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305 heads on a 350.

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305 heads on a 350.

samoht samoht
I love my Chevy Chevette! | Posts: 1 | Joined: 11/13
Posted: 11/20/13
06:08 PM

im not going to bother searching through everything even though im sure this question has been asked numerous times. every thing I have found while trying to research this is people doing the opposite of what im trying to do, which would lead me to believe it should work, but I want to know for certain before I start on this. I have an 89 chevy 1500 4x4 that originally had a TBI 350 in it, the guy that had it before me put a burnt out TBI 305 in it, which has pretty much run its course, the motors got over 300,000 miles on it, and its falling apart. now I can get my hands on a 1997 vortec 350 with 150,xxx miles on it for free, and I need to know if I can just switch the heads and intake over, since from what ive seen the intake wont bolt up to the vortec heads. I would tear it apart and check myself, but if it wont work then my truck will be out of commission till I find a motor, instead of just a few hours. any help would be appreciated.  

wayne712222 wayne712222
V-6 Camaros rule! | Posts: 60 | Joined: 11/13
Posted: 11/21/13
03:54 AM

NOOOO!!!!!!!!!! there is a  MUCH BETTER WAY...

not cheeper. as the manifold is not cheep. but far superior..

a Vortec bolt pattern intake manifold for the TBI fuel injection..

what a way to go..  so much better air flow thru the vortec heads..

this makes it a perfect replacement..  every threaded port is there to bolt stuff back on..

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you can also.. go to a conventional vortec  bolt pattern 4 bbl intake and a tbi adaptor plate..  but you won't have enough holes to mount all the TBI stuff on most manifolds..

because i know TBI motors.. when you are going to perform the swap..  please examine the reluctor and pickup coil of the TBI small cap HEI for signs of cracked magnets..

please.. also .. check the ignition coil for signs of external high voltage leaks..

both of these can hurt TBI normal operation...  you might want to check those first.. as they can drive TBI owners crazy as they are not obvious failures..


this is a cardone reman distributor that replaces the GM design above.. and is far superior in design of the components



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please.. also check the TBI throttle shaft play... engine off.. grab throttle lever.. open throttle part way and wiggle.. if you have throttle shaft bore wear..

(o ) ( o)   instead of (o) you will have idle issues.. where it will want to stall and may have other issues like poor fuel economy and rough unstable idle..

this is because the throttle position sensor voltage has to come back to the EXACT SAME fraction of a volt.. usually 0.52 volts to 0.98 volts...

and.. please take the time and read the part numbers off the top of the injectors.. or look at the colors of the insulation pins where the injector connectors stick up.. there are a bunch of injectors.. and with a set of 305 injectors you won't be happy with the flat spot.. you will want to search out a set of 90/91 9C1 cop car 5.7 injectors as they flow slightly more than the conventional 5.7 and a lot more than 5.0 injectors..

if your replacement motor comes with oxygen sensors. with connectors and the pigtail.. you might want to actually think about using the HEATED oxygen sensors when you swap.. its a little more work.. but the monitoring of the air fuel ratio by looking at the percentage of oxygen left with a heated oxygen sensor is far superior.. usually 94/95 3 wire oxygen sensors from some 5.7 pickup applications are easier to wire.

lastly..  when removing and installing the TBI motor in this.. please get under the passenger side of the dashboard.. find the computer. unhook it..  unplug the other plug that feeds across the dash to the cluster..  pull the U clip off the elbow where the harness comes out of the firewall..  and push the underdash computer connector thru and lay it across the top of the engine.. this makes it much easier to install the replacement engine..  as there are grounds to remove on the back of the heads...

if your throttle body has a worn shaft..  there are places that will rebush them .. or new replacements might still be available..  and holley sells new ones also..

lastly.. install a SU102 coolant temp sensor and pigtail from autozone or wells .they go bad and cause issues.. under 20 bucks for the pair.

you have to have a 192F thermostat unless you are going to get a custom chip burned.. but the TBI is self tuning for the most part if everything is hooked up properly..

just trying to cover the bases..