Summit cam #1103 with 442 lift int 465 ext. 112 separation,
advertised duration 272 int/282 ext.
Cam timing int. 0 btdc, closes 34 abdc , max lift 107 atdc, duration 214
" " ext. 49 bbdc, closes -5 btdc, max lift 117 btdc, duration 224.
What do I set timing at. and what is max timing for this setup.
350 auto, mild convertor 1800-2200 rpm range. 3:08 rear

 

If you mean cam timing, don't. It already has five degrees of advance built into it.

If you mean ignition timing, then it really depends. That cam will build a lot of low-rpm cylinder pressure. I would start at 10-degrees and work from there. But it really depends on how well you can tune and balance the initial, centrifugal and vacuum advance curve for peak performance.

 

Yes I'm talking ignition timing. I have the stoch HEI distributor. Do you think I should have someone recurve it. Also how far advanced in timing should I / could I go. It was at 10 btdc with the stock cam.

 

You need to set the timing at APP 52 total....hmmmmm or is that 38 on the small block? :seeya

 

Trial & error will prevail here, as with tuning any other motor. Experimentation will be the name of the game. There is just NO WAY anybody can tell you what timing is going to be best for your application. Sorry to be so blunt, but, somebody had to tell ya.......... :cheers:

 

Whoa, 38 degrees is about all you want on a full tilt SBC.

Hope this helps.

 

Okay I learned that there is no set numbers. Started engine with old timing mark settings and it fired right up. Today I hit it with the timing light and it was firing at about 25-30 degress btdc?. Reset dist at 12 degress btdc. Idle a bit on the lumpy side. I set this with the vacum line to distributor plugged off. I ran the car and its a dog of the line. it won't kick in till about 2500 rpm. temp was at a constant 150 deg. (with the hood off). I did notice that the timing won't advance when I rev motor? It will drop about 2 degrees and than advance slowly but not past the 12 degree initial setting. Could this be due to a vacum problem with the new cam or is it a distributor problem??

 

Getting good 18hg vacum at idle through manifold and carb. steady reading so no leaks. I checked vac on dist. hose and also 18hg. I than removed dist cap and rotor to do a visual on centifugal wieghts & springs. All intact but I noticed that I could barley move the advance mechanism by hand. It seemed like it was frozen. I covered the internals and sprayed some bolt remover , cleaned & silicone spray after that . It started moving so I worked it by hand for about 5 minutes. It loosened up somewhat from a static position to one that moves very sluggish. Rust was evident and I suspect that it may be causing the problem. It is the original 77 dist. as far as I know . What kind of fix is invoved outside of buying a new distributor?. Oh yea after doing all this I started it and checked timing again. it did advance another 6 degrees upon a 3000 rpm run . but thats it. I ran the car with a initial 20 btdc setting and it was much more responsive with a better idle. But upon nailing it to floor it took awhile before the secondaries kicked in and it went like hell but it started the dreadful knock at 5000 rpm,s..

 

With 272 on the intake and 1800-2200 stall and 3.08 gear, its gonna be a little sluggish from a dead stop. I used to have 268 int and even though the cam manufacturor said this cam was ok with stock convertor I wouldnt run less than 2500 stall for a good launch. Especially with 3.08.

As for your ignition timing question. Your dist should advance even with the vacuum line plugged. It does this by the way of centrifigal force on the dist weights. If yur not getting any advance when you rev it up I suggest one of two problems.

1. The dist springs are worn or too light or missing causing the weights to advance even when at idle. What idle speed are you taking your initial readings? The idle needs to be low enough to insure that the weights are closed and not adding any advance.

2. The weights are binding and not allowing any mechanical advance.

A good setting would be, 12 to 16 initial at idle(800rpm or so) Then 36 total from mechanical(weights) alone with vacuum line plugged, all in by no later than 2500rpm.

I suggest pull the cap and rotor and make sure the weights and springs in the dist are working properly.

 

J Vette73
I pulled the cap and the springs are there. Its the movment of the mechanism that bothers me. I did the timing check with a 650-750 idle speed. When I hand advance the weights with the cap off they just kind of sit there for a short while & than creep back. In the retracted psition (static) they flop around somewhat.

 

If I'm reading this right then the vacuum hose to the vacuum advance on the distributer has 18hg at idle? This doesn't sound right. If this is the case then you are getting timing advance from vacuum at idle. I think you are sposed to use a ported vacuum outlet on the carb which has no vacuum at idle. Is this right or should I go back to sleep?

 

Its correct what I said. I'm getting vacum from the carb outlet that goes to the distributor advance. It is a quadjet carb.

 

It is the outlet from the from top drivers side thats hooked up to the distributor. Perhaps thats not the right one? If so the timing was checked both ways on & off from that outlet.

 

Dogboy, you can do some things to get your dist working better in the advance curve. The problem is when emissions came in they really began to cut out advance curve to make engines cleaner. one of the ways they did so was to limit the amount of mechanical advance. You can increase this advance by modifying you current dist. If you pull the dist out and remove the gear. Then the shaft will slide out of the housing. Look underneath the advance weight portion and you will see a pin that slides in a slot. The length of this slot is one of the things that limits the advance. Also the pin will usually have a bushing on it. Youn can remove the bushing and get a few more degrees advance as it will let the upper plate slide further. I did this withj mion in conjunction with installing lighter springs and was able to get 3 degrees additional mechanical advance. This allowed me to run less initial timing and still get enough advance. In stock form to get 36 total from my dist, i had to run 22 initial. This meant that in stock form the most my dist was gonna give me was 14 degrees. After removing the bushing it gave me another 3 degrees of movement. Now I was able to achieve 19 initial and 36 total. Later I went in again and lengthened the slot with a grinder giving me another 3 degrees movement. Now , as far as mechanical advance goes im can set @ 16 initial and have enough movement to still achieve 36 total in by 2500. All these tests are done with out any vacuum advance as vacuum advance is rendered usless at full throttle since vacuum is practally nill then. i messed around with different advance springs till I got a comination that would not advance at idle, and allow all advance in by 2500. Next I moved to the vacuum can. It, when connected was adding another 12 degrees advance. This meant that with vacuum connected and cruising anywhere above 2500rpm I was getting 36 from mechanical and 12 from vacuum totaling 48 degrees. Although the car ran smoother and had better part throttle response with vacuum connected I wasnt crazy about this 48degree# so heres what I did to that. I removed the vacuum can from the dist and installed a small strap of metal with a tiny set screw across the pull slot in the advance can. This limited the rod movement by half. I was now only getting 6 degrees advance from the can. Just enough to improve part throttle response but no so much as to load the timing too high on top. Other than a few bucks for the little springs, none of these mods cost me a dime. I hope I havnt confused you. I know how to do it. Not sure how good I am in explaining it in words though.

 

Once more..forget about the vacuum untill you get the mechanical curve right. Vacuum advance is non functional @ WOT

 

good article on dist advance and recurving here
http://www.angelfire.com/on/geebjen/timing.txt

 

ok check the article.. acording to them the advance curve on an HEI, which is what I assume you have, is controlled by the shape of the center lobe and weights. The mods I did were to a points dist, although they may still apply to the HEI...im not sure.

 

Jvette73
Great advice. I'm running the HEI dist. I will try those mods and see what happens. I believe it is the mechanical advance that is causing the problems. Funny how I never noticed it with the stock cam. as I set the timing at 8 btdc and never checked the advance above idle. With this new cam eveerything has changed.
Big Thanks... :cheers:

 

While that cam's idle characteristics are tame enough to work with the stock converter, with 3.08 gears I would expect performance to be a little lazy at lower rpms. As far as the timing goes, shoot for 36º-38º total with the vacuum advance disconnected and 48º - 52º connected. Many factory distributors don't achieve full mechanical advance until well past 4,000 rpm so make sure that you're reving it high enough to see it's actual total. Ideally, you want full advance in asap but, especially with an auto and tall gears, too soon may create problems. Up to a point, more advance will improve idle and torque but too much will kill high rpm power (and can cause damage). Get yourself a recurve kit and experiment with the different springs to see what works best for you.

 

Just ordered the recurve kit and crane vac advance kit from summit.
Thanks again. :seeya