Molnar rods

Picked up a set of Molnar 6.700 BBC rods for my next 470 project. These rods are very lightweight at only 740 grams. I have SCAT I beam rods in my 470 right now and they are light but not that light.

got a set of gm pin 6" Molnars in my W8 mill. Definitely smaller in stature than the Eagles I had in the other engine.

Andy, you are going to like them, I have the 6.535 rod in my 512, and they checked out spot on.

I used the 7.1" rod in my 505 and love them.

I posted the weights when I built the motor and it was amazing how light my internals were!

https://board.moparts.org/ubbthreads/ubbt...440-cranks.html

Edit, not as light as I thought, but still only 1490 grams for rod and Mahle piston.

What do you think the horsepower limit is on those? Birdtracker

Are they pretty close to the K1-s?

I cant find me balance sheet or it should show.

Mines never been on the dyno but runs 9.0@148 3350lbs. 7.100" Molnar with 2.200 pin". Bob weight with a little careful ring pack choice was less than with my BME aluminum rods.
Doug

If you ask that question of Tom Molnar (who is a great guy), he will tell you horsepower has nothing to do with it. It is a function of piston/pin/ring weight and RPM. Give him the weights and he can tell you the RPM you should not exceed with the rod.

Bill

Exactly. I told Tom my piston/ring/pin weight along with no power adder. Gave him a self imposed 7500 rpm limit. He said that they were more than enough.
Doug

That weight total is making me laugh.

The stock piston/rod/rings/pin assembly from my '86 318 weighed more than that! Something like 1540 grams.

Shoot, the late LA motor rod at 758 grams is heavier than AndyF's bigblock rod!

R.

Wait until you see the pistons for this engine. JE is designing a Mopar big block piston based off the LS design. The sides are moved in so the pin is shorter than normal. Should be really lightweight.

sheeeeyit.

is it 1.32CH? so it could be used in a 451?

It looks like my numbers (in the other thread) translated to over 6 lbs. of savings in the rotating assembly vs. the factory LY rods and cast pistons.

I'm curious to see rod/piston total!

I have Molnar rods and crank in my engine, along with Ross pistons. I was concerned that the crank was so light, that I would have to add mallory to the crank to balance it (because of the piston weight). The rods were light enough that I actually had to remove weight from the crank to balance it.
Very nice parts for the price.

Brian

same here with Icon pistons.

My Mahle pistons:

same here with molnar crank rod and icon piston combo. rods could be used right out of the box.

Yes it will be, that is the rod length and piston Ch I have with my 3.9 stroke crank.

Factory piston and pin in a big block mopar is a little over 1000 grams.

horsepower has nothing to do with it. It is a function of piston/pin/ring weight and RPM

X2, reciprocating weight X RPM^2 (with a tiny adjustment for rod thrust angle) determines rod breakage.

Could you go through a calculation of this for us?

A modern design piston for our antique motors That's almost a unthinkable as a modern combustion chamber or a cam not designed 50+ years ago.

Don't encourage him...

Actually there is a spreadsheet that has the program built into it to calculate acceleration and velocity of the piston for any stroke, rod length and rpm. I have it on my computer, don't know how to attach it, maybe I'll figure it out.

R.

Note in the spreadsheet the max acceleration numbers are always at the top, where velocity = zero. These numbers have units of ft/sec^2. To convert to Gs we divide by 32.2.

60,085 / 32.2 = 1,866 Gs. At that point a 500 gram piston is exerting an outward pull of 933kg or 2,055 lb.