gillesdetrail

iTrader: (1)

Hey everyone, so last week-end I replaced my tired old, smokey and knocking block with a good one. At the same time I put on aluminum rockers and an adjustable cam gear. Before the swap, the engine would run happy at around 8 degrees timing. When I installed my adjustable cam gear it was set at 2 degrees advance on the cam (so 4 degrees crank timing advanced). I decided to leave it there to move the powerband a bit lower just to try. When I finished the swap I timed the ignition and it was sluggish at 8 degs btdc. It runs well at around 12btdc. OEM spec is 5btdc but with my weber, just like other people who ran webers, they usually like around 8 btdc. So here is my question;

Does advancing the mecanical timing on a cam gear 4 degs with an adjustable cam gear means I have to compensate 4 degs on ignition timing as well?

12 degs btdc seems a lot compared to the stock 5, but that's just where the engine likes it, I'm sure it would like even more, it runs really smooth at 14btdc. It is more responsive and torquey. I would like you guy's opinion.

It has a 20r ported head, o/s valves, stock cam, 4-2-1 header on stock bottom end.

Thanks!

wyoming9

iTrader: (1)

It has been to long but there is a whole science of cam timing.

Quite a lot has to do with the grind of the cam.

As long as your engine does not start knocking and general carrying on Set the timing how it runs the best.

Back in the day (late sixties ) we just used the timing light to verify after setting it by ear.

fierohink

Give Engbldr a call. He'll be able to explain the effects of advancing cam timing and he'll set you up with a good baseline for overall ignition timing based on cam grind, advance, etc..

jimbyjimb

iTrader: (1)

People make a big deal out of everything being factory compliant. In the late seventies and on manufacturers had a lot of pressure to dumb everything down to satiate the man's desire for emission compliance.

In short, running considerably more ignition timing is a good thing unless you're pinging. Rule of thumb is to advance it until it pings, then back off slow until it doesn't. LCE recommends 10 btdc, but there isn't anything wrong with running more if you can. It's generally best to keep the total advance at 35 or under.

Welcome to the world of engine modification. If you're running mainly LCE hardware call them up. I have found their baseline settings for mods to be spot on every time. Engnbldr is probably good to call as well, I'd just feel weird calling him for help with components that aren't his. If you're looking for mild mods he's a great way to go.

Bingle

2x What Jim said.
I run about 10°-12° on my rig becausse it's where it's happiest with the mods I have on it. Could go a little more but then I get an occaisonal bit of pinging pulling a steep hill. Super vs. regular gas makes a difference with this as well (at least on my truck). I drive my truck so seldom that I always run super to keep the old girl happy when i do take her out.

My dad was and old school hot rod guy and he taught me to use the light for initial setup, then tune by ear and drive test (listen for ping, seat of pants dyno) after any performance mod. Then use the timing light to check it so you can get back there easily if you need to.

gillesdetrail

iTrader: (1)

Thanks guys! I won't give engnbldr a call since I know he gets asked so many questions everyday I won't bother him with that, I am running 14 btdc at the moment and it likes it very much. I am running the stock cam at the moment. To me I was worried so much timing was a sign of poor flame travel and uneffeciency. On past fuel injected builds I'd run stock timing then it was adjusted on the dyno in the ecu. I do run premium all the time. There is no ping heard but I know I need a bit re-jetting on the main, I'll wait for my wideband for that, for now it has never ran this strong and I am very happy for a stock compression stock cam setup, I have some forged lightweight pistons and trd stage 3 cam and other goodies in a box waiting for the next rebuild I can't wait but for now I'm really happy, thanks a lot.