The Stovebolt Site Forums The Shop Area Engine Shop Somebody Please Tell Me The Truth!

I have ask a few different people, and received
a few different answers about 250 and 292 cranks.
Can I use a 292 crank in my 250 block? My 1970
C/10 Fleetside is an unmolested all original
daily driver. I want to keep the original
engine for the sake of matching numbers ect,
but I want it smokin' hot. My dad thinks I
should stay with the 250 because the shorter
stroke winds up quicker, but I say nothing
replaces displacement like displacement.
So what does it take to use a 292 crank in
a 250 block?

I dont know what it takes, but thay say nothing rules the street like torq and thats what you would get whith 292 crank
you would have better take off at the stop lights but for shure lose some top end power whith longer stroke

Clifford Performance has a forged piston (22-6343) for 292 crank in a 230/250.

Larry
68 C20 327 daily driver
63 C20 292 Camper truck
65 C10 ? Custom Cab AC,PB,PS,$flasher

Main journals are the same size, rod journals are 2.000 (250) and 2.100 (292). Stroke is 3.53 vs 4.12. Also, the balance on the stock 292 crank is horrible, and requires grinding off 15-20 lbs of metal to be able to turn high rpm. I think you could make it work, but you would be better off starting with the tall deck 292 block.

You will be notching out the crankcase to make room for swinging the rod ends around. Side loads on pistons are big with the shorter rods and reduced deck height.

http://www.sissellsautomotive.com has a crank kit to put a 292 crank in a low deck motor. It has been done, it has been raced, it blows up a lot.

sounds like a lot of work and expense. Just get a 454...

Just start with a real 292 and be done with it!

[img]http://photo.starblvd.net/fstyler/2-2-1.jpg[/img]

This is my own 292, bored .060 over, with a little hotter than stock cam, 4 barrel and 36 inch headers. Probably produces 180 peak horsepower.

-ftyler

Okay --- lots of great input. It sounds like
the guy who told me it is difficult and expensive
back a couple months ago was right. What if I
go displacement hunting in another direction?
What are the largest oversize pistons I can use
without altering anything other than the bore?

Bob

Maximum bore recommended is .060. Beyond that you get into block flex problems. Santucci's book recommends using flat top pistons for street use, but you can put small block pistons in these engines. Do you have a copy of Chevrolet Inline Six-Cylinder Power Manual? Most all of this info is in it.

If you want something that will still look like the original engine and give you lots of reliable Hp, find a 270/302 GMC. They were designed before the companies decided to save every penny by making things as weak as they could get away with. and they along with other inlines cost less to build--especially if you can run a torch and die grinder to do the head and make your manifolds!
Holiday cheer;
ROAR :p

FT, Your engine is lookin REAL pretty. Looks like alot of time and mula. I gotta tell yah though I've seen those plastic fuel filters break or seperate. Also I use that rubber fuel line hose and never had a problem it but a few people here have had problems with that also. I've tried bending pipe and for me it was a real pain. When I get some time and money I might try it again. I'm not criticising yah bro really just lookin out for yah, and again I know yah don't need me or anybody else lookin out for yah, but Tough! change the filter.
Adios, Kip

So how do ya do the math? If I bore my 250 .60
over, how much displacement will I gain?

And by the way, that 292 is lookin' real good, but what's with the blue color? It looks like
a **** color. I have always believed that ****
stuff would make a Chevy sick. Like with my dad's 65 1/2 ton van. He put **** wheel covers on it, and now he's on his 3rd motor!

Happy New Year Stovebolters!!
Bob

According to this site, you would gain 9 cubic inches (244 instead of 235). Don\'s Auto Pages

(Standard bore is 3.563. Boring .060 over would make it 3.623.)

Even boring a 350 0.060 over only adds another 11 cubic inches, and that's with two extra cylinders.

It looks like, if you want bigger displacement, you buy it, not bore it.

Two words: Big Block

Easiest way to get more displacement out of a 250 is to replace it with a 292 or 302. The 292 will be a lot cheaper, GMC 302 blocks are getting somewhat scarce and parts aren't cheap.

Other than that you can use the 292 crank in the 250, find the right rods and have a long stroke enginge with a lot of work invested. Or you can bore a 250 .120 over, but you lose block stability, which requires a lot of work to stiffen the lower end of the block.

I am going to stay with the 250 at .060 over.
Joe is working up some numbers for me with
his dyno simulator now so I can determine
some things about cam, carbs, et.

I just really want to stick with the orginal
engine because this particlar truck is TOTALLY
original. However I also want it to GET when I say GET!

Bob

The 292 I believe is a taller block than the 230/250 blocks are.

When worried about matching numbers I save the original motor by pulling it and putting it away and then bolt in a go fast alternate. That way later on I have an original numbers matching engine if I go to sell and dont risk irrepairable damage to the original block. 500 caddy would be my choice although members here have 409's and other very desireable mills.

Hey Panhead -- What year is your pan?

The alternative you proposed is a good one, and I am still thinking of using a 292 inline because that gives it a stock and orginal look while gaining 42 inches. (Thats a lot of inches on motors this small!) If build a hot rod 292 I'll do as you suggest and keep the original motor. I might go through it using stock GM stuff, so if I ever want to sell this truck I could advertise it with an all original fresh motor. I may also say screw it all and put a monster 292 in the truck, radicalize the 250 and stick it in some rusty old 4 door sedan for a sleeper just for kicks and grins!

Best ways to wake up a 250 include a healthy cam, HEI, MSD-6 box which helps smooth out the lumpy cam, headers, intake and carb, porting and shaving the head. Unfortunately, the items that help the most affect the exterior appearance of the engine. You can also gain a few hp by using an electric fan, but you have to up the alternator to compensate.

Or, you can salt away the 250, and drop a few grand on a 502 hp big block, but the rear tires don't last very long!

3 words "Three, Twenty, Seven"

I found out that I can purchase a 292 from a local auto wrecker for $150. It would be a worn out one, but guaranteed that the block, crank, and major components are okay. In other words, a good start for a rebuild project. With that in mind I think I am going to go with the 292. I have been around some pretty hot 235's but never a 292. I am already looking forward to mustang hunting! (The season is open year around in Oregon ) Bored .060 a 292 is 301 inches. For those of you who, like me, are mathmatically challenged that is a gain of 51 cubic inches over my original 250 while maintaining the "six banger" status. 3 carbs on an offy intake with offy headers, isky cam, and some machine work, and I will be buying tires 3 times a year!

Gotta Do It!!
Bob

You will be very happy with the 292, I run a couple of them. A much as I like the GMC 270/302, they are a much older design and use the old-style bellhousing pattern (the 292 uses the sbc pattern). The 292 is a 7 main bearing motor with a very efficient head design.

fleetside,

The 292 you see in the picture above is as you want yours to be (.060 over - 301 cubic inches). If I had it do over again the only change I would make would be to bump the compression higher by using the liquid propane pistons - they give a 9:1 compression ratio to an otherwise stock 292. Because of the slight shaving of the head and large overbore I would probably have ended up 9.3-to-1 or a little more.

My engine is built for torque, but the cam and intake and carb upgrades puts the torque peak higher than stock. So it's a little sluggish off the clutch but really opens up about about 2500 rpms.

If you want really good power from your street 292, then in addition to what you already plan I'd do a very good port and polish of the head. I'd probably shave it a bit and recess the valves the same. And definitely wing-shape the intake bolt boss.

If you want high HP, then plan on higher rpms. That means balancing the stock crank, magnafluxing and balancing the stock rods, and lightweight flat top pistons. At this point you want to go with the Clifford water heated intake instead of the Offy.

-ftyler

FT makes some good points - to go along with his notes on compression and head work . . . what is your budget for making all this power?

The single biggest improvement you can make (besides all the bolt on stuff) is reworking the head to improve flow. You are no doubt going to rebuild the head (new valves, springs, guides, screw in studs and new rockers (to work with a decent cam), etc. This isn't going to be a drop in the bucket, yet when you are done, the head will only flow marginally better than stock.

If you want to wake it up and get it done right, send your head to Mike Kirby of Sissels Automotive in California http://www.sissellsautomotive.com - if you are an active inliner he will give you about 10-15 percent off and you will have a head that will give you way more bang for the buck. If you ever decide to put the 250 back in, you can always put the new head on the 250.