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Author Topic: Gearing for Bonneville  (Read 10380 times)

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Offline Truckedup

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Gearing for Bonneville
« on: December 14, 2012, 04:00:38 PM »
 I did a search but??? When you increase the altitude above sea level the power drops.Is the power that is left still peak at the same RPM before? Or will the engine not rev as high with increase in altitude?
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #1 on: December 14, 2012, 05:02:46 PM »
It has to with TE  what your tires put to the ground---if you are geared too HI because your eng does not have enough power to overcome the total drag ---  it will not tach as hi
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"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

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Offline Truckedup

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Re: Gearing for Bonneville
« Reply #2 on: December 15, 2012, 04:04:55 PM »
 Ok,But for this example let's say the engine is on a dyno at sea level and HP peaks at 7000 rpm.At 4000 feet with the carburetors adjusted for alttitude,will the engine still make peak HP(somewhat less because of altitude) at 7000 rpm?
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #3 on: December 15, 2012, 06:26:34 PM »
that should not change
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Truckedup

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Re: Gearing for Bonneville
« Reply #4 on: December 16, 2012, 07:59:57 AM »
 Thanks.This is a 650 cc Triumph pushrod gas cycle engine in non streamlined frame.Typically these engines peak at 6800-7000 rpm when tuned for 1.5-1.6 HP per cubic inch at sea level.Less power at elevation ,more drag on the surface,go from there...
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #5 on: December 16, 2012, 10:32:04 AM »
If you have any idea what a dyno sheet on that eng looks like how high you can keep it together and how fast the torque falls off will tell you how to gear it--- I gear for the rpm through the first light to be just about peak power and the last --past peak power for a torque curve that falls of fast.---If its pretty flat I and it is still climbing I would lower my gearing--- :-o YMMV
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Truckedup

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Re: Gearing for Bonneville
« Reply #6 on: December 16, 2012, 11:48:24 AM »
 In general,these 2 valve hemi engines get peaky when modified.But it''ll have a somewhat flat power curve from 5000-7000 rpm.And 7000 is a good rpm limit but 7200 is ok for the last 10-15 seconds.The record is 124 mph,the bike is geared now for 130 at 7100 rpm,and it will run up against the rpm limit at low elevation on hard pavement.I am new to Bonneville and have to guess .I think running 124 on the first outing will need a little divine help  :-D
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #7 on: December 16, 2012, 12:26:58 PM »
I would gear for 124.5 at 7050 at the beginning of the mile and try to have 7075 or 7100 at the exit!!!  and see where you are going to find DA from best ever heard of 2800 to 8800 so it is a crap shoot!! :roll:  you will be at the mercy of the track, the DA, the wind gusts ect ect ect---work on your tuck and try to fair your rear body all you can---any minute think is going too be the difference  over bore to your absolute maximum!! :evil:
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Stainless1

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Re: Gearing for Bonneville
« Reply #8 on: December 16, 2012, 12:57:18 PM »
Running NA, leave it the way it is now, take gear changes up and down, and run it in October.... the air is a lot better in October for NA Motors.  It is always a crap shoot running the salt.
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Offline 55chevr

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Re: Gearing for Bonneville
« Reply #9 on: December 16, 2012, 01:06:31 PM »
Just about everyone over gears their first time out.   The informed sources believe that there is about a 15% power lose at the altitude of the salt flats. Bring enough sprockets to cover all possibilities. 
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #10 on: December 16, 2012, 01:15:14 PM »
SS #1 and 55 you guys said it best  :cheers: :cheers: :cheers:
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline JustaRacer

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Re: Gearing for Bonneville
« Reply #11 on: December 16, 2012, 01:43:56 PM »
Quote from: Truckedup on December 14, 2012, 04:00:38 PM
I did a search but??? When you increase the altitude above sea level the power drops.Is the power that is left still peak at the same RPM before? Or will the engine not rev as high with increase in altitude?

Take with grain of salt.  Not an expert.

This comes from drag racing naturally aspired engines in thin air (LACR, Bandimere, LVMS, etc).  My Bville experience is limited to turbocharged engines.

B'ville sees wild changes in DA.  IIRC, I saw from 3500' DA to 8800' DA.

Get a DA computer, but DON'T lend it out.  My first one grew legs and ran away.

You might have to advance the timing.  Thin air takes longer to burn.

Depending on carb design, you might have to drop main jet size.

Thin air acts like a smaller cam.  Your HP peak rpm will drop.

Or at least that's what worked for me.

Remember to tighten the axle bolt when switching sprockets.  I learned that one the hard way when I got in a rush at OCIR.

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Offline Truckedup

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Re: Gearing for Bonneville
« Reply #12 on: December 16, 2012, 01:54:55 PM »
October huh???? I'm the builder,a younger friend of mine,experienced dirt racer, is financing the bike and trip out there.I'll tell him...Old Triumphs do like cooler weather ...And it can be run a little leaner without the need for  safety cooling by using a slightly rich mixture...
 
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Offline SPARKY

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Re: Gearing for Bonneville
« Reply #13 on: December 16, 2012, 02:27:10 PM »
Remember,  Aircooled engs cooling capabilities are affected by DA!! as well as air temps
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Miss LIBERTY,  changing T.K.I.  to noise, dust, rust, BLUE HATS & hopefully not scrap!!

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

We are going to explore the racing N words NITROUS & NITRO!

Offline Truckedup

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Re: Gearing for Bonneville
« Reply #14 on: December 16, 2012, 02:35:49 PM »
 DA is air density?
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