does low comp. for turbo limit redline

[driftsentrab13]

i have never ask anyone or heard anyone answer this question. does taking a engine say the redline is 11,000 rpms, that a has a 11:1 cr and lower the cr for turbo will that in turn lower you redline?

[beef_bourito]

it depends, it might or it might not. the turbo will create backpressure which will limit engine speed but it will also create a bigger, faster explosion in the cylender. im not sure whether or not it lowers it but i tend to think no.

[Jet-Lee]

I don't think LOWERING the compression will hurt the redline, since the explosion isn't as hot so it's not as forceful. Redline is determined by what the pistons/rods/crank can take and what the valves can take before floating. If you've got strong enough valve springs so floating isn't a factor, then your only limitation is the strength of parts. In which case, a HIGHER compression will lower your redline due to more pressure = stronger explosion = more heat = more force. I don't think the turbine has any factor in this, as it will spin regardless. As it spins, it will be creating boost which will outweigh any backpressure that may be created.

[beef_bourito]

i'm sorry, i was confusing redline with peak horsepower.

[Moppie]

Redline is determined by the phsyical strength of the engine, and how much air it can flow.

If lowering the CR reduces how much air the engine can draw into, or pump out of the combustion chamber then it will lower the redline, although its unlikely to have much of an effect.

[Schister66]

I don' think it limits redline, but you won't make any power over a certain RPM so there's no point to rev any higher. Really the only thing that limits redline is if the engine will hold together and can actually continue to spool up on its own power. I've seen dyno videos of turbo civics that are pullin nearly 12000 rpm on a dyno. You're going to need a cam that supports those kind of RPM's, high tensile valve springs so that you don't clap the valves shut, and you're just going to have to build the engine in general. If you do that, it should rev as high as you want, until it inevitably lets go.

[Jet-Lee]

Originally Posted by Moppie

Redline is determined by the phsyical strength of the engine, and how much air it can flow.

If lowering the CR reduces how much air the engine can draw into, or pump out of the combustion chamber then it will lower the redline, although its unlikely to have much of an effect.

Volumetric Flow and Physical Strength are apples and oranges.

A 12L diesel engine will displace a LOT of air, but it will not hold up very well at higher rpms.

A built up 1.8L Honda will displace little air, but could be capable of 12k rpms.

Volumetric Flow <> Physical Strength

[Moppie]

Originally Posted by Jet-Lee

Volumetric Flow and Physical Strength are apples and oranges.

But you need both to reach high RPMs.

For example Lotus never fitted a rev cut to any of thier 4cyl Esprits, even the Turbo models because the engine reached its Volumetric flow limits before it reached its physical strength limits.
Quite simply the engine couldn't rev high enough to do itself any damage.

[Jet-Lee]

But that doesn't mean the redline was lower, it was just unable to reach it. Redline is where the engine can start to damage itself. If it never reaches that point, it's either weak in power or strong as in parts strength. Just because an engine can't rev to redline doesn't mean the redline is lower.

[Moppie]

The redline is the red mark on the Tach.

Differnt manufactors use it in differnt ways, and it has differnt meanings depending on context.
Its a realitivly meaningless number.


At its most basic level its the point at which the engine can not be reved any higher.
It dosn't matter if thats because the engine has reached the limits of its volumertic flow, or its physical strength, or its where the manufator wants it to be.

[Schister66]

The redline is usually where the engine is starting to enter its highest stage of unbalance. In an engine there are 3 stages of unbalance at certain rpms, the redline is shy of the third unbalance....that's what i was told by a sprint car engine builder

[nissanfanatic]

Piston speed/valvetrain setup determines how fast the engine can spin. Physical strength is important, but the strongest piston in the world will not hold up to excessive piston speeds.

http://dictionary.reference.com/search?q=redline

[CBFryman]

fule can affect it as well if volumetric flow and physical strength are to a maximum... your piston cant travle down any faster than the flame head.