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stock 305 4bbl vs crate 350 question

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Old September 12th, 2018, 8:25 PM
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Default stock 305 4bbl vs crate 350 question

good morning good day good evening wherever you may be
i have a couple of questions about replacing my 305 stock 4bbl quadrajet in my c10 with a 350 crate motor from gm (stock no major changes)
so the first question is in regards to the accessory changes (i.e. alternator power steering pump a/c etc) are they basically all bolt on or am i in for a shock
second can i use the 305 distributor in the 350 crate motor
third does anyone know what the initial timing set is prior to hooking up vacuum advance on the 350
so the plan is to bolt on a edelbrock performer intake and a 600 cfm holley carb
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Old September 12th, 2018, 9:25 PM
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Originally Posted by bulldogtt View Post
good morning good day good evening wherever you may be
i have a couple of questions about replacing my 305 stock 4bbl quadrajet in my c10 with a 350 crate motor from gm (stock no major changes)
so the first question is in regards to the accessory changes (i.e. alternator power steering pump a/c etc) are they basically all bolt on or am i in for a shock
second can i use the 305 distributor in the 350 crate motor
third does anyone know what the initial timing set is prior to hooking up vacuum advance on the 350
so the plan is to bolt on a edelbrock performer intake and a 600 cfm holley carb
Pretty sure everything will bolt up nicely. Good choice on the Holley 600 CFM Carburetor. The Quadrajet was only OK, but they never seemed to work well, and would lose tune way to easy. TDC is normal for timing, but it varies to a degree.
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Old September 13th, 2018, 10:28 AM
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thanks oil can henry for the reply so i only have one issue with bolt on parts so far the power steering pump needed to be spaced out from original bracket. anyways i have another question if you have the time to answer i read here alot about the setting of the timing and i think im confused or maybe over thinking it. the 305 motor has vacuum advance that comes from the carbureutor. i read in many areas that it is better to get vacuum from the intake direct is that true and why. the other question i have is with regards to the timing so i will disconnect vacuum advance and set timing to the same as the 305 or should i be altering that. i have started the engine now and it seems to be a bit lumpy at idle with the timing set to 4 degrees with vacuum advance working properly. i am just not a 100% happy with the lumpy rock of the motor it seems the timing is incorrect or again maybe im just over thinking it. th
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Old September 13th, 2018, 2:26 PM
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Originally Posted by bulldogtt View Post
thanks oil can henry for the reply so i only have one issue with bolt on parts so far the power steering pump needed to be spaced out from original bracket. anyways i have another question if you have the time to answer i read here alot about the setting of the timing and i think im confused or maybe over thinking it. the 305 motor has vacuum advance that comes from the carbureutor. i read in many areas that it is better to get vacuum from the intake direct is that true and why. the other question i have is with regards to the timing so i will disconnect vacuum advance and set timing to the same as the 305 or should i be altering that. i have started the engine now and it seems to be a bit lumpy at idle with the timing set to 4 degrees with vacuum advance working properly. i am just not a 100% happy with the lumpy rock of the motor it seems the timing is incorrect or again maybe im just over thinking it. th
Does the crate engine have the stock camshaft? Of course a higher performace cam will have a bit of "lope" to it As for the vacuum advance, they came stock from the factory, usually hooked up to the carberator outlet. I dont see why the intake manifold wouldn't work. Perhaps a somewhat higher, more central vacuum at the carburetor?
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Old September 13th, 2018, 7:14 PM
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Originally Posted by oilcanhenry View Post
Does the crate engine have the stock camshaft? Of course a higher performace cam will have a bit of "lope" to it As for the vacuum advance, they came stock from the factory, usually hooked up to the carberator outlet. I dont see why the intake manifold wouldn't work. Perhaps a somewhat higher, more central vacuum at the carburetor?
thanks again for reply as far as i know it is plain stock. i was wondering if you anthing about waht they call a timing tape for the harmonic balancer to ensure when the vacuum advance is working it advances to (what everyone suggests) between 32 and 36 degrees. i am assuming it is a tape that you zero out on the timing make and gives you the capability to see where the vacuum advance has taken the timing degrees to. is that correct or do you have any idea what i am talking about?
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Old September 14th, 2018, 2:46 AM
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Originally Posted by bulldogtt View Post
thanks again for reply as far as i know it is plain stock. i was wondering if you anthing about waht they call a timing tape for the harmonic balancer to ensure when the vacuum advance is working it advances to (what everyone suggests) between 32 and 36 degrees. i am assuming it is a tape that you zero out on the timing make and gives you the capability to see where the vacuum advance has taken the timing degrees to. is that correct or do you have any idea what i am talking about?
Yes, I know what you are talking about, but I have never used those. We'd simply mark the harmonic balancer out with yellow or white chalk, or similar, both at the TDC mark and were we expected the timing to advance to at the given RPM or load. Most people would advance till it knocked on the road, then back it off a bit more. Checking the vaccuum advance verses the centrifical advance was real simple. Just disconnect the V/'A hose, and plug it up to check for internal weight advance. Plug the vaccuum hose back in and watch it advance as well.

I didn't even need to know when my old Jeep CJ-5 blew the vaccum advance diaphram, as was very common with the Prestolite electronic ignition system distributor it had. The power-drop was easily felt, along with the gas-mileage drop too. The V/A part was cheap and easy to replace, and that old Prestolite distributor could take lots of water and keep on running like a champ!.
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Old September 14th, 2018, 11:50 AM
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Originally Posted by oilcanhenry View Post
Yes, I know what you are talking about, but I have never used those. We'd simply mark the harmonic balancer out with yellow or white chalk, or similar, both at the TDC mark and were we expected the timing to advance to at the given RPM or load. Most people would advance till it knocked on the road, then back it off a bit more. Checking the vaccuum advance verses the centrifical advance was real simple. Just disconnect the V/'A hose, and plug it up to check for internal weight advance. Plug the vaccuum hose back in and watch it advance as well.

I didn't even need to know when my old Jeep CJ-5 blew the vaccum advance diaphram, as was very common with the Prestolite electronic ignition system distributor it had. The power-drop was easily felt, along with the gas-mileage drop too. The V/A part was cheap and easy to replace, and that old Prestolite distributor could take lots of water and keep on running like a champ!.
thanks again for your post in digging a little deeper into my new purchase (the truck that is) i have found out that the previous owner bypassed the esc i did not realize till i was messing with distributor the ecm side of the wiring had a soldered jumper that goes to an internal under the dash esc in a little metal box above the parking brake assembly i have never seen this type usually they are located on the passenger side on the rocker cover. i guess because it is a us truck it is different tried to get a replacement with no luck two ordered both are the type i described earlier in this post. do you think that i could just rewire to the esc type on the rocker cover maybe get the wire loom albeit short from a junker and bypass? from what i can tell it just seems to be a different type of esc style. any ideas would be greatly appreciated. i really do appreciate your help and if ever you need any help let me know i have a lot of information i can dive into if needed.
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Old September 15th, 2018, 3:04 AM
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Originally Posted by bulldogtt View Post
thanks again for your post in digging a little deeper into my new purchase (the truck that is) i have found out that the previous owner bypassed the esc i did not realize till i was messing with distributor the ecm side of the wiring had a soldered jumper that goes to an internal under the dash esc in a little metal box above the parking brake assembly i have never seen this type usually they are located on the passenger side on the rocker cover. i guess because it is a us truck it is different tried to get a replacement with no luck two ordered both are the type i described earlier in this post. do you think that i could just rewire to the esc type on the rocker cover maybe get the wire loom albeit short from a junker and bypass? from what i can tell it just seems to be a different type of esc style. any ideas would be greatly appreciated. i really do appreciate your help and if ever you need any help let me know i have a lot of information i can dive into if needed.
I am not certain about your ignition system, bulldogtt. Is your's the stock 1985 HEI GM ignition system, or something else? Some of the 1985 GM motors were using a modified carburetor with electronic controls on some of their models of vehicles back then, before switching to the TBI injection, and a distributor that eliminated the poorly designed HEI ignition system, Many people were tossing the HEI units out into the garbage can,in favor of electronic-controlled distributors, they were so unreliable.
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Old September 16th, 2018, 3:40 PM
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Originally Posted by oilcanhenry View Post
I am not certain about your ignition system, bulldogtt. Is your's the stock 1985 HEI GM ignition system, or something else? Some of the 1985 GM motors were using a modified carburetor with electronic controls on some of their models of vehicles back then, before switching to the TBI injection, and a distributor that eliminated the poorly designed HEI ignition system, Many people were tossing the HEI units out into the garbage can,in favor of electronic-controlled distributors, they were so unreliable.
good afternoon oil can henry,
yes this truck has the infamous hei ignition system. the wires that were jumped are from the distributor and head to the drivers side and through the firewall and go to a metal box by the parking brake pedal behind the kick panel. i was shocked as usually as far as i knew the esc was usually on the passenger side rock cover area. i am finding out now that some but not all (go figure i have that type) esc were designed as an almost ecm style box with a circuit board. i haven't traced all the wires individually yet but will when i have time maybe i have a corroded or broken wire. i was wondering if i could use the common style and rewire to it as opposed to the style i have. so i tried a few times to add pictures sorry i am not a home computer guru i have no idea how to. anyways if you google the esc for a 1985 electronic control module you will see it is a little square module usually mounted on the passenger side rocker cover. you also may be able to find box style one in the same images search i found one but still i am having issues ordering one. again thanks for the responses sorry about the previous post i tried to incorporate pictures and it didn't turn out well.
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Old September 16th, 2018, 7:43 PM
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Originally Posted by bulldogtt View Post
good afternoon oil can henry,
yes this truck has the infamous hei ignition system. the wires that were jumped are from the distributor and head to the drivers side and through the firewall and go to a metal box by the parking brake pedal behind the kick panel. i was shocked as usually as far as i knew the esc was usually on the passenger side rock cover area. i am finding out now that some but not all (go figure i have that type) esc were designed as an almost ecm style box with a circuit board. i haven't traced all the wires individually yet but will when i have time maybe i have a corroded or broken wire. i was wondering if i could use the common style and rewire to it as opposed to the style i have. so i tried a few times to add pictures sorry i am not a home computer guru i have no idea how to. anyways if you google the esc for a 1985 electronic control module you will see it is a little square module usually mounted on the passenger side rocker cover. you also may be able to find box style one in the same images search i found one but still i am having issues ordering one. again thanks for the responses sorry about the previous post i tried to incorporate pictures and it didn't turn out well.
Hello bulldogtt,

I think this YouTube video might help us solve the prob;em with your ignition system. Yes, some ignition control modules were mounted in the engine bay, but it sounds like the original owner decided to mount it on inside your 1985 C-10. This is where some ESCM's were mounted back then, on the passenger side rear of the engine:



The original owner may have replaced it with an aftermarket unit, I am guesssing here, and installed it in the passenger compartment, cutting a hole in the firewall to run the wires. This YouTube video might be of some help in diagnosing your ignition problems too:

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