Suggestions for piston upgrades

[ForcedFirebird]

They can be re-used, specially in a stock-ish motor. It's obvious the timing belt had failed in that engine at one point. 90% of the time the exhaust valves make contact, the other 10% they all do. Just clean off any sharp edges.

[McGyver]

81mm crank, 130mm rods, stock compression-height b25 pistons, 2mm off the block deck. They do quite well...

I've been reading through several of your threads and have a general idea of what route to go, but would really appreciate a sanity check.

My info:
I'm rebuilding an m20 for a turbo with a goal of hitting 300 whp (less than 15psi of boost). I will be using MegaSquirt 2 with wasted spark as the engine management.

Several of my rod bearings in my m20b25 decided to go on vacation, which left me with a pretty bad 75mm crank. I bought a used m20b27 seta with the intent of rebuilding it with an m20b25 885 head, but only 2 of the 6 seta pistons are worth reusing.

My new plan for the bottom end is to use the best block, stock used 81mm crank, stock used 130mm rods, stock used m20b25 pistons, and mill the block .070-.080 to regain compression (machinist will measure). Per your posts, this should net around 9.4:1 CR and NA 180whp/wtq. I plan to replace the crank, rod, and head bolts with ARP hardware. I plan to use an OE head gasket.

For the head, I plan to use an adjustable cam gear, radius valve job, stock rockers, replace valve springs if needed. If I am going to replace/regrind the cam, I'll probably modify the seta 885 head for all 7 oil feeds. (Leaving me with a turbo 885 head and stock 885 head)

Questions:
1) Should I use OE rings and bearings? I'm guessing that Total Seal rings is unnecessary for low boost.
2) Should I be looking for some sort of turbo cam?
3) If I'm staying below 7000 rpm, should I even look at HD rockers or valve springs?
4) Am I missing anything?

[Andre3127]

Why use 130mm rods when he can use the 135mm he already has for a better rod ratio. Get a 81mm crank and some off the shelf low compression pistons from VAC or somewhere. No skimming the head or block. Simple.

Not everyone wants to use the longest rod possible. Longer rods may have some advantages but they reduce low end torque and response.

When I build my 2.9 - 3 liter (depends on what bore I choose) I am deliberately going to use a short rod just because of this.

[ForcedFirebird]

The 885 seta head has all the journals drilled, but used a unique cam, similar to eta, but with more journals. Seta also came with single valve springs, you will want to add the inners.

You really don't need to do much to a b25 to get 300whp on turbo. A small t3 at 12psi has proven to me a reliable 300. I had a local with a Volvo jy t3 on it through his whole college career. Drove that thing many miles until the car was wrecked - the motor went into a 2002 and ran around a couple more years until he sold it. His new car has the same setup and has been banging off the limiter constantly as a drift car, and aside from the occasional rocker breaking, it's been lasting for a few more years. This is on a stock ECU we made a chip for. Only modifications is injectors, head studs and o-ringed block.

[digger]

Not everyone wants to use the longest rod possible. Longer rods may have some advantages but they reduce low end torque and response.

When I build my 2.9 - 3 liter (depends on what bore I choose) I am deliberately going to use a short rod just because of this.

You’re talking about peanuts, better off focusing on things that matter.

a big m20 stroker is never going to have what’s called a long rod so it doesn’t make sense to try and make it shorter IMO

using a shorter rod makes things harder than it needs to be and it’s not advisable with a turbo engine.

[McGyver]

You really don't need to do much to a b25 to get 300whp on turbo. A small t3 at 12psi has proven to me a reliable 300... This is on a stock ECU we made a chip for. Only modifications is injectors, head studs and o-ringed block.

I realize a stock m20b25 should be able to hit 300whp. I guess my question at this point is, would a different cam "future proof" the engine? While everything is apart and getting rebuilt, I'd like to do the entire job the first time.

I feel like my build is "mild" in terms of what can be done, so I really don't want to reinvent the wheel. I guess that this will be an iterative process. Any suggestions on books to read on engine building/design? I've already got Maximum Boost and cramer& Hoffmanns Performance fuel injection systems.

[E30 Wagen]

using a shorter rod makes things harder than it needs to be and it’s not advisable with a turbo engine.

Why? For a turbo engine wouldn't you actually want to maximize low end response, and wouldn't that help build boost faster? Not arguing, just asking.

[digger]

Except that effect is negligible it’s an internet myth, what’s real though is that a turbo engine makes more torque mostly from the cylinder pressure happening further past tdc when the rod angle is higher which makes it more prone to wear.

[E30 Wagen]

you wouldn't use 130 mm rods with custom pistons. i would also use OE pistons and 130 mm rods over the VAC forged random domes made from 2618. forged pistons need to have the correct dome and be from a material suited to the application.

I guess I'm still confused by this post then. What's wrong with getting a good set of aftermarket pistons? I just used VAC as an example b/c i had been browsing their site.

[digger]

I guess I'm still confused by this post then. What's wrong with getting a good set of aftermarket pistons? I just used VAC as an example b/c i had been browsing their site.

A good set is ok, most aren't good they are just generic flat style that are not anywhere near optimal for a 885 head. This is why i'd use OE pistons over a generic set but only if its a fairly mild build in which case you're stuck with 130 mm rods but that's a better compromise IMO. If you wanted a high boost turbo engine the stock ones wouldn't be up to the job in which case you'd order something specific not generic and use a 135mm rod. Some places say they have pistons for the 885 but they are talking from a cc point of view not a dome shape point of view.

[vWBIRDWv]

generic flat style that are not anywhere near optimal for a 885 head. This is why i'd use OE pistons over a generic set but only if its a fairly mild build in which case you're stuck with 130 mm rods ,Some places say they have pistons for the 885 but they are talking from a cc point of view not a dome shape point of view.

As digger stated The Dome shape is pretty important, Unless your going forced induction then ordering a set of custom pistons would be the way to go..