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Old 05-31-2010, 06:56 AM   #1
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Default Your thoughts on reduced throttle EPA settings

Just something i have been doing since about 2002 i run a smallish restrictor and set the epa to 1/2 open and tune for it. I was thinking this is a very common thing to do since it works out well yet at the track when i bring this up people look at me like i have a martian tapdancing on my head.

your thoughts? i know it works good for me but thought it would make a good discussion.
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Old 05-31-2010, 08:20 AM   #2
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OH!!! NOW YOU'VE DONE IT LOOPER!!!
Now everyone knows how to gain better
control of there car, resulting in better
lap times. Not to mention alot better run
times too.
I took it a step further by setting up the
dual rate button on my radio to pull the
carb to 50% and 100% of slide travel.
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Old 05-31-2010, 08:35 AM   #3
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Hi Looper

I started racing 2 years ago and one thing I did which I think was very smart was use small inserts that gave me more than enough power to get me around the track.

Running small inserts like 6 or 6.5mm in buggy and 6.5 or 7mm in the truggy when I first started racing I think was the best thing a newbie could do as it made you drive the car and choose your lines. Soo many times I see new guy's running 9mm inserts flat chat and they're not improving with their driving because they're constantly on their lid or overshooting corners.

I'm not trying to sound cocky but I have improved greatly in my driving and now to attempt to keep up witht he quicker guy's, I'm having to go bigger in inserts for the more power to clear technical jump sections that you can't do with smaller inserts and to get out of corners faster aswell.

I was always known as the guy that could do 10 min qualifiers without a pitstop and that was due to the smaller inserts. I did gain some time on others without requiring a fuel stop but now that i've stepped up in my driving, I can make up the extra fuel stop on the track now.
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Old 05-31-2010, 09:43 AM   #4
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okay just to clarify, i use a 7.5mm insert and set the epa so it opens half way but it is tuned for max performance, if the carb opens more than 1/2 way it lean bogs. main motivation for this is fuel economy and lightning fast response to throttle input
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Old 05-31-2010, 09:53 AM   #5
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Looper,

In order to do this, I would limit the servo and then lean the top end correct? This does seem like something I would be interested in trying, my motor right now is a gas hog.

Thanks
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Old 05-31-2010, 09:56 AM   #6
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Question- Why not get a super small venturi (like a 5mm) and have your carb open the full width of the venturi for smooth air flow?
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Old 05-31-2010, 10:08 AM   #7
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i had a thought here ...assuming you have a nicer radio that has exponential adjusment ...what i do is this ...if the track is loose ...sometimes i will throw some negative exponential on the throttle ....maybe like 10-20 % ..what this does is for the first 10-20% of the throttle pull whichever % you select ..the radio will slow the servo down up to that point .. this can act similar to a slipper clutch in theory ...especially if you are hard ont he trigger ....then after the first 10-20% of the full pull the radio moves the servo at normal speed ....i run a nova 4 c with a 6.5 restrictor ...i run the epa to about 1mm before the carb barrel gets to full lenght of the opening ...just my opinion ...but thought i would toss it out there as it seemed relevant
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Old 05-31-2010, 03:53 PM   #8
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Quote:
Originally Posted by zixxer View Post
i had a thought here ...assuming you have a nicer radio that has exponential adjusment ...what i do is this ...if the track is loose ...sometimes i will throw some negative exponential on the throttle ....maybe like 10-20 % ..what this does is for the first 10-20% of the throttle pull whichever % you select ..the radio will slow the servo down up to that point .. this can act similar to a slipper clutch in theory ...especially if you are hard ont he trigger ....then after the first 10-20% of the full pull the radio moves the servo at normal speed ....i run a nova 4 c with a 6.5 restrictor ...i run the epa to about 1mm before the carb barrel gets to full lenght of the opening ...just my opinion ...but thought i would toss it out there as it seemed relevant
That is interesting and something I have thought about doing but when I played with the exponential it didn't really seem to make a difference. I didn't try it on the track, just visually looked at the servo as I made adjustments. I figured maybe I was doing something wrong, but now it occurrs to me that maybe it did work, but you just can visually see it. Can you visually see a difference in the servo speed at 20%? I
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Old 05-31-2010, 04:40 PM   #9
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That is interesting and something I have thought about doing but when I played with the exponential it didn't really seem to make a difference. I didn't try it on the track, just visually looked at the servo as I made adjustments. I figured maybe I was doing something wrong, but now it occurrs to me that maybe it did work, but you just can visually see it. Can you visually see a difference in the servo speed at 20%? I

i can see it the further you go in one direction the more evedent it is ...just test on your local track ...set the car down in some loose stuff ..try it normal then just start playing with it ...you can always set it back to neutral
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Old 05-31-2010, 04:45 PM   #10
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Exponential will make no difference at all if you drive like the trigger is a light switch. It does NOT affect servo speed, only how much throw you get of the servo at different points of the trigger but full throttle is still full throttle. I HAVE used throttle speed from time to time. Actually slowing down the servo can help a bit in slick conditions.

As for half throttle epa's, I think it's a valid option if you can't find a small enough restrictor to do what you want. Another option is to use less nitro. 16 or 20% with a 7mm insert is probably pretty close to 30% with 6mm insert and cheaper to boot.
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Old 05-31-2010, 05:20 PM   #11
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Exponential will make no difference at all if you drive like the trigger is a light switch. It does NOT affect servo speed, only how much throw you get of the servo at different points of the trigger but full throttle is still full throttle. I HAVE used throttle speed from time to time. Actually slowing down the servo can help a bit in slick conditions.

As for half throttle epa's, I think it's a valid option if you can't find a small enough restrictor to do what you want. Another option is to use less nitro. 16 or 20% with a 7mm insert is probably pretty close to 30% with 6mm insert and cheaper to boot.
the futaba manual lists exponetial as calming down the action of the input given ...ie...it may have more to do with the actual pulling of the trigger ..as to where the speed is the actual speed of the servo ...either way both options are listed to do about the same thing ....actually exponential would be better for someone who grabs trigger to fast ...im thinking ...either way there are the options in the radio if you have a decent radio ...i know when im on a loose track i adjust exponential ...not the speed
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Old 05-31-2010, 06:19 PM   #12
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The exponential curve is completely different than servo speed. Your adjusting the throttle curve. If you understand the math. Think about what you are doing and see the results in your imagination.
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Old 05-31-2010, 09:06 PM   #13
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Just use an even smaller venturi. Set your carb to open the venturi completely and tune.


Your killing your mid range power band be tuning that way.

If you only need half throttle to clear everything at your track then use a smaller venturi. Having the slide block the opening of a nice, smooth, round venturi is not effiecient or good for your power band at all.

Drop to a 5.5 or 6mm venturi and if thats too strong still change to a fuel economy quiet pipe or a weaker 3-5 port engine.



I screwed up tuning my 3 port Novarossi mill. It had all kinds of balls at low speed with very little throttle opening. But when I opened it up it had all kinds of weird spikes and drps in its powerband. I accidentally tuned mine like yours.
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Old 06-01-2010, 07:02 PM   #14
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Playing with the throttle EPA will also affect the ratio between the radio trigger and servo displacement. In other words...when you pull full throttle on the radio, the servo can reach full throttle quicker since it has to rotate less degrees. For some people, this could be tricky on the track!

I would suggest selecting the restrictor size first...then "fine tune" with the throttle end point.
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Old 06-01-2010, 07:50 PM   #15
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Some motors do not like a small restrictor. I know a bunch of us could not get a 5.5mm to work on a particular motor. I think in that case using epa with a slightly larger restrictor can be really useful.
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