Engine rpm down temperature up

B

bullerman

Member
I ran this weekend myself. My hot laps ok. High rpm was 5762 and fast lap 12.51.
Heat race high rpm was 5847 and 12.66 fast lap.
Feature race high rpm was 5727 and fast lap was 12.92. The motor just didn't feels like it had the power. It popped a couple of times when i let off the gas going into the turn. After the race was over it seemed unusually hot to me.
I haven't checked the valves lately. I set them at 0 lash cold. Would if loose power if the lash is too much. Going to check it. Will check timing also.
 
I don't know. I ran white vegas for hot laps and heat and maxxis for feature. My tach just showed that i didn't have as much grip from the hot laps to heat to feature. Engine rpm was ok i think.
 
bullerman said:
I ran this weekend myself. My hot laps ok. High rpm was 5762 and fast lap 12.51.
Heat race high rpm was 5847 and 12.66 fast lap.
Feature race high rpm was 5727 and fast lap was 12.92. The motor just didn't feels like it had the power. It popped a couple of times when i let off the gas going into the turn. After the race was over it seemed unusually hot to me.
I haven't checked the valves lately. I set them at 0 lash cold. Would if loose power if the lash is too much. Going to check it. Will check timing also.
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the track gained grip and inturn that pulled power out the motor, i know at TC, when the track gets black the maxxis bites up pretty good, for the feature i dont prep very much and nothing harsh
 
When an engine pops letting off the gas it's telling you it's lean I would carefully clean the carburetor especially all the little openings.
 
If your highest rpm is at the same place on the track each time you reported it to us, then it's impossible to go slower with a higher rpm without your clutch slipping.

If your highest rpm is earlier then again your clutch is slipping.

If your highest rpm is later then your lugging it down and on the go pedal when track grip is actually slowing you down.
... the only thing you can fix is the driver when there on the go pedal when track grip is slowing down what your racing.
... or free it up and take a better faster line thru the corner
It puts lag time between when the engine recovers because of being forced to slow down when on the go pedal, which would not be there if the drivers foot wasn't so heavy on the go pedal.

.... or fix your entry point and driving line to the same or different start of the exit.

??? maybe ???
 
Did check the valves. I had set them at 0 lash. Both had backed off to six or so. Don't know if that would have mattered or made the engine run hot. I have reset them.
I talked to another racer about slowing down from hit laps to feature. They said they slowed down too.
Most everyone was having trouble with 1 and 2. They had brought in some new dirt. A lot of it was probably me. I was trying a different line going into that turn. Thanks for the help.
 
Alot of times the track will "bite" up for the feature and take power out the motor due to the bite and that can make your engine run a little hotter, most tracks around where we run, you can run a less prepped set of tires for the feature.
 
We run at a track that continually gets faster as the show goes on. It's not unusual to be on a three or four smaller rear gear by main event time to keep the engine at the same rpms. That seems to me to be an awfully lot of rpms for a stock Predator. It has been posted here many times that they pull the best in the 4900 rpm range. Whats different about yours?
 
Komet99 said:
Thats a stupid rule. How do I determine correct tuning based on the weather?
Click to expand...
In most stock classes you are not allowed to change jetting. Some give a small step up just to cover inconsistency in the motor as shipped. It is not the tuning method, at least in my area, that is not allowed, but the changing of jets. Also wondering if the OP meant 4,700-4,800 range instead of the 5,700-5,800 he referenced. Otherwise I am guessing his rule package is way different than it is here.
 
Its not just now a stupid rule. I can't tune my carburetor? Cmon who is making this stuff up? Can you name any other class in any other form of motorsports that has a fuel curve tuning rule?

What if I take my stuff to Kansas, where the air is different than Texas? I can't go up one or 2 jet sizes to get max performance out my engine?

I dont have an agenda, I have a motor that just needs to be tuned...
 
The rule was put in place to head off a different use for that hole being allowed in the exhaust.
4 strokes are different than 2 strokes in this respect.

Search EGT threads. The reason is less than obvious.

Hint
The uses mimics 2 strokes using expansion chamber, at least in principle.

Rules makers wished to shut down this loophole for getting more air into restricted engines.

The rule doesn't keep you from tuning your carb, just restricts you using that method during competition.
 
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