4 main crank vs 7 main crank (just curious)

Hey everyone. Thanks for the help on the previous topics. Today I was just reading on the i6 and on Wikipedia I saw it said that 4 main cranks have better torsional stiffness than 7 main and are therefore used in some high rev engines? This confused me because to me it seems the longer distance between the mains would make the twisting action worse not better. Can anyone just kinda explain that to me. Because it would pretty cool since my engine is a 4 main if it actually could handle higher revs thanks
Jarod

The weak point in a six cylinder engine is the long crank.
The seven main bearing block & crankshaft give it more support for crankshaft deflection.
Ford is cost conscious, if there was no gain they would have stayed with the four main crank.

falcon_master":2ru66d91 said:

Hey everyone. Thanks for the help on the previous topics. Today I was just reading on the i6 and on Wikipedia I saw it said that 4 main cranks have better torsional stiffness than 7 main and are therefore used in some high rev engines? This confused me because to me it seems the longer distance between the mains would make the twisting action worse not better. Can anyone just kinda explain that to me. Because it would pretty cool since my engine is a 4 main if it actually could handle higher revs thanks
Jarod

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If it on the internet it must be true. :rolflmao:

Seems non-intuitive but I was at a sports car - track car garage recently and the main mechanic was explaining the physics behind additional friction losses with 3 more bearings and reason for four main sixes revving higher than seven main. I was there consulting on front suspension mods for a 65 Mustang Fastback being built for race track with class restrictions .

Conversation centered on my opinions on the Fastback's conversion from six cylinder 170cid grocery getter to full tilt racer and the legendary Falcon six powered "Philson Falcon". a purpose built track car with a Ford 144 six layed over like a slant six and supposed 9K rev limit.

have fun

Built by machinist and USAC tech inspector Norbert Philson in 1959, the Philson-Falcon features a tubular ladder frame of Philson's design and a considerably reworked Ford Falcon six-cylinder engine fed by three SU carburetors. The special is owned by Charles Bordin of Scarsdale, New York.

the first thing is that we need to know the difference between the two cranks. the big difference, after the three extra main bearings, is the number and size of the counterweights. the four main cranks has more and larger counterweights, which does in fact improve the torsional rigidity of the crank. and those counterweights are right where the extra main bearings are with the later seven main cranks.

in this case it is six of one, half a dozen of the other. the four main crank has better torsional rigidity, but less support. the seven main crank has more support, but less torsional rigidity. the only thing i dont know is the weight of each crank. either way though, how many ford six cranks have been broken over the years?

Bump on this thread, ive wondered this myself

Paul Knotts famous 170 AU falcon has triple DCOE 45 webers and i believe is still a 4 bearing car that makes 280 Flywheel HP

so theres gotta be something they know that we dont

powerband":14uacfya said:

Seems non-intuitive but I was at a sports car - track car garage recently and the main mechanic was explaining the physics behind additional friction losses with 3 more bearings and reason for four main sixes revving higher than seven main. I was there consulting on front suspension mods for a 65 Mustang Fastback being built for race track with class restrictions .

Conversation centered on my opinions on the Fastback's conversion from six cylinder 170cid grocery getter to full tilt racer and the legendary Falcon six powered "Philson Falcon". a purpose built track car with a Ford 144 six layed over like a slant six and supposed 9K rev limit.

have fun

Built by machinist and USAC tech inspector Norbert Philson in 1959, the Philson-Falcon features a tubular ladder frame of Philson's design and a considerably reworked Ford Falcon six-cylinder engine fed by three SU carburetors. The special is owned by Charles Bordin of Scarsdale, New York.

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very interesting -anyone got a photo of the engine /engine bay ? my gooogling didn't turn up anything

actually posted Too soon :

think this is it : not as laid over as I thought

got a pic of other side of the engine? like the intake!
wonder Y the solex.s Coulda had anything I imagine...
And Y the 'slant' ford6? Did they say just for space?

my '68 170 has h u g e counter weights 8^0
adds to the lill tractor nature of it's great tq~

I will agree that the 4 bearings have large counter weights

I think mine's a 7 as it's '68, will look'n hope 2 report back~

where yours has sm holes in the center (of the 'counterweights'), mine seems to have lrg, more ovoid (almost square w/rounded corners) holes...
I'll tellya - in the bronk it could plow some heavy wet sno upa steep hill, skid some huge logs up outta the swamp a mile up the hill to the band saw mill. 3.03, D44, 9 inch rear w/411s in it. Musta been the 411 gears, eh?
But lookit those counterweights...

Has anyone ever seen a US 7 main 170 ?

The race car pictured was run before the 7 mains came out. So thats all they had then.
I wish "X" would chime in on this from down under.
I would love to see comments from Argentina also.
The Aussi's & the Argentines modified these engines, where the US used the six for fuel mileage.
If you wanted power we had V-8's. Back then fuel was dirt cheap so the cubic inch war started.

wsa111":3dnq98z6 said:

I wish "X" would chime in on this from down under.

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I met him over on another site recently. We sent some cross posts. I carried his "Ford6 will not allow me to log on, send this screen shot to somebody over there" to 1 of our admin (Perry) but no msg were sent back to me.

Is he banned or sompin? It's been at least 4 months no show here...

Fri I'll look at my '68, the pan's off. I understood (IMSMC) after bout '65 all the falcon motors went 7 mains...?
What say U?
bubba? David?

X isnt banned, he is just having issues logging on. apparently firefox does like his email addy.

Has anyone ever seen a US 7 main 170 ?


... and has anyone seen a 4 main 200 of any year?.

have fun

One thing to remember about the 170 is the stroke is shorter than the 200 (2.940" vs 3.126") with the same rod, so that portion of the crank is closer to the centerline. This would help stiffen the crank along with the thicker counterweights as opposed to a four or even seven main 200. The shorter stroke would also allow the engine to rev higher if allowed to breathe.

I've never seen a seven main 170 crank. I've called around to some of the early Bronco graveyards and have never found one; I'm starting to believe they are unicorns. The only four main 200 crank I've seen was on eBay.

Ak told me that there were some 7 main 170s, but i think that they came from South America to Cal where his shop was located. I sure have never seen any, but I am close to Canada.

You know the 144, 170, and 200 are all oversquare engines which means they are inadvertently designed for higher RPM, i just havent ever seen anyone put as much effort into doing a full rotating assembly balance, and complete over work with better valve springs and performance cam for the 170 or 144. I think its cause the majority have come to the conclusion that the 7 main bearing set up is stronger or at least has much more support than the others. I makes me want to tear my engine back out and give it the race workover and see what it can really do.

yep, my 170 (some 1 put a car engine in the bronk - 2 dipsticks - one regular, 1 in the pan) frm 1968 is just like the rest - 4 mains. Not the 7 I thought. The 250 is buttoned up now (1969) so can't ck it, it's 1/2 in the rig now. But again, the counter weights in this 170 R different than those in the above pic.
Later 200s have 7?