4 stroke vs 2 smoker?
- Thread starter Dav
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Burris Racer
Member
Jon Brogden
Member
With almost equal HP , I think the 4 stroke should keep up quite well on any track. It's bound to have more torque and it's at a much lower rpm.
Sprint, paved. 7 slow corners 30 to 34 mph, one long 65 mph straight
There is a big misunderstanding of hp figures and how they apply in the context of karting or racing. The software used with dynos corrects power for gear ratio, among other things, for both observed and corrected horsepower and torque. Once you put the engine on the kart, the gear ratio working as a torque multiplier increases the power output. In other words, you are making more torque at the axle than at the crank. Take your Z06 and accelerate in first gear vs. 5th or 6th. The engine still makes the same power but is applied differently.
In this case, the power is roughly the same at 20hp, but there is a 2000-3000rpm difference. How many teeth different would that be? At 65mph, that could be four teeth on the clutch or about 20 on the rear. That means 65mph at 8000rpms is a 4:1 ratio and 5.23:1 at 10500rpms if we multiply our power at the crank by the gear ratio, 20 x 4 = 80hp or 20 x 5.23 = 104.6hp. Mathematically, 20hp at 8000rpm is 13.13ft/lb, and 10ft/lb at 10,500rpms; again, we can multiply by our ratios. At 8000rpms, that is 52.52ft/lbs, and at 10,500, that is 52.3ft/lb. Very close to equal. However, we are talking about peak numbers. The KA100 has another 4000-6000rpms in it; if it's an industrial 4-cycle engine, you may have another 1000-2000. I would give the KA100 the edge.
You would also want to validate that the engines are tested on the same dyno since most are improperly calibrated and read differently. This, of course, is only part of the equation. Handling, driver, etc. can make up for the differences in horsepower.
In this case, the power is roughly the same at 20hp, but there is a 2000-3000rpm difference. How many teeth different would that be? At 65mph, that could be four teeth on the clutch or about 20 on the rear. That means 65mph at 8000rpms is a 4:1 ratio and 5.23:1 at 10500rpms if we multiply our power at the crank by the gear ratio, 20 x 4 = 80hp or 20 x 5.23 = 104.6hp. Mathematically, 20hp at 8000rpm is 13.13ft/lb, and 10ft/lb at 10,500rpms; again, we can multiply by our ratios. At 8000rpms, that is 52.52ft/lbs, and at 10,500, that is 52.3ft/lb. Very close to equal. However, we are talking about peak numbers. The KA100 has another 4000-6000rpms in it; if it's an industrial 4-cycle engine, you may have another 1000-2000. I would give the KA100 the edge.
You would also want to validate that the engines are tested on the same dyno since most are improperly calibrated and read differently. This, of course, is only part of the equation. Handling, driver, etc. can make up for the differences in horsepower.
"J'-remy
Member
its all in the torque curve. whatever engine can utilize the most of it on any said track will win especially if hp is identical (which poster said they are)
horsepower is a mathematical calculation. A Dyno is and instrument used to measure torque at RPM. why they are all over the place is beyond me. and yes i understand the weather correction. but this dyno says 18 hp and this one says 10 is the equivalent of my Starrett micrometer says 1 inch and his says a 2 on a 1.5 part. your tool reads wrong. get it fixed.
horsepower is a mathematical calculation. A Dyno is and instrument used to measure torque at RPM. why they are all over the place is beyond me. and yes i understand the weather correction. but this dyno says 18 hp and this one says 10 is the equivalent of my Starrett micrometer says 1 inch and his says a 2 on a 1.5 part. your tool reads wrong. get it fixed.
Why are dynos different? You basically said the answer, a dyno measures torque at rpm. No one is calibrating their dynos based on torque.
Most believe a 212 Predator or a 196 clone makes 6.5hp; this is inaccurate. If you look at the Predator 212 box, it only lists torque, not horsepower. The hp is listed on the website because it was originally duplicated from the Honda GX200(now 5.5hp), but we can disprove it using math. The max torque of the Predator 212 is 8.1ft-lbs at 2500rpm. That is maximum torque, but for argument, let's say it's making 8.1ft-lbs at 3600, which is the most common standard for small engines, or 3800rpms, as is listed as the maximum rpm on the box. 8.1 x 3600 / 5252 = 5.55hp or 8.1 x 3800 / 5252 = 5.86hp. For the Predator 212 to make 6.5hp, it would need to make 9.48ft-lb at 3600 or 8.98ft-lbs at 3800rpm which is higher than its listed max torque, a major contradiction.
Interestingly, Honda, which lists 5.5hp at 3600rpms, also makes 9.1ft-lb at 2500rpms. How many engine builders can say that the Predator 212 makes 8.1ft-lbs at 2500rpms while 6.5hp at 3600rpms? Another reason the torque number would be more accurate than the advertised horsepower number goes back to a class-action lawsuit with Briggs in the early 2000s, where the horsepower numbers were taken out of context or manipulated to sell engines. Torque is now the legal representation of the engine's output. Those lawsuits are why the Honda is listed at 5.5hp, not 6.5hp. Harbor Freight, to my knowledge, doesn't give an SAE number, so you don't know what correction factors or test procedures it is using, but Honda does. You can get really messy with correction factors(observed vs. corrected), net vs. gross power, test conditions, etc, which are rarely if ever, provided along with the dyno sheet.
If the question is serious, which of the two engines is faster, the engines have to be comparable, and the only way you can do that is by having them on the same dyno. Regardless of the numbers, we are overlaying them to look at power under the curve and how that power is applied on the kart(gear ratio/tire size).
Most believe a 212 Predator or a 196 clone makes 6.5hp; this is inaccurate. If you look at the Predator 212 box, it only lists torque, not horsepower. The hp is listed on the website because it was originally duplicated from the Honda GX200(now 5.5hp), but we can disprove it using math. The max torque of the Predator 212 is 8.1ft-lbs at 2500rpm. That is maximum torque, but for argument, let's say it's making 8.1ft-lbs at 3600, which is the most common standard for small engines, or 3800rpms, as is listed as the maximum rpm on the box. 8.1 x 3600 / 5252 = 5.55hp or 8.1 x 3800 / 5252 = 5.86hp. For the Predator 212 to make 6.5hp, it would need to make 9.48ft-lb at 3600 or 8.98ft-lbs at 3800rpm which is higher than its listed max torque, a major contradiction.
Interestingly, Honda, which lists 5.5hp at 3600rpms, also makes 9.1ft-lb at 2500rpms. How many engine builders can say that the Predator 212 makes 8.1ft-lbs at 2500rpms while 6.5hp at 3600rpms? Another reason the torque number would be more accurate than the advertised horsepower number goes back to a class-action lawsuit with Briggs in the early 2000s, where the horsepower numbers were taken out of context or manipulated to sell engines. Torque is now the legal representation of the engine's output. Those lawsuits are why the Honda is listed at 5.5hp, not 6.5hp. Harbor Freight, to my knowledge, doesn't give an SAE number, so you don't know what correction factors or test procedures it is using, but Honda does. You can get really messy with correction factors(observed vs. corrected), net vs. gross power, test conditions, etc, which are rarely if ever, provided along with the dyno sheet.
If the question is serious, which of the two engines is faster, the engines have to be comparable, and the only way you can do that is by having them on the same dyno. Regardless of the numbers, we are overlaying them to look at power under the curve and how that power is applied on the kart(gear ratio/tire size).
Compu-kart
Member
We have raced clones and LO206 for several years and more recently two cycle engines on asphalt short and long tracks. With optimal gearing the 2 cycle consistently gave us lower lap times. Bonus: They are more fun to drive too.
All your comets r interesting. My budget modified w f has a 4 lb flywheel and a 2.3 lb clutch. A ka 100 or vlr 100 has very little reciprocating weight. When we come off the slow corners the 100’s squirt away. Plus my rpm curve is still stockish 4000 to 6700 rpm. I have similar end straight away speed. 62, 64 mph. I know it’s probable not getting enough air in and out. I’m sure there’s a lot of people that know the recipe for power better than I Do. It’s a great hobby!
I have Dyno results from the same shop in town for a lo206, blue printed w f and a ka 100. I run 3.93 gr. 8100 rpm end of straight speed, ka100 use 8.00 gr. 16,000 rpm. I feel proper cam and carb will complement my 11.7 compression, ported head. To raise my power band 4500 to 7700. I think the gr will b 4.25. 8800 rpm to run 64, 65 mph.
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mike97760
Site Supporter
What I remember of racing the KT's vs. the 4 strokes is that they are driven differently on small tracks. The 2 strokes back off the throttle much earlier going into the corners so that they can get back on the throttle earlier, too, so that they are at a decent rpm on corner exit. So, while the lap times are similar, they race differently. Was a fun race and traffic played a big role in who did what.
rainman
Member
I have raced both 4 and 2 strokes on sprint tracks at top level, and at a Sprint Asphalt track a small 4 stroke has no chance to run close to a 2 stroke. The Yamaha classes can be considered as the lowest power 2 cycle classes, and I was seconds from them even when practicing with open small block 24 cycles. On a dirt oval it is a very different story though.
Evan had to work his way through the traffic