m20b25 pistons

[sx_turbo]

hello again everyone,

right,

my engine is down at the engine builders, and having a variety of jobs done,

the engine builder has hatched a plan to up the compression to 11:1, but he wants me to buy new stronger pistons,

all very well and good but thats an extra £700+ that just isnt really in the budget.

can the stock pistons take this kind of CR and be reliable? the car will be used on the odd track days etc

or shall i stop being a tight arse and just pay the money

[maggspower]

Hi there and welcome.

We could do with a bit more info here. I assume it is an m20b25? What crank, cam, other mods? Secondly, and I dont wish cause offence, genuine question, but does your "engine builder" know these engines?

I ask because, even with the highest compression pistons available you cannot simply skim your way to a 11:1 static CR. I'm not saying it can't be done but it wont be easy. If there is a crank change going in then maybe.

As for the pistons, this is a BMW A good set of pistons, within tolerance and not too much scuffing on the thrust side is more than capable of running 11:1. Forced induction, these engines can make 300bhp all day on standard internals.

The key to it all is the tuning, if the engine is badly set up, running lean and detonating, then even a set of brand new forged pistons life expctancy will be measured in minutes. Detonation kills pistons.

PMed

[sx_turbo]

the pistons that are currently in the block are the 9.7:1,

i'm also lucky with the 99 ron petrol as there is a shell garage just round the corner to where i live, and i'm gonna go megasquirt to sort the timing and fuelling.

the engine builder is just worried about the pistons breaking up with the high revs, he also wants to up the rev limit, probably upto 7-7.5k.

the spec of the engine is gonna be the following

m20b25

schrick 284/272 cam, with shrick springs
lightened and balanced bottom end
ttv lightweight flywheel
Total seal piston rings
ported head,
ported inlet manifold
hopefully ported throttle bodie
e36 m3 race air induction box modified to fit


the guy building the engine has done an m20 before but that was just mild, he has also built a lot of m3 race engines and currently does ferrari race engines and also lesser race engines like pinto rally engines for mk2 escorts and such like.

with this one he wants to push the m20 envelope a little bit,

one its all up and running, a megasquirt will be fitted, and will be mapped by track and road in romford essex.

as i say the only issue is the pistons, as were unsure whether they will last, as the engine builder is worried about the ammount of silicone thats in these standard pistons, (the more silicone in a piston the tighter the tolerence and quiter the engine, but they also get very brittle)

whereas with forged pistons there is generally a lot less silicone in the alloy,

the engine builder is not worried about dett as this has been taken care with a different ecu and remap as soon as its fired up, what he fears is when revved hard with the higher pressures of the compression being upped that they will just crack.

[reggid]

i'd be worried about rockers a long time before pistons flying apart. you arent going to be needing to rev to 7.5k with that spec in all honesty the power wont really be up there..............if you do pay top dollar for new forged pistons you'd be crazy not to use a bigger crank.........also 11:1 is probably a bit much for a 284/272 that is actually gonna flow air and build high combustion pressures (unlike the 11:1 stock eta), id only be using something 288 or above

with 9.7 pistons and a 2.8L you can get mid 10's on the CR and with a 284/272 and some tweaking a nice allround engine that wont break the bank

[sx_turbo]

a 2.8 would be nice, but i know my engine is good,

and there is to many variations of the 2.8 and i dont want all the cocking around that goes with it to make it all work, if someone said you need x crank x con rod with x piston, then it would be easier but they dont and there a few combinations, i want it to just go smoothly

or if anyone knows of or has the required parts for sale let me know

[basketweave]

M52B28 Crank

M20B23 or M20B27 Rods

9.7 M20B25 Pistons (Flycut for larger cam)

+ deck block 0.5mm and add VAC motorsports Adjustable cam pulley.

Cam: 288 Schrick

JB Racing Flywheel

IE HD rockers


All this would make a very nice M20 with mid 10's compression as Reggid says.

[HairyScreech]

A much easier source of the 130mm conrods is the m20b20.
Stock rockets will fatigue put fast over 6.5k continuous rpm.
E36 m3 induction equipment is far too large for even an b20b28, the velocity in the induction system will be too low limiting you to around 95% ve.
Stock pistons won't be the limiting factor in this set up.

[sx_turbo]

Thanks guys, this is what forums are for,

Hairy, I been reading all the stuff you been expirementing with, excellent post dude.

Maggspower has been helping me loads with this via pm, and I thank you all,

Me and the engine builder shall be having a meeting next week, and sit down and thrash out some ideas between us then, at least I am armed with information now, so we can have a good think tank