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big bore pan

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bikerwilly

Posts: 3

Joined: Wed Oct 24, 2001 12:01 am

Location: Junction City KY.

Post Sun Feb 17, 2008 7:27 am

big bore pan

I'm going to build a new motor with 3 5/8 cylinders and stock stroke of 3 31/32 will this be a good combo?
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Chris Haynes

Posts: 2631

Joined: Wed Jul 05, 2000 12:01 am

Location: Los Angeles, CA

Post Sun Feb 17, 2008 9:38 am

Re: big bore pan

bikerwilly wrote:I'm going to build a new motor with 3 5/8 cylinders and stock stroke of 3 31/32 will this be a good combo?


Why not just build the Square Motor? 4" x 4".
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panic

Post Sun Feb 17, 2008 11:20 am

Re: big bore pan

The big-bore, short-stroke combination has been invented every 10 years as a new idea.
Since re-balancing is required anyway, it offers no advantage over the same displacement (81.9") achieved through stroke increase (4-3/8" is about the same at 81.2"), which is more effective.
More stroke will eventually limit engine life and maximum RPM, but not near where you are now.
You might get a better squish band - but only if you actually machine the parts yourself, they won't come like that.
The flywheels also offer you a choice of at least 3 weights.

What is it you're trying to do?
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bikerwilly

Posts: 3

Joined: Wed Oct 24, 2001 12:01 am

Location: Junction City KY.

Post Mon Feb 18, 2008 6:05 am

Re: big bore pan

I have flywheels out of a 56 74in was going to use them with std 3 5/8 bore cases . just though i'd use the wheels i have as it in good shapr and has rods on them.
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Cotten

User avatar

Posts: 2674

Joined: Thu Sep 30, 1999 12:01 am

Location: Central Illinois, USA

Post Mon Feb 18, 2008 8:00 am

Re: big bore pan

I have no experience with such a combination in a Pan, but a big-bore stock-stroke Chubble turned out to be a delightful torque machine, able to pull a fully-loaded sidecar faster than anyone should, for several round trips to Sturgis from Illinois.

The owner insisted upon an overhaul at ~25,000 miles, as he had never gotten that out of a motor before.
I found nothing to fix, leading me to conclude that it is a very durable formula.

....Cotten
Note: It was originally an 80", but that is still a 'short stroke' to a lot of us.
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panic

Post Tue Feb 19, 2008 11:18 am

Re: big bore pan

Certainly preferable to stock bore, needs smaller compression dome for the same ratio, no down-side except that it's slightly more knock-prone than a std. bore if the quench is too large, but has better quench than stock if the quench is properly limited.
You're going to rebalance it, yes?
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DICK LEMAY

Posts: 79

Joined: Thu Dec 08, 2005 12:08 pm

Location: No. Andover, Mass. USA

Post Tue Feb 19, 2008 11:40 am

Re: big bore pan

Someone mentioned 4 inch bore. Were would you find heads to accomodate this?

Dick

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