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TORQUE not BHP
extreme90:
ad, does snapping a half shaft at idle rpm count for me :P :P
ok mate,
you heard about weston coyney tho :shock: there filling it in soon :shock:
dan
Xtremeteam:
--- Quote from: "TheBlueySilverThing" ---ill keep my tractor engine for the challenges
shows any v8 up on the rough stuff
just not blistering on road
--- End quote ---
i love my TDi cos i can plant it,take it to 20psi o boost & it spools up & <edit> off, 8)
Hobnailkelly:
Just to digress a bit and as we have some experts on.
Why do diesel engines make such a knocking noise ?
Mine makes a hell of a racket at tickover (Diahatsu 2.8 td) When it's moving I can't hear anything above the whine from the turbo, rumble from the tyres and droning noise from the snorkle so I don't know if it gets better or worse!
disco-v8:
--- Quote from: "sptb" ---As far as I've grasped over the years it's down to what revs the engine is optimised as, all the things already mentioned, inlet and exhaust tract lengths, cam profiles etc all change the optimum revs of a particular engine.
Using different combinations of cams and lengths etc it is possible to produce engines that mange to get greater than 100% filling of the pistons at precise revs by using the harmonics of the inlet track to pulse air in when required.
High reving engines just haven't got the time to fully fill the cylinder but they make up for it by having more combustion cycles instead. This is one of the reasons for high compression ratios on these engines - the dynamic cylinder pressures aren't what they should be cos the cylinder wasn't full anyway.Also the long duration race cams mean that the pressure from the combustion is only being used to push the pistons for a relatively small l% of the cycle.
So on a race engine each small push from the piston means there isn't an awful lot of torque but the fact you have so many of them means that there is plenty of power there.
On the torque optimised engine the high % cylinder filling means compression ratios don't need to be high to get a good burn, and the short duration cam and low revs means each combustion can be used to it's max, this gives good torque but the small number of cycles means lower torque, as there is simply less fuel being used so less energy input.
Personnally I (fly in the face of convention) see no reason why a higher reving powerful engine can't be used off road provided the gearing is low enough. Low gearing multiplies torque, it does not multiply power though
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--- Quote from: "Eeyore" ---
Also, at greater spark advance you need to run quite rich (up to 25% in some cases) otherwise you end up spitting combustion into the exhaust and melting stuff. The exhaust products'll hit 1100+degC - which isn't healthy! The solution to overheat is to over fuel and use the fuel itself to lower the temperature and pressure in the cyclinder (you'd be trying to run at about 850degC in a road engine)
Optimal torque is made when the moment of highest cyclinder pressure corresponds with the sector of the crank being horizontal - quite literally the force is pushing down on the longest effective lever. Flame propogation in the cyclinder happens at a fairly constant speed, so inorder to optimise the pressure in the piston with the crank as the speed of crank rotation increases, the spark has to be produced earlier and earlier- the higher the revs, the earlier the spark is required otherswise you still get maximum combustion when the crank has exceeded bottom dead centre, which drops the power somewhat.
Engines - seemingly so simple yet, so darn complex!
It's one o' them subjects that needs someoen with a pad and pen and a lot of knowledge - and that ain't me!!
This won't have helped!
Cheers
Eeyore
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now this is the stuff i enjoy to read, the stuff that takes a few times of reading to actualy understand, anything thats very technical i love......
so basicaly what im starting to understand with torque is, that its all down to compression really!!!! as with a racing high BHP engine your losing some compression through the cam overlap. plus as petrol has a certain way of burning, it has less room to ignite to full combution so has more force on the piston pushing it down relating in more torque. but as petrol has a lower igniting point its hard to get high compresion ratios with out preignition, without changing the fuel to a higher RON/EON rating......
so as silly as it sounds but would adding more fuel help to lower the preignition of petrol by trying to keep the combution chamber cooler, or wud it make the hole thing even worse as theres more substance in the chamber that cant be compressed (a liquid) making it even high comp ratio and preigniting it even sooner???????
or is it alot more of a timing thing where they would leave the ignition timing alot later so its not trying to push on the piston BTDC and and slowing the piston down and losing power, and make it so that it ignites just ATDC so all the power is on the down stroke, but then again the fuel might not have enough time to fully burn, but then again torque happens at lower engine RPM so mite be better
ok ok bit late at night now and think im confusing myself and cotradicting everything ive ever learnt about engine fueling and timing!!!!!!
Eeyore:
Higher cycliner pressures usually result in more pushing force. In short throw engines this translates as lots of speed. In engines with a longer throw on the crack it translates as more torque (same force working with longer leverage).
So yeah, upping the cylinder pressures helps - but it depends on what end result you want out!
Anyone remember the good old 1.5ltr turbo F1 engines? They used to generate a cylinder pressure that exceeded the yield limit of aluminium , therefore everytime the cycle went pop it would have bent the conrod. So, they couldn't use aluminium as it would have bent or fatigued to death . Steel can have an infinate fatigue life if loaded properly, but it was too heavy, so they went for titanium instead. Mind you in qualifying trim the engine was out-putting about 1500bhp!! :shock:
I beleive they had very short throw cranks.
...and just don't get started on dragsters! :lol:
Again, more ramblings!
Cheers
8)
Eeyore
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