Cam degree effect on ignition timing

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Cam degree effect on ignition timing

Postby Bluejay » Wed Jun 05, 2013 10:13 am

I tore down Chevy 350 put in new summit cam .488 / .488 lift. also advanced cam additional 3 degrees buy flipping stock crank gear, old hot rod mag trick for stock pollution chain. I Figure 13 degree total cam advance ,without having fancy degree wheel to know for sure. Cylinder compression about 180 psi. Motor runs great, good low end response, plenty of quik rev, great on fuel. Had to lean carb way out . but cannot set ignition timing anywhere near factory 12 degree base. Or even power tune to 38 degree. Takes 40-60 degrees ignition timing to run decent. What the heck!
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Re: Cam degree effect on ignition timing

Postby Mallow415 » Wed Jun 05, 2013 1:31 pm

that shouldnt have anything to do with your timing did the balancer ring move? Need to make sure you have TDC first and make sure it lines up with the timing mark? Thirteen deg advance is a bunch?
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Re: Cam degree effect on ignition timing

Postby THE BOSS » Wed Jun 05, 2013 5:36 pm

what distributor and timing lite do you have?
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Re: Cam degree effect on ignition timing

Postby Bluejay » Thu Jun 06, 2013 12:05 am

Thanks guys. Cheap timing lite from autozone with no advance adjustment. I don't think? the harmonic balancer slipped around because I was able to time it correctly just before I switched cams. I changed timing often ,Usually for street cruising I advance timing a little, to help part throttle fuel economy. For severe use, I pull it back down to 12 degree base setting, (at idle, vacume disconnected) , which helps open four barrels at lower rpm. It timed well before tear down. Now it pukes and puts like a tractor with anything less than 40-60 advance ( at idle, vacume disconnected ). As far as top dead center, I pulled #1 plug, put screwdriver in, roll motor over till piston gets to top. But at top of cylinder, crank can roll 30 degrees before or after without piston moving so its hard to tell exactly where tdc. Is at. Mark piston drop before and drop after TDC. In the middle would be exact TDC. And it seems right. Too much cam advance then maybe?. It freakin runs great ,starts easy. Guess thats all that matters. Is this why people degree their cams, and how hard is that to do. Two more days to first race at Tri county Lisbon, I ain't tearin it apart again. Trying to get u joints in front axle, and 35" boggers mounted. I've been working like a dog to get this thing ready, When I look at all your nice race cars on race day I have a new respect for them, because i see it takes an insane amount of work to get there.
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Re: Cam degree effect on ignition timing

Postby Bluejay » Sun Jun 09, 2013 12:30 pm

Definatly something wrong. Too much advance at cam. Lacked low end power that was easily noticed on the sand. Tried setting ignition timing several different ways. Seven passes still way short of best time with stock cam stock cam timing. Damn float stuck stuck on carb flooding oil and motor started rappin hard. Changed oil to 90 weight gear oil , quik in pits , and was able to finish the nite. Had fun but motor is done.. Two weeks till next race. If I cant find cheap junk yard Sbc my short lived racing career is over for a while. Sure was fun while it lasted.
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Re: Cam degree effect on ignition timing

Postby Bluejay » Sat Jun 15, 2013 1:12 pm

Ok just bought new gm crate motor 350 md. Stupid timing acts the same way as motor I blew ! It responds well with timing way advanced. This is very irritating. Sounds and acts like sick dog with timing set on factory specs. Another thing the elderbrock carb needs little more than 1/4 turn on screws to idle. Shouldn't it take at least two or three turns. My buddies all say you gotta time them by ear. Well that ain't so easy. Ear is great , idling in driveway or putting around, but under load full throttle, thats a little different game. On another note, pulled the summit cam out of blown motor noticed one burned lobe, and little chips of casting missing out of several other lobes. Couldn't have had 9 passes on it . Thank you summit racing , deserve it or not , they gave me a new cam and bottle of zinc. It will be interesting to see what new times will be with crate motor. . New stock timing chain wasted also in old motor so loose could touch block. Double roller or better is a must with larger cam.
Last edited by Bluejay on Thu Jun 20, 2013 6:47 am, edited 1 time in total.
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Re: Cam degree effect on ignition timing

Postby Hot Stuff » Sat Jun 15, 2013 7:46 pm

Are you sure the dist. gear isn't one tooth off? This could throw the timing way out of whack.
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Re: Cam degree effect on ignition timing

Postby grey ghost » Sun Jun 16, 2013 9:00 pm

Could you have rolled the timing chain and not know it when you had put it on
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Re: Cam degree effect on ignition timing

Postby Bluejay » Mon Jun 17, 2013 11:44 pm

I set carb jets back to original specs ,1405 elderbrock, on new motor. Had trouble getting four barrel to come in , and could hear a little poppin in intake like lean miss fire. So I changed jets to 8% richer on primary and secondary , this did result in less initial timing necessary. Less so but Still stumbling a little when I kick 4bbl, lighter sound on popping. So I ran it a little , checked plugs, they were pure white like new, still too lean. Popping sound worried me so I compression checked all cylinders. Very uniform , 90psi first hit , 120psi second hit, thankfully checked out good. But, I'm surprised new crate 350 has such puke low compression. Must be 8:1 . I like to see 165-195psi. That makes a motor run good at least at low rpms. Took it out and ran it a little and it heated up quick under heavy acceleration, so I backed timing down a little more, that kept her cool. Richer fuel mixture made timing work closer to factory specs. But I still have to add more fuel to mix. I'm already past what adjustments I can make with calibration kit, so I'm filing down metering rods a little, checking with micrometer. Fuel ratio crap is so much easier with a/f ratio gauge ! But have to weld in bung, buy sensor, buy gauge. It amazes me how lean 305 heads can run on a 350, and how much more fuel low compression engines need. If I can get 4bbl, to kick right in like it should I will be happy. There will be no more testing on street with boggers! They wear down so fast! Especially, with welded rear diff. New trac bar for front end , made crappy cj steering problems go away. I made bar exact length and angle as steering arm and It works great! Wonder how it will jump. Lol
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Re: Cam degree effect on ignition timing

Postby Bluejay » Mon Jun 17, 2013 11:50 pm

It's hard to believe but too lean on carb seems to be what was making motor only respond to lots of timing advance.
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