EGmikeH22

i was just wondering, what determines redline for any engine, i mean what is the max you can safely rev a specific motor, and how do you determine that point.
what exactly happens when revs are brought too high?
what can be done to bring your safe redline up?
what is the determining part causing the stock redline, what is the weakest factor of the honda 4s?
How do you know when you are revving too high?

This came up when i borrowed an XS engineering ecu that took out (or moved up) the rev limiter on my jdm h22a. I took it to 8k, all of the time, like every day for weeks. I had an injen intake, and 2.5" exhaust, other than that it was stock at the time. I just wondered if it was safe, how far is it safe to go, what happens when you go too high, and without trial and error, how do you know how high you CAN go, so you can determine how high you SHOULD go, then how high you DO go.

Thanks for any input (with substance)

slateraptor

1.) rev limiter determines red line
2.) you'll float your valves, then everything's downhill from there...
3.) a lot of things, especially valvetrain work
4.) might wanna ask honda about that, i think weakest part are the sleeves
5.) if you hear funny noises, and smell something funny, but you're not laughing

dirtySOHC's

im not exactly an educated man on the subject but i would think its determined by how much power the motor can make up to a certain point. also i think its highly dependent on the motors geometry. if a motors rotational assembly was not made for high revs then there is not point in trying to rev it past the desired limit.

Ajax

Well, one thing is optimal power. I guess thats what you'd call it. I've heard that if you take it to much above redline you start to loose power rather then gain/maintain power.

My question is how can a high-reving engine beat an engine that has a lot of power at low RPMs? Like a 4 cylinder vs an 8 cylinder. When you rev higher does it have a wider range where its at peak power? Is it because on a V8 lets say your peak is between 3000-6500(Just made up random RPM ranges ) and on a 4 cylinder you might have a peak at 3000-9000, so your holding your peak for longer then a V8?

Sorry if thats a bit hard to understand... just worked 3rd shift on 4 hours of sleep so I'm pretty tired.

AzntaggeR

honda engines; mainly the VTEC engines lack low end power which is why it has to be made up for in the top end. that is how some of them can beat or hang with much larger displacement engines.

Caretaker

true that, vtec engines compensate in the top end.

AzCivic1.6

roadawg

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AzntaggeR &raquo;</TD></TR><TR><TD CLASS="quote">honda engines; mainly the VTEC engines lack low end power which is why it has to be made up for in the top end. that is how some of them can beat or hang with much larger displacement engines.</TD></TR></TABLE>

The point of VTEC was to have the best of both worlds, low end torque and high end HP. The reason they have no power down low is because they are small motors. Crank torque is directly related to the amount of air/fuel that can be burned per engine cycle so a small motor is not going to be making gobs of torque at low revs. While Honda designed a VTEC motor to have optimal low end torque and high RPM HP, they still have relatively low torque outputs because of the small displacement. They make so much HP because they make peak torque at very high RPM. HP = Torque * RPM / 5252.

Regarding the ability of an engine to rev it is based mainly on the valvetrain. For example, the valve springs on a stock b20 or LS are pretty weak and will snap if revved above 8k constintently, causing the piston to hit the valve(s). The bottom end of the motor is kind of along for the ride, however it does play a factor in high how the motor can rev. Rod Stroke ratio is important which determines piston speed inside the cylinder, and load on the cylinder walls, but R/S is not nearly as important the valvetrain.

EGmikeH22

okay, thanks roadawg, i get how shorter rods would make the pistons go slower, (they have less distance to travel in the same time) so that makes a lot of sence. Other than that please everyone read to learn and post to educate. who said "rev limiter determines redline" after they read my question, and why are they even posting, that person needs to read and ask questions, not just post to bring up the counter.
Now, what can one do to raise the safe limit of how high they can rev their engine.
I would like to rev to about 9k, what would that take?
What would it take to go to 10?

As far as i hear from my local buddies stiffer valve springs and new retainers can make high revving safer for the head, which (to them) seems to be the first thing that would go.

jspresso

the ecu

hellshock2182

stiffer springs in the valvetrain would be a good place to begin work (so the valves can open and close faster with increasing rpm's) I'm looking into doing the same thing but I would like to increase my redline to 8500 in a built d16 w/ a stock bottom end.