50 degrees initial timing?? possible??? I did it. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-30-2006, 09:02 AM
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50 degrees initial timing?? possible??? I did it.

I'm new to the boards, so hello everyone. Have a 48 Ford pickup with a 350 and 700R4, and a 68 camaro, 406, 6speed, cage, etc.

My post is about the camaro. (sorry it's kind of long, but strange, read on)

Dart Pro1 230cc, 64CC, 2.08, 1.60
Team G single Plane
Holley 750 vac. sec.
MSD 6AL and BIllet dist.
about 10:1 C/R with reverse dome piston
Crane Powermax Hyd. roller, 304/314 adv. (240, 248 @ .050), 112 lobe


Recently put this motor together, but didn't have a timing tab. I proceeded to "power" time it, and I thought I had it running good. Started decent, no big kicks when it was hot. So I thought I was in the ball park.

Along the way of tuning I decided that I should know where I had the timing set. So I added a timing tab, and used a piston stop to make sure I knew that the marks on the balancer and tab were correct. I had to bend the tab just a touch, but it was pretty much on.

NOw for the strange part - I was at 51 degrees initial timing!! I wouldn't have believed it if I hadn't seen it. At first everyone thought that it must have been wrong. I check again with the piston stop. Marks were correct.
Hmmmmm. It started okay, and ran pretty well. (high 7's in the 1/8). Add in a 21 degree mechanical and you have like 72 degrees total. And I can honestly say I couldn't hear or feel the detonation, which I'm pretty sure there had to be.

I now have the motor timed at 16 initial plus the 21 degree bushing. I have not changed anything but the idle mixture screw, which had to be richened a couple turns. It was idling around 12" with the 50 degrees initial, but now will only idle at about 9-10" max.

The car definetely runs better than it did before. No question.

SO, my question is, how is 50 degrees initial possible at all? The car should have been impossible to start!! BTW, running 93 octane!

Freak of nature??????

I don't get it. Everything I know tells me this should not be possible! who knows what up??

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Old 03-30-2006, 10:25 AM
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It's not possible for that to happen with it not running like crap and detonating all over itself.
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Old 03-30-2006, 11:21 AM
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The cam is long enough with the compression real low like that, I could see it. Probably why you lost vacuum. The higher intial timing helped the overlap. Check you plugs closely.
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Old 03-30-2006, 12:56 PM
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You'd have peak combustion prior to TDC, it would labor like crazy and run like dog doo doo. The combustion pressure would be pushing the piston down while the crank was trying to push the piston up.
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Old 03-30-2006, 01:49 PM
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I certainly agree with both you. It should have been a total turd. It ran pretty decent though. I just can't understand how it would even crank over. And how is it possible that the detonation couldn't be heard. Others have rode in the car with the timing at 50 and no one could hear any problem.

I was reading Smokey Yunick's book, and he does state that you can't always hear the detonation - sometimes the only clue is a failure of the bottom end. Guess I'm glad I never made it to that point.

Actually I had even sprayed it with a 125 shot and ran a 7.49 at the track. It would seem this motor is more detonation resistant (or maybe detonation tolerant?) than most. does that make any sense?
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Old 03-30-2006, 01:53 PM
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ive seen detionation described as a scale of one to 10

a "4" is enough to start causing damage, but you wont start hearing it till like a "7" ... and 10 is immediate engine destruction

so its quite possible to have detonation, and never hear it
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Old 03-30-2006, 02:57 PM
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So then the ultimate question is:
How do you find the perfect timing curve that doesn't detonate (if you can't hear it), and also not so slow that it affects performance adversely?

If I go with what "everyone" says should be correct, I should use an initial of around 16-20degrees, plus a 18 degree mechanical for a total of about 36 at around 2900-3500. Does that sound about right?
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Old 03-30-2006, 03:06 PM
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if you REALY want to add as much timing as possible, buy a knock sensor from jegs or summit and use that

the typical way us fuel injection guys do it is add advance till you get knock, and then back it down 2 degrees
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Old 03-30-2006, 03:27 PM
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the way we do it is on the dyno, engine or chassis. We pick a variety of loading points and tune for best torque then pull about 2 degrees out. If an engine starts detonating power will fall dramatically. Very mild detonation can take away 50 ft/lbs of torque and is very noticable on a comparitive dyno graph.

The difference in the way we look at this is setting timing to knock levels and dialing back 2 degrees does not in any way relate to what the engine will like best, it can easily be way to advanced for best power. There are way too many variables to use a rule like that as gospel to even get you close. What you are trying to do is light off the mixture at a point in time BTDC so you reach peak pressure at about 14 ATDC. If you have peak pressure to soon or too late relative to this point the piston is not working at it's highest effectiveness. That's why a dyno is more effective than a knock sensor. The more work the piston is doing the more torque your going to make. The more torque the more HP.

Tuning the timing curve is much easier though with digital ignition systems or EFI, with these systems you can literally map the curves. With stock type distributors it's a compromise. In that situation you simply try to adjust more around best average torque rather than at specific points through the powerband.

In general the better the cylinder head combustion chamber and the smaller it is the less total timing your engine will want. With nitrous total timing needs will ALWAYS be less on the spray than off the spray. That is due to nitrous always causing the fuel mixture to burn much more rapid.
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Old 03-31-2006, 10:51 AM
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Cool, thanks for the info everyone.

Anyone have a dyno I could buy???


he he. If only it were that simple (and cheap).
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Old 03-31-2006, 10:58 AM
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50 degrees of timing.

It's not common to be able to run this much timing on a modern cylinder head. It was common to have to run more timing on older CI heads. On an old B/A destroked race engine we had I would run about 60 degrees total timing without any problem. Normally a modern head like you have is going to want in the low to mid 30's for total timing.
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Old 03-31-2006, 11:33 AM
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I say 23 degree heads like 36, 18 degree stuff 32, Sb2.2 likes 31, and anyfast burn chamber lkes 32.


This is what my engine builder tells me.
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Old 03-31-2006, 12:14 PM
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Trust me, it isn't cheap.
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