No vacuum advance on new engine?

[AirSpeed]

The paperwork that came with my new 290hp crate engine says to not use the vacuum advance, it says "the engine is designed to only use the mechanical advance". Am I reading this wrong?

[Fitz]

Originally Posted by AirSpeed

The paperwork that came with my new 290hp crate engine says to not use the vacuum advance, it says "the engine is designed to only use the mechanical advance". Am I reading this wrong?

No, you read it correctly. Many of the newer crate motors use a re-curved mechanical advance and have no need for the vacuum advance.

[geezer#99]

Nah!!
That's not it Fitz!
The motors don't even come with a dizzy.
It's the bean counters and warranty guys.
They don't want you putting too much timing in it causing warranty issues.
And it also likely says somewhere in the paperwork not to run more than 10 degrees initial.

[RodnRudy]

I installed that same engine in a 50 GMC for a guy and I set the initial timing with the vacuum plugged at 10 degrees. When I set the total advance which I think was 32 degrees the initial timing came out to 12 degrees. It started and ran like a top.

[mechanicalman]

Originally Posted by geezer#99

Nah!!
That's not it Fitz!
The motors don't even come with a dizzy.
It's the bean counters and warranty guys.
They don't want you putting too much timing in it causing warranty issues.
And it also likely says somewhere in the paperwork not to run more than 10 degrees initial.

That particular engine is over-cammed and ultra low compression. It needs at least 36' total timing and can swallow 15'-18' base easy and still crank freely plus it needs an aggressive timing curve.

You can run it without vacuum advance and it won't make one iota of difference at the drag strip. It will, however, show up at the gas pump and suck your wallet and your gas tank dry faster.

You hit the nail on the head about the bean-counters. Shameful, and to sell a brand new engine without a new dampener is silly.

[Fitz]

Originally Posted by geezer#99

Nah!!
That's not it Fitz!
The motors don't even come with a dizzy.
It's the bean counters and warranty guys.
They don't want you putting too much timing in it causing warranty issues.
And it also likely says somewhere in the paperwork not to run more than 10 degrees initial.

Is that a fact? Geezer, Geezer, Geezer. You need to get out more, buddy!

Here's the Instructions for start up on my crate motor:

Start the engine and adjust the initial timing. Set the ignition timing to 15° before top dead center (BTDC) and
the engine idle to 950 RPM (ZZ572/620) or 1200 RPM (ZZ572/720R) with a timing light and the vacuum disconnected
and plugged. Rotate the distributor counterclockwise to advance the timing. Rotate the distributor
clockwise to retard the timing. Leave the vacuum advance disconnected

Here's a photo of that motor taken when I unwrapped it in the shipping crate. Unless I'm completely delusional that looks suspiciously like a distributor with 8 plug wires all neatly connected and loomed. But , of course I could be just dreaming and none of that stuff actually arrived in my Garage!

Isn't that a lovely sight? It looks even better with a truck wrapped around it!

[AirSpeed]

Originally Posted by Fitz

Is that a fact? Geezer, Geezer, Geezer. You need to get out more, buddy!

Here's the Instructions for start up on my crate motor:

Start the engine and adjust the initial timing. Set the ignition timing to 15° before top dead center (BTDC) and
the engine idle to 950 RPM (ZZ572/620) or 1200 RPM (ZZ572/720R) with a timing light and the vacuum disconnected
and plugged. Rotate the distributor counterclockwise to advance the timing. Rotate the distributor
clockwise to retard the timing. Leave the vacuum advance disconnected

Here's a photo of that motor taken when I unwrapped it in the shipping crate. Unless I'm completely delusional that looks suspiciously like a distributor with 8 plug wires all neatly connected and loomed. But , of course I could be just dreaming and none of that stuff actually arrived in my Garage!

That's a beauty! I came very close to getting one, if I hadn't just bought $1,200 worth of tires I would have done it! I will be content with my 350, I guess! But damn the more I think about it I wish I had just done it!

[geezer#99]

Originally Posted by Fitz

Is that a fact? Geezer, Geezer, Geezer. You need to get out more, buddy!

Here's the Instructions for start up on my crate motor:

Start the engine and adjust the initial timing. Set the ignition timing to 15° before top dead center (BTDC) and
the engine idle to 950 RPM (ZZ572/620) or 1200 RPM (ZZ572/720R) with a timing light and the vacuum disconnected
and plugged. Rotate the distributor counterclockwise to advance the timing. Rotate the distributor
clockwise to retard the timing. Leave the vacuum advance disconnected

Here's a photo of that motor taken when I unwrapped it in the shipping crate. Unless I'm completely delusional that looks suspiciously like a distributor with 8 plug wires all neatly connected and loomed. But , of course I could be just dreaming and none of that stuff actually arrived in my Garage!

Isn't that a lovely sight? It looks even better with a truck wrapped around it!

Fitz! Fitz! Fitz!!
Guilty of only one thing.
With some people you need to be very specific what you write.
I failed on that!
He didn't get a dizzy, but you did.
You get a roller cam in that little motor?

[Fitz]

Originally Posted by geezer#99

Fitz! Fitz! Fitz!!
Guilty of only one thing.
With some people you need to be very specific what you write.
I failed on that!
He didn't get a dizzy, but you did.
You get a roller cam in that little motor?

Roller cam & roller rockers.

[crazy longhorn]

Originally Posted by geezer#99

Nah!!
That's not it Fitz!
The motors don't even come with a dizzy.
It's the bean counters and warranty guys.
They don't want you putting too much timing in it causing warranty issues.
And it also likely says somewhere in the paperwork not to run more than 10 degrees initial.

I am with you....1 geezer to another Yes you can run that mill with no vac advance....but it will KILL the fuel mileage ! On the street, I would suggest 32-34 total, in tween 2800-3200 (depending on gears/ect). Shoot for about 10 degrees @ the crankshaft, on the vac advance, & hook to full manifold source. If you are a street cruiser, I will bet that you will like the curve? On the track, we set @ 38, all in @ 2600...no vac advance. On the street, your plugs will burn cleaner, & your engine will run cooler, with that vac can longhorn

[1972BlueC20]

So if I go with the 290 hp crate, do you think I'll be happy with it? Its just a daily driver, but I like to romp on it from time to time. I got a rebuilt th350 with mild shift kit and 4.11 gears.

What are the downsides of being "slightly" over cammed?

[Fitz]

Originally Posted by 1972BlueC20

So if I go with the 290 hp crate, do you think I'll be happy with it? Its just a daily driver, but I like to romp on it from time to time. I got a rebuilt th350 with mild shift kit and 4.11 gears.

What are the downsides of being "slightly" over cammed?

"slightly overcammed"? I really don't know what that means, but, duration overlap and lift determine how much of a charge you can get into and out of the cylinders. So, for a suck, squeeze, bang, blow (4 cycle) engine the cam increases the suck and the blow. A bit more of both means more response to the throttle and a slight drop in mileage. Since this truck is a daily driver, go for it. Mileage will drop from somewhere near 14 mpg to 12 or so but that's a pretty small penalty.

[1972BlueC20]

Well I don't know what that means either, a few others stated the 290hp engine has a cam that's a little much for the engine. Whatever that means. I know nothing about cams. I just want a good engine with plenty of power. I can buy pretty much any engine below $3k so I just want to make sure I make the right decision.

[68350]

I'm not sure about your motor in particular, but both my 383 stroker and 496 stroker do not use vacuum advances.

[AirSpeed]

Thanks guys! I have to say it does run better without the vacuum. My truck is very different since I installed the new engine, my shift points are better, more solid and I can now get it to downshift at more than 50 mph! I used to have to slow to 50 in order to get it to shift in order to pass someone. My passengers always wondered why I slowed down to go faster! It's like a new truck! Thanks again!

[AirSpeed]

When I first set the timing I could not get it to time for crap! I know absolutely that I had the dist in to perfection but it would not time. I only ran the engine for maybe three minutes total and it was suggested I break in the cam before I played with it anymore. I got it to run as smooth as possible then broke in the cam. Once that was done the engine ran much better and I was able to get it timed. I don't know why, maybe I had a dry lifter, I don't know but it's sure running nice now. It has a really nice idle that sound great in my flowmaster 40s.

[dfrank]

I don't use vaccum advance on my 383 stroker.

[mechanicalman]

Originally Posted by AirSpeed

The paperwork that came with my new 290hp crate engine says to not use the vacuum advance, it says "the engine is designed to only use the mechanical advance". Am I reading this wrong?

Wow, I read the instructions twice and it mentioned 2 or 3 times that the engine is designed to run on mechanical advance only. I'm flabbergasted by that.
http://www.chevrolet.com/content/dam...e-12499529.pdf

I don't buy it. GM knows it will get into fights with people installing their own engines, using old dampeners that have slipped, etc. and are really being shamefully coy about how to install their engine with only their own money grubbing interests at heart.

Not only are you going to sacrifice gas mileage, I'd be betting you will over-heat on cruising at lite loads for anything over 15 miles give or take.

Make sure you have a piece of vacuum hose in your truck if you decide to take it for a long drive just in case you need to hook that thing up.

[AirSpeed]

So, should I just hook up the vacuum? Is it going to cause an issue with it hooked up? Why would it cause GM issues for people to use the vac advance?

[mechanicalman]

Originally Posted by AirSpeed

So, should I just hook up the vacuum? Is it going to cause an issue with it hooked up? Why would it cause GM issues for people to use the vac advance?

Do you have this specific distributor?
http://www.summitracing.com/parts/nal-93440806
MAYBE it's curved for performance engines with large cams, and consistent with what I've said, it has an aggressive advance curve and MAYBE they are afraid the vacuum pod will give it too much too soon.

If you DON'T have this specific distributor, hook up the vacuum pod. You can always un-hook it. Or keep a piece of vacuum hose in the glove box and if it over-heats you can put it on. Check your mileage with it off, then with it on. Let me know if it causes problems, I highly doubt it. The following off GM instructions:

"Recommended distributor is the HEI (High Energy Ignition) distributor P/N 93440806. This distributor is a self-contained ignition system that includes a magnetic pickup, a module, a coil, a rotor, and a cap. The HEI’s large diameter cap minimizes arcing and cross-firing between adjacent spark plug terminals. The cap’s male terminals provide a reliable, positive connection for the spark plug leads. However, the HEI’s large diameter cap may interfere with other underhood components in vehicles not originally equipped with HEI ignition systems. Check for adequate clearance before installation. The HEI system requires a 12 volt power supply for proper operation. The HEI ignition system should be connected directly to the battery with 10 or 12 gauge wire through a high quality ignition switch. If you are installing an HEI ignition in an early-model vehicle originally equipped with a point-type ignition, be sure to remove or bypass the resistor in the wiring harness to ensure the HEI receives 12 volts continuously. Use distributor connector package P/N 12167658, which includes connectors and wires for the HEI’s tachometer and 12 volt terminals. Set spark timing at 32º before top dead center (BTDC) at 3000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle (WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve".

Knowing the compression ratio, and the size of the camshaft, I still feel GM is out to lunch on leaving the vacuum pod dis-connected for a street driven car that will see extended light load cruise and needs to have good gas mileage.

IF IT WERE MINE, even if I DID have THAT SPECIFIC GM distributor, I'd hook up the vacuum pod and time it to 36' total and go from there.

[AirSpeed]

Originally Posted by mechanicalman

Do you have this specific distributor?
http://www.summitracing.com/parts/nal-93440806
MAYBE it's curved for performance engines with large cams, and consistent with what I've said, it has an aggressive advance curve and MAYBE they are afraid the vacuum pod will give it too much too soon.

If you DON'T have this specific distributor, hook up the vacuum pod. You can always un-hook it. Or keep a piece of vacuum hose in the glove box and if it over-heats you can put it on. Check your mileage with it off, then with it on. Let me know if it causes problems, I highly doubt it. The following off GM instructions:

"Recommended distributor is the HEI (High Energy Ignition) distributor P/N 93440806. This distributor is a self-contained ignition system that includes a magnetic pickup, a module, a coil, a rotor, and a cap. The HEI’s large diameter cap minimizes arcing and cross-firing between adjacent spark plug terminals. The cap’s male terminals provide a reliable, positive connection for the spark plug leads. However, the HEI’s large diameter cap may interfere with other underhood components in vehicles not originally equipped with HEI ignition systems. Check for adequate clearance before installation. The HEI system requires a 12 volt power supply for proper operation. The HEI ignition system should be connected directly to the battery with 10 or 12 gauge wire through a high quality ignition switch. If you are installing an HEI ignition in an early-model vehicle originally equipped with a point-type ignition, be sure to remove or bypass the resistor in the wiring harness to ensure the HEI receives 12 volts continuously. Use distributor connector package P/N 12167658, which includes connectors and wires for the HEI’s tachometer and 12 volt terminals. Set spark timing at 32º before top dead center (BTDC) at 3000 RPM with the vacuum advance line to the distributor disconnected and plugged. This setting will produce 32º of total advance at wide open throttle (WOT). The HEI vacuum advance canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve".

Knowing the compression ratio, and the size of the camshaft, I still feel GM is out to lunch on leaving the vacuum pod dis-connected for a street driven car that will see extended light load cruise and needs to have good gas mileage.

IF IT WERE MINE, even if I DID have THAT SPECIFIC GM distributor, I'd hook up the vacuum pod and time it to 36' total and go from there.

I'm using an HEI out of an 80s truck, nothing special. Couldn't tell you if it's the same dist GM speaks of. I've only got about 35 miles on my engine so far, haven't really given it much gas, I guess I'm afraid it's not broke in yet! I have noticed it makes more power at higher rpms, can't feel a lot from a stop but again I haven't really stomped on the gas yet! I do notice it runs a little warmer than my last engine, I have factory gauges still so I can't be specific in the temp but it used to ride right on the second line on the gauge, now it sits right above it. Hasn't gone past there even up hills. I installed a new 180f thermostat and a new water pump on this engine. My radiator is a year old. I really hope the power at low speeds is going to be a little more than I'm feeling now once I get brave enough to give it some gas.
Thanks again!

[Coach]

I have the same engine and it's correct, no vacuum advance, especially if you also purchased the recommended HEI distributor. The timing directions state 10 degrees initial timing with total advance timing at 32 degrees. There is a very slight hesitation upon initial acceleration, which is due to the timing setting, so I will probably change mine to 14 & 36.

[AirSpeed]

Originally Posted by Coach

I have the same engine and it's correct, no vacuum advance, especially if you also purchased the recommended HEI distributor. The timing directions state 10 degrees initial timing with total advance timing at 32 degrees. There is a very slight hesitation upon initial acceleration, which is due to the timing setting, so I will probably change mine to 14 & 36.

I've noticed that hesitation as well. Does your engine feel strong from a stand still? What carb are you using? I have a quadrajet on mine, never had any problems with it on my last engine. Above 2000rpms I can definately feel this engine has more power than I ever had with my old 350, it's very strong at speed. I did full my tank today so I'll check out my mileage on the next fill up. Thanks.

[1972BlueC20]

I'm about to buy this engine :

http://www.summitracing.com/parts/na...4450/overview/

Is this the same one you got airspeed?


Are you pretty happy with it so far? I'm hoping the power will be a noticeable difference from the stock 175HP, certainly it will be.

I too am interested in this no vacuum advance thing....I was thinking i'd be using the vacuum advance like on my current stock engine....I was thinking of going to HEI, so I guess I should?

Right now I'm running a stock distributor with the pertronix ignitor points eliminating setup.....was going to buy the pertronix ignitor distributor originally but my mechanic told me to go HEI......I'm still learning so I will probably listen to him and yall LOL......

[mechanicalman]

Originally Posted by 1972BlueC20

I'm about to buy this engine :

http://www.summitracing.com/parts/na...4450/overview/

Is this the same one you got airspeed?


Are you pretty happy with it so far? I'm hoping the power will be a noticeable difference from the stock 175HP, certainly it will be.

I too am interested in this no vacuum advance thing....I was thinking i'd be using the vacuum advance like on my current stock engine....I was thinking of going to HEI, so I guess I should?

Right now I'm running a stock distributor with the pertronix ignitor points eliminating setup.....was going to buy the pertronix ignitor distributor originally but my mechanic told me to go HEI......I'm still learning so I will probably listen to him and yall LOL......

Get this one, comes with HEI, dual pattern intake/gaskets and dampener.
http://www.jegs.com/i/Chevrolet-Perf...06#moreDetails

Put this cam/lifters in it.
http://www.summitracing.com/parts/sum-1103/overview/
http://www.ebay.com/itm/SBC-DELPHI-L...662d12&vxp=mtr

This carb
http://www.summitracing.com/parts/edl-1406/overview/
http://www.summitracing.com/parts/ed...VX8aAuZa8P8HAQ

You will have enough money left over for fancy valve covers, gaskets, roller timing chain, etc. And you will have a better, more powerful engine.