So my 350 swapped 87 firebird has a broken crank. Having a hard time finding a replacement motor as i wanna drive the care rest of this year. It was originally a 305, did someone likely tune the carb or did they just swap a 350 in it and drove. I ask because there are many available 305s by me but very little 350s. Just want it to cruise the rest of the year so im not worried about power. Thank you!

 

No idea what "somebody did". Impossible to even guess. Could have been absolutely nothing, could have botched everything they touched, could have created a masterpiece. No way for anybody out here to even GUESS, let alone know, what "somebody did" to a carb via a picture of a broken crank & main cap.

That said, the easiest thing they could have done is NOTHING, so that's the most likely. And is usually entirely satisfactory if the cam in the 350 is moderate enough. If you want to re-downgrade your car, odds are, it'll work fine. Or in any case, won't be the thing most limiting the new combo's potential.

That's an interesting catastrophe BTW. Cranks hardly ever break in the middle; the most normal place for that is the same spot as that except at the front where the #1 & 2 rod pin meets the throw.

 

I guess im asking how different the tuning would be if I juat slapped in a 305 long block for the rest of the year while I build a 350. Not sure what or if anything was changed just trying to get it together to drive.

 

Different from what?

"Different" is a comparative word. It requires a known quantity to compare something against. Since you don't know what it is now, you can't compare it to anything else, including what it might need to be in the future.

Again, as already said, the tuning for a 350 doesn't need to be all that different from a 305, if the 350's cam was relatively moderate. You haven't told us. Hopefully the carb hasn't already been butchered somehow. You haven't told us that either, if you even know. Butt, if the 350's cam was mild, and it ran OK on that, then it'll run OK enough on a 305. No way to know HOW "OK" until you do it. Since you say you're "just trying to get it together to drive", it might be suitable enough for that. No real way to know.

 

I get it, im in the same boat, bought a mystery car but love these body styles and they are affordable. Im learning but everything seemed in tact and nothing was hacked. All I know is it was a 305, then was swapped to a 350 and the crank broke, so ill do some reading in my manual they should arrive in the mail and try see if I can spot the differences. Block that came out was a 5.7 but not sure if it was cammed. For sake of time I may just pull the trigger on a cheap 305

 

More or less what the difference is between the two engines tunes in stock form.

 

Negligible.

The way a Q-Jet works, it's almost completely CID agnostic. The main thing that affects its operation is the cam, specifically, the resulting idle intake vacuum. Acoupla other minor differences are in the secondaries: one intended for 305 use has a lump of metal cast into the secondary venturi area, that prevents the air valve from opening fully; and the air valve spring is tighter for a 305 since it needs to be richer under those conditions. Neither of those things materially affects "driving around" though.

 

Since GM never offered a CCC, carb'd 350 in anything that I am aware of, (and certainly, not in an F-bod), then the "difference" is entirely unknown.

If they HAD but a CCC carb'd 350 in an F-bod, the difference in the tune from a 305 would have been indistinguishable to any driver of such vehicle. The difference would have been entirely to meet emissions criteria that we don't have to meet, and don't care about. So, like Sofa said; "negligible".

Put in a 305 and run the wee out of it until you find/get a better solution.

 

This all has helped make my decision, seem to be a few decent options in my area, and then itll be nearly original as it came with a 305. Im not sure the likelihood of my 350 being saved but a main cap bolt extraction and a replacement cap plus machine work may happen this winter. Thanks for the replies!

 

Good luck. Stay away from L03 305's, and I'd think that you could buy a decent 350 block cheaper than you could machine that one, but that depends on how you want to handle it.

 

One im looking at Friday is out of a 85 camaro, said to run good. What years would be ones to avoid?

 

This is very true as far as I also am aware.

All I can do is extrapolate from non-CCC ones from earlier years. For example 7029202 (69 350 Q-Jet) works well on everything I've ever put one on, from 283 to 454, with only very minor tweeeeking. Same for Holley 6210. Carbs in general are like this, at their core, anyway; for example, the Holley 3310 was used on the highest performance 427, 327, 302, 396, and 350, from 65 to 71. Might even have been used on 454, I don't recall what those had (not talking about the truck version of course). Most of the "lore" about carbs being different for different CIDs is bull plop to begin with.

 

Good to know, I plan to learn these carbs when the manual comes.