what max RPM on low comp 273

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lilredridinghoo

lilredridinghoo

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Hi folks,

maybe a silly question but....

what rpm would you suggest should a nearly stock low comp 273 make at pedal to the metal with a 3,23 and 904 tranny. (only modification on engine is an offy-intake and a 4bbl road demon jr. carb 525cfm and an FBO-ignition)

got mine last weekend on the autobahn and could only make 4000 rpm (at approx. 118 mph) is this okay, or should would a more healthy engine make more rpm ??

while normal faster acceleration the tranny shifts a approx. 4500 rpm what seem okay to me
 
Chances are your valve springs are weak and holding it back. I have changed valve springs both with using the rope in the cylinder trick but best to pull the heads off and have a valve job done too.

Yeah you camshaft isn't so great but 4,000 rpms is bad, that is a solid camshaft too I believe, it should get up to 5,500 min.
 
I've spun my stock 273 to 6,000 with larger cam and heavier springs
unless you've changed these 2 items, I wouldn't run it over 5,000 you could damage something
 
You guys missed something........

He was doing 118mpg. Thats fast for a 273, he was past his torque curve, sorry to say, but without a higher power band, and more power, I think thats all she's got.
118mph is pretty fast. How many Big trucks passed you? LOL
 
I believe on some parts of the autobahn you better stay in the right "slow" lanes going only 118mph, lol

But yeah, what about 1st and 2nd gear, can it rev past 4000 rpms easily and smoothly--if so you have a lack of power at high speeds.
 
I Have a stock 67 273, 904, 3.23 gear barracuda. My engine is under 30K and runs healthy. I have only had it up to 100 or so. I think 118 is prety darn fast for a 180 hp motor. I'm not sure if mine would run that fast.
 
dodgetkboy78 said:
You guys missed something........

He was doing 118mpg. Thats fast for a 273, he was past his torque curve, sorry to say, but without a higher power band, and more power, I think thats all she's got.
118mph is pretty fast. How many Big trucks passed you? LOL
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I agree with dodgetkboy.
 
Even with stock exhaust manifolds I hit the rev limiter at 6750rpm. Clogged exhaust?
My 65 did 115mph(or so the gauge said) with the heat riser froze shut with stock exhaust and 2-bbl intake even before rebuilding the engine. His should get past 118 real easy. How many miles on the engine?
 
You didn't mention anything about the exhaust. My "refreshed" 318 2-bbl. with single exhaust (and Lunati Voodoo cam, doesn't do much now) can barely top 100 MPH in a '70 Duster with 2.76 gears. Of course, that's at 7000 ft. above sea level, but I think 118 is pretty good for your car. I think with a cam and a good dual exhaust system you should be able to push 130 MPH with power to spare.
 
thanx to all for your input.

conc. your questions

- it hasn´t solid cam and lifters (if i´m right not common for a 64/65 engine, or ?)

- if i push her in lower gears. i have no problem to get her to 5000 or so (but i haven´t had the balls yet to force more)

- current exhaust is stock manifolds and y-pipe, after y-pipe i mounted a straight 2,5 inch pipe and a force-muffler (chambered) dumped at rear-axle. (plan for this winter is to modify the y-pipe for better flowing and mounting a low restriction stainless steel exhaust (copy of the commando/formula S one)

118 mph doesn´t seem so bad for this old engine....as i get you right..
 
lilredridinghoo said:
thanx to all for your input.

conc. your questions

- it hasn´t solid cam and lifters (if i´m right not common for a 64/65 engine, or ?)

- if i push her in lower gears. i have no problem to get her to 5000 or so (but i haven´t had the balls yet to force more)

- current exhaust is stock manifolds and y-pipe, after y-pipe i mounted a straight 2,5 inch pipe and a force-muffler (chambered) dumped at rear-axle. (plan for this winter is to modify the y-pipe for better flowing and mounting a low restriction stainless steel exhaust (copy of the commando/formula S one)

118 mph doesn´t seem so bad for this old engine....as i get you right..
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You could rev it to 6000 without worrying about anything breaking, but there would be no point, of course. Also your 273 should have a solid cam; the 273 didn't come with a hydraulic cam until 1968. If you pull off a valve cover and see adjustable rocker arms chances are it's a solid cam. While you're at it you could set the valve lash too, that might free up some power...
 
MOPEkidD-3 said:
You could rev it to 6000 without worrying about anything breaking, but there would be no point, of course. Also your 273 should have a solid cam; the 273 didn't come with a hydraulic cam until 1968. If you pull off a valve cover and see adjustable rocker arms chances are it's a solid cam. While you're at it you could set the valve lash too, that might free up some power...
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thanx - i know that i should normally have a solid cam find adjustable rockers ander my valve covers - but there isn´t something like that - i´d only found non-adjustable ones :-k i guess someone has changed this in the past.
 
The guy who had my 67 before me had a 273 in it, it was a stock long block with a HUGH solid cam, single plane manifold, and a 750-800holley and that thing wouldn't make power till about 4000 and then would tap out at about 7800-8000. It didn't last too long though.
I'd say free up the exhaust a bit more, a bigger carb might help, and what kinda timing do you have?
Do the 904s have some kind of governor?
What town are you in? My family and I are from Hallstadt next to Bamberg (more central Germany)
 
Nitrous340Dart said:
and what kinda timing do you have?
Do the 904s have some kind of governor?
What town are you in? My family and I are from Hallstadt next to Bamberg (more central Germany)
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cannot really tell, what timing (have to figure it out exactly with a light-gun) i guess somewhat about 10 or so...

i´m coming from Nördlingen - it´s a small town in Bavaria - about 170 km far from Hallstadt
 
You guys are trying to kill him, 118 is fast enough for that thing! I doubt it would panic stop to 70 without smoking the brakes from that speed...
 
You guys are funny! Keep the speed down.......save your life. Rebuild your front suspension and your brakes and decide whether 120+ mph is safe. Wait a minute....are you talking about 120kph? That's a different story. The 273 with the correct parts will rev to 7 or 8,000 rpm but everything has to be right. Fresh
valve springs a free flowing exhaust and a good ignition system will get you there. You also need a bigger carb that will supply fuel at 8000 rpm and a fuel system to go along with it. Cars that go for the land speed records at the Bonneville Salt Flats are built a bunch different than a street car. toolman
 
just cool down...

okay - we´re talking about 118 mph not kph.. i know it´s fast and i will get her beyond saftey limits. (btw. breaks are rebuild, suspension is up-graded with Koni-shocks and sway-bars on front and back, switched from power to manual-steering) okay i´ve got no seat-belts in this car.

back to topic - if i get you guys right, 4000 rpm it´s well okay for an older engine... if i want more... it would be better to up-grade valvetrain and cam, even the carb.
i think the first step, i will do, is to put the car on a dyno and let some professionals figure out what the limits are for the current compo, also let them adjust the carb (jets etc) while the cars is on the dyno. Goal is best MPG >< HP ratio.

but keep on posting your suggestions - every input is appreciated
 
E Production Pickup (E/PP) Scroggins 8/08 126.073


1973 or 1974, not sure. 3/4 ton pickup with a de-stroked 273 (258CI).

Thats a 4500 pound truck powered by a small cubed small block
 
but keep on posting your suggestions - every input is appreciated
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If you want R's, single plane manifold, up about 10* on the cam, and a bigger carb.

A 273 will run 5.5K allll dayyyyy looooong.........
 
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