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General Question about high rpm and peak torque and bhp

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General Question about high rpm and peak torque and bhp

kyle96

kyle96

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Hi all I just have a couple questions that some knowledgeable people here could answer, please don't think that these questions are 'boy racer' ish they're more out of curiosity than that.

As for gear changing, is there any bad effect of changing up once you hit the rev limiter? I wouldn't do that personally but I'm curious, if not the rev limiter then a very high rpm such as 6k+
There was a couple times on my old gearbox when 3rd gear would slip out, without me knowing I would hit the limiter when it slipped out into neutral, would that have had any detrimental effect to the engine?

Also, does anyone know the peak torque and bhp rpm range? For a 1.2 8v, iirc peak bhp is at the limiter which would be a pointless waste of petrol and strain on the engine would it not?, if the engine even gets strained, so what is 'technically' on a warm engine the peak rpm to change up? If there even is one

Also speaking of warm engine, I know its bad to drive hard with a cold engine, but why actually is this?

Thanks for any replies
 
kyle96 said:
Hi all I just have a couple questions that some knowledgeable people here could answer, please don't think that these questions are 'boy racer' ish they're more out of curiosity than that.

As for gear changing, is there any bad effect of changing up once you hit the rev limiter? I wouldn't do that personally but I'm curious, if not the rev limiter then a very high rpm such as 6k+
There was a couple times on my old gearbox when 3rd gear would slip out, without me knowing I would hit the limiter when it slipped out into neutral, would that have had any detrimental effect to the engine?

Also, does anyone know the peak torque and bhp rpm range? For a 1.2 8v, iirc peak bhp is at the limiter which would be a pointless waste of petrol and strain on the engine would it not?, if the engine even gets strained, so what is 'technically' on a warm engine the peak rpm to change up? If there even is one

Also speaking of warm engine, I know its bad to drive hard with a cold engine, but why actually is this?

Thanks for any replies
Click to expand...

The reason it is bad to drive hard with a cold engine, is due to the fact hat it hasn't warmed up ,the oil is still thick ,and can't get to all he parts its should and keep that crucial film of oil ..Don't get me wrong oil will be there but the protection isn't the same especially if driven hard..

Taking the engine up to the rev limiter will (a) just waste fuel (b) may induce valve bounce

When your old car slipped out of gear it should be ok as you would have let of the throttle as soon as you heard the revs rise

Haven't a clue in the peak torque etc of the 1.2 8v

Hope that has been of some help
 
I wouldn't worry about hitting the rev limiter from time to time, it's set at a safe level. I don't know how true it is but someone once told me that vw run an engine at the rev limiter on a dyno for 7days solid before signing it off for production.

As for optimum gear change point, it varies from car to car (and even from gear to gear) and depends on the power/torque/gear ratio characteristics but as a rule of thumb changing up just after peak power is a good starting point. Hopefully that will drop you back into the rev range somewhere near peak torque. Keeping the engine between peak torque and peak power makes for maximum progress.

I'm guessing here but I'd say a 1.2 8v probably produces peak power somewhere around 5500rpm. 16v engines are usually a bit higher as the larger valve area allows them to breath better at high revs. turbos often make peak power a bit lower down as the turbo can't shift a high enough volume of air to keep the boost pressure up at high engine speeds.
 
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cinquecenpunto said:
that also shows the 1.4 8v has the same gear ratios as the 1.2.
pity they didnt give it a slightly longer 5th for motorway cruising.
both are doing 3840 rpm at 70 in 5th, with std 175 65 15 tyres.
Click to expand...

Pity indeed. The 1.3Mjet with the 5speed is more of the same. its most comfortable at 60Mph in 5th, at 70Mph the engine sounds like its starting to strain. It has the torque but it really needs to be at 2Krpm @ 70Mph in 5th, not near the 3Krpm mark. :(

Humour
 
My rpm used to be in sync with the speedo needle in 5th gear, I attached a cold air feed to the airbox (since the old intake pipe fell off) and pointed it out my fog cap facing forward and revs have dropped about 500 rpm in 5th, 4th is now the one that is in sync with the speedo needle (as in both needles point the same direction and move the same) haha, bit strange eh

It's annoying that the 1.2 and as humour pointed out the 1.3 struggle to sit comfortably at out national speed limit without using a fair amount of fuel.



cinquecenpunto said:
.
Click to expand...

Humour said:
.
Click to expand...
 
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kyle96 said:
My rpm used to be in sync with the speedo needle in 5th gear, I attached a cold air feed to the airbox (since the old intake pipe fell off) and pointed it out my fog cap facing forward and revs have dropped about 500 rpm in 5th, 4th is now the one that is in sync with the speedo needle (as in both needles point the same direction and move the same) haha, bit strange eh
Click to expand...

Not possible! Your engine's air intake has diddley squat to do with the gearing and therefore the engine speed at a cruise.
 
48615629.jpg
 
Lol you are asking about peak torque/bhp?! And when to change up without damaging the engine?

Mate look, just enjoy driving, go from A to B, drive economically, let your premiums lower, don't kill anyone etc
 
Magic Johnson said:
Lol you are asking about peak torque/bhp?! And when to change up without damaging the engine?

Mate look, just enjoy driving, go from A to B, drive economically, let your premiums lower, don't kill anyone etc
Click to expand...

Its out of curiosity really, considering I unfortunately have to drive a lot the question cropped up into my mind and I thought I could ask on here without people taking me as a joke.
Don't forget that me nor a lot of other people on here don't know as much as you might do

In reply to your 2nd point, that's exactly what I'm doing, I need 2/3 yeah no claims for my ideal next car, a focus :)
 
kyle96 said:
My rpm used to be in sync with the speedo needle in 5th gear, I attached a cold air feed to the airbox (since the old intake pipe fell off) and pointed it out my fog cap facing forward and revs have dropped about 500 rpm in 5th, 4th is now the one that is in sync with the speedo needle (as in both needles point the same direction and move the same) haha, bit strange eh
Click to expand...


That's actually pretty impossible..
 
chricol said:
That's actually pretty impossible..
Click to expand...


it must have been that redex octane booster, no other explanation

I'm joking, jokes aside however it's true, it's common knowledge on the 1.2 that the speedo and rev needle are in sync, my revs have literally dropped 500 odd in 5th.

I'm sure one of the smart arses on this forum can explain :)




Mjet220 said:
View attachment 134633
Click to expand...
Lol people think this thread is another how to get more power from a 1.2, which it isn't
 
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