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Old 09-23-2012, 09:09 AM
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recommendations for distributor timing

Hi all,
Well, I have most of the bugs worked out of my '37 truck and now am moving on to some tuning and optimizing. Right now, I have decided to convert from a MSD pro billet distributor to a similar model that has vacuum advance. I am going to convert to aid in overall performance of the engine....something I should have done a long time ago.

Current setup is:
355 SBC, with comp cam XE 262 camshaft with 1.6 rockers. There are aluminum vortec style heads, Holley 650cfm carb shorty headers. This engine was dynoed at 370hp/380ft-lb torque. Overall, this engine runs well....just want to make it as good as it can be.

Current timing is set at 18deg initial, with all in at 36 deg at 3000rpm.

I do have an issue with the engine getting slightly hot during stop and go traffic, and am hopefull that adding some part throttle advance will help. No issue with temp when driving down the road. In any case, this is a sperate issue....just wanted to add it to the equation.

So, with that said, any ideas on a baseline setup?

Without any input, I think starting with the same basic setup that would simply add up to 10 deg of timing with the vacuum advance at part throttle.

Any ideas??? Comments would be apprecitated.

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Old 09-23-2012, 09:52 AM
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that soundslike a very good place to start.maybe use a little less gas?,,,lol.
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Old 09-24-2012, 06:42 AM
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Use full manifold vacuum. Your initial timing is most likely causing it to run warm @ stop and go. You'll need to reset your idle speed after connecting vac advance.
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Old 09-24-2012, 06:57 AM
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Quote:
Originally Posted by revspan View Post
Hi all,
Well, I have most of the bugs worked out of my '37 truck and now am moving on to some tuning and optimizing. Right now, I have decided to convert from a MSD pro billet distributor to a similar model that has vacuum advance. I am going to convert to aid in overall performance of the engine....something I should have done a long time ago.

Current setup is:
355 SBC, with comp cam XE 262 camshaft with 1.6 rockers. There are aluminum vortec style heads, Holley 650cfm carb shorty headers. This engine was dynoed at 370hp/380ft-lb torque. Overall, this engine runs well....just want to make it as good as it can be.

Current timing is set at 18deg initial, with all in at 36 deg at 3000rpm.

I do have an issue with the engine getting slightly hot during stop and go traffic, and am hopefull that adding some part throttle advance will help. No issue with temp when driving down the road. In any case, this is a sperate issue....just wanted to add it to the equation.

So, with that said, any ideas on a baseline setup?

Without any input, I think starting with the same basic setup that would simply add up to 10 deg of timing with the vacuum advance at part throttle.

Any ideas??? Comments would be apprecitated.
Even though you might be able to use 36 degrees total, you may find that you make as much or maybe even more power by using 32-34 degrees total. This will also give you a safety zone against detonation should the engine run hot or you get a bad tank of gas, etc.

Generally, using as much initial timing as possible will give the best vacuum and throttle response. But you don't need to run too much initial w/that cam. In fact I would think 18 degrees should be about right, and that 28 degrees initial is too much. A little info on setting up the distributor is here. Be sure the damper TDC line is correct, and that it's showing you true TDC. There were several combos of timing tabs and dampers used through the years, more on that here.

Use a vacuum advance can set to give you 10-12 degrees timing and hook it to a manifold vacuum source.

But I don't think timing is the cause of the heating problem. How hot is it getting? You using a shroud, clutch fan positioned correctly in the shroud? Some info on the cooling system is here.
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Old 09-24-2012, 09:51 AM
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Thanks for the feedback, very good information...the reason I like this site.

I agree that I should verify TDC. At the current 18 deg base timing, I never have a problem starting the car...even in the hottest conditions. Maybe the measurement is actually lower than it really is as it never fights turning over. One way to find out....I will verify the tab on the timing cover and be done with it.

Regarding the overheating, I have a large Walker copper/brass radiator which is the "Z" model for high heat loads. In front if it(I know this isn't the best...but needed due to the cramped engine compartment) there are two electric fans. The larger of the two is an 18" 2700CFM(biggest I could buy), and the smaller one is a 9" 900CFM(max size for space available). There is no shroud, but the fans are very close to the radiator, and there is a small fraction of radiator surface area that isn't exposed to one of the two fans. I know this isn't optimal, but it is what it is.

The engine runs great, but can get up to 215/220 during hot days with stop and go traffic. At cruising speeds, I can turn the fans off and it runs about 180deg. This brings me to the conclusion that I really do need a shroud(easier said than done), or that the timing is adding heat to the situation. I can say that I have never had the temp get to a point where I was really nervous(230 and above), I just know that the temps should be a lot closer to my thermostat temp.....so an improvement needs to be made.

This is why I decided to first fix the distributor as it really needs to be fixed for a number of reasons....and will be a lot easier than the fan shroud project.


Thanks again for the comments
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Old 09-26-2012, 07:16 PM
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Update

Well, the shiny new MSD vacuum advance came last night and I installed it tonight. Ended up setting the base timing at 15deg, and left the 21 deg bushing in, that limits the total advance to 36 deg. When I add the vacuum, the idle timing goes up to 35 deg(which I don't understand because it is supposed to add only 10 deg). The MSD directions said to hook to ported source, but I went right for the manifold vacuum.
I also documented the curve for base+mechanical, and base+ mechanical +vacuum.

Timing is all in at 3000 rpm without vacuum, and has a nice progressive curve starting about 1200 rpm.

With the vacuum, it will pull 43 deg at 1800 rpm, and will run up to 51 at 2500 rpm. This is where my truck will cruise as I have a 7000r4, and 4:30 rear end.

Tomorrow I will take it for a ride and see how it behaves on the road. I can tell at idle that it runs much smoother and had to drop the idle about 300 rpm with the vacuum advance. I am hoping that there will be an impact on the low speed engine temp. Too early to tell right now.


Any concerns with the advance numbers that I have? Is the 20 deg vacuum advance too much? Thanks.....
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Old 09-26-2012, 07:27 PM
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you test it out and let us know how it works.Im sure you can limit teh vacuum advance? If all else fails,read the instructions,some guys do
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Old 09-27-2012, 05:19 AM
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Well I looked closer at the instructions and the vacuum advance is supposed to be 10 deg, and it is non-adjustable. I know it is pulling almost 20 deg, as I am using a very good digital dial back timing light. Did a little web surfing on the MSD website and it seems that there is a lot of variation in the "10 deg" vacuum pod. Seems that some pull 15 deg, 17 deg etc. It is what it is, so I may simply work around it if it becomes and issue.

I will take it for a drive tonight. If there is too much advance, I will adjust by moving base timing down a little and install a different max advance bushing to keep the 35 deg "all in" number. More to come...
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Old 09-27-2012, 02:55 PM
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For some god awful reason MSD instructions may be refering to 10 degrees total dist advance with the vacuum adv canister, which will show up as 20 degrees at the crank so their number may be accurate in that regard.

You can install a vacuum advance limiter plate for the msd dist to get you back in line towards 10-12 crank deg maximum advance, 20 is way too much. Try not too exceed 48 total with everything including vac adv all in.
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Old 09-27-2012, 06:56 PM
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Well, I took the truck for a ride tonite. It was kind of cool out here in Michigan....about 65 deg.
Before I left, I retarded the base timing to 13 deg. This made the all in number at 34, with the max including vacuum at 48 deg.

I tried to put the engine in many different situations to see if there was any detonation, or other problems. Overall, I have to say that I was VERY impressed. While the max acceleration wasn't really effected, the part throttle, idle, and cruising characteristics were much improved.

In addition, while driving around, I shut off both of my fans and the engine temp stayed right at the thermostat temp of 160. When I got back to my house, I kept the fans off and let the engine add some heat. I got it up to 210, then switched on the fans. The temp leveled off, then slowly started to drop. I shut it down after about 10 minutes and it had dropped to about 190. Of course, I need to have it hotter out to really test the temps, but I am VERY encouraged as I know it is better......just don't know if it is bulletproof yet.

As for the vacuum advance, I called MSD and they said that it will pull 10 deg at 10"..., but will go up to 16 deg if there is enough vacuum, AND there is a +- 2 deg spec on that. SO, the directions aren't very good from MSD when they say the max is 10 deg as it could be....and is....20 deg n my engine.

I need to think about limiting the vacuum by either putting a stop in, or adding a non-MSD vacuum can.

I am considering the following:

Limit vacuum to 10 deg.....now at 20
Set base timing back to 18...... Now at 13
Change bugshing to limit mech advance to 36 deg..... Now at 34


Any suggestions? I think I could live with what I have if there isn't a reason to make a change.
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Old 09-27-2012, 08:29 PM
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I dont think anyone needs to tell you anything.You seem to be close already and will likely have it perfect before any ideas come up. Im glad I read your thread
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