[giddygoat]

I have an few extra OHC engines and access to a 300 six chev and had at one time spoke with a guy that claimed to have put the 300 crank into the 250 OHC? Has anyone here done this?

[GTOWAGON]

Do you mean a 292 crank this is possible but requires a lot of work

[b-man]

Rod angle will be pretty severe with the 292 crank in a 250 block. The 292 block deck is 1.75" taller than a standard-low deck Chevy 194/230/250 or OHC-Pontiac 230/250 to accomodate the longer stroke and the longer rod used for the big stroke 292 crank.

The 292 (4.12" stroke) uses a 6.76" rod as compared to the low-deck sixes that have the 5.7" rod (3.25"stroke - 194/230 & 3.53"stroke - 250).

The severe rod angle will play havoc on the cylinder walls with heavy side loading and a lot more internal friction, not a long-lived combo.

[TheSilverBuick]

The reasons mentioned above is why I abandoned the idea.

Here is a 250 crank.


A Chevy 292 crank.


Had some pretty close clearances with the crank throws, but would spin with out hitting anything. Some grinding or cutting some where would have to happen I'm sure to clear the rods.


The OHC balancer and sprocket slid right on to the 292 crank though.

[Cammer-6]

292 crank throw have enough meat to offset grind to 2 inch
use 6 inch rods and short CH pistons
when you get below 1.6 on rod/stroke you live on borrowed time.
They made a few different 292 cranks
forged(I have one of these)
cast fully counterweighted
cast partially counterweighted
last one is least desired

[marks73ta]

Dumb question but would an OHC head fit on the 292 block? Build a 292 with the head and just add a longer belt?? I know that this must be too easy, but just a thought. Mark L

[Bill Eveland]

I have a Hotrod article from the 60's where the bigger stroke crank was added in, I'll have to find it and post it up here...

[BruceWilkie]

Originally Posted by Cammer-6

when you get below 1.6 on rod/stroke you live on borrowed time.

Really??? 455 is 1.57 Plenty of strong 4.21 stroke 6.625 rod combos these days. Some at greater stroke with that rod length. 400SBC is far worse 383 SBCwith 5.7 rod a tid better than the 400 but still worse than 1.57. Common 347 SBF stroker is at 1.54 with 5.4 rod and 3.5 stroke.

Adequate pin height and crank clearance would be the real concern putting the 292 crank in the 250 block.

[Cammer-6]

Originally Posted by BruceWilkie

Really??? 455 is 1.57 Plenty of strong 4.21 stroke 6.625 rod combos these days. Some at greater stroke with that rod length. 400SBC is far worse 383 SBCwith 5.7 rod a tid better than the 400 but still worse than 1.57. Common 347 SBF stroker is at 1.54 with 5.4 rod and 3.5 stroke.

Adequate pin height and crank clearance would be the real concern putting the 292 crank in the 250 block.

ask any racer if he shoots for 1.5 or lower on rod stroke ratio.


in stock form a 292 crank using 5.7 rods has a 1.38 ratio
I say thats awful.

[g68mike]

Are the valve lash adjusters still available?

[455Grandville]

Originally Posted by Cammer-6

292 crank throw have enough meat to offset grind to 2 inch
use 6 inch rods and short CH pistons
when you get below 1.6 on rod/stroke you live on borrowed time.
They made a few different 292 cranks
forged(I have one of these)
cast fully counterweighted
cast partially counterweighted
last one is least desired

Hondas run 1.6 : 1 ( & under) with that r/s ratio and run 300,000 + miles.

I've found 1.53 : 1 to be the perfect ratio on short circle tracks and they hold up with repeated 8,000 + rpms bursts.

[camerjeff]

Well when I have time I will post the long SAGA of my "drop in Stroker Kit" that I bought in the early 80's from a retired GM Engineer. I was able to Use the Drop in crank after major modifications, and the block I bought.

[giddygoat]

Its been maybe 20 years ago but the guy was from Florida and drag raced OHC sixes at tracks down there, claimed to have one stroked with the 66 head running in the low 11s in a lemans or tempest 66 or 67.

[camerjeff]

As promised the short version of my 69 FB's 301 OHC-6 Stroker.

On my old/new school 301, we did use a chevy 292 crank. I would have to look up the specific's (this was done 15 years ago, and my memory is not what it used to be) We ended up using Eagle I-beam rods for a Toyota Supra and had to cut down the big end alittle to fit the crank. They are alittle short, so the rod/stroke ratio is not Ideal, but I didn't plan on the engine lasting 100,000 miles anyway.
We ended up cutting alot more of the counter weights off than planned. When I bought this "KIT" from an old GM engine engineer I was told it was "ready to install" Yea right!!!!! It came with stock SBC pistons that must have been from a displacement that was never made. closest thing we could find was a 283, but the would have had to been overbored about .080. He was going to use the stock OHC-6 rods with the caps reversed to make up the extra width of the 292 rod journals. Needless to say I did not use them. We ended up using a stock 250 OHC-6 piston for Aries to reverse engineer with a higher mount for the piston pin and the correct size to fit the Supra rods.
The ready to go "KIT" ended up costing me about $350 for rods, and they cut me a break on the custom forged pistons and let me have them for $580 and that was 15 or so years ago!!!!
As for the block, I was told that the interference I saw with the block and the "CUT DOWN" 292 crank was "NORMAL" and that they would actualy cut holes (below the water jackets about midway thru the skirt) in the block for the crankshaft counterweights, and either weld them up with an external plate, or drill and tap the block for bolting external cover plates to cover up the holes.
I did not like that Idea either, so we cut down the Cranks counterweights some more, but still ended up having to clearance the block some (but not cut all the way thru the casting) so the crank would clear and rotate without interference. We also had to modify the oil pick up tube to clear the crank, and the oil pan to fit the reworked pick up tube.
We then had to modify the ID of the manual flywheel to fit the crank. I didn't find that out until we went to have the rotating parts balanced. And then we actualey able to save some money by using a stock SBC fluid Damper. But that required moving all the accessories forward about 3/4" to line up the belts on pulley's of the fluid damper.
This was because unlike the stock Harmonic Balancer of the OHC-6 that has the pulley drive grooves cast into the rear 1/2 of the balancer, the Chevy Balancer requires the pulleys to be bolted onto the front face of the balancer. As you can see I still haven't gotten around to a final fix on this issue.

So as you can see every thing just went together in one afternoon right? Just as I was pitched in the sellers home. But I did get a good 250 block, and a 3/4 modified crank for $600. And I did get to curse the man to this day!!!!

[Pontirag]

back in the late 70's (77-80) hotrod cam out with an excellent article on racing six's. one was the pontiac. I kept that article for years but chucked it bout 3 years ago.