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will a 350 chevy fit in place of a 305


Guest bswenson1956

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Guest bswenson1956

I have a 1998 chevy silverado with a 305 vortex engine. Will a 350 vortex fit in place and all the 305 parts work. (itake manifold, transmission,ect

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I have a 1998 chevy silverado with a 305 vortex engine. Will a 350 vortex fit in place and all the 305 parts work. (itake manifold, transmission,ect

It's Vortec, not Vortex, and yes, it bolts in. Unfortunately, the injectors and ECU are different. You will need the parts for that engine displacement. Also, unless you completely install all the correct factory emissions equipment, this swap may not pass emissions testing in your area, if required.

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As I recall, the injectors MIGHT be the same, as the TBI units were of the same throttle bore diameter (but sometimes with a different base gasket . . . i.e., two specific holes rather than a gap joining them), BUT the chip in the computer would be specific to the 350. This would govern not only the ignition timing "map", but also the fuel curve and idle speed. I don't recall any specific differences in the guts of the transmissions, though.

In the later 1980s, HOT ROD magazine replaced a 305TPI V-8 in a Camaro with a 350. It seems like the injectors worked, but they had to change the computer chip to get the idle speed to be right. I know, that was a tuned-port situation and the pickup is a throttle body injection, but this just proves that the injectors might have enough flow capacity rating to handle the extra fuel needs of the 350 with no other changes.

You will ALSO need to check the specific sensors on the engine to see if they are the same (from GM, NOT an aftermarket situation) for things like EGR. I know the knock sensors for the 305s and 350s were different for many years, though.

Having it pass your state's emissions tests should be of extreme importance! Generally, you might well need to have a donor vehicle with a 350 (NOT a 3/4 ton rather than a 1/2 ton, for example, though, but an EXACT-THE-SAME donor vehicle) to get everything off of.

Here's an observation . . . a good running 305 is not that far from the performance of a mediocre-running 350. Therefore, you might better spend your money and time doing an exhasut system upgrade with the 305, keeping all catalytic converters in place, but possibly adding some emissions-compliant headers and a larger diameter pipe exhaust system "cat back". Some years used very large pipes from the factory and other years didn't . . . or large pipes in front of the muffler and small pipes afterward (which used to be a Chevy "trademark" of sorts).

Just some thoughts . . .

NTX5467

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Guest Jim_Edwards

I would believe those to be very good thoughts!

Given changes in sensors and on-board computers from one year to the next, even stepping out into a like setup one year either side can be a disaster. Hasn't been like the "good Old days" for quite a few years. Those "good old days" when if an engine would bolt up with no issues you could do just about any swap around you wanted. The day computer controlled fuel/air mixtures, EGR valves, and oxygen sensors entered the scene things just got a whole lot more difficult.

Jim

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As I recall, the injectors MIGHT be the same, as the TBI units were of the same throttle bore diameter

The TBI throttle bodies were the same for the 305 and 350, but the injector flow rates were different. Of course, this is irrelevant to this post, because the 1998 motors are CFI (central fuel injection) with the center injector module and the fuel pipe "spider" to the individual cylinders.

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The "central port injection" system, which first appeared on the Chevy S-10 4.3L V-6 motors, still has a flow rating just as any other fuel injection system will. I believe it's still a "batch fire" situation rather than "sequential", though.

Even if the 305 FI system might allow the 350 V-8 engine to start and run somewhat normally in normal driving, it could still be very lean under any kind of sustained power situation . . . which can affect many things, including the life of the catalytic converter. Sometimes, even small increases of engine displacement require changes to higher-flow injection parts for reliable performance.

Just some thoughts,

NTX5467

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