I have a running 350 vortec in a 91 donor sierra. I was just wondering what all is needed to convert it to carbuerator, and if it was feasible, or should I just put it in with the throttle body? I have a intake and carbuerator off an old 350, and I was wondering if these could be re-used on the vortec block at all. Any advice appreciated. Thanks.
CK5
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350 Vortec question.
- Thread starter Streyker
- Start date
If the engine is the original in the 91 it IS NOT a vortec engine, those didn't come out until 1996. Now if it is just a 87-95 style TBI then you would need to swap a carbed intake on (might have to modify the 4 center intake bolts or buy the proper manifold for those years). Now if it is truely a vortec engine (96-later) then you need to buy a special intake manifold because the vortec engine only uses 8 intake bolts to hold it on and they pretty much go straight down whereas the 1995-earlier engines used 12 intake bolts and they were at an angle (72* IIRC).
greengiant0311
1/2 ton status
I have a vortec 350. With a carb how do I know if the intake is right?
Corey 78K5
1 ton status
What Scott said.
I have a 92 350 in my K5 with a carb. I just used an Edelbrock performer intake and hogged out the (4) center holes due to the different angle on the TBI heads. I made sure I used silicone on those bolts and made washers with an offset taper to make up for the difference in the angle. Everything else was just like any other 350.
I am not sure of the years but I do know that some Caprice Classics were made with center bolt/TBI heads and a factory four barrel intake on a 305. My dad had one a few years ago on a donor car.
Also keep in mind for anyone wanting to run a carb on a TBI engine. You will need to use an electric inline fuel pump on 92-95 engines as they were not machined for the mechanical fuel pump rod.
Corey 78K5
1 ton status
Correct. Vortecs do not have the four center bolts. Easy to spot and a dead give away.
I think GM performance makes a TBI manifold for a the vortec engines:
GM Performance Parts Vortec Intake Manifolds with TBI Intake Manifold - Vortec EFI - Aluminum - Natural - Throttle Body - Chevy - GMC - 5.7L
Brand: GM Performance Parts, Mfr Part#: 12496821
Not cheap though!
GM Performance Parts Vortec Intake Manifolds with TBI Intake Manifold - Vortec EFI - Aluminum - Natural - Throttle Body - Chevy - GMC - 5.7L
Brand: GM Performance Parts, Mfr Part#: 12496821
Not cheap though!
greengiant0311
1/2 ton status
I have an aftermarket Edelbrock aluminum intake. How do I find out what year my engine was made?
There should be a casting mark on the back of the block, right above where the transmission bell housing bolts to the engine.
Martin
Cornfield creations
1/2 ton status
I have a GMPP vortec 350, GMPP makes a quadrajet intake for the vortec heads. I believe edelbrock does too. 8 Bolts go straight down on the vortecs, also make sure you have a coolant bypass on them, vortec heads require it as they DO NOT have an internal coolant bypass as typical heads do. Must run a hose from the intake to the water pump.
MUST is an understatement. If you don't run a bypass, you will have a big problem with running HOT. I made this conversion about 10 years ago on my 85, and never learned about the bypass. I took those heads off twice thinking a head gasket or something else was wrong. All I needed was the bypass from the water pump to the intake front, like an old big block does.
greengiant0311
1/2 ton status
Do either of u hav a pic of what that bypass should look like? I don't think I have one of them. Now I'm worried thanks
greengiant0311
1/2 ton status
Ok what about the GMPP? I looked at mine today and it has a GM symbol and the race flag stamp on the intake
Cornfield creations
1/2 ton status
It's for the front passage. I used the port on top where the water neck would go. I just Used a straight neck housing and a hose for a newer 454
FINALLY someone that understands what I'm talking about. I discovered this some time ago myself, and I've asked others what their thoughts are, and no one seems to understand what I'm talking about.
Even though the two engines that my son and I have put Vortecs on haven't had any cooling issues, I've considered that something probably should be done for the thermostat bypass. The L31 had an external bypass so it makes sense that one would be needed when the heads are used on another application. What I've thought of doing is simply drilling the passage in the heads like the earlier heads had. That way it would bypass thru the water pump.
I would like to see how you guys are plumbing a bypass into the water pump. I know a lot of the short pumps have a plugged port in the top of them that was originally used for a bypass, but what about a long pump?
Even though the two engines that my son and I have put Vortecs on haven't had any cooling issues, I've considered that something probably should be done for the thermostat bypass. The L31 had an external bypass so it makes sense that one would be needed when the heads are used on another application. What I've thought of doing is simply drilling the passage in the heads like the earlier heads had. That way it would bypass thru the water pump.
I would like to see how you guys are plumbing a bypass into the water pump. I know a lot of the short pumps have a plugged port in the top of them that was originally used for a bypass, but what about a long pump?
GM stopped using the bypass (from water pump face to passenger side head through the block) even earlier than the vortec engine and there was no external bypass hose used. 
