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Fuel mileage??

Old 06-23-2022, 03:23 AM
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Default Fuel mileage??

Hi guys, im running a 220mm converted 733 with 2009 353 engine, 2660 pipe and shortest conical manifold. Having a blast, but i could use some more speed, the very fastest touring car guys are about 2 seconds a lap faster than me, 16 versus my 18seconds a lap. One thing ive noticed though is they struggle to make 5 mins on their fuel, running out ocassionally on the cool down lap etc. Hoewever i can easily make minutes maybe even slightly more (i refuel at 6 mins). Anyone any ideas why theyre using so much more fuel? I have removed the venturi restricter and put on the lowest pinions available too.
thanks for any help
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Old 06-23-2022, 04:12 AM
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Is there any chance you're running slightly lean in an attempt to go as fast as they are, and actually making less power in the process? Aside from that, there are several parameters that could be adjusted inside your engine to improve its power output, but it's not something that can be explained in a how-to list of steps. 2-stroke engine tuning and modification is very much a hands-on, trial-and-error activity.

Also, depending on the track layout, running the smallest pinion gears may not actually make you faster. It depends on whether you're falling behind when accelerating out of corners, or when sprinting down the straightaways.
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Old 06-23-2022, 04:36 AM
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running a small pinion will never make a rc faster. running a larger one will. that's basic knowledge.
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Old 06-23-2022, 04:41 AM
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Easy....

Back in those days a 5 minite qualfy needed to be reached if you do not want a fuel stop. In the last years thanks to the ENS many organisations switched to a 4 minute qualify with which the engines could be configured (timed) faster.
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Old 06-23-2022, 06:20 AM
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I know using smaller pinions gives less top speed lol, i was doing it cause i thought perhaps i was overgeared before. Ya could be onto something with the timing though. Perhaps i could shim up the liner very very slightly to increase timing and power since i easily make the distance for fuel.
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Old 06-23-2022, 11:24 AM
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Running smaller pinions will give you less mileage actually. With smaller pinions the engine is at higher RPMs more of the time, using more fuel.
The 2s deficit is probably because they're driving faster than you, and that would makes sense of their fuel mileage. Concentrate on your driving, get a setup that you can drive and just practice. Eventually you will get closer.
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Old 06-23-2022, 03:28 PM
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Fuel mileage is a very complicted issue that will involve all parameters: wind, humidity, body drag coefficient, gas quality/oil content, engine condition/tune, drivetrain weight/efficiency, gear quality, tire size/wear rate/drag, driving positions while racing, trigger finger habits, clutch setup, etc.....The list goes on and on...
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Old 07-08-2022, 03:04 PM
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Originally Posted by coupehdi
Hi guys, im running a 220mm converted 733 with 2009 353 engine, 2660 pipe and shortest conical manifold. Having a blast, but i could use some more speed, the very fastest touring car guys are about 2 seconds a lap faster than me, 16 versus my 18seconds a lap. One thing ive noticed though is they struggle to make 5 mins on their fuel, running out ocassionally on the cool down lap etc. Hoewever i can easily make minutes maybe even slightly more (i refuel at 6 mins). Anyone any ideas why theyre using so much more fuel? I have removed the venturi restricter and put on the lowest pinions available too.
thanks for any help
Carb tuning will get more runtime, but it is not that noticeable. A larger pinion will go faster and can save fuel too. A larger fuel tank will add the most time .
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Old 07-08-2022, 04:09 PM
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The answer is easy, you're 2 seconds a lap slower than them. That means they are doing several more laps in 5 minutes than you are. In terms of actual mileage instead of time, you're probably getting about the same mileage.
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Old 07-08-2022, 04:31 PM
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A little math to back up my post.

Let's say the fastest guy runs exactly 15.0 second lap times. He will finish with 20 laps in 5:00.00 and run out right at the line.

You run exactly 17.0 second lap times. You do 18 laps 5:06:00. To go the same distance as him, you need to run 2 more laps. That's 34 more seconds plus the 6 seconds longer you have already run so if you get the exact same MILEAGE as he does, you should be able to go to 5:40.00. 40 seconds more run time with the same mileage. Of course because you're going slower, you should also get better actual mileage. Slower means lower RPMs, less time at full throttle, slightly less air resistance, etc. so that buys you another 20 seconds allowing you to go to 6 minutes. But 6 minutes only gives you 1 more lap in distance traveled over him, plus just a few seconds more so you see your mileage is not much different than his.

To see actual mileage:
He's burning 3.75cc's per lap.
You're burning 3.57cc's per lap.

I don't know about you but I would gladly trade .18cc's per lap of mileage for 2 seconds a lap in laptime. Pit stops don't take that long
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Old 07-08-2022, 04:33 PM
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Originally Posted by the rc guy
running a small pinion will never make a rc faster. running a larger one will. that's basic knowledge.
Say you are exclusively an electric racer without actually saying it
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Old 07-09-2022, 12:24 AM
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Originally Posted by the rc guy
running a small pinion will never make a rc faster. running a larger one will. that's basic knowledge.
When the motor has a straigh power curve... yes!
But no motor has a straight power curve so there is an effect that is called overgearing and under gearing. The max speed you will find to have the best compromise between the motor and gearing.
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Old 07-09-2022, 03:13 PM
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walk the track with your measuring wheel. get distance now get total now multiply the two numbers get a total distance now put down minutes divide by minutes get # now multiply by 60 get another number now figure out cc and divide once you figured out # of cc per hour.
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Old 07-09-2022, 11:29 PM
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For 1/10 onroad nitro cars, I know most top racers gear their cars around 7.1fdr for first gear and 4.8fdr for second gear with 62mm rear tires and 60mm front tires. If you have to gear higher than that, then the track is huge like lostallo or something, but if you have to gear lower than that, then the track is very small like Wagner Rc Park or something....Now I am assuming you are running a Murnan Modified or Ab mods motor, not a stock unmodified motor....Hopefully you can compare your current gearing with the gearing above to see what you can improve from there...
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Old 07-11-2022, 01:36 PM
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Thanks for all the help guys. Few points to add, the purpose of my question was more to figure out what if anything im doing wrong compared eith the fast guys. You are of course right that yes, if i ran my car until it ran out of fuel i would have done the same amount of laps as the fast guy just took me longer.

Some things that i have tried for next time out (2 weeks). Car was weighing in at 2002grams, so ive lightened it as much as i can easily, its now around 1850g. So hopefully thatll help even a tiny bit.

Anyone have experience with 220mms? Are they usually faster in laptimes than a fast 200mm? As Im the only 220mm i have no one else to compare against.

Also what do most people do for tyres? Ive always run 4 new tyres from morning practice through the heats and then put on a new set for the 20minute final, im starting to wonder is this what im doing wrong? All my fastest times are at the end of the final, and during the heats im much slower like at least a good second a lap. I was running 62mm front 64mm rears, i get 4mm wear on the outer rear tyre, so it ends up around 60mm and inside rear about 62mm, but i noticed alot of guys are almost down the rim at the end, from what others
have said in this post some people seem to start with tyres same size i finish on lol, is it the case thst i want to run the tyres JUST big enough to last the final? Or maybe just use 1 set all day and rotate them?
Sorry for the long post just trying to figure this out.
thanks to all who have offered their advice and experience much apperciated
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