[enduro54]

Do i need new injectors? Also, do I just need the injectors or do I need a whole new throttle body?

[DoubleVision]

You`ll need a 350 knock sensor, 350 injectors, a 350 ECU. There`s something else you`ll also need but I can`t recall it now off the top of my head.

[crussell85]

the tbi's are exactly the same, they are even the same on the 4.3 liter v6's. just swap the engines don't worry about anything else. Everything is the same except the bore sizes of the engine.

[oldbogie]

Originally Posted by enduro54

Do i need new injectors? Also, do I just need the injectors or do I need a whole new throttle body?

Actually you need the computer or the computer's chip for the 350. The 305 and 350 use the same TBI. That said there's quite a range of injectors for both depending on what car (including cop) or model truck the engine was destin to go into.

As for size changes to flow in the TBI you need to think about all that's been done to 350. Cam, head, compression, exhaust changes; those things that change the mass flow thru the engine and those things that effect the factory's relationship of manifold vacuum (referred to Manifold Absolute Pressure or MAP in things you read about this stuff) to throttle blade position and RPMs. These are the primary three things the computer uses to calculate air flow passing thru the motor. Unfortunately the computation doesn't result in a direct number that's equal to air flow, but rather ends with a number of a block in which the computer goes to in order to select the fuel quantity and spark advance. When you do anything to change the mass flow thru the engine these measured relationships also change and often as not, the computer builds a block number that isn't compatible with what the motor needs. That said, a stock 305 to a stock 350 assuming both are light duty truck like a half ton; the computer will come pretty close and the thing will run. Often by installing a variable pressure regulator in the TBI, it can be tweaked pretty close. If you're also juggling cam timing, valve lift, head flow in and or out, or using a bigger bore throttle body, then a new chip needs to be programmed. Lots of places to have that done here's a few:

http://www.fastchip.com/

http://www.hypertech-inc.com/

http://www.tbichips.com/default.htm

http://www.superchips.com/

http://www.tpis.com/

Here's the Holley site;
http://www.holley.com/HiOctn/ProdLin...AV/STAVFS.html

Bogie

[M&M CUSTOM]

Originally Posted by crussell85

the tbi's are exactly the same, they are even the same on the 4.3 liter v6's. just swap the engines don't worry about anything else. Everything is the same except the bore sizes of the engine.

MIS-information if there ever was. . . the injectors flow at a different rate of pounds per hour of fuel at the same given pressure, and your poor advice would let me swap out a 4.3 TBI to a 7.4 engine- or the other way around and all would be fine, I think not. What about the 2.8 liter TBI, would you try to swap that without worry of problem too?

The knock sensors would not be an issue, some are listed as the same part number between the 2 engines, but not all applications, the ECM has specific parameters but for a TBI just a swap between a 305 and 350 with the use of the PROPER sized injectors (the ONLY real difference between the engines) as they flow differently between the 4.3 5.0 5.7 and 7.4 liter TBI units would be fine if everything else stayed the same.

The injectors from the factory were known to be as badly matched as 15% flow rate in the pair, you can use 350 injectors on a modified 305 but a new chip or programming controller would be needed. You cannot properly feed the needs of the LO5 350 engine with the LO3 305 fuel injectors as the flow rate would create a constant lean condition, and the injectors from a 4.3 would likely not give enough fuel to run without raising the fuel pressure well beyond what the entire system is designed to operate at which is a range between 8 and 14 PSI.

[enduro54]

Wow.... I thought the only difference would be the injectors. Are you sure my 91 chevy pickup even has a knock sensor? if it does, where is it and would I be able to use a old block for the swap? I have (2) 350 4 bolts. One out of an 82 truck and one from the 60's or 70's. They are both 2 piece rear mains obviously. Do I need a newer (1 piece rear main) block for this?

[M&M CUSTOM]

The knock sensors should be in the water jacket drain hole between cylinders 3 & 5 on the driver side and 4 & 6 on the passenger side just above the oilpan mounting surface.

You can use the older series block, but if your compression ratio and cam specs are much different from the LO5 350's specifications you will need a new computer chip made to be able to adjust to those differences.

[sbchevfreak]

The knock sensor is just above the oil pan rail, just foreward of the starter. Only one in the TBI chevys. Blue Streak P/N KS7. But you don't need to replace it. Just The PROM chip in the ECM, and the injectors

[enduro54]

I guess the cheapest way would be to find a chip from a truck that actually had a 350 in it, correct? if I did, would it matter that I'm putting vortec heads on the engine? I assume that would increase the compression a little.

I guess what I'm asking is, if I had a tbi 350 truck and put vortec heads and a GMPP vortec intake on it, would I need to get a new chip?

How is this much different than a putting a 3.4L in a 87 camaro that had a 2.8L originally? I did this to a car I used to have and did not need to change the chip. It was multi-port FI and had a MAF sensor, not a MAP.

[M&M CUSTOM]

Put it in and try, I have seen and heard both ways on needing a new chip, you just might lucky and the ECM not have a problem, as long as it sees what it wants and sends the info the injectors need to properly feed your engine that's all that really counts.

[crussell85]

[QUOTE=M&M CUSTOM]MIS-information if there ever was. . . the injectors flow at a different rate of pounds per hour of fuel at the same given pressure, and your poor advice would let me swap out a 4.3 TBI to a 7.4 engine- or the other way around and all would be fine, I think not. What about the 2.8 liter TBI, would you try to swap that without worry of problem too?

according to the title of this thread and the first post he is coming across that he is swapping a tbi 305 to a tbi 350 pretty much just needed a motor in a truck and that is what he has lying around or has found cheap. If it was me I would run the same tbi from the 305 to the 350 to the 4.3. Go to your auto parts store and ask for injectors for a 305/350/4.3 liter for the same vehicle with the different engines and I bet they sell you the same injectors for all three engines. I didn't say anything about a 7.4 throttle body. I said a 4.3 throttle body. the tbi setup is such a poorly designed efi system I wouldn't worry about fine tuning the thing. The fuel pumps that are in the full size pickups aren't really large enough to supply enough fuel to the 305/350 engines. That is why most of the time a 4.3 will keep up with them is because they are getting plenty of fuel because they are the same fuel pumps. If you want to put real fuel injection to it edelbrock makes a conversion setup to go from tbi to multipoint. If it was my vehicle and it was just a daily driver that your not looking for serious performance and your just looking to get from a to b just swap the engines, don't waste your money on chips and injectors and throttle bodies to fine tune it and not even notice a difference in the vehicle.

I think before we go any further with this post and end up arguing over this subject and not helping this guy out (which is why were all here right?) we need to find out what he is wanting to do with this thing.
What vehicle is this going in, what are you building or is it just a stock engine and your going to do a head swap on, what do you want to do with the vehicle?
If you are putting vortec heads on you won't beable to use the stock tbi intake you will need a vortec intake. Give us some more information to help you out with.

[M&M CUSTOM]

The injector part numbers are different from several different sources.

You are spouting BAD information that isn't followed up by any form of proof that the thing will actually work.

YES the injectors will swap between pods on the different throttle bodies but the flow rates for each size engine are the only difference between them all except the 7.4 having larger throttle bores along with a larger housing to allow that.

The rest of the TBI fuel system is exactly the same flow and pressure rate across the board, the injectors and ECM's are the only real differences.

READ a little before giving an opinion, I have and only repeat here what is found from several sources. Try Google, it'll give the same results I have.

[enduro54]

Ok, the truck is a 91 chevy pickup. the engine details will be:

350 4 bolt main 010 block. Not sure what years these were from. early 70s? or I have a 4 bolt 350 block from a 82 dumptruck either will be bored at least 30 over

stock crank cut .010
Probably stock rods
stock replacement cast flat top pistons
stock 062 vortec heads
Probably stock manifolds from the 91 truck
No smog in my area. Might keep a cat on it so the exhaust does not smell.
700R4 stock trans from the 91.

Truck will be used to tow a car now and then, I might put a snow plow on it, and will also be used to haul mulch etc. Just basic DD truck stuff.

[crussell85]

I don't care what anybody else says, you are not looking for high performance with the engine you are building. If you want to spend the money on tuning this thing to peak performance then do it. I am done here now but I will leave on this, if you run the 305 throttle body with the stock prom you will not notice any difference at all if you run a throttle body from a 350 with a prom burnt for your setup. If you call one of those places that burns proms they will probably tell you to run the stock prom and if they don't they will probably sell you a stock prom and the only difference you will have made to the computer is going from and old prom to the new prom. Just build the engine and put it in the truck with everything the same, I bet you it will run just fine. In fact I will GUARANTEE it. If it was my truck I would find a one piece rear main block at a junkyard.

[DoubleVision]

Was years ago a used to be friend of mine replaced the rod knocking 305 to 350 and no other changes. It ran fine in the low end but if you kicked it when it got to 4000 RPM it fell flat on it`s face and went into a bog. We did a plug chop and found it was going dead lean. He later swapped the injectors over and this helped a great deal but it didn`t entirely cure it. Next came a 350 ECM and a knock sensor and that cured it. I`m not saying knock sensors can`t be interchanged but it was my understanding they work off frequencey and if that`s the case there is different frequencey`s created by different bore sizes. With the 350`s bore being considerably larger and since knock sensors are cheap, I`d swap it.