Calling all the people that opened up the w11 motor and did a full rebuild:

I am writing up a full build sheet for my r53 including a bored out block with pistons. I definitely want to go larger pistons. So I have a couple questions:

1.) How much boring is too much? This also goes for the same question; is bigger better? What is my limit? I see pistons for 77, 77.5, 78 mm. Which one should I purchase?
2.) For my pistons; what should my skirt size be, the shape of the piston face?
3.) Rods; is lighter always better or should I get just new oem rods?
4.) I am planning on getting the TPR2R bvh not sure of cam yet but is it basically just bolt on or do I need to make sure that they are all compatible with each other?
5.) Are there any performance cranks out there?

Or is this stuff I should ask my machine shop lol. Thought I'd ask you guys since I am sure there are some old timers here that know more about this motor than MINI themselves!
TYIA

 

I believe 1.8L is the largest a W11 can go due to the proximity of the water jackets so your overbore will be small.

 

I'm no MINI engine expert but until one replies...

While there is no replacement for displacement I doubt there is that much increase in displacement to be had by going over sized on the bores.

If more power is what you want -- and who doesn't -- if the engine is naturally aspirated there's always turbo/supercharging.

With minimal over bore you keep the cylinders stronger, the block stronger. Cylinders with thin walls can result in head gasket issues. Or worse...

You are I think better off just having enough material removed to clean up the bores and ensure proper clearance for the pistons.

(I built a Datsun 510 1.6l SOHC engine, naturally aspirated, and just went slightly oversized on the bores, but fitted higher compression pistons (factory pistons from the 240Z engine), aftermarket cam, and dual side draft Weber carbs.)

For skirt size I can't help you. My experience -- granted some time back -- was skirt size/style was not an option. One got what he got with the pistons.

Same for the face (crown) of the piston. Higher compression pistons could have a raised crown -- or the piston pin will be a bit higher up the piston -- but regardless of how the higher compression is obtained one has to be sure there was sufficient clearance between the valves and piston tops. Too much crown though can interfere with charge flow into and exhaust flow out of the cylinder.

For rods it depends upon what increase in output you intend to achieve and what RPMs you are looking to spin the engine too. The stock rods can handle some of course but there's a limit.

Choosing a cam, the right cam, is of course extremely important. With more compression, you have to be careful about more lift. So you need to be sure there is sufficient clearance between the valves and pistons.

Also if the engine is turbo-charged (or super-charged) the cam must be selected with that in mind. Bigger valves, huge lift, and lots of duration is not as beneficial as one might think since the chambers are being filled by man (turbo/super charger) and not God.

Have no info on performance cranks. Like the rods the factory crank has some margin.

Have you talked to the automotive machine shop? If they have done MINI engines they probably have some ideas/recommendations.

Or you need to seek out a MINI engine builder. But he may not be as generous with his knowledge as you might expect, since he came by it by experience. Experience is the best teacher but it is also the most expensive teacher...

 

I see just like the rmw stroker. So what bore size does that limit me to?

 

Pretty sure RMW sleeves their strokers that have 79 mm pistons... so I'm guessing you should probably just limit yourself to 77.5 mm and 1.62 L or something unless you plan on sleeving the block. I'm certainly no expert though.

 

Block is windowed among other things with proper sleeving on the w11. 77.5 is more than fine 78 makes the walls so incredibly thin. Proven time and time again even with sonic testing that 78 is to risky without proper ductile sleeves from LA sleeves windowing and notching.

Again find Unbreakable Lumps posts and take everyone elses even mine if they differ from his. Again he designed the engine. Everyone else is just not as reliable.

 

Unbreakable Lump and the tritech development.

https://www.northamericanmotoring.co...oper-here.html