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Old 06-22-2013, 07:16 AM   #1
Ras Thurlo OP
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80RT vs 80GS

Guys:

I have both a '85 80RT monolever (now urban scrambler) and a '92 80GS.

The 80RT seems to have a bunch less low down pull and only really get going above 3k revs, this is despite the fact that the bevel box says 37/11.

The 80GS had a bunch more low pull when it was still on a 32/10 paralever, its now on a 37/11 monolever and its now a grunty beast (in relative r80 terms)

I'm confused - what other differences are there between the two bikes that would cause this low torque discrepancy?

Ras Thurlo screwed with this post 06-23-2013 at 12:51 AM
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Old 06-22-2013, 07:24 AM   #2
Clay Spinner
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One needs an engine or carbs spruced up... Or heads rebuilt as i would think the engines would have been the same... But im not sure....over to the learned!
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Old 06-22-2013, 07:25 AM   #3
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Timing, valve adjustment, carb settings and adjustments....fuel flow through petcocks.
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Old 06-22-2013, 10:54 AM   #4
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The GS has 36mm and the R80RT 38mm exhaust pipes.
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Old 06-22-2013, 10:59 AM   #5
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Any pics of this "urban scrambler"?
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Old 06-22-2013, 11:11 AM   #6
Rob Farmer
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Quote:
Originally Posted by Prutser View Post
The GS has 36mm and the R80RT 38mm exhaust pipes.
Since when?
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Old 06-22-2013, 12:18 PM   #7
Prutser
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Quote:
Originally Posted by Rob Farmer View Post
Since when?
Since always.(on this side of the pond )

R100R 100GS 80GS all have 36mm headers.
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Old 06-22-2013, 12:27 PM   #8
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small headers make better grunt
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Old 06-22-2013, 12:32 PM   #9
Rob Farmer
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Quote:
Originally Posted by Prutser View Post
Since always.(on this side of the pond )

R100R 100GS 80GS all have 36mm headers.
No they don't! I had an US R100GS and it had 38mm exhausts like all the others.


No doubt Supershaft will be along soon to give you a kicking
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Old 06-22-2013, 12:49 PM   #10
Prutser
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Quote:
Originally Posted by Rob Farmer View Post
No they don't! I had an US R100GS and it had 38mm exhausts like all the others.


No doubt Supershaft will be along soon to give you a kicking
The fitting in the heads is 38mm but they get thinner after that.

I'm ready to for that kick although I might not deserve one this time .
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Old 06-22-2013, 12:57 PM   #11
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Stock R100GS was 38mm at the exhaust manifold, necking down to 36mm shortly after that. This was on a 40mm bing carb model. Measured on a few GSs here to be sure that I wasn't caught with a barstardisation on Gus. Prutser is correct.
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Old 06-22-2013, 05:32 PM   #12
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Also, the RT might have the higher CR 9.2:1 pistons that were used on some euro R80 models whereas the GS would have the 8.2:1, but that should HURT power.
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Old 06-23-2013, 12:52 AM   #13
Ras Thurlo OP
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Quote:
Originally Posted by villageidiot View Post
small headers make better grunt
is this right?
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Old 06-23-2013, 01:31 AM   #14
Prutser
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Quote:
Originally Posted by Ras Thurlo View Post
is this right?
Yes it is. But it doesn't mean a good set-up exhaust system with bigger headers can't give even more.

I tried my Siebenrock exhaust system on my stock ST and all the low down torque was gone.
But after the new camshaft was put in, the exhaust made a big big improvement.
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