Re-Bores and Throttle bodies

[Richy325i]

Hi everyone newbie here,

I have a 325i (E30) which is currently in a mild state of tune, problem is the big / main end bearings are starting to show signs of wear. So I'm planning a re-build in the near future. What I would like to know is, How much can the cylinders be bored out to?. Also, how much can the throttle body be bored out by?.
What sort of gains can be expected by a large bore throttle body?

All help apprieciated
Richy

[winfred]

i have a varly modded 90 325ism and have gone almost as far as you can with bolt on's short of forced induction, i am planning internal engine improvements for the near future, i have long tube headers, 5.5mm overbore throttle body (m20 tb honed out for a m50 butterfly, don't do it crooked, the walls are 1-1.5mm thick when done) modded 535 afm (don't have money for ams conversion yet) the ob'd tb is worthless with the stock sized afm, the 535 afm is much larger then the 325, mustang 19# disc type injectors, mildly ported intake, performance catback, theres probably some other stuff that i've forgotten over the years. the general accepted ob done on a m20 is 1mm, that and a e crank gets you around 2.9 with about a 6200 redline, if you want more rpm get a 85-86 524td diesel crank, it's forged and not cast like the gas crank (this is what i have to build into my motor) the e and diesel crank have a 5mm longer stroke then the i crank.
are you sure that you need main bearings, oil light staying on longer then it use to? most likely you need a oil pressure switch they get old slow and crappy, my motor's light was getting slow and after a new switch the light goes out almost instantly and it has 192k hard miles, i have fixed this on many other cars at my shop. i make no clames on the horsepower that i have found other then it's faster with the mods, without the posi diff pulling out into traffic would melt the inside tire because it'll break em both loose in a slow turn now

custom semi wrinkled paint

don't smoke so i put the ashtray to good use, af ratio gauge to tweek in the 535 afm

Hi everyone newbie here,

I have a 325i (E30) which is currently in a mild state of tune, problem is the big / main end bearings are starting to show signs of wear. So I'm planning a re-build in the near future. What I would like to know is, How much can the cylinders be bored out to?. Also, how much can the throttle body be bored out by?.
What sort of gains can be expected by a large bore throttle body?

All help apprieciated
Richy

[Richy325i]

Cheers for that Winfred, The bottom end on mine is definatly worn, theres a small but noticable knocking noise when its first started and cold. this almost goes once it has warmed up. I have heard many problem tales around the M30 AFM, thats why I havnt tried it yet, did you have any problems setting it up afterwards?. I have heard alot of over-fueling, resulting in power loss instead of gains!.
I've got a modified cylinder head, chip, induction kit, E36 M3 injectors, full stainless exhaust (excluding manifold). So in my quest for more power, I didnt know whether to re-bore and re-build the M20 engine depending on what level of gains / overall HP could be acheived, or possibly look into the 3.5 M30 conversion, for overall longevity and long term tunability.

[winfred]

the biggest issue with the 535 afm is getting the spring tension set for the m20's air needs, my af ratio gauge helped with that, at anything but wot it's useless, start off with the spring loose and start tightning it till the motor stops going lean at high rpm, you want the flap to go full range without bottoming out, when it bottoms out the motor goes lean, or if you have $6-700 to burn a better bet would be a ams conversion, but you still need to tune that

[Richy325i]

Cheers again Winfred, I might give it a go with the M30 AFM. Its due a trip to the dyno soon anyway once I've fitted the larger throttle body and ported inlet manifold, so they should be able to set it up fairly accuratly.