305 modification question.

[87-Wrang-a-tang]

Well, I've never been given a chance to do any real motor work, and don't know anything about it really.
I am to beef it up in some way or another, and many have told me to throw on some 350 heads. I don't know what the thing to do is. The piston rings are shot so I figure since I do have some money to spend on it, might as well do it now. I don't want to be spending a ton of money, and I don't need any fantastic performance. Just something that I can have fun in. What are your suggestions for better performance and easy enough for a first timer like me?
Thanks in advance for helping me out!
-Brandon

[billnorman]

IMHO you've got it backward, put your heads on a 350 block. 350 heads have a larger combustion chamber and will lower your compression ratio which will lower your power. Compression and volumetric efficiency are the keys to power and economy. If the 305 heads have smaller valves, then keep the port velocity up by not overcarbureting it. Many studies show that if you have a 305, it's better to just get a 350 than building the 305 up if power is your goal. The bore/stroke ratio is much more favorable, and they are relatively cheap.

[87-Wrang-a-tang]

My goal was to kind of keep the 305, but your suggestion is now a big consideration.
I'm not necessarily going for big power, just want more than what I have.
Is there anything I can do for a bit more power, but keeping the same 305 heads?
Like I said, the rings have to be done anyways, and I hear it's a relatively big job.
So I figure since I do have the money, I might as well try and do something fo slightly better power.
Thanks for the help Bill!

[79gmcc15]

check out what I did for my 305. I am in it for about $500 installed. So far everything is going well. though Ive only put maybe 200 miles on it. I have never done anything like this. and it was a fair bit of work, with lots of cleaning LOL. If it wasn't for Joe, I would have been lost a few times. So, for the first time, it really really helps to have someone with you that knows what to do. But it was fun and very rewarding! I am glad I did it.

http://67-72chevytrucks.com/vboard/s...d.php?t=408210

[billnorman]

I admire 79GMC for cleaning and re-ringing a 305 for his own use, but I wonder what a low compression engine with a performance cam which will lower it even more will do on gas.
Readers here such as myself can give you all kinds of free advice, because we don't have to pay for it, so here's my 50 cents worth, keep the change.
I'd look for a reputable rebuilder and get a 350 long block. I'd try to get close to 9.0 static compression. If you get an aluminum head motor, you can go a little higher. It depends what you want, and what you can afford. You won't learn as much as you would if you overhauled your own motor, but you'll stay cleaner and get it done faster. Keep your EGR system it will let you burn lower octane gas without pinging. A properly rebuilt motor will have reground crankshaft, all new bearings, oil pump, timing chain, resized rod big ends, line bore or honing, 3 angle valve job.....the list goes on and on. I have seen Cadillac Sedan de Villes that weigh 5000 pounds get 20+MPG with a 350 automatic on regular. Compression is the key to efficiency. A built 305 can approach a stock 350 in horsepower, but the torque will be a lot lower. Keep efficiency in mind, gas is going up and up, and we can't make it we have to buy it.
Personally, I think I'm going with a LS or LQ 4.8 to 6.0 in my '85 and '96. My 315 HP 2007 fullsize gets me 20 MPG in my x-cab that weighs 4900# on the open road. Efficiency.

[allengator]

I know it can be frustrating to ask what to do to a 305 and have people tell you to go get a 350... But...
IF your 305 was in GREAT shape, and you wanted to tweak it a little I would say "have fun"...
But your 305 needs a rebuild, it will cost the same to rebuild that as a 350 and they are a WORLD apart!
I have a perfectly fine 305 in my shop, and I hate to let sit... but I cant justify doing anything to it...

[billnorman]

I had written a quick reply along these samelines with respect to cost. Here's an ad for a 350, with the drawback that it has a mild performance camshaft. It's .040 over so it will have a true bore, but maybe no more room for another one. This engine with a stock or torquer cam and some fel-pro composition head gaskets might make a fine truck motor. It's just an example, I'm not recommending it. E bay number 250738392731 found under cars/boats etc. 350 chevy rebuilt. Good luck

[russgt]

How much money is in your budgit?

[87-Wrang-a-tang]

Well, I could go up to 1500 if I wanted, but my goal was to keep it around or under 1000 if possible. And I don't mind the getting dirty part, that's part of the reason I wanted to build my 305 up, for the learning experience.
Thanks again guys.

79GMCC15
I took a quick skim over your thread and it looks like you've done some nice work.
I'll definitely have to read over it all. It's so hard to know what to do.
I could just leave my motor as is besides doing the rings, and throwing a cam in there. I want to do headers an exhaust too.
I'll have to give it some good consideration and start looking around for prices on rebuilds.

[russgt]

Stick with your 305, stick in a mild cam during the rebuild and run it. The experience you gain by doing the work yourself will be very valuable in your future projects as well as this one. Buying a used 350, while being a good upgrade, is a crap shoot. You could easily end up going well over your $1500 budgit if anything goes wrong with the motor. Crate motors are the easy way out for someone that doesnt want to do the work. Cheap crate motors are a risk because of the cost savings that goes into the parts and the labor to assemble them. I have first hand experience repairing a "new" 260 horse GM 350 that at about 150 miles ate 3 rod bearings. All 3 were in the .005 to .006 clearance range, which is very loose, but GM would not stand behind the warranty because the owner had swaped in a mild cam. Anyways, take the time to learn how to build the engine yourself, buy and use plastigauge to check your clearances, and dont be afraid to double check that you torqued everything correctly.

[Doug_J]

Or find a decent salvage yard take your 305 in for a core trade him out for a 350 save you some money, And I said decent salvage yard because when you take it in to have machine work done and you maybe find a crack they should swap you out for another block. And really you should find 350s around all day long for couple hundred bucks that need rebuilt. I think in the end you would be happier with a 350, and if your wanting to get the exp of building the motor just take it in have the machine work done to the block, the balancing on the internals, have the shop put the cam bearings in because their a pain and then assemble the block yourself.

[russgt]

But if you get ahold of a bad block, you are out the cost of having it tanked and maged. Machining costs alone will put close to your limits on your budgit

[Doug_J]

I think last time I had one dipped it was about 50 or so $ and about five or so years ago now dont seem that long ago, but I had a 350 rebuilt an for him to do the machine work tear the block down and reassemble it out the door was 975 and the first one I took in was a cracked block. Now just about a yr 1/2 ago I took a 454 in had machine work done assembled it my self and with parts order and his cost I was in it for 1200 to 1600 if I remember right I'd have to dig out the recipt for it. Now you can save some money by reusing connecting rods, some times they can reuse the valves dont know tell they clean them up.

[C-10 simplex]

Originally Posted by russgt

Stick with your 305, stick in a mild cam during the rebuild and run it. The experience you gain by doing the work yourself will be very valuable in your future projects as well as this one. Buying a used 350, while being a good upgrade, is a crap shoot. You could easily end up going well over your $1500 budgit if anything goes wrong with the motor. Crate motors are the easy way out for someone that doesnt want to do the work. Cheap crate motors are a risk because of the cost savings that goes into the parts and the labor to assemble them. I have first hand experience repairing a "new" 260 horse GM 350 that at about 150 miles ate 3 rod bearings. All 3 were in the .005 to .006 clearance range, which is very loose, but GM would not stand behind the warranty because the owner had swaped in a mild cam. Anyways, take the time to learn how to build the engine yourself, buy and use plastigauge to check your clearances, and dont be afraid to double check that you torqued everything correctly.

i heard that the lower end goodwrench crates are assembled in Mex, but the higher end GMPP crates, i.e., zz4 350, zz383 etc. are assembled in Michigan by 2 GM employees? How can we confirm this? (Basically, i am asking someone else besides me to do the legwork )

Originally Posted by Doug_J

Or find a decent salvage yard take your 305 in for a core trade him out for a 350 save you some money, And I said decent salvage yard because when you take it in to have machine work done and you maybe find a crack they should swap you out for another block. And really you should find 350s around all day long for couple hundred bucks that need rebuilt. I think in the end you would be happier with a 350, and if your wanting to get the exp of building the motor just take it in have the machine work done to the block, the balancing on the internals, have the shop put the cam bearings in because their a pain and then assemble the block yourself.

Originally Posted by russgt

But if you get ahold of a bad block, you are out the cost of having it tanked and maged. Machining costs alone will put close to your limits on your budgit

Most machine shops should have a stack of good 350 blocks on hand?


P.S. my stock LG3 305 does the 1/4 in 17.9, this is with a 2.56 final axle ratio. The crate 350 that was in there previously did it in 16.8 secs.
Based on my limited experiences so far, i don't think the mpg difference between the 2 engines when installed in a truck is going to make much a difference if at all; i get 16ish mpg either way.

[Coreyterry]

imo i love the 305, there cheap reliable, not as much hp as 350 but they last just as long if you take care of them. the reason 350 are more popular is because theres so much more for them.

i would keep your heads, if there 1.85 then there ok anything bigger for a 305 is just to big, 307 heads are pretty good, i had a 305 in my 67 for the longest time and i loved it. it lasted me its hole life till i tried to put new heads on it and they blew up in my face. but a decent cam and have everything balanced and call it good, another thing you can do also is buy thinner head gaskets, it will give you more compresion but they sometimes tend to go out if you hot rod them to much, and putting a spacer between the intake and carb will give you a little more torque.

but you should really consider keeping it. but for a 1000 bucks you can buy a pre-asembled 350 and drop it in and keep the 305 for a learner build, kind of a learn from your mistakes build. thats how my engine is now haha too bad i cant afford to make any mistakes.

[wardee1977]

I have a 305 in my '77 short box with a 700r4 and 3.08 rear. I just bought it this fall and can't wait to get it out this spring. Most of my budget is going into the lowering kit and wheels for this year. There is nothing wrong with the bone stock 305 that is in the truck now. It had been recently been rebuilt by a reputable engine builder before I got it. I can't afford to build a bigger motor this year, so I was thinking of throwing a few parts at the 305 for now to get a few more horses out of it. I need to be able to do some light towing(lawnmowers) now and again, so I can't get too radical on the cam. Just wondering if you guys had any good ideas for a cam that would wake up the 305 a little and still have enough on the low end for a little towing? The engine was rebuilt to stock specs.

[Coreyterry]

just a mild rv cam would be fine, as far as im conserned a stock oem cam works just as good, i towed alot with my 67 and it never gave me any trouble.

[80_cutlass]

Used a 305 in a boat I had......and not as an anchor. I tend to agree with the 350 idea expressed through most of the responses.

Does the truck run now, at least well enough to use to gather parts? That would allow you to use the truck and build a replacement motor on the side. Just a thought.

If you want to build your 305, just remember a mild cam in a small engine is better. Get as much compression (9.xx to 1) as you can and still use pump gas, tune it and you will be surprised at the difference.

When choosing parts for the build be sure to take the whole package into consideration: transmission, TC, gear ratio/tire size, intake system, exhaust, intended use and how much 'hot rod' character you want to deal with.

sb