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ledhed76
Cochise

USA
302 Posts

Posted - 16 Nov 2011 :  10:47:05 AM  Show Profile  Reply with Quote
What should my initial timing be set at on my new 400 build? The factory setting for the stock engine was 16 degrees BTDC. Is this going to be good for my new engine? It was a stock 1976 400ci but it now has more compression (around 9.3:1) due to my #62 heads and it also has a a new camshaft (XE262). I already have the distributor set for 21 degrees mechanical advance at around 2700 rpm. Thanks.



Complete specs on this rebuild can be found here...

http://psp.aquacomp.net/topic.asp?TOPIC_ID=5245

Edited by - ledhed76 on 16 Nov 2011 11:07:57 AM

Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 16 Nov 2011 :  11:48:38 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Total mechanical advance is important. The amount of advance the MSD distributor provides is subtracted from that number. That should give you the approximate initial setting.

E.g. 36 degrees total mechanical advance (desired) less 21 degrees provided by your MSD results in 15 degrees initial.

Similarly 34 degrees total mechanical advance (desired) less 21 degrees provided by your MSD results in 13.

Fine tuning--advance initial--however, if the engine becomes hard to start when hot, it's too far; drop it off a degree or two to get best start-up.

Hope this simplistic explanation helps.

Bill

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 16 Nov 2011 11:51:13 AM
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ledhed76
Cochise

USA
302 Posts

Posted - 16 Nov 2011 :  12:38:43 PM  Show Profile  Reply with Quote
So if it is hard to start when hot, then the initial needs to come down. Gotcha.


Is 36 degrees total advance around 2700 rpm about what i should be running in this street motor??
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Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 16 Nov 2011 :  12:56:25 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
36 is a great starting point. It could be 34, 35, or 37. You have some flexibility. 2700 rpm is about right.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 16 Nov 2011 12:57:25 PM
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cortcomp
Coyote

USA
4316 Posts

Posted - 16 Nov 2011 :  2:36:37 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
What would be the issue with getting all the timing in by, say, 1800?

CB is always saying to have all the timing in by your cruise speed. For me, that'd be about 2200-2500 rpm at about 65-70 mph if i recall correctly.
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BearGFR
Bear

USA
569 Posts

Posted - 16 Nov 2011 :  3:31:20 PM  Show Profile  Visit BearGFR's Homepage  Reply with Quote
Your motor will tell you what it likes, but you have to know how to ask and how to listen for the answer.

36 total is a great starting point. To find the optimum, you need a track (or a stretch of "safe" road) and a good, accurate, repeatble way to measure time.

Start off with something "less than" 36 total, say --- oh, 32 or so.

"Make a run" - record the time. Bump timing up a degree, maybe two --- lather, rinse, repeat. You're looking for the point where your times stop improving and start to fall off again. Once you find that point, back off to your previous setting (which you now know is "best" for your engine). Now take your timing light and read how much initial timing that is, just so that in the future you'll be able to return to your motor's "happy value" without having to go through all that again.

Bear
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Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 16 Nov 2011 :  8:23:49 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
To get a distributor to curve in by 1800 rpm can be done. My HEI was that way for a while. I had no issues with it starting and accelerating. However, I was never really happy about my idle. This was before I installed the bigger cam and had the Qjet re-calibrated by Cliff.

What happens is that to get such a fast curve requires loose springs. If there's not enough tension the springs don't always return to their proper start position and you may have more advance than you want when you don't need it. This can lead to an idle that is inconsistent.

To eliminate that possibility while tuning my new combo, the HEI was changed so it comes in a bit slower. To do that required testing a bunch of spring combinations. It took a while even using a distributor machine.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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cortcomp
Coyote

USA
4316 Posts

Posted - 16 Nov 2011 :  9:27:07 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
If you had vacuum advanced hooked up, at a given lower rpm, wouldn't the part throttle vacuum signal get you to the same advanced timing at a lower rpm (like 1800-2000) as that kind of setup you just described w/o one?

Just something to think about as the car comes back together, kicking around in my head. With the random after market HEI i had in the car, it cruised fine at 2200, but this will be a totally different motor.
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Cobrabill
Talking Dog

Aruba
2851 Posts

Posted - 16 Nov 2011 :  9:46:28 PM  Show Profile  Reply with Quote
Agree with what Bear says.The engine is gonna like what it's gonna like.But a good starting point is around 10 intial and 36 total by 2500 rpm.Then let the timing games begin!!

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Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 17 Nov 2011 :  07:06:59 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Cortcomp-- If you were to install the distributor with "all in" at 1800 rpm with a functioning Vac assist it could be determined how much vac is available at part throttle with a gauge hooked to manifold vac or the base of the carb (ported). A physical test would be to drive it at 1800 rpm and see how many inches of Hg you have at that speed. This would be at part throttle. More than likely you would be getting several degrees of vac advance in addition to the total mechanical. Drive under the threshold rpm and you will probably see vac there too.
This would enable a car to cruise at lower rpm. However, the weak spring issue is still not a good thing for idle quality.

Computer (ECM) controlled and distributor less engines can motor along in 6th gear cruising at very low rpm and get very good fuel economy. Harder to do with a distributor (old technology).

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Cobrabill
Talking Dog

Aruba
2851 Posts

Posted - 17 Nov 2011 :  6:30:30 PM  Show Profile  Reply with Quote
quote:
Originally posted by Bill Boyle
Computer (ECM) controlled and distributor less engines can motor along in 6th gear cruising at very low rpm and get very good fuel economy. Harder to do with a distributor (old technology).



Harder?You mean flat out impossible.This is the problem with people wanting to up-grade their older cars.Computers are what is really driving the MPG increase(s).

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Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 17 Nov 2011 :  7:06:04 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
ECMs are amazing and getting better all the time. The auto industry can thank the aeronautical and space engineers for all the fly by wire computer stuff that has spilled over. A 505 hp Corvette can get nearly 30 mpg running at 70 mph today. Amazing.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Phil
The Great White Buffalo

USA
6371 Posts

Posted - 17 Nov 2011 :  7:17:31 PM  Show Profile  Reply with Quote
quote:
Originally posted by Bill Boyle

A 505 hp Corvette can get nearly 30 mpg running at 70 mph today. Amazing.



Yeah, but it STILL looks like a Hoover Vacuum Cleaner.

"Chevy": even the name sounds cheap.
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 17 Nov 2011 :  11:03:49 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
quote:
Originally posted by Bill Boyle

To get a distributor to curve in by 1800 rpm can be done. My HEI was that way for a while. I had no issues with it starting and accelerating. However, I was never really happy about my idle. This was before I installed the bigger cam and had the Qjet re-calibrated by Cliff.

What happens is that to get such a fast curve requires loose springs. If there's not enough tension the springs don't always return to their proper start position and you may have more advance than you want when you don't need it. This can lead to an idle that is inconsistent.

To eliminate that possibility while tuning my new combo, the HEI was changed so it comes in a bit slower. To do that required testing a bunch of spring combinations. It took a while even using a distributor machine.


I had a full size 1985 Blazer that was totally gutless. I installed a recurve kit and light springs. I think the compression was about
8-1 . When I took it for a drive, talk about detonation. In went the stock springs and the detonation was gone. I've helped alot of people fix their detonation problems with our high compression heads by tightening up the springs, richening up the carb and running cooler. And the performance increases bigtime. I'm also going against the grain by not liking the Comp cam 110 degree cams with the 10-1 compression street engines. 114 degree works awesome with mid 220/230 duration and running temps of 170-180. I believe all my distributors are all in at about 2,800-3,000. 0-60 ft in 1.60s
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Bill Boyle
Horse Feathers (Charter Member)

USA
4009 Posts

Posted - 18 Nov 2011 :  09:27:03 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
What do you have against Hoover Vacuum cleaners Phil. I know a nice guy with a bright yellow Corvette (not Hoover) and he loves the economy and performance. The guy is clearly missing a few screws; his elevator surely doesn't go to the top; and, he's clearly not the sharpest knife in the draw. He loves that car. He says it's so easy to drive "a caveman could do it."

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Heddman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 18 Nov 2011 09:27:45 AM
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1badgoat
Buffalo

68 Posts

Posted - 19 Nov 2011 :  10:45:29 AM  Show Profile  Reply with Quote
those hoovers..i mean those new vettes are a real nice ride with performance and great fuel economy, but they just dont come close to the looks and style of a true pontiac muscle car!
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ledhed76
Cochise

USA
302 Posts

Posted - 29 Nov 2011 :  5:42:34 PM  Show Profile  Reply with Quote
Should i be running vacuum advance also??....my buddy (who is a chevy guy) thinks i am insane with these timing settings...he thinks that 14 initial + 21 mechanical + 10 vacuum is way too much...he says he never runs vacuum advance on any of his street rods...he told me most engines wont live real long with 45 degrees of total timing....i told him that i havent heard any knocking and it seems to be running strong....should i be concerned or get rid of the vacuum advance??
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Phil
The Great White Buffalo

USA
6371 Posts

Posted - 29 Nov 2011 :  6:04:39 PM  Show Profile  Reply with Quote
Street rods are lighter and thus require a different approach. Run the VA, it will perform better on the street. The numbers aren't linear like your Chevy friend wrongly assumes.

"Chevy": even the name sounds cheap.
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cortcomp
Coyote

USA
4316 Posts

Posted - 29 Nov 2011 :  6:07:28 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
"he says he never runs vacuum advance on any of his street rods...he told me most engines wont live real long with 45 degrees of total timing"

He is mistaken, to put it kindly. From the factory, cars run crazy vacuum advance....for fuel economy they really stretched it out later in the years. Remember, the vacuum is only there at light throttle cruising...when there's not near as much load on the engine, so detonation risk is minimal vs loaded up wide open, when there is no vacuum advance. Also, a lot of after market HEI setups use a hex key to adjust the total amount of vacuum timing you'll get in a few seconds, so if everything timing wise is great but vacuum is too much, you can dial it in easily.

Most street rods are a hodge podge of mismatch parts that, while looking good, never run as smooth as a factory setup, and rarely as efficient MPG-wise. Most guys just eave of parts they don't understand or disable things that don't play well when they mixmatch parts instead of understanding why they don't play well. Maybe a distributor curved for a 1977 chevy vega doesn't play well in an overcammed higher rpm motor in a 3800 lb muscle car?

In any case a) i'm sure there are here running more timing than you, but it matters more if the engine LIKES it. Set your engine where it runs best, and it will "live real long" because it's running at max efficiency, which means less wear.

b) vacuum doesn't affect power at all, it's for fuel economy, and it's a fine setup.

c) most will tell you to use ported vacuum

d) timing doesn't kill or hurt motors at all or affect their life UNLESS you're getting into detonation or pretty far out of time, and you'd know because it would run poorly.

and e) don't listen to chevy guys, even machinists. You're working with a different animal. I write down directions for my machine shop that others here give me, to be sure that i get a good running pontiac motor, instead of a pontiac build that replicates a chevy and runs just so-so
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ledhed76
Cochise

USA
302 Posts

Posted - 29 Nov 2011 :  9:34:21 PM  Show Profile  Reply with Quote
"The same thing occurs under steady highway cruise conditions; the mixture is lean, takes longer
to burn, the load on the engine is low (it only takes about 40 horsepower to cruise at 50mph) and
the manifold vacuum is high, so the vacuum advance unit is again deployed, and adds 15 degrees
of spark advance over and above whatever the distributor centrifugal advance mechanism is
providing at that engine rpm. If you had a timing light connected so you could see it as you cruise
down the highway, youd see about 45-50 degrees of spark advance; your fixed initial advance of
10 degrees, 20-25 degrees provided by the centrifugal advance mechanism, and the 15 degrees
added by the vacuum advance unit."


excellent link...

http://www.corvette-restoration.com/resources/technical_papers/Timing101.pdf

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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 29 Nov 2011 :  9:56:51 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
quote:
Originally posted by cortcomp

"he says he never runs vacuum advance on any of his street rods...he told me most engines wont live real long with 45 degrees of total timing"

He is mistaken, to put it kindly. From the factory, cars run crazy vacuum advance....for fuel economy they really stretched it out later in the years. Remember, the vacuum is only there at light throttle cruising...when there's not near as much load on the engine, so detonation risk is minimal vs loaded up wide open, when there is no vacuum advance. Also, a lot of after market HEI setups use a hex key to adjust the total amount of vacuum timing you'll get in a few seconds, so if everything timing wise is great but vacuum is too much, you can dial it in easily.

Most street rods are a hodge podge of mismatch parts that, while looking good, never run as smooth as a factory setup, and rarely as efficient MPG-wise. Most guys just eave of parts they don't understand or disable things that don't play well when they mixmatch parts instead of understanding why they don't play well. Maybe a distributor curved for a 1977 chevy vega doesn't play well in an overcammed higher rpm motor in a 3800 lb muscle car?

In any case a) i'm sure there are here running more timing than you, but it matters more if the engine LIKES it. Set your engine where it runs best, and it will "live real long" because it's running at max efficiency, which means less wear.

b) vacuum doesn't affect power at all, it's for fuel economy, and it's a fine setup.

c) most will tell you to use ported vacuum

d) timing doesn't kill or hurt motors at all or affect their life UNLESS you're getting into detonation or pretty far out of time, and you'd know because it would run poorly.

and e) don't listen to chevy guys, even machinists. You're working with a different animal. I write down directions for my machine shop that others here give me, to be sure that i get a good running pontiac motor, instead of a pontiac build that replicates a chevy and runs just so-so


Actually I tend to dissagree with your logic. Maybe rat rods but most Streetrods are well thought out and when they buy the driveline, its all a combination that is already well chosen.
On the otherhand. Most guys that have old Musclecars that have changed through a few hands have a bunch of missmatched parts . Like an HEI ignition that came off of a mid to late 70s Pontiac on a high compression 1960s engine or a Cam that is made for a high compression 400 in a low compression 70s engine, or a 2 series rear end with a high rpm cam. Or a Q- jet that is from a later 1970s engine because its rated at 800 cfm but is leaner than ever because it was set up for real low emissions. People in general don't have the concept of how a good combination works. Alot of people that I know with Streetrods, buy a crate motor with everything chosen using the Edelbrock packages and just want a reliable car that starts up and drives. Nothing more and nothing less.

Edited by - sixt8bird on 29 Nov 2011 10:06:38 PM
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 29 Nov 2011 :  10:03:55 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
Also depending if the distribor was set up with a vacuume can originally or not makes a difference. I run a mallory Comp 9000 in the car I race but its more of a street car and is killer on the street. The vacuume advance will give better gas milage and thats about it. Anyone that has ridden in my 400 cannot believe how tame the car is until I put my foot down. I actually prefer running no vacuume whether on the street or not. Is it right or wrong? Not at all, its sort of like comparing a Holley to a Q-jet, opinions will vary but they all will perform good when set up right.

Edited by - sixt8bird on 29 Nov 2011 10:04:19 PM
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cortcomp
Coyote

USA
4316 Posts

Posted - 29 Nov 2011 :  10:53:42 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
"most Streetrods are well thought out and when they buy the driveline"

Oh, i would normally agree when you're walking around goodguy's with 6,000 streetrods worth a years salaries...usually a bought and dropped in package. Most of the cars in the cheaper price range, which there are more of in numbers, that have nova and camaro subframes and a later weak 80s sbc in them and, as you say, the wrong carb or an dist from somewhere else, those are the ones i find where things were just kind of slapped together because it bolted on.

For every streetrod done great with thought, planning, and due diligence as to how it will be driven, there's 10 backyard projects that were parts swaps from other cars, not package kits, and the result is so so. You wouldn't believe how many guys with 49-54 chevies, switching to open drivelines and swapping rears and talking which cars to get them from, don't even consider the axle ratio! Just, is it the right width? will i have to move spring perches? how much will it cost? those things are way less important to me than: what's the ratio? is it posi? disc rear? can parking brakes be used?

I'd say maybe the bar for a streetrod has been raised with so many bolt in kits that look great, and the average mash together car isn't cutting the mustard for picky hotrod fans, but that's a topic for another day.
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 30 Nov 2011 :  10:57:46 AM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote

[/quote]
People in general don't have the concept of how a good combination works. [/quote]

And this is why I posted the blanket statement. It doesn't matter what kind of cars. Streetrods, Hotrods, Muscle cars. etc.

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dgray
Cochise

845 Posts

Posted - 30 Nov 2011 :  11:51:39 AM  Show Profile  Reply with Quote
post removed by dgray.

Edited by - dgray on 01 Dec 2011 08:27:55 AM
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 30 Nov 2011 :  11:16:42 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
Floor any car and the vacuum is really close to 0 . Ported and non ported equalling no vacuume advance.
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cortcomp
Coyote

USA
4316 Posts

Posted - 01 Dec 2011 :  12:14:08 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
yes but, if i recall correctly and i might not, cliff and others recommended the ported timing port for some reason or another to avoid some issue or another at idle. I don't think it had anything to do with WOT.
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Phil
The Great White Buffalo

USA
6371 Posts

Posted - 01 Dec 2011 :  2:57:39 PM  Show Profile  Reply with Quote
Part throttle cruising, efficiency, economy, longevity and driveability improvements on the street.

"Chevy": even the name sounds cheap.
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 01 Dec 2011 :  6:25:36 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
I use ported vacuume on the cars that have vaccume advance all the time. I prefer it also over non ported.
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bnorris_74
Crazy Horse

USA
1410 Posts

Posted - 02 Dec 2011 :  06:58:22 AM  Show Profile  Reply with Quote
quote:
I have my distributor vacuum advance limited to 10 degrees

Same here and ported as well.
Limiting the vac adv stopped jerking feeling at lower cruise speeds in my case.
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 02 Dec 2011 :  11:27:23 AM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
quote:
Originally posted by bnorris_74

quote:
I have my distributor vacuum advance limited to 10 degrees

Same here and ported as well.
Limiting the vac adv stopped jerking feeling at lower cruise speeds in my case.



This is typically created by very lean operating conditions. Removing some of the advance just became a bandaid to help the lean out.
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bnorris_74
Crazy Horse

USA
1410 Posts

Posted - 02 Dec 2011 :  12:10:26 PM  Show Profile  Reply with Quote
quote:
This is typically created by very lean operating conditions. Removing some of the advance just became a bandaid to help the lean out.


Nope, Not in this case.
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sixt8bird
Chief Many Horses

USA
1114 Posts

Posted - 02 Dec 2011 :  11:21:47 PM  Show Profile  Visit sixt8bird's Homepage  Reply with Quote
quote:
Originally posted by bnorris_74

quote:
This is typically created by very lean operating conditions. Removing some of the advance just became a bandaid to help the lean out.


Nope, Not in this case.


Have you run a wide band to show this isn't the case?
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455 Formula
Sitting Bull

USA
244 Posts

Posted - 14 Dec 2011 :  12:15:31 AM  Show Profile  Reply with Quote
I have a totally different approach on setting the timing curve.

I advance timing at idle until vacuum peaks, then retard until you drop 1 in/Hg of vacuum, lock the distributor down and take a reading with the timing light.

Record the value in crankshaft degrees. This is your ideal base timing setting. As long as the engine will crank reliably when hot, use as much advance as it will stand.

Then, set the rpm at 3000 rpm and advance the timing until the engine runs the smoothest/fastest (RPM) and keep advancing until you can hear a 'fluff-----fluff--fluff---fluff' (slight intermittant misfire) in the exhaust. Back the timing up until the miss goes away, then retard 4 additional degrees.

Take a reading with the timing light and record the value in crankshaft degrees. This is your best total timing value.

Now, you know the idle timing that produces the highest vacuum and the total timing that gives the best high rpm power. You can now select the centerplate/weights (HEI) that will give you the desired curve.

For example, on my 8.75:1 compression Pontiac 413 with UD 231/235-110 camshaft, the highest idle vacuum came in at 23 degrees BTDC. I retarded that 1 degree, so my base timing is 22 degrees BTDC.

Starting at 3000 rpm, the engine obtained both the highest rpm and vacuum readings at 50 degrees total timing.

Using a 472 centerplate and 139 weights (HEI) I built a 20 degree mechanical advance curve. So, with 22 degrees initial and 20 degrees mechanical, I had 42 degrees total timing. Roadtesting confirmed the engine ran the quickest at this setting.

It was a dog at 34, 36 and 38 degrees total timing.

I then added 8 degrees of ported spark advance with a Crane adjustable advance, set to apply at a low 5 in/Hg of vacuum, for 50 degrees total timing.

While every engine is different, the method will allow the engine to tell you exactly how much timing it wants....Robert

Edited by - 455 Formula on 14 Dec 2011 12:19:36 AM
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455 Formula
Sitting Bull

USA
244 Posts

Posted - 14 Dec 2011 :  12:22:53 AM  Show Profile  Reply with Quote
quote:
Originally posted by Jeff K.

I prefer ported also..

My car pulls out harder at slightly off idle, runs the same temps as manifold, idles with much more stability and doesn't bang into gear..

With My Cliffs Quadrajet, I used a tee and connected both ported ports together to get the same vacuum off idle as manifold.. It's best to have Cliff modify the carb for ported spark. If your just trying one of the timed emission ported ports, it's not going to work well..

I have my distributor vacuum advance limited to 10 degrees..



I sometimes use (2) one-way check valves and a vacuum bleed device (From the underdash climate control system of a Mercedes-Benz) to enable the use of BOTH manifold and ported vacuum advance.

The bleed is placed in the line at the vacuum advance with a simple 'T' fitting. One end of the line is hooked to the ported vacuum fitting (with a one way check valve) and the other to manifold vacuum with yet another one way check valve.

When manifold vacuum drops, ported vacuum applies, so the vacuum advance is applied at idle and switches automatically to yield better off-idle performance. The bleed valve simply allows all vacuum to drop when the throttle is opened.

Been doing this for over 30 years when a very large cam produces less than desireable idle vacuum...Robert

Edited by - 455 Formula on 14 Dec 2011 12:25:17 AM
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Total Jackass
Tribal Scout

0 Posts

Posted - 14 Jan 2014 :  04:38:22 AM  Show Profile  Reply with Quote
ignore my post.

I'm a first class jerk and don't you forget it!
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Phil
The Great White Buffalo

USA
6371 Posts

Posted - 14 Jan 2014 :  6:03:09 PM  Show Profile  Reply with Quote
TTT

"Chevy": even the name sounds cheap.
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