Trying to cool my 59 on hot summer days - update

[Bob S.]

Duke, et all. This is an update to my earlier post.

For review here are the specs from the ST-12.

The centrifugal advance data from the ST-12 is as follows: Centrifugal Advance (Distributor Degrees and RPM)
Start .5*-2.5* @ 400 RPM

Intermediate 9.5*-11.5* @ 1300 RPM

Maximum 13*-15* @ 1850 RPM

Under Vacuum Control it says:

Inches of Hg. to Starts 7-9"

Inches of Hg. full advance 15-16"

Max Dist. Advance 7.5*


The old VAC when tested with a vacuum pump had a start/stop of 9/17. The B26 is 6/12. My vacuum at 500 RPM idle is 15". The B26 obviously is more suited for the Two-Inch Rule.
I have now installed the B26 VAC and run the car with the following results. (This is all crank RPM)

@530 RPM - 12*
@1300 RPM - 22.5*
@1850 RPM - 28*
@3500 RPM - 34*

W/VAC @ idle (640) - 26.6*

From this data I have improved my idle advance (w/VAC) by 4.6* but I am just a little short of where I want to be at WOT. I will be getting a set of distributor weight springs tomorrow and will experiment with those to bring WOT up to 38*.

Thanks everyone for your help and input. Sully

[Frank D.]

Re: Trying to cool my 59 on hot summer days - update

Be aware a lot of those repro dizzy weight springs are not 'hardened' as original - the lighter ones can go out of spec after a time.

[Bob S.]

Re: Trying to cool my 59 on hot summer days - update

Thanks Frank. I'll see if the repro's do anything for me. If I do use them I will make a note to check the curve periodically.

[Duke W.]

Re: Trying to cool my 59 on hot summer days - update

Duke, et all. This is an update to my earlier post.

For review here are the specs from the ST-12.

The centrifugal advance data from the ST-12 is as follows: Centrifugal Advance (Distributor Degrees and RPM)
Start .5*-2.5* @ 400 RPM

Intermediate 9.5*-11.5* @ 1300 RPM

Maximum 13*-15* @ 1850 RPM

Under Vacuum Control it says:

Inches of Hg. to Starts 7-9"

Inches of Hg. full advance 15-16"

Max Dist. Advance 7.5*


The old VAC when tested with a vacuum pump had a start/stop of 9/17. The B26 is 6/12. My vacuum at 500 RPM idle is 15". The B26 obviously is more suited for the Two-Inch Rule.
I have now installed the B26 VAC and run the car with the following results. (This is all crank RPM)

@530 RPM - 12*
@1300 RPM - 22.5*
@1850 RPM - 28*
@3500 RPM - 34*

W/VAC @ idle (640) - 26.6*

From this data I have improved my idle advance (w/VAC) by 4.6* but I am just a little short of where I want to be at WOT. I will be getting a set of distributor weight springs tomorrow and will experiment with those to bring WOT up to 38*.

Thanks everyone for your help and input. Sully

A couple of things are not clear to me. ST-12 says that the centrifugal should start at 7-800. So does 12 @ 530 mean that initial is 12?

If this is the case then the centrifugal is only 22 versus the ST-12 nominal spec of 28.

Did you rev the engine beyond 3500 to determine the actual centrifugal stop point? Maybe there's more as revs increase.

Here's how I like to specify a spark advance map and idle behavior. The example is a late 327/300 manual with lighter than OE springs and a B22 VAC, which is about ideal for a base engine with manual trans.

Initial timing: 8

Centrifugal start @ 700
Max. Centrifugal 30 @ 3500 (The curve is nonlinear, so most of it, about 27, is in at about 3000)
Total WOT advance: 38

Vacuum advance: Start @ 8"
Max vac. advance: 16 @ 15"

Total idle advance (500 RPM @ 18"): 24

Max cruise advance, >3500, >15": 54

With a 3.36 axle, cruising at 80 MPH on level ground, advance will be at about the cruise maximum, and the engine will be operating at peak efficiency.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days - update

Duke, I set the initial at 12*. I'm not sure I know how to get the start of the centrifugal advance on the car. The data I had shows 1* at 400 RPM. Assuming the numbers I have from the SUN machine are distributor degrees, then I am at the low end of the specs.

I took the engine to 5000 RPM and timing stayed at 34*. With VAC the number at 3500 RPM and higher is 48.3*.

[Duke W.]

Re: Trying to cool my 59 on hot summer days - update

It's very simple to pick-off the centrifugal start speed. From idle or lower, slowly increase engine revs and the point where advance begins to increase is the start point.

It can be difficult to pick off on some engine.s For example, the OE spec for centrifugal start on 365/375 HP engines is 700, but they won't idle stably or for long at that speed or below, which is why setting total WOT advance above the max centrifugal speed is a better way, and since the OE full centrifugal is all in at 2350, you only have to rev it to a little over 2500. I also recommend blipping the throttle to higher revs to verify that the timing does not advance any further.

It's easy to screw up timing if you don't have the OE spark advance map data and then verify what you actually have on the car.

A case in point is a recent buyer of a Cosworth Vega. He said the car had little power and wouldn't rev, but was not missing. The OE setup is start @2000, 17 @ 3650 and the OE idle speed is 1600 due to the extreme valve overlap. However, his engine has "reindexed cams" (that I designed), which dramatically reduces overlap and allows an idle speed as low as 700, but he set the initial at about 1500.

When I had him map the total WOT advance it was only about 17, and the optimum is 32. It turned out that it had very light springs that gave full centrifugal at about 2000, so what he thought was 15 initial was actually about zero. He didn't have a dial back timing light - just a conventional one - but he had some stiff springs, so I told him to install the stiff springs, set the timing at 15 at 700 or less, then check that the timing mark did not advance until above the speed that he set timing.

Upon test driving the car it ran as expected. The previous owner or whoever worked on the car was totally clueless. When the optimum total WOT advance is 32, but it's actually only about 17, the engine is going to be a total dog.

You should investigate why your max centrifugal is short of OE spec.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days - update

OK - Here is what I came up with on the SUN machine this weekend. I did the work myself after a brief tutorial on the machine (it's really not that complicated). I acquired the distributor weights and springs kit from Paragon (#10950K) and after trying various weight and spring combinations, and some coaching from my tech, this is the best curve I could come up with. All numbers unless otherwise specified are distributor RPM and degrees. VAC is a B26 with a start/stop of 6"/12". Idle vacuum is 15".

Numbers on the left are from the ST-12 - On the right is my distributor on the machine. (Centrifugal)

Centrifugal advance starts at 300 RPM
Start .5*-2.5* @ 400 RPM @400 RPM - 2*

Intermediate 9.5*-11.5* @ 1300 RPM @1300 RPM - 11*

Maximum 13*-15* @ 1850 RPM @1850 RPM - 11.5* (This number remained constant on up to 3000 RPM)
No combination of weights and springs would get me any higher than 11.5* WOT

Advance with VAC added with 15" of vacuum applied produced 18* at WOT.

With the distributor reinstalled on the car the following numbers were observed (engine RPM and degrees). I set initial timing at 12* to try to achieve an idle advance w/VAC of 24*-32*.

@510 - 12* initial setup
@1300 - 25*
@1850 - 30*
@3500 - 36* (constant through WOT)

w/VAC @ 650 - 25* -- WOT 49*

Driving the car I did feel better performance particularly in 4th gear accelerating to merge on the freeway. Now I will wait for a good warm day to see how this affects my cooling.

[Duke W.]

Re: Trying to cool my 59 on hot summer days - update

If the current setup doesn't cause detonation, it's probably okay, but the max centrifugal advance is still short of spec. This could be caused by having a bushing on the advance limit pin, when maybe there should be none, or it could be the geometry on the weights. Sometimes the weights retract all the way to the cam, but on some designs the weights hit each other before contact the cam.

I'm not familiar with the kit you bought. I generally recommend the Mr. Gasket 928G, which just has three sets of springs and a limit bushing. Most aftermarket weights are not hardened, so the pin hole can wear. I always prefer using the OE weights and tailoring the centrifugal curve with just springs, and on early 327 base engine I like to grind out the slot to increase max centrifugal from 24-26 to 28-30, which allows less initial timing, so at low revs there is less advance than what you have in order to keep the engine out of detonation with modern fuel, which has a few points lower RON that sixties fuel, especially in California (91 PON = 95-96 RON).

The advertised CR of the 283/230 is 9.5:1, but as built most are probably closer to 9:1 and if everything is OE spec including the centrifugal advance curve, most will operate detonation free on 87 PON unleaded. Higher octane might be required with a more aggressive centrifugal curve.

Since you current setup has more low rev advance, it makes more low end torque, and this is most noticeable when accelerating from low revs in to gear.

Duke

[Bob S.]

Re: Trying to cool my 59 on hot summer days - update

Duke, Thanks for all of your help. So far - so good on detonation. I did use the original weights. The new ones put everything out of whack. I will stay with this setup to see what happens when it gets up into the 90's, which probably won't be to long here in Oklahoma. When I get more time I may completely disassemble the distributor, do a thorough cleaning, and re-assembly checking things on the way per your suggestions.

Thanks again. I learned a lot. Sully