Looking for some input. After 3 years restoring my '69 I finally started it Saturday. What a feeling! Apart from a few small leaks and some setup it ran great. Here's the thing, it's a ZZ383 crate motor, Griffin aluminum rad and a Flex-a-lite Syclone fan rated at 2500 CFM, 180 thermostat. I had to do the breakin in a couple of sets as the temp started to creap up to around 220 or so before I shut it off and let it cool a bit before continuing with the breakin. I was pretty sure after reading many of the posts that this fan on this rad would be more than adequate for cooling. I know that a fresh motor will build more heat. Plus the 1500-3000 rpm breakin speeds with nothing but the fan cooling might be a bit much. Any input? I haven't road tested it yet as I have one fuel leak to fix before going out. I really like to know if I'm out of line in thinging this fan will be enought with Vintage Air etc. Thanks in advance.

Noel

Well, I think you might have answered your own question...kinda. When I break-in my motors I always put a floor fan in front and a hose if I have to use it. I think the rpms/heat was too much for the electric fan on your radiator this time.

The Syclone fan is just a middle-of-the-road product in my opinion, I know I have one and use it as a pusher on my 383. While I live in Atlanta, I have never tested it with this combo with the air on ...yet. Your ZZ383 is a pretty hp laden motor and with air it's going to be close even in moderate climates. I would try it with a 180 thermostat and high flow water pump. It might even see over 200 temps in hot, heavy traffic w/air days...but it might just do. I expect over 200 days with mine for sure but am not anal about going to 220 with a 16lb cap etal. I really have no choice but to run a high output pusher. I am taking a peak at the new 3000cfm Spal tho!

If you want an alternative I would suggest either Mark VIII, Taurus or Windstar fans. The new Spal 3000.

Thanks for the reply! Really appreciate the input. I still have to set up the TV cable on the 700r4, so I'll do the fan in front and hope that helps the process until I can actually see what it's going to do on the road. The sending unit is right by the thermostat housing where the water is at its hottest leaving the motor. Even still, I'm not comfortable going that high. It's a pain as the Syclone is brand new. I also understand that it's only covering about 200sq inch of a possible 400sq inch surface area. That being the case I may go to a derale flex as I'll be surprised if it doesn't pull more than 3000 cfm at the lower rpm range.

Noel

I recently put on a black magic fan setup.. pulls 2800 cfm and covers all but a 1/2" on either side of the shroud. Drops the temp down in a heartbeat.. I'd look at your motor again and go through the timing and fuel settings. She may be running retarded and lean. those will heat you up reall quick.

noels, when I did my cam breakin last week, it ran pretty hot too. I was able to stabilize it at 210 with a box fan in front of the radiator and the heater going full blast. Made me nervous as h*ll cause I was running straight water. This was with a 17" derale flex, and no shroud.

I've run it several times since, and it never went over 180. 2500 rpm for half an hour not moving makes a lot of heat and is an unusual sitation, something that would never happen in normal driving.

If you do go with a derale flex, check out my post in forum classifieds for a group purchase custom alluminum rad shroud.

Guys,

I really appreciate the input. I have the parts to fix my fuel leak tonight and will fire it again after. The timing is 6*. I am going to set it to 8* as GM recommends 32* all in. My Proform distributor is 24*no vaccum advance as GM doesn't recommend it with the ZZ383. I'll also be setting the idle mixture tonight as well. I'll let you know how it goes with the heat after trying a fan in front. I guess an actual test drive will confirm things one way or the other.

Noel

I think GM DOES recommend vacuum advance in all the specs that I have seen on this engine. They recommend a distributor with a vacuum advance???? Where have you read this...or who said it because it doesn't make any sense? Vacuum advance is as necessary as good timing is???

Steve,

My ZZ383 manual said 32* in by 3000 rpm with vacuum advance disconnected. I did emial GM, here's what they said.

Noel

My question to GM: In the manual that came with the ZZ383 it says to not use a vacuum advance at all. I ordered the Proform billet HEI without an advance. Did I make a mistake here?


GM Reply:
NO, not at all, the one you ordered without vacuum advance is perfect! Set your timing so total advance is 32° and you will be good to go. I recommend the vacuum advance units that I posted above, because some people have a hang up with not using vacuum advance. You will be in great shape with the one you ordered!

"My ZZ383 manual said 32* in by 3000 rpm with vacuum advance disconnected" means........as in any case when looking at total timing......simply disconnect the VA for this setting. It does NOT imply not to use it at all....and in fact

Ususally the guys who work at these "GM Performance Centers" are a myriad of excellent, good, okay and terrible. I have run into these guys at GM Performance Centers as techs...or whatever (and I am assuming you bought this from one of those centers), and most are pretty smart about street applications. But, I can tell you that this guy gave you poor advice.

Here....take this to heart from a GM Engineer John Z right here at Camaros.net that designs performance engines and understands VA to a fault. It is one of the best explanations that I have ever seen written.


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 crap, 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."

So, I would reconsider the purchase and send it back if it were mine and get one with a vacuum advance. It will run cooler and have better part-throttle response!

I realize that the ZZ383 doesn't come with an intake or a distributor - but all of the ZZ4's and their cousins that DO come with a distributor have vacuum advance. I'd definitely use vac advance on the street.

As a side note - that is a roller cam motor, so there is no need to do the 2500 RPM cam break-in. Won't hurt anything, but not necessary.

that is a seriously good timing tutor.... maybe it should be a sticky in performane or a tech atricle?

Guys,

This is getting good! On the roller cam break-in. My brother said the same thing for the cam. I didn't spend much time over 2000 rpm for that reason. It isn't the same, you're right! He also said that the rings are a low tension ring that seat very quickly as well. A quick break-in is likely all it took to get everything seated properly.

I re-looked the ZZ383 manual. The last section on the ignition system section reads, "Set spark timing at 32* BTDC at 4000 rpm with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32* total advance at wide open throttle. The HEI vacuum advance canister should remain disconnected." For sake of the discussion, as it's great info, I'd be happy to scan it as a pdf file if anyone is interested. There is also more on this at the Sallee Chevrolet forum. They have a great site. The 383 doesn't come with a distributor or intake. The VA info posted is excellent material for reference. Someone should email that to a few of the magazines.

On a side note, part of my cooling problem was a mis-wired fan. Flex-a-lite reversed the wiring. There was some flow out due to a billowing effect which led three of us to conclude it just wasn't pulling much... Live and learn. Thanks!

Noel

This from the GM Performance Parts Dealers/Distribution site Mar/2005 supplied by SDPC folks (note your setting of total timing remark at 4000 is wrong?? according to all the documents that I have seen). Again, vacuum advance for the street is not debatable really if you understand the science. Racing at WOT...different deal. I have talked to no less than four separate dealer techs on this an all agree vacuum advance is a needed feature on ALL their engines for the street. See notes below.


12498772 ZZ383/425 Crate Engine


With GM's legendary Fast Burn cylinder heads and 383 cubic inches, the ZZ383/425 delivers incredible torque with smooth, linear delivery. If you're looking for a small-block package that delivers big-block power, then you've found it. 425 horsepower at an incredibly low 5400 RPM, and 460 ft-lbs. of torque at 4500 RPM make this the ideal hot street engine or off road powerhouse.

The excellent air handling and combustion characteristics of the Fast Burn cylinder heads combined with the ZZ383/425's 3.800" stroke, make this engine the benchmark against which all other 383 inch small-blocks should be measured. And it's tough, too. The 4340 nitrided and induction hardened crank and unique forged PM rods see to that. The 9.1 to 1 compression ratio ensures that the ZZ383/425 is 92 octane pump gas friendly.

The ZZ383/425 gets a stout .509/.528 lift steel camshaft, with 222/230 duration at .050 lift. Hydraulic roller lifters and GM's time tested 1.5 to 1 roller rocker arms round out the valve train. And, of course, it has the Fast Burn head's lightweight stainless steel valves and retainers for reliable performance at extended RPM.

GM's testing was completed using a GM single plane intake, P/N 12496822 and a 750 CFM Demon carburetor with mechanical secondaries. Test header specs are: 1 3/4" primaries, 33 inches long with 4-inch collectors.

GM dual plane intake P/N 12366573 may be used for hood clearance on the ZZ383/425, but results in a decrease in peak horsepower of approximately 4% horsepower.
GM Crate Engines are horsepower rated to SAE 2005 Standards.

Technical Notes: ZZ 383/425 Technical Information

Horsepower 425 @ 5400 RPM
Torque 449 @ 4500 RPM
Max. Recommended RPM 6000
Compression Ratio 9.1:1
Partial Engine 12499106
Block 88962516 Four bolt main, cast iron
Crankshaft 12489436 Steel "4340"
Connecting Rods 12497624 PM rods
Pistons.005 O/S 12499103 High silicon aluminum
Piston Rings .005 O/S 12499107
Camshaft 12370846
Cylinder Heads 12464298
Head Gasket 10105117 (.28 thick)
Intake Valves 12555331 2.00"
Exhaust Valves 12551313 1.55"
Valve Springs 12551483
Rocker Arms 12370838 1.5:1 roller rockers kit
Tortional Damper 12498008
Flex Plate 14088765
Lifters 5232720 Flat Tappet
Spark Plugs R 44LTS or R42LTS for racing
Fuel Premium 92 octane
Static timing 8 degrees BTDC/ full (unported) manifold vacuum advance recommended/limited to 12 degrees
Ignition Timing 32º total @ 3000 RPM with vacuum advance disconnected

Bottom line is that it's your engine and you can do what you want, however there is nothing special about a ZZ383 that would change any basic requirement for VA. YOur engine will run cooler , idle better and have a more crisp tip-in and throttle response with full time vacuum advance.

Thanks Steve,
I've always run VA on any car I've had. It did seem pretty strange to me that this one wasn't recommended. The distributor I have has no advance supplied but does have the lockout tab. So, I'm assuming without going any further that all I need to do is get a cannister and install it. The Proform billet distributor I have is curved to have 24* advance all in by 3000 rpm. I didn't touch this as it seemed nuts to be trying to get the advance in by 4000.

There is one more reason for VA, I am running a 700r4 with a 3.08:1 rear axle. It's going to cruise pretty low in the rpm range and having the VA for that alone seems wise.

Noel

if i am going to hijack the thread, i guess i should do it right...

i love all the bright ideas...but will an aftermarket can FIT on this vacuum advance distributor........AND will it then fit into my engine bay without a BFH........also, has anyone did this 8361 with an aftermarket vacuum can....

its really easy to spit out data, but how bout the actual fitament and real world install......

i only have 7" at 950 rpms.......could someone tell me if i can use a vacuum advance distributor on my motor............we better results than i have now.

current ignition is all msd, with a centrigual advance distributor

because the engineers advice stated the aftermarket vacuum can would fully deploy at 8" would that be 7+1=8" or 7-1=6" fully deployed....

could someone tell me if i have to little vacuum for this CID and cam?

402(396) comp cams 292 magnum........ 244 on the I/E . 550 lift on a 110 LSA

should i be looking for vacuum leaks, the guage read steady....the car has to idle at 950ish..... manual tranny.......

car runs good...but i think there is more....dont we all:)

now lets see if i get some more regurgitated plagerism shoved down my throat. :p j/k