The Stovebolt Site Forums The Shop Area Engine Shop 235 to 261 Stroker

When I purchased my 1948 Chevy 3600 a year ago I found that it came with a full pressure 235. I've heard plenty of people talk about having those engines being rebored to 261 strokers. If I did this how much of a power increase would I get and how hard would it be to get parts?

Impossible- - - - -a 261 has a 3 3/4" bore, and you'll hit the water jacket before you get a 235 bored that big. The 261 has a totally different cylinder wall thickness and the adjoining cylinders are "siamesed" together to allow the necessary machining to fit a piston that big. There are also extra cooling holes in the cylinder head to accommodate the lack of water flow between the cylinders.

A 235 and a 261 use the same crankshaft, so the term "stroker" definitely doesn't apply. The 261 crankshaft can be offset-ground to use a 292 connecting rod for a stroke increase, but a set of custom-made pistons are required to make that combination work. It's possible to get almost 300 cubic inches from a 261 block and a stroker crankshaft with the right piston/rod combination, but get ready to spend mega-bucks to build that engine!
Jerry

I saw a 261 dyno pull on youtube, that had been modified like Jerry stated.

It topped out at 225 Hp, and 330 ft. lbs of torque. Seemed like alot of work for not alot of performance.

Your best bet is to find a 261, stick some 848 heads on it, add a hotter cam, and live with it.

If you want more power and torque, find a 292 and stick a hotter cam in it and a 2bbl. It'll run a 261 under the table any day of the week.

When I purchased my engine, I thought I was getting a 235. It turned out to be a 261 with an 848 head. It had the starter, bell housing, water pump, carb and everything. It just slipped into the engine bay, no issues. The only minor thing was to put a larger pulley on the water pump, no relocation issues. I am quite happy with the performance, 20 mpg is a bonus.

Bet that was a pleasant surprise

20 mpg?? What differential ratio / transmission are you using?
John

Original 4 speed with torque tube. Diff ratio is 3.55.

We are talking gallons, not litres?? I may have to think more about going the 3.55 route.

John

Yes, we are talking about gallons, imperial gallons. Not trying to get off topic though. Just trying to point out how good the 261 is. It is rated at 150 hp, that's with the stock 1 barrel and most everything else stock. There is potential for more, but where does one stop with trying to do more?

When you run out of money.

"There's no substitute for cubic dollars!"
Jerry

One Imperial gallon equals 1.201 US gallons. Are you therefore saying that you are getting 24 miles per US gallon? DO you have a body on this frame or do you drive down steep hills everywhere you go?

Are you therefore saying that you are getting 24 miles per US gallon?


New math?
Remember the imperial gallon is larger than the US gallon.
1 imperial gallon = 1.201 US gallons.

20 miles per Imperial gallon = 20 miles per 1.201 US gallons.

20/1.201 = x/1
x = 16.623 miles per US gallon.

Cliff

Here's the 261 Cadillac article.

261 Cadillac Build

I don't mean to get off topic. My point was about the 261 engine, that it's a good engine. (My actual mileage to KC and back, a distance of well over 2000 miles was 21.5 mpg, a bit less if you use American gallons. John Milliman was right behind me for the last stretch, ask him about the body or the downhills)

I get 18MPG (USA gallon) highway-driving at 55-60MPH with a 261 and 3.55 rear-end and 31.5" diameter tires. The MPG drops to 12-14MPG at 65-70MPH (most likely a result of higher RPM and higher wind resistance).

It's also possible the power valve spring in your carburetor is a bit too strong. When manifold vacuum drops enough to open the power valve, fuel economy goes south in a hurry. What kind of carburetion are you running?
Jerry

I got similar results at similar speeds with:

Dual single-barrel Rochesters (too much "carb"/flow at low RPMs) - rebuilt by whomever JC had rebuilding carbs 16 years ago

Dual progressive two-barrel Carter-Webers (no significant "power" at higher RPMs - new from Langdon

Single two-barrel Holley AA-1 (with adjustable jets) - rebuilt by a professional who has a good reputation

That's exactly my setup and gas mileage.

Thanks Cliff. No, not new math, old brain. I did the math backwards. Now the point is that this guy gets about 1.6 more miles per gallon than my stock 216, 4.11 torque tubed 52 3100. I'm not going to challenge him to a race, but we can stop at every gas station together along the way.
Carl

Carl
Yeah, multiplied instead of dividing. Been there, done that.
That's why I like to write the problem out as equal ratios.
I figured you would eventually see the error but had to get my $0.02 in. 8~}
Cliff