 Franken engine could not be made to breath in high rpm.

I hope to gave some new wind into the M20 stroker thing, because parts are only getting rarer in the future and this could be a nice opportunity to create a good engine out of trash.

Kind regards
Marvin

[digger]

may not get much response on this forum, 731 heads are rare in USA. so not viable there.

The issue is the 731 in stock for is very sub par, you need it ported by someone competant to add 885 valve sizes and then port it properly and thoroghly which i have a suspicion may have trouble clearing the 80mm bore iirc at best will be shrouded . The average guy in his backyard is not going to mod a 731 to be a good performer (this will limit widespread adoption) so its going to cost more than 100 euros to get someone with appropriate skills and knowledge to do the job at rate of 50-100 per hr. Its much more involved that cutting seats for a bigger valve which normally in isolation does nothing without the corresponding work to the throats, bowls, SSR, guide boss, and port proper infact many so called porters dont know what the hell they are doing.

id be suprised if you can cut pockets for decent cam into a OEM pistons with 27mm compression height and stock rod. i havent seen the pistons but on a casting something must be getting pretty thin at that point as 24V engines typically dont need uber deep pockets and the underside is spacious as stock rods have a large small end

if you own an e30 the price of them these days is nuts and the costs to get the conventional stroker parts is a pittance in the overall scheme given the global community we live in. I dont see how you cant get parts from somewhere in Europe may be some shipping and taxes but if just after those numbers thats what i would do. No harm in trying though as a learning exercise and fun project if thats the main purpose but id be suprised it met expectations.

Always remeber the cylinder head is the most important part of the engine, if your modded 731 is barely an improvment on a stock 731 then the engine will struggle to make stock m20b25 power so thats probably the starting point

[ForcedFirebird]

If you like torque, that sounds like an OK combination. The high compression, long stroke, small ports (as Digger pointed out), and small bore, you will have a low RPM tractor engine.

IF (yes, caps) you spend a good amount on your head being professionally built, it has the capability to support power, but at great expense. I'd guess in today's money, you'd be looking at $4k just in the casting for something like that in my shop (seat machining, porting, flow testing etc).

Then you would need to get a decent valve train. I have successfully used tested/new OEM rockers (Febi snap easily), 288 shelf Schrick, SuperTech valves, springs/locks/retainers and spin a 75mm crank to 8500. And it's not a dyno queen, think it might have 4+ seasons now (broken/inspected every year), and the b25 makes 208whp. Porting is not allowed in his class, valves have to be stock diameter, along with the throttle, and exhaust port. Link to dyno and Link to track abuse

That being said, you might be better off using the small crank, getting the head to flow, good compression with the decent bump stick and RPM capability, you can get a lot of power from the stock hardware.

Power comes from the head and cam. The bottom end just needs to rotate.

[hasa]

Thanks for the videos FF ! I love how the B25 revs. Thats something that is hard to obtain with longer stroke.

[ADEN]

Hello from Austria,

as collecting so much M20 Parts that are not useful/wanted in any way, i made some thoughts about and easy, cheap M20 Build out of crap parts, which is easily rebuildable by anyone with unwanted parts.

The goal is to have around 200bhp and 280nm of torque.
So, to start about,some thoughts to introduce some of you into my ideas.

- 2.5 block are getting rarer and more expensive
- Eta, M52B28 etc Cranks are getting more expensive
-130mm rod is not nonsense, but still not the optimium.
-885 heads gettint rarer and more expensive, tend to crack, are often worn whatever, AMC Heads are shit without serious modification


So, i already did some calculations an measurements:

(Sorry, if some of the parts are more of an Euro thing, but i think you will still be able to collect them from ebay or something else. I wrote the estimated prices for the parts behind, thats what i paid/would have to pay in Austria using Ebay etc..

Recipe:

M20B20 Engine Block, stock 80mm bore (100€)
M57D30 88mm Stroke Crankshaft (100€) (I already made it to fit the M20 Cambelt wheel, easy with lathe)
M54B30 or M52B28 135mm rods (because more clearance and significant lighter than M20 shit rods) (80€)
M54B22 Pistons (Need flat pistons for 731 head)(Mill 2mm from the top, cut valve reliefs and they should fit fine) (30€ for 6pcs, unpopular engine) Compression height is 29.7 stock form)
731 head, slightyl reworked ports, 885 Valves in it (100€ + work)
Camshaft ?

I already calculated engine specs and it resulted in 2654ccm displacement, 11,3:1 compression with 1.25mm squish.
I already put the 88mm stroke crankshaft in an B20 Block with Piston and rods and it will fit perfectly with small work on the lower piston bore in the block, despite the small bore size.

So, to come to an end, with some questions:

1. Do you think this will work fine or do i oversee something?
2. Will 885 Valves sit in stock 731 Valve seats? Does anybody have personal experience, not only words from other people?
Plan to help the 731 head is to give it an 3 angle cut, fit 325i valves and work slightly on the port.
If you need new valve seats, are there anywhere new ones avaible for the 885 head?
3. Ho do you think will the engine perform despite being small bore long stroke? Since S54 Engine is Long stroke too, i see no reasons the M20B26,5 Franken engine could not be made to breath in high rpm.

I hope to gave some new wind into the M20 stroker thing, because parts are only getting rarer in the future and this could be a nice opportunity to create a good engine out of trash.

Kind regards
Marvin

I am living in an area where no b25 but managed to get b25 block and put my 731 i only gain noticable torque in low rpm till i hit 3k-3.5k (comparing to my previous b20).

Getting rid of the stock afm put cone filter gave it more torque and throttle response.

My m20b20 used to start making torque at 3k till redline i believe the 731 is designed for 2.0 MAX. and can't breathe in b25 at high rpm a slightly bigger turbo low boost is my next move to fix after 3k weakness.

[varg]

Flow is power, the head is number one priority for NA. I haven't seen the big diesel crank but I doubt it is better at high RPM than the M54 cranks, and S54 cranks are a totally different animal plus paired with a good harmonic damper.

[Northern]

may not get much response on this forum, 731 heads are rare in USA. so not viable there.

Not to mention the M54b22 and M57.

I don't understand how 84mm cranks can be hard to find, given M52/tu/M54 engines all came with them.
For 400 Euro plus full gasket set, bearings, labour. Surely there's an M20B25 laying around in that price range even if you have to ship it?

11.3:1 sounds high for pump gas based on others' builds here over the years

[hasa]

At least in Europe you can find B28 crank easily. M57 crank is forged too, but needs wizardry with lathe to fit M20 timing gear.

[Wuddelwu]

I have very limited time at this moment, but just for interest i will continue with this project.
Today i fitted M20 belt wheel to the M57 crank. No wizardry if you know how to use lathe and milling machine.