Technical we need a dedicated 261 thread.

"Well I took it to the track this last summer, and it seems that the motor stops making power at 3000 or really stops puling at that point."

Sounds like the cam is too mild to let the engine rev. The stock cam was made for torque, mileage and long life not speed or performance.

As to who makes the best cam, or what cam to use, I can't help you. If you talk to one of the old time cam grinders like Isky or Crower they may be able to advise you.

 

Thats kind of what I was thinking on the cam not getting the motor rev.

 

Peak torque on the stock 261 cam in a stock 261 is around 2000 rpm.
http://chevy.oldcarmanualproject.com/chevyresto/59ted04.htm
It was a 2-1/2 ton truck engine...

When you let a stock 261 breath better with more carbs and headers, you should also use a better cam.

1/2 race grind up to and below 264 adv. duration gives max torque around 3000 rpm.
3/4 race grind gives more HP.

But with a hotter cam you don't want to use an overdrive transmission gear with a low gear ratio on your rear, or the engine never makes power at 2000 or less rpm.

 

Check your head casting number.
With todays higher octane gas, compared to the 50s, you want to use the highest compression head available at the time.
After 1958 the 'high-compression 848 heads' were milled at the factory matching the gasoline at the time and if your 261 was bored up to .060 you are just about right with todays regular octane gas at the pumps.

 

Thanks for that info and link. Do you know where I should get a hot cam for the motor? And I'm looking to get more hp on the grind probably. Thanks jeff

 

I had good luck with Delta cams in Tacoma, WA, who also supplies Patrick's in AZ and Tom Langdon Stovebolt Engine Co, both offering Delta's popular 'Bulldog' 261 grind.

 

This "high compression 848 head" stuff is nonsense. i dont know where it comes from. the head is only going to give you .25 (or .50 at most) compression boost on an 8.0 motor. it isnt a high compression head - it is a "less low compression head". any good head will work

 

Awesome, thanks. As far as the head goes, I'm not switching that out for the 848 head, as 6inarow posted thats a lot $ for not a whole lot of hp.

 

Be sure to get the lifters when you get the cam - we have had lifter trouble the last several years

 

Depends on the head you have now. Years ago I switched a 913 head for a milled 848 on my 235 and it sure made a difference in power and gas consumption on my daily driver. The new head was rebuilt and in storage for years, costing me less than a new intake, let alone the carbs.
The switch took a couple of hours.

Some folks spend big bucks on elaborate engine mods to just gain a few more HPs.
Going from 7s to 8s with just a had swap can make a difference to some of us.
Doesn't take a lot of effort to check your head, do a little research and see what gains you can make or not.

When the 261 first came out in 1954, it used a head giving around 7 CR
A shaved 261 block with .060 bore gives around 9 CR with a milled 848 head.

Pontiac cars in Canada of the early 60s came with the 261 and 848 heads.
After 1956, you could only get 848 heads as replacement for all previous years matching the bolt pattern.
There used to be 6 different head castings with the lowest CR at 6.7
So depending on what head casting you have, the 848 can make more or less difference.

 

Ill check the casting number on the head but I don't believe its the 848 head.

 

Give us the last 3 digits of the casting number and I can tell you what data I have, if any.

If you lift the valve cover you can also find out the casting date that is located near the temp sender between cyl 4 and 5.

 

Here is the casting number on the head. 3836850 GM5

 

This head was used on 261s after 1956 and on a stock 261 had 7.8:1 CR according to GM specs.
After 1958 all heads were milled at the factory and the 261 had 8.0:1 CR.

Doing the math, your reconditioned .040 bored 261 with a milled 848 head could give you 8.9
That's a better match for todays pump gas octane, wasting less gas and giving more power and mpg.

I found 2 already built and milled 848 heads in storage, a few months apart for both my 235 and 261 and for not much expense. - They are out there.

 

Really, thanks for the info. I know the motor is a 1961 but didn't know much about the head info on it besides that it was probably stock.

 

Finally some more progress....Got the reground cam back from Oregon Cam Grinders today . Degreed the cam and it was spot on.Advanced it 2 degrees with a SBC offset key like I've done in the past.
About the compression mentioned above.Every 261 with stock type pistons I messed with had the pistons sitting down 50-70 thousands at TDC.Available head gaskets are about .052 compressed ,some are closer to .060.You have to mill the shit out of a 848 head to get a real 9-1 compression,yes? And then the piston is still way down in the hole with very poor quench.

 

What cam specs did you get?

Original stock 261 pistons have .030 less compression height than 235 pistons.
Stock type ones sold these days are .020 lower yet.
Just another reason to use a head with least compression for an already built block.

 

The cam is a #818 grind, 211 degrees at .050 lift and .420 total lift at the valve,lobe centers 106 on intake and 114 on exhaust.moderate grind and easy on the valvetrain, and about the limit for a reliable reground cam or so they tell me.
I took apart a standard bore 235 with GM pistons a few months ago.The pistons were .017 below the block deck.So the 261 would be .050-.070 below deck depending on pistons.The actual compression on these engines is close to 1/2 point lower than advertised from what I see.

 

yep - if you start milling the head to get the compression you want you are going to create all sorts of problems for yourself.

See post 23 and post 36 then use any head you want

 

Too bad that the old Jahns high compression pistons for early sixes are hard to find anymore. I lucked out and picked up a N.O.S. set at Hershey a couple months ago---the guy sold them to me cheap because the box was marked "STD". The thing is, Jahns always seemed to call their pistons "standard", regardless of what size they were. These were actually oversize.

 

Tell me about it,Ross pistons and rings set me back nearly 700 bucks.Oh well,a lot of money for 180 hp but Flattie V8 guys pay more for less HP

 

Yeah, buying the set of Jahns slugs for $100 was the highlight of Hershey this year.

 

That's very similar to my Delta 254 adv. duration regrind on a stock 261 cam.
211.4 degrees at .050, .433 valve lift with 110.3 and 109.7 lobe centers.

Makes peak torque around 3000 rpm, which is great for power and mileage on freeway trips at around 70 mph with no overdrive, 3.55 rear and 28.3" tires.

 

The 261 is going in MY 50 Chevy pu,3.40 gears ,truck 4 speed,2500 rpm at 65 with 16 inch tires.
This is not a "hot rod" engine so much as a good torque and fuel mileage build.

 

I'll give you $125 for them right now

 

That's cool! - I like to see and hear more early chevs on the road and getting good use.
A well-breathing 235/261 with moderate cam and this head designed for economy, is very efficient around 2500-3000 rpm with another 500 rpm for the 261.
No stress, stays cool at 180 degrees, even on the hottest days through the desert.
20 mpg on the freeways at 65-70 mph and even better mileage on the country road.
The low-end torque and sounds it makes is just pure vintage motor fun at its best to me.

For a hotrod straight 6, I'd favor the 292 or even better the 302 Jimmy.

 

Sorry, I don't take produce in trade.

 

how about I pull your front tooth for free?

 

....but then I wouldn't have any left!

 

Subscribed... I have a 56 261 waiting in the wings for my 55.1 3600. Will definitely be referencing this thread!