Turbo M20 2.8L Stroker w/ 135mm rods

[ForcedFirebird]

The pins on the m20 are heafty and can be smaller diameter, BMW did it on the s54. Just broke two of them for turbo rebuilds, pretty excited to flow the heads personally, but that's for another thread.

[digger]

Also best to look at what rings are available, some sizes have more choices. Total seal are great

[ForcedFirebird]

Yes, but if you call them, they will try and sell you gapless for nearly every application. Stay with a conventional top ring and napier second (which is OEM on BMW's anyways).

[digger]

Yeah they make more money on gapless, ask them for conventional they have a nice 1mm 1mm 2.5mm with 2nd being Napier. You can just look in their catalog find a size with several options decipher the difference and ask them which is best while telling them the purpose

[ForcedFirebird]

Gapless works in boosted applications, but not sure anyone has experimented with gas porting the domed b25 design.

[dvallis]

LoL. Digger and ForcedFirebird probably have 10,000 hours engine building experience between them. I would listen to their advice.

My spreadsheet above is a decent approximation of all the stroker data I could find around here. If either of you guys want to tweak the numbers, send me an update. I'll host it and repost.

[digger]

Gapless works in boosted applications, but not sure anyone has experimented with gas porting the domed b25 design.

Gapless top does, 2nd isn't so good as the top ring seals worse . You won't find any data on gapless vs conventional other than hearsay as people keep some stuff to themself. Often you will hear people compare conventional and gapless but going from thicker conventional to thinner gapless which tells you nothing about the gapless part. Sometimes you will see data on end gap vs hp vs blowby and it's seems to suggest gapless shouldn't be worth much premium from a hp point of view. Gapless is good for reducing oil contamination so e85 and methanol it's helpful

[SLEEPYDUB]

See Post 55

[SLEEPYDUB]

Gapless is good for reducing oil contamination so e85 and methanol it's helpful

This car will be full time E85, so what should I do?

[SLEEPYDUB]

Without question bore it at least .25mm, but .5 is more common, +1 gives you matching gasket size to bore, which is great to avoid edges and hot spots. I have had blocks measure out for reuse of stock replacement pistons after deglaze, but no quality machinist will hone a used block the extra few thousandths for forged replacements. The bores will not be round. Don't forget to rent a torque plate, your local v8 shop probably won't have an m20 setup. These long siamese engines will move when the head is bolted.

Just talked to my machinist, he said the bores measured out perfect for stock replacement, he couldn't believe how good it came out. He said to order stock sized pistons for it. He also mentioned the intermediate shaft bearings and said its not problem for him to replace them, as he was planning on doing that regardless. At this point a torque plate will not be needed.

Should I be weary of this? Or trust my machinist?

[ForcedFirebird]

I have seen quite a few blocks like that, was discussed in the piston thread a few days ago. You can trust him if he carries a warranty. As I mentioned earlier, forgings are going to need more wiggle room. The BMW piston clearances are very tight in stock configuration, much tighter than domestic builders are used to. Did he understand the intermediate shaft bearings?

[SLEEPYDUB]

I have seen quite a few blocks like that, was discussed in the piston thread a few days ago. You can trust him if he carries a warranty. As I mentioned earlier, forgings are going to need more wiggle room. The BMW piston clearances are very tight in stock configuration, much tighter than domestic builders are used to. Did he understand the intermediate shaft bearings?

Do the forgings need more wiggle room because they expand? I think I remember that being mentioned when I was running Wiseco. In that case, he must bore it out a few mm to make room? As far as the intermediate shaft bearings, he said that the process to do that isn't much different from what he is used to on other engines. Same concept applies to both. I still haven't had a chance to go by there and discuss everything in person, I plan to do that tomorrow

[ForcedFirebird]

The intermediate shaft isn't quite the quite the same. Most machinists think it's similar to cam bearings from a push rod engine, but those type bearings just press in and done - they will have to be burnished to size - but it's not rocket science for a machinist.

When you purchase pistons, they will come with a pamphlet and specify how much piston to wall clearance is needed depending on coating and such - yes they will expand more the stock castings.

When upgrading rods and going forged pistons, it's a good idea to rotate the balance assembly. If you weigh parts from a BMW engine that has all of it's factory parts, they are extremely close. +/-2gm (4gm total variance).

[SLEEPYDUB]

The intermediate shaft isn't quite the quite the same. Most machinists think it's similar to cam bearings from a push rod engine, but those type bearings just press in and done - they will have to be burnished to size - but it's not rocket science for a machinist.

When you purchase pistons, they will come with a pamphlet and specify how much piston to wall clearance is needed depending on coating and such - yes they will expand more the stock castings.

When upgrading rods and going forged pistons, it's a good idea to rotate the balance assembly. If you weigh parts from a BMW engine that has all of it's factory parts, they are extremely close. +/-2gm (4gm total variance).

When I bring him the bearings for the Intermediate shaft, ill be sure to give him some literature on the process so there is no mistake. Ok so no worries on the pistons then since it will come with what tolerances are needed.

He is definitely balancing the rotating assembly, that has already been discussed

[SLEEPYDUB]

Who do you guys recommend to order pistons through? VAC Seems to be the only place I've found. I've seen some bad reviews on the Ross pistons through Ireland Engineering. So who do I go with? I've seen digger mention TopEnd as a good supplier for JE.

From their site:

Total-Seal Gapless Rings - NOTE: You use Gapless Top OR Gapless 2nd. You do not do both Gapless.
None
Total Seal Gapless Top Rings (Endurance Road Race, Extreme Turbo and NOS Use) - $38 each + $152 +$228.00
Total Seal Gapless 2nd Rings (Street and mild Race use) - $25 each +$100 +$150.00
Other Piston Options
High Heat Ceramic Coated crowns and Moly coated skirts - $43 each +$258.00
Moly or Tuff coated skirts only - $23 each +$138.00
Heavy Duty Wrist Pins - $15 each +$90.00
FSR Forgings (Limited to certain bore sizes and applications only.) - $20 each +$120.00
Vertical or Lateral Gas Ports (For Drag Race and High Compression engines, also good for NOS use.) - $22 each +$132.00
Contact Reduction Grooves - $8 each +$48.00
Accumulator Grooves - $6 each +$36.00
Milled Side Relief Lightening - $6 each +$36.00
Brushed and Milled Dome Crowns - $4 each +$24.00

That is a lot of options...i dont even know what I do or dont need as piston options...