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Old 05-30-2008, 02:36 PM   #1
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SOHC Cam Advance (FREE mod) - Better Torque/Better FE?

I just advanced the cam by 9 degrees on my '94 Acura Vigor. It has a SOHC so both intake and exhaust are advanced by 9 degrees of camshaft rotation. To do it I simply loosened the timing belt, took it off the cam gear, rotated the cam gear "one tooth" advanced, then slipped the belt back on and tightened it back up.

Low rpm torque has increased significantly. I usually shift at 1800-2000rpm, but now I can shift at 1500rpm. It's an inline 5-cylinder so it already had decent torque...the cam advance just enhanced it that much more. Before the cam advance I could lug along in 5th gear at 25mph, but if there was a slight incline or I had to accelerate then I had to downshift. Now I can shift into 5th at 25mph if I'm accelerating on a level road, and can easily maintain 25mph going up slight inclines in 5th. 1st gear is now more of a nuance than anything; as long as I'm rolling forward in the slightest I can start in 2nd. If I didn't care about the clutch I could start in 2nd all the time.

The idle is still smooth and the engine starts just fine. No negatives as far as I can tell. I'll post any FE changes once I've run through a few tanks.

I would recommend anyone with an engine that does NOT have any sort of valve timing/lift management like VVT-i or VTEC try this out. If you have less than 36 teeth on your cam gear, then one tooth advance might be a little more than you should advance it, but cam gears on most engines are usually 36 or more teeth; so one tooth advance is 10 degrees or less.
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Old 05-30-2008, 03:09 PM   #2
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If your torque comes in at 4000 this might help, but don't go doing it if you've got decent pull at 2-3K already, 'coz you can't really use it at idle speed...

An adjustable cam gear would allow finer tuning of this, such that if your torque is a little higher than you'd like at 3200ish say, and you'd like it at 2500ish, then advancing just a couple of degrees might be good. Adjustable cam gears can probably be found on eBay for popular "tuner" models. For less popular models, they can be made from 2 identical stock cam gears, with the hub cut out of one, and the gear cut off another, and place them back to back with spacers, and curved slots for bolts, so that one can slip one round with respect to another...

A second option for those with a cam gear held on with a "woodruff key" is to dicker with that. Either with an offset woodruff key, which is staggered a little, or the ghetto method is to file the slot a little larger in the cam gear and shim it on one side. Do not do this if your cam gears are made out of unobtanium, 'coz if it ends up loose, you wanna be able to revert to a stock on. You can buy offset woodruff keys. Or you can cut a chunk off a steel bar and file one yourself. 1/8" off a swaybar or the face of a spare hammer may work.

A third option, is to bolt an extra tensioner assembly on the tension side of the belt, and deflect the belt slightly with a pulley there to advance timing slightly, retensioning the stock tensioner accordingly. DO NOT DO THIS ON INTERFERENCE ENGINES, it may cause excessive belt stress, and/or jump off when high RPM is used frequently and/or for long periods. The innovators here will note that with two pulleys bolted to a slide, one toothed, one smooth, one could rig variable valve timing, solenoid, vacuum, or choke cable activated.
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Old 05-30-2008, 03:48 PM   #3
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I tried advancing my cams 3 degrees on my motorcycle, gained lowend torque, but had problems with pinging, so had to put them back. thought about retarding the timing to compensate but never tried it.
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Old 05-30-2008, 04:12 PM   #4
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Well yes, if you've got a camshaft driven dizzy, and have the ignition timing advanced to optimum already, then you'll need to retard it back as many degrees as you advance the cam, for a start... you might be able tweak it either way a bit still for better results, since conditions in the chamber might have altered a little.
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Old 05-30-2008, 06:32 PM   #5
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10 degrees at the cam is 20 degrees at the crank. Only half the cam gear teeth move past the same point in one rev of the crank.

regards
gary
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Old 05-31-2008, 09:43 AM   #6
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Quote:
Originally Posted by mikehallbackhoe View Post
I tried advancing my cams 3 degrees on my motorcycle, gained lowend torque, but had problems with pinging, so had to put them back. thought about retarding the timing to compensate but never tried it.
Advancing the cam timing increases your dynamic compression ratio and that may have been what caused the pinging.

Something to keep in mind with this, and may have been the case above, is that most engines take their distributor timing or their electronic spark pickup based on cam timing so you should reset the ignition timing after making an adjustment like this. Also remember that with cam timing advanced like this you will lose top-end power.
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Old 05-31-2008, 09:47 AM   #7
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Acceleration does feel a little "flatter" above 3500rpm.
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Old 05-31-2008, 12:00 PM   #8
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the honda valkyrie makes maximum torque at 4700 rpm, 5th gear at 55mph is around 2500 rpm, so advancing the cams helps lowend power. top end is higher than I need to go, so I don't care if I lose a little on the top. I am also trying power lynz and want to test the results before advancing cams and changing timing, one mod at a time.
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