How high can you rev

[clawhammer]

Did a quick search but didn't find anything.

How high can you rev an engine? What determines the redline? Is there a special formual used to find out what it is? How can you make it higher?

I'm not just talking about looking it up for the engine in the manual, I'm asking about what determines the physics of it.

[Moppie]

In the simplist possible terms?

Airflow and phyiscal strength.

And engine needs air to rev, the more air that can be fed into it, the higher it can rev.
Air flow is of course dictated by intake design (from intake through manifold, head ports and past valves), camshaft profile and timing and bore/stroke ratio. And of course fuel supply.

Phyiscal strength depends on metals used, hardening techniques used on the metals, and of course physical design.

Manufactors build a rev cut into modern engines at a safe point before one of the above is reached, and in most cases if this is by passed most enignes will run out of air or fuel before reaching thier strength limits.
Running out of air or fuel can cause lean or rich burning which can damage an engine, and of course reaching the strength limits of internal parts can be catasrophic.


To make an engine rev higher you have to increase the air/fuel supply and or make the engine internals stronger.

[CBFryman]

::Claps:: standing ovation everyone. well done moppie.

[clawhammer]

So if you add a cold air intake with cone filter, racing camshafts that keep the valves open longer, remove restrictor plate if it has one, how high above the previous redline can you go?

[ales]

There are too many other variables for anyone to give you a simple fit-all answer.

[ec437]

How high can I rev? 8000 with my quad cam V8

In my previous car I could only go to 4500. I hit that limiter every single day lol

[CBFryman]

well removing the restrictor plate alone will bring most completely OEM engines up at least 1k. cam shaft can extend the revs as far as you want it really. but if other restrictions cut your torque even with a cam shaft there is no need to go higher simply because iwht out torque engines stop making power and power is what you need. you can spin an engine untill a rod snaps and a piston goes flying un controlled into the head or the crank shaft brakes but the engine will have stoped making power a long time before this happens. most stock rev limiters are set to cut the engine at the safest RPM for thoes internals where that cam shaft, intake manifold, exaust set up, head designs, intake set up stops making power. really there is no point in removing stock rev limiters unless you are putting in a high RPM racing cam shaft and giving an intake manifoldand exaust system to compensate. then you will need a fule system to compensate. there really is no reason to have your engine turning at 10,000 RPM in a daily driver. 7000 tops will do you fine. unless yo uare in a rotary where they continue to make useable power into the 9000 and even 11,000 range. but you have to ask yourself "how often will i be reving my engine to 8,000 to make peak power in my every day driver?" if you answear is slim to never you may want to look for a goo middle RPM power ban rather than high RPM race power ban. and if its for all daily driving i suggest low to mid rage RPM power since that is where the engine sits at most of the time 2,000-4,000RPM.

[snoopyloopysk8a]

My tach reads to 8k, with a redline at about 6750.

[bjdm151]

A lot of this goes into determing the capabilties of an engine at whatever rpm, but what allows the engine to spin to said rpm is the engine geometry. the engine geometry, composed of the rod/stroke lengths, determines piston acceleration. By the way, don't knock me for spelling, it's Christmas break and i really don't care. A closer ratio of 1:1 (for example a 4" rod and 4"stroke) will produce faster piston acceleration than a ratio of say 2:1 (4"rod and 2"stroke.) I can't remember the formula and my books are at school, but with those numbers you can determine mean piston speed at a given rpm. From there you can select rod/crank materials which might give some extra strength and figure the nesesarry (see spelling) parameters of intake exhaust and blah blah blah.

Ok lunch is over back to work

Jim is a slave driver

[CBFryman]

Well Really if yo uwant to get into engine geometry the fule will limit the engine RPM. if it burns quickly engine speed will be quicker. when it comes down to it....

-Intake Set Up
-Intake Manifold Design
-Cam
-Piston Mass
-Rod Length
-Rod Strength
-Crank Strength
-Crank Balence
-Head Design
-Valve Design
-Exaust Manifold Design
-Exaust System Set up
-Fule and fule delivery
-Lubrication
-Engine Tempature (which is dependant on cooling system)
-Flywheel Weight
-Load on the engine
-Valve Spring Stiffnes (in higher RPM's if it isnt stiff enough you will get valve float)
-Head Gasket Ability To contain pressure
-Compression Ratio

Did i miss any?

As you can see the whole design of the engine will eventually determine the maximum safe speed of an engine. you can take any old engine. say a factory redline of 6000 RPM. with the removal of the govenor you hit maybe 7000RPM. at this point cam restricts airflow. you give it a super high RPM cam. then you get to 8000RPM and your intake manifold and exaust manifold restrict air flow. you replace thoes and then your fule delivery system isnt up to par. you replace that and then you can reach 11,000RPM. Then your vualves really start to float like crazy so you get extra stiff springs or even electronicly controlled valves (F1 style). you reach 12,000RPM and your crank brakes so your replace it along with the heads and noy you are reaching 15,000RPM then your engine is about to fuse the pistons to the cylender walls so you replace the pistons and cooling system. and the cycle continues. but as i said in a previous post. there is no need to rev to 16,000RPM on the streets unless your jsut out to strike fear in the hearts of Honda Civics and Accourds.

[bjdm151]

yes all those factors go into how high you can rav an engine, but piston acceleration is the main factor!!!!!!!! Whan designing an engine where do you start??? You don't say hey this is a really great intake manifold, lets design an engine around this. My drill instructor used to tell me strength flows from the center (working out your abs,) the same goes for an engine. If the rotating assembly can't handle the acceleration and speeds (piston and rods going up and decelerating to 0 and then reacelerating to infinity and beyond and doing it all over again) everything goes kablooey. Once you have determined the characteristics of your new application, then you design the rest of the engine around that.

Does this thing have spell check????????

[bjdm151]

Why would fuel ultimately limit the rpm of an engine. We cannot do much to change laminar flame speed anyway, only how it moves through the combustion chamber through combustion chamber design. If you are running out of fuel, up the volume, pressure, injector on time, bigger jets or injectors. Outside of rod stroke ratio, the ultimate factor in useful engine rpm is how much air can be ingested by the engine, not fuel.

[public]

Let my wife drive, it WILL rev higher. Until it blows..

[CBFryman]

The Fule itself is the ultamite limiting factor. you can have the biggest cams and the most flowing manifolds of all time with the lightest pistons and the shortest rods but if your fule isnt burning fast enough to make the engine accelerate more then the engine cant accelerate any more.

[public]

Originally Posted by CBFryman

The Fule itself is the ultamite limiting factor. you can have the biggest cams and the most flowing manifolds of all time with the lightest pistons and the shortest rods but if your fule isnt burning fast enough to make the engine accelerate more then the engine cant accelerate any more.

Yep, the maximum speed of the piston can never be higher than the expansion rate of the combusting fuel.