Engine hp

Never raced a dyno. How fast are they? I know when we use one its for comparing what we had vs what we have now. The numbers can sound impressive with just the sharpening of a pencil. What matters is when the rubber hits the dirt in our case. Our Honda probably doesn't have the biggest dyno numbers out there, but it's usually got plenty of what it needs to go fast on the track. That's if I do my job and my driver does his. Heard stories of some really big numbers, but havnt seen anything that just walked us off the corner yet.
 
Taft Racing said:
Jerry you bring up some interesting thoughts. On the 250 2 stroke the shorter stroke engines have the ability to turn more rpms and should be a smoother torque curve than the longer stroke engine. Those do to the longer stroke need to get the job done on a shorter rpm range do to piston velocity.

On the 450's the shorter stroke allows them to turn higher rpm also, on a Bike they tend to short shift the big bores and let the torque do the work. On a Kart we may be able to use the higher rpm range, On the Jawa it's been refined for speedway racing for years, I think thats why it has the right stuff right out of the box for karting. I don't believe we have use for or can use what were now tapping into HP wise.

Steve I question your thread because you make a turn key 250, you know dyno numbers for the BRC and your PK 250 and yet you start a thread asking a question you already know the answer too. I know you work in a industry filled with secrets and holding what you know close to the vest is business as usual. In what were doing does that really give you a advantage? seams to me it would be a great selling tool to expose real dyno info for the masses to see and compare what these things are capable of.

I'm hoping to have a Jawa to dig into here soon. I intend to steal info left and right and incorporate that knowledge into my 450 cases. I know once I have a dyno in house I'll plaster the info all over the internet.
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Tim you are reading in to it to much .. I was just seeing if people were going to throw out crazy numbers

I sent you my Dyno sheet. But it's all relative
 
Sjg22 said:
Tim you are reading in to it to much .. I was just seeing if people were going to throw out crazy numbers

I sent you my Dyno sheet. But it's all relative
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Ahh so you were just stirring the pot LOL. I thought so. I understand relative.

Jack thats kinda what I'm talking about when I said real numbers. I've heard that the Sudam makes 50+ HP for years now. Yet the YZ 250 I built for you was rated at about 42 HP back in 90 when it was made. That YZ will blow the doors fenders and every other body part off any Sudam made.( drag race) So real numbers the Sudam would be a easy 10hp under dog to the 250 in the real world. . Just saying.
 
if you guys wanna get right down to the nitty gritty of it the JAWA and the 450's both have more power than we actually need. so lets be honest here we all know were darn near over powered now for some of the tracks we run so why worry about numbers. HP is affected daily depending on atmospheric pressure, elevation above/below sea level, relative humidity, and temperature. just because the dyno in your shop says your making 55hp on an 80 degree day with a humidity level of 58 300ft above sea level does not mean that on a 68 degree night with a dew point of 70 100ft above sea level your getting 55hp. i think we should start putting wheels and tires on the dynos and race them since thats all anyone wants to talk about anymore.
 
I can second that, my sudam runs good but not nearly as good as Jacks stock yz. Bugs aside I could dispatch at will everthing on track besides maybe Baldwins monster billet at limerock. But there again were talking stock 90 vintage 50$ motor :)
 
I too was curious to see what made the Jawa tick, and also found engine specs on it. The most telling spec is the compression ratio, a very healthy 15 to 1 which was designed for methanol. The 2013 450 Honda designed to run gas has a 12.5 to 1 comp. ratio , that is a huge difference giving the HP edge to the Jawa. The Jawa cam with it's 280+ degree duration at .040 lift on the exhaust and 284 degree duration on the intake at .040 shows it's obvious top end potential, that's the first model listed but they are all similar with the 02 model having the most low end with it's quicker intake shut. Once the fourstrokes wet to multiple valves and developed valve trains capable of turning the kind of rpm's they are doing now they've caught up a little to the smoker's. Used to be if you had a two stroke that was 1/2 the size of a 4 it would outrun it. IMO the two stroke that's gonna have the best chance to run with these state of the art 4's will be the 250. The smaller more radical 131's and 150's might have a decent peak HP number , but look at the torque curve, as compared to a big 4 they will always have less off the turn, be harder to hook up and harder to drive. Time will tell. Jon
 
Well said Jon
Jon Brogden said:
I too was curious to see what made the Jawa tick, and also found engine specs on it. The most telling spec is the compression ratio, a very healthy 15 to 1 which was designed for methanol. The 2013 450 Honda designed to run gas has a 12.5 to 1 comp. ratio , that is a huge difference giving the HP edge to the Jawa. The Jawa cam with it's 280+ degree duration at .040 lift on the exhaust and 284 degree duration on the intake at .040 shows it's obvious top end potential, that's the first model listed but they are all similar with the 02 model having the most low end with it's quicker intake shut. Once the fourstrokes wet to multiple valves and developed valve trains capable of turning the kind of rpm's they are doing now they've caught up a little to the smoker's. Used to be if you had a two stroke that was 1/2 the size of a 4 it would outrun it. IMO the two stroke that's gonna have the best chance to run with these state of the art 4's will be the 250. The smaller more radical 131's and 150's might have a decent peak HP number , but look at the torque curve, as compared to a big 4 they will always have less off the turn, be harder to hook up and harder to drive. Time will tell. Jon
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We can compare HP all you all want. Ask yourselves a simple question. Why do we choose certain engines for our karts? The answer is simple. We don't want to just move from point A to point B but we want to accelerate in a positive manner from point A to point B. So, does it not make sense that we should actually be measuring rate of acceleration instead of some mathematical equation? My engine builder does.

You all are wasting your time examining the wrong thing.....because they are different. They are related but they are very different.
Mike
 
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. The 125-150 Sudam based engines do the work in a much narrower rpm band and they require clutch /pipe/ gear ratio's to be in that window. By comparing HP/torque numbers builders can look for and fine tune engine combinations to get that desired perfect blend. IE hp/torque numbers from the Wankle vs the Jawa vs the 450 vs the 250's ect. These kinds of discussions are very much heading in the correct direction and it's very useful information especially when there's actual documentation being discussed.

For example Jerry's comments on the Jawa's numbers how and why the engine is so successful and then comparing those numbers to the 450 and 250's. I saw some of steve's Dyno numbers for the PK250 They told me what I already suspected and I saw my low ball guess on HP was pretty close, But I was low. I also saw a engine curve that is and will be tuned to the kart very easily and very soon. Knowing which way to tune and where to go to get that tune is where a dyno can be instrumental. HP numbers are just as important as torque numbers.
 
Virtually all expert engine builders will use a dyno and use this to improve the hp numbers and for comparison to determine how it will perform. I have spent allot of hours on both a flow bench and a dyno. I always felt that I knew exactly how my motors would perform. If the car didn't match the performance I knew to work on the car, suspension or the support items such as fuel system, scoop or ignition because these were fixed items on the dyno. Our onboard computer would tell me how much time we spent at each RPM so knew what I was looking for as to where we should concentrate our efforts. If a person is sweeping a pull across the RPM band and watching their fuel curve they can deliver a great deal of information that will translate to the track. We swept out motors at a known RPM per second. This helped me to make sure that the motor was accelerating at a fast rate. This was all state of the art drag motors. How fast the motor would accelerate is how fast the car would accelerate. However if we were of by 25 hp we were not likely to win a race. I knew before I ever put a new motor on the dyno what the peak torque should be and what the peak hp should be and at what RPM this would happen. I summarized by knowing the cubic inch and the flow of the head. If these number were off the tuning began. The tool most often used to do this was the fuel curve or wide an O2. Most of the work would be concentrated on moving the cam, lash, rocker ratios, air bleeds etc. In summary a dyno can deliver a great deal of information if you know what you are looking for.
 
Unless you give me a transmission, I'll take a Tq curve like this: ......------------....... instead of this ............../\.... every time. :)
 
So to stir the pot a little more, why not build a Polaris 500 with a CVT on it to widen out the torque curve instead of trying to build it in an engine?
 
No Jack, I'm not talking about max lift numbers , that imfo wasn't supplied, the opening and shut times were figured at .040 lift, and I figured duration from there also at .040 lift. Jon
 
Brian Montgomery said:
So to stir the pot a little more, why not build a Polaris 500 with a CVT on it to widen out the torque curve instead of trying to build it in an engine?
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simple it is not a racing engine kinda like the industrial engines you can race them but they will more than likely break trying to keep up with a purpose built racing engine.
 
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