Rod Ratio ?

[Guest Anonymous]

I'm building a stroker motor with S14 crank and have heard varying opinions on whether or not to use the stock M10 or S14 rods. After looking at www.e30m3performance.com and reading up on the S14 rod ratio tech articles I'd be inclined to use the S14 rods as they were designed by BMW for the S14 crank.

What do you guys run and what's a good piston to match?

TIA

[Anthony]

It depends what you are looking to do. Is this a race motor? Street motor? Etc.

I run a dual purpose car with 10.8:1, schrick 304, alpina injection etc. The pistons were design by Perry @ skidmark. They utilize a hemi design and as a result require some machining of the head as well. 10.8 is about the minimum in this connfiguration.

I am also preparing to build a new raqce motor using teh same pistons but designed for a schrick 328. Different compression ratios etc.

You could try and use stock s14 pistons but they were really designed for the twin cam pentroof design and probably wont work as well. Either way you need "custom" pistons. If you just want to run a stock head then you can call the usual suspects top end, korman, ireland etc as they all have designs for the longer rod.

IMO I would always run the longer rod. My dyno experience tells me that the longer rod tends to breath much better with the s14 crank especially at higher rpms (longer dwell, higher cylinder pressures etc). My old Dave Cruise/Metric Mechanic motor pretty much hit a brick wall @ 6000 rpms and my new motor just keeps breathing. All m10s can probably benefit from a slightly longer rod (in a performance application) and many racers run the 144mm rod with the stock 80 mm crank.

However if you are rarely going to see above 5000 rpms a shorter rod is probably better but it will cause a bit more friction on the cylinder walls and piston skirts due to the low ratio.

So it goes back to you. What kind of engine are you building? What is your budget? I have a set of s14 rods with new ARP bolts if youa re interested.

Send me an email.

anaphe@gmail.com

anthony

[Guest Anonymous]

I'm building a dual purpose car just as you suggested. I'm willing to give up almost everything in terms of creature comforts to have - well a race car that's also street legal. I'm not on a budget really (just got engaged so I can spend what I want when I want for the next little bit) and will spend what it takes to get the job done right. I was thinking Pauter rods, some type of custom pistons mated to the combustion chamber - not sure exactly what or where yet. Other than the S14 rods putting more friction on the walls/skirts what are the other drawbacks? It sounds like if the M10's don't breathe at higher end then it's a no-brainer.

I can email off post but how much do you want for your S14 rods? Would I be foolish to go with the Pauter rods?

[Anthony]

M10s in general breathe fine at higher RPMs, but with my 292 and short rods, torque and hp litterally dropped like a stone after 5900 rpms. The new motor climbs steadily to 7000.

S14 rods wont increase friction they will decrease friction due to the reduced angle an m10 rod will cause more friction.

As I mentioned before I would do the following.

Custom Pistons Skidmark Racing 10.8:1 $650

Head Machining $250 approx

Head Porting $250-$700 depending on who does it

Minimum schrick 304 cam $375

Double springs $100-$300

New Rockers (stock are fine for up to 304) Billet rockers needed for 316 or higher

S14 rods $350 (Pauter $1000)

ARP Bolts $139 (Vac)

Pulleys $250 skidmark

That represents about 2500 in parts. If you go with a 316 then you can add an additional $650 for billet rockers.

email me.