Time for 261 upgrades

EL-Swervo · Veteran Member

Time for 261 upgrades

long stroke · Canadian Poncho Superstar!

David, you might want to consider a two barrel Rochester carb on a after market Clifford or Offenhouser intake. A four barrel, even a small four barrel would be too much carb for that 261 unless you did other things to the motor, which you do not want to do. Keep in mind that to use a two barrel carb, you would have to use a four barrel intake with the two barrel adapter plate. The two barrel Rochester is a great carb and is generally cheaper to buy than a Holley. Good luck and cheers mate. George.

73SC · A Poncho Legend!

If I am not mistaken the original carb was the same one used on the Corvette engines with the Blue Flame 6. Seems to me that carb could be sourced, might be pricey once "Corvette" is added to the PN though.

GLHS60 · Poncho Master!

Corvettes with the Blue Flame 6 had 3 side draft carbs so I doubt that would be an option.

Thanks
Randy

73SC · A Poncho Legend!

The Forgotten 261 Six-Cylinder

Between 1954 and 1962, Chevrolet produced their famous full oil pressure 235 cubic inch six-cylinder in trucks and it soon proved to be one of the greats among engines. However, at the same time a lesser known "big brother" to this base engine was being used. This was the quality built 261 cubic inch six cylinder! This 261 was available only in 2-ton (6000 or C60 series) trucks and school buses. During it's early years (1954-57) it was an extra cost option above the standard 235 six-cylinder.

In 1958-62 (the 261 now had a full flow remote oil filter) it became standard in the 2-ton chassis up to 19,000 pounds gross weight. Above that Chevrolet substituted a V-8.

This larger six was not offered in US cars, however there was an exception in Canadian built full-size Pontiacs. Their base engine, also produced only in Canada, was the 261 not the V-8 as in the US. This provided basic power, great dependability, and better gas mileage.

Basically, this larger engine was a 235 with the same crankshaft but GM engineers made various modifications to give it extra strength and horsepower. Its standard bore diameter increased from 3-9/16 inches to 3-3/4 inches. The connecting rods were heavier and attached to increased diameter piston wrist pins.

Its higher lift cam shaft, for better breathing, was shared only with the early 235 six cylinder Corvette. A modified larger Rochester carburetor was also a 261 only feature. Unfortunately, most of these larger sixes have long since had their original Rochesters replaced with 235's and therefore do not perform to their full potential.

In pure big truck form the 261 has a larger thermostat housing holding a double acting thermostat. This is designed to circulate water through the block and head before the thermostat opens to allow hot water into the radiator. Thus, no internal steam hot spots during warm ups, especially in winter. This is particularly important with very cold coolant. Vital engine spots can become very hot before the total coolant becomes hot enough to open a normal thermostat on the front of the block.

Yes, it is the cam that is from the Corvette and a modified larger Rochester carburetor.

GLHS60 · Poncho Master!

Sorry Ray, that's just how you are interpreting the 261 article.

The 261 shared the Corvette 235 camshaft.

The Corvette had no room under the hood for a conventional carb so three side drafts were used.

Thanks
Randy

"Its higher lift cam shaft, for better breathing, was shared only with the early 235 six cylinder Corvette."

"A modified larger Rochester carburetor was also a 261 only feature."<<

Gregory · Addicted!

early corvettes used 3 carter YH carbs , they were also used on turbo corvairs and also in many marine applications.

Indian · Guru

Contact The Carb Shop in Eldon Missouri, they can help you with all your carb questions, its who I use, over 150,000 carb rebuild kits in stock, they know carbs. Clifford Intakes California have some very cool carb/intakes for your ride, one, two, four barrel setups, tripower, dual carb and custom intakes for your 6cyl

-- Edited by Indian on Tuesday 7th of April 2015 08:05:55 PM

LeeRoy · Guru

73SC wrote:
The Forgotten 261 Six-Cylinder
Between 1954 and 1962, Chevrolet produced their famous full oil pressure 235 cubic inch six-cylinder in trucks and it soon proved to be one of the greats among engines. However, at the same time a lesser known "big brother" to this base engine was being used. This was the quality built 261 cubic inch six cylinder! This 261 was available only in 2-ton (6000 or C60 series) trucks and school buses. During it's early years (1954-57) it was an extra cost option above the standard 235 six-cylinder.

In 1958-62 (the 261 now had a full flow remote oil filter) it became standard in the 2-ton chassis up to 19,000 pounds gross weight. Above that Chevrolet substituted a V-8.

This larger six was not offered in US cars, however there was an exception in Canadian built full-size Pontiacs. Their base engine, also produced only in Canada, was the 261 not the V-8 as in the US. This provided basic power, great dependability, and better gas mileage.

Basically, this larger engine was a 235 with the same crankshaft but GM engineers made various modifications to give it extra strength and horsepower. Its standard bore diameter increased from 3-9/16 inches to 3-3/4 inches. The connecting rods were heavier and attached to increased diameter piston wrist pins.

Its higher lift cam shaft, for better breathing, was shared only with the early 235 six cylinder Corvette. A modified larger Rochester carburetor was also a 261 only feature. Unfortunately, most of these larger sixes have long since had their original Rochesters replaced with 235's and therefore do not perform to their full potential.

In pure big truck form the 261 has a larger thermostat housing holding a double acting thermostat. This is designed to circulate water through the block and head before the thermostat opens to allow hot water into the radiator. Thus, no internal steam hot spots during warm ups, especially in winter. This is particularly important with very cold coolant. Vital engine spots can become very hot before the total coolant becomes hot enough to open a normal thermostat on the front of the block.

Yes, it is the cam that is from the Corvette and a modified larger Rochester carburetor.

What about the 292? Any engine family connection with the 235/261? They were popular in late 60's early 70's local stock car racing.

GLHS60 · Poncho Master!

The 292 is from the 194-230-250 family but the carb might be adaptable as it's a single barrel.

Thanks
Randy

EL-Swervo · Veteran Member

Thanks Guys, there is a lot to research here!

I have not thought about the two barrel Rochester before, will look into that.
I still have the original carb, just need to re-build it and replace the plastic parts that melted with a blow-back one afternoon, so could go that route? and contact the carb shop?

Or blow the budget and go for the Clifford set up?

I am going to California in August, I should be able to wedge a carb and manifolds into my wife's case!