M42 stroker / turbo , stroker + turbo options

[Karolis]

Hello!

After blowing definetely my 2.5 (m50 nv) I made a step back and picked up an m42b18 after discovering it's potential with forced induction and stroker options. All this because putting an M54B30 is too easy :D

1.8is - Very interesting motor. Initially I don't even thinked about it with a 2.5 running, but later I started to like it. My "new" engine is still on the floor but I know I'll miss the power from the beginning so started to collect info about what I can to do.

Basic start, 2871 low boost on all stock internals, Micriosquirt ecu (already have it), about 180 200hp, but I'll want more, I know :) .

But what about more serious turbo? Let's say 1 - 1,5 bar, about 300hp.

The pistons seems to be always the weak point. What to do?

I know I can use M54B30 pistons for lower compression (M42 crank and rods, CR 8,5 or 9,2, right?), but aren't they still weak too, particulary if compared to M50B25 pistons?

What happens to the compression if I use M47 crank but M50 135mm rods and pistons? I immagine this setup should be stronger for boost, but I have not enough numbers for some calculation.

I would like to avoid block shaving, piston decking and other machine shop operations to keep the cost low but good power output. Not trying to beat absolute power records, so "smart" compromises are researched (or simply looking for cheap miracles, maybe it's possible :) .

Any good idea? :yawn:

[Karolis]

Ok, by mi primordial calculations with M47 crank, M50 rods (135mm) ant oem m42 pistons we have 1950cc and something around 8,4-8,6:1 . Good.

Also it's possible to put the M54B30 pistons to the stock M42 engine, and will have similar CR numbers (8,4-8,6). My question is if they're strong enough because they have less metal from the top to the first ring.

M50 pistons are out of play, to much height.

I would like to skip custom pistons, head gasket change and arp studs because of their price - these are pretty expensive things even if going on higher hp, so for the beginning would like to see if it keeps around 0,8-1 bar on stock components only with reduced compression, and something less without reducing compression. Would like to try how much is resistant in oem form, and a blown gasket will be cheap enough (30$ the gasket, 12$ the bolts and something for head skimming eventually)

The fuel will be Lpg, should be better vs. our european 95 octane.

I would like to have around 250hp reliable, but I know that passing the 200hp on stock engine this word is to be excluded :)

[TobyB]

You might be onto something, there, especially on more knock- resistant LPG.

The usual 'wisdom' is that up to 1 bar, the stock components last pretty well-
reduced life commensurate with extra load, but no overloading failure.

IF you get fuelling right, keep things cool, etc.

Keep us updated.

t

[Karolis]

My luck is that I can get a full working engine pretty cheap, so a kind of "destructive experimentation" can be done. Sadly, in winter I'll not have the car running (banal rust prevention) so for the moment I can only catch information and components.

By the way, if the stock engine can resist 1 bar, the hp numbers should be already very interesting! Around 250-260 hp I suppose.

[varg]

AFAIK you can't build a stroker M42 without machine work. 250bhp? I don't think you need to go through that kind of trouble for that output. A slightly thicker than stock MLS head gasket and some head studs should be all you need for that modest power goal. M42 internals are pretty strong, I believe mine would still be in use if it weren't for a cooling system issue, and I was pushing 18psi of boost and seeing performance that I believe put the car at around 300whp.

[Karolis]

By my calculations the only kind of machine work that I need is on the crank.

No block, no head.

This is because of the combination of longer stroke, piston height too high for standard rods and at the end shorter rods. Maybe I'm wrong because all this is only from info of the internet, but should be done. About 8,5 CR in this way.

The power is never enough, I just liked to stay realistic pessimistic.

The problem of the MLS and Arp studs is their price. 200$ mls, 200$ studs, lets say 100$ on shipping to Europe, and if they decide to put taxes on it it's maybe 20-30% more again. For 500$ I can get 2-3 working engine swaps, so would like to try to avoid expensive tricky parts if it's possible, even is high power is always very nice thing :) . The stroker is more for reducing compression and keeping stock pistons. I could reduce with 3.0 pistons too (cheaper and simplier), but they don't look that I could trust a lot them :) (maybe I'm totally wrong, I don't know)

[TobyB]

I think you should try it, stock. Save the money on the fasteners- at least until
something blows up the first time!

The big variable here is tuning- if you can keep it cool and detonation- free,
I think your power levels should be well within the design limits of the M42-
it IS a pretty tough little lump.

Go for it. Post pictures. Especially if it explodes.

t

[varg]

Well the studs are not an avoidable expense, you're going to lift the head and blow that stock HG in a hurry if you start shooting for power. Maybe you can get something comparable locally, but it isn't going to be optional.

[Karolis]

Thanks for the encouragement and the tips. Will see what will be possible to do. For the moment I still have to remove the old engine, and see what's missing for the 1.8, because it's electrical and vacuum tubes system is all in bits, sadly was not removed in a clean and correct way from the car where it was.

[ccsdo5]

Eventually you'll need studs and to drop compression in one way or another. A MLS gasket is the best way without having to do machine work on the bottom end of the M42. I haven't seen many people push past 10 psi on a bone stock M42. I have a 150,000+ mile m42 in my car right now around 10 psi with a T25 all seems to be fine and I suspect around 190-200whp. MY goal is to be at 1 bar once I fix some silly issues I've been having and see how long the stock HG and head bolts can take the abuse, but with 10:1 compression I don't think it'll be for very long. I'll more than likely end up with a MLS HG and ARP's or get another block machined with the CP pistons I have.

[berlow94]

I wouldn't recommend using an MLS headgasket without having a machine shop deck the block.
There's a reason most machine shops also call decking the block "MLS Prep".
It's even more important with MLS that both mating surfaces be perfectly true


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[Karolis]

Yes me too heard this about mls and block decking - with no block shaving it's a big NO NO somebody said, but maybe it's not true.

If go for more seriuos boost and more seriuos way to build the engine, I would prefer a standard head gasket with only arp hardware and dished pistons to get something about 8-8,5 : 1. Should be a good compromise for some money saving on mls. I don't know how about piston resistance, but for the head fixing should work. It seems that there was more than few guys using this method for the head (and some super pistons, not oem) and running succesfully 1 - 1,2 bar.

Anyway, the curiosity to see what a std engine can resist is high :) And by resisting I mean pedal to the metal, not drag or drift where you use power for small time.

What's the "theorical" general crank, pistons and rods limit? 300hp?

p.s. if the stock engine resists 10 psi that isn't bad at all, I thinked that I'll have to stay on something like 7 8 psi.

[varg]

You can always o-ring the block instead of going MLS. You do not need an 8:1 compression ratio IMO, that will just leave you with a laggy little lump of an engine, BTDT. I'd stay around 9:1. The stock internals will handle 300bhp, you should be able to put 300whp down if you don't make any tuning errors and blow it up. Based on previous performance I would say I crested 300whp on my M42 when all was working well, and the problems I had probably wouldn't have occurred with an o-ringed block that didn't have 200,000mi+ on it. Unfortunately I never put it on a dyno when I was running 18psi, just couldn't afford the dyno time and probably left some power on the table because of it.

[Karolis]

And what kind of gasket is used with o ringed block? For me this is an unknown system of doing things, even if I heard about it.

[varg]

OEM. O-ringing is just cutting a channel of appropriate size and depth in the block, cramming in a wire ring that is interference-fit and filed to be as close to gapless at the end as possible, and clamping the head down with the OEM gasket. The piece of wire presses into the fire ring of the headgasket and creates a strong seal which coupled with the ARP or otherwise stronger-than-stock studs won't fail under high boost. As with any stock internals tune, keep that bit conservative and on point, because O-ringing and MLS gaskets eliminate the weak point that is the head gasket, and the next weak point is the pistons.