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Discussion Starter · #1 ·
Okay, so I've been thinking about camshafts. From what I can tell on this forum, this is kinda viewed like an oil thread! So if this sort of thing makes your eyes glaze over, please hit 'back' and move to the next thread!! :)

Anyway, for those who are experienced with camshaft design, I've got these specifications for the '01 790 cams:

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2001 Bonneville 790 Cam Specs

Intake
Open 19* BTDC
Close 43* ABDC
Duration [email protected] 1mm, 9.5mm lift
Exhaust
Open 38* BBDC
Close 22* ATDC
Duration [email protected] 1mm, 9.4 lift

Overlap of 41.00 degrees and has in Intake Duration of 242.00 degrees. The Exhaust Duration is 240.00 degrees. The Inlet Cam has an Installed Centerline of 102.00 degrees ATDC. The exhaust cam has an Installed Centerline of 98.00 degrees BTDC.
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I bolded the last line above since I find this to be really whacked. That is a really tight installed centerline and makes me wonder what triumph was thinking...typical installed exhaust centerlines are generally at least 104* btdc and range upwards to around 108*.

This begs the question: Has anyone advanced their exhaust cam one tooth/revised the exhaust cam timing to get this cam opening earlier/closing earlier and effectively move the centerline to a more typical value? If so, could you please share?

I think this was done by someone on the now defunct delphi 'modified bonneville' group, but since the group is closed I cannot know for sure.

Thanks,

--Rich
 

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I should elaborate, you can advance the 790 exhaust cam 1 tooth and pick up a little bit of torque at lower RPMS at the cost of several hp on the top end. If you like to lug it around it might be a worthwhile thing to try, I prefer to rev rev rev!
 

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Pity you don't have the links, I would be very interested in knowing exactly what the torque gains and HP losses were.
well, maybe Jorgen could chime in here and post them, or you could try PMing him, jojje1963 is his handle on this forum. They were posted on another forum and for some unknown reason the cruel master of that forum pulled the plug on the forum with no warning, losing all the good info posted therein.
 

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I know our German friends are swinging both the cams in all kinds of directions!

Im told a dyno day is arranged for next month to determine the best results of jumping teeth on both.
Should be interesting!!


V.
 

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Discussion Starter · #11 ·
Dang it. I searched before posting and didn't find that thread. Thanks!

According to Jojje, who replied to my cross-post on Delphi, he lost 1-2 HP up top and gained slightly more than that at low to mid rpm range when he advanced the exhaust cam on his bike. Overall, he was surprised a 15* shift had so little impact...

Something to try and dyno when I get bored I guess...glad I have a stock 790 ignitor to fit since the extra 3* provided by my pieman modified ignitor will probably be unwanted in that scenario.

Regards,

--Rich
 

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the extra 3 might still help you.To me I cant see why you would want to take power off the top when useing the old 790 cams because the main reason to use them is to pick up power on top.If thats not what you want to do you might be better off with the newer 790 cams.
 
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