SBC cooling/ timing advance etc...

Hey John,
If you're talking about the vacuum adv. port.Why don't you save your self from a head ache and go buy your self a vacuum test gauge.They always come in handy.
With the engine on,one port will have constant vacuum even under accelerating and the other port will pull vacuum upon acceleration.Connect vacuum advance hose to the port that pulls under acceleration.

Frank

 

I had all sorts of heating problems, and did some really stupid things to try to fix it...
But the bottom line for me was to get a good electric fan with it's own shroud....problem solved....I just wasn't pulling enough air thru the radiator...
My 283, bored .60 over, with 305 heads, cam, Edelbrock Performer intake, Edelbrock 550 carb, etc...now runs in the ~195 range in this 90* plus heat we are having here in WI...and idles at about 200*. This engine only has about 600 miles on it, so isn't really broken in yet either........
Good luck, but my advise is to make sure you are getting the full benefit of your radiator thru proper air flow..
Cheers,
Bob
On EDIT...I am running a 185* stat...

 

Wrong. The advance should always go to the ported vac port... No reason to have advance at idle.

Also, I vote for going with a 180-195* thermostat... I used to live in Las Vegas, Nevada and the higher degree thermostats work a lot better in the hotter climates. Give the water more time to 'cool' in the radiator...

 

On a Chevrolet the vacuum advance was hooked up to manifold vacuum. Yes you want the timing to be advanced at idle so that it won't over heat. The split second that the ****erflies open the timing is retarded and you never know a thing about it. There was no such thing as a ported vacuum port on the carbs on pre-smog engines. These replacement carbs have both ports because it has to fit both smog and pre-smog engines. If you want it to run cooler like the pre-smog engines use manifold vacuum. If you are concerned about the environment then you can hook it up as a smog engine and live with the higher operating temps. I personally recommend the former.

Get an old shop manual that explains how to set the initial timing. They always tell you to disconnect the vacuum connection, PLUG THE HOSE CONNECTION and then use the light to set the initial timing. Why??? because it will have a high vacuum reading at idle that advances the timing at idle. You set the initial timing with it disconnected. I always left the light hooked up and checked to make sure that the timing mark jumped up off of the timing tag with the hose reconnected to make sure that the advance was working correctly.

 

X2 with what he said ^

 

If the water in the rad has more time to cool,doesn't the water in the block have more time to heat up?

 

I see what you are saying, I will discuss this with my buddy today, who is a gearhead and trained engineer (used to work for Navistar).

also I don't know whether my electric fan setup is adequate, hard to tell with so many variables.

I'm sticking with the 160 stat and 6 psi cap for now, only because if they help it will be noticeable, and if they don't help, it's a p*** through. I can eliminate them as variables.

 

...I agree completely....I have always used the manifold side for vacuum on pre smog motors with success..A few weeks ago stumbled on a tread about Ported & Unported vacuum.. It explains why each is used....I would also recommend reading it as a homework ***ignment....Also sounds like a vacuum leak under the carb....

 

The Ported Vac advance came about for smog reasons to create higher exhaust gas temps and burn off hydrocarbons and such,at the expense of performance. Those set ups also used very low intial timing settings like 4* advance or less and are not even close to optimal.

 

So my engine is set up as pre-smog, so I'll look seriously into using intake manifold vacuum.

 

This is something I came across a few years ago.

I did not write it but it has very good info in it.

...Courtesy of Corvette Action Center...
Ported Vs. Manifold Source: Vacuum Advance

This was written by a former GM engineer as a response to a similar question:

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word do***ent if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like ****, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts. ​

 

"I'm sticking with the 160 stat and 6 psi cap for now"

Why would you put on a lower pressure cap when all that will do is allow your engine to boil over at a lower temperature? (As someone posted earlier!)

 

Thanks for the big cut'n paste, that jibes with what my friend the gearhead with the engineering background said. I'll see where I can tap in for intake vacuum. Very informative read!!!

EDIT: I get what you are saying Vette.

 

The proper vacuum for advance on a chevy is available on the driver's side port on the front of your Edelbrock carb.

 

Wow! Thats some great info. I thought I had a pretty good grasp on timing and vacuum,but know I have a way better understanding.

Thanks for charing info 52poncho

 

Some other pics:

 

When you move that vacuum advance line over to the drivers side (full manifold vacuum)port-don't be surprised when your idle speed increases-you may need to dial it back a couple hundred RPM.

 

You should'nt need hose clamps on those vac lines, if they are the proper size they will be fine without.

 

I recently had a similar problem with an almost identical set up, I disconnected the heater core hoses,it is summer after all, insulated the fuel line to carb,better gaskets between intake and carb, with some improvement, I got another identical carb from a 2x4 set up and, worse. Both carbs are from an old 2 four set up I've had for awhile, It had a bad stumble in it, I put the heavier meter rod springs, but what really caught my eye was the miss matched meter rods, hard to read without magnification I found an old matched set good for this al***ude the improvement was dramatic I also use a 185 degree thermastat and 7lb cap. if you did'nt buy the carb new it might be worth a look at the jets and meter rods and have a look at the floats while you'er there.

 

Thanks guys. I'll be ready to fiddle with the rpm screw.

The engine compartment gets pretty hot with the hood shut, my buddy questioned my carb air source. I'm know I'm getting carried away, but who's pulled cold air from the front or under the car?

 

The better question is can the hot air get out from the engine
compartment?
Getting cool air in is only half the battle.

It doesn't matter if your car runs 220 as long as it can maintain and control the temp (not boil over)at low vehicle speeds.

 

Yeah I think you are. All engine compartments get hot but I've never heard of that to be a cause for overheating. Sure cool air is denser and helps with the HP but causing an overheating problem is "out there" pretty far. IMHO

 

The first thing I do is always start with a new aluminum radiator with dual 1" tubes. This solves most overheating problems before they start. Next, I use a nitrogen capilary Autometer direct read temperature gauge. The gauge is extremely fast acting and very accurate. This eliminates the +/- 5 degree doubt that you will have with most sender gauges.

I run a flex fan and also an electric puller. I run AC with a SBC in the AZ heat. I do not overheat. This setup is in a 47 chevy truck. My second similar setup is a 31 Ford with a zip riser and flex fan only. AC, SBC same. Both have TH700R4 trans.

Anybody that tries to tell you that a br*** radiator out cools aluminum is either in sales, talking out their ***, or both. My aluminum Griffin is easily 15 degrees cooler than my 4 row walker was with no other changes.

My two most recent builds are running a Hayden HD fan clutch and an OEM fan. There is not much out there in the electric fan world that will efficiently move as much air as a clutch fan and a rigid fan. Both of these also have aluminum radiators.

I noticed in desert communities, there tends to be a lot of aluminum radiators in cars at shows. This may also be a good clue to what works.

 

Have you flushed you cooling system? You may have **** in the water jackets. Give it a good flush and new antifreeze. Then put a new thermostat in it. Also check the rad hoses to make sure they do not have any swelling on the inside restricting flow. Hoses are cheap just put new ones on.

 

Thanks again. I'll have to see my rad has a pet****. A new rad would rock was trying to avoid that.

 

I had issues with my edelbrock carb, ignition, vacuum, etc. I replaced all vacuum lines 10 bucks max, adjusted my fuel pressure down, shouldn't be an issue for you (with your mechanical fuel pump) but Edelbrock carbs will perform very poorly with too much Fuel Pressure (should be less than 5PSI). I replaced my Distributor and wires with an HEI unit about like the one your using, although that didn't change much. I set and re-set the timming with the vacuum plugged off at the carb and not connected to the vac advance. All these things made a marked improvement but it was still falling on its face from a dead stop. I downloaded the Edelbrock manual for my carb "its very thorough", did some trouble shooting and came to the conclusion that my accellerator pump was shot. I have not rebuilt the carb yet but I have the good forturne of having a good Holley as a back up. I put the holley on and its running just fine now.
As for the over heating issue there are a lot of good suggestions on here. The whole AC system throws me for a loop. I would be worried about the belt slipping/not slipping.
Good luck with your belly ****on! I guess its true we all do have one!

 

As it's 99F outside I won't be messing with the car for a while.

I'm a dumb***, I can't remember what puller e-fan I ordered, I'll see if I can find it.

 

An earlier post you mentioned a 6lb radiator cap, but no mention of a surge/ puke tank...(mine's a vodka bottle) If you have a tank just make sure the cap has gaskets on both surfaces so that it can **** coolant back in when cold or under acceleration

 

Hello sir, I have a 16 lb cap on there at the moment. I need to buy and install an overflow recovery tank, I just have a line dangling. FWIW when I had my old cap on it did puke a bit, maybe half cup to cup.

 

Stay cool man. Every sbc thermostat I touch also gets a less than 1/8" vent hole