Engine hp

I agree with Tim on HP figure being as important as torque, here's an example for those who feel torque is all that matters. These numbers are from Honda , I did not dyno these motors. A 2010 Honda CBF 125 makes 8.3 ft.lbs of torque @6250 rpm and 11.3 HP @8000, a 2001 Honda V-twin Varadero makes slightly less torque 7.9 ft.lbs at 9500 rpm but because of having much higher rpm capabilities, makes 15 HP @ 11,000 rpm. You see , torque alone does not tell the whole story. Jon
 
Taft Racing said:
Mike I'd have to disagree, a run on a dyno does exactly what your talking about. It takes a engine and accelerates a given mass and measures the hp and torque required to do so.
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I hate to be a nit picker but that is not how a hydraulic dyno works. An inertia dyno does work by accelerating a given mass. Using one of those measures acceleration rates. The rpm changes per second are measured. Everything else is computed....not measured. Again, there is a significant difference. That is why torque and hp are not the figures that matter. Yes, they are a factor in the acceleration rates but who cares? What matters is the ability of the engine to accelerate the kart from point A to point B and that's about it.

Everything matters BUT when it comes right down to it, acceleration rates tell us about all we need to know, given the heat recovery of the engine can sustain running under a load without overheating for the length of a race.

Mike
 
A small block Chevrolet engine can make 400 hp and 400 lb/ft of torque pretty easily.

A Chevrolet truck engine that makes 365 hp, makes 660 lb/ft of torque!

What have you learned? Hum, that's not really clear, is it? The acceleration rates would tell you exactly what you need to know. That's why acceleration rates tell us what we need to know.

Mike
 
There are two key principles in this that no one is mentioning that allows the smaller purpose built race engines to compete competitively with larger motors. And kart weight isn't one of them.
 
Chris,
Are the "two" you reference not a part of the larger displacement engines because none of the larger displacement engines have been built with those advantages?
Or is there an inherent design advantage that the smaller displacement engine has due to it's smaller physical size and weight?

A close relative of Mike's acceleration rate is the "speed bin".
These are both very useful bit's of information.....one accessed by the dyno, the other on the race track.
 
SeayHiPerformance said:
There are two key principles in this that no one is mentioning that allows the smaller purpose built race engines to compete competitively with larger motors. And kart weight isn't one of them.
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The 2 corners lol. Mike accelerating a given mass is one thing maintaining the desired rpm and speed is what counts. Not just acceleration. Hp is what maintains that speed not torque.
 
A very fundamental “fact”; The dyno does not “measure” HP. The dyno measures “torque” and “RPM” and the computer, taking into account, (hopefully) the barometric pressure and the air temperature, (air density) calculates the “HP”.
Torque is a measure of “work”!!
HP is a calculation of the rate of “work”
Torque X RPM / 5252.1 = HP
If you want to know where these numbers come from, read up on James Watt in any dictionary. He’s the person that first came up with the idea of, and the calculations for, “Horsepower”. Very interesting stuff.
Comments, compliments, criticisms and questions always welcome.
 
SeayHiPerformance said:
There are two key principles in this that no one is mentioning that allows the smaller purpose built race engines to compete competitively with larger motors. And kart weight isn't one of them.
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If kart weight isn't the reason that the small little engines can run ok against the big ones than lets make them weigh 430# plus and see how they do. @ thanksgiving thunder in 2012 your BRC qualified outside pole to my big engine but I gave you more than 100#'s in weight advantage I don't see that even being close if you added 100#'s to your kart. JMO
 
Hmmm. I don't know jerry . Ed Schriefels sat outside pole at the big. O and he ran a 131. Now Ed is a pretty big boy. I know his kart and he weighs in at 415 lbs. Now I don't know what weight Robbie weighs in at but you are allowed to get down to the 430lb mark. So I'm not sure what chris is saying . I'm not good at guessing but I know the recovery rate for making a mistake on the little purpose built engines kills them against the big engines.
 
Jon, it sure seems funny to me that such a low number is given for degreing a 4-stroke cam, it seems in direct contrast to what has been a standard for the B & S cams and all the SBC, BBC and old style Chrysler hemis., I've done in the past. Something to hide? Do their cams have opening and closing ramps?
 
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Sitting on the pole is more about overall set-up and tires, not an engine. I've seen a Yamaha set fast time but get CRUSHED on a start of the race and nearly get lapped. This is exactly why acceleration rates are so important! Racing isn't about who can set the fastest lap time. We don't do time trials for trophies.

Staying on topic, an inertia dyno does not measure torque. It computes it. It measures the RPMs of the wheel and the time it takes to get there. A hydraulic dyno measures torque and RPMs.

Tim,
Why would we want to hold RPMs? We aren't running a conveyor belt. We're not running a lathe or a mill. That's what motors are for. If holding RPMs was important, we would not accelerate down the straights. What we had in the corners, would be all we get. We need a whole lot more than the ability to maintain RPMs.

You're focusing on something that isn't important. HP is a fake concept in an internal combustion engine. It was manufactured. That's why any torque curve will cross the HP curve at 5252 RPMs. Once you accept that, you can focus on what we really need. We need the ability to accelerate. That's what an engine provides us.

We can have 2 engines that make the same HP at a given RPM and thus they make the same torque at that same RPM but they will accelerate a given mass at different rates. Chris is talking about one of the factors that comes into play with that. (I have to be honest. I don't know what the other is.) The bottom line is, the acceleration rate tells us which one is best. That's the one I want bolted next to me. There is no need to complicate it beyond that.

With that said, less mass is easier to accelerate.....period. That is because less mass takes less force to change direction. Less force is easier to obtain than more force. It is a law of Physics. It's not like our laws that the government provides us. These laws are not arbitrary. Laws of Physics exist and they can not be broken. To this day, we do not comprehend all that Physics offers BUT this isn't magic. It is reality. The most intelligent people that have ever lived can't explain it but they can still recognize what exists.

Many of these computations come from a desire to relate two or more things. HP can be related to torque. HP can be related to energy used.....thus torque can be related to energy used. It's more about a numbers game than anything else. It just darkens what was clear water. There is no need to make things complicated. Acceleration rates over a given band width is all we need.

Mike
 
4-5 years ago when I brow beat Hotdog, into letting us run the big engines, the general consensus was there was no replacement for displacement, the big engines make more h/p and torque at a much lower rpm, they are cheaper to build, parts are readily available..

Inherent to the lower rpm, and displacement, the torque curve is flatter and a more gradual up curve, which makes them manageable getting the power to the ground, the weight of the kart helps handling, as the karts in the track instead of on top of it.. this works as well for the 2 or 4 cycles..

As far as acceleration, it's pretty obvious the more TQ/hp, the faster your going to accelerate, if you can hook it up.. the thing with the big engines, you really can't screw up the powerband.. I can tell you on my 250, it's stock porting, with head work, on dual alky atomizer 181's, and 2 pipes i've designed for it., is plenty for anyone..

I have a taft lowerend coming, can't wait to try it..
 
There are principles in establishing acceleration rates that gives some motors advantages over others, even though one may have more torque. One is inherit to the motor, the other is to mechanical setup.
 
More weight helps you handle? OK. That doesn't address being able to go as fast as you can. We are racing. If you are trying to say, more weight makes you go faster, tell that to NASCAR. Tell that to F1. No one that has a fair understanding of Physics wants their race car to be heavier.

My 250 shifter was a rocket at 400lbs. Adding 30lbs, to make weight, caused me to sell it and go back with a Sudam based engine. 30lbs killed it. Just because adding weight makes the kart easier to drive around the track does not mean it is faster.

Mike
 
SeayHiPerformance said:
There are principles in establishing acceleration rates that gives some motors advantages over others, even though one may have more torque. One is inherit to the motor, the other is to mechanical setup.
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To add what is stated above: There is a reason that Speedway motorcycle engines are in a laydown configuration and it's not just to lower the CG.

Mike
 
I'll have to agree to disagree Mike, karts don't have suspension, I'd say you just didn't tune your 250 kart to the track.. it takes a quite a bit different setup.. i'm guessing you had a trans 250, alot more weight on the right rear..

I'd take a 30# weight break, as we have run it light, it's just not as well handling.. with the big engine it's kinda mote anyway, as there's more power than any sane person can handle.

I can think of only one reason a laydown jawa is perferred, is to lower cg, the upright and laydown engines weigh the same.. same reason I don't want the extra 25-30#'s of a trans and clutch hanging on my right rear.. not conducive to a good handling kart..
 
Mike on the start we accelerate. Once up to speed we do all we can to maintain that speed. The big engines can recover from mistakes much easier than the little high rpm engines. As for weight and NASCAR why do they look for more down force? Thats more weight to the tire which equals more bite. More bite more grip more speed. And before you say it. No I do not think its possible to lock down a jawa 450 or 250. I'm not real sure you could lock down a 131 or brc either.
 
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