More mods=Higher redline?

[SilviaSR20DET]

Hi, i have a injen cold air intake and an apexi n1 dual and im just wondering if the power increases all the way to redline rather than the big drop after 5700 rpm shown from some of the dyno sheets. Thanks

[tnord]

yes i do believe that the reason the power drops on the KA in the upper rev range is due to a lack of air, not fuel. therefor, increasing the breathing abilities of the engine tend to alleviate this problem, although to what extent i do not know.

or i could be completely wrong.

[kandyflip445]

Power drop off at the top end is almost always due to the engine not being able to breath at higher rpms. Be it not big enough valves, bad intake runner design, intake, etc. I think lighter internals would also help...someone correct me if I'm wrong.

[mrdirty]

anything that helps the engine breath will help the most in the upper rpm region,

Why? Because the air charge is more prone to staying in the laminar region and you won't waste energy by mixing the air. Mixing (turbulence) is directly related to air velocity.

INOTW: smooth air is good, but u sacrifice velocity w/ a larger dia intake/exhaust so low rpm chamber filling and scavanging suffers...

[mrdirty]

oh, also fuel mixing suffers.

I think that's it...

[240 2NR]

Well when I put my exhaust on (5Zigen fireball NA) I felt like it shifted the powerband by a few hundred rpm, but otherwise it still tanks just after 6k. It think a big part of it is the cams and the long intake runners.

Bolt ons will only effect breathing to a small degree (a few hundred rpm), but you have to go internal (cams, compression, stroke) to really effect the shape of the powerband.

[ForceFed97KA]

Cams are responsible for changing the power range of an engine.

[mrdirty]

cams are not ALL that's responisble for changing power range...

[drift freaq]

improving air fuel flow , lightening inertial drag on the bottom end and changing cam profiles can all help the engine in the upper rev range.
There is one thing though that will affect the rev range of the KA that cannot be changed without major work. That is the stroke of the engine.
The KA is a long stroke big bore engine i.e. much akin to a big block V8 . The only way you can really make it rev nicely have and live in the upper rev band is to destroke it. This has been speculated about and even attempted on the Nasport engines (KA24e's using Naps z22 or Z20 crank) It does take a lot of work and no one I know has actually attempted it. Rebello racing who did the Nasport engines in Pacheco CA could give you more info about this mod.


Dave

[tnord]

correct you are.......

with that in mind, we're talking about only shifting the powerband a few hundred rpms, not a few thousand.

[ForceFed97KA]

Wow, I never new that I have always been told Cams are what will increase red line, I also new about stroking but did not see it as a viable option for the 240. I just thought that other mods would increase horse power, but the fall off point would be the same. Thanks for the education, I also emailed Crane Cams to help clear things up for me. I think their respone is will written and maybe of assistance to others as confused as i apparently was, 10 years of thinking the wrong thing. I was was alway told that valves begin to float.

Here is their responce:"

Cams are the primary thing that determines where in the RPM range the power band occurs, but they are not the only thing.



Intake—Runner length and diameter affect the RPM range of the power band. Larger diameter runners raise the power band. Small runners lower it. Long runners widen it. Short runners make it narrower, more peaky.



Exhaust—Long header tubes lower the power band. Small diameter tubes lower it. Short tubes and large diameter tubes raise the power band. Equal length headers concentrate the power to a narrower band. Unequal length tubes flatten and smooth out the power band.



Heads—Same thing—Large capacity runners raise the power band. Smaller capacity runners lower it.



Valves—Small valve lower the power band. Large valve raise it.



Turbo and super chargers—Have a definite affect on the power band, depending on the RPM where maximum boost is occurring.



So, to summarize, the cam sets the base power band, but you can tune the power band—raise it, lower it, peak it, flatten it—with the rest of the parts you choose. Basically, parts that hinder flow tend to push the power band down. More free-flowing parts tend to raise it. So you see all-out drag machines have short exhaust, big intake runners, and large capacity runners in the heads. Street machines favor unequal-length, smaller tube headers, with long intake runners
"

[240racer]

Originally posted by ForceFed97KA
Wow, I never new that I have always been told Cams are what will increase red line"

This "sentence" is pretty hard to read, try to type a little more clearly. In addition to that, cams do not affect redline, all redline is is some rpm where we decide not to go above. It is usually enforced by fuel cut or something like that and there is a red area on the tach that tells you where it starts. It is generally recommended that you don't exceed it, but it isn't the cams that will fail if you go beyond it, it's the con rods. You may be trying to say that cams can change where your torque peak is located and if it is smooth and flat or sharp with a peak. This is true, but has nothing to do with the redline capability of the con rods. There is also valve float, but lets not get into that too much for now. In general larger cams allow more flow and therefore can flow more air and fuel which results in a ablity for run a higher rpm before the volumetric effeciency drops. The reason the KA has such problems at high rpms is because the volumetric effeciency sucks at high rpm. this is mostly due to cams, but other things as well. Vtec is what causes the volumetric eff to stay high for a wider rpm range. The use different cams, so at idle it's smooth (unlike a muscle car) and at high rpm it can still flow well.

[ForceFed97KA]

Sorry I have been home sick with a 104 degree temperature and Pneumonia. I see that I made a few mistakes in my writing, but that sentence in particular seems fine to me, I think your an asshole.

[240racer]

Originally posted by ForceFed97KA
Sorry I have been home sick with a 104 degree temperature and Pneumonia. I see that I made a few mistakes in my writing, but that sentence in particular seems fine to me, I think your an asshole.

hey I'm sorry I'm not trying to piss you off. All it needed was a comma after "that" and it reads just fine.

[BRB240]

I thought a shorter stroke meant a lower rpm range.

This is what I know.

Short stroke engines accelerate away from top dead center faster than a longer rod.
That faster acceleration means shorter stroke engines work better in lower rpm ranges because,

The higher acceleration means more stress on the engine, so the higher the engine speeds, the closer the engine is to failing.

Secondly, the rapid acceleration of a short stroke get port velocities up sooner, which improves low rpm cylinder filling, fuel atomization, and low rpm torque.

Longer stroke need more rpm to do this.

I don't think I am wrong but I could be.

[adey]

AFAIK, which isn't very far at all--

the reason why shorter stroked engine can get up to higher RPMs is (of course, AFAIK) due mostly to the fact that they take a shorter amount of time to travel the stroke distance. That, and the lower mass of a shorter rod/arm/whateverit'scalled... (?)

If you look at different engine specs, engines with short strokes compared to bores tend to rev higher (and make power higher) in the RPM range than longer stroked engines (compared to their bore). That is to say, an 86*86 bore*stroke would tend to rev higher than an 86*91 bore*stroke engine of similar design. Or at least that's what I've noticed just going by specs.

:confused:

[BRB240]

Oh I just realized something. I forgot about rod ratio. My bad.
In what I wrote in my previous post, replace short stroke with shorter rod. I don't want to get into explaing this now. To much typing!

I need to get more sleep, I am slipping up!

[FSPtwo4d]

The single biggest factor in power drop-off is the intake manifold. A larger plenum, and better, shorter runners virtually eliminate power drop-off. Look at the dyno sheets jun posted on their intake manifold. This is assuming your engine can keep up on the fuel side of things.