no vacuum advance?
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
You must have interpreted my post incorrectly....the FI cars {my own} received the mileage I referred to, was my 61 and 62...., not the modern whatever's and done with a 4.1 and 4.56 gears...Some may have thought I was against a VC can......not so if I misled you....Its important on most ofl the non performance engines used by the membership....However I agree a 290 HP modern engine is not a performance engine, at least not to me and maybe a few others here....
maybe I could use that little 290 HP thingie to start my 'BIG' ones though....
maybe I could use that little 290 HP thingie to start my 'BIG' ones though....
Le Mans Master
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From: Oxford MA-----You just lost the game!!!!
You must have interpreted my post incorrectly....the FI cars {my own} received the mileage I referred to, was my 61 and 62...., not the modern whatever's and done with a 4.1 and 4.56 gears...Some may have thought I was against a VC can......not so if I misled you....Its important on most ofl the non performance engines used by the membership....However I agree a 290 HP modern engine is not a performance engine, at least not to me and maybe a few others here....
maybe I could use that little 290 HP thingie to start my 'BIG' ones though....
maybe I could use that little 290 HP thingie to start my 'BIG' ones though....
Scott
Thread Starter
Racer
Joined: Apr 2007
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From: Lafayette/marquez La/tx
well..... Interesting. I did not mean to open a can of worms. I kinda tend to agree with the warranty answer. The little 290 thingy was all I could afford at the time. Upgrades are in the making or at least i'm saving up for them. with an intake, headers it's still fun to drive. And it's still a vette. We can't all afford 67 427's.....I wish. But a 400hp small block would put a bigger smile on my face
Safety Car
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From: New York
I think the directions are accurate and the people reading them are messed up .
It is not saying never to use the vac advance it is saying to SET TIMING .. Come on now read it and re read it ... SET TIMING if you got that part NOW realize all our distributors only use centrifugal to achieve total advance and achieve the correct curve. Thats because we all know under wot throttle the vac advance totally drops out of any function affecting timing advance. Matter of fact the instant vacuum drops the advance is pulled off from functioning .
I am wondering if this whole topic was designed to be a play on words to spur a pointless discussion
Lastly the vac adv , its main reason to exist is for steady cruse and idle , where fuel can go un-burned and cause pollution ,the vac adv compensates for this by creating a spark earlier in the pistons travel to TDC making sure the flame front gets a chance to burn the most amount of fuel present. Can this cause better mpg I have never looked at it that way and thus have no idea but I guess ya sure it might help...
It is not saying never to use the vac advance it is saying to SET TIMING .. Come on now read it and re read it ... SET TIMING if you got that part NOW realize all our distributors only use centrifugal to achieve total advance and achieve the correct curve. Thats because we all know under wot throttle the vac advance totally drops out of any function affecting timing advance. Matter of fact the instant vacuum drops the advance is pulled off from functioning .
I am wondering if this whole topic was designed to be a play on words to spur a pointless discussion
Lastly the vac adv , its main reason to exist is for steady cruse and idle , where fuel can go un-burned and cause pollution ,the vac adv compensates for this by creating a spark earlier in the pistons travel to TDC making sure the flame front gets a chance to burn the most amount of fuel present. Can this cause better mpg I have never looked at it that way and thus have no idea but I guess ya sure it might help...
Your topic as it started was answered by me quite some time ago however as usually happens at this forum topics go off on a side line from other members injecting opinions or other irrelevant information
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I think the directions are accurate and the people reading them are messed up .
It is not saying never to use the vac advance it is saying to SET TIMING .. Come on now read it and re read it ... SET TIMING if you got that part NOW realize all our distributors only use centrifugal to achieve total advance and achieve the correct curve. Thats because we all know under wot throttle the vac advance totally drops out of any function affecting timing advance. Matter of fact the instant vacuum drops the advance is pulled off from functioning .
I am wondering if this whole topic was designed to be a play on words to spur a pointless discussion
Lastly the vac adv , its main reason to exist is for steady cruse and idle , where fuel can go un-burned and cause pollution ,the vac adv compensates for this by creating a spark earlier in the pistons travel to TDC making sure the flame front gets a chance to burn the most amount of fuel present. Can this cause better mpg I have never looked at it that way and thus have no idea but I guess ya sure it might help...
It is not saying never to use the vac advance it is saying to SET TIMING .. Come on now read it and re read it ... SET TIMING if you got that part NOW realize all our distributors only use centrifugal to achieve total advance and achieve the correct curve. Thats because we all know under wot throttle the vac advance totally drops out of any function affecting timing advance. Matter of fact the instant vacuum drops the advance is pulled off from functioning .
I am wondering if this whole topic was designed to be a play on words to spur a pointless discussion
Lastly the vac adv , its main reason to exist is for steady cruse and idle , where fuel can go un-burned and cause pollution ,the vac adv compensates for this by creating a spark earlier in the pistons travel to TDC making sure the flame front gets a chance to burn the most amount of fuel present. Can this cause better mpg I have never looked at it that way and thus have no idea but I guess ya sure it might help...
If you're going to go to all the effort to try to scold some of the posters here in your recent post, at least get your facts correct. Additional advance (via VA) is not there to reduce unburned fuel and reduce emissions (additional advance will often increase emissions). Vacuum advance was standard equipment years before anyone gave a crap about tailpipe emissions. The fuel is going to burn rather completely even if the timing is too retarded. (It just completes its burn as it's passing the exhaust valve in extreme cases.) The function of vacuum advance is to position the combustion peak pressure point at 15-20* ATDC (despite the engine load changing) for maximum thermal efficiency (ie: fuel mileage).
Safety Car
Joined: Jan 2009
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From: New York
Wrong.
If you're going to go to all the effort to try to scold some of the posters here in your recent post, at least get your facts correct. Additional advance (via VA) is not there to reduce unburned fuel and reduce emissions (additional advance will often increase emissions). Vacuum advance was standard equipment years before anyone gave a crap about tailpipe emissions. The fuel is going to burn rather completely even if the timing is too retarded. (It just completes its burn as it's passing the exhaust valve in extreme cases.) The function of vacuum advance is to position the combustion peak pressure point at 15-20* ATDC (despite the engine load changing) for maximum thermal efficiency (ie: fuel mileage).
If you're going to go to all the effort to try to scold some of the posters here in your recent post, at least get your facts correct. Additional advance (via VA) is not there to reduce unburned fuel and reduce emissions (additional advance will often increase emissions). Vacuum advance was standard equipment years before anyone gave a crap about tailpipe emissions. The fuel is going to burn rather completely even if the timing is too retarded. (It just completes its burn as it's passing the exhaust valve in extreme cases.) The function of vacuum advance is to position the combustion peak pressure point at 15-20* ATDC (despite the engine load changing) for maximum thermal efficiency (ie: fuel mileage).
I may have flubbed the emission point however ,, anyone who thinks GM intended no VAC advance EVER on a crate motor is not reading it correctly ,, It is not never it is only disconnect to set initial then hook it up and mechanical will handle all curve and max timing under load.
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
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 -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). Uh, no. Vacuum Advance is not there to compensate for carburetor fueling errors. The VA canister has no clue what the A/F ratio is in the cylinders. It does have an indirect indication of the cylinder pressure (via manifold pressure readings), and is there to compensate for the differing combustion burn rates due to the varying density (pressure) in the cylinders.
I may have flubbed the emission point however ,, anyone who thinks GM intended no VAC advance EVER on a crate motor is not reading it correctly ,, It is not never it is only disconnect to set initial then hook it up and mechanical will handle all curve and max timing under load.
I may have flubbed the emission point however ,, anyone who thinks GM intended no VAC advance EVER on a crate motor is not reading it correctly ,, It is not never it is only disconnect to set initial then hook it up and mechanical will handle all curve and max timing under load.
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Safety Car
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From: New York
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
No one is going to change anyones opinion or say boy is he smart, you either like to run a vacuum advance or you don't. If a GM engineer gave me instructions not the run a vacuum advance on a brand new engine then I wouldn't run one, if your smarter than the guys who put the motor together and designed it / set it up to run with no vacuum can then run a vacuum advance. I don't run one and get good gas mileage with a 600HP engine.
It's pretty clear to me anyway "Set spark timing at 32deg @ 3000rpm with with vacuum line from dist. removed and plugged. says this will produce 32 deg of total timing at WOT and the vacuum canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve"
Someone tell him to disregard this and run a vacuum advance and offer to pay for the motor if it detonates or anything else timing set wrong can ruin an engine.
So to the OP you get 10mpg, what is your A/F readings at idle, part throttle, cruise and WOT ? If you don't know that's why you get 10mpg
It's pretty clear to me anyway "Set spark timing at 32deg @ 3000rpm with with vacuum line from dist. removed and plugged. says this will produce 32 deg of total timing at WOT and the vacuum canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve"
Someone tell him to disregard this and run a vacuum advance and offer to pay for the motor if it detonates or anything else timing set wrong can ruin an engine.
So to the OP you get 10mpg, what is your A/F readings at idle, part throttle, cruise and WOT ? If you don't know that's why you get 10mpg
Last edited by MotorHead; Dec 29, 2012 at 10:48 AM.
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
No one is going to change anyones opinion or say boy is he smart, you either like to run a vacuum advance or you don't. If a GM engineer gave me instructions not the run a vacuum advance on a brand new engine then I wouldn't run one, if your smarter than the guys who put the motor together and designed it / set it up to run with no vacuum can then run a vacuum advance. I don't run one and get good gas mileage with a 600HP engine.
It's pretty clear to me anyway "Set spark timing at 32deg @ 3000rpm with with vacuum line from dist. removed and plugged. says this will produce 32 deg of total timing at WOT and the vacuum canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve"
Someone tell him to disregard this and run a vacuum advance and offer to pay for the motor if it detonates or anything else timing set wrong can ruin an engine.
So to the OP you get 10mpg, what is your A/F readings at idle, part throttle, cruise and WOT ? If you don't know that's why you get 10mpg
It's pretty clear to me anyway "Set spark timing at 32deg @ 3000rpm with with vacuum line from dist. removed and plugged. says this will produce 32 deg of total timing at WOT and the vacuum canister should remain disconnected. This engine is designed to operate using only the internal centrifugal advance to achieve the correct timing curve"
Someone tell him to disregard this and run a vacuum advance and offer to pay for the motor if it detonates or anything else timing set wrong can ruin an engine.
So to the OP you get 10mpg, what is your A/F readings at idle, part throttle, cruise and WOT ? If you don't know that's why you get 10mpg
OBTW, that mythical design isn't in your engine.
Regarding mpg, IIRC, your previous posts concerning your mpg neglected to state that you were using imperial gallons, not US gallons.
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
He needs to follow the instructions, then hook up VC to manifold vac and check total plus VA @ 3000 all in steady RPM and make sure initial + mechanical + vacuum is less than 54 @ steady 3000 RPM
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I'll repeat what I said in post#6: I'm not buying it. Show me a cylinder/head design where the combustion burn rate is independent of cylinder pressure (ie: doesn't need load based VA timing adjustments).
OBTW, that mythical design isn't in your engine.
Regarding mpg, IIRC, your previous posts concerning your mpg neglected to state that you were using imperial gallons, not US gallons.
OBTW, that mythical design isn't in your engine.
Regarding mpg, IIRC, your previous posts concerning your mpg neglected to state that you were using imperial gallons, not US gallons.
I just looked at my records and I used 4.56US gal ( converted from Imperial ) for pretty close to exactly 100 miles converted from kilometers and it works out to 22us gal per mile on the highway @ 80mph. As I said I think I can do better know that I have it leaned out.
I always keep records of everything for times like this and have better things to do than make things up. You are arguing with yourself as I have said nothing negative about your posts.
I am happy to see you know more than the engine builders for this particular engine
Last edited by MotorHead; Dec 29, 2012 at 01:01 PM. Reason: Someone would have made a big deal about exactly 100 miles
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
) If the instructions for this particular motor (not every small block ever made) clearly state "Set spark timing at 32deg @ 3000rpm with with vacuum line from dist. removed and plugged. says this will produce 32 deg of total timing at WOT and the vacuum cannister should remain disconnected. This engine is designed to operate using only the interal centrifugal advance to acheive the correct timing curve"
This means that you ignore the instructions and run a vacuum canister ?
Drifting
Joined: Feb 2005
Posts: 1,879
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From: Los Gatos CA
I would run vacuum advance. Not all instructions are the best way to go. If they were, why does everyone say to re-curve your stock distributer? In this case, it just makes sense. Unless, of course, you are only running a narrow rpm/load. Just my 2 cents. Oh yeah, can't we just have a good oil or thermostat fight? My Rotella T will beat your 160* 'stat any day...
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I don't think I am disputing what you say and being sarcastic attacking me tells me a lot about you. Can you point me to where I said I would not get better gas mileage with a vacuum can ? I have said from day one I get good gas mileage without a vacuum can.
I just looked at my records and I used 4.56US gal ( converted from Imperial ) for pretty close to exactly 100 miles converted from kilometers and it works out to 22us gal per mile on the highway @ 80mph. As I said I think I can do better know that I have it leaned out.
I always keep records of everything for times like this and have better things to do than make things up. You are arguing with yourself as I have said nothing negative about your posts.
I am happy to see you know more than the engine builders for this particular engine
I just looked at my records and I used 4.56US gal ( converted from Imperial ) for pretty close to exactly 100 miles converted from kilometers and it works out to 22us gal per mile on the highway @ 80mph. As I said I think I can do better know that I have it leaned out.
I always keep records of everything for times like this and have better things to do than make things up. You are arguing with yourself as I have said nothing negative about your posts.
I am happy to see you know more than the engine builders for this particular engine
I'm not convinced that any SBC iteration possesses that level of design sophistication. Others are apparently disagreeing with that.
Race Director
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I never made that claim. I have, however, built enough Chevy engines (for my personal toys), and spent enough time on OEM test tracks and in dyno rooms working on fuel and spark calibrations to have a decent working knowledge of what engines want. And that experience keeps leading me to the item I've asked about multiple times in this thread: Show me a cylinder/head design where the combustion burn rate is independent of the pressure in the cylinder (ie: doesn't need load based spark curve adjustments).
I'm not convinced that any SBC iteration possesses that level of design sophistication. Others are apparently disagreeing with that.
I'm not convinced that any SBC iteration possesses that level of design sophistication. Others are apparently disagreeing with that.
They are just telling him not to run a vacuum advance with this particular motor so who is arguing with you ?
I'm not yet you choose to call me out and put down. Where I live people say they are sorry they don't keep repeating the same thing over and over they read on Wikipedia
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I don't see anywhere in the instructions where they say anything about " cylinder/head design where the combustion burn rate is independent of the pressure in the cylinder" You won't, for two reasons. Those mythical engines don't exist, and 99% of users wouldn't understand WTH they were talking about anyway.
They are just telling him not to run a vacuum advance with this particular motor so who is arguing with you ? You are. Look at your post to 63Mako. You stated that this engine is designed to operate at the correct timing curve without vacuum advance. I'm saying an engine with that "capability" doesn't exist.
I'm not yet you choose to call me out and put down. Where I live people say they are sorry they don't keep repeating the same thing over and over they read on Wikipedia
They are just telling him not to run a vacuum advance with this particular motor so who is arguing with you ? You are. Look at your post to 63Mako. You stated that this engine is designed to operate at the correct timing curve without vacuum advance. I'm saying an engine with that "capability" doesn't exist.
I'm not yet you choose to call me out and put down. Where I live people say they are sorry they don't keep repeating the same thing over and over they read on Wikipedia
I'm an engineer. I'm not interested in squabbles. Give me some facts (data) or physics to show this engine doesn't require vacuum advance for correct spark curves at non-WOT conditions. Otherwise I'm putting the "no vacuum advance needed" story in the same category as pressing the brake pedal to get the transmisssion out of PARK. A waste for 99% of people, but it keeps the skill-limited 1% from doing something stupid with the vehicle.
Just trying to discuss basic engine tuning here.