Caporegime
Meridian said:
They are specifically designed for JUST that though. The barely last a weekend if they last at all.
Would you really want a car that you had to get serviced once a week?
An Engine Question
- Thread starter Acolyte
- Start date
They are specifically designed for JUST that though. The barely last a weekend if they last at all.
Would you really want a car that you had to get serviced once a week?
Associate
- Joined
- 18 Oct 2002
- Posts
- 1,145
This is the most sensible answer so far. Everyone else just seems to quote something they've read elsewhere. I don't understand it myself either and would love to if someone can explain it...
Associate
- Joined
- 18 Oct 2002
- Posts
- 1,145
Soldato
I think it must be due to fuel injection characteristcs. Most Bike engines don't even start to sing until 7Krpm, (well fours anyway) and come on song a couple of thou later. as stated earlier F1 engine really rev (though they only need 70 odd laps).
I think that manufacturers must decrease the fueling at higher revs to artificially limit power so that engines last 200K miles.
The "Volumetric efficiency" thing sounds quite plausible too, so i guess it must be some combination...
I think that manufacturers must decrease the fueling at higher revs to artificially limit power so that engines last 200K miles.
The "Volumetric efficiency" thing sounds quite plausible too, so i guess it must be some combination...
aztechnology said:
It is a little more complex, you are correct. However, the only reasons manufacturers reduce fueling is for emmisions and economy purposes. In fact reducing the fueling too much can destory an engine very quickly, especialy a turbocharged one.
Here's a brief description of the problem: power is proportional to RPM * Torque. Torque is mainly dpendant on cylinder filling and compression ratio, hence on a normaly aspirated shopping car engine, you lose torque (and therefore power) at high RPM because the cylinder gets filled with less air and fuel. With a normaly aspirated engine, there is only so much air you can get into the cylinders, because you only have the atmosphere to push it in. That means that generaly you can't get significant increases in torque, so to get more power you have to move the point at which peak torque occurs higher in the RPM range.
Now, you can make the valves and ports bigger to get more air through, but then at lower engine speeds the gas velocity through the ports becomes too low, and the fuel drops out of the air causing power loss and increased emmisions. You can also change the cam profiles, to hold the valves open for longer and opening and shutting them faster to let more air through. Again this works well at high engine speeds, but at low engine speeds it again loses you power because cylinder filling becomes inefficient and it puts lots of stress on the valve gear.
So you have a compromise, a torquey engine that pulls well at low RPM, or one that produces a lot of power but at high RPM e.g. a bike engine. Variable cam timing and inlet manifold geometry (e.g. VTEC, VVC, VANOS etc.) are designed to try and get the best of both worlds. This is also what there has been some work into variable compression ratio designs.
The easiest way to solve the problem is to give the atmosphere a helping hand by strapping a turbo onto your engine. This pushes the volumetric efficiency far higher than you can ever hope to acheive with a normaly aspirated engine, hence the large amount of torque that these engine produce. As always there's a trade of but that's a different topic.
Dogbreath said:
This is why I'm such a fan of the positive displacement, low-pressure supercharger setup.
Run an Eaton M45 at 6-7psi, you don't see 'boost' (which is just an indication of a restriction in your system anyway
), you don't need an intercooler and you'll see roughly a 30% increase in peak power.BUT!
The most important bit is that you will see volumetric efficiency raised to approximately 125% across the rev range, your torque curve will be virtually flattened and it will be raised up 'quite a bit'
Or...Slap a chargecooler in your system, crank it to 18psi and rock a phat one.
*n
Zip said:What are those?
http://www.alpinerenaulttuning.co.uk/avt/liquid1.htm
There's a drag-racing Vauxhall Firenza running close to 600bhp on a standard 2 litre 16v engine with a massive turbo, ice-filled chargecooler and a ****load of nitrous. My kind of car
*n
Sorry - to explain further, they're like an intercooler...But mounted very close to the manifold (keeping inlet tract length down) and cool the air in the 'charge' by running it through a radiator-style matrix which is filled with water. The water is circulated through a system and is often cooled itself by a secondary radiator (to the engine's primary radiator)...
Make sense?
*n
Make sense?
*n
