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R33 Powerbands!

MattO

By MattO,
in R Series (R30, R31, R32, R33, R34)

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JezR31 Mentor

JezR31

Posted
Posted

The power band doesnt come from the gears it comes from the engine.

A powerband is where the engine is most efficient.

There are 3 efficiences to look out for when getting a HP/torque monster:

Those 3 are Volumetric efficiancy, mechanical efficiency and thermal efficiency.

- Volumetric efficiency is How well you engine can breath. An engine that has 100% volumetric efficiency is one that has all its cylinders 100% with air and fuel.

This can be improved with Mods like extracters, cams , exhaust system and the intake system.

Cams can increase air flow to provide more bottem end torque but sacrifice top end power and vice versa. Ive seen an RB30E dyno chart from an ordinary skyline and one out of a GTS1 and the normal Rb30E dies of at later RPM while the GTS1 engine can keep going for more RPM.Because the GTS engine uses a different cam and has had mild head work from factory while the other RB30E hasnt.

The exhaust system also can change the power band. Small diameter pipes can help to increase bottom end power while bigger pipes sacrifice bottom end power for better top end power.

For forced induction motors eg RB25DET bigger diameter pipes are suited to this engine as it would suffocate with smaller diameter pipes. Low back pressure is better.

But for an NA back pressure is better.

- Thermal efficiency is how well you engine can change the air/fuel's energy into rotating energy.

This is effected by the Compression Ratio, timing, combustion chamber design.

-Mechanical efficiency is how well your engine limits the amount of energy exhausted to power the engine itself from friction between parts.

Mechaincal effieciency gets worse as RPM increases because its takes more power to turn the engine at higher RPM than what it does at lower rpm.

Cams for racing use usually have narrow Powerband characteristics. They are usually put with a "Close Ratio Gearbox" to stop the revs from falling and to keep the engine reving at its powerband. Otherwise Revs would fall and your engine loses power. They usually have a very agressive power band eg (flat power, then when boost comes "strap on and feel the Gs")

The Best cam would be one that has great low end torque, a 10,000 RPM redline and and idle as smooth as silk. But no cam can deliver a Powerband from Idle to Redline. Your best bet to getting that would be to buy an after market cam. Head work and a high-flow exhaust systems and filters can help get better high end performance.

I hope I could clear that up abit. took me 1hr 14 mins to write.

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JezR31 Mentor

JezR31

Posted
Posted

There are also things like VTEC which i think is in Hondas.

There are a few advantages with Vtec. Its like having the cams switched to a different profile for higher top end power while before the Vtec comes on having good bottom end torque.

The result is an engine with a broad powerband

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sven laptop Community Regular

sven laptop

Posted
Posted

I've noticed the same thing with my R33 GTSt.

Boost comes on at about 3,000rpm & gradually builds, but then there's a noticeable extra kick at about 5,000 that feels like a second turbo coming on or something.

Obviously my car only has one turbo, so I'm buggered if I know what that's all about.

My engine has no mods at all & I rarely take it up to 5,ooo revs, but jeez it's fun when I do!

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Lozza150 Proficient

Lozza150

Posted
Posted

I believe it's a cpu mapping change....

It happen's when the AFM sesnor's the "foot flat" aspect and changes air fuel ratio's.....

why it does it after 5500 rpm i dont know.... Might have to consult a nissan engineer.....

where ever they are....

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Endorean Proficient

Endorean

Posted
Posted

The 'kick' that most people feel once their car reaches 5000rpm is the factory boost controller changing to a higher boost pressure.

Between 3000-5000rpm the turbo is running about 5-6psi, after 5000(or 4500rpm on my car) the boost will change to 8-10psi.

The factory nissan boost controller that is on the 33 has 2 settings, depending on RPM.

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R31Nismoid Grand Master

R31Nismoid

Posted
Posted

It is not RPM dependant... Or anything releted to the stockj boost controller.

it's the VCT/cam and Also.. ECU

if you look at a dyno sheet, the ECU fuels right up around 4000-4500 rpm, and all stock ECU's get a dip around the point in their graphs.

After 4500 it goes away and the car's power picks right back up again.

Factory ECU.

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kjb_r33 Experienced

kjb_r33

Posted
Posted

@ 5000 RPM the cam solenoid is switched on, adjusting the valve timing, (only if the engine is under load though, wont do it just revving it). It also switches on the stock bleed valve (solenoid) in the waste gate actuator line to bleed some pressure off, (back into the low pressure side of your intake). The waste gate spring itself will limit boost top about 5 PSI, but bleeding some pressure off from the waste gate line gives you a little more boost (@5000 rpm). The amount of bleed is controlled by the size of the orificew in the solenoid.

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