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Discussion Starter #1
I was wonderign what I would have to do to make my engine's rpms go higher. In my friends XRS his revs to 8200 compared to our 6500. I would like to rev higher how can i acheive this?
 

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there is no reason to. the car stops making power around 6k.

unless you've done mods where you are able to flow enough air that high, you're wasting energy.

the xrs is a 1.8l motor. they have to rev that high to make power.
 

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Discussion Starter #3
i know that but think if you are staying at maximum power longer you will accelerate quicker then when you shift to the next gear it wont take as long for you to hit that mazximum power again because your recs will be higher
 

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you dont understand the way an engine works.

here is a dyno chart


see how it peaks at 6500 and starts falling....after that point, you aren't making the most hp. so you have to shift to the next gear and start climbing up the powerband
 

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because they dont know what they are talking about OR they are building a n/a car in which case you need to rev higher to make more power but it takes a lot of mods to do that. so here's what you need

intake
header
valves
forged rods
high comp pistons
intake manifold
standalone ecu
exhaust
 

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[quote author=the415 link=topic=69352.msg1203550#msg1203550 date=1171331339]
you dont understand the way an engine works.

here is a dyno chart


see how it peaks at 6500 and starts falling....after that point, you aren't making the most hp. so you have to shift to the next gear and start climbing up the powerband


[/quote]

i conquer but the power falls because of the operator only ran to that rpm then let out the clutch and ended the run it he had ran it to the red line it would have gone to around 7K like the car does atleast mine does and i run it that far it does make power there with the right mods it really flies after around 5500
 

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are you looking at the dyno?? the power starts to fall back down. if you are running to 7k, you're loosing power. just because there is s red line doesn't mean that's where you are supposed to shift. there is nothing in your mod list that will make power to 7k before falling off.

go get dyno'd and you'll see what im talking about.
 

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Shifting exactly at peak power isn't necessarily going to give you the quickest overall acceleration. You've got to take into account where on the powerband you'll fall after the shift, and weigh that against the torque advantage of being in a lower gear longer. In order to accurately calculate the ideal shift points, you'd need to look at where the wheel-torque curves in each gear overlap.

I mean, I guarantee you that winding out first gear to the rev limiter is going to give you better results than shifting when you hit peak hp simply because, for a given amount of crank torque, you're delivering so much more torque to the wheels in 1st than in 2nd.


I don't mean to turn this into a long-winded discussion... just wanted to clarify that "peak hp" does not directly translate to "ideal shift point"
 

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dont know about your car but when i shit im usually around 3500 in the next gear. that's the meat of our powerband.
 

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Hmm, for me 3500 feels like it's right in the middle of the ramp to max torque, up to around 5k. I really only take it to/past 6500 in 2nd gear, because I don't feel like the torque advantage is as useful in higher gears, but the 2-3 shift feels best to me when it's right at about 7k.



btw....

[quote author=the415 link=topic=69352.msg1203882#msg1203882 date=1171339245]
dont know about your car but when i shit im usually around 3500 in the next gear. that's the meat of our powerband.
[/quote]

:lol:
 

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hahahahahaha....it's my shitty wireless keyboard. i hate this fucker.
 

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[quote author=the415 link=topic=69352.msg1203882#msg1203882 date=1171339245]
dont know about your car but when i shit im usually around 3500 in the next gear. that's the meat of our powerband.
[/quote]

:lol:

I know Hiboost Juan revved his car to 8600 rpms. Another user supposedly made 192 at the crank revving to 9300 rpms, unsure which mods we're on it though.
 

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[quote author=boardumb link=topic=69352.msg1203949#msg1203949 date=1171340884]
[quote author=the415 link=topic=69352.msg1203882#msg1203882 date=1171339245]
dont know about your car but when i shit im usually around 3500 in the next gear. that's the meat of our powerband.
[/quote]

:lol:

I know Hiboost Juan revved his car to 8600 rpms. Another user supposedly made 192 at the crank revving to 9300 rpms, unsure which mods we're on it though.
[/quote]

yeah juan has supporting mods and a need to rev that high
 

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even when forcing air, we die off up top. until you start changing intake manifolds and cams...that's just how we are...

 

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Just because you are using a turbo or super charger that doesn't mean you are going to make high RPM power. Look at the MS3, its power curve plumets once you get high up. If your turbo is not large enough or your supporting systems (intake manifold, exhaust manifold, DP, engine, etc) are setup right then you of course aren't going to make high RPM power.

However, the setup of the motor can be changed to make more high RPM power. A cam grind that provides more overlap in addition to more duration with a slower lift profile (I am pretty sure you want a lower lift accel profile) and more lift will generate higher RPM power. Also shorter intake runners will do this for you. Longer exhaust runners can manage this as well in addition to larger exhaust tubing. More spark advance is another big high RPM dealy-do.

Basically there are a number of things you can do to make more power at higher RPMs. In terms of allowing the engine to operate at higher RPMs you need to either hack the PCM and change the cut-off value to something higher then 7100rpms for fuel cut or else you need a standalone PCM.

There isn't much point reving higher then the 2.0 and 2.3 do now. Its not just the power fall off, it is also that you won't achieve a much higher accel with where you will fall in the power band after the shift if you had a higher fuel cut off (a little more room might help, but the 'ideal' if it isn't already at 7100rpm might only be like 7250).

For the engine to reliably handle the increased engine speeds I think you would want to look more at a 2.0 motor due to the better rod ratios (shorter stroke and longer rods)...and/or forged pistons with better piston rings (maybe chrome-moly) Stronger rods, better bearings, stiffer valve springs, lighter valves, etc.
-matt
 

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i said all that already.
 

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[quote author=the415 link=topic=69352.msg1203550#msg1203550 date=1171331339]
you dont understand the way an engine works.

here is a dyno chart


see how it peaks at 6500 and starts falling....after that point, you aren't making the most hp. so you have to shift to the next gear and start climbing up the powerband


[/quote]

I disagree somewhat. Yes, power falls off after 6500. Yes, a shift there will put you in the power band. No, it's not always the most optimal point to shift. Gear shifts are not instantaneous. They do rob you a good fraction of a second where you are not on the power. A no-lift shift will reduce this, but is murder on the drivetrain. Assuming we are both driving a 3 with the same setup with a close launch; while you are shifting at 6500, I will be accelerating away for 600 more RPM a fraction of a second longer. By the time I shift, I will be slightly farther ahead and even closer to the maximum torque point. This car doesn't accelerate fast enough for you to make up the lost ground from shifting early.

Another thing, in your list of mods for high RPM power, you didn't mention the cams which is the single biggest factor next to the intake manifold. The cam profile is what dictates volumetric efficiency other factors remaining constant. We already sort of have a short intake runner. That's what the Variable Induction Manifold is supposed to provide a means for.

Also, about the dyno from Bean, I thought these engines were supposed to have at least 90% of maximum torque available from 2500 RPM all the way to the redline. Did those mods affect this, or was Mazda exaggerating a bit?
 

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ok you shift at 7 and i'll shift right before 6500 and we'll see where we stand.

and i didn't forget cams. cams aren't available right now without some major modification
 
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