Author Topic: M42 turbo piston application (possibly) (Read 7808 times)

E36Al · « **on:** November 10, 2008, 04:02:52 AM »

Hi, name's Alan, from Australia.
Ive been involved in drift with corollas and silvias mainly.
Now own an E36 318is. Only natural to want more power!

Having worked on many sr20det's (Nissan factory turbo 2l s13/14/15 silvia)
I figure these pistons may be close to suitable and an easy solution for FI m42s. They are very strong, even standard.
They are 86mm and utilise a little end gudgeon size of 22mm.
Many aftermarket brands and compression ratios are available through differing dome heights.
Genuine nissan items are cheap and plentiful, for the budget builder.

Seems like they would couple 'mechanically' to standard conrods or upgraded m42/44 aftermarket shelf items.(140mm length 22mm top std bottom)

There is loads of information regarding piston pin heights, dome dish and cc size, suitable block clearance, deck height, head gasket thickness etc about the nissan engine, and most brands of aftermarket pistons have their specs readily available.
Brands like CP,Wiseco,Arias,ACL all have sr20 listings.

Now here's the question, what are the standard bmw m42 piston specs, regarding pin height, dome height, valve fly cutaway, deck height and clearance, etc.

I cannot find any information other than standard static compression ratio, which doesn't help much.

Any help/information would be appreciated.
Cheers Alan

Wiseco example here-useful specs.
http://http://www.wiseco.com/Catalogs/SportCompact/NissanSubaruToyotaVW.pdf

crazzy_hippo · « **Reply #1 on:** November 10, 2008, 05:08:25 AM »

Hoho.... You aren't the first to ask this question.

I too was scouring for those info.

I think its best you contact wise europe (if you contact US, they will direct you to europe) directly to make some custom pistons for you.

I contacted them and one of their engineers managed to get back to me. All I need is to provide them with the stroke, wrist pin diameter (22mm), rod length and desired compression.

Now just waiting for them to get back to me and make my pistons!:D

E36Al · « **Reply #2 on:** November 10, 2008, 05:17:55 AM »

Not the first in relation to the sr in particular? I've searched alot of forums with no hits!
I can have custom pistons made right here in aus, easily enough.
This is potentially a cheaper option.
Just need some stock bmw m42 piston specs and ill calculate the static compression.

I would rather use ludiagsm's setup and pay for block machining to suit the honda rods than paying for custom pistons.
That way pistons are off the shelf items, if ever required again.
Have you considered this?

crazzy_hippo · « **Reply #3 on:** November 10, 2008, 05:39:25 AM »

Yes, I did consider his setup. The only issue is that he is using the stock crank and I wanted to use the M47 crank. Due to this, I don't think the Wossner pistons could be used.

The biggest problem is that I have no idea how to calculate compression. Thus its impossible for me to find which piston I could use. In the end, decide to go for wiseco custom ones.

E36Al · « **Reply #4 on:** November 10, 2008, 05:45:13 AM »

Just google compression calculator, there are loads of programs.
Just need the correct figures.
Wiseco produce excellent parts, you'll be happy.
Using the diesel crank actually opens up more possibilities, because the bigend size is more common to aftermarket rods.
Id go m47 too but cranks are only available as new genuine bmw parts here though, out of the picture for my tight arse!

crazzy_hippo · « **Reply #5 on:** November 10, 2008, 05:45:16 AM »

Btw, they replied me with this email:

Compression height std. 31.65 mm. + 5.00 mm. ( due to the shorter rod) - 3.50 mm. ( due to the longer stroker) makes CH. 33.15 mm.
Displacement will raise from 449 cc to 511 cc Compression Ratio will go from 10:1 to 9.0:1 so you'll need 14 cc extra volume in the piston dish.

I don't know how they use compression height to calculate the the pistons I need though. Btw, I will be using eagle M50 rods and they are 135mm long (stock M42 is 140mm).

E36Al · « **Reply #6 on:** November 10, 2008, 05:46:49 AM »

Thanks man, that helps a little.
You're using standard length conrods, yes?

crazzy_hippo · « **Reply #7 on:** November 10, 2008, 05:54:22 AM »

No, I will be using Eagle M50 conrods. They are 135mm. Btw this thread has the dimensions of the stock piston.

http://www.318ti.org/forum/showthread.php?t=16611

E36Al · « **Reply #8 on:** November 10, 2008, 03:10:42 PM »

Sorry, it was late.
I meant standard m50 rod length, cheers for info and link.

E36Al · « **Reply #9 on:** November 12, 2008, 03:01:26 AM »

Well, ive found a set of good condition s/h sr pistons for $50aud.
Ill use the pistons on m42 rods,with 86mm bored block and lower static compression with head gasket thickness of choice.
Based on once i receive pistons, measurement to determine true compression height and dome cc differences.

Ill post results once certain.