305/350 swap

[4x4K5]

Do they have the same motor mounts? and will my flywheel work on a 350?
After my intense research, I am really considering it. But I want to know if it really is that easy?

[T-bone71]

Do they have the same motor mounts? and will my flywheel work on a 350?
After my intense research, I am really considering it. But I want to know if it really is that easy?

The motor mounts are identical on them both use the same mounts. The flywheel can be different- here are the differences Pre-1986 has a 2-piece rear main seal and an oblong/funny shaped mounting flange for the flywheel-Post 1986 gm went to a 1 piece rear main seal and a round mounting flange for the flywheel. The bell housing will bolt-up to either one and your accs. should be a direct bolt-up also as well as the exhaust.

Yes it is that easy, gm in there great wisdom (tongue in cheek) made the 305 and 350 externally identical and almost all of the outside parts will swap from one to the other. The insides are a bit different.

[4x4K5]

The motor mounts are identical on them both use the same mounts. The flywheel can be different- here are the differences Pre-1986 has a 2-piece rear main seal and an oblong/funny shaped mounting flange for the flywheel-Post 1986 gm went to a 1 piece rear main seal and a round mounting flange for the flywheel. The bell housing will bolt-up to either one and your accs. should be a direct bolt-up also as well as the exhaust.

Yes it is that easy, gm in there great wisdom (tongue in cheek) made the 305 and 350 externally identical and almost all of the outside parts will swap from one to the other. The insides are a bit different.

Ok thanks. The only thing that sucks is my k5 is 1986. Which is like the last year they made carbs, and I dont want to switch to fuel injection because I dont want all the extra stuff. I just want a easy to tune carb, no ecu, and no 02 sensors. Does anyone have a 350 laying around for a good deal?

[T-bone71]

A carb will bolt onto either motor w/ the correct intake. You don't have to go to efi if you don't want to. You could actually run vortec heads if you wanted to w/ a carb w/ the correct intake.

Oh by the way I love my tbi fuel injection, starts great, runs great, up hill, down hill, off camber, on it's side, and pointing to the sky almost on it's rear bumper, as long as i had oil pressure i let it run and never missed a beat.

[4x4K5]

If I can find the right intake manifold style for the vortec heads, I will run them. I just need the 350 before I change my plans.

[jkillion]

Check craigslist. I see em on there pretty often. a 350 is a real common motor, so you shouldnt have too much trouble finding one.

[CarolinaKid]

I would like to clear up some misconceptions about the 305 vs. 350. The ONLY DIFFERENCE IS IN THE CYLINDER BORE!!! The crank stroke, main journal, rod journal, and connecting rod length are all the SAME!!!!! As a matter of fact the cast iron cranks most commonly found in both engines have the SAME casting numbers! Imagine that! Everything inside EXCEPT FOR THE PISTONS are identical! Cranks and rods WILL interchange. The only exception being one or two piece rear main seal cranks. You have to keep the same style rear seal. The 305 did not suffer from any more problems than the 350. Don't take my word for it, look it up. Even better take the crank and rods out of 82 305 and put it in a 86 350 becouse the 86 spun the bearings. Then tell me how different they are.

[4x4K5]

I would like to clear up some misconceptions about the 305 vs. 350. The ONLY DIFFERENCE IS IN THE CYLINDER BORE!!! The crank stroke, main journal, rod journal, and connecting rod length are all the SAME!!!!! As a matter of fact the cast iron cranks most commonly found in both engines have the SAME casting numbers! Imagine that! Everything inside EXCEPT FOR THE PISTONS are identical! Cranks and rods WILL interchange. The only exception being one or two piece rear main seal cranks. You have to keep the same style rear seal. The 305 did not suffer from any more problems than the 350. Don't take my word for it, look it up. Even better take the crank and rods out of 82 305 and put it in a 86 350 becouse the 86 spun the bearings. Then tell me how different they are.

I knew that the only difference was the bore size, but these other guys are making it seem like I am just wasting my money bulding my 305. I was on wikipedia the other day, and they said that both motors stock can handle about the same power. Now that I have a second on what I read, I might rethink all that hard work of swapping. After all mine is already bored to 310, so its not to much smaller. Only like .300ish difference between mine and a stock 350, plus I have forged pistons that are good for boost. plus I am running 8.5:0 CR right now.

[CarolinaKid]

That 305 will handle and make nearly the same amount of power the 350 will. My tbi 305 will run down most 350's, especially if they haven't changed cams.

[4x4K5]

That 305 will handle and make nearly the same amount of power the 350 will. My tbi 305 will run down most 350's, especially if they haven't changed cams.
see man, that is what I was thinking, because my buddy has a foxbody mustang, and he said he could run down 351s. I knew that it was not worth the swap, and I think I will stick with my 310, and show some people a nice and fast k5.

[ogrerick]

I've been watching this thread, telling myself that I would keep quiet and not say a thing. Lied to myself again! If you consider the bore vs. stroke ratio for the 305 you will see that having a bore smaller than the stroke does not allow for enough breathing. If you have it in something lightweight, don't want it to rev, and are looking for something that will run at 2,500 rpm or less the 305 will not give you much trouble. Compare the old 307 to the 305. Because the bore is bigger and the stroke is smaller than the 305, you can build a 307 using the same parts as the 305 and the 307 will be stonger. The 302 and 327 are other examples of the bore being larger than the stroke. Take some time to read Lingenfelter's research. However, there is no substitute for cubic inches. The 350's bore and stroke work better together. Put a stroker crank from a 400 and you will get even more torque. 305 heads have small ports and small valves. With a 4bolt 350, add some Vortec heads with the new beehive springs, a high lift short duration cam, intake for either 1,000 - 5,000 or 1,500 - 6,500 rpm depending what you'll need. Chevy Hiperformance built a Goodwrench 350 and made close to 400hp. Check out their site, the tech section, type in Goodwrench 350. Switching out motors is not hard, can be done in 8 hours if you don't goof off. If you're not comfortable switching them out, with as common as the sbc is you should easily find someone to help. $ for $ the 350 just makes more sense.

[T-bone71]

see man, that is what I was thinking, because my buddy has a foxbody mustang, and he said he could run down 351s. I knew that it was not worth the swap, and I think I will stick with my 310, and show some people a nice and fast k5.


Not w/ a 305 you won't, and not on a reasonable budget. Here you go--- My .040 over built 350 (currently in my rig)will may make as much or more power and torque and a 305 built any way dollar for dollar. If your building a high rpm motor that could use the boost of a turbo or two, then go ahead $$$$$$$. The mustang arguement is completely different, 2 different vehicles -a lite weight car-vs- a heavy K5 w/ a granny geared trans. If what your saying is true then let me say this in the performance world why is everybody working for more cubic inch, even in the ricer world they are doing it in small packages and big budgets. One more thing to consider, twin turbo 305 the machine work required to make that block handle that forced induction will be considerable and not come apart like a hand grenade. You will need to upgrade to 4 bolt mains as 305's did not come w/ them, and if your going to spend that money go ahead and go w/ splayed caps because your going to pay for the machine work anyway. With forced induction the extra forced placed on the crank during boost will cause the crank to move around in the bearings and chew the bearings up. While the motor is out and down spend the money to have the rotating assy balanced so it will be less likely to stress and fatigue w/ the extra force placed on it. The list goes on and on and on. It's your rig and your money, but there is alot more than just throwing on a couple of turbos on a motor and it going to live for any amount of time.

[jkillion]

Ive been thinking about this alot here lately. Is the whole goal of building this motor because you don't want to take it out of the K5? If so, I think you are going to have one hell of a time crawling around under the hood trying to swap a cam, etc to get this motor the way you want it.

If you are going to take the motor out and put it on the motor stand and build it from there, then why not just build a 350 on a motor stand. Either way, the motor will be out of the truck, so might as well do a swap.

If your goal is to build up a 305 or 310 or whatever kind of as a proof of concept that you can have a 305 run like a 350, then thats fine, you should go for it.

What I am saying is this. An engine swap will take 8 hours. If you build the engine on an engine stand, itll take probably 8 hours or so (maybe less). If you build the engine in the actual truck, then i feel it is going to take at least 20 hours, a lot of frusturation, cuss words, loss of motivation, and thrown tools.

That being said, I live in an apartment complex, so yanking the engine out is not an option for me. I don't know about your situation, but swapping an engine might not be an option for you either.

Just my .02

[4x4K5]

I just want to built the 310 to show that the 305 will run down a 350. We wont have to much troubl without pulling the motor. I built my blue chevy motor still in the truck. The only thing I didnt put in the 350 was the high compression pistons, rings, and crank. The whole top end was done in my driveway. Now we have somewhat of a decent shop that just got set up, s I have adequate supply of any tool you can think of. To put the cam in the 305, all I have to do is drop the radiator and slide it in through the grille.

[4x4K5]

ok so now I guess I am looking for a different motor. If anyone has anything they are looking to trade or sell let me know.
I can trade my tires(33 TSLs), rims, 310 v8, and put cash on top if the right deal comes along.

[jkillion]

If you are lookin for a 350, try craigslist. I just did a quick search and quite a few came up... Anywhere from $200 bucks to $1800 (crate motor).

[4x4K5]

I been looking quite a bit also. I just figured I would ask here because I have 51k origional miles on my 310, and I thought someone might want one, and be willing to make a deal

[79k5]

that would be a nice motor to put in a jeep. i bought a long block for mine for $1200 and added goodies that i already had from a 307 that was in it. dad just bought and old cj5 with a 232 in it and im trying to talk him into putting the 307 in it. good motor, not enough power for the k5

[4x4K5]

that would be a nice motor to put in a jeep. i bought a long block for mine for $1200 and added goodies that i already had from a 307 that was in it. dad just bought and old cj5 with a 232 in it and im trying to talk him into putting the 307 in it. good motor, not enough power for the k5

Its yours if you got a bigger SBC, I will even it out too. You can hear it run before we pull it. Hell, you cane even drive it.

[79k5]

sorry only other motor i have is a built pontiac 400. im looking for a 67/68 firebird to put it in

[Runt90]

Freind of mine has a 96 or 97 ( not sure off the top of my head ) Vortec 350 for sale. I think he was asking $750. PM me if your interested, I am sure he will deal.