thinking of a motor upgrade?

[d-nice]

I'm thinking of upgrading my 72 gmc Jimmy to a 350. I've seen motors on cl and other sites and they are advertised as 2 bolt or 4 bolt. What is this?? Is there a plug and play option for my project. Can I just match an engine to my existing trans?

As you can tell I'm a complete novice and was just hoping for some advice / direction.

Thank you.

[Critter]

2 bolt or 4 bolt refers the the number of bolts though each main bearing cap which holds the crank inside the block. Kinda hard to explain but here is a pic of a "2 bolt main" on top and a "4 bolt main" on bottom. Notice the 5 main caps that have either 2 or 4 bolts EACH.


You will probably hear many people talk negatively about 2 bolt mains when it comes to performance. Truth is unless you are over 500 HP a 2 bolt main shouldn't have any problems. What is happeing is a 4 bolt will have more clamping force to hold the crank in place. Once you start really hopping up an engine you put a lot of stress on those lower end components. Anyway, that is the basics but there is A LOT more to the discussion on the subject.

It might be a little too basic but there is good info here for someone learning engine basics.

As far as what engine will "plug and play" we need to know what you currently have, inline 6 cylinder, V8, auto tranny, standard, etc???

[d-nice]

(As far as what engine will "plug and play" we need to know what you currently have, inline 6 cylinder, V8, auto tranny, standard, etc??? )

Yeah, I guess a bit of info would help.


I currently have a v8 (307 I believe?) with an automatic transmission.

And thank you for the info and the pics!!!

[truckster]

Most of the parts will be a pretty straight swap. Of course, you probably have a 2-barrel carb, and if you drop in a 350 you'll want a 4-barrel, which will require a different manifold. You'll probably need a different starter and I don't remember but maybe a flex plate.

As far as 2-bolt or 4-bolt, I agree with Critter that you don't need a 4-bolt at least until you go over 400 hp. If you build a serious high-hp motor you're going to want a splayed 4-bolt, which is different from the factory 4-bolt. The factory 4-bolt has 2 bolts on each side of the main bearing cap which are parallel to each other. A splayed 4-bolt puts the outer bolts at an angle, which gives them more metal to hold on to. The truth is, for most applications, having a 4-bolt is just one of those things you say to impress fellow bench racers.

Bottom line: Its not a very difficult swap if you're at all mechanically inclined. If you find a good 2-bolt for a reasonable price vs. the price of a 4-bolt, I wouldn't hesitate to buy it.

[72gmcshorty]

Sorry to jump in here, but what years of motor are desirable now. I always see ls-1, lt-1, vortech this or that, basic 350 with carb, tbi, tpi, etc, etc. I will be looking for a motor soon and was wondering do any of these offer best bang for buck while maintaining some kind of fuel efficiency?

[pumpkin]

All depends on what you want out of the engine/ money you have to spend.

[old man jimmy]

sounds like you already have a different motor then came in it. So if matching numbers are not important to you. I'd just go to Chevy & pick up a new goodwrench 350. Put one in my chevelle a few years ago, and the older models were around $1100.00. But then you have a brand new motor with warranty. Probably still have to round up a 4 barrel and intake. everything else should drop right in.