building the upper end and the cam xe268h says 1600-5800, The stealth intake says Idle-6800 the heads are powerheads cnc ported compression should be about 10.2:1 So what determines the rpm range of an engine? wheres the redline? I have no idea what dictates this. Forgive my lack of knowledge and Thanks
what determines the rpm range of an engine?
snugs
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building the upper end and the cam xe268h says 1600-5800, The stealth intake says Idle-6800 the heads are powerheads cnc ported compression should be about 10.2:1 So what determines the rpm range of an engine? wheres the redline? I have no idea what dictates this. Forgive my lack of knowledge and Thanks
The lower end was bought by PO it was suppose to be a fresh rebuild and according to him has only about 3000 miles on it now. When I asked him for info on it he said he didn't know any specifics just that the guy built engines for the local round track guys. So I have no idea. I am not planning on doing anything to the lower end it has good oil pressure and no leaks and I really don't have the money either. Thanks
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The cam that you have should be fine. If you are keeping the engine under max 5500 rpm you should be ok. Your cam, Carb size of 600-625 with vacuum secondaries and a dual plane intake, is a great formula for a nice streetable small block. Use a set of small diameter long tube headers for greater torque
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Sounds like you have a good plan.
I am in a similar situation with the engine we have. It was built by another owner, and has about 7K.
I debated taking it all apart, but the compression checks out okay. And it would be a costly exercise.
I am going to change the heads, intake, carbs, add headers, but probably keep the bottom end as it is, including the low rpm hydraulic cam.
I am in a similar situation with the engine we have. It was built by another owner, and has about 7K.
I debated taking it all apart, but the compression checks out okay. And it would be a costly exercise.
I am going to change the heads, intake, carbs, add headers, but probably keep the bottom end as it is, including the low rpm hydraulic cam.
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Valve train lets the engine breath an achieve high rpms, but the crank and the rods hold it together. Forged rods and a steel crank are essential if you are going to be running >6500 rpm.
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Valve float will be your limiting factor. I can spin my engine up to about 6,200 rpm although that is a past where it is really making power. The bottom end of a 289/302 should take that with no problem. My friend spins his basically stock Shelby up to 7K thanks to the solid lifter cam.
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dont take it past 5500k rpm too often or you might regret it...........
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There are other things that can affect RPM limit like your exhaust system, torque converter, parasitic drag from accesories like A/C & P/S.
Even thought the motor might be able to reach a higher RPM these things will not let it so they do affect the RPM range of the engine
Even thought the motor might be able to reach a higher RPM these things will not let it so they do affect the RPM range of the engine
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You don't necessarily need a steel crank to spin the engine above 6500, and all rods in our engines are forged. We use a cast crank and stock rods/pistons in a 93 drag car we have consistantly been spinning to 7500 shift points for years. If I was going to turn 7500 all the time like on a race course then I would want a steel crank, but a street car or weekend drag car does not usually need one.
Two quick concepts, there is a redline at which the engine may self-destruct, and there is a functional limit at which something limits the ability to go faster - that could be heads, exhaust, valve float, etc.
The first constraint is a function of the strength of the components, having forged rods, forged pistons, a strong crank, and having everything balanced down to a tiny fraction of a gram will allow an engine to spin to very high RPMs. Also the length of the stroke determines the piston speed for a given RPM. The longer your stroke the faster the piston will be moving at a given RPM and the more likely your engine will self destruct - all else equal. So a 289 in theory can *safely* spin about 250 to 350 RPM faster than a 302, which in turn can spin a bit faster than a stroker - again if all the parts and assembly are of the *same* quality/strength across the engines in question. Meaning a very strong stroker can safely spin much faster than a engine built to stock specs, but less than a 289 built to the same level of quality as the stroker.
For the second constraint, doing things like roller rockers, good porting, good manifolds or headers (intake and exhaust), correctly sized carb, etc. will increase the realized RPM.
One final note, many engines will spin up to a level were they aren't actually making any more significant power they're just spinning faster (i.e., the loss of torque is offsetting the increase in RPM at the margin - horsepower is just torque times rpm divided by a constant). In this case you would get a faster result by shifting once the power starts to level out rather than trying to wrap out the RPMs.
Without knowing what is in the bottom end, your engine's self-destruct redline could be anywhere from ~5,000 to ~7,000.
John Harvey
The first constraint is a function of the strength of the components, having forged rods, forged pistons, a strong crank, and having everything balanced down to a tiny fraction of a gram will allow an engine to spin to very high RPMs. Also the length of the stroke determines the piston speed for a given RPM. The longer your stroke the faster the piston will be moving at a given RPM and the more likely your engine will self destruct - all else equal. So a 289 in theory can *safely* spin about 250 to 350 RPM faster than a 302, which in turn can spin a bit faster than a stroker - again if all the parts and assembly are of the *same* quality/strength across the engines in question. Meaning a very strong stroker can safely spin much faster than a engine built to stock specs, but less than a 289 built to the same level of quality as the stroker.
For the second constraint, doing things like roller rockers, good porting, good manifolds or headers (intake and exhaust), correctly sized carb, etc. will increase the realized RPM.
One final note, many engines will spin up to a level were they aren't actually making any more significant power they're just spinning faster (i.e., the loss of torque is offsetting the increase in RPM at the margin - horsepower is just torque times rpm divided by a constant). In this case you would get a faster result by shifting once the power starts to level out rather than trying to wrap out the RPMs.
Without knowing what is in the bottom end, your engine's self-destruct redline could be anywhere from ~5,000 to ~7,000.
John Harvey
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You have almost exactly my setup. I rebuilt my engiine last fall. I had the bottom end machined and balanced, new hyperutectic pistons (.040), CompCams XE268H, Weiand Stealth (port matched to the heads), Poweheads 302 CNC heads (9.3:1 compression though), Edlebrock 600 (1406). I did use CompCams magum 1.6 rollers and lifters. I also have Tri-Y's and 2.5" exhaust with H-pipe. My 8" rear is open with 3.08 gears and I have a toploader 4 speed. No AC , no power steering or breaks. Very basic.
It is very streetable. In fact it drives very nice but a little loud thanks to the Flowmaster 40's. I am still dialing it in but so far I am very happy with the results.
Mark
It is very streetable. In fact it drives very nice but a little loud thanks to the Flowmaster 40's. I am still dialing it in but so far I am very happy with the results.
Mark
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To me - valve float should not be considered as your rpm limit. While it will certainly stop the engine in it's tracks - (lived that with my '86 5.0) - I certainly wouldn't leave 500 or 1000 rpm on the table due to weak/defective valve springs.
But back to the basic question - as touched on earlier, it could be a number of things - but I'd go further and say that it will be ONE specific thing... i.e. - the rpm limit will be determined by that one part that is the bottle-neck.
Build a 7000 rpm longblock with huge heads, huge cam, and huge headers/exhaust - but put on the stock 2-bbl iron intake manifold - that will be the limiting factor.
Likewise - run the same shortblock but with a tunnel-ram intake and big carb - but run the stock iron heads. The heads will be the limit - and so on...
I'm sorta going through this with my '86 5.0. The unique '86 "high swirl" heads had great low-end torque - but my shift point was ~4600 rpm. It would just fall flat on it's face at about 4800 rpm. (Also had valve float at just over 5000, but I never had a need to go there.) Then I did a head swap - stock (lightly ported) E7 iron heads and a stock ported lower intake. I can now blast the motor to 6000 in 1st gear - not much power up there in any other gear - but my normal shift point in 2nd/3rd gear is 5400/5200. I'm pretty sure the stock upper intake is my current bottle-neck.
I'm also working on getting more rpm out of my '67 289. I just swapped cams - went from a Crane 272 Energizer to a Comp XE262 (1 step down from your cam, advertized to 5600.) The motor seemed to die just above 4200 with the Crane. I haven't driven it too much, but now it seems to want to pull to almost 5000. I believe an intake swap is in order, as I want to go from the current Edel Performer 289 (rated to 5000) to a single plane Weiand X-celerator which should certainly get me above 5000 rpms...
Man did I ramble on...
But back to the basic question - as touched on earlier, it could be a number of things - but I'd go further and say that it will be ONE specific thing... i.e. - the rpm limit will be determined by that one part that is the bottle-neck.
Build a 7000 rpm longblock with huge heads, huge cam, and huge headers/exhaust - but put on the stock 2-bbl iron intake manifold - that will be the limiting factor.
Likewise - run the same shortblock but with a tunnel-ram intake and big carb - but run the stock iron heads. The heads will be the limit - and so on...
I'm sorta going through this with my '86 5.0. The unique '86 "high swirl" heads had great low-end torque - but my shift point was ~4600 rpm. It would just fall flat on it's face at about 4800 rpm. (Also had valve float at just over 5000, but I never had a need to go there.) Then I did a head swap - stock (lightly ported) E7 iron heads and a stock ported lower intake. I can now blast the motor to 6000 in 1st gear - not much power up there in any other gear - but my normal shift point in 2nd/3rd gear is 5400/5200. I'm pretty sure the stock upper intake is my current bottle-neck.
I'm also working on getting more rpm out of my '67 289. I just swapped cams - went from a Crane 272 Energizer to a Comp XE262 (1 step down from your cam, advertized to 5600.) The motor seemed to die just above 4200 with the Crane. I haven't driven it too much, but now it seems to want to pull to almost 5000. I believe an intake swap is in order, as I want to go from the current Edel Performer 289 (rated to 5000) to a single plane Weiand X-celerator which should certainly get me above 5000 rpms...
Man did I ramble on...
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Honestly Mark, I have never taken it past 5000 RPM. It was still pulling when I let off the gas but how much more I could go I was afraid to find out. I only have about 100 miles total on the engine since it was built. Still breaking it in and also dialing it in. I know enough to be dangerous so I am taking it slow, but I am learning thanks to this forum. :biggrin:
Snugs, with your compression you should have more HP and torque than I do so based on my own experience so far with this combo, I would say you will be happy.
Snugs, with your compression you should have more HP and torque than I do so based on my own experience so far with this combo, I would say you will be happy.
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