2.8l stroker for future turbo setup q's

[Kozworth]

Hey guys, I have been researching a lot and just want to make sure I'm retaining the info correctly before dropping a ton of money into this build.

I'm looking to make a 2.8l m20 stroker.

I have:
885 head
Ix block gutted
Eta crank
Soon to be s52 rods

I was looking to bore out to 86mm.. so I would be at 2.8l correct?

Not sure if I'm milling this, or what gasket but what would the cr be at approx?

I keep reading that the ix block has a different lubrication system.. will I run into any issues with this? I thought all 2.5 blocks were the same when I got.

I am basically looking to mostly beef up the bottom end a little, so I have a safe engine for a turbo. Will do the head later on. I'm looking for 250 to 300 whp type build.

Ps: I am going to keep this my gen 'stroker q thread' to prevent clogging the thread and for easy help for those looking to build this.

Thank you in advance

[acolella76]

That is 2.7L not 2.8. The eta crank has an 81mm stroke.

Also, since you will have to use custom pistons for the 86mm bore you can make the compression ratio whatever you want it to be when you order the pistons.

For your power goals, I would just run a stock motor. It's pretty easy to get into the 250whp range with a stock b25 motor and 8psi boost.

[Kozworth]

Yea that's right boring it would only affect cr.. not the stroke for displacement.

I would, but I am an auto student and figured best way to learn is doing it yourself. Also, my m20 runs but has nearly 215k on it. If I were to turbo, I would like to put it on a beefy setup. I got some engine bay work to do too, so id rather put a more reliable setup in while the engines out.

Lastly, if I bored why couldn't I use s50 pistons.. they are 86mm and aren't they 'beefier'?

[acolella76]

Sorry, I used the stock bore size when calculating displacement. It would be 2.8L.

I get that you want to rebuild it to have a fresh motor to boost, but I think buying custom pistons isn't entirely necessary for a low boost build.

And S50 pistons will not work for a few reasons. I believe they will be too sunken in. The S50 crank stroke is 86mm I believe, so using it with a 81mm crank and the same length rods, simple math and logic tells me they will be 5mm away from where they should be at TDC. Those pistons are also flat topped where the 885 head is made for domed pistons. So if the -5mm didn't drop compression enough the domed head will drop CR even more.

The easiest way to get to 2.8 using stock internals is M52 crank, 325e 130mm rods, and M20B25 pistons.

[MR 325]

The easiest way to get to 2.8 using stock internals is M52 crank, 325e 130mm rods, and M20B25 pistons.

Winner!

The crank AND piston skirts will have to be cut down to clear each other though.

[Kozworth]

Ok, since I'm still learning I feel that cutting down skirts and such is out of my reach.

I think ill stick with a 2.7 with eta crank, 325I pistons, and s52 rods.. is this going to give me much of an advantage over a regular 2.5 for boosting? I'm now debating since I want nothing too crazy just buying a spare m20 if a 2.7 isn't that much stronger and probably save money

[acolella76]

umm... that combo won't work. Have a look at this: http://www.e30tech.com/forum/showthread.php?t=48288

(forgive my cross post to another forum almighty moderators)

Bobbing the counterweights and pistons is something any machine shop can do, and since you will be taking everything to a machine shop anyways, it's not big deal for them.

[LJ851]

And S50 pistons will not work for a few reasons. I believe they will be too sunken in. The S50 crank stroke is 86mm I believe, so using it with a 81mm crank and the same length rods, simple math and logic tells me they will be 5mm away from where they should be at TDC.

Not 5mm, 2.5 mm.

[Kozworth]

Sorry, I just realized why the s50 rods wont work. I keep thinking the bigger the better but I realize that s50 rods on an eta crank would put me 5mm above tdc.

Not that this can be measured, but building a super eta on an 885 head, would this really give me that much performance for just .2l more? Would this hold up a lot better for boosting then a regular 2.5?

Ultimately I am looking to boost, Im looking more to 300whp or so. Im debating whethor building a 2.7 would give me that much of an advantage over a 2.5i m20, or if I should look into a more complex stroker to yield more suitable results.

My budget to get my bottom end done is around 2k about if that helps any.

[devon.818]

2k into your bottom end?

thats a lot for idk what!

lower compression=good for boost, you want boost, than run eta block with i head, gives 8.3.1 compression, boost to 13lbs with cometic/mls headgasket, run some arp head studs, boom 270hp

you are welcome

[Kozworth]

2k into your bottom end?

thats a lot for idk what!

lower compression=good for boost, you want boost, than run eta block with i head, gives 8.3.1 compression, boost to 13lbs with cometic/mls headgasket, run some arp head studs, boom 270hp

you are welcome

well, i figured this is going to cost more then i could expect. I want a solid, safe boosted car. thats basically running eta crank, 130mm rods, and 325i pistons correct?

[acolella76]

well, i figured this is going to cost more then i could expect. I want a solid, safe boosted car. thats basically running eta crank, 130mm rods, and 325i pistons correct?

That's good. A lot of people think 'budget' builds will end up being budget but in the end cost 2x more than they were expecting. It's refreshing to see someone have some realistic goals.

That is running eta crank, rods, and pistons and the 325i head. The CR is closer to 8.5:1. It is good for boost because low compression = more boost before you get detonation and knocking. But again, with your power goals you don't need a CR that low since you won't be pumping 40psi boost through the motor. My favorite all-stock stroker combo is the 2.8 with M52 crank, eta rods, and 325i pistons. Cheap and easy. And with a budget of 2k that gives you PLENTY of room for extra go fast stuff like MegaSquirt.

[MR 325]

My favorite all-stock stroker combo is the 2.8 with M52 crank, eta rods, and 325i pistons. Cheap and easy. And with a budget of 2k that gives you PLENTY of room for extra go fast stuff like MegaSquirt.

I'm most definitely with you. The parts can be found very cheaply to build this engine. Find a good machine shop to do the mods to crank and pistons and you'll have yourself a great engine. My good friend (Myster-e on here) built this engine and did 185whp with his with potential for more with a bit more tuning time and intake changes. This is a NA engine of course.

If you want to keep it super cheap, just to the Eta bottom end with a fresh rebuild and ARP hardware. This along with a nicely built 885 head and boost will produce nice power.

[Kozworth]

One thing I don't understand is if a 2.5 has a 135mm rod and 76mm crank, and an eta has a 130mm and a 81mm crank, wouldn't the displacement be the same since the rods equal since ones shorter.

[LJ851]

^ Rod length has no effect on displacement. Bore, stroke and # of cylinders= displacement.