There are special "multi-keyed" timing gear sets that allow cam phase adjustments but most people buy a set of off-set bushings to use in the top cam gear.
The cam gear's dowel pin hole is drilled oversize to accept the bushing.
DD
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| Need advice on cam setup for a '77 super six https://slantsix.org/forum/viewtopic.php?t=42076 |
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| Author: | olafla [ Wed Sep 29, 2010 3:54 am ] |
| Post subject: | Need advice on cam setup for a '77 super six |
I am replacing the radiator and fitting a new electric fan, and thought I should use the opportunity to replace the cam drive at the same time. Does anyone have practical experience and/or suggestions on modifying the cam timing for the stock '77 cam, or should I leave it as it is? 1977 Aspen Wagon, stock super six setup, 904 auto. The only changes from stock is HEI ignition, electric fan, new carb (Mototrcraft 2150, 1.08 ), 904 shift correction kit. Olaf. |
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| Author: | 66aCUDA [ Wed Sep 29, 2010 6:22 am ] |
| Post subject: | |
Olaf if it were me i would install an Erson 270. I think that would be enough of an improvement over stock to be worth while. It should still work well with a basic stock engine. You do have a 2 1/4 or better Exhaust system right? This cam would also allow you some growth if you decide to go with larger valves and mild port/polish. Frank |
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| Author: | Doc [ Wed Sep 29, 2010 9:48 am ] |
| Post subject: | |
When changing a timing set, I always like to do some "before & after" checks to ensure proper installation of the new gear & chain set. I check the valve lash and then take some compression readings. Once the timing cover is off, I use a degree wheel to find the intake valve closing point. When the new timing set is installed, recheck cranking compression (in psi) and intake valve closing point. You can experiment with advancing the cam (Intake valve opens and closes sooner) and usually see the cranking compression increase. DD |
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| Author: | olafla [ Wed Sep 29, 2010 5:21 pm ] |
| Post subject: | |
Thanks 66aCUDA and Doc. I have another engine that will be built from ground up with extensive modifications. The engine in the Aspen has about 425.000 km on the clock, so I think I'll basically leave it alone until rebuild time. Replacing single 'big' parts like a camshaft in an engine with high wear, has given me a lot of trouble earlier, so I will wait with a new cam until a future rebuild for that engine, but the advise about which cam is exellent. I did not formulate the original question good enough, what I really want to know is if someone had done changes to the timing that gives a noticeable effect for the stock engine in a heavy wagon. Very often a few degrees advance may give a positive change in an engine, but different types of engines react different to the treatment, and I see no reason for me to do a lot of work, if it doesn't give results. There is one other mod I'll do though , and that is distributor recurve Olaf |
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| Author: | hellion_locdogg [ Wed Sep 29, 2010 5:37 pm ] |
| Post subject: | |
Do the valve lash, a recurve and tune your vac advance. http://www.dutra.org/doug/draft-webpage ... ibutor.htm ,Cliff |
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| Author: | olafla [ Thu Sep 30, 2010 4:02 pm ] |
| Post subject: | |
Will do, plus compression testing. Olaf. |
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| Author: | Old Car Scott [ Thu Sep 30, 2010 4:52 pm ] |
| Post subject: | |
Quote: You can experiment with advancing the cam (Intake valve opens and closes sooner) and usually see the cranking compression increase.
How does one 'advance' the cam on a slant six? Is the adjustable timing gear require, or do you move and additional tooth of the cog?
DD |
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| Author: | Doc [ Thu Sep 30, 2010 5:36 pm ] |
| Post subject: | |
There are special "multi-keyed" timing gear sets that allow cam phase adjustments but most people buy a set of off-set bushings to use in the top cam gear. The cam gear's dowel pin hole is drilled oversize to accept the bushing. DD
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