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where i race we have to have a cam that will pull 18# of vacum at 800rpm. the cam i have in now will pull that but now their complaining that it doesnt idle smooth. is there any way to smooth out the idle without taking away performance... advance the cam, different rocker ratio????? thanks
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if you fulfilled the rule requirement of pulling "X amount" of vacuum why would they car how the thing idles? a racing cam is going to have some "lope" in it. im going to guess that there is no rule in their rule book that you have to have a "steady idle" i mean we dont run a super aggressive cam but it "lopes" over a little bit....especially at that low of an idle. we keep our idle at around 1000ish rpms anyway. i dont think we could back the idle screw out far enough to get down to 800rpm and keep it from wanting to die lol
does the track require a specific cam? -
the cam rule states"must pull 18# at 800 and must idle smooth" at 800 i think the car is wanting to die. so it lopes... didnt know if we put 1.6 rockers on the intake valves if that will take some lope out has 1.5s now????Comment
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hmmm....im not totally sure about how much changing the rockers will increase the smoothness of the idle. could some by hanging the valves open a little longer. the rules that say "it must be smooth idle" is pretty subjective if you ask me. a smooth idle to a tech guy one night can be very different from smooth idle another night or even just the next car.
does the car idle "smoother" after it is warmed up? maybe make sure it is warm when you go to have them do the check.
might try playing with your timing a little bit. try advancing or retarding when they do this check then putting it back to where you want it for race time.
maybe try playing with your idle screws on the carb to smooth it out some.
is your distributor locked? if so you might unlock it for when they do the check. and unlocked distributor with the right spring/weight combo could probably make it idle much better at low rpm
sorry i know im rambling but im trying to give you some things to try without having to swap out to many parts or even worst case change the cam.Comment
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Man, you have to wonder where some of these rules writers get their ideas. What exactly is the definition of a "smooth" idle? LMAOOriginally posted by heneryss View Post
Sorry, just couldn't help but vent a little at yet another stupid rule. If you pass the vacuum rule, that should be the end of it.Comment
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Got to agree with Swaybar on this one. Do they have a special "idle smoothness" meter or a way to tell how "out of smooth" your engine is running?
Guess they could take a beaker, fill it with water, sit it on top of the air cleaner, and measure how much movement is in the water. If it moves more than so many ml's over a givin time frame........JD's Performance
13034 Hwy 99
Wapello, IA 52653
319-931-0677Comment
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hell,..tell'um its a lil skip ya cant quite get out...smooth idle is fer g'ma's grocery getter not a RACE motor! ...could try addin some exhaust pipe lenth to it maybe?white trash motorsportsComment
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when we had that crazy vac. rule if you would tighten the valve lash would give the idle a little shake. alot of the guys would tighten valves for heat race,then back the lash off for feature,less lash means more engine vac. hated vac. rule glad its gone at our track,good luck!Comment
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Different hydraulic lifters if that's what you run.Comment
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playin with timing an backin off on rocker a lil,..playin with exhaust an maybe a smaller carb bout all i can think of that might get some lope outwhite trash motorsportsComment
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I think it's roads lifters that pump down at idle to help with bigger cams for a vacume ruleComment
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Vacuum rules are dumb anyway, they can be gotten around too easily. Smooth idle rule is dumb too, its subjective. I myself think max lift @ valve rules make more sense.Originally posted by swaybar View Post"If racing were easy, everybody would do it."
#77 Leon "Slick" SellsComment
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If dizzy advance isn't locked out. Lock it out, so it runs full adv, that will smooth out the idle and allow the carb to be tuned alittle easier at idle.Josh K.Comment
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See heres the whole problem, When guys ask questions on the forum boards they need to tell you everything about the rules for the class.
The class he races in is a new class for 2011 and is called PURE STOCK. These cars are to be as stock as possable with a few exceptions and I mean very few. The Rule states the Engines must pull 18ins of vacuum at 800rpm/idle. The cams must idle smoothly like a stock cam would and can not have any lope. He was given a brake and told to take the cam he was running out of his engine and, because of the rules I could have D.Q.d him but I did not because it was very early in the season. Guess I should not have been a nice guy, that won't happen again. He races at the track Im the Tech Official at.
I am the Head Tech official at HPT.COM SPEEDWAY and HUMBOLDT SPEEDWAY in Kansas.
Carl Flower.Last edited by techracer44; 05-04-2011, 11:00 PM.Comment
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Still not good rule setup!!! You can spend more money on vacuum cams, when if you left that rule out a guy could buy ONE cam and run it till something happens. With vacuum rules, guys either spend extra and get a custom cam or go thru several finding one that they like. I have a cam that pulls pretty hard to 7000 rpm and will pull 17" vacuum at 900 rpm (rules I have to run under) and idles pretty smooth also. But at the same time, we have went through several cams that sounded better (lope wise) but didn't seem to make near the power and pulled the same vacuum. In my opinion vacuum rules make absolutely NO sense!! These are still race cars, let them sound like race cars!! If the motors are pretty restricted, teched good, and you have good protest rules, then the guys that will be winning won't have hard loping cars anyway more than likely.Originally posted by techracer44 View PostComment
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