M20 2.8 Stroker Build Proposal.

[Coyote_ar]

while we are on the subject of pistons for 135mm rods. is there any company out there selling off the shelf, 84mm forged pistons compatible with the 135mm rods and under 9:1 compression?

[SkiFree]

while we are on the subject of pistons for 135mm rods. is there any company out there selling off the shelf, 84mm forged pistons compatible with the 135mm rods and under 9:1 compression?

Off the shelf? No.

4-6 weeks? Sure, there are many.

[AntParker]

Thanks guys, Great Info as usual.

I plan to push the button on a set of IE Forged 85mm Pistons Early next month.
Regarding Rockers, Perhaps ill go with MM Shot peened :)

Many thanks

[djjerme]

i
Which ever pistons you choose you should easily make your 240bhp goal provided you get the RHD itb kit. Another member on here with similar build using the lower compression oem Pistons did it quite comfortably with a much smaller 272 cam and headwork. A properly fettled cylinder head is never a bad thing, the number 1 restriction is always the inlet valve.

This is actually the build we have on the stand right now for my buddies new ST class build. We tried to keep the compression reasonable.. Using MS to control the mess.

Once we get some free time to actually stick it in the car, I can report back what we see on the dyno. Though, our ST class is a hp/weight class, so we will probably need to dial it back since our chassis is stupid light (built on an '83 316)

*EDIT: Now that I think about, I think we did go with the 288 in that motor, the 272 I think went in to my enduro M20 which grenaded at the end of last season..

[AntParker]

This is actually the build we have on the stand right now for my buddies new ST class build. We tried to keep the compression reasonable.. Using MS to control the mess.

Once we get some free time to actually stick it in the car, I can report back what we see on the dyno. Though, our ST class is a hp/weight class, so we will probably need to dial it back since our chassis is stupid light (built on an '83 316)

*EDIT: Now that I think about, I think we did go with the 288 in that motor, the 272 I think went in to my enduro M20 which grenaded at the end of last season..

I'd be very interested to hear what this engine makes when the time comes please buddy!

[AntParker]

Sorry guys, going back to the topic of pistons- I was planning to use the 'IE Custom forged pistons' for this build- allowing me to run 85mm bore, 135mm rods and either 10.5 or 11:1 Compression.
Looking back now, i think perhaps the pistons you guys were recommending were the Mahle Ones, these fit the requirements i have except the Compression. (they are also $300 more expensive)

Is there any huge advantage of the Mahle pistons over the 'custom forged' pistons?
If so, how would be my best way to raise the compression when using these pistons, skim the head or deck the block, and would this then give me valve-piston clearance issues which then lead to having to further machine the pockets in the brand new mahle pistons?

Interested to hear your thoughts. Just want to make sure i select the right/ best pistons for my application.

Many Thanks

[digger]

for a 2.8L the IE Mahle MS ones are the go unless you are doing something different besides fast road and require a different design. they have coatings, have correct dish-dome (not guaranteed with other custom ones unless you ask the right questions), and are the right alloy for what you want

how much compression do you want?

[Eric]

Injectors will be too small. We ran out of injector @5k RPM with 200cc, and were at 80-ish % duty with 250cc with the following engine we did for a client not long ago...

Made 217whp/202tq using a 272 cam and stock pistons, 130mm rods and OEM +.5mm over pistons. With a 288 cam and a bit more compression, you will do better with your setup - probably closer to 240whp/230tq to make a guess based on the dyno curve we got. We took .010" off the block (.4mm) and .004" (.1mm) off the head to give a final clearance of .045" head-to-pistons clearance. With the 272 it gave us a .057" intake and .075" exhaust valve-to-piston clearance. Of course your numbers may vary, but these can give you a guide to get you close.

I have a M20B20 sitting in my backyard... should I scavenge the rods from it? Anything else good on that thing?

[ForcedFirebird]

I have a M20B20 sitting in my backyard... should I scavenge the rods from it? Anything else good on that thing?

If you want to do a 2.8 m20, sure. The 731 head is a boat anchor and should be sent to me immediately for proper disposal lol. Actually, let me know if you want to get rid of it, I would like one to play with on the flow bench.

[AntParker]

for a 2.8L the IE Mahle MS ones are the go unless you are doing something different besides fast road and require a different design. they have coatings, have correct dish-dome (not guaranteed with other custom ones unless you ask the right questions), and are the right alloy for what you want

how much compression do you want?

The engine will be in a track car and rarely see road action. I had not realised that the domes would be different on the others... I guess the coatings on these pistons will also help with longevity.

Ideally looking for around 11:1 Compression...

[digger]

The engine will be in a track car and rarely see road action. I had not realised that the domes would be different on the others... I guess the coatings on these pistons will also help with longevity.

Ideally looking for around 11:1 Compression...

yes, the Mahle are a high silicon alloy basically the same as 4032 alloy in compostion. the silicon has lower thermal expansion and better wear properties. the coating also reduces friction and helps with preventing galling during run in or conditions where there is less than ideal lubrication or clearances

in a street engine you want many miles and years of service i would recommend 4032 but if your not doing much street time then 2618 will work fine. So now there are other manufactures who can produce a similar piston, for example topend can get JE pistons so you can get the OEM 9.7:1 dome style which will put you close enough to 11:1 with 85mm bore 84mm stroke

[AntParker]

yes, the Mahle are a high silicon alloy basically the same as 4032 alloy in compostion. the silicon has lower thermal expansion and better wear properties. the coating also reduces friction and helps with preventing galling during run in or conditions where there is less than ideal lubrication or clearances

in a street engine you want many miles and years of service i would recommend 4032 but if your not doing much street time then 2618 will work fine. So now there are other manufactures who can produce a similar piston, for example topend can get JE pistons so you can get the OEM 9.7:1 dome style which will put you close enough to 11:1 with 85mm bore 84mm stroke

Thanks Digger, Thats useful to know, are any of these pistons regarded as better than the Mahle MS ones, or are they kind of considered the 'Holy Grail' Pistons?

[mr2peak]

Thanks Digger, Thats useful to know, are any of these pistons regarded as better than the Mahle MS ones, or are they kind of considered the 'Holy Grail' Pistons?

What do you mean "better"? Depends what you're building. From what I understand, they make a nice not-quite-track motor.

[digger]

Thanks Digger, Thats useful to know, are any of these pistons regarded as better than the Mahle MS ones, or are they kind of considered the 'Holy Grail' Pistons?

thing to note is aluminium at temperature suffers drastic loss of strength, ductility and fatigue resistance. different applications input different amount of heat and pressure the piston has to survive and a NA m20 is a long way from a turbo charged nitrous engine so somethings are probably overkill.

for a race engine 2618 alloy offer better strength, fatigue resistance and ductility at high temperature i.e. long periods of WOT. the better mechanical properties offer better resistance to damage from knock so the tuning window is probably better if you are pushing the boundaries but if you dont tune properly at the track you probably going to break it eventually. the only real downsides with this alloy are they wear more quickly and require more cold clearance which is not even really an issue for a predominantly dedicated track engine

for a race engine 4032 still works if the engine is specced well and tuned properly as it is a good step up from cast and many still track cast pistons

for about $900-1000USD topend should be able to do a set of 2618 pistons that will be excellent on the track, give approx 11:1 compression with the 9.7: style dome they have scanned on record (if you ask for it), modern skirt profile etc (but no coatings unless you pay extra for a 2.8L not essential). so the choice is yours really, both options and others will work

[Eric]

If you want to do a 2.8 m20, sure. The 731 head is a boat anchor and should be sent to me immediately for proper disposal lol. Actually, let me know if you want to get rid of it, I would like one to play with on the flow bench.

Where do you find the head type? I found this stamped on the intake side looking through the intake manifold runners.

Untitled by ericandshovin, on Flickr