273 Commando redline

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brodphish

brodphish

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I have a 1965 Barracuda very original with what I believe to be a 1966 Commando in it, I mean I believe it is a 1966 motor from the block castings and similarly dated heads.

It is not a Formula S car and there is factory tach (I have since added a period correct looking Sun tach).

Simple question I know but can someone tell me the redline for this motor?
 
I bounced the SW tach a few times on my 65 "S" but I think the tach was so heavy that it was not that accurate. Id say 6500 if there isnt any red on the stock tach? Forged internals and a pretty small stroke...
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I wouldn't spin it more than 6K at the absolute most. 5500 would be MY limit.
 
Mine always spit out push rods till I got good valve springs and 3/8" push rods, then it would rev to 6500 with no problem, then after a year of beating on it, a problem, it spit out a rod bearing. It was a stock motor with a 292/.500 cam so it held up better than expected. I was 17 years old and was learning the hard way.
 
D-Dart 7K shifts, 8500RPM circle track stories, 7000 Dyno pull on a 318...they seem to be a pretty stout little motor with maybe the valve springs ad cam being the limiters. your redline will be your cam powerband..maybe..the heads will stop revs enough to keep from blowing it? Dont find out.
 
My 2cents is 6,000rpm.
The valve springs are the limiting factor.
Steel crank, short throw and solid cam make it a 8,000rmp candidate BUT the valve springs are going to break or float the valves at one point. Also points ignition is a limiting factor. Be safe- set it to 6k and drive it like you stole it - respectfully. She’s a 50 year old motor.
 
For a stock engine, peak torque is at 3500 and peak horsepower is at 5000. Why go any farther than that
 
Start at 5K. find a 1/4 mile test strip with no one around and shift at 5K and note mph at the end. Bump it 200 and re test. When it stalls, go back to the previous shift rpm. No use in winding her up if she is not pulling. Do you have a windage tray? What oil pressure do you have? Is the 273 Commando stock?
 
A lot would depend on the condition of the engine. If it was an "original" 1966 engine that hasn't been apart since 1966, I would tread lightly above 4500. A 3.31" stroke LA engine in good condition shouldn't be bothered by an occasional trip to 6000.

If you are running the original exhaust manifolds, much past 4500 is pointless unless you just want to make more noise and vibration.
 
The valves floated above 5500 rpm on my bone stock '65 Dart when I raced it in 1966. On an old stock engine I wouldn't travel north of 4500-5000. What would be the point?
 
So I detailed the car this weekend and took it out for a spin. Still pulling hard at 5000. Lost my nerve after that. The motor has an Offenhauser intake and headers (ceramic coated?) of unknown make (see pics) and an MSD ignition. Assuming the internals are stock any guesses if the power band is upped from the 3500 / 5000 stock peaks?
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stock by these mods?
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Yes it is a Q-Jet. I thought they had a pretty bad rap though some say undeserved. Plus I thought they were a GM carb.

I have to say the car runs pretty good though.
 
318's had them for a few years...Carter went on strike? valve springs are the first things to go.
 
brodphish said:
Yes it is a Q-Jet. I thought they had a pretty bad rap though some say undeserved. Plus I thought they were a GM carb.

I have to say the car runs pretty good though.
Click to expand...

They are a good design. You just have to fix the typical GM unwillingness to spend what it takes to do the job right. If you have a good Q-Jet they are keepers.
 
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