Vortec Head Retrofit Question

[jjewett444]

Would jetting the carb richer be at all beneficial to my wot power or lack of?

 

[4WDKC]

If it runs correctly with the .060 gap then the coil can make the arc. Possible the coils have improved greatly since 74. An aftermarket coil should also have more output which should be able to make the arc.

 

[jjewett444]

i think i come to the conclusion that either vortec heads or comp 268h cam suck

 

[4WDKC]

HI guys, i thought this was the appropriate section for this thread so here i go.
After searching every forum i can find about what plugs and gap for the vortec heads on a gen.1 block everyone is saying .045 for the average gap. well i have a '75 350 .030 over dish pistons 906 vortec heads performer rpm intake manifold edelbrock 1405 600cfm carb and stock manifolds with true duals. truck only seems to run correctly with .060 gap which is the required for the 96-00 trucks however it is said to be too much gap for non computer hei dizzy. tried with ac delco rapidfire 14 plugs and autolite 605 both at .045 and absolutely no power and misfires.. anyone at all have any real expirence with this setup or reccomendations? thanks in advance

-Jim

You say it runs good with .060 gap why are you fighting it?

 

[jjewett444]

it does at idle and cruising at part throttle. I was under the assumption that a fresh rebuilt 350 with vortec heads, a comp 268h cam edelbrock 600cfm carb, performer rpm intake manifold and 2.25in true dual exhaust would make more power than a bone stock 350 with smogger heads and many miles and probably a worn cam.

 

[4WDKC]

it does at idle and cruising at part throttle. I was under the assumption that a fresh rebuilt 350 with vortec heads, a comp 268h cam edelbrock 600cfm carb, performer rpm intake manifold and 2.25in true dual exhaust would make more power than a bone stock 350 with smogger heads and many miles and probably a worn cam.

It should, the vortec heads flow better then older heads, have you changed anything on the carb? It could be lean not making any power but not lean enough to backfire. for example my TBI when I do vortec swap will require upping the fuel pressure from the 9-12 psi GM specs for the TBI heads to 18 PSI and adding alot of fuel to the tables to run correctly.

 

[jjewett444]

It should, the vortec heads flow better then older heads, have you changed anything on the carb? It could be lean not making any power but not lean enough to backfire. for example my TBI when I do vortec swap will require upping the fuel pressure from the 9-12 psi GM specs for the TBI heads to 18 PSI and adding alot of fuel to the tables to run correctly.

i have not changed anything on the carb except for converting the choke to electric.. would it be worth the money getting a edelbrock jet/metering rod calibration kit? i will snap a pic of the plug color and post tomorrow if it will help with this. thanks

 

[MikeB]

I was under the assumption that a fresh rebuilt 350 with vortec heads, a comp 268h cam edelbrock 600cfm carb, performer rpm intake manifold and 2.25in true dual exhaust would make more power than a bone stock 350 with smogger heads and many miles and probably a worn cam.

Yes, like at least 25% more power from 1800-2000 RPM up, and maybe even 40%.

The 268H cam is not your problem, assuming it was installed correctly and the valves were properly adjusted. And a stock 1406 carb should at least put you in the ballpark. I have run several on engines with similar and bigger cams. Is the carb new?

 

[4WDKC]

Yes, like at least 25% more power from 1800-2000 RPM up, and maybe even 40%.

The 268H cam is not your problem, assuming it was installed correctly and the valves were properly adjusted. And a stock 1406 carb should at least put you in the ballpark. I have run several on engines with similar and bigger cams. Is the carb new?

The original post said 1405, isn't that an economy driven carb? Definitely get pics of the plugs, having a carb tune kit on hand wouldn't be a bad idea. If the carb has set for any kind of time, make sure the secondaries are opening, floats are working correctly, etc.. How old is the fuel pump and can you check the pressure from it?

 

[74 Shortbed]

The original post said 1405, isn't that an economy driven carb?

Nope, 1406 is the economy, 1405 is performance..

 

[gpmorgan]

Did you get a cam kit with new springs? With any performance oriented engine I've had, I always eliminate the vacuum advance and run light springs. Initial at 14 to 16 and total around 35. All in by 2500 to 3000. Fuel economy will suffer without advance but that is expected with performance. Crank that timing up until she rattles and back down a couple degrees until it stops. Set it till it runs and cranks the best. If those plug like 60k, run them.

 

[jjewett444]

Did you get a cam kit with new springs? With any performance oriented engine I've had, I always eliminate the vacuum advance and run light springs. Initial at 14 to 16 and total around 35. All in by 2500 to 3000. Fuel economy will suffer without advance but that is expected with performance. Crank that timing up until she rattles and back down a couple degrees until it stops. Set it till it runs and cranks the best. If those plug like 60k, run them.

i need my vac advance, along with my 700r4's overdrive; truck is a daily driver. somehow it ran a little better today because i turned timing down to 12 deg, and ran 89 octane with 10 percent ethanol.. might try to bump it to 14 tomorrow and see what it likes. if i go too high it will ping cause i cant fing the correct weights and center plate for my accell to limit my total. BTW it still falls flat at full throttle, only power i get is if i hold it at 1/2-3/4..

 

[4WDKC]

i need my vac advance, along with my 700r4's overdrive; truck is a daily driver. somehow it ran a little better today because i turned timing down to 12 deg, and ran 89 octane with 10 percent ethanol.. might try to bump it to 14 tomorrow and see what it likes. if i go too high it will ping cause i cant fing the correct weights and center plate for my accell to limit my total. BTW it still falls flat at full throttle, only power i get is if i hold it at 1/2-3/4..

Did the previous setup make power to redline? I am wondering if maybe the pump is weak and cant keep up with the new fuel demands.

 

[jjewett444]

i was better at full throttle and that was to be expected from that engine. pump is new ac delco one i got from i think rockauto or summit or one of them.. will try and get plug pics tonight

 

[jjewett444]

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pics of number 3 and number 6 spark plugs i randomly took out