The Stovebolt Site Forums The Shop Area Engine Shop Inline 6 230 cid rebuild into 250cid?

Hi I have a old 1965 chevy truck 230cid engine casting #3788406 F0215NE. And a 1972 GM250cid engine casting #348675 with Water jacket crack.
The 250 cid has fairly new internal parts and Head is good.
So I wanted to know if the 250 head and all the other internal parts like crank,cam,rods ect. would fit on this 1965 230cid chevy truck engine? Making it into a 250 cid not 230 cid?
So what mod's if any would I have to do?
And would my 1972 250 cid head bolt right on a 1965 230 cid block? Or would I have to rebuild the 230 head and use it?

I know the head will enterchange & the 72 would be a better choice as it is designed for no-lead fuel. I don,t know about the rest but you could get a good idea by checking the specks. Compare the bore, main & rod brg. sizes. I,m shure someone will come in with some more advice.

You should be able to change the crank, 3.250" stroke for the 230, to the longer stroke 3.530" 250 with out any problems. The bore is the same, 3.875" for both engines. The other parts will all enterchange. If you need to bore the engine, I would change it over to V-8 pistons, flat top 307 ci Chevrolet, to get the compression up for better performance. You can get in to 9.0 to 1 range with just a simple piston change. Joe

I thought the 307 has different dia piston pins?
What piston rod bushings do you use with the original 250 cid piston rods?
This engine will run at MAX RPM for long times. So what do you recommend to use part wise?
Want engine to handle it. Not blow a rod,piston or something. Want it to be dependable last longtime. Advise on best parts?
Again Thank You so very much for the help.

I have built several flattop piston 250's using 307 pistons. They're exactly the same, weight, pin diameter, and compression height. The dish top/flat top is the only difference. Since the pin is a press fit in the rod, there's no small-end bushing to be concerned about. I've combined the flattops with an .050" mill job on the head to bump the compression a little more, and still ran 87 octane gas.
Jerry

Hey There Hotrod Lincoln, I've got an 87 Chevy 1/2 ton 4x4 with a 700R4 and 3.73 gears and have been looking at putting in a 250. How did your 250s run using those 307 pistons? What carb did you use? What about roller rockers? Who makes a just better than stock cam for better breathability for them or is the stock one best with some headwork. It would be a daily driver. Not for racing. I have 3" Magnaflow already in there. I have had a 250 and 230s both ran very good. Had one 292 stump puller which also ran real good. Had low gears on that one so it was not too efficient to run. But it was a strong runner. Love them ole' inline sixes. Just thought I would ask. H.

Henry G, if you looking for a cam check out Clay Smith Cams. They make custum cams for $200 flat. I called them up and told them what it would be used for, daily driver, towing, hot rodding ect... They ask for specs on my truck and they milled it and I got it in about 2-3 weeks. They have been around for a long time and since dealing with them I see why. I very highly recommend them.

Hey ApacheFiend, Thanks very much for that info. Something I will consider. My truck has a 350 in it now. It runs good but vibrates. So I changed the harmonic balancer a few weeks ago, plus a double roller timimg chain and a new water pump. Its got 95k on it. Still vibrates when you get on it or going at highway speeds and going down a pass and give a little gas. I was told either flex plate or torque converter. Soooooo I bought a enw stage 1 converter yesterday and a flexplate to solve this. Otherwise I'll have to pull this engine. I love the ole' sixes. Simple to work on and tons of room under the hood. I'm a nostalgic for sure. Thanks again for the info and will know in a few days I hope whether I'll pull this motor or not. I'm not a 350 lover. They are good to say the least but its not what I prefer. H.

Henry, one of the engines I built was a project by one of my auto mechanics shop students, in a early-70's Nova. He ran a Comp Cams 260H High Energy cam along with the flattops, and used the original Rochester carburetor with a little bigger main jets. That one was spooky fast, keeping up with his friend's Pontiac Firebird with a Pontiac 350 in it. They would race about 20 miles to school every morning, with neither one able to get an advantage over the other. I think a radar trap put a stop to those shenanigans one morning! 100+ MPH speeding tickets for both parties!

Never thought about roller rockers for that engine, but it might be a good idea.
Jerry

Hey Hotrod Lincoln, Thanks for the info. I'm more and more surprised what these inlines can do with some work on them. Been talking to two machines shops along with two guys from inliners.org on the phone and the all agreed that a 292 for my 87 4x4 would be a real good choice and would climb hills and passes better than a 305 or some stock 350s. Plus a lot of room under the hood. Could gain about 20-25 hp with roller rockers plus a nice race balance will boost it up some. Hmmmm, think I might go to the bone yard in the next few days to find one. Thanks! H.

Just don't get tempted to change the rocker arm ratio while you're at it. The smallblock V-8's have a 1.5:1 ratio rocker, and people try to fudge on the valve lift by going to a 1.6 ratio. It botches up the geometry of the pushrod/rocker/valve stem to the point that a very expensive relocation of the rocker stud position and some other mods become necessary. The power gain really isn't worth the cost. I believe the sixes use the same 1.5:1 rocker ratio as the 350's.
Jerry

Inline six use 1.75 rocker arm ratio and dont inter change with any other engine. also you can use a 327 piston in the 250 engines.

Thanks Hotrod for the advice. I'll keep then rocker ratio stock at 1.75 according to the book. The SMC uses 1.5 and 1.6. However the rollers will help out probably with some headwork and possibly a slightly higher lift cam for more torque. Been about 19 years sincew I owned a 292. There is someone in the midwest that running a chevy inline in the high 9s. Thats just amazing! I just want some good power and reasonable economy. Theres a 292 racing here near Medford Oregon in the White City drags and stays up with most V8s. And his is only moderately modified. Went to one yard today but too muddy due to the rains. Didn't look like they had one anyhow. I'll check the others later. For those interested I know where there are a couple 235s. H.

A 327 has a 4" bore. That would be a .125" overbore, and you could read a newspaper through the cylinder walls. The 307 piston has the correct bore/compression height to be a direct replacement.
Jerry