I have a question about my 305 buildup...
Can I use a 350 crankshaft(the ones found in the Summit catalog)
that has the same stroke(3.45) as my 1989 RS 305.

Also, if it's possible, can I purchase a 350 crankshaft that has a bigger stroke(3.75)


What's the most I can bore on the 305. (Is 0.060 possible)

 

305's & 350's use the same crankshaft, so you could get a 350 crank for your 305. Also, you can use a stroker crank (3.75" stroke) in your 305 if it has been cut down to fit in a 350.

 

305 and 350 cranks have the same stroke, they are balanced didfferantly becaue the differance in mass of the rods and pistons. you can get cranks with more or less stroke that'll fit i na 350 block.

 

I've seen stroker kits for a 305, with a 383 crank, which makes for a 335. They can be had for $600 at: http://www.enginekits.com/.

 

Black92Z28,
What do you mean...I can use a stroker crank (3.75) for my 305 if it has been cut down to fit in a 350?

 

The 305 & 350 use a different journal size on the crankshaft in comparison to the 400. If you buy a stroker crank, basically what it is is a 400 crank that has been cut down to fit in a 350 block. If it will fit in a 350, it should also fit in a 305. If anyone else has anything to add, please feel free. I'm not an expert on this topic.

 

You got it. Aftermarket crank manufacturers make cranks for both 400 and 350 journal sizes in various strokes. If you look hard enough (and are willing to pay enough) you can find the parts you need for any combination, from mild to wild.

 

So what needs to be done to put a 305 crank into a 350 block?

 

A lobotomy is a good first step...

It has to be bored .030" over, typically (I've seen .040" over pistons for a stroker 305).

You have to grind the oil pan rails so the rods clear as they spin around. Rod bolts hitting cam lobes can be a problem, depending upon your cam.

You need externally balanced flexplate/flywheel and damper.

Makes a lot more sense to get a builder 350 block and put the stroker in it. 383 vs 334 CID, better bore-to-stroke ratio, better heads available. Building a 383 costs about the same as a 334, even if you have to buy a 350 block first.

 

You just have to have it balanced. Same stroke (3.48) but the weight of a 305 piston is lighter than a 350 piston.

 

I'm not looking to stroke. I have a 305 crank I also have a 350 block. I'm just trying to find out if I can use the two together. What I've read in my searches and here I can use the 305 crank. I just need to get it balanced with 350 pistons and have the journals messed with.

 

You don't have to have a crank balanced to the pistons. That's not how it works. Any weight pistons can be used on any crank.

What you do have to have the crank balanced to, is the weight of the big end of the rods. 305 and 350 cranks are often made from the same casting; but since 305 rods (in general, with a few exceptions) are thinner in critical areas than 350 rods, the cranks that come from the factory set up for the weenie rods have alot of metal shaved off the counterweights.

You can downgrade a 350 by putting a 305 crank in it, as long as you downgrade the rods at the same time. You can go the other way as well. You cannot turn a 305 crank into a 350 crank if you're using 350 rods, unless you put weight back onto the counterweights somehow; or you lighten the 350 rods rather brutally. You can however turn a 350 crank into a 305 crank by removing metal from the counterweights, by drilling or whatever.

So to answer your question, yes you can use your 305 crank in your 350 block with 350 pistons, with no further balance work required other than a normal trim-up if you want it, as long as you also use your 305 rods.

 

Exactly the type of answer I was looking for :hail: even if it's not what I'd prefer to do. Maybe I will just get a 350 crank. Was trying to save a couple of bucks.
Thanks!

 

Why would you put a 305 crank in a 350? Is it still a 350 afterwards?

 

Because I have a 350 block with no crank and a 305 crank with what may be a cashed block. The 305's in the car I just bought.
Looks like it'd still be a 350 just on the weak side. It's not going to be a track car it's just a daily driver.

 

Yes it will still be a 350. The 305 and 350 (and the 267 as well) all have the same 3.48" stroke.

 

I got crossed up somewhere. Thought I read "stroker" - excuse all of previous post, please.

 

OK maybe I see things different, but a rod is a rod. You balance by taking all rods and matching the weight at the small ends first, then the large ends. Then you match the pistons to each other, that makes your bob-weight card. All rods were the same till about the mid to late 70s thats when GM decided to switch to a lighter ,thinner rod on all V8's w/ 5.7 rods. Ive seen many engines come in with the pads differernt sizes at trhe small end yet still be balanced to each other. Now if you took a stock 305 piston from an 87 LB9 and a stock 87 L98 piston your going to see that the piston is about 50 grams lighter on the LB9, so the difference is in the pistons

Now lets say you took a 305 crank and used 350 LW pistons it comes real close to be balanced, with out adding weight to the counter weights.


To the best of my knowledge there is no such thing as 305/350 rods. Just talked to my father-in-law and he never heard of it either. All rods are weight matched to within 5 grams as per GMs specs.

 

Pistons don't rotate. You don't have to rotationally balance anything that just goes up and down to something that rotates. At any given moment, there are exactly equal numbers of pistons going up and down, at exactly equal speeds, so as long as all 8 are equal, that's all that matters. They could be one gram or 1000, it doesn't affect how things that rotate are balanced in the slightest.

305 rods are considerably narrower in the beam than 350 rods. I'd say they're around 80% as thick just as a guess. Somebody around here (maybe Jester?) has a great pic of the 2 sitting side by side; it's like real obvious which ine is which. Seems like they're different where the beam meets the big end too, much like 396 rods are different from 454 rods right there. Some of that mass appears as rotating (the closer to the big end it is, the more of it proportionally is rotating), and therefore has to be taken into account when balancing a crank.

Cranks that are factory-balanced to 305 spec usually have their counterweights cut down about 1/8" farther than 350 cranks, to make up for the lighter rods. Notable exceptions to this are at least some L69 motors; mine for instance came with "X" rods in it, same as 350 rods. That crank is still in use incidentally, except with PM rods now; and it balances up to them just fine.

GM's methods, at least a few years ago, was to take rods as they came out of the finishing process, and essentially put them in an n-dimensional array of boxes, each of which was to contain rods of a given length, big end weight, small end weight, total weight, etc. When one "box" got one engine's worth of rods in it, they would take a crank that came from a similar selection process, and assemble a motor out of those parts. They did not "balance" a motor, in the same sense that a machine shop does, at all. Rather, by selecting parts with known balance characteristics, they could run a production line without custom work being done to every one of millions of engines. I would assume that they still do something similar, that being the cheapest way to the desired goal.

That's also why a factory motor always seems to run smooth, but a motor built out of a bunch of rods from wherever is pretty hard to get right.

350s in the 70s came with at least 4 different rod forgings that I know of, each with its own unique weight. Those were the unmarked plain-vanilla ones; the "B" rods; the "O" rods; and the "X" rods. The ones with letters had .... letters forged onto them.

 

Here's a pic of one "X" rod, showing the beam. I don't happen to have any others laying around. If anybody has a 305 rod, take a good pic of it from the same angle as this, and let's compare the beam thickness.

 

Here's another that shows a side view, where you can see how the beam flares out where it meets the big end. Again, a similar pic of some other types of rods would be instructive.

 

what your pics are showing me is what I was talking about about during the late 70's all chevys came with the narrow rods, not just 350 or 305s.

Yes pistons dont rotate, but they are mass hanging from a rotating piece.



Here is a link for engine builder magazine, do search on "balancing" and click on the first item that comes up
here

That will explain to you a little more about balancing and how weights affect force.

Here is a pic of me at work. Im balancing a SBC

 

If you already have a 350 block, go that route. As for using the 305 crank, I would just but a cast 350 crank from Summit or something and be done with it. 350's are are strong motors the hold up to a lot of abuse, why weaken it with a 305 crank.

 

Its the same crank, even the casting number is the same on some 350/305's

 

Maybe the same crank, but a 305 is drilled more and lighted to give it less rotating mass.

 

yeah but drilling them does not make them weaker. Ive had to make some look like swisss cheese when a customer wants to run a LW piston. You can grind/drill on the counterweights all you want, on a 4 cylinder engines ive even ground the counterweights completely off.

 

So what's the verdict?

I'm with Viprklr...... I have a 350 block that I want to put in my third gen parts hauler ('83 Pickup). The truck has a 305 right now. I just want to yank the crank and rods from the 305 and install them in the 350 with new pistons, rings, bearings, etc.

Can it be done without paying out the butt on machine work to have everything balanced, or not?

 

you have to have it balanced if your switching from 305 pistons to 350 pistons.

 

Even if all the pistons (all the 350 pistons) match each other's weight??

Granted I'm no expert, but that would mean even if I replaced 305 pistons with 305 pistons (obviously not in the 350 block) and they were 20 grams heavier, I still have to have the assembly rebalanced??? That just doesn't seem right.

That sucks butt. I didn't want to spend the money to have that done. Looks like I may as well get a 350 crank and rods.

Sometimes the truth sucks big butt!! Not as much as throwing rods I guess.

 

Hey...... I just thought of another question.

What RPM do you balance the assembly at?

 

500 RPM is the industry standard

 

yeah, that happens quite often also, I balanced a 3.1 GM motor yesterday that the federal mogul .030 over pistons were 10 grams lighter than the stock pistons. And to top it off the whole piston/rod combo was lighter than my bob weights with no weight attached to them, I had to grind off about 6 grams per side.

 

Well thank you. I better understand what I didn't want to hear.

Seriously, I'd rather do it right than do it twice.

Thanks again.

 

I just talked to the machine shop yesterday and they told me 305 and 350 rods were the same. This conflicts with what I'm reading here. What's the deal? I'll be calling another machine shop to see what they have to say as well.

 

305 and 350 rods are the same. But starting in the late 70's they went to a thinner rod.

 

listen to aron. he knows what hes talking about.

 

Ok, just to make it known if your reading my post for more info on the topic stop now, I'm just commenting...You guys know your stuff! Regardless of whomever has it right you defenetly make it so you want to look into the subject more...I know I will be. I never even thought about rods and diff. cranks (nowhere NEAR enough money for any kind of swap like that yet) just wanted to say....well.....wow.....:hail: :hail:

 

I know what I'm talking about!!!!!

That don't mean I'm right, but I know what I'm talking about.

 

haha your an ***. you know what i meant

 

Yes, the 305 crankshafts are drilled. That is NOT what makes them weak. The crank itself is identical to that of a 350. But with all of the metal dilled out of the 305 crank, you have to use the thin rods to keep it balanced, and THAT is the weak point.

 

Your not getting it, you balance rods by the big end and little end, it has nothing to do with thick or thin rods, that was just a matter of years. If you go open up a early 305 you will find the "thick" rods. Call a 100 machine shops and you get 100 answers of there is no such thing as 305 rods. All 305/350 rods are the same.

 

i think ima call the machine shops and record the convos. so we can end this lil charade