Raising Rev Limiter
03-17-2012, 01:39 AM
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Raising Rev Limiter
I'm curious what you guys are revving your car to and what needs to be done in order to safely raise the rev limiter.
I've always stuck with a 7000-7200 limiter on my car. Are people going a bit higher than that on stock motors? Is there a point at which the valves/springs start to become an issue? Or a point the stock oilpump starts to crap out?
I know some of the built guys are revving up to 8000, but I seem to remember others offering some pretty strong opinions against going over 7400-7500. I can't find much on the site discussing any practical limits.
I've always stuck with a 7000-7200 limiter on my car. Are people going a bit higher than that on stock motors? Is there a point at which the valves/springs start to become an issue? Or a point the stock oilpump starts to crap out?
I know some of the built guys are revving up to 8000, but I seem to remember others offering some pretty strong opinions against going over 7400-7500. I can't find much on the site discussing any practical limits.
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03-17-2012, 07:16 AM
#9
https://www.miataturbo.net/showpost....4&postcount=38
These numbers will sound conservative, but I am a track junkie and my cars see more abuse in a single 20 minute session than your average street car sees in a month of commutes. You can probably exceed these numbers in a street car and be OK in the short term, but if you want long term reliability or track reliability, I'd stick to my numbers.
Revs:
Stock rods will not accept anything past about 7800rpm without stretching. Spec Miatas are documented to stretch rods on single sub-8000rpm overrevs. If you push past 7500 on a regular basis, you need forged rods.
Stock oil pump gears have a generally accepted limit of 8000rpm due to crank harmonics. Push past that (or run at 8k for a long time) and billet gears are strongly recommended.
OEM valvetrain is good up to the ~7800rpm mark. At a certain point, the valves will start to float, which means you either need stiffer springs or lighter retainers.
Making power at 8000rpm is hard. You need a huge centrifugal blower, a lot of port work, big cams, or a combination of at least two of those things. Most people do not spin the motor this hard.
FOOTNOTE: VVT users MUST adhere to a strict 7400rpm limit due to an intake cam harmonic. Change the intake cam and you may press past that limit.
Revs:
Stock rods will not accept anything past about 7800rpm without stretching. Spec Miatas are documented to stretch rods on single sub-8000rpm overrevs. If you push past 7500 on a regular basis, you need forged rods.
Stock oil pump gears have a generally accepted limit of 8000rpm due to crank harmonics. Push past that (or run at 8k for a long time) and billet gears are strongly recommended.
OEM valvetrain is good up to the ~7800rpm mark. At a certain point, the valves will start to float, which means you either need stiffer springs or lighter retainers.
Making power at 8000rpm is hard. You need a huge centrifugal blower, a lot of port work, big cams, or a combination of at least two of those things. Most people do not spin the motor this hard.
FOOTNOTE: VVT users MUST adhere to a strict 7400rpm limit due to an intake cam harmonic. Change the intake cam and you may press past that limit.
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03-17-2012, 01:17 PM
#10
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I may bump the rev limiter up a couple 100 and see how she does. After looking at my dyno, running above 7500 on my current setup would be pointless.
Seeing that 300hp "limit" on stock pistons is a bit scary, but it doesn't seem like too many people are dumb enough to install rods and not pistons. Hopefully their a little stronger than we're assuming, mine seem to be holding up well so far.
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03-18-2012, 12:16 AM
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Bah.
not every miata is driven as EXTREMELY as all these track "gods". I have revved to 8000rpm for 10k miles and my motor is fine. I drive on the street. Savingtons VVT data is based on a limited sampling.
Even if you have a power sag over 7000, if you are makig more power at 8000 than at ehatever RPM you drop to post-shift, having the extra rpms in boost for a bigger turbo can make a significant positive impact in driveability.
not every miata is driven as EXTREMELY as all these track "gods". I have revved to 8000rpm for 10k miles and my motor is fine. I drive on the street. Savingtons VVT data is based on a limited sampling.
Even if you have a power sag over 7000, if you are makig more power at 8000 than at ehatever RPM you drop to post-shift, having the extra rpms in boost for a bigger turbo can make a significant positive impact in driveability.
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