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Stroker?

Tonerjockey

Tonerjockey

High Miler
GT Contributor
Joined
Oct 28, 2008
Messages
788
Location
San Jose
Hey Fellow Guzzi Mavens,

Has anybody had success with stroking a Guzzi? As far as I can tell, 78mm is the max stock crank for loop and Tonti's. I am pondering stroking to modify (enhance?) some efficiencies on a V7 Sport or LeMans.

Experiences? Theories? Been there, seen that's?

Tonerjockey

109.jpg
 
There was a stroker crank on Fleabay recently.

Big issue with using a stroker is that you need to use Carilos or similar otherwise the rod bolts will foul the cam. If you're chasing serious performance a stroker crank is one of the very last things you try.

If yiu decide to use a 750 crank you can chase much higher revs as piston speeds are lower with the 70mm crank. If you want to go that route I have a set of 4mm over Carilos that will allow you to use the mid valve heads with the shorter stroke crank but you'll need special pistons to get the CR up. The advantage of the short strokers is their increased VE, I got 84 RWHP out of 891cc with a 70mm crank . Problem was that it did it at 9800RPM and at that speed the oil pump cavitates badly and it ate big end shells like a sea-lion necks fish!!!:laugh:

Uh,but you know all that. I just realized who I was talkin' to!!!:blush:

Pete
 
hhhhmmmm

70mm stroke x 95mm bore would be just under 1K cc. The LeMans would be legal in 1000 P-PP class. I think the intake side would hafta be significantly modified to take max advantage of the potential gains... maybe more than the class allows....

Dunno if I could handle 9800 RPM... that's gotta be a two shorts ride. 7500 gives super pucker power to me.

Takin the V7 Sport to EL Mirage for this Sunday. This will give me somethin to ponder during the drive.

Thanks, as always, for the thoughts.

Tonerjockey


SaltonRepsol2.jpg
 
Hey Pete,

A short stroke LSR LeMans sounds like an interesting project. Have the 4 over Carillos spent much of their lives over 9000 RPM? Whadia want fer the Carillos?

ready-getset-.jpg


Tonerjockey
 
https://www.guzzitech.com/Strokerdyno.html

82x90 stroker I built awhile back....~83 hp without trying hard at all. More to come in the next 6 months.

The only real reason to build stroke instead of bore on roundfins is if you're run out of bore...

You'll easily spend thousands to build a stroker racing motor right, too.

Ed
Strokerdyno0908.jpg
 
The main limitation is the maximum piston accelerations possible .... which usually boils down to preventing ring flutter.

The rule of thumb used to be 4000FPM ... now it is pushing into the 4500 - 6000 range for drag bikes.

Stroking it will reduce the maximum RPM possible with the benefit of increased torque - so theoretically good for the road but not so good for long tracks/bonneville.

An oversquare engine (ie. by using the earlier crank) will reduce the piston speeds and allow higher RPM. It also has the benefit of requiring a bigger piston for the same capacity which gives more squish which is good but also a potentially less compact combustion chamber. Dr. John on his battle of the twins went this route and it was pretty successful.

Changing the length of the conrod can also have a fairly significant effect on the engine's output as it increases the dwell period at TDC.

It really boils down to different horses for different courses....

ChrisR
 
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