4cyl/8cyl..Same Car..Same Power..

[solaris=amazing]

Ok, lets say you have 2 EXACT same cars.. For ex. both are RWD, both are 3000lbs and A/T..

Let's say they both have 300hp/290lb ft torque.

Now, wouldn't the 8 cyl be faster, even though the 4cyl has the same specs....?

The only major difference would be weight transfer-which i believe the 8cyl would do better-cause the front end would have less weight. Giving more transfer to the rear wheels.. Then again, both cars weight EXACTLY the same..

By faster i'm talking 1/4 mile times. Someone told me if 2 cars identical in design, with the same amount of power..would be dead on the same. Even though one is a smaller engine....?

[peter i]

More Piston more"pure" torqe ...

[Evil Result]

it a perfect world both would be at the end of the 1/4 at the same time..the only thining the V8 has over the L4 is smoother running characteristics.

the V8 would weight more than the L4 so that means the L4 would have more weight else where perhaps the back of the car...there for more weight on the driving tires so perhaps the L4 would get a better launch than the V8.

[Reed]

If and I4 and a V8 had the same torque curve, CG, gearing, weight, tires, drag, lift and everything else the same then they will get there at the same time.

Do the I4 and the V8 have the same displacement and red line?

i guess im just trying to say that there are just way too many variables to answer that question.

[sracing]

Originally Posted by solaris=amazing

Ok, lets say you have 2 EXACT same cars.. For ex. both are RWD, both are 3000lbs and A/T..

Let's say they both have 300hp/290lb ft torque.

Now, wouldn't the 8 cyl be faster, even though the 4cyl has the same specs....?

The 300hp/290 torque isn't enough to work with. The curve is what is important. IF they produced the same hp/torque at all operating RPM points, they would run identically in speed. (Assuming all else equal). The world of physics doesn't care whether they a 4 cyl, 6 cyl, or 12 cylinders, NA, Boosted, or NOX. If the curves are the same, the same work will be done.

Jim
SR Racing

[sracing]

Originally Posted by peter i

More Piston more"pure" torqe ...

What exactly is "pure" torque, and why would an 8 give more than a 4, given the above ratings?

Jim
SR Racing

[solaris=amazing]

Thanks sracing, very true..

Either way, i'd take the 8..

[peter i]

Originally Posted by sracing

What exactly is "pure" torque, and why would an 8 give more than a 4, given the above ratings?

Jim
SR Racing

The 8 piston usually able to give more torque over the 4 piston engine .
because it have more power overlaping compare to 4 piston

[FikseGTS]

he said same power/torque, exactly.... so negating any weight differences, they would perform the same....

[sracing]

Originally Posted by peter i

The 8 piston usually able to give more torque over the 4 piston engine .
because it have more power overlaping compare to 4 piston

Not only is this not generally true, it does not apply to his scenario. He said eaxctly the same torque and HP.

That is whay I asked you what "pure torque" is. You seemd to be saying that 8 cyls gives more "pure" torque than 4 cylinders.

Jim
SR Racing

[CBFryman]

Same Weight? Same Power? Since getting a 4cyl to have the same torque cuve charitcteristics is nearly impossible this is what the major differnce is. if they have the same torque curve they would perform the exact same way. here is the 411.

assumeing that we live in the real world their otrque curves are not the same so...

4cyl would loose in the 1/4 mile. why? more power in the low end means a better launch as long as your tires have the traction to hook all that power up. it is a given that the V8 (generally) will hit its powerban at a lower RPM. and in order to keep the 4cyl (which will probably hit its power ban at a much higher RPM) in its optimal RPM range feather the clutch will be needed on take off. which meanspower loss. the sooner you get the clutch released completely the sooner you start putting a full 300 to the ground.
Other senario... Solo 1. it is really all about weight balence. because the v8 is so much heavyer it will probbaly be more front heavy than the 4cyl. in fact, because they weigh the same the extra weight (as already mentioned) should be in the back to get it closer to 50/50 (49/51-48-52 is actually best) which will give it more neutral handleing which means that as long as steering box and all are the same the 4cyl should be able to take turns slightly tighter at a slightly higher speed shaving 1/10th's of a second of the time. but also solo1/2 you will never have the exact same run, your line iwll always be slightly off. but the 4cyl would be optimal.
Because we are talking about 1/4mile i would go with the v8. as long as you have tires that can hook with the weight transfer you have then the 4cyl will have no traction advantage. but me being an autoX/road racing fan i'd go with the 4cyl. better MPG should be obtained on top of that. but hte 4cyl may require a higher octane fule. it may also brake down more often. so if i had the money for reairs i would buy the 4cyl. if i didnt have the money i wouldnt take the 8cyl beause of MPG and i wouldnt be driving no car with 300hp from a 4cyl.

[bjdm151]

What kind of question is this? If you had two eggs, exactly the same wheigth and dimensions, laid by the same chicken, inseminated by the same rooster ( thats what a rooster does right?) but one of the eggs was on crack but the other was just as stupid, which one would roll down the quarter mile faster.

If a tree falls.........

[SaabJohan]

If one just says V8 vs. I4, identical cars and identical power/torque peaks one can't really say that much about the performance of the cars aswell as smoothness or weight of the engine!

In this thread several people has tried to answer, but their answers isn't based on the facts in this case but on their own assumptions, which can or cannot be true.
For example:

"A V8 is smoother"
Here it is assumed that the V8 engine in question has a cross plane crankshaft with counterweights + that the V8 has more powerpulses = smoother. But this was never mentioned in the "facts". It can aswell be an inline 4 with balance shafts vs. a V8 with a singleplane crankshaft. The inline engine can also use a heavier flywheel to smoothen out the powerpulses. So unless anymore facts are given the I4 can be the smoothest engine aswell as the V8.

"The V8 has more low speed power"
Where did it said that? Once again we have assumptions that may or may not be true. This one is probably based on that the V8 should have a larger displacement, which is also why some people thinks that the V8 engine is the heaviest engine of the two.

If we have two different engines, in two equal cars. If the engines are producing equal power curves and have the same response the performance of both cars will be equal. It doesn't matter if it's a single cylinder engine vs. a V16 engine or a steam engine vs. a turboshaft engine.

In "the real word" the V8 engine that we talk about could be one of those 2-3 litre motorcycle derivatives vs. a turbocharged WRC engine. In that case the inline engine will be the heaviest of the two but it will also have the best powercurve.

If anyone just says a V8. vs. I4 it could also be a top fuel engine vs. one of those large turbocharged two stroke diesels or a V8 "model engine" vs. a turbocharged nitromethane fueled I4 engine developing 4000 hp.

Also, the torque of an engine depends on the brake mean effective pressure and the displacement of the engine. Not on the number of cylinders!