What determines a true redline?

[7thGear]

Most stock cars today have redlines at 6500 or 7000. Once you hit that, fuel delivery is cut off and you go to ground zero. Thats how most stock cars have it.

But what really makes a true redline? I understand that the redline is what the manufacturer says is the maximum RPM the engine can safely produce without going bust ( actualy its probably a few K back, most manufacturers dont expect people to cruise in 5000 all the time )

So in that case, when installing lighter and stronger internals, doing things like balancing the crank shaft, installing double springs and better vavles etc etc etc, in theory increases the strength of the motor

is it safe to assume that an engine modified in such a way can rev higher with less chance of brake down than before?

if yes, then how would one go about calculating the new "true" redline? Other than stomping on the gas and waiting until you see smoke isnt exactly the best way, IMO .

and as a tid bit, that AE 86 engine that supposed to rev till 11 K, if custom interal jobs are done on THAT engine, can the car rev even higher??

But i guess the next question that follows, does it need to rev that high?? Why and why not?

[Rockenreno]

may be wrong, but i dont think thats the AE86... i think its the AE101 or something... once again, not sure, just what I've heard..

[C-Kwik]

There are a lot of different things that can limit engine speed. In most cases, it is piston speed or the valvetrain. But things like rod strength, crank strength, oil pump capabilities, harmonics, balance, fuel delivery, ignition capabilities, the list goes on, can all limit engine speed.

As far as determine a new redline after mods, you have to consider the weakest link and use that as your base for determining redline. There is no easy calculation though. You'ld need a lot of hard scientific data to determine this with any certainty.

[corn322]

we found out a few weeks ago that an RSX's redline is well below 15,000 rpm

[C-Kwik]

lol

[7thGear]

yeah i remeber that one, thats the easy way to find out, lol

i wish i had a job like that, rev engines until they blow up

" um sir, your new redline is 12 000, now give me my money"

"um, what about my engine?"

" heh, um... heh,.... well there is a peice of it here,., some over there, ohh look i think thats a piston in my pocket, here you go" ** hands over piston **

[MadSideways]

Typically, as in the 95-98 US 240sx case, the marmonics of the crankshaft make it unable to spin any faster without vibrating itself to pieces...

In all engines theres a certain RPM where the OEM valves are in a constant open state, termed as floating.

If an engine becomes fuel starved, it will run lean and predetonate, usually causing a domino affect of internals collapsing. Fuel injectors have a maximum rpm where they are dumping fuel at wide-open-throttle, and cannot possibly release anymore fuel.

Some engines may run fine at or above redline. But after extended use the internals may become weakened over time and fail prematurely.

Typically to raise the redline, you would have to supply enough fuel, have the engine balanced atleast 2k rpm's above where you'd like to redline, and have the valve-train upgraded to support the rpm's desired...

Ofcourse, this engine would never be anything like the factory engine, probably unreliable as hell. You'd be better off getting a drop-in stroker kit from JUN and double your hp/tq numbers, for half the cost of raising your RPM's and making a rwd honda.

[Aries]

an engine's redline is determined by where a stock motor will:

A. Experience valve float due to car rotation speedsB. Experience detonation/pinging due to flow capabilities being excededor C. Flow becomes inverse due to the ammount of backpressure built by exhaust gasses flooding back into the clyinders

[C-Kwik]

Adding to Aries's list,

D. When the tensile load on the rod snaps the rod. Not common - Usually something else will want to give first.

E. The Centrifugal/Centripetal(whatever) force of the crank rotation draws oil through the channels faster than the oil pump can keep up with. Causes the bearings to go dry and viola! Spun rod bearing.

I'll leave out fueling and ignition capabilities as Aries is focusing on the mechanical redline.

[7thGear]

wow thanks alot guys, kinda hard to peice it all together.

in that case,

If all the mods i lsited ( plus some more i assume), i should just think of my current redline as being a safer zone, ie, i can rev the engine back and forth and risk less of a problem than before

instead of thinking of a higher redline

or would both assumptions be correct.

And would raising my redline even benefit me if i wont use a larger cam? I understand that engine peak HP drops off at some point, and that point is usualy raised by a higher duration cam, so then can i assume than need for rpm is proportional to cam duration?

[corn322]

yeah, the current redline would be safer to operate at, 'cause the lighter, correctly balanced stuff wouldnt' make vibration so bad that it weakens the metal.

raising the redline might help, but I dunno how low the torque and hp curves drop off after stock redline, so I really couldnt tell ya

if for instance, say your hp curve goes like this (for show only, numbers aren't real)4000 - 1254500 - 1305000 - 1375500 - 1426000 - 1386500 - 1307000 - 123

say when you shift, it drops 1500 rpm. if you shifted at 5500 rpm (power peak, 142hp), it would drop down to 4000 @ 125hp.but, if you waited past peak power, and shifted at 6500 (130hp), it would drop to 5000 hp @ 137hp, so you'd have more power initially during the shift, and would be able to gain revs faster.

I believe what you wanna do is not shift at peak power, but kinda straddle it, so you go past peak power, and it starts dropping, but when you shift you'll be making same hp only at a lower rpm