for those with hi compression engines: max advance?

[falcon fanatic]

So I'm breaking-in and tuning my new engine as I go and I keep having to take out timing. I'm running mechanical only right now to try and determine my max advance and I still get a little occasional pinging with only 27* all in. Looks like I'll be maxing out at 25*. Does this sound right for a 10:1 motor? It sure runs great.

Of course since my dizzy has 24* advance that means I'm setting my initial at 3*, which doesn't do much for my idle. The recurve is going to be significant, especially since I really want to incorporate vacuum advance. Right now It's looking like I'll set it to about 14* mech advance at 3,000 rpm. Then I can set my initial around 12 and use an adjustable vacuum canister so that it has to pull at least 8" or 10" to advance. I seem to pull some good vacuum at part throttle and that was giving me some pinging, too.

 

[66 Fastback]

What octane fuel are you running?
Are your temps elevated with the reduced timing?
When I bought my Pontiac, I think it just flat out had a mix of parts that I could not get to run right once the premium fuel in our area dropped to 91 octane. It became a catch 22 in that by the time I retarded timing enough not to ping, the temperature rose and helped created more heating that helpd perpetuate the timing and dieseling inssues.
Doug

 

[80Stang]

With a poorly burning head like the log head I'd say you should be within 35*-38* total advance range, or somewhere there. To my eye I'd see two possible problems, in this order:

- too small cam for the compression, thus dynamic CR is too much for the fuel being used. Cure; more octane to the fuel, but more likely you could install a longer cam to decrease dynamic CR. A 274/274 would do a lot better for that CR. I'm pretty sure you'd be even happier with the engine with 10* longer intake on the cam...
- too lean mixture

 

[rocklord]

Make sure you're not running lean and use premium, 91+, before adjusting timing.
After getting the timing worked out, then you might be able to try mid-grade.

10-1 is a pretty high CR to run with a log head. What CR is recommended for the 264/274 cam?

 

[rbohm]

8) check your fuel mixture, and your actual engine temperature first. it is also possible that your mechanical advance is coming on too fast.

 

[falcon fanatic]

it is running hot, gauge ggets up to round 210. Then again it ran hot before the rrebuild. Too. As for the mix, I ruun a wideband ssensorr and have set my jetting round 12.5:1 at WOT. Sometimes it goes as lean as 13.5. Still...

10:1 does not strike me as outrageously high, althogh the cam with the ratio rockerss is taking a pretty big guulp, I suppose. As for running 38* advance, I couldnlt eve do that when the engine was at 8.5:1. Hmmm...

sorry bout my typing: using my phonne

 

[JackFish]

What head gasket are you using? Can you install a thicker one?

 

[80Stang]

10-1 is a pretty high CR to run with a log head.

A log head works nice with a 10:1 CR with suitable cam.

I made a 200 for my customer with E0BE log head with 10.3:1 CR. The head was alot ported, the chambers too. Mike's 274/274/110 cam, headers, Holley 350-2V and it put out 176hp. I don't remember what total advance was ok for it but it was way over 30. I'd remember right out if it was even close to 30. Now I'm in USA so I can't check as the data is at the office in Finland.

In V8 world where I have a lot more experience during the past two-three years, I've built a lot of SBF engines with CNC machined heads like AFR. They just run the best with around 32-33 degrees of total advance, and I'd say they burn real well. We came up with similar total advance with a stroked BBF with Trick Flow heads too (non-CNC chambers). These engine builds usually get 10.3-11 CR and cams at the high edge what can be run with a hydraulic roller, or mech rollers.

I recall when my own 200cid engine was "new" i.e. just totally rebuilt with a log head. I ran 28* basic advance with 43* total with absolutely no problems. More like the cam being too big for the CR, as I had and still have (unfortunately) 9.3 CR and the 274/274 cam. The 274 cam would enjoy like 10+ CR.

Anyways, I'd try a bigger cam in the engine if it pings at wot. If the pinging comes in at cruising and while sligtly accelerating then follow rbohm's advice and slow down the ignition curve, and /or modify the dizzy to give less mechanical advance, say like 15-20 degrees. This also allows you to add to the base timing so it will run better down low and while idling.

 

[falcon fanatic]

LOL: rule #1: If it doesn't make sense it probably isn't right.

When I had to start setting my initial timing ATDC I knew something wasn't right. I had the radiator out yesterday to put in my new aluminum radiator and decided to pull #1 plug and stick my finger in there to see if TDC really was, and it wasn't. Turns out that someone, either the builder or the guy who R&R'd the engine painted a timing mark at 40* BTDC. Why? Who knows, but when I thought I was running 27* total advance I was actually running 67* . Anyhow, painted the right mark (which I had made using a dial guage on the top of the cylinder last time I had the head off. With inital at 12 and total at 36* it runs like it should. Even with the vacuum attached. Yay!