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Old 04-24-2006, 04:37 PM   #1 (permalink)
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I noticed that the 1975 and the 1979 have different part numbers for these cams. Also this is what i know for sure for differences from my loaned manual:
1975
Valve timing:
Inlet opens 5 deg BTDC
Inlet closes 50 deg ABDC
Exhaust opens 50 deg BBDC
Exhaust closes 5 deg ATDC

1979
valve timing:
Inlet opens 5 deg BTDC
Inlet closes 35 deg ABDC
Exhaust opens 40 deg BBDC
Exhaust closes 5 deg ATDC

The manual I have (Haynes) has different specs regarding the two cams so that I can't directly compare them other than the above. The 75 quotes cam lift, and the 79 quotes lobe height. I am about to do a single head swap, and would like to know if i should swap the cam also. Also which one would be "lumpier" ? Thanks!
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Old 04-24-2006, 04:41 PM   #2 (permalink)
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I do know that performance was much better on the earlier 1000's over the later ones. Carburation changed and got leaner, performance slowed, but, less emissions... If you remember, the 70's were when we started to think about air pollution... lots of really DUMB things were done to engines to make them emmit less... usually performance and mpg suffered
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Old 04-27-2006, 04:55 AM   #3 (permalink)
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Thanks rcmatt007
I was curious because the specs of the carbs dropped a mm. I wondered if they might have cammed it a little to make up the difference. But i've seen that the 79 specs show 78 HP and the 75 state 82 HP, but at 7000 and 7500 rpm respectively. I can't verify these specs as they are internet based, but they agree with your point. I do remember my dad's 69 lincoln had 375 HP stock (stamped on the plate) and his 1978 lincoln (with the same 460) had, well, a lot less...

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Old 04-27-2006, 05:58 AM   #4 (permalink)
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nomados wrote:
Quote:
I noticed that the 1975 and the 1979 have different part numbers for these cams. Also this is what i know for sure for differences from my loaned manual:
1975
Valve timing:
Inlet opens 5 deg BTDC
Inlet closes 50 deg ABDC
Exhaust opens 50 deg BBDC
Exhaust closes 5 deg ATDC

1979
valve timing:
Inlet opens 5 deg BTDC
Inlet closes 35 deg ABDC
Exhaust opens 40 deg BBDC
Exhaust closes 5 deg ATDC

The manual I have (Haynes) has different specs regarding the two cams so that I can't directly compare them other than the above. The 75 quotes cam lift, and the 79 quotes lobe height. I am about to do a single head swap, and would like to know if i should swap the cam also. Also which one would be "lumpier" ? Thanks!
Nomados, those numbers are meaningful ONLY IF the specs are measured at the same lift height (same lift point on the cam lobe).. Assuming they are, the biggest controller on can power range (place the cam becomes effective) is the closing point of the intake valve.. The second biggest effecting factor is the opening of the exhaust valve.. In the two cams speced out above the one with the 50° ABDC intake would be the highest performance cam (BUT the power band would come in at a higher RPM).. Be careful with cam selection as the trans & final drive gear ratios have a big effect on how those cams feel & allow the engine to utilize the cam.. Intake size/restruction & exhaust restriction/flow, & compression ratio also have a largeeffect the cam selection..

Twisty
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Old 04-27-2006, 10:54 AM   #5 (permalink)
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while no expert, I believe carbs would also have to be "adjusted" accordingly for a meaningful , efficient difference. When you introduce the new cam, you now need new fuel and air requirements.
Everything I have ever read had the earlier wings as the better running ones. Having now ridden a 77 and a 78, there is a difference. The 77 does seem quicker in the lower gears while 5th gear seems to be much more an overdrive. The 78 seems to handle the lower speeds in an upper gear better-less downshifting. There are alot of variables, so these differences could be particular bike dependent.

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Old 04-27-2006, 12:33 PM   #6 (permalink)
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Old 04-27-2006, 07:50 PM   #7 (permalink)
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Thanks guys,
and thank you to Randakk. Welcome to the site, and i hope you stick around awhile.
Don't take this the wrong way, but i hold you somewhat responsible for my newly aquired gl1000 addiction. I was initially drawn to the bike, and then after reading all of your extensive information (and subjective opinions) on your website I couldn't help but take the plunge. Now i am pullin motors, changing heads, swappin points, checking cam specs, all stuff i thought i finished in my early twenties. And the outcome is happily driving a 30 year old bike through a Canadian winter. Gave away the minivan, wondering why it took so long to get back to two wheels.
So yeah, thanks. Having a blast.
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