As per "California Bill's" little blue speed manual from the '50s, 252 is as far as a 235 can go (HEATHEN has confirmed this in the past). "They" say that the best way to achieve more horsepower is by adding inches to your CID. I'm not trying to build a race motor, just a "rompy" street job. Do more inches mainly help with top-end speed (max mph)? Any thoughts as to the +'s and -'s to boring a 6 to the "max"? thx, ns ps- I've only owned "stock" motors and have never done a rebuild, which explains the "carpet bombing" of threads on the subject.
Can you get pistons?, the only other thing that I could think of is would a stock head gasket fit properly or would it overhang the edge of the cylinder, and does that really matter?
The engine architecture is very different. Going to the 194-230-250-292 series would require, at the very least, a bunch of rework on motor mounts, possible relocation of radiator and firewall, and changing out the stock trans or finding an adapter. Are there any known problems with boring the motor out that much (i.e., do you need to use hardblok to keep the walls from flexing?) that would make use in a street car undesirable?
Just opening up the exhaust and intake help alot, and these engines are rpm limited, so top end if more a matter of things holding together. If a bad ass stovebolt is what you crave, the 261 with an 848 head would be cool, but the gmc 302 is the ruler. The old 3 speeds in 49-54 chevies won't live long behind a REAL motor. They are tiny.
The extra inches could improve the torque curve somewhat. The main difference between the 235 and the 261 is in torque. You aren't going to get more rev's out of it just by boring it out. Don't know too many people that wind them up past 4000 rpms anyway. I just bore them out enough to clean it up. 80 over is the largest non-custom piston you're going to find. The last 235 I had, I bored it to 60 over, and the holes were pretty close to the head gasket. Bigger than that and you may want to look for a 261 head gasket.
Thanks! To respond to some of the posts: I already have a '54 long block at the machine shop. I sought out the '54 SPECIFICALLY because it's going into my '52 and the mount bosses are exactly the same('52-'54 have the same nightmarish side-tower motor mount assembly). I'm going to run dual-carbs, headers, and a cam, so an HP boost should be noticeable. Sounds like .060 is the way to go... if punching it out too far isn't going to give me much and I risk wasting a water jacket, it's not worth it! -ns
I know that it's common to take a 261 and bore it to the max and install different rods and pistons to make it a 290. This large of a bore can be done apprently with no ill-effects, but you will be prehaps pusing your luck on an engine that sees a lot of miles or hard miles
Try to lean on a 235 too much and it's flaws will show. The nickel content is not ideal so cylinder wear is an issue which will only be magnified by boring too much. Power gained by increasing cid will be hampered by the heads ability to breathe. Far better solution: Conservative bore Decent compression ratio(pump friendly) Split exhaust Large single or multiple small carb intake Cam matched to the breathability and compression Will work great with a manual or auto(with conservative cam) and be reliable with decent power(200-215).
Good parts and getting it to breathe without overstressing it and it will live a reliable life. Like others have stated the stock 3spd will give out once torque is mixed with traction. Power at the wheels will differ but a 235 is there for aesthetics so keep it simple and the suggestions will make it run great (and sound great)for what it is.
More displacement= more hp and torque. Should go faster and get there sooner. I would try for a 261 or 302 gmc also.
To get an honest 200 hp out of a 235 would require it to be nearly unstreetable, not counting "cheating" with the likes of a supercharger and/or nitrous. Concerning the bore size question---.060 makes it a 244, and if you can't get acceptable street power out of 244 cubes, you probably won't get it out of 252 cubes either. As others have said, improved breathing via intake, exhaust and camshaft profile will get you way more than the extra eight cubic inches will. Of course, if you happen to find a 261 block, you can punch it a conservative .060 and have 270 cubes under the hood.
Also, keep in mind that when the bore limits were found by the speed merchants whose experiences were used to write the hop up manuals, they were working with blocks that were a year or two old and had not been thinned out by 40 to 60 years of internal corrosion.
I know a guy in CA who has a real thick casting 54 block for sale. He thought it might bore to 261 size. It was for sale last time we spoke.
The Jalopy Journal
