Cooling and ignition advance

Hi Marlin,

I appreciate this is subject where it's easy to get tangled and every board has at least one of these threads.

The reason I chose ported was that I did not want full vacuum at idle. I have experimented with that in my other car in the past, and found that it worked well, except in stop and go traffic where it wanted to keep revs up a little, unless I blipped throttle. Why, I don't know, and I understand it could well have been a side effect from some other issue.

Had a chance to drive a little yesterday. Warmed up real good with high speed highway driving and did some fifth gear acceleration tests. With full throttle, heavy load, relatively low rpm acceleration test (which should be the worst case for detonation) I hear some pinging, not much, but it's there. So, I have little too much advance there, either vacuum or centrifugal. In smaller gear acceleration I don't hear any detonation.

You say that ported vacuum keeps rising with throttle opening and manifold goes down. Intuitively that makes sense, and will be easy enough to test if going to manifold vacuum helps in my case.
However, I found someone had datalogged ported and manifold against each other and throttle opening, showing they are the same outside small throttle opening.

It may be that I still need to adjust centrifugal. And still may be that direct manifold would work better with lower temps at idle. And direct manifold might not have the erratic idle behavior with this engine. I'll probably need to get that IR temp gun as well to make sense of it all for myself.

Here's the datalog I found at www.gofastforless.com. I don't post this to argue your experience, but for information only, as someone has gone to trouble of measuring it. Depending where the ported vacuum source in the carb venturi resides, there may be differences between carbs?

The datalogs are a great display Jannem. Here are a couple of pics regarding the ported source. Obviously not an edelbrock but the same idea applies.

As you can see the orifice is exposed to manifold vacuum at very small plate opening.

quote:

Originally posted by PanteraTurbo:
As you can see the orifice is exposed to manifold vacuum at very small plate opening.

True, and at thinking about this a little more it would make sense why it follows manifold vacuum at WOT too. If you consider that the air velocity profile in the throat is not even. At the throat wall you get to the boundary layer, where the velocity is close to zero. Would be interesting to test for myself with two meters.

...So went to buy a temp gun to test idle temps. It was 60degF outside, so it wasn't real acid test, but learned something.

My 71 has Fluidyne rad with two temp switches, and only one is connected, and it switches the other of the flex-a-lite dual fans. The other fan is manual. Thermostatically controlled one was connected to upper switch, which is 82/77 and I think the lower one is the same because the switch on temps measured from engine were about the same.
I tested both and the difference was that the upper one switches off at about 195 deg measured from engine to coolant bottle steel line and the lower one doesn't switch off until engine is about 180-185deg (I was little late measuring, tested with both fans on). It makes sense, because upper switch sees coolant that has been cooled in the radiator already, therefore switching off earlier. The lower one has to see a real temperature drop in the incoming line.

The car was static when I did this and I found that in the lower position the fan would run continuous until I'd begin to drive, letting the engine temp fluctuate less. I decided to use the lower.

Then I measured the temps with my relatively hi initial advance and ported vacuum vs. manifold vacuum. I had to do this at 1000rpm, as I couldn't get revs lower with manifold vacuum. (I might have been able to, by removing my vac secondary holley and adjusting the secondary idle position. I did not check if there was adjustment left to close the blades.)

I got 197deg stable with manifold vacuum, and 201 with ported. It's hard to say exactly, but there was some difference.
Ported at 800rpm gave 199deg.

I did not notice that the idle speed would have wanted to "stick" like what happened in my Mustang. Mustang has much more radical engine...

Did not yet test drive to see if manifold vacuum would reduce the hi gear, low rpm, acceleration pinging. My guess is it wont, but I've been wrong before, so I'll test.

Jannem, you could try an EGR gauge (home-built airplane shops like in the Los Angeles area have them) to see why your idle air bleeds are affecting your cruise engine temps. EGRs can use either thermocouples or thrmisters. Thermocouples typically have a very slow temp response but are cheap while thermisters are very fast but expensive. Both can be about as accurate. Normally, one only needs one sensor in each header collector, with a selector switch. That would make a good Pantera tuning article.

As usual, this List strips ALL web addresses! The place is aircraft spruce at www.aircraft-spruce.com.

quote:

Originally posted by Bosswrench:
Jannem, you could try an EGR gauge to see why your idle air bleeds are affecting your cruise engine temps.

Bosswrench, I think I'm not following... Do you mean actually the carb air bleeds? Meaning idle mixtures against exhaust temps? My previous experience has been that if I lean up to 16:1'ish, the temps will begin to creep up in hot weather.
Now, I never tested what would have happened if I increased the idle air bleed some and gave it more fuel to get to the same 16:1 ratio...

The only thing I can see that would affect your low rpm high gear acceleration pinging would be a heavier set of springs. This is where the engine will be seeing its highest cylinder pressures and likely it is just getting too much timing. There is a chance it could be lean as well but I would lean more towards timing.

By retarding the ignition at idle the ignition advance is not optimized for that rpm or load (no load) and since less heat of combustion is turned into work, more of it becomes waste heat and puts additional load on the cooling system at idle.

Ignition timing:

Traditionally the Cleveland is set up with 20° of centrifugal advance, mostly because that was the least amount of centrifugal advance that could be attained with unmodified factory parts.

Ford of that era had two centrifugal advance cam plates, one marked 10L/15L and one marked 13L/18L. Using the smallest choice, marked 10L, resulted in 20° of centrifugal advance. Adding 16° to 18° of initial advance as recommended by Ford resulted in total ignition advance in the range of 36° to 38°. In 1970 they recommended having the advance curve all in by 3000 rpm (street motors) and in 1972 they recommended having the centrifugal advance all in by 2000 rpm (race motors).

The Cleveland generally likes lots of initial advance; I've found many engines would tolerate more than 18°. It is possible to modify a Ford cam plate, or to set up an aftermarket distributor for less than 20° of centrifugal advance, and dial in the "optimum" amount of initial advance. But too much initial advance will often make a motor difficult to crank-over when it’s hot, especially motors with lots of compression. So 16° to 18° is advanced enough for good low rpm pep and good vacuum at idle, without making the motor difficult to start when it’s hot, and doesn't require modification of a cam plate if you're using a Ford distributor.

That's more or less the logic behind Ford's settings.

Ford’s recommendation for 36° to 38° total ignition advance is a generally good recommendation for motors equipped with factory iron heads, flat top pistons and a reasonably “normal” amount of clearance between the piston’s dome and the cylinder head (i.e. squish); normal being in the range of 0.050” to 0.075” total clearance (total clearance = deck clearance plus compressed head gasket thickness). Motors equipped with piston’s having pop-up domes will usually require more total ignition advance, motors that have been zero decked and equipped with dished pistons will usually require less total ignition advance, and motors equipped with modern alloy heads having high swirl combustion chambers will also require less total ignition advance. Optimum “total” ignition advance is best determined on a dyno however.

It is possible to determine the “optimum” advance at idle if the marks on the crankshaft damper are reasonably accurate. Here’s how:

(A) Connect a manifold vacuum gauge, an accurate tachometer or an exhaust gas temperature (EGT) gauge to the motor. Leave the vacuum advance hose connected if the motor has vacuum advance. Loosen the distributor clamp bolt if the motor is equipped with a distributor, start the motor and allow it to warm up to full operating temperature.

(B) While the motor is running at idle speed in neutral (manual transmission) or in drive with an assistant firmly pressing on the brake pedal (automatic transmission), and assuming the initial advance is in a retarded setting; begin slowly turning the distributor clockwise to advance the initial advance setting. As you do the idle speed shall increase, the intake manifold vacuum shall increase and the EGT shall decrease.

(C) Continue advancing the initial advance until it reaches the setting where idle speed no longer increases, manifold vacuum no longer increases or EGT no longer decreases. The setting where the readings first stabilize is the optimum initial advance setting.

(D) You can tighten the distributor clamp bolt and leave it at this setting, or return it to the previous setting.

(E) If you leave the distributor at the new “optimum” setting, the idle speed will need to be readjusted (lowered) to the rpm where you normally set the motor’s idle; and the amount of centrifugal advance will require adjustment (less centrifugal advance) to attain the proper total advance.

High compression motors often have trouble hot starting with the ignition set at optimum initial advance. If your motor will not hot start after setting the initial advance as described above you have three choices to resolve the problem:

(A) Install a new or more powerful starter and/or a battery with more cranking amperage

(B) Install an ignition module that retards the ignition during starting

(C) Set the ignition for less initial advance and compensate by increasing the centrifugal advance.

Street motors should utilize vacuum advance for optimum efficiency during part throttle (high intake manifold vacuum) operation. Vacuum advance will more than improve fuel economy, it will prevent burning up the exhaust system during partial throttle (high manifold vacuum) cruising. The general consensus is to limit vacuum advance to about 10° to 12°.

I prefer not to enter into a debate over the superiority of either ported vacuum or manifold vacuum, rather I prefer to state that either method can be used, each has its advantages, the auto manufacturers used both. I think it’s important to keep in mind the sole reason the ported vacuum connection is provided on carburetors is to control the ignition’s vacuum advance, automotive engineers and carburetor manufacturers obviously think ported vacuum has merit. To state that only motors with emissions controls used ported vacuum is historically in error.

Ported vacuum sets a higher limit to how low the advance will be retarded under low rpm/low manifold vacuum conditions; it allows a race motor type ignition calibration while taking advantage of vacuum advance for cruising (high manifold vacuum, part throttle) conditions. It is the method I prefer and the method recommended by aftermarket ignition manufacturers such as MSD. This method results in peppier throttle response. Since there is no "ported vacuum" at idle, the ignition timing is not worsened by a lumpy idling camshaft. It should never cause a problem if a car is geared low enough and if a motor is in a good state of tune. However, the manifold vacuum method is useful when a high compression motor has trouble hot starting using the ported vacuum method, because the static/initial advance is significantly retarded. It is also useful for high geared or heavy vehicle applications in which the motor "pings" with the ignition tuned for ported vacuum.

For example:

Assuming a motor's optimum total advance is 36°, its optimum advance at idle is 16°, its vacuum advance is limited to 10°, and it idles at 1000 rpm.

Ported vacuum:

• 16° initial advance + 20° centrifugal advance = 36° total
  
• Centrifugal advance curve starts at 1200 rpm, ends at 2800 rpm (10° per 800 rpm)
  
• Advance at idle = 16° (16° initial setting, no vacuum advance)
  
• Advance gain above idle is a combination of centrifugal advance plus vacuum advance
  
• The vacuum mechanism always supplements total advance

Manifold Vacuum:

• 6° initial advance + 30° centrifugal advance = 36° total
  
• Centrifugal advance curve starts at 1200 rpm, ends at 3600 rpm (10° per 800 rpm)
  
• Advance at idle = 16° (6° initial plus 10° vacuum advance)
  
• Advance gain above idle is solely due to centrifugal advance
  
• The vacuum mechanism can either supplement or diminish total advance under various engine speeds and loads

Ignition advance can actually take a "dip" at throttle tip-in using the manifold vacuum method, because manifold vacuum will dip when the butterflies open; ignition advance will increase at throttle tip-in using the ported vacuum method, because ported vacuum is “zero” at idle and begins increasing as the butterflies open. This is why ported vacuum provides peppier throttle response. As motor speed increases the centrifugal mechanism increases advance while decreasing manifold vacuum results in the vacuum mechanism decreasing advance, therefore the advance mechanisms oppose one another using the manifold vacuum method, resulting in less advance during part throttle cruising compared to the ported vacuum method.

Here’s a universal ignition calibration for iron heads & flat top pistons based on Ford’s recommendation:

• 16° to 18° initial (i.e. static) advance
  
• 20° centrifugal advance
  
• 16° to 18° initial advance + 20° centrifugal advance = 36° to 38° total
  
• The centrifugal advance curve should start advancing a few hundred rpm above the motors idle rpm. I'm assuming the motors idle will be set around 800 rpm +/- 200 rpm.
  
• Centrifugal advance curve = 10° per 800 rpm to 10° per 1000 rpm. If the curve starts at about 1200 engine rpm it should end at 2800 to 3200 engine rpm
  
• Use ported vacuum for the vacuum advance
  
• Vacuum advance should be limited to about 10°
  
• Advance at idle = 16° to 18° due to the initial advance setting, there is no vacuum advance at idle with ported vacuum

Donor motors for a 351C compatible Ford Duraspark distributor are 1975 through 1982 351M, 400 or 460 V8s. The distributor’s centrifugal advance curve will require re-calibration.

To achieve a 20° advance curve the Ford distributor will require a 10°/15° centrifugal advance cam assembly (#C5AZ-12210-B; stamped 10L-15L) installed in the 10° position, and new advance springs from either Mr. Gasket (kit #925D) or Crane Cams (kit #99607-1). The Mr. Gasket kit includes one pair of springs, the Crane Cams kit includes 3 pairs of springs AND an adjustable vacuum advance canister. The Crane Cams kit is obviously the way to go as it will allow you to adjust the vacuum advance as well as the centrifugal advance.

The magnetically triggered MSD #8477 distributor is superior to the Ford distributor in my opinion; it is made of billet aluminum, it has better shaft bearings, and it has a centrifugal advance mechanism that will operate smoother and more accurately for a longer time than the advance mechanism in a Ford distributor. The MSD magnetic trigger is compatible with the Duraspark modules; the wires even have the same color coding. It is easier for the home mechanic to adjust the MSD centrifugal advance mechanism and the narrower/taller distributor has fewer intake manifold clearance issues.

To achieve a 20° centrifugal advance curve that is all in by 3000 rpm with an MSD distributor use the blue stop bushing and 2 blue springs included with the distributor.

Radiator fans & switches:

The replacement Pantera radiators sold by Hall Pantera and Fluidyne have one M22 fitting in the lower radiator inlet tank and one M22 fitting in the upper radiator outlet tank for fan control switches, one switch is used to control each radiator fan instead of controlling both fans with one switch. This is the same design as the OEM radiator. It is the experience of many owners that once the coolant temperature stabilizes one or both fans will run continuously, even when the car is traveling non-stop at cruise speed. If the engine is in a good state of tune and the cooling system is in good condition and vented properly the fans should turn-off completely when the vehicle cruises non-stop at higher speed. Constant running indicates (1) the motor is in a bad state of tune, (2) the cooling system has a problem, or (3) the reset setting of the fan switches is too low.

The M22 threaded fan switches used in the Pantera radiator tanks are a common style of temperature switch for controlling electric radiator fans in older European vehicles. They are manufactured by many aftermarket parts companies; Wahler and Intermotor are two companies whose switches are frequently used in motorsports because information regarding the settings of their various switches are readily available. The settings of the fan switches are expressed by two temperatures, such as 92°/87°; these temperatures are in degrees Celsius. The higher number is the temperature at which the switch closes its contacts to turn the fan on; the lower number is the temperature at which the switch resets (i.e. re-opens its contacts) to turn the fan off.

There is no reason to use individual temp switches for controlling the cooling fans. I recommend utilizing only one fan switch installed in the lower (i.e. inlet) tank to control both fan relays; this shall cycle the fans off and on simultaneously. Plug the M22 bung in the upper tank with an unused switch or an M22 plug. The ideal switch mounted in the lower tank, for use with a 192°F (89°C) thermostat is an Intermotor #50104 which has settings of 97°/92°. The ideal switch for use with a 180°F (82°C) thermostat will have settings of 90°/85°; however I am not aware of a switch with these settings having M22 threads. Alternative switches having M22 threads but slightly higher settings (92°/87°) are a Wahler #823.959.481.F or an Intermotor #50200.

-G

Thanks George.

That was informative and lengthy way of confirming I'm on the right track with my choices so far...

Based on my testing, I can say that 15ish degrees initial seems to be good compromise for my purpose, with no hard starting issues and temps were only 4degF (~2degC) up from full manifold vacuum. Although I did not attempt to optimize dizzy vacuum advance amount when using manifold vacuum. (It may well have given too much advance?)

Lower temp switch seems to be the one to use. It was also interesting to note that in 60degF weather the coolant temp drops at least 10-15 degrees before getting to the rad. And the separately grounded Veglia gauge seemed to show accurate info.

One thing I'm curious though is your recommendation to use higher temp fan switch than thermostat, considering the temperature drop in the cooling pipes. It would seem to me that about the same temp or little lower than thermostat opening could be used, and it would still cycle the fan off when driving at highway.
I admit I still haven't looked what thermostat I have, as I want to do some other stuff once I let the coolant out. But eventually, I'll check this out.

By the way, I happened to test the other day one 160deg Robert Shaw thermostat against five 180degree ones with boiling water (212F). Curiously enough I found that stabilized at that temperature, the 160degree thermostat was fully open and all 180degree ones were open, but not fully.

So it could be interpreted that 160degree thermostat might help cooling with high temperatures compared to higher rated ones? It doesn't just open earlier, it opens further as the temps continue to go up.
So despite the possible increased wear out (and possibly increased power), it could help with cooling when temperatures rise way above thermostat degrees.

With a carburetor and no air pump, egr, the leanest you can be THEORETICALLY is stoiochemic which is 14.7:1. This is only safe for idle since there is no load on the engine.

If you are attempting to reach this a/f ratio at cruise I wonder why? All you are doing is melting you valves and burning out the headers right near the mounting flanges.

You don't need to get fancy equipment to read this. You will see the headers glowing red in the dark, and you will see your spark plugs melting the tips off.

The leanest running carb that you can safely use is a Ford Motorcraft Holley 4180.

For a performance setup you can use a 84-85 Mustang GT carb but I have found that the 84-85 Ford Truck carbs are cheaper and have a simpler automatic choke.

Either of these carbs, untampered with, will give you the safest lean idle you can get out of the box and either can be set up to run economically. As a matter of fact, the E4 truck carb is probably what you want right there and you shouldn't even need to rejet it.

The idle should be set to run at 775-800 rpm as is. If it idles too fast, you will need to turn down the advance until you get it where you want it.

Don't expect any rpm over about 5,200 rpm though with the carb stock. That is all they are designed to offer.

Cruise a/f is going to be more like 12.5 to 13, which is lean with any carb.

If this isn't good enough for you, go to EFI. That's the only way you can do better but you still risk destroying the valves and seats, not to mention cracking the pistons if you insist on running ridiculously lean with a 351c.

Yes, you aren't imagining the engine running hotter lean...because it is.

A 160 thermostat in a Pantera is a good idea. The engine does not need to constantly operate over 212F. It just needs to reach close to that once during it's running cycle to clean the sludge out of the engine oil.

In summer weather it should idle up within about 1 minute and with this thermostat the fans will only come on at idle in traffic. Moving on the road they will not run.

The engine will show around 200F operating normally.

If you try to run on regular grade fuel 87 octane, the engine will run hotter as well.

A wheel only works one way, it has to round.

The whole idle mixture discussion was maybe a sideline here and my experiment with lean idle just proved something that many know very well. However, many do not know or actively remember it. I knew it, didn't come to think about it at the time and it took a hot day and some hands on to really sink it home.

Perhaps the Pantera crowd is more knowledgeable than others, but I've found that not many know what their idle mixture actually is. The engine can be quite insensitive to mixture screws if you are looking at revs and vacuum, and it may not sound really any different if you are that much off with mixture. It's just not always that easy without AFR meter.

It's not uncommon either to some guys try to save a little gas by leaning the idle out some, when they really should try to tune the transfer slot with air bleed and idle fuel restrictor, or main jet and PV restriction, or main and respective air bleed, depending where in the fuel curve the work really needs to be done. However that's difficult to most for several reasons.

My 16:1 idle trial was on a road trip, tuning the 1050 ultra hp dominator on my 12.3:1 compression, pump gas stroker small block with super victor and mech roller. Probably an insane combo to try to make run nice on the street, but but it does work very well these days and has been a learning experience. Gotta admit I like the easiness of almost stock engine in my Pantera these days. LOL.

Here's a pic from that trip in 2008 You can even see the dizzy manifold vacuum that caused the idle speed issue.

Well I wish you well with that combination.

There are other factors involved in that combination though. for one thing, the combustion chamber shape, flame travel, total cylinder pressure, and more.

I find a better combination considering the fuel quality most readily available, is a closed combustion chamber, 10-10.5:1 static compression ratio, a camshaft with overlap over 64 degrees and total advance of 34-36 degrees.

This gives you the ability to dial the advance down to a minimal of about 28 degrees in a fuel emergency, run pump gas, and still maintain a large percentage of the power of the engine.

With a built in 12.5:1 c.r., you have no flexibility with it at all. The only thing that might work would be to use alcohol injection?

I went that route with a 12:1 Cleveland with closed chamber heads and it wasn't enough. The only thing that worked was 106 octane gas.

That was $7.50 a gallon here so I would presume that is about what you would pay per liter for it in Europe?

That combination, 12.5:1 is the maximum mechanical efficiency you can build into an engine but with the cost of the 106 fuel, the cost makes it just an academic point to be made.

I got lectured by a refinery manager for Exon that to make that fuel it comes right from the top of the "barrel" and for every one gallon of 106, they could make five or more 87 octane gallons, and that would be "socially irresponsible" as far as he was concerned? Gee-ze!

At some point 92 is going to disappear for that reason I suppose?

I wouldn't recommend the combo I have in the Mustang to anyone, but after all the trials it works well with with euro RON98 pump fuel, which equals roughly your 93. The spark is not overly retarded. I run 34 without detonation. Even since I advanced the cam (which ended up being wrong move for power). The combustion chambers are not stock AFR205 though, but I've messed with them as well. With 3" stainless exhaust it sounds pretty good and makes people stare, but I need ear muffs on the road trips.

It does want to run on though. I intended to try an idle solenoid, but the Pantera ate most of my time this summer.

Why don't you post a soundbite and let us all hear it?

Here you go, it's from our wedding last year. The soundtrack is in the end, when we get to the asphalt.

Mustang noise

I don't see anywhere that you stated what this engine is.

I presume that it is a 347 built on a 302 block with aftermarket heads?

The Mustang engine is a 408W based on stock block (351W), AFR205's, Forged crank, 6.125 h-beam rods, forged flat top pistons, TS rings w. steel gapless top (was thinking NOS at the time), Super Victor+HVH adapter, 1050dominator, FPA 1 3/4" headers, stainless 3" magnaflow exhaust with x-pipe, Comp street solid roller (if I recall 248/254@ .050,110deg separation, lift around .6", could be more aggressive IMHO).
Surprisingly enough, it pulls nicely from 1600rpm accelerating in 6th gear. Maybe it's the compression that helps.

Had a chance to try high gear acceleration tests with manifold vacuum connected. --> Zero detonation. I admit being little surprised.

Now, the weather was clearly cooler, so it might have had an influence, but I'll keep it in manifold vac for little longer and then switch back and forth on the same day.

The Windsor head design is less susceptible to detonation then the closed chamber Cleveland is. Put another way, the closed chamber Cleveland head is one of the most sensitive I have seen to detonation.

I heard you car in a soundbite (thanks, it was cool). I doubt very, very seriously if you would actually hear it in that car. It's a little bit loud.

A lot of times in the Mustangs, in order to hear it, you need to take off the shifter boot. That's what I do.

During the fuel shortages we had here in the '70s, people were running the cars on whatever gas that they could get.

Many of the 10.5:1 289 Shelby GT350's and Cobras were running on regular, which is 87 octane, without pinging or detonation.

It's just a benefit of the shape of the combustion chambers.

You're right, It's not easy to hear over the noise. I had it open when I changed the clutch. I got it honed and put in the new rings gapped for nitrous. No signs of detonation whatsoever. It's been driven hard as well.