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Premium Member
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Discussion Starter #1
Hi there folks.

I'm after a bit of advice. The other day I was driving my Lag II 1.8 16v Dynamique and fancied opening it up a bit. :devil: Droped the box to 2nd and put my foot in it, I wound her right up and went right through the rev range, to my surprise the rev limiter kicked in at 5600 rpm. Is this right? :confused:
On the counter itself it doesn't start going into the red intill about 6400rpm. I had to remind myself I'm driving a petrol not a diesel!!!!
It took me a while to get used to this car as my prievious was a V6 Mazda MX-3. The rev limiter wouldn't kick in on this untill about 7.5k rpm.

I know it is pointless taking it up to the red line as tourque dies off well before then, but as I said I'm used to the Mazda and often took that past 6.5k rpm. But then that was a bit more sportier than the Lag, but I'm a family man now so had to get the family car!!! :d
I won't make a habit of thrashing my Lag mainly because I want it to last me a bit and I don't put much faith in these French engines, but it is nice to have the option to use the whole of the rev range from time to time, and I most certainatly won't be using this car for racing. It's just handy for overtaking.

I do have issues with the idle on this car, as when comming to a stop and dipping the clutch the revs do drop to about 400 before settling back on 700. I wondered if the 2 might be related? The car it self otherwise runs A1 and is full of life with plenty of lowdown tourque so I don't think the ECU is in limp mode or anything.

It's not a major issue as I often don't take this car past 4k rpm but as I mentioned before, it would be nice to have the option to use the whole rev range if I wish!
 

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Discussion Starter #2
Sorry for posting this twice. The page had timed out on my computer so didn't think it had posted. Please delete if you wish as I'm not sure how.

Cheers
Mike
 

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Tourerman
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I have only tripped my rev limiter once going uphill in second on a motorway slip road and I was surprised how early it kicked in just above 5,000, probably normal.
 

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Administrator
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Car manufacturers normally will set a rev limit a bit below what the engine can handle safely. There are manufacturing tolerances involved as well as how the car is expected to be driven (as well as the power/torque delivery of that model).

You are correct to observe that power will (normally) taper off before the revs get close to the rev limiter.

Turbo cars, and those fitted with a racing/hot cam will be the exceptions.

If you feel that the engine is 'holding back' a little at high rpm, then check the air filter for blockages.

Hope that helps,

Paul:)
 

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I've never had the 1.8 16v, but I'm surprised it won't rev to the red-line. My 2.0 IDE did, and I'm pretty sure my first 2.0 8v RXE did. My second RXE didn't actually have a red-line on the dial, but the limiter kicked in at the same point as it did on the old car (same engine I think, except that the later one had coil packs instead of a distributor.)
 

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Just to add:

I'd expect a proper 16v engine to still be pretty close to its torque peak at around 5.5K. Certainly close enough for the power curve to be heading upwards until you got to within a few hundred RPM of the redline. My IDE was certainly pulling well past 6K with a 6.6K redline, and even my old 2.0 8v only started to run out of steam at around 5-5.3K with (if I recall correctly) a 6K limit.

If it's actually running out of welly before this, then I'm wondering if the rev counter dial is miscalibrated. Perhaps the engine is hitting the 6.5K limit, but the needle isn't going that far up the scale.

Don't forget that it's torque at the wheels rather than torque from the engine that provides acceleration. As road speed would be the same in any given gear, it's power that you're looking for from the engine, along with the best gear to output that power as the maximum torque for the current road speed. The optimum change-up point will be past the torque peak and a little way past the power peak too. You only need to change up when power in your current gear drops below what it would be in the next gear up.
 

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I'd be inclined to agree with most of what's been said above except I think there's a bit of confusion about brake horsepower and torque. Most standard family petrol engines will develop maximum BHP (or PS) at 5 - 6,000 RPM. The maximum torque is usually between 2,500 - 4,000 RPM.

Peak torque at 5,500 or over is usually the preserve of VTEC and VVTi engines, as they are virtually undriveable in normal use - unless you are willing to rev the nuts off them.

Paul:)
 

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I agree that most multivalvers don't peak their torque quite that high, but the torque generally doesn't tail off so fast that power suffers. As you say, most hit their power peak at 5K+ - my point was that it's the power curve rather than the torque curve that matters when it comes to acceleration through the gears.
 

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Discussion Starter #10
Thanks for the info guys, very useful.

I was drving the other day and decided to give the Lag another go around the dial. This time she went right the way round to 6.5k rpm and then hit the rev limiter.

I think the prob might have been last time was, I wound the car up not long after leaving work, say 20 mins or so. The temp guage on the car was reading about half, where it normaly sits, so I thought it was at right operating temp. The ECU must have disagreed and limited me to 5.5k rpm unitl the engine had reached it's optimum temperature. The second time I did it, and it did reach 6.5k rpm I'd been drving for a while so the engine was nice and warm. Not sure how accurate this is but it sounds like a plausable theory to me!!
 
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