Optimal Timing?

Your motor is set up much like mine with the same cam. I have a Street Demon 650 cfm and closed chamber heads with about 10:1 compression. Right now I have mine set at 17 degrees initial advance and total advance of 40 degrees. Prior to this setting, I had mine at 16 degrees initial and 38 total. This seemed a better setting and my engine ran well. I was interested to see what impact, if any, more advance would have. I would be interested to know where you finally end up. Based on my experience and a sort of trial and error method, I would start with an initial of between 12 and 16 degrees and go from there. My car seems to make its best power, idle reasonably well, and not overheat at 16 initial and 38 total.

Thanks for the reply.

I had read somewhere on the internet that most people set it to 9+ initial, you've suggested 16-17 & I've had one other suggestion through TPOC (my POCA chapter), which was between 34-36 (maybe he meant advance??? because that sounds like too much to me).

When I put the light on to measure what I had set by hand, I got a reading of TDC... no wonder I was getting lousy performance! I hadn't read all of the e-mails at the time, so I set it to 8 btdc initial (I didn't measure the advance) & than readjusted the carb.

The car sounds real good and idles well. So I took it for a test ride & got sideways around a corner when the backend broke loose. I smiled the rest of the way home.

I'm going to leave it at 8 initial for now, for at least 2 tanks of gas to figure out mileage. After that, I'll test advancing it even more.

If you found yours at TDC, pull the distributor and control the gear! It's urgent, if the distributor was tightend right. The distributor can't disadjust itself.
Roland Jaeckel
DeTomaso Parts Center Europe
roland@detomaso.de

The most commonly recommended starting point seems to be 16º at idle and total advance to 38º at 3,000 RPM. That should be close enough to get you to the dyno shop.

determining full advance is best done on a dyno under load, it will be the setting that nets the most rwhp, also the lowest exhaust temperature. Depending upon the heads, cam, exhaust system, etc I have seen Clevelands with as little as 32 degrees or as great as 42 degrees total advance.

initial timing can be determined at home. with the engine running, slowly twist the distributor in the advance direction until maximum idle rpm is achieved, this should also achieve maximum intake manifold vacuum. If you are running vacuum advance, leave it connected during this proceedure. The point of maximum idle rpm is your new initial distributor setting.

Your distributor will need to be set up so that the centifugal advance curve doesn't kick in until some point (a few hundred rpm) above your idle rpm.

George

Gr8 Kat,
What size jets are you running in your 750 ?
I am going to rejet mine, running to rich.

My motor is set up much like yours. I'm running 8 to 9 degree BFTDC, it's quick, but still runs a little to rich.

Holley 750cfm

MSD 6AL & MSD Billet Dist

Crower Cam #15242 specs:
grind: 280HDP
lobe center: 112 deg
advertised duration intake: 280 deg
advertised duration exhaust: 286 deg
duration @ .050 intake: 220 deg
duration @ .050 exhaust: 226 deg
gross lift intake: .526"
gross lift exhaust: .540"
rpm power range: 1800 to 4500
redline: 6000+

ttyl
Roydon }8-)>[/QUOTE]

Hey Coz,
I bought my carb new from Jerry @ PI just 2 or 3 months ago. Mine is stamped 3310-10 on the choke horn. Oddly enough mine does not a have a choke plate.
The Stock Jetting for this carb should be a 72 primary jet and a 21-Plate secondary jet (which is equivalent to a 75 jet).
I don't think that Holley or PI changed the stock jets and I didn't open the carb up to check before installing.

I'm going to pull mine in the next couple of days and I'll let you know what mine are for sure.
Thanks GR8.
Gives me something to go on.

Keep in mind that the jets I have are for the Holley 3310... they could be different for other carbs.

http://www.mortec.com/carbs.htm
http://www.holley.com

The installation manual that came with my carb also states that for almost all cases, it will be unnecessary to increase the jet sizes by more than 4 numbers from what they supply out-of-da-box.

Pulled my jets today. They were 80's, way to big. I'm dropping them down to 74's and see how it runs.