I am guessing a bunch a variables combined. IE forged versus cast, cam range, lifters and valve (the lack of valve float) and so on but do things like piston speed and VE effect it to? How do I determine redline, without blowing holes in the side of the block?
Take it to where shit flies every where..Note the RPM at that point..and than next time back it off about 200 RPM
I don't have a mathematical genuis answer for you, but i'd say redline for me is about 200 rpm past where the engine quits making power. Your engine should be set up for the cam you're running. Going past what the cam is capable of is what I consider "red lining". To others, i'm sure the term red lining means the point at which it will blow up... that's anyones guess and each engine is different. You'll probably float a valve before it just grenades on you... but who knows until it happens. You can look at your cam and valve train specs to theorize at which point the engine would blow or be seriously damaged, but in the real world... you might get lucky, you might not. Anyways... just my thoughts.... I'm sure one of the HAMB PHD's will give you a much better answer than mine.
simply put, weight & balance. and engine life expectancy...from a performance aspect wouldn't it be where the torque and horsepower curves intersect?
The first bottle-neck will top out the power curve. modify that and then the next one shows up a bit higher and so on. Then....well .....The weakest link breaks first.
Honestly what determines redline outside of the parts list, displacement, rotating weight, and breathing ability is who put it together... You can have the nicest parts off the shelf, but if the tolerances are not there, the balance is just good enough, and the valve job is done by whoever was cheapest, you are in for trouble. What do have in mind for an engine and what are you doing with it?
Like you said, many factors involved. High end of power band is mainly determined by cam choice but also how well the heads, intake carb/injection and exhaust flow along with compression ratio, etc. The mechanical limit would be like previously noted by VRG, just before parts failure such as rods breaking or valve springs floating and so on.
When you reference redline to catastrophic failure, bore to stroke ratio has a lot to do with it. Engines with a larger bore to stroke ratio will generally rev higher, all other variables being equal. Some formula one engines have huge bore and short strokes and will rev to near 20 grand. On the other side of the coin, the old MOPAR slant six had a long stroke and small bore and redlined under 5 grand. It is all related to the leverage the crank can place on the rods.
No, because then the red line on every engine would be 5252 RPM. Look at any dyno pull of any engine that can spin that fast, and you will see that the torque and HP numbers are always identical at that RPM. It's part of the equation (HP = Torque x RPM ÷ 5252). I have a stone stock 248 CI babbit-bearinged straight eight Buick, and I KNOW its red line is way below 5252 RPM.
more of a general question didn't know if there was a formula / guideline to come up with when I build an engine. more over what If I wanted to build a 675-7.5 k sbc.. I was thinking a short stroke 302/327 forged bottom end for a gasser idea I have... Any suggestions would be appreciated.
when the pistons and rods sling out the side, the redline should be a few hundred rpm's below that point.
damn,beat me to it. always a smart ass in every bunch, I just thought it would be me this time. hate being second
thats ok Turbo..I learned it the hard way..but it sure sounded cool as hell..right before shit went everywhere to be honest..I wasnt watchin' the tach either..i was getting the F away!
Not true, plenty of engines peak HP wise past 5252. So if you dyno an engine that makes it peak HP at 7200 and it will last, make the redline just past that.
The stroke and quality of parts are the main factor.The feet per minute the piston travels, a short stroke motor will have less feet per minute than a long stroke motor.A 283 or 289 will live at a higher rpm than a 400 ar 383 with the same quality parts.But from a performance view you want to shift where the rpm will drop to your peak tourqe after each shift. keep in mind a piston comes to a complete stop at the top and bottom of each stroke so if your gonna rev it up you better have good parts.
Two words, Valve Float! Once you hit this point push it a little farther and see what happens! All kidding aside though I use the general rule that when you feel it stop pulling that should be your redline, if you can feel the power drop off at 6500rpm then it is done pulling, shift and start over.
What is the RPM range on your cam ? Small blocks can do 6000 + ! Be careful winding out a Big Block ! If it sound like the bottom end is going to come apart , then you found it . It really does matter the internal parts used to build your engine also .
I don't know what your budget or expectations are but a 327 might be cheaper to build than a 302 piston wise. Dart Iron eagle or equivalent heads would fit the bill too. For rods you could use a new I beam rod like Scat w/forged or hypereutectic pistons, 11:1 comp.and a solid or hydraulic flat tappet cam w/.050 dur. around 250 deg. Which would probably work on pump gas. Along with that a single plane intake or tunnel ram, main studs,windage tray, decent rockers like comp roller tips an SFI approved balancer and a good ignition. If this is a stick car a rev limiter wouldn't be a bad idea either. I don't know if any of this fits your plan but maybe it will get the ball rolling.
I think a stock motor they recomend around 3500 feet per minute piston speed and up to 4000-5000 fpm on a race motor.A 302 chevy reved to 7000 rpm is about 3500 feet per minute.If you have good parts you should be safe there is not much to be gained on most motors to go much higher.
The type of engine, oiling system, type of cam/lifters, and the sum of the parts determine the redline. I was going to be a smarty and say "The redline is exactly one RPM shy of the point where the smooth-running cohesive engine assembly explodes into many smaller parts than originally existed!"
I would define redline as the shift point that gives you the best E.T. provided your parts are up to the task. even if you could spin 7500 RPM and not grenade your motor, if you get a better ET shifting at 6500 then 6500 should be your redline I always figure "redline" was the red line on your tach
What determines the red line? Camshaft Duration providing the rest of the engine is up to it. Peak power (or ideal shift point which is a better way of looking at it) is often about 500 RPM below that. Don
I think he said that torque and hp are equal at 5252. If that's not true, you better find yourself another dyno operator unless 2+2=5. It's math. "........more of a general question didn't know if there was a formula / guideline to come up with when I build an engine. more over what If I wanted to build a 675-7.5 k sbc.. I was thinking a short stroke 302/327 forged bottom end for a gasser idea I have... Any suggestions would be appreciated......." It shouldn't be too hard to build a 7500 rpm smallblock. Lots of "local" circle track cars turn that straight after straight, lap after lap with 350 and 400 cubic inch engines. It takes good breathing (cam,heads, intake, exhaust) along with a stout bottom end (forged crank, good rods, light pistons, etc.) It's pretty basic stuff now days. Larry T __________________
It's your wallet divided by your balls. It's also what 49 ratfink says, the one that gives lowest ET. Run your car enough and don't be suprised when the quickest way down the track isn't same shift point in every gear. It's not just max rpm, it's also about the rpm drop on the shift, and every gear has a different drop. good luck
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