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Discussion Starter #1
Hey all

Me and my bud Tom at school were talking how he could mod his 305 that is in his Elky. He was thinking of just getting a 350 anyway, but since he already has a small block, why not just bore it bigger! Heres the big question, is it possible that we could over bore it to a 400's size bore, and is it possible just to get some 400 rebuild pistons and pop them in there (con-rod and stroke size compatability)
We then thought just get some 350 heads, port and polish, and slap them on, I heard that the 305's valves and ports are smaller, making for less room for improvement.

Thanks,

Jerry
 

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"is it possible that we could over bore it to a 400's size bore, and is it possible just to get some 400 rebuild pistons and pop them in there"

No.

Advise your bud Tom that he's starting on the wrong end of the car. Begin by changing the rear gear out for a shorter one (3.70-3.90) and installing a posi. Do a search for Auburn, Detroit Locker, etc. Bolt up some good rubber and new shocks. Now, move forward on the vehicle and change out the converter for a looser unit, something no more than a 2,500 stall for everyday street driving. Then install headers and a good dual exhaust system. The car will be much quicker and you haven't even cracked a bolt on the motor yet.

When you do decide to do motor work, start with the biggest motor you can get your hands on. Staying with a small block means searching for a 400. They have dried up in the past few years, but you could still find them in the Chevy station wagons from the early to late 70's. Find an old wagon with the motor still in it and buy the whole car for cheap.

That's my best advice from 50 years of experience in the hobby.
 

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MAX OVERBORE on 305 is. .060 Max overbore on 350 is .080 (not recommended). The limitations are cylinder wall thickness. Thus no 4"- 305's or 4.125"-350's.
 

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No way possible to bore a 305 to 350 let alone 400 sbc bore size. Most everyone is going to say just go to a 350 and be done with it. The best possible option with a 305, if you really want to keep it, is to stroke it with a 400 style crank; but by the time that's done the money is still better spent on a 350 or, if you can find one, a 400. Even a cam change with a 305 is usually disappointing. That's just the unfortunate truth. Been there ,done that.
 

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I agree with junior stocker. Boring that 305 won't do much at all, but stick a 400 crank in it and you'll have gobs of power for something with such small bored. .030" over with 400 crank makes about a 329, .060" over with it makes it a 339.
 

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Jerry, I'll explain the bit about thin cylinder walls. Even if the walls are thick enough to take the overbore on any particular motor, that doesn't mean that the motor will not overheat. It takes a certain amount of mass to squelch the harmonics of the piston rings as they skid up and down the cylinder. (I'll bet you thought they slid smoothly, didn't you?) When the cylinder walls get too thin, these harmonics are passed through the walls to the water jacket on the other side of the wall. The resulting rapid vibration of the water forms air bubbles which cling to the water jacket side of the cylinder, thus preventing cooling water from carrying away heat and the motor overheats.

The minimum thickness for a cylinder wall is 0.135" (One hundred and thirty five thousandths). Cylinder walls are not concentric due to casting irregularities, but the thin side should not be less than 0.135".
 

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Discussion Starter #9
Thanks all for the speedy replies! I learned some new things in such amount of time. :cool: We were looking for some cheap stuff to do, chaging the rear end gearing is a little bit pricey for now, good idea with the 400 crank though, maybe we can see if we can find one. Also could just be eaqsier getting a low-milage 350 from a later model (mid eighties- 90's pickup)

Jerry
 

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If you can get your hands on a 350 then that would be your best bet. What has been done to that 305 already? Consider such upgrades as a Performer intake, headers with dual exhaust and new mufflers, a small cam upgrade (maybe something in the 204int/210exh range), maybe a set of roller rockers. What carb does the engine have? If it's a 2bbl then upgrade it to a small 4 bbl, if it already has a 4bbl then consider rebuilding it or installing something like a 500cfm Edelbrock 4 bbl. Do you know what gears that Elky has in it now? You could consider a set of 3.42s or 3.55s...
 

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Discussion Starter #11
As far as I know, its bone stock. A 2bbl is in there right now, Tom had already thought of getting a better 4bbl manifold and all that. Might be cheaper just buying a 350 in the end, rather than adding speed parts to the 305, then again, sbc parts are a dime a dozen compared to my small block mopar's parts! ;)
 

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techinspector1 said:
.........Chevy station wagons from the early to late 70's. Find an old wagon with the motor still in it and buy the whole car for cheap.
Don't mean to be a wet blanket but your chances of finding a "cheap" 70's GM wagon in the Midwest are drying up faster than the supply of 400's. ESPECIALLY the '70-'76s the 400's came in. Most of those rusted away and were scrapped years ago around here and those that weren't are now in demand, they are one of the favorites of the Demo Derby crowd around here and they wil pay big money for one. They usually sell off the 400 in favor of a 350 but it's normally sold before they ever get the car home and they don't give them away. Now on the other hand IF you did find one and beat them to it you could yank the 400 and then sell them the rest and have a realltively cheap 400 core but I can't tell you the last time I saw one and I always have my eyes open for anything "cheap" that might have a 400 in it. ;)
 
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