Box Stock

5500 rpm stock motor

I'm no motor guy but there's gotta be more to this story than being told, we have the 5500 RPM rule here at 3 local tracks some drawing counts in the 20's and this has not been an issues.
 
20 is a small count but you gotta remember theses are sealed engines it does not effect us we win most everywhere we go but it’s sad to see it happen to new racers and kids
 
I dyno in a non climate control shop. I have seen a difference in hp between night and day, even with correction factors. What I suspect is ,if you are on a .031 jet . A .0305 might be what you really need . As the air gets better the motor leans and makes more hp.
 
triton03 said:
Then why when we dyno put in the correction factors for that dyno pull if it made no difference then why put it in or use auto correction heck they are none even turning them close to 5500 on the track I have even made several (over 20 ) pulls with the governor set at 56 to 5800 and most at 4800 drop drastically in hp and yes humidity and temperatures has a big difference in hp and torque if not get on your dyno and do some testing for the public like some on here do
Click to expand...
Don't forget barometric pressure, it's just as important as temperature. Better yet, get an air density gauge, it measures barometric pressure against temperature.
 
RCJ said:
I dyno in a non climate control shop. I have seen a difference in hp between night and day, even with correction factors. What I suspect is ,if you are on a .031 jet . A .0305 might be what you really need . As the air gets better the motor leans and makes more hp.
Click to expand...
As the air gets better (higher air density) of course the engine makes more HP. If the motor "leans", (more air means you need more fuel ) that means you didn't have it jetted right in the first place. A 1% increase in air density, according to Longacre, calls for a 1% increase in jet area. With a .038" jet, a 1% increase in jet area is about .0002" in diameter. Understand the difference between "diameter" and "area".
 
So, back to the original question. If I want to set up a stock predator to run, how do you get it to turn 5k without removing the governor?. There is a series here in NC that runs Hoosier tires, no prep allowed, that I want to run.
 
mmeck said:
So, back to the original question. If I want to set up a stock predator to run, how do you get it to turn 5k without removing the governor?. There is a series here in NC that runs Hoosier tires, no prep allowed, that I want to run.
Click to expand...
Stiffer spring on the governor, or, as suggested, a zip tie thru a portion of the existing spring, making it a stiffer acting spring.
If your rule is 5000 rpm on the stand, the engine will start falling off (ie governor closing throttle blade) somewhere below this number.
To get 5000 rpm on the track, you may need to be somewhere above 5500 rpm on the stand. Camshaft / valve springs may be falling off as well.
Spring stiffness and position on the lever will alter this slightly.
 
Last edited:
95 shaw said:
Stiffer spring on the governor, or, as suggested, a zip tie thru a portion of the existing spring, making it a stiffer acting spring.
If your rule is 5000 rpm on the stand, the engine will start falling off (ie governor closing throttle blade) somewhere below this number.
To get 5000 rpm on the track, you may need to be somewhere above 5500 rpm on the stand. Camshaft / valve springs may be falling off as well.
Spring stiffness and position on the lever will alter this slightly.
Click to expand...
Track rule is stock motor, may change jetting, 5500rpm Max checked on stand, must surge.
 
RCJ said:
I dyno in a non climate control shop. I have seen a difference in hp between night and day, even with correction factors. What I suspect is ,if you are on a .031 jet . A .0305 might be what you really need . As the air gets better the motor leans and makes more hp.
Click to expand...
Look at these two dyno charts. Notice the HP numbers are identical. Notice the torque numbers are all different. Notice that the correction factor number is different. Notice the barometric pressure is the same but the temperature is different. The correction factor is calculated using the barometric pressure and temperature as data points. If your dyno is not doing something similar to this, then your have a problem with the software.
What acquisition systems are you using? Does your software list barometric pressure and temperature at the time of the test?
With these two runs, the barometric pressure is the same, but the temperatures are 20° apart, the chart on the right being at 80°.

correcrion factore 1.jpgcorrecrion factore 2.jpg
 
Last edited:
DynoDon said:
If you can get it to turn 5500 on the stand you will win races at 4850 to 5050. Do not plan on seeing anything above that on the track
Click to expand...
I have heard that some motors don't surge at peak RPM, what causes this, and how do you correct it?
 
The surge is most likely from a not so strong spring. Some do and some dont. I am not positive of my answer but I have encountered both ( surge and non surge ) in the engines i have teched. It does not matter if it surges on the stand when checking maximum RPMs. It will not surge on the race track if the engine is set at 5500 because the engine on the track is only going to turn between 4850 and 5050
 
DynoDon said:
The surge is most likely from a not so strong spring. Some do and some dont. I am not positive of my answer but I have encountered both ( surge and non surge ) in the engines i have teched. It does not matter if it surges on the stand when checking maximum RPMs. It will not surge on the race track if the engine is set at 5500 because the engine on the track is only going to turn between 4850 and 5050
Click to expand...
My only concern is that the rules state that the engine must surge on stand when Max RPM is checked
 
DynoDon said:
Whoever made up that rule needs to do some research. There will be some racers dq’ed unnecessarily.
Click to expand...
That is what I'm worried about. I have four different predator, and clone engines in the garage, only one surges, and it's no where near 5500rpm. It's bone stock.
 
I orig. lobbied for a 5000 limit that's an RPM that's obtainable by 99% of the "out of the box engines" but somebody made it 5500 right a way so that's where we are,,, some can get it and some can't we have won several races at 4800- 5000 max RPMs .
 
You must log in or register to reply here.
Back
Top