Engine needs a rebuild, but into what?

Scott,

I may not know much, but I know what it's like to get ripped off. That really sucks and I'm sorry to hear that. We all have to trust someone at some point, so don't feel bad.

I bought a '64 Chevy g10 with a 250 from a '73-'79 Olds/Chevy/Pontiac. I knew it might need a rebuild and was OK with that. However, when I got it out and to a trusted machine shop, I was told it was previously bored .060 and that's as far as it can go.

Machinist says if he put new pistons, rings and honed the cylinders... it will run. It may smoke a little and not last as long as other rebuilds. Who wants that? Now I need another 250 block.

If I were you, I'd consider having it bored out another .030 and rebuilt. You get to keep all the cool stuff you already have invested. It's much easier than going to a V8. On the other hand, you have the large dogbox so it wouldn't be all that bad.

Good luck... and if you go with a V8, I may want to buy your 250 off you. Provided the machinist tells me he can work with it. Food for thought!

wishbone

I see.

Back in the '70s when gas was hard to come by, I had a friend who converted his 72 Chevy pick-up to run on propane. It was mostly just a unit sitting on top of the carb with a rubber diaphragm in it. On one side ran hot water (coolant), the other side was the propane. The heat from the coolant liquified the propane, fed the carb, and it ran like normal. I'm pretty sure that's how it worked.

He placed a 100 gallon tank in the bed and bragged that, on a full tank he could get out of the U.S. in any direction without stopping. He got great mileage, never waited in line for fuel and propane was cheaper than gasoline... back then. I remember he mentioned propane ran at about 95 octane and there were no carbon deposits on the valves or piston heads.

One extra benefit was he could release a little propane on a warm beer can and cool it down for drinking a cold one!

Those were the good old days and yes... I'm very old. Healthy but old!

I drove a lot of miles in my 230 powered first gen in the seventies.... Stock with a one barrel carb it would do 17s in the quarter mile while chirping the N50s into second, all while getting about 17 mpg.....
The early vans were designed to run a bit higher RPMs with the sixes and that was reflected in the cooling layout and gearing.....
The 2004r suggests that you want to run lower RPMs, but fuel mileage of a six suffers unless it's got the power to easily pull the gears (low load)....
All three of my Astro vans were "overgeared" as is my 06 Trailblazer and as a result, none of these got (get) particularly good mileage at less than 75 MPH.... All four of these vehicles got/get about 12-13 around town and all were/are factory fuel injected with overdive transmissions....

Matching horsepower, gearing, cooling strategy, and RPM strategy to the weight of the vehicle will get you the best economy.....It's not wrong to believe you can achieve this with a six because the Nova-generation straight sixes are very potent for their size.....The straight six doesn't block airflow like a v8 does and runs much smoother....The exhaust note won't be mistaken for a v-8, but the six will keep up.....
I'm a v8 guy, but I won't bore you with the v8s advantages as I'm sure you've heard them all...
I would say that if you want a good six built, you should choose and buy your parts and work with a local reputable machinist/engine builder on doing a short-block and head separately and bolt the head on yourself after checking the decks for straightness....New oil pump, degreeing your cam and cam break-in etc......

I am running a straight 6 but went the opposite direction, not caring about mileage in the least. I still get 10-12 mpg. running around town and much better on the interstate. A .030" over bore verses stock is negligible for power or mileage. Your rebuilt short block would be bored over anyways. The 390 cfm. is close to the upper limit but should be fine. A friend just installed dual webers on his bone stock 230 and is fine. They are around 380 cfm combined. He tried the 38/38's (around 470 cfm.) and was a bit much. A few performance mods may not hurt as much as you think. An underpowered motor at full throttle drinks lots of gas! An RV cam probably helps mileage! You need to match your cam (duration) with your cruising rpm's. The bigger the cam, the higher you want the cruise rpm's. A slight bump in compression would work well with an R.V. cam, 0.060 of the head will give you a little more h.p. and even though it uses slightly more fuel, you would definitely get that back by not needing to floor it as often. With a modest cam and compression increase, the 390 carb will be better matched and spend more time at part throttle (primaries only). You didn't mention what rear gears. As 3.36 is most common, it should cruise down the highway at 2200-2300 with the 200 4r. My 4.11's turn about 3000 r.pm at 75-80.