[NarutoRamen]

Originally Posted by speed_kills

I think it is 7250 for the Impreza. I remember seeing in the net a Evo revving to 8000, on the redline of course...

Thanks for confirming it for me...7250 is still pretty damn high, especially considering it's 2.2L motor pumping out 290bhp/263lb-tq...that's just a little bit over 130bhp/liter, out of a 4banger....now that is badass.

[vedjo01]

Thx,Naruto..this is "THE IMPREZA" IMO..This new version just doesn´t have appeal of old beast(I´m quite szre it´s beast under the skin ).Japan cars never stop to amaze me..just how do they do it ?

[NarutoRamen]

Originally Posted by vedjo01

Thx,Naruto..this is "THE IMPREZA" IMO..This new version just doesn´t have appeal of old beast(I´m quite szre it´s beast under the skin ).Japan cars never stop to amaze me..just how do they do it ?

yep, I'm with you on this one. That right there is my favorite impreza, the new ones are good too but I just love the look of the old one. The old had a brutish look with a little bit of style. The new ones are just straight up brutes. But the way the new hatch is turning out to be, I've gained some love back.

Now this question is for the technical guys. I've heard that the more cylinders you have the harder it is to get a higher redline? is that true or is the the opposite? I'm confused on this one. Martinbo, chonkoa, care to help?

[Sunny]

Originally Posted by NarutoRamen

yep, I'm with you on this one. That right there is my favorite impreza, the new ones are good too but I just love the look of the old one. The old had a brutish look with a little bit of style. The new ones are just straight up brutes. But the way the new hatch is turning out to be, I've gained some love back.

Now this question is for the technical guys. I've heard that the more cylinders you have the harder it is to get a higher redline? is that true or is the the opposite? I'm confused on this one. Martinbo, chonkoa, care to help?

For a given displacement, it is the opposite. So a 5L V10 can have a higher redline than a 5L V8 (everything else being equal). The biggest impediment to a higher redline is the weight of the moving parts - pistons, connecting rods etc - the heavier they are, the slower they will accelerate and lower the redline (also the stresses go up with weight - making it even worse). And for a given displacement, the more the number of cylinders, the lighter the individual pistons/cylinders and hence higher they can rev.

So the obvious follow on question is, why not make every engine a V20 or V50 with really small cylinders/pistons and rev it to the heavens - but unfortunately as you increase the number of cylinders, the engine as a whole gets less efficient cause of higher parasitic looses: for a given displacement, the more the number of cylinders, the higher the contact area between the cylinders and pistons increasing friction. So it is a balancing act between these two factors. Also more the number of cylinders, higher the manufacturing and maintenance cost. So like most other things in life, it is a balancing act.

Of course, I am simplifying things here in my very limited knowledge.

As for the 1st gen WRX, my favorite too, fell in love with it playing the first Gran Turismo along with the Skyline GTR.

[chonkoa]

Originally Posted by NarutoRamen

yep, I'm with you on this one. That right there is my favorite impreza, the new ones are good too but I just love the look of the old one. The old had a brutish look with a little bit of style. The new ones are just straight up brutes. But the way the new hatch is turning out to be, I've gained some love back.

Now this question is for the technical guys. I've heard that the more cylinders you have the harder it is to get a higher redline? is that true or is the the opposite? I'm confused on this one. Martinbo, chonkoa, care to help?

In addition to what Sunny just said which in my limited opinion is 100% spot on.

I believe the most important factor with rev limit is the combustion pressure in a cylinder.
Some of the factors that affect combustion pressure are:
1. The type of fuel mixture for a given displacement. A good example is between Petrol and Diesel. A diesel combustion generates more pressure than Petrol due to the heavier Carbon and Hydrogen composition. The higher combustion pressure is due to more exhaust gases that are generated per stroke. There is a limited space(outlet valves) for the gas to escape which limits how fast the engine can make the next stroke, thus a lower redline than petrol engine. The same can be said of Petrol versus Natural gas engine, the natural gas will rev faster than the petrol engine because of the lower combustion pressure. It is important to note that this combustion pressure is what gives the engine its torque.
2. For the given fuel mixture, the displacement affects the redline like Sunny pointed out. If you increase the displacement by increasing the stroke length instead of the bore diameter, the piston will have to travel a longer distance per stroke, thus reducing the redline. One way of dealing with this is to increase the bore diameter rather than the stroke length. Either way, increasing the displacement will increase the combustion pressure of the cylinder thus creating the same limiting effect on the engine speed.

[Sunny]

Originally Posted by chonkoa

In addition to what Sunny just said which in my limited opinion is 100% spot on.

I believe the most important factor with rev limit is the combustion pressure in a cylinder.
Some of the factors that affect combustion pressure are:
1. The type of fuel mixture for a given displacement. A good example is between Petrol and Diesel. A diesel combustion generates more pressure than Petrol due to the heavier Carbon and Hydrogen composition. The higher combustion pressure is due to more exhaust gases that are generated per stroke. There is a limited space(outlet valves) for the gas to escape which limits how fast the engine can make the next stroke, thus a lower redline than petrol engine. The same can be said of Petrol versus Natural gas engine, the natural gas will rev faster than the petrol engine because of the lower combustion pressure. It is important to note that this combustion pressure is what gives the engine its torque.
2. For the given fuel mixture, the displacement affects the redline like Sunny pointed out. If you increase the displacement by increasing the stroke length instead of the bore diameter, the piston will have to travel a longer distance per stroke, thus reducing the redline. One way of dealing with this is to increase the bore diameter rather than the stroke length. Either way, increasing the displacement will increase the combustion pressure of the cylinder thus creating the same limiting effect on the engine speed.

Thanks, I knew combustion played a part too, was just not sure how.

Going back to turbo engines and red line, I can't think of a reason why turbo engines have inherently a lower redline. I think the reason why turbo engines usually have a lower redline is cause with a turbo engine it is easier (and cheaper) to increase output by just increasing the turbo pressure rather than increasing the redline - just manufacturers resort to just increasing the turbo pressure than increasing the redline.

One reason I can think of is that the fans driving the turbos are not efficient across a wide RPM range. But the new variable fans in the 997 turbo addresses that.

[NarutoRamen]

^^Thanks guys for the info. Now I have some reading to do. I'm gonna go ahead and read a few technical definitions so I can expand my car knowledge. It's good to have smart technical guys on this board.