Im sure you've heard of the "magic" 100 hp per liter figure some naturally aspirated cars can claim (eg M3, s2000, etc.....). But, have you ever heard of 100 ft lbs. of force per liter (N/A)? The only things i can think of would be an f1 car, or a diesel....Maybe theres some math i dont understand...

 

I think the closest thing there is are the trucks that pump out 500. Silverados, Dodge Hemis, Ford heavy duty.

 

yeah, thats what i was thinkin...its been bugging me though...

 

how about a rotary engine?? those natural aspirated 13B

 

yeah, good thought. but i thought there was always some controversy on their actual displacement...there were different ways to calculate it, or something

 

You can count them as a 1.3 or a 2.6. If you count just one rotar then it's 1.3 if you count both it's 2.6.

2004s/05s
159 tourque @ 1.3 = 122 pr/ liter
@2.6 = 61 pr/ liter

 

so why would you only count one rotor? it has two...

 

Yeah, I thought the confusion came in because there were several combustion cycles on one rotor...3 iirc...
I'm no expert, but I do know that the rotary engines were not known for high torque. Linear torque and high revving abilities, but no high torque.

If you think about it, torque is the amount of work that is being done, which is basically a function of displacement and compression ratio. Horsepower, oth, is a time function of torque, so the way these small displacement engines produce so much horsepower per liter is by spinning really, really fast.

 

But only one of them is full at a time.

I agree that it should be counted as a 2.6L just like cylinder engines are counted on every cylinder full or not.

 

For 100ft/lbs of torque/liter, you are doing UNBELIEVABLY well on a NA motor. As an example, we dynoed the 498ci BBC in my boat at 821hp at 6200RPM and 704ft/lbs at 5700rpm. At 498ci, the motor is 8.161 litres small. If you're not familiar with domestic based hp to ci ratios this wont mean a lot, but the motor makes 1.649hp/ci which is absolutely freaking amazing, especially considering the motor was designed to make that HP on 91 octane and about 1000rpm lower than most motors that are similar. Even with amazing efficiency and an unblievably flat torque curve, I was only able to come up with 86.264 ft/lbs per litre. The cost of comming up with a combination of similar efficiency regardless of overall displacement would make it cost prohibitive by a long shot in terms of production vehicles.

As for someone's statement about domestic Diesel trucks making 100ft/lbs per litre, those powerplants are turbocharged, so obviously you can't use them in a discussion about NA torque figures.

Chris

 

Sounds good enough to me, Chris! An srt-4 of boats...lol

 

Not really. For the circles I occaisionally rub elbows with, my numbers leave something to be desired. It does't relate too much to the orriginal thread so I don't want to hi-jack, but a lot of the stuff that is happening now on the NA marine front is bettering 1000hp at 565 and greater ci. But once again at relatively low (6500ish rpm) and on 91 octane which makes it even more impressive.

Back to the 100ft lbs/litre question, I'm going to do a little digging to see if I can find a domestic(thats where my information base is) NA setup that dyno'd over 100 per litre. Then look at the rod/stroke ratio, and the bore/stroke/ci ratio to see if there are any common import setups running similar ratios. Obviously if they are even close with the added flow capabilities and port velocities of 4 valve heads compared to 2 valve heads, it seems like something that could be attainable. The only problem I would see is that you might have to get over a certain displacement threshold to get there and that might fall outside of most 4 cylinders, inline or boxer.

Chris

 

great response guys...i really like that marine engine. for such a big motor 100 hp per liter is pretty damn hard...congrats. tell it to the honda boys when they starting whining about their 100 hp/l engines damn at only 6200 rpm...sweet...

Well, i thoght that if their is one engine out their that might be able to make 100hp/l, i thought the bmw F1 engine could. we know that hp = (torque*rpm)/5252. And we can assume bmw is making around 850 hp at close to 19,000 rpm. But we could only figure out the torque at 19,000 rpm, not at the torque peak...any ideas....?

 

Well, if you knew the actual power curve of just the HP, and assume (which in a motor of this calliber would be a highly probable false assumption) that torque and HP intersect at 5252, you could extrapolate a rough torque curve using some basic graphing and trending in excell. Not having any knowledge of the motor you are refering to I'm going to go out on a limb and say that the peak torque isn't as high as you would think. Because of the RPM function in the equation listed, if the motor were to generate its HP well above 5252 (as it does if it peaks at 19k), it is highly likely that the motor is soft on torque.

I'll do a little searching for info on the motor you're talking about, but I would suspect that at those RPMs, the HP is high only as a result of the amont of cycles that the motor can provide in a given time. Remember that Horsepower is defined as 550 ft lbs per second. So in a loose extrapolation, HP is torque over time or cycles. With the high number of cycles in a given period in the motor you are talking about the HP will will be much higher than the torque in comparison to other motors that spin much more reasonable RPM.

Chris

 

good thoughts, the motor is a bmw p83, theres some info about out there just google it.