Vortec Head Retrofit Question

[74 Shortbed]

which limiting bushing do you spaek of? and what do i do if i need to add more?

It would be under the weights, that's if someone put one in there but odds are you won't have to mess with with that, one thing a ta time, set your total first and see how it works and go from there..

 

[jjewett444]

It would be under the weights, that's if someone put one in there but odds are you won't have to mess with with that, one thing a ta time, set your total first and see how it works and go from there..

finally got to mess with total i guess. set static to 18 degrees btdc which ran pretty good at light to part throttle but it started up great with just a touch of the key. also put in about 10 degrees of vac advance on top of that for a total of 28 deg at idle/part throttle/ high vac signal. HOWEVER, had about 30 deg with vac advance plugged off at 2K rpm and about 40 deg at 3000-3500 and this is with accel dizzy and the medium springs that summit racing makes. so i retarted static back 2 deg for 16 btdc and it doesnt start or run as good, like i have to pump it and crank it at same time for it to fire up. but i ended up with like 32 or 34 total at about 3000 or 3500 cant remember, and still absouletly no top end power whatsoever.wondering if i should put some stock gm hei dizzy springs into my accel unit for a try being as the ones in the accel and my summit recurve kit arent helping me at all and i have like 3 or 4 old gm hei's laying around

 

[77 K20]

I've heard a lot of bad things about accel products- so I haven't used them. If you have extra parts lying around maybe swap in a stock GM ignition module and the coil.
Or drop in the while GM dizzy if you could.
That would eliminate a ton of things.

 

[jjewett444]

well i had issues with the factory gm one so i bought the accel and i like it just trying to get my top end power. have a suspision it has something to do with timing somehow. unless a 3970014 worn stock 350 with stock smogger heads is more powerfull than my new freshly rebuilt 3970010 1975 350 with 906 vortec heads eddy performer rpm intake and comp 268he cam, cause after i checked just about everything im clueless and starting to think that lol

 

[MikeB]

A stock large cap HEI may not like the additional current required to jump a .060" gap. GM specified .060" for the HEI's first year (1974), but they had so many failures they changed it to .045", as I recall. I didn't read how the smaller gap affected your engine performance, but that would be very strange indeed for it to be noticeable.

"Vacuum advance plugged."
That's great if the throttle is always wide open! You have nothing to lose and everything to gain with 10-12 degrees vac advance. But choose the canister carefully, Many of the stock ones had as much as 25 degrees or more, which means you have to back way off on your total (initial + centrifugal), which of course is very bad for WOT performance. A very common mod is to limit the "pin travel" on the canister. Of you can use an AR12 / VC1835 canister.

The big thing with Vortec heads (besides very good flow at low-medium lift) is they only need around 32 degrees total advance because the flame front travels much faster than old school heads with D-shaped chambers.

I didn't read everything you tried, but this should get you in the ballpark.

12-14 initial
32 total, all in by 2500-3000 RPM
Now connect the distributor to a manifold vacuum port.
In the ideal world, you would have 10-12 degrees vac advance at idle. So that means 10-12 initial + 10-12 vacuum = 20-24 degrees at idle.

Vac advance should start to go away at 10-12" vacuum and be gone at around 7-9". The only real way to test it is on a bench with a vacuum tester like a MityVac. FYI, as I recall, 10 degrees advance = approx .120" pin movement.

 

[jjewett444]

A stock large cap HEI may not like the additional current required to jump a .060" gap. GM specified .060" for the HEI's first year (1974), but they had so many failures they changed it to .045", as I recall. I didn't read how the smaller gap affected your engine performance, but that would be very strange indeed for it to be noticeable.

"Vacuum advance plugged."
That's great if the throttle is always wide open! You have nothing to lose and everything to gain with 10-12 degrees vac advance. But choose the canister carefully, Many of the stock ones had as much as 25 degrees or more, which means you have to back way off on your total (initial + centrifugal), which of course is very bad for WOT performance. A very common mod is to limit the "pin travel" on the canister. Of you can use an AR12 / VC1835 canister.

The big thing with Vortec heads (besides very good flow at low-medium lift) is they only need around 32 degrees total advance because the flame front travels much faster than old school heads with D-shaped chambers.

I didn't read everything you tried, but this should get you in the ballpark.

12-14 initial
32 total, all in by 2500-3000 RPM
Now connect the distributor to a manifold vacuum port.
In the ideal world, you would have 10-12 degrees vac advance at idle. So that means 10-12 initial + 10-12 vacuum = 20-24 degrees at idle.

Vac advance should start to go away at 10-12" vacuum and be gone at around 7-9". The only real way to test it is on a bench with a vacuum tester like a MityVac. FYI, as I recall, 10 degrees advance = approx .120" pin movement.

Thank you for your help, i am running a accell large cap conventional HEI with the ac delco rapidfire 14 plugs meant for the vortec heads but when i gap them at .045 the truck runs like absolute **** and misses severley. with me cam, it likes 18 deg of initial without vac advance, and with vac advance 30 deg. i moved initial back to 16 deg. to limit my total to 32-34 because i do not know another way to do it, i would like to keep my 18 deg static if there is another way to limit total... and my plugs i noticed are a gray color, could i not be getting enough fuel at wot? sometimes it stumbles at quick wot if im in 1st gear.. carb is a edelbrock 1405 600cfm bolted on out of the box

 

[MikeB]

I have no clue why the engine runs bad with .045 plug gap.

It's unusual to need 18 degrees initial advance with your engine and cam. The best way to limit total (initial + centrifugal) to 32-34 would be to use stiffer springs, but start by replacing just one.

Are you sure the #1 piston is at TDC when "0" on the timing tab is lined up with the mark on the damper? And that the dots on the timing gears are lined up when #6 cylinder is TDC?

 

[jjewett444]

i know for sure that everything is timed correctly because i assembled the engine, and for initial break in/start up i was at 10 degrees on initial (vacuum advance plugged) and then when running add the stock vacuum advance to that (not sure what it was) since the i have added my new accell dizzy with adjustable vac advance and it just seems to idle smoother with more initial (16-18) deg in this case with my cam.. right now at 16 deg the exhaust really smacks my hand but smooths a little if i go 18. not sure if the cam will make it do that but with my stock cam my rule of thumb was always it should be smooth when hand it at tailpipe not smacking hand.. and as for the plugs, idk they are meant to be gapped at .060 so is there any that are the vortec length but are meant for a .045 gap? i tried the ac delco rapidfire 14 and the autolite

 

[jjewett444]

so i seem to have go it pretty much ok at idle and part throttle etc.. except for heavy to full throttle. in 1st gear (being a 700r4) it obviously pulls at WOT, however any other gear it literally seems to be slower than at about mid-throttle.. i have two of my own theories on this which i believe is either a timing issue or a fuel related issue.. i have never jetted my edelbrock 1405 600cfm carb (carb is stock out of the box) so my .454 lift cam matched with my vortec heads and edelbrock performer rpm intake should allow a ton of more air than stock 70s 350 right??? which should want more fuel i would assume. i have ac delco new stock fuel pump too.. i can take a pic of the plugs if needed, they are a grayish color on the entire ground part and grayish on the electrode as well.. anyone have any good thoughts on this???

 

[74 Shortbed]

Don't know if you're aware but the 700 has a wide spread between 1st and 2nd gear, and that will pull the motor down especially if you're out of the max torque range of the motor.

 

[Honky Kong jr]

Going lean?

 

[Crdude]

Going lean?

This is my guess. He stated his plugs are grey which is a strong indicator to being lean.

 

[HotRodPC]

Going back to the plugs question.....x2 on this:



The "L" in LTS is for LONG - very important. ("T" is for tapered). Vortec plugs require the longer threaded section. Plugs for older style sbc heads are too short. I didn't check the plugs you're using, they may be correct, but I just thought I'd stress this point. I could see the spark not being deep enough into the combustion chamber, potentially causing misfiring. I believe the mentioned delcos go from a 42 (colder) to 45 (hotter). I run either 44 or 43s in my Vette.

Tis True. And don't forget, as most think a HOTTER plug means more performance and it's opposite. A COOLER plug is better for performance so long as it's not to cool. Only time you want to run a hotter plug is on a tired engine with worn rings. The hotter plug will help burn off the oil and help with oil fouling plugs.

 

[4WDKC]

if it runs good with .060 gap why do you refuse to run it with that gap? Never been a fan of Accel, swaping in a known good GM dist. could also help eliminate a possible bad coil or module on the Accel.

 

[jjewett444]

if it runs good with .060 gap why do you refuse to run it with that gap? Never been a fan of Accel, swaping in a known good GM dist. could also help eliminate a possible bad coil or module on the Accel.

from what i have read online from multiple sources, the .060 gap is too wide for a conventional style (HEI) distributor. Maybe it is better for the computer controlled distributor engines from which my heads are from. and i had a stock gm hei that i removed because it was old and developed wear. the accell made it run a lot better but still didnt solve my wot issue.