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Just purchased a 90 YJ that was in the beginning stages of the v8 conversion, I have a 305 & 350 engine just wondering which motor is a better swap in the long run and what kind of milage i can expect when I'm done?
 

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350 hands down.

The 305 is about the same weight as the 350 with less hp an tq. The 305 was not one of GMs best ideas. The gas mileage increase with the 305 will negligible if any at all.

The 305 is nothing more than a boat anchor IMHO
 

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It also depends on the 350. A lot of the small port mid 70's 350's were no better than the 305. A bit more torque but still kinda worthless in stock form. Honestly your best bet is an ls motor. Most bank for the buck. You can get 5.3's with all the wires, ecm, and accessories for about 5-800. They are also very well suported.

A lot of the mid 90's truck motors are not bad either. Stay away from most anything from 75-87 IMHO unless you plan on building it up.

Most of the time I am unimpressed with a lot of 350 swaps. Yes the SBC is one of the best motors ever made but A lot of them are pretty weak.
 

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5.3 ftw. 300hp in stock trim aint bad at all.
 

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I don't want to be misunderstood here either. I think older 350's are great motors. If they are built. I have a 4 bolt lm block in my monte carlo. Thought needs to go into pistons, rods, and heads to get out of them what you should. But for the cost involved you can easily swap an lsx even with the wiring and adapters it's cheaper and imho more reliable and consistent.
 

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Just purchased a 90 YJ that was in the beginning stages of the v8 conversion, I have a 305 & 350 engine just wondering which motor is a better swap in the long run and what kind of milage i can expect when I'm done?
Both are good motors; depending on who you talk to as to how good. Generally speaking I have had little problem with either; they are both decent small blocks and fit the same in the hole. Lots of parts between the two are interchangeable too. Intake, heads, exhaust, carb, so that right there might help. If you dont like one motor, or you blow it up, you can swap right over to the other with very little changes.

Here is my assessment of the 305, its slow, and expensive to rebuild as compared to the 350. But on the plus side it is a tad better than the 6cyl, and most of your existing system can handle the power it creates.

The 350, lots of parts and accessories that make it wake up, very cheap, and decent to great HP if you want to build it up. Basically cheapest $ to HP than the 305. Stock is fine, but if you have a decent model, the HP could make you replace parts quicker.

Depending on how you drive, they both will probably be about the same gas mileage. I would guess about mid teens since the YJ is so light, and if you kept your foot out of it they could do a bit better than the 6. But I would suggest that is the absolute most if you were lucky. Tuning and gearing would really come into play with that.

In other words, I dont think you can go wrong with either depending on what you want your jeep to do.
 

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That helps for sure. The pistons in the older 350's were a big issue too. A lot of those motors had "8.5:1" compression but they actually ran closer to 7.6:1.
Yeah, early to late 70's motors were rated at the 8.5:1, but like you said once built you can really wake them up.

and parts are cheap, my master rebuild kit, upped to 9.X:1 comp, good heads and intake brought me up to 350HP. Kit was $150 plus shipping, and minimal machine work to clean up the block and crank.
 

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Well, in reality, any new heads except for the stock ones. :)

Agreed :thumb:

but vortec heads are cheap and plentiful. Pull a set of junk yard heads and run them. Yes you can get better with aftermarket but not this cheap. Good bang for the buck.

As for stock, there are lots of good stock GM heads out there, though few from the mid-late seventies, or early eighties for that matter. Unfortunately there is a lot of myth and misinformation out there regarding the SBC. Some heads out of the 70s are great with a little port work work. The smaller combustion cambers help to boost the compression a little to sqeeze a few more ponies out, but they usually suffer from lesser valves.

As for the OP, would you keep these engines stock? Do you know what year they are from? If not post up the codes off the block and we can decipher them for you, assuming I can find my book ;) You always have the option of dropping it in stock form and making some HP changes as funds permit.

Ultimately, if you have both a 305 and 350 handy, the 350 wins hands down in all categories.
 

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Dirttracker18 said:
Agreed :thumb:

but vortec heads are cheap and plentiful. Pull a set of junk yard heads and run them. Yes you can get better with aftermarket but not this cheap. Good bang for the buck.

As for stock, there are lots of good stock GM heads out there, though few from the mid-late seventies, or early eighties for that matter. Unfortunately there is a lot of myth and misinformation out there regarding the SBC. Some heads out of the 70s are great with a little port work work. The smaller combustion cambers help to boost the compression a little to sqeeze a few more ponies out, but they usually suffer from lesser valves.

As for the OP, would you keep these engines stock? Do you know what year they are from? If not post up the codes off the block and we can decipher them for you, assuming I can find my book ;) You always have the option of dropping it in stock form and making some HP changes as funds permit.

Ultimately, if you have both a 305 and 350 handy, the 350 wins hands down in all categories.
I have a site for codes... :)
 

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I figured there was one out there but I guess I am getting old now :confused:

I still go for my book :D

Mind sharing the site with me as I would love to have access to a good one.
Nastyz28.com

Guess what kind of site it is. :D
 

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I would go with the 350, you can go stock now. and do more down the road cam's. heads etc. I would just make sure the one you go with is a 4 bolt main alot tougher and can handle any more power you want to add to it.
4bolt is heavy duty, towing and dragging and the like; but honestly a two bolt is more than adequate for most applications.

For DD or generic 4X, I would not go out of my way to find a 4bolt.
 

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4bolt is heavy duty, towing and dragging and the like; but honestly a two bolt is more than adequate for most applications.

For DD or generic 4X, I would not go out of my way to find a 4bolt.
Again agreed,

A standard 2 bolt main SBC will easily handle into the 500hp range no problem. In fact it has been argued that the configuration of the stock 4 bolt main actually may weaken the sturcture and not add to it. An aftermarket splayed 4 bolt is far superior but only really needed when you get really serious.
 

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Nastyz28.com

Guess what kind of site it is. :D

Been there :)

I don't have one now but I had a 1980 Z back in the day. I would love to find another one with T tops and a 4 speed to make a modern day muscle car from. I have so many ideas and so little money.

I show you a pick of the old girl but my post count is too low.
 

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Been there :)

I don't have one now but I had a 1980 Z back in the day. I would love to find another one with T tops and a 4 speed to make a modern day muscle car from. I have so many ideas and so little money.

I show you a pick of the old girl but my post count is too low.
Yup... same here.

I wanted a pre '74, but settled for the '76 since they are dirt cheap in comparison. Built it up to 350hp and its a nice street machine but it needs lower gear ratio. Well, that and a new transmission... :D

I really wanted a 4 sp, but settled for an auto for now, someday though.
 
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