305 to 350 swap question

[Xrrider280]

yeah that's what i've read. I never tried it though.

[rpreston]

The 305 manifold is the same as the 350. The 305 injectors will work, but the diameter of the injector nozzle is smaller, so less fuel will go thru it as compared the 350's. Also the 350 chip has a longer pulse width to keep the injectors open longer. You can even use the 305 injectors AND the 305 chip and it will run OK, but you won't get all the power you should have. I bought new injectors from AutoZone. They were about 60 bucks a pop. I couldn't find a stock chip locally for mine so I wound up getting a Hypertech (also from Autozone) for 80 some bucks.

[profox02]

Ive Got A Jet Stage 2 Proformance Chip In The Truck....also A Helix Tower Of Power Tbi Spacer...can I Still Use These???....cause When I Orderd The Spacer It Says Its For The 305/350 Engine....so I Think Its Ok....i Dont Know Bout The Chip....what u guys think.......

[profox02]

also when i look for injectors for the 350 all i get is 305/350 injectors....so are they the same???

[rpreston]

The injectors are not the same. The nozzle size is larger on the 350 injectors. The helix spacer is no problem. I'm not familiar with the Jet chips, but if was specific to the 305 engine, again the injector pulse widths would be shorter. Most of the OBDI stock aftermarket chips change only the algorhythms used for the ignition timing in the different RPM ranges to gain HP and performance.

[profox02]

what do u mean "algorhythms"...what is that?..also i cant remember if the chip was just for the 305...if not i'll just get a new one for the 350...

[rpreston]

By "algorhythms" (don't know if I spelled that right?) is the term used for the "formula" the chip uses to set the timing advance. For instance, say the stock chip "formula "says "Hey, at this certain RPM level the timing should set to 18 degrees advanced." The performance chips algorhythm or "formula" will say that at that same RPM, the timing advance should be set at 22 degrees advanced for better performance and HP etc.

As compared to pre-pollution computer controlled engines, the factory de-tuned the engines to run on regular unleaded gas. If the timing is advanced to high running low octane gas you'll get spark knock. That's why most performance chips say to use 93 octane or higher. The chips set the timing for higher advance to gain power. If your using low octane gas, the higher advance can cause knocking and the computer will retard the timing till the knocks gone, thereby killing any performance gains.

[rpreston]

Maybe I could explain further. How do you gain Hp and performance from any engine? Its quite simple. The exploding fuel/air mixture is where the power comes from. How do you increase this exposion for more power? Add more fuel and air!
Thus you can go to a larger carb or fuel injector for more fuel and change the types of air handlers for a better mixture, add a higher and longer duration cam to keep the valves open longer to stuff as much as you can in the cylinder as possible AND get the burned vapors out, increase the bore to handle even more or increase the stroke to increase the compression (the more compressed the fuel mixture, the hotter and bigger the explosion), etc, etc.
OR, you can burn the fuel/air mixture you already have more efficiently. That's where the ignition timing comes in to play. Start the ignition process a little sooner and you burn more of the fuel mixture, getting a bigger explosion. That's what the new algorhythm in the chip does. Increasing the the amount of spark advance over the engines power curve increases the amount of fuel burned = more power. Up to a point...Not enough octane in the fuel + higher spark advance = spark knock and LESS power. Higher octane gas in itself does NOT increase the power of the explosion. What it does do is allow you to increase the amount of advance for a more effecient burn.

[profox02]

Ive Got Another ?...IS THERE A BOOK OR MANUAL TO DO A ENGINE SWAP.....OR ....DO I JUST HAVE TO DO IT AND IF THERE IS ANY PROBLEMS I JUST CORRECT THEM AS I GO...IM GONNA SWAP THE ENGINES THIS WEEKEND WITH A BUDDY THAT'S GOOD AT THIS STUFF BUT I HAVE NOT DONE IT YET....ALSO HOW LONG WILL IT TAKE ....(JUST 2 GUYS WORKING ON IT)....THX 305 to a 350..ohh yeah

[rpreston]

I think they give a pretty good description in the Haynes manual. It took me (by myself) a full day (8 hrs) to pull the old 305 out of mine. Depends on whether you have the right tools, good hoist, garage, air tools etc. Just make sure to mark all the wires etc before taking anything off. It wouldn't hurt to take a few good pictures under the hood beforehand, too.

[profox02]

Ok...sounds Good...thx.

[Xrrider280]

I have a question. I just put the second 350 in my truck in the last month, first one was defective, but I have noticed a large problem. When I step on it to accelerate it chuggs then if i hold the gas down it will go after a few seconds. My dad told me It may be the gas I am using from the local gas station. (Not very good gas). But, I never had a problem running that gas in my 305. Would it make a difference in the 350? I got myself the stock GM 350 chip, new cap, rotor, plugs and wires. I set the timing at 0 and everything should be in working order. Could it be the gas or should I try to advance my timing a little bit? Sombody please help. I am going to go into the closest city tom. and buy some 93 octane (for 2.13 a gal) and put in some IsoHeat and Injector cleaner to see if that does anything.