Box Stock

rpm rule

they come with a .28 most people agree a .32 is the ticket but depends on your altitude. get it dyno pull. any body with a small engine dyno will know what these motors like.
 
bullerman said:
What size jets do most box stock come with? I was thinking I heard around a .030. So for a box stock on the track could use a .042 to help out?
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Ive read that the stock jets have been found anywhere from .025 to .030. I have pin gauged my collection of stockers and found this to be true.
 
J'-remy said:
they come with a .28 most people agree a .32 is the ticket but depends on your altitude. get it dyno pull. any body with a small engine dyno will know what these motors like.
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I may do that. I don't know anyone around here that has a dyno. I did get the trade school here to dyno a flathead years ago. I may call and see if they could still do it. I think I will check the jet in it to see what it is. Thanks
 
Not to hijack this thread but mine has a .030 main jet and an .020 low speed jet and its finnicky to start unless its stone cold. Runs great after you get it warm but if its only partially warm and dies it is impossible to restart. Any ideas on making it restart easier?
 
mike97760 said:
To the original poster- You will find 95% of the time that the guys blistering you are doing it in a number of ways that do not have anything to do with the motor unless theyre cheating. Their karts roll very freely and their chassis setups are on point, not to mention their tires. Theyve learned that you never take your foot off the gas, they trail brake if they need to slow a bit. Foot still to the floor. Deceleration on these things is fatal. Yeah I am sure you can tweak it a bit to make it better. The governor arm has a lot of holes in it where the long spring attaches. When assembled the worker that checks rpms attaches the spring in the hole that gives it 3650 rpms. Move the spring to a further hole to get more rpms with governor. And dont get confused about the rpm rules, the 5500 or whatever rpm limit number is checked on the kart stand not on the track. 4900 is all you care about, and thats while racing. As far as the story about a completely box stock motor that ran 5000 rpm right out of the box goes, somebody in China was drunk when they checked that motor. Imagine the poor soul who could have bought that motor to put on his poor little rototiller. Ive been doing this a little while, running stock appearing stuff and small block opens. There was a big box stock race one day and I bought one just to try it. Its kind of maddening trying to get every one my my ducks in a row to run up front. The big race I went to? It was won by a guy who pitted next to me and yanked his open motor off the kart and borrowed a motor from the race track owners water pump. Had to remove it from the pump himself. I loaned him linkage parts to hook it up. And he kicked our butts. Motor was still muddy from its water pump life.
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I may try the trail breaking. I guess with that you should have very little rpm drop. I have just started back racing. I used the brake but let off on the throttle. Will give it a try.
 
mike97760 said:
To the original poster- You will find 95% of the time that the guys blistering you are doing it in a number of ways that do not have anything to do with the motor unless theyre cheating. Their karts roll very freely and their chassis setups are on point, not to mention their tires. Theyve learned that you never take your foot off the gas, they trail brake if they need to slow a bit. Foot still to the floor. Deceleration on these things is fatal. Yeah I am sure you can tweak it a bit to make it better. The governor arm has a lot of holes in it where the long spring attaches. When assembled the worker that checks rpms attaches the spring in the hole that gives it 3650 rpms. Move the spring to a further hole to get more rpms with governor. And dont get confused about the rpm rules, the 5500 or whatever rpm limit number is checked on the kart stand not on the track. 4900 is all you care about, and thats while racing. As far as the story about a completely box stock motor that ran 5000 rpm right out of the box goes, somebody in China was drunk when they checked that motor. Imagine the poor soul who could have bought that motor to put on his poor little rototiller. Ive been doing this a little while, running stock appearing stuff and small block opens. There was a big box stock race one day and I bought one just to try it. Its kind of maddening trying to get every one my my ducks in a row to run up front. The big race I went to? It was won by a guy who pitted next to me and yanked his open motor off the kart and borrowed a motor from the race track owners water pump. Had to remove it from the pump himself. I loaned him linkage parts to hook it up. And he kicked our butts. Motor was still muddy from its water pump life.
Click to expand...
I read that one of the tracks let's you tie wrap a few of the coils of the spring to raise rpm also. Seems like all the holes in the arm are about the same but it makes a difference which hole the spring is in. My new Hemi is at 4900 out if the box with throttle screw backed all the way off. Want to get it to 5300 on the stand at least.
 
At the tracks around here the rpm rules are the engine cant exceed XXXX rpm on the kart stand and the motor must surge when checked.
 
Kj26 said:
Our rules allow zip tying the spring, its basically the same as pulling the gov without pulling the gov lol.
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I tie wrapped the governor spring with it in the closest hole to the inside of the motor. 5450 in the stand with some surge. I think as long as we aren't over the 5500 on the stand we are fine.
Hoping I pick up a couple of tenths with butterfly opening all the way with the governor.
 
Raced last night and won the feature. They checked us. I have a mychron 5 on the kart. The track has a mychron 4. When he checked mine he was going to use my tach but I asked him to use him and we could compare. His showed dead on 5500. My heart dropped. Mine showed 5613. I passed but I have to govern back some more. I still was only racing at 4443 average. I guess I will tighten up my accelerator spring a little more to take of a few more rpm.
 
I guess. They say 5500 on the stand so that's what I am going for. I just can't get the get on the stand and the gear on the track to together. Looks like to me to turn 4800 or 4900 on the track I will be over on the stand and get dq. I don't know i am still trying to figure it out.
My next question is will I get the same performance if I go to 5300 on the stand out on the track.
 
I don't see why not . At 4900 rpm it still has the ability to rev up another 600 rpm. The throttle blade is full open at that point .
Provide it can make enough steam to do it .
 
It's about getting the best performance from a mass produced industrial engine only ever intended to turn 3600 rpm.
Your engine may only be capable of peak hp at the rpm you are seeing.
Still need the butterfly to be fully open at the top rpm you are looking for on track.
Once the throttle blade starts closing, no way to get last bit of power.

If you can make the throttle blade still be open at 5000 and surge to 5400 max, that would be ideal.

Congrats on your win.

Keep looking at stopwatch, and comparing to track conditions to verify you are tuning gearing in the right direction.
Could still be gearbound.
 
What rpm drop are you seeing in the corners?

Edit I saw the gearing in the other thread.

Trying to figure out the average rpm you are talking about.
4900 should be peak rpm on the lap.
 
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