 This is the "stupid question" of the week for.....
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Joined: May 2007
Posts: 512
Adjunct
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OP
Adjunct
Joined: May 2007
Posts: 512 |
.....all you perfomance experts. If you use the 790 cams or the thunder cams in an 07 speedmaster with the wimpy 865 cams, will you need to rejet if you touch NOTHING ELSE? I would assume that an immediate valve adjustment would be in order, or is that the stupid STATEMENT of the week? 
-Tony
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Re: This is the "stupid question" of the week for.....
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Joined: Jul 2008
Posts: 1,440
Learned Hand
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Learned Hand
Joined: Jul 2008
Posts: 1,440 |
Not to hijack the thread, but are the specs for these two cams available online? I'd be interested to see the comparative duration and overlap.
Jack
'08 America Blue/White; Custom Headlamps, Custom Lowers, Clearview 20", Bafflectomy
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Re: This is the "stupid question" of the week for.
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Joined: Jan 2005
Posts: 3,753
Loquacious
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Loquacious
Joined: Jan 2005
Posts: 3,753 |
spec for 790 cams are, t bike no. and from the regular bonnie guys yes you will have to rejet. tony i am a phone call away. i dont bite  Frank
(Former)05 BA tbike pipes, ai removed, Freak, mikuni hsr 42's, 904, ported/polished head, 1mm oversized valves
NOW-2010 silver and black tbird
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Re: This is the "stupid question" of the week for.....
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Joined: Sep 2006
Posts: 1,457
Learned Hand
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Learned Hand
Joined: Sep 2006
Posts: 1,457 |
Quote:
I would assume that an immediate valve adjustment would be in order...
Installing the correct shims would indeed be part of cam replacement.
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Re: This is the "stupid question" of the week for.
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Joined: Jan 2005
Posts: 8,639 Likes: 3
Old Hand
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Old Hand
Joined: Jan 2005
Posts: 8,639 Likes: 3 |
I forget which, but I think it's the pilot jet that is a size smaller on the 865. You would do well to make sure your jets are at least as big as the 790 and maybe a size or two bigger.
Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python
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Re: This is the "stupid question" of the week for.
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Joined: Aug 2005
Posts: 2,726
Loquacious
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Loquacious
Joined: Aug 2005
Posts: 2,726 |
I think the 865s come now with 40 pilots where the 790s came with 42s. I have a question about cams. What was the advantage to change the cams for the 865s? If the cams in the 790 are better with the BB, why would they not be better in the 865s?
Bob
2005 America, 904cc - sold. 2014 Trophy SE.
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Re: This is the "stupid question" of the week for.
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Joined: Jan 2005
Posts: 6,308 Likes: 4
Worn Saddle
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Worn Saddle
Joined: Jan 2005
Posts: 6,308 Likes: 4 |
I would assume that you would not need to rejet, you are changing the mechanical timing of the intakes and outs, not the breathing really. But I could be wrong.Swap em out and try, won't hurt nothing. Also, you can get a better price for custom made cams from Megqacycle Cams. But you have to send them your originals, they take a few weeks but can give you 3 different styles depending on your riding. Give them a call, they are pretty smart folks. I currently have their "Medium Street Grind", which give me a little more torque then stock, about 4 ft/lbs but took away 2 hp at the top end. Better for mid range stomping around town and climbing the hills in this area. Wifey's 750 Magna is still faster though. grrrr.
A word to the wise is not necessary. It is the stupid ones who need the advice.
Pat
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Re: This is the "stupid question" of the week for.
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Joined: Dec 2005
Posts: 604
Adjunct
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Adjunct
Joined: Dec 2005
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Quote:
What was the advantage to change the cams for the 865s? If the cams in the 790 are better with the BB, why would they not be better in the 865s?
Like the Tbkike cams, the 790 cams are more of a high rpm hp type grind.
The 865 cams are more for low end torque.
I think Tbike even takes the position that they offer no improvement over the stock 790.
I take this to mean the 790s & Tbikes are a similar grind.
All this would basically hold true regardless of engine displacement or CR.
It still strikes me as odd that the 790 engine has the "hotter" cams but lower redline of the two engines.
Said Molly to James, that's a fine motorbike.
Richard Thompson
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