Why Si HP & TQ falls off at high rpm?

[Wht-Si]

Does anyone know why our engine HP and TQ falls off at high rpm. RSX-S seem to maintain good linear HP curves up to the limit.

Just curious.

[Quicksilver]

From my research into various people's dyno runs using different parts, it seems that the Intake (whether CAI or SRI) is the only mod in the I/H/E combo that makes power most of the way across the rpm ranges. Exhaust and header give more upper rpm power, but appear to lose low end torque. The midrange power seems to show varying results, but appears to gain a few hp on average.

The nice thing about the Hondata flash you just got is that with I/H/E and increased rev limiter, you may be losing some bottom end power but your power is now moved up the rpm band. Where as the "sweet spot" for power used to be between 6200 and 6700 before the power starts dropping off (and the rev limiter kicks in). With I/H/E, your ideal power range should be between 6200 and 7500.

If you look at the Hondata website, the stock setup with ECU flash started losing power around 7200 (where they stopped the dyno run). But if you extrapolate the curve another 500 rpms and compare it to the I/H results, the I/H setup would have about 7-12 more horsepower between 7000 and 7700 rpm. The drawback is that you're losing 4-8 lb ft of torque between 2500-3800 rpm. So you'd be having to rev the car more to stay in the stronger powerband (like an S2000).

The fact that we don't also have the high-lift VTEC cams and better flowing heads contributes to our lower powerband. But we have more torque than them until VTEC kicks in, so there always seems to be a tradeoff.

Enough of my ramblings.... I hope that helps.:o

[myeverlovinsir]

Why our engines are dropping power at about 7500rpms is totally
related to head flow, even with I/H/E, hondata and TB mods, as
Quicksilver stated. If you want more power in the higher rpms,
you will have to do a head swap, or get the a tune and cams, along with larger injectors.

Only benifit of having a higher redline above 7500rpms, even
though your not making any more power, is that you get a nice jump
when you shift into the next gear. hth

[B18CXr]

the problem is directly related to the B-pipe and it's tiny 1.5inch diameter.

[myeverlovinsir]

Originally posted by B18CXr
the problem is directly related to the B-pipe and it's tiny 1.5inch diameter.

The b-pipe or midpipe I was talking about include a 2.25" upgrade
along with the I/H and TB and hondata. To be more accurate
the stock midpipe is 1-3/8" ID and seems to flow nicely with
the rest of the stock items. This factor is not as critical as the
head flow is. hth;)

[Cone Killer]

Ok guys....I'm not sure if you guys are joking...but the power band of any car is dicated by the cam, not what mods you have or how big the b-pipe is. This explains why you need a head swap, ie different cams, to get the high rpm power. It's really that simple.

[myeverlovinsir]

Originally posted by Cone Killer
Ok guys....I'm not sure if you guys are joking...but the power band of any car is dicated by the cam, not what mods you have or how big the b-pipe is. This explains why you need a head swap, ie different cams, to get the high rpm power. It's really that simple.

You are correct sir!

[Quicksilver]

Originally posted by Cone Killer
Ok guys....I'm not sure if you guys are joking...but the power band of any car is dicated by the cam, not what mods you have or how big the b-pipe is. This explains why you need a head swap, ie different cams, to get the high rpm power. It's really that simple.

I respect your opinion Cone Killer, but I'm going to have to disagree. The cam is not the be-all end-all in determining the power band. Altering the flow characteristics of the air going into and out of the engine is what determines the powerband. If you alter the intake, exhaust, cam, or heads, you can change the power characteristics of an engine.

I was merely stating that powerwise, on the dyno, if you add I/H/E that low end torque is lost somewhat while high end torque (what people like to see as horsepower) is increased. This is due to the altered velocity in the intake/exhaust track. In my example, the air flows more efficiently with less restrictions at higher rpms, but the lack of velocity at lower rpms causes a dip in power down low.

The Hondata ECU reflash will only help those with I/H/E more, because then you're giving the car the extra rpms it wants since you've opened up upper rpm velocity. Even stock I was bouncing off the rev limiter. Now that I have I/H/E, it's killing me to not have the extra rpms because I know I'm still making power when the fuel cutoff occurs.

Not trying to start any great debate or start an argument. I'm just saying cams are not the only factor which can alter a power band. Maybe we're just using the same words for different concepts.

[myeverlovinsir]

Originally posted by Quicksilver


I respect your opinion Cone Killer, but I'm going to have to disagree. The cam is not the be-all end-all in determining the power band. Altering the flow characteristics of the air going into and out of the engine is what determines the powerband. If you alter the intake, exhaust, cam, or heads, you can change the power characteristics of an engine.

I was merely stating that powerwise, on the dyno, if you add I/H/E that low end torque is lost somewhat while high end torque (what people like to see as horsepower) is increased. This is due to the altered velocity in the intake/exhaust track. In my example, the air flows more efficiently with less restrictions at higher rpms, but the lack of velocity at lower rpms causes a dip in power down low.

The Hondata ECU reflash will only help those with I/H/E more, because then you're giving the car the extra rpms it wants since you've opened up upper rpm velocity. Even stock I was bouncing off the rev limiter. Now that I have I/H/E, it's killing me to not have the extra rpms because I know I'm still making power when the fuel cutoff occurs.

Not trying to start any great debate or start an argument. I'm just saying cams are not the only factor which can alter a power band. Maybe we're just using the same words for different concepts.

Ok, I read your response a few times and think you are a little confused.

First off, HP and TQ are inter-related, the power gains are evident
for both at once. HP gains don't occur separately from torque.

Second, I/H/E only can improve flow and power, some will say
higher rpm gains are attainable with certain headers, and better
torque gains are attainable with certain headers. Where it occurs
is the only difference.

Third, on a dyno you will not see any gains with the hondata flash. (unless you are stock)
You will however notice a better part throttle response due to
adv. timing and fuel management with the tune. The higher redline
only helps upto 7500rpms, I and others have shown this on the
dyno. Sad to say, you may even see some detonation with the
flash because of it's adv. timing. I was lucky to have minimal
detonation. JSIR and smoothoperator saw terrible detonation
with the first flash I had.

Fourth, the velocity of the air flow decreases with increased diameter of I/H/E. (backpressure is a myth) This is why even with
the small diameter of the stock setup, torque is quite good and
power is maintained, because of the velocity of air. When you add an intake you increase the
front end air flow, and can notice a gain with just that. Your stock
exaust and midpipe are gonna have restrictions.

Fifth, only when you increase the combination of I/H/E can you
realize the power gains and flow available. (again proven on the dyno)
The only thing restricting air flow now is the head itself.

Finally, the hondata flash is an added benifit to stock components.
If you do have an I/H/E and TB mods, then you are in the same
boat as myself and I can say that on a dyno you will not be
pleasently surprised, however on the road it is a much livelier
drive.

Cams/head are the crutial factor when it comes to flow and power
in the higher rpms, regardless if you are stock or have I/H/E.

One thing that must be considered as well is NA compression.
Cams will do nothing for it, but rods and/or pistons will. hth:D

[Tenacious G]

Originally posted by Quicksilver


The Hondata ECU reflash will only help those with I/H/E more, because then you're giving the car the extra rpms it wants since you've opened up upper rpm velocity. Even stock I was bouncing off the rev limiter. Now that I have I/H/E, it's killing me to not have the extra rpms because I know I'm still making power when the fuel cutoff occurs.


i thought that on hondata's Web site, the dyno numbers of the reflash showed minimal gains on the K20 w/ I/H/E compared to stock w/ 91 octane.

[myeverlovinsir]

Originally posted by Tenacious G


i thought that on hondata's Web site, the dyno numbers of the reflash showed minimal gains on the K20 w/ I/H/E compared to stock w/ 91 octane.

Minimal is right, in fact you will see no gains on the dyno sheet
with the flash compared to stock. I/H/E also show the same poor
gains. You have to drive it on the street to know there is a difference.

BTW, I would not trade in the hondata flash for the stock ECU,
reason being it's a much better ride and 1/4 mile times have
shown it! ;)

[chunky]

Looks like i hopped into this one a little late. myeverlovin's got it covered pretty well, and cone killer is absolutely correct.

Your powerband location IS dictated by the cams. There's no getting around that fact. While you can change the magnitude of the powerband with blotons, typically they only accentuate the natural powerband that the cams create. The cams control the amount of air going into and out of the cylinders. Since we don't have infinitely variable cam profiles (we only have two stages) you can optimize for two rpm ranges.

Flow is an important part of making power at high rpms, but the cams are what either allow you to take advantage of the air flow or not. the version of the k20 head the ep3 has flows quite well. The dropoff in high rpm torque is not related to lack of flow. Rather the cams are no longer able to generate the lift to allow enough air in at those speed, and there is not enough overlap to allow all the spent exhaust gasses to escape. The only way to truly fix this is to get cams with more lift/duration/overlap.

Also, as myeverlovin pointed out, you need compression. Higher static compression ratios allow for a quicker burn. 9.8:1 compression typically makes power n/a up to 7500-8000rpm. To go above 8000rpm, you need higher than 10:1 compression to have complete ignition of the air/fuel in the short amount of time there is (at 8000rpm you have less than 1/4 second to ignite the fuel).

So part of the all motor theory is compression & cams. Everything else you do is subordinate to that.

[Cone Killer]

Originally posted by Quicksilver


I respect your opinion Cone Killer, but I'm going to have to disagree. The cam is not the be-all end-all in determining the power band. Altering the flow characteristics of the air going into and out of the engine is what determines the powerband. If you alter the intake, exhaust, cam, or heads, you can change the power characteristics of an engine.

I was merely stating that powerwise, on the dyno, if you add I/H/E that low end torque is lost somewhat while high end torque (what people like to see as horsepower) is increased. This is due to the altered velocity in the intake/exhaust track. In my example, the air flows more efficiently with less restrictions at higher rpms, but the lack of velocity at lower rpms causes a dip in power down low.

The Hondata ECU reflash will only help those with I/H/E more, because then you're giving the car the extra rpms it wants since you've opened up upper rpm velocity. Even stock I was bouncing off the rev limiter. Now that I have I/H/E, it's killing me to not have the extra rpms because I know I'm still making power when the fuel cutoff occurs.

Not trying to start any great debate or start an argument. I'm just saying cams are not the only factor which can alter a power band. Maybe we're just using the same words for different concepts.

When I said "power band" I was refering to the actual slope of the curve in relation to what wht-si said about the power dropping off at high rpms, and is furthur seen with the Hondata reflash. The reason it drops off, regardless of apmlitude (hp, tq) is because the cam is not designed for high rpm power like the A2 head is. What's the difference mainly between the A2 and A3? Cams. Sure, when you add bolt ons the power moves around, but the general charateristics of the slope of the power remain the same.

[Quicksilver]

Originally posted by Cone Killer


When I said "power band" I was refering to the actual slope of the curve in relation to what wht-si said about the power dropping off at high rpms, and is furthur seen with the Hondata reflash. The reason it drops off, regardless of apmlitude (hp, tq) is because the cam is not designed for high rpm power like the A2 head is. What's the difference mainly between the A2 and A3? Cams. Sure, when you add bolt ons the power moves around, but the general charateristics of the slope of the power remain the same.

On these points, I totally agree. My point was just that if you want more higher-end power with bolt-ons alone you can free up in intake and exhaust side at the cost of some low end power. And if you're going for that top end power, it's worth it to get the extra rpms that the ECU flash gives you.