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Thoughts on Straight 8 Spark Advance


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When I take my '53 for long highway runs, the temp gauge always creeps up as I drive. Before it was rebuilt and after. It never overheats, probably never gets above 220 (at idle after a freeway run), but it's gotten me to thinking. **It does have a recored radiator***

I've tried jetting up to no avail (other than ruining my mileage).

Looking at my 1954 Motor manual, I notice that the centrifugal advance curve on this engine is 24 degrees at the crank, all in by 4000 engine RPM. Factory initial is 4 degrees, leading to a total (not including vacuum advance) of 28 degrees, pretty weak for a 7.6:1 (maybe) compression engine. I have mine running maybe 6 degrees initial for a total of 30. So at freeway speeds, we're maybe looking at 20-25 degrees of timing, plus vacuum advance (which has a quite heavy spring). I can't advance initial anymore because of the 6 volt starter (drags it down).

My 60s cars all seem to like much more initial timing on today's gas, but their compression ratios preclude advancing the curve too much, so I end up limiting the total by messing with the weights. But the '53, with much higher octane available now than then, seems to have an opposite issue.

I've been thinking of using lighter advance springs in the distributor to get the total 24 degrees in by highway speed. With 87 octane in the tank, I would think the car should easily handle this much advance without potential damage. It should run cooler and have a bit more power too. It might even be easier on that long exhaust manifold by running cooler. Any thoughts, for or against?

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From what I hear from several sources, the ethanol (10%) in the gas does cause the engine to run hotter than originally back in the day when gasoline was gasoline. I run mine at the manual specification, around 4 degrees.

I have been toying with the idea of running low on gas and then getting some gas from a marina that offers straight gasoline with no ethanol just to see if there is a difference in engine operating temperature.

I might even try moving the advance up to 6 degrees to see if there is an effect on operating temperature.

Joe, BCA 33493

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Well, I spent a couple hours doing this today...

You have to pull the distributor to do this, because you have to pull the breaker plate to do this...it could PROBABLY be done in the car, but pulling it is a lot easier. It gave me an opportunity to clean stuff up in the distributor too.

I used the heaviest springs in a Mr. Gasket spring kit for GM top advance distributors...they worked great. My guess is that full centrifugal now comes in at 3000 RPM rather than 4000 RPM. It runs the same as it did before, but it makes an odd, loud moan when I floor it at 60 MPH...it may have done that before; I don't often floor that car. No audible pinging, even when flooring it from a dead stop. It's hotter than heck today, too...at least 90 degrees. With the 180 thermostat, it got up to around 200 or so after a 15-20 minute drive, but cooled back down to 185 or so idling in the driveway (using an infrared thermometer on the thermostat housing)...We'll see how it works this summer on my longer drives on hotter days.

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Change the thermostat to a 160deg. version, be 100% sure the radiator core is clean as it is common for cars that spend time parked up for the core to partially block. Check the exhaust system is unrestricted and the muffler,(silencer), is clear. Don't forget to check the tire pressures as under inflated tires contribute to over heating. Make sure the radiator pressure cap is the correct one, seats correctly and has the specified pressure rating.

Regards,

Mike.

Christchurch, New Zealand.

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Change the thermostat to a 160deg. version

Mike brings up a good point. Why did you go with the 180 degree thermostat? It seems I remember reading in the manual that 180 was for winter driving and 160(I think it actually said 151 but you can only get 160 nowadays)for summer. The manual also states that the engine may reach up to a temperature of 212 without cause for alarm.

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Joe: I've never tried ethanol free gas in it...like you said, it would only be available (maybe) at marinas around here...

Mike: The radiator's recored and all of those things are good...

Robert and Mike: I switched to a 180 because when I ran a 160 it snotted up the oil breather and draft tube because the oil didn't always get hot enough to burn out the condensation...

I don't think it's running so hot as to be a problem...I just like to tinker and make things better if I can. :)

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Dumb question. Is the vacuum advance working correctly. Many straight 8 Buicks have a lot of wear on the dist housing where the breaker plate rotates when pulled on by the advance and they don't advance smoothly if at all. The outer housing wears where the 3 ball bearings sit.

Bill

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I used the heaviest springs in a Mr. Gasket spring kit for GM top advance distributors...they worked great. My guess is that full centrifugal now comes in at 3000 RPM rather than 4000 RPM.

This doesn't sound right. Heavier springs usually inhibit advance until higher RPM is reached. One of my references shows for 1950 centrifugal advance starting at 250rpm and full centrifugal advance of 13* at 1500 rpm; vacuum advance max is 5.5*. Another example for 1955 is full centrifugal advance of 12* at 1750 rpm; vacuum max of 12-14*. Maybe others can check your specific model...

Willie

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Hi Willie,

The heaviest springs in my kit were way lighter than the factory springs...

My Motor manual has the distributor specs for all the engines...it's amazing how much they played around with the curves from year to year...

The '53 263 has 12* centrifugal all in at 2000 distributor RPM and 11* vacuum advance.

The '52, on the other hand, had 12* centrifugal all in by 1700 distributor RPM and has 8* vacuum advance... (or something close to that).

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Thanks, that clears that up. Now get a vacuum gauge and google how to time or tune an engine with a vacuum gauge. Using one on my 55 it likes 8* initial timing vs 5* that the factory recommends.

Willie

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I've already done that Willie...it definitely likes more advance, but the 6 volt starter limits the initial I can use (at least when it gets chilly out), which is why I changed the curve to come in earlier. I haven't had a chance to drive it enough to see how it likes it, but in the 15-20 minutes I drove it, it seemed to run at least as well as it did before. I need to hook up my dial back light to it, but I need to use a 12V battery to trigger it...the 6 volt one won't do it...

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I just ran the dial back on it...I'm getting about 45* total timing at 3000 RPM with the vacuum advance connected. That adds at least 15* timing, so I'm right about at 30* total centrifugal at 3000 RPM (with initial, which I set at 5-6*). Setting initial is hit or miss because the mark is on the flywheel and it's tough to set right on. Seems about good to me...

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One thing about "distributor advance specs", you have to make sure WHICH rpm they are in . . . "engine degrees" or "distributor degrees". "Distributor degrees" x 2 = "Engine degrees".

In normal driving, I somewhat doubt that "up to 10% ethanol" will make any significant difference in operating temperature, except under continued full power or heavy throttle.

Although the radiator might be in good "flow" condition, do NOT forget about the water jackets in the block! In a thread a few years ago, the "heat" issue went away when the owner did a full "freeze plug replacement" and (messily) flushed the block's coolant passages to get out all of the gunk that had accumulated AND settled toward the rear of the motor. After that operation, he noted the operating temps were right were they used to be.

I suspect that with a "creeping heat" issue at highway speeds, it's more related to coolant flow than carburetor mixture and/or gasoline use. As you've already experimented with richer carb jets, you've already done the basic thing to compensate for ethanol'd fuel, anyway. E10 has an optimum air/fuel ratio of 14.2, whereas E0 is 14.8, so the E10 will tend to burn a little leaner, which will need the slightly richer jets to get things back to "stoich" for E10 fuels.

How difficult might it be to get some "unfluxxed" welding rod and bend it into a "timing marker" and then mark the crankshaft pulley (possibly a shallow notch filed into its edge?) to ref TDC? Just a thought.

From my experiences, using a vacuum gauge to set initial timing can be problematic. As it seems that combustion chamber design plays a great part in this whole situation, too. For example . . . on our '66 Chrysler 383 (closed chamber heads), the idle speed increases with base timing setting. On my '70 Dodge Monaco 383 (open chamber heads), adding more base timing barely makes a difference in base idle speed.

Using a vacuum gauge to set ignition timing . . . Rather than use idle speed, it might be better to run the engine to about 2000rpm or so and use THAT rpm instead . . . this would better relate to the total advance in the distributor + base timing rather than just base timing itself. NOT unlike what hot rodders in prior decades did when they set the 2500rpm (or so) timing "by ear" for maximum rpm, then backed it back a little (or if spark clatter happened when driving).

Please keep us posted as your "tinkering" progresses!

Enjoy!

NTX5467

Edited by NTX5467 (see edit history)
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I've considered the water jacket issue, but the engine's been rebuilt, and I'm fairly certain my shop has a hot tank...One of these days I'll pop a freeze plug and check it out...

As far as marking the balancer, I thought about it, but my dial back timing light works fine if I hook it to a 12 V battery...I just used my Dad's fishing boat battery.

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I would buy a good aftermarket temperature gauge and install it to confirm the actual temperatures you are running.

If you are running high and since you wrote the engine was rebuilt it would be best to check that some component or gasket is not partially blocking coolant flow. The head gasket may be wrong. The lower hose may be collapsing. A water pump passage might be blocked.

I serviced a Hudson straight eight with similar symptoms and found that someone had fabricated a gasket for the distribution plate and forgot to cut out the center!

Don't speculate and make it too hard.

Bernie

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Hi Bernie,

It behaved like this before it was rebuilt, too, so I doubt it is a gasket...I don't want to make it sound like this thing is habitually overheating or anything, it runs under 200* most of the time (verified by my infrared thermometer)...I'm guessing that after long highway runs on hot days, and getting off the freeway and idling, she will start to push over 210, which the shop manual said may happen. It's only boiled over a couple of times, just after I bought it 7 years ago, because the radiator was plugged. I installed all of the water pump and thermostat housing gaskets, so I know they're open. Thanks!

I WILL check the lower hose though...I can't remember if I put one in that has a spring or not.

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  • 3 weeks later...

I got a definitive answer to the advance question today...going up a long bridge approach, I got some pinging when I pressed down on the gas. Oh well, the heavier springs go back in. I pulled over and backed the timing down a little.

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