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Rod Lengths

Tonerjockey

Tonerjockey

High Miler
GT Contributor
Joined
Oct 28, 2008
Messages
788
Location
San Jose
Greetings fellow Guzzi mavens,

I am headed towards a 76 Lemans makeover for Land Speed Racing. My fantasy is a short stroke and WAY oversquare combination. The class will be 1000cc P-PP.

The idea would be to use an Ambassador crank and 95mm pistons (=1000cc if my cackle-ate-her is correct). Today's concern is max pressure at crank angle etc. or... how long a con rod.

I have the stroke specs (78mm vs. 70mm) but am interested in the con rod legnths. I haven't taken the Lemans apart yet (still negotiating space in a frined's shop), but will measure that one once I do the work.

The concept I wish to explore is getting high HP at high RPM (for a Guzzi). This, like all racing modifications, is a complex issue with an unlimited number of sceanearios to consider. Today I am concentration on rod length for max power.

So ... anyone know the rod legnths for an Ambassador and a 850 Lemans?

I'll need to get the cylinder legnth of an Ambassador as well. I want to position the max pressure in the cylinder at the most advantagoeus crank angle. Seems that the Ambassador cyl. length (height?) will be shorter than the Lemans.

Thanks for any ideas,

Alex
 
No. The 750's all used pistons with a higher deck height. Rod lengths were all the same, (Although construction changed a bit over time.). I've got a pair of 4mm over-length Carilos I used in my hot rod if you'd like to play with them? They're only small-bolters but I used to rev that to 10,000 or close enough, (At those speeds VE drops off severely and the oil pump cavitates. Be warned.) and they never let go.

Pete
 
Hey Pete, thanks for the note.

I plan on using the 750 Ambassador crank with Lemans cylinders, case etc. The engine should look like a stock 76 Lemans but will have a short stroke crank and huge pistons.

Were the 750 Ambassador rods the same length as Lemans' 850?

If this hair brained scheme of mine progresses to the point of actual assembly, those 4mm longer Carrillos might be perfect for me.

Longer rods will influence multiple engine relationships. I found this article useful to me
http://www.stahlheaders.com/Lit_Rod Length.htm This may be old news to you but it's virgin territory to me. I'm still trying to get it all sorted out.

Alex








Alex
 
Cool project.

If you really want to go for P-PP use a Lemans4. 40mm carbs...... Lemans 1 = 36mm. Big restriction. :shock:
 
For what you would spend on doing a short stroke, big bore engine you can buy a MK 4 and then talk to Bill Ross on MK 4 hot-rodding...... :D
 
I think I'll avoid atempting to compete with Team Stubby Crowbar. :whistle: Those guys go out and actually break records!
 
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