73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: philo_beddoe on June 04, 2015, 07:38:48 am
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I have a 77 Boinanza, 305 4bbl., all GM parts. The spec sheet in my shop manual shows this model/year with a 305 2bbl. When I bought the truck some jerk put a eddlebrock intake and eddlebrock carb on it. So I put it back to the original GM intake and like new fully rebuilt quadrajet 4bbl. The reason i put the 4bbl is because the primary jets are smaller than the 2bbl. So I'll actually save gas with the 4bbl. (I won't "get on it" because 305's are not exactly muscle engines)
Here's the problem, the manual (and the sticker under the hood for timing says 8 degrees BTC, @ 500 rmp. BUT, that's for the origianl 2bbl. In the Manual,,,,it does show a 4 bbl 305 for the like 82-86 years...and that is 4 degrees BTC.
Which should I time it to? 8 degrees or the 4 degrees. (one mechanic said keep it at the original 8 degrees since that is the original 1977 305 engine. Thanks,,,
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Start at 8 and see how it runs. You might be able to even get 10 or 12 out of it.
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Thanks, I will. Also, what are the symptoms of an engine when it is set too far advanced, and too far retarded? How will it run each way?
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Thanks, I will. Also, what are the symptoms of an engine when it is set too far advanced, and too far retarded? How will it run each way?
Too retarded will make the truck gutless. Too advanced can cause pinging under load.
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Ok, got it. Thanks for the help. I have an original 1970's sears light and the old dwell tach. Should be fine..
Will post results.
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Wait, for what reasons would I want to get 10 or 12 degrees BTC out of it???
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Wait, for what reasons would I want to get 10 or 12 degrees BTC out of it???
More power, better response better fuel economy.
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^^^ x2. More advance is always better, right up to the point where you get knocking. This will normally be at low rpms, high load, and high throttle settings, like trying to start from a stop on steep hill and putting your foot in it, so that's how to test for it. I am running my 350 at 16* BTDC. The difference in performance is awesome.
BTW, that's what modern computer controlled cars do. They use the knock sensor to run the ignition timing right at the knock limit.
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Great, that's what i'll do then. Which way advances the timing, turning clockwise or counter c.?? Thanks
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Great, that's what i'll do then. Which way advances the timing, turning clockwise or counter c.?? Thanks
Counter for Advance
Clock for Retard
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Ok, just set idle to factory specs w/dist. vac plugged, put a light on the scale while at 500 rmp and advanced to 10 degrees BTDC. Factory specs calls for 8 degrees, took for test run and she seems very smooth and peppy...(for a 305 anyway). So, will I be okay having it advanced 2 degrees? Thanks,,and by the way, what does the pinging or knocking sound like when and engine is too far advanced. Is it very noticeable? Thanks again.
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If it knocks you will hear it. Sounds like it says...
Your perfectly fine +2 degrees probably be ok at 12 but stick with 10 for a bit and see what you think.
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Ok, sounds good. Thanks for all help. Next project: Valve seals! :-[
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i don't think 4 vs. 2 bbls in and of itself would matter for timing. Experiment to see which is best for your combo.
Also, based on my research and testing the quadrajet may not necessarily get better mileage than the 2bbl. Alot depends on how you drive and other factors.
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Well, i almost never open up the 4 bbls. I only putt around town. No towing or hauling. I have heard from many sources the 4bbl primaries are smaller than the 2bbl jets. I guess...
As i mentioned, factory it came with a 2bbl setup. I bought it with an edelbrock intake and carb that i believe was too big for the motor. It ran horrible. Now she runs real smooth, its quieter and has a bit more power. Big difference. And does a whole lot better on gas.
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Is it okay that the idle drops when we plug the vac line at the dist. When doing the timing?
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Yes
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Adjust your idle accordingly when setting timing, then readjust idle after unplugging your vac line and reconnecting to distributer.
You are removing vac advance when vac line is plugged to dist causing your idle to drop.
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Thanks,,,amazing as it seems, coincidently, plugging the vac line to the dist. just happens to bring the idle to 500 RMP which is just about the same as NOT plugging the dist. vac line and putting it in drive, which obviously drops RPM also. Does this sound normal?
I did set the timing while the dist. vac line was plugged and rpm was at 500 rpm, factory specs recommended. Gonna do a full test drive today.
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Thanks,,,amazing as it seems, coincidently, plugging the vac line to the dist. just happens to bring the idle to 500 RMP which is just about the same as NOT plugging the dist. vac line and putting it in drive, which obviously drops RPM also. Does this sound normal?
I did set the timing while the dist. vac line was plugged and rpm was at 500 rpm, factory specs recommended. Gonna do a full test drive today.
Another tip.. vac advance for distributor on manifold not ported.
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Ok, what do you mean "not ported"? Vac line coming from carb base (below throttle plate) and connecting to manifold or dist.?
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http://forum.73-87chevytrucks.com/smforum/index.php?topic=28857.msg241110#msg241110
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Ok, what do you mean "not ported"? Vac line coming from carb base (below throttle plate) and connecting to manifold or dist.?
Ported is a vac line that sits above the throttle plates and only gets vacuum when the throttle plates open. Manifold means a constant source of vacuum no matter what the engine is doing.
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Ok, I understand fully. I probably have that nipple on the carb blocked off. It is on the carb right?
Also, I have a lot of connections on this M4ME carb. Sure would love to see a diagram as to what they are all generally for. The ones I know are the vac for the dist., pcv valve, exhaust to charcoal canister and in the back..the power brake booster. There is one nipple in the back on top center that I have blocked off, and two in the front that are blocked off, lower right and upper left, (facing the engine). Does this sound about right as far as my connections?? Thanks again.
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http://forum.73-87chevytrucks.com/smforum/index.php?topic=11934.msg89184#msg89184
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and MODEL M4MC/M4ME/4MV CARBURETOR (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_77_1977_Chevrolet_Light_Truck_Service_Manual.pdf#page=553)
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That's a major help? Thanks!!
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Ok, so which nipple on the carb is port and which is manifold?? And once I re-attach, do I need to make any adjustments? Wont the idle be low?
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rule of thumb if you have a port and at idle theres no vacuum that means its ported. if you have a port that theres vacuum at idle it manifold ;) but set your timing with the vacuum advanced hose plugged and set your idle the same way. then plug it in and youre good
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Now that makes sense! Hey, thanks again. BTW, that is how I did the timing and idle rpm.
ps. wow, over 8k posts, where do you find the time,,,,and w/family! Lord bless!
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Now that makes sense! Hey, thanks again. BTW, that is how I did the timing and idle rpm.
ps. wow, over 8k posts, where do you find the time,,,,and w/family! Lord bless!
wait i have family lol.
if you look at my "stats" (http://forum.73-87chevytrucks.com/smforum/index.php?action=profile;area=statistics;u=2948)
you will see most my post are between 12-2am
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Yea, amen brother! I say if I were single I'd have a barn full of hot rods and a heavy bank roll. But the Lord says, "Oh yeah, go ahead and try it!" I' guess i'll stay in his will and be happy with my little project 77 Bonanza. Amen.
Have a blessed weekend.
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yeah money is tight, but over the years ive gotten a couple good deals. none are hot rods but they do serve their purpose or they just have sentimental value
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Yes sir, amen. I fully understand that. Once this 77 c-10 is done, I'm just gonna drive it until something needs fixin. My next big project will be a 63 or 64 impala or chevelle. I just need to find one for a few grand that ain't a ball of rust. Supersport preferred!
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I have been watching youtube videos both in favor of and against porting the distributor vac line. So what's the truth and why?
I have a 77 c-10, 305 4bbl. All stock. Thanks,,
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read this
http://www.corvetteactioncenter.com/forums/c3-technical-and-performance/60830-ported-vs-manifold-source-vacuum-advance.html
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Great write-up! Makes good sense, and thanks!!! I should have looked back at your other post too and re-read it. This one...
http://forum.73-87chevytrucks.com/smforum/index.php?topic=28857.msg241110#msg241110
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yeah i wouldnt know much about this stuff without rich's help. he got us all started on it
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yeah i wouldnt know much about this stuff without rich's help. he got us all started on it
That's just 'cause I started messing with cars before 1968, so the whole ported vacuum thing was like WTH?
BTW, you don't need to plug anything. You can just pull the vac line off the carb, set the timing, and plug it back on. All you need is the engine to keep turning over, it doesn't have to run great for setting the timing.
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BTW, you don't need to plug anything. You can just pull the vac line off the carb, set the timing, and plug it back on. All you need is the engine to keep turning over, it doesn't have to run great for setting the timing.
Wouldn't this give you a vacuum leak and make the rpms higher than normal? At what point do you set the idle speed or do you set it when the v/a is being used?
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BTW, you don't need to plug anything. You can just pull the vac line off the carb, set the timing, and plug it back on. All you need is the engine to keep turning over, it doesn't have to run great for setting the timing.
Wouldn't this give you a vacuum leak and make the rpms higher than normal? At what point do you set the idle speed or do you set it when the v/a is being used?
Sure, but who cares? You are setting the timing, that's all. The spark needs to fire there. Got it. As long as the mechanical advance doesn't start to kick in, it just doesn't matter. Idle speed is adjusted once the timing is set and the vacuum advance is reconnected.
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dont know why ive always done it the other way, make sense this way also. guess it doesnt matter if the v/a if its on ported cause its not active at idle so with it unplugged or plugged the rpms would be the same.
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...As long as the mechanical advance doesn't start to kick in, it just doesn't matter....
X2
The RPM needs to be low enough that the spark doesn't advance from the weights moving outward. On the other hand, if the idle becomes erratic when the vacuum hose is disconnected, it's better to plug the hose.
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One more thing. I have to unhook the manifold vac line to the tranny modulator in order to loosen the dist clamp. Can i leave it unhooked when setting the timing? Thanks.
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Hook it back up or plug it.
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Will do, thanks!!