I'm planning my NA M20 build and have stumbled onto a bout of curiosity...
I plan to do a 3.0L stroker. I plan to use a Dblias 296 cam with adjustable gear, wasted spark, itbs, Megasquirt, a ported head, 11:1 compression, and am considering Meth Injection.
So the question has arisen: how do I want to play the stroker internals?
I was planning on running a 89.6 mm M54 crank, M54 rods, and custom 84 mm bore pistons. This is a safe option that needs no boring and produces a displacement of 2979cc. This creates a noticeably undersquare motor. Benefits include the safety margin in the block as mentioned before, a motor that will tend to be fairly thermally efficient for what it intends to accomplish. This also means it will make better low end torque, which is really quite good since I'm running a hot cam and ITBs that will sap power from the low end in exchange for ultimate top end power. The cons: running that cam and itbs also inherently means I need to rev the motor higher. Because of the increased piston velocity, that's a considerable amount of wear and tear on the bottom end and piston rings, especially since the motor will be high compression. Also the undersquare does mean it won't be as rev happy, though I want to lighten the bottom end as much as possible and run a lightweight flywheel to make up for some of that. Another con is that I currently do not posses the M54B30 bottom end and sourcing one will cost extra money.
So then I started thinking. I already have a M52 84mm crank and M20B25 connecting rods (though I'd much rather switch to M/S5x rods for less weight and more strength if I were to go this route). How far can you push the displacement on the B28 crank? Well, after looking around for the maximum bore an M20 can tolerate, I found the 87mm number. So an 87mm bore on 84mm stroke comes out to 2996cc. So I get more a bit more displacement, and get an oversquare motor. It will like the revs more for the displacement it makes, and favor top end power where the cam and itbs will be catching their wind. I already have the bottom end in my possession so cost is gone there. However, the custom 87mm 11:1 pistons aren't gonna be cheap. I'm sure they fall into "special" in the Ireland Engineering handbook so I would expect to pay more than the listed 900-some dollars for a set. The M52 crank is also, I fathom, considerably heavier than an M54 crank, though I admit I haven't weighed either. Then I still have to source the better rods for the added security. The motor also will inherently be mess thermally efficient, which is dangerous as I read that an 87mm bore gets uncomfortably close to the oil gallerys, so it brings the question of block integrity into the equation.
So pulling that together, really either option has equal points in the pros and cons. I thought about doing an 86.5mm bore if that's even possible. That still a bit oversquare and gives a little more marginal security on the block, but it works out to the least displacement of the lot at 2961 or something close to that, and at that point I'm not making a significant difference over the usual 2.9L I don't imagine.
At the end of the day, the car has to be reliable enough to drive long distances. I know I'm asking a lot of a motor that borders on a race motor either way, but witch option would you guys go with?
I plan to do a 3.0L stroker. I plan to use a Dblias 296 cam with adjustable gear, wasted spark, itbs, Megasquirt, a ported head, 11:1 compression, and am considering Meth Injection.
So the question has arisen: how do I want to play the stroker internals?
I was planning on running a 89.6 mm M54 crank, M54 rods, and custom 84 mm bore pistons. This is a safe option that needs no boring and produces a displacement of 2979cc. This creates a noticeably undersquare motor. Benefits include the safety margin in the block as mentioned before, a motor that will tend to be fairly thermally efficient for what it intends to accomplish. This also means it will make better low end torque, which is really quite good since I'm running a hot cam and ITBs that will sap power from the low end in exchange for ultimate top end power. The cons: running that cam and itbs also inherently means I need to rev the motor higher. Because of the increased piston velocity, that's a considerable amount of wear and tear on the bottom end and piston rings, especially since the motor will be high compression. Also the undersquare does mean it won't be as rev happy, though I want to lighten the bottom end as much as possible and run a lightweight flywheel to make up for some of that. Another con is that I currently do not posses the M54B30 bottom end and sourcing one will cost extra money.
So then I started thinking. I already have a M52 84mm crank and M20B25 connecting rods (though I'd much rather switch to M/S5x rods for less weight and more strength if I were to go this route). How far can you push the displacement on the B28 crank? Well, after looking around for the maximum bore an M20 can tolerate, I found the 87mm number. So an 87mm bore on 84mm stroke comes out to 2996cc. So I get more a bit more displacement, and get an oversquare motor. It will like the revs more for the displacement it makes, and favor top end power where the cam and itbs will be catching their wind. I already have the bottom end in my possession so cost is gone there. However, the custom 87mm 11:1 pistons aren't gonna be cheap. I'm sure they fall into "special" in the Ireland Engineering handbook so I would expect to pay more than the listed 900-some dollars for a set. The M52 crank is also, I fathom, considerably heavier than an M54 crank, though I admit I haven't weighed either. Then I still have to source the better rods for the added security. The motor also will inherently be mess thermally efficient, which is dangerous as I read that an 87mm bore gets uncomfortably close to the oil gallerys, so it brings the question of block integrity into the equation.
So pulling that together, really either option has equal points in the pros and cons. I thought about doing an 86.5mm bore if that's even possible. That still a bit oversquare and gives a little more marginal security on the block, but it works out to the least displacement of the lot at 2961 or something close to that, and at that point I'm not making a significant difference over the usual 2.9L I don't imagine.
At the end of the day, the car has to be reliable enough to drive long distances. I know I'm asking a lot of a motor that borders on a race motor either way, but witch option would you guys go with?
Comment