Author Topic: Lead substitute  (Read 3206 times)

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Offline clubmet

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Lead substitute
« on: December 06, 2012, 11:58:19 AM »
I am preparing a bike for P / PV competition.  I know gasoline is supplied at the event.  Can you legally add a lead substitute?  If so, is it purchased at the event or do you you bring it?  The bike currently has original valves and seats.

Offline sabat

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Re: Lead substitute
« Reply #1 on: December 06, 2012, 03:00:37 PM »
You can't add anything to event gas, but there is leaded gas available.

Offline clubmet

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Re: Lead substitute
« Reply #2 on: December 06, 2012, 03:07:38 PM »
Sabat,  Thanks for the quick response.  I didn't know about the leaded fuel availability.  It takes away my concern.

Offline wobblywalrus

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Re: Lead substitute
« Reply #3 on: December 06, 2012, 08:17:52 PM »
It is a 110 octane leaded gasoline that works good in old bikes.  An advantage is gained when you tune the engine with it in mind. 

Offline Stainless1

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Re: Lead substitute
« Reply #4 on: December 06, 2012, 08:38:06 PM »
oversize valves and 14:1 will make it better... all legal as they are modifications that are not in view
Stainless
Red Hat 228.039, 2001, 65ci, Bockscar Lakester #1000 with a little N2O

Offline Chris V

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Re: Lead substitute
« Reply #5 on: December 07, 2012, 10:54:55 AM »
Yes, but are you taking a chance if a record is set that someone in same class may protest your faster then normal production engine ??
1972 Yamaha R5  350cc

Offline Peter Jack

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Re: Lead substitute
« Reply #6 on: December 07, 2012, 11:10:00 AM »
Yes, but are you taking a chance if a record is set that someone in same class may protest your faster then normal production engine ??

No. If the modification is not visible from the outside it is legal.

Pete

Offline wobblywalrus

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Re: Lead substitute
« Reply #7 on: December 07, 2012, 10:38:56 PM »
We raced the AMA modified production streamliner class with production engines when they were legal, in both 175cc and 1,000cc classes.   The carb body needs to be the same as OEM on the outside.  The trick to building a production engine is to realize this is the limiting factor - the amount of air that can be sucked through the carb.  This is the first thing to figure out.  Second is to calculate the power you can get with this air.  Third is to figure out is if this power will give you the speeds you need.

Its basic engine math and a good idea to do it before the build.  We did this the other way, the expensive method.  We built up to the motors to the limits of what their carbs would flow and found out how fast they would go.

Offline wobblywalrus

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Re: Lead substitute
« Reply #8 on: December 09, 2012, 11:21:18 PM »
There is an easy to use chart at this web address.  http.www.ducatimeccanica.com/dellorto_guide/dellorto_3_1.html

Basically, you look at the carbs you have and see it they will produce the power you need with the maximum allowed displacement for your class.  Then you build the motor with all original castings so it looks like an OEM engine from the outside, it does not exceed the displacement limit, and it runs on the same type of fuel as the OEM engine.

Example.  The Triumph had 36 mm carbs from the factory.  They had throttle plates that rotated on shafts in the middle of the bores.  Their equivalent round diameters were 33 mm when the areas obstructed by the throttle plates were subtracted from the total choke areas.  The chart says 33 mm dia carbs are adequate for twins producing 42 to 64 horsepower.

The bike had problems getting over 68 horsepower with those OEM carbs.  I asked myself "can I do what I want in the production engine class with this power?"  The carbs limited me form getting any more horses.