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Discussion Starter · #1 · (Edited)
I bought a 350 crate motor I little while back from GM and it recommends no vacuum advance. Looking through the installation instructions on thier web site they say that for all thier 350's. 32 degrees max advance. Not the 54 or so I read on many a post.

Do other guys run their's with no vacuum advance? I took it out tonight and it seems to run great. I also tried it with the vacuum on both of the Edelbrock ports. Runs best as recommended.

Just curious.
 

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What 'create' motor did you buy? Can you quote the part of the instructions that say not to use a vacuum advance can? You'll notice one on this ZZ4 motor.
 

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Discussion Starter · #3 ·
Sometimes I amaze myself with my spelling. I bought the 290 hp. Anyway, here is the part from the ZZ4 instructions on page 4 but it is the same for all the 350's

"Set spark timing at 32º before top dead center (BTDC) at 4000 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."
 

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I can't see why GM would recommend no vacuum advance. VA has many benefits and most any motor can use it. To what degree though is the question no pun intended. Most people toss the vacuum advance because they don't understand it or have a can that's totally wrong for their motor, therefore claiming it's junk and not needed because their motor runs better without it.

I'll agree that a very long winded cam might not be suited to use a vacuum advance can as vacuum will be all over the place. VERY difficult to set up and eliminating it accepting the downfalls of not having one, nothing wrong with that really. However in a normal hi-po engine it most certainly will have some benefit in several areas. Cooling, better gas mileage at part throttle, and cleaner plugs are some. Gas mileage isn't a dirty word either, who wouldn't want better mileage if it didn't cost any horsepower? That's basically what it does, causes the engine to run at peak efficiency at part throttle and idle.

Your normal centrifugal advance sweeping 12-36° is OK for an engine used only as an all out power machine. But if you want a nice cruiser additional vacuum advance keeping the engine at peak efficiency is advantageous.

I can't see how vacuum advance made you motor run worse unless it was pulling in too soon and too much. But at that point you should have heard some pinging. The 54° you speak of would only be with added vacuum advance and only at light load on the motor.

Some motors certainly won't like 54° mine doesn't, 42° to 44° is about the most I can throw at it during cruise without pinging. Even at that though the 10° of vacuum advance I add from the total centrifugal 32° is enough to notice a mileage and cooling benefit.
 

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If it was my motor, I'd have the vacuum advance connected. With such a short cam and 10:1 compression it's not surprising that the mechanical advance is limited to 32° @ 4000 rpm, and a typical VA curve isn't going to work either. You'll need to limit the VA to 10-15°

I think the initial timing is set at 10° with 22° added by 4000 rpm. If you're running at 2500 rpm at part throttle, you're only going to be halfway up the advance curve, about 21° or so. You're giving up a chunk of efficiency with this little advance under part throttle conditions.
 

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Discussion Starter · #6 · (Edited)
ALLT4 - I didn't know what to think when I read that also, but there it was in black and white. I originaly went there to check on a couple thinks because the engine was also pulling low vacuum. Believe it or not they say that it will pull 10-12" at idle. What!!!

I agree with all the things you say about the benefits of vacuum advance but I would assume they know better than most.

Some of these things just seem a little out of the ordinary and I was wondering what other guys with this type of motor have experienced.

MIKE- Thanks for the input, I will probably try that. My VA unit is an adjustable one. So tomorrow night I will do what you recommeded.

Thanks
 

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I think GM says that to error on the side of caution. Eliminating the vacuum advance eliminates any chance of the customer dialing in too much advance or too soon being unfamiliar with it. I think they know that most customers aren't totally familiar with how to correctly set it up and suggesting not using it protects themselves from complaints of pinging and internal damage from over advanced motors coming back.

I use it on my ZZ383, yes it was biatch to set up. Especially with the Fastburn heads. Skipping it would have been easier and just relying on the centrifugal it would have ran well. But with it the idle is smoother and lower, the part throttle tip in is crisper and the temps are cool, too cool in fact now LOL. When I unhook it of course I get that rumpity rump idle people love so much but setting the idle is a pain, it doesn't feel as responsive at tip in from cruise speed and of course the temps are a little higher.

I'm not going to knock anyone for not using it anymore because you do wind up with that real muscle car sound and easy set up. To each his own.
 

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I bought a 350 crate motor I little while back from GM and it recommends no vacuum advance. Looking through the installation instructions on thier web site they say that for all thier 350's. 32 degrees max advance. Not the 54 or so I read on many a post.

Do other guys run their's with no vacuum advance? I took it out tonight and it seems to run great. I also tried it with the vacuum on both of the Edelbrock ports. Runs best as recommended.

Just curious.
Hey I have the new 350/265 I tried different combinations. And I'm telling u honestly set it at 14 initially with NO vac advance that leaves u with 36 total. It runs idles drive with great power. No
 

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I bought a 350 crate motor I little while back from GM and it recommends no vacuum advance. Looking through the installation instructions on thier web site they say that for all thier 350's. 32 degrees max advance. Not the 54 or so I read on many a post.

Do other guys run their's with no vacuum advance? I took it out tonight and it seems to run great. I also tried it with the vacuum on both of the Edelbrock ports. Runs best as recommended.

Just curious.
No advance. I tried lots of combinations and the best Is 14 initial 36 total no advance. And that thing rocks. Runs cool idles perrrrfect
Sometimes I amaze myself with my spelling. I bought the 290 hp. Anyway, here is the part from the ZZ4 instructions on page 4 but it is the same for all the 350's

"Set spark timing at 32º before top dead center (BTDC) at 4000 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."
Set it at 36 total no advance, lots of power.
 

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Just so you know..... you are replying to a thread that hasn't been active for 13 years. Sometimes these old threads pop up from time to time. May want to look at the date before replying. No worries here.
 

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Old but new thread. Thanks for giving us a run down on this engine. I saw the video
couple of weeks ago. I think it is the same GM 350/190 HP from years past, maybe reworked the cam slightly to go from 260 to 265 HP with a four barrel and headers. There seems to be some confusion about using vacuum as per their instructions, which are misleading, it seems to me that what they mean is no vacuum when setting initial and total timing, but they do not follow up with what to do once timed. I think GM is just assuming that everyone knows that you should reconnect your vacuum to the dizzy once you have it timed. Also there is no standard cam break in procedure in their instructions, tchicbears69, did you have to do a cam break in? How much vacuum are you getting at idle and what is your idle set at? Also do you have power brakes, standard or auto trans.? I am looking for a smoooth purrrring idling engine with normal vacuum for power brakes. Thanks
 
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