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Old 10-29-2007, 09:10 AM   #106
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Questions?? tune

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Originally Posted by xspower View Post
I think that the bottom end of the engine was to lean. Was the track dry or wet. And also was the engine laying over on top or loosing bottom end?
It's hard to tell, because in racing conditions there's too much going on!!! heheheh

It was ok in the qualifiers (only 5 minutes with cooler weather) but then just before the sub-finals, the sun came out and it got a bit warmer, so I just hurriedly ritchened both needles a bit and got on the track.

In the warm-up laps, the motor ran and sounded ok, so I decided to not fiddle arround with it. I'd say after 15 minutes (in the last couple laps) it had a bit of power loss in the low end.

The problem is last week end I could not tune the motor with a Medium plug and it ran fine with hot, so maybe this weekend, as the morning went by and the weather got a bit warmer, instead of just ritchening both needles a bit I should have changed from hot to medium plug and re-tuned if I'd had time to....???
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Old 10-29-2007, 10:01 AM   #107
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It sounds to me for sure the bottom was lean. This will happen as the weather changes as well. I do not know where you are located or how far above sea level but you have to remeber that when the engine is running and there is a real big change in temp for atmosphere this results in a more dense air equaling more oxygen that will make it run lean. Keep that in mind. The hotter the plug the easier it seems to tune as the cooler the plug the more adjustability you have but at the same time the more sensitive to changes it will become. When rain or humidity come into effect it also throws off the figures as well.
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Old 10-29-2007, 11:16 AM   #108
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Originally Posted by xspower View Post
It sounds to me for sure the bottom was lean. This will happen as the weather changes as well. I do not know where you are located or how far above sea level but you have to remeber that when the engine is running and there is a real big change in temp for atmosphere this results in a more dense air equaling more oxygen that will make it run lean. Keep that in mind. The hotter the plug the easier it seems to tune as the cooler the plug the more adjustability you have but at the same time the more sensitive to changes it will become. When rain or humidity come into effect it also throws off the figures as well.
Yep!! That's what I have noticed too. The hotter the plug, the easier to tune. I've heard many people recomend to always run "the hottest plug you can get away with" How do you know when the plug is too hot??

Also, this track I raced at is about 300ft above sea level, where mine is at 50ft or so...how does that affect the motor tune?

And what happens to the motor if with the same air temperature, it rains abit, so the air becomes more humid?
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Last edited by DR ZAIRUS; 10-29-2007 at 11:28 AM.
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Old 10-29-2007, 04:03 PM   #109
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The higher the elevation will be the lower you want the cyl. head. you need to lower the head because the engine does not have a dense enough air charge to compress. The lower the more dense the air is and the higher the head clearance will need to be. As far as the plug goes I have seen everything used from o.s plugs to nova. The hottest I would say would be a 5 and that would really have to be for freezing cold weather. I would not really see anything lower then a 6 in the engine. It is a .21 and also it is running 30%. You can also tell you have a hot plug by the way the engine looks on the top of the head and the piston. They should be a silky black with some carbon build up no detonation at all. You can start to detonate the engine with to hot of a plug that means that the plug will still be good but the combustion chamber as well as the top of the head are pitted. If the engine is doing that and the plug is still good you can be sure that the plug is hotter then it needs to be. With the relationship to fuel and humidity, Remember the basic fact that the rain or for that matter a humid air carries water. The engine likes and also does not like that. It will affect the needle settings greatly. There is only so much space inside the chamber for the engine to compress the air/fuel. So with that in mind the carb venturi opens the same amount all the time. And the restrictor you have just slows the air speed does not really limit the volume. This has been misunderstood for along time. The restrictor slows air. But you have to remember that the venturi diam. is still the same and you are only talking at the most a difference of what 2mm? From a 7 to a 9mm. Now that is understood. The engine draws in the same amount of volume of air filled with either less or more water from the humidity. There is still only so much space, now taken up by water particals. No room for more less air intake so I will let you answer less or more fuel is now needed? Let me know!!!
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Old 10-29-2007, 07:38 PM   #110
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its funny, but STS and Go-tech rods will fit !!!!
I think you already know but this is completely false. The rod length is different and will totally change the sleeve timings and compression.
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Old 10-29-2007, 07:45 PM   #111
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I think you already know but this is completely false. The rod length is different and will totally change the sleeve timings and compression.

Yuppers... LOL !!!!!

Sadly I have learnt you cannot use STS rods in a Picco P7R..... STS rod is 1.16" and the P7R rod is 1.18" ...seems to affect power a little......

funny part is my buddy won two A-Mains with cobbled together P7, STS rod and all.....
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Old 10-30-2007, 03:31 AM   #112
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This is true it shortened the stroke without the difference in a crank or anything so the sleeve timing was actually raised. I would guess it lost some bottom end but gained top. I am amazed only that the piston did not hit the skirt on the crank!!!! It may have worked ok.
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Old 10-30-2007, 02:43 PM   #113
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A v-spec rod is the same length, you will have to drill a hole for oil.

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Old 10-30-2007, 04:05 PM   #114
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Originally Posted by xspower View Post
The higher the elevation will be the lower you want the cyl. head. you need to lower the head because the engine does not have a dense enough air charge to compress. The lower the more dense the air is and the higher the head clearance will need to be. As far as the plug goes ....it is running 30%... With the relationship to fuel and humidity, Remember the basic fact that the rain or for that matter a humid air carries water.....
Yep: I agree about altitude needing less head clearance, but I didn't think this difference between 50 and 300ft would make such a big difference to take out any shims, just some needle adjusting...??

About glow plugs, I run 25% fuel (not 30%), and I though detonation is a sighn of too low combustion chamber, not of too hot a plug...hmmm. I'll keep it in mind.

About humidity, I'm not really sure (that's why I asked , heheheh) if it makes motors leaner or ritcher...(?)
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Old 10-30-2007, 06:00 PM   #115
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You are correct the detonation is a sign, the thing with this is that the detonation can be cause by a number of things. Example would be way to hot of a glow plug. Also could be lean, along with wrong head clearance. The reason for the plug is just think that the plug is always hot. Now that the plug is hot the engine is running and the burn and the reaction between the fuel and the glow plug element cause it to stay hot. So if the plug is too hot it will make the mixture flash way before the piston reaches the top or near top is what should be said. When a cooler plug is in the engine the engine will be able to reach a higher part of the stroke before the fuel lights off. That is the true definition of "Detonation" is. The premature ignition of the air/fuel mixture prior to top dead center. Same definition as a real automobile engine. Also when there is alot of moisture in the air it will cause your engine to want to run rich. You need to take away some fuel as there is not as much oxygen in the mix when there is water in the air. The 50 to 300 ft. Should really not be a issue of a head shim. maybe 50 to 1500 feet yes. But then again all engines act different and some want more clearance. You have to find the sweet spot. I have some engines that my drivers run they are set at like .024 thousandths, now this is on road so you tend to run a bit taller due to the high rpm. Now some others want to run at .028 to 031. Same engine same case. You figure. Just made by hand makes the difference. Hope it helps!!!!!!
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Old 10-31-2007, 03:54 PM   #116
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Man!! This engine tunning thing is a whole world of it's own!!

Any way, I guess you learn little by little, by experience, but still, I'll try to keep these tips in mind:

-More humid air, means ritcher mixture, so I'll probably need to lean it a bit.

-More altitud, means thinner air, so the mixture will be ritcher: you must lean it a bit.

-More altitud, thinner air, less head clearance.

-Detonation= plug too hot or bottom too lean or too low chamber...
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Last edited by DR ZAIRUS; 11-02-2007 at 12:53 PM.
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Old 10-31-2007, 06:15 PM   #117
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Quote:
Originally Posted by DR ZAIRUS View Post
Man!! This engine tunning thing is a whole world of it's own!!

Any way, I guess you learn little by little, by experience, but still, I'll try to keep these tips in mind:

-More humid air, means ritcher mixture, so I'll probably need to lean it a bit.

-More altitud, means thinner air, so the mixture will tend to lean out. Richen mixture.

-More altitud, thinner air, less head clearance.

-Detonation= plug too hot or bottom too lean or too low chamber...
I believe at higher altitude, you will run richer, so it needs to be leaned. There is less air at higher altitude, so the the needle settings at sea level will be too rich at say 1500 ft. But you only take this into account though if your racing all over the place. At your local track, temp & humidity are the main factors. Take into account fuel if you switch brands or nitro content also.
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Old 10-31-2007, 08:04 PM   #118
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I finally got to race my jammin evo 2 in a rc8 on a small indoor track. The motor had 3/4 gallon odonell 20% run through it as per jammins instructions. Its got about a half of gallon of 30% blue thunder. I dont want to overheat this motor as Im trying to become comfortable with its tendencies. I am only running about 1/2 epa on the throttle, but also with a 7mm venturi. The difference between 200 and 230 degrees was about 1-2 hours of bottom needle or. The motor does not run clean until 220. Will this motor start to run cooler as it breaks in. Is it normal to run this motor at 230-240? Do you tune the carb differnt if you are running the throttle closed as much as I am to make it run most consistant.

Last edited by Scootersisters; 11-01-2007 at 02:04 PM.
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Old 11-02-2007, 12:36 PM   #119
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Originally Posted by Scootersisters View Post
I finally got to race my jammin evo 2 in a rc8 on a small indoor track. The motor had 3/4 gallon odonell 20% run through it as per jammins instructions. Its got about a half of gallon of 30% blue thunder. I dont want to overheat this motor as Im trying to become comfortable with its tendencies. I am only running about 1/2 epa on the throttle, but also with a 7mm venturi. The difference between 200 and 230 degrees was about 1-2 hours of bottom needle or. The motor does not run clean until 220. Will this motor start to run cooler as it breaks in. Is it normal to run this motor at 230-240? Do you tune the carb differnt if you are running the throttle closed as much as I am to make it run most consistant.
It will loosen up little by little. I run arround 230-240. I find the low needle to be pretty sensitive....
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Old 11-02-2007, 12:44 PM   #120
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I believe at higher altitude, you will run richer, so it needs to be leaned. There is less air at higher altitude, so the the needle settings at sea level will be too rich at say 1500 ft. But you only take this into account though if your racing all over the place. At your local track, temp & humidity are the main factors. Take into account fuel if you switch brands or nitro content also.
Woops!! Absolutelly right!! I wrote it the other way round...There!! Edited!!

-More altitud=thinner air=mixture is ritcher= lean out carb.
-More humidity=heavier air=less OXYGEN in mixture= lean out carb.

Phew!! I hope I can get this straight someday!!
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Last edited by DR ZAIRUS; 11-15-2007 at 05:27 AM.
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