Turbo M20 2.8L Stroker w/ 135mm rods

[apostate]

IMO, those are both "low comp" stroker examples. Why not take the block deck down another .5mm (~.020")?

What if he decides in the future to go to a 3-3.1-3.2L stroker (as I did)?
Will the decking of the block seem a very good solution then?
CR is achieved through pistons, not through decking of the block or shaving the head.

[ForcedFirebird]

Have a look at this spreadsheet from my Das Beast build. I used the "Std Comp Stroker" formula. .You can tweak numbers as desired.

IMO, those are both "low comp" stroker examples. Why not take the block deck down another .5mm (~.020")? Since the pistons are already below deck in this situation, further adding quench with a thicker gasket is a power-robber, specially when going boost. I have confidently pushed many 9.6:1 SCR engines well above 1.5 bar and had nothing but good results. Besides bragging rights for the psi-gauge number 8.3:1 is not better for turbo than 8.8:1 - sorry. More boost does not always mean more power. The more power the engine cam make N/A the better - even when adding boost. The internet has been passing this bad/wrong info around for years. The only drawback for higher compression is your tune needs to be better spot-on then with lower comp, but the benefits out-weigh that small handicap.

[digger]

Note it is better to use 206.0-206.2 or thereabouts for deck height as it's the stack height that is 206.7mm not the deck. This is why stock piston sits above the deck.

Also imo you are better off buying Pistons a bit oversized get fresh bored and honed to suit.

[dvallis]

Have a look at this spreadsheet from my Das Beast build. I used the "Std Comp Stroker" formula. .You can tweak numbers as desired.

[SLEEPYDUB]

That's a good plan. We use the 130mm rods so we can use shelf pistons, but that changes when we go forged pistons. The longer throw cranks is where the issue lies and we are forced to run shorter rods since the wrist pin can only go so high before it interferes with rings.

Your bearing choice is going to depend on the block, you can't just use late bearings in an early block. The early bearings have an oil groove all the way around both shells, the late have a smooth cap bearing and grooved upper shell. The early blocks will have one large locating tang on each shell, so technically it uses all the same bearings whereas the late models have a two tang shell that is dedicated to the cap side. (and this design carried all the way up to s54).

Thank you for that bit of info. Looks like I may need a new set of bearings if this block is an early. But it came out of a plastic bumper car so Im sure its the late model.

[ForcedFirebird]

That's a good plan. We use the 130mm rods so we can use shelf pistons, but that changes when we go forged pistons. The longer throw cranks is where the issue lies and we are forced to run shorter rods since the wrist pin can only go so high before it interferes with rings.

Your bearing choice is going to depend on the block, you can't just use late bearings in an early block. The early bearings have an oil groove all the way around both shells, the late have a smooth cap bearing and grooved upper shell. The early blocks will have one large locating tang on each shell, so technically it uses all the same bearings whereas the late models have a two tang shell that is dedicated to the cap side. (and this design carried all the way up to s54).

[varg]

Your piston compression height would just need to be 5mm less than it would be with if you used a 130mm rod. I don't see why that should be a problem, given the desired engine specs (desired compression ratio, stroke, rod length, deck height, combustion chamber volume, etc) the manufacturer will be able to make you the piston you need, and pistons made to suit the 885 head's combustion chamber are readily available so that won't be a problem.

[SLEEPYDUB]

I'm in the process of building my 2.8L M20 stroker for turbo application, and I just need to know if this recipe will work.

M20B25 Block
M52B28 2.8L 84mm Crank and ARP Main Studs
Crank Spacer
FCP Forged H Beam 135mm rods w/ ARP Rod Bolts
Calico Coated Late Model Rod and Main bearings

I am going to have Forged Pistons made once I know how large I need them to be. I am trying to get away with 84mm stock size so I dont run into any issues with boring, and also I would like to use a square engine setup.

My main concern is that I do not see many people running 135mm rods with the M52 crank. I usually see the 130mm rods. So what is the solution? Do I just tell the company that is making the pistons that I need them to be able to fit 135mm rods? Is it that simple?

Thanks in advance