my M110 performance build thread

[odl21]

Originally Posted by Frank Reiner

Would you mind sharing the dimensions of the con rods;
And rod journal size and the stroke?

rod big end is 1.8897", piston end 20mm, centre to centre 143mm (vs 132mm for stock rod). stroke is 81.8mm (3mm increase). journal size is 1.7705". with the bearings i'm using, that gives 1 thou oil clearance which is about right for a piston guided rod (which this has to be) using 5/30 oil.

these are actually an off the shelf rod from carrillo. the journal size is standard honda/jap 4 cylinder size as used on NASCAR engines. the bearings are performance clevite bearings for a little mitsubishi. if its good enough for over 100hp per cylinder in a NASCAR V8, i'm sure its good enough for 50hp/cylinder in this engine.

[odl21]

Originally Posted by JUNAID786

I was also under the impression that a shorter stroke will allow an engine to rev up more freely. I do understand that the lighter rod could compensate for that. What about the rev limiter? What's your max rev going to be and how you going to do it?Is there any distinct advantage of the weber carbs over the mfi? Will you be using the stock fuel pump? If so how are you going to get the fuel pressure down for the carbs?

yes, but then the capacity is too small and the compression also suffers. the engine is under square as stock and so the stroke increase is fine given the huge weight saving from the crank, rod, piston and pin. it would be fine to about 10000rpm with this bottom end but i'm looking at 8500 max as more would require radical changes to the head to suck in that much air and consequently torque would suffer too much for a rally engine. surprisingly enough, i don't need stiffer valve springs to get up to 8500rpm because of the massive weight saving on my valve train.

the rev limiter is long gone!

the k-jet would be impossible to tune to these changes without massive expense. it also doesn't react anywhere near as quickly as a DCOE for a fast reving engine like this. also the inlet manifold is far from ideal.

the stock fuel pump puts out about 75psi. i actually use a bosch 044 at 95psi on my k-jet engine. the webers need about 3psi, so require a completely different fuel pump. i have a 7psi feed pump feeding a swirl pot from a 130 litre fuel tank before a pair of 044 pumps, so for this engine, i'll just bypass the high pressure pumps and fit a low pressure regulator in the engine bay. simple given everything is already plumbed with -8AN hose and fittings.

[odl21]

the stock mercedes flywheel is lightened considerably without compromising strength by removing the outer flange and switching to a flush mounted heavy duty clutch designed for a BMW E30 M3 which is the same size clutch disc.

[JUNAID786]

Interesting. Now you got me excited about building a carb motor.

[Frank Reiner]

With reference to your original post, you stated that the crank rod journals were to be offset ground. Are they to be only ground to 45mm (all material removed from the inside), or is there to be welding (on the outside half), and then grinding to the selected arm.

[odl21]

No welding. Almost all material was removed from the inside. The offset is exactly 1.5mm from the original centre giving a total of 3mm stroke increase.

[Frank Reiner]

Original journal diameter: 48mm
Ground journal diameter: 45mm

Since no material was removed from the outside, the inside surface was moved 3mm (48-45), and the center of the journal was moved 1.5mm.

Stroke change: 3mm.
New stroke: 81mm

6 cyl. @ 87x81 = 2889 cc

If the stroke had been increased to 84mm, disp. would = 2996

[odl21]

apologies, you're correct - the centre of the journal is 1.5mm offset giving 3mm stroke increase. however the standard stroke is 78.8 not 78, which gives a cylinder capacity of 2918cc.

[Frank Reiner]

"which gives a cylinder capacity of 2918cc."

Right you are!

What is the width of the big end of the con rod that you have chosen?

[odl21]

Narrow. A lot of side clearance, hence the need for the rod to be piston guided (a tight fit of the little end in the piston) and a very accurate oil clearance for the bearing.

I probably wouldn't recommend this for a road engine but changing rod bearings every 10-20k miles is not an issue for a rally engine.

[Frank Reiner]

"Narrow" ?!

At the risk of pointing out the obvious, the side clearance of the big end of the rod on a pressure lubricated journal controls the outflow of the oil that is supplied to the journal. The clearance ranges up to about .020" for one rod per journal and .030" for two rods. Given what you have indicated so far, it appears that the assembly will have over .100" side clearance. With that much clearance there will be no control of outflow, and nothing to keep sufficient oil in the radial bearing clearance.

From an earlier post of yours:

"that gives 10 thou oil clearance"

This, we should hope, is a typo on your part! Appropriate radial bearing clearance would be .0008-.0012" (8-12 tenths of one thousandth of an inch).

[odl21]

Yes I meant 1 thou, of course! Lots of editing here - I should read my posts more carefully!

If you have a 1" pipe flowing water under a fixed pressure with a 6" opening on the end, it won't flow more water if you put a 12" end on it. Essentially the bearing clearance is what meters the oil flow.

This is a fairly common trick on race engines to reduce rotating mass. The issue is not low oil pressure but piston tip and wear at the edges of the bearing. Controlling the rod at the piston end minimises this.

[odl21]

some photo updates:

1) align honed mains with new studs
2) checking straightness of crank. 1/1000" - acceptable
3) the flywheel cut flat for M3 clutch pressure plate
4) stock flywheel showing what was cut off
5) silicon plug of the combustion chamber to aid the custom manufacture of pistons.

[odl21]

and finally, the long ARP head studs in the pre-decked and semi honed block. final hone with be done after final deck which needs pistons for pre-assembly.

also a photo of the carrillo rod installed and the large side clearance.

[fha772]

That's looking great Owain!!

How much weight have you removed from the flywheel?