very inconsistent ET's

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very inconsistent ET's

Postby Zeke » Tue Sep 11, 2018 11:46 pm

trying to run 8.90's with a 3.5 X 3 motor, I know its not the best thing to do but its what I have. engine was just rebuilt everything new, 42 mm, 4.97 gear, about 500 lb package, I have runs from 8.47 to 9.44 and MPH from 64 to 77 all with NO changes. 60 fts are all 1.821 to 1.888 , I know I have carb issues cause it won't heat up and turning the adjuster seems to do nothing, very cold at the track both engines started at same time mine was barely 100 on line and buddies was 200, mychron only showed mine as 202 max on the run and EGT at 750 max, I'm getting lots of opinions and none are the same LOL some say its cause its a fresh motor , others cause the carbs too big, some say carb is screwed up ( that I agree on ) some say its clutches ????? if its clutching shouldn't it be consistently good or bad ? I know most say using the big motor will cause inconsistances but not a second up and down that sounds crazy to me. any ideas ? haven't down loaded graphs yet but on the mychron they look very similar, max RPM on all runs is 7950 to 8200. help
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Re: very inconsistent ET's

Postby Kern Family Racing » Wed Sep 12, 2018 7:07 pm

I would put a 33mm on it to slow it down a bit and add some weight to the car. Right now you are pig rich and that is why it won’t heat up and I am surprised your oil in the crankcase isn’t overflowing with alcohol. You should be around 150-160 at launch and 300ish at the finish with EGT around 1150-1200 at WOT. Don’t touch the clutch until you fix the jetting or carb.
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Re: very inconsistent ET's

Postby RNorton » Thu Sep 13, 2018 8:49 am

Are you using a restrictor?

We are running the same engine combination as you are with a 3.520" by 3" engine. We are running a 33 MM carb to keep the charge velocity up and Im not convinced a 42 is the best route to take. Your idle CHT is a different adjustment than your main, start with that first. Id be blowing out the air bleed circuit on the pilot side of the carb real well. Your main wont flow until your well into the throttle so its not going to typically affect your idle temp. Your pilot circuit flows fuel at all times so it can cause both circuits to appear rich.

Fix the idle circuit and Id be surprised if the car didn't come around A to B.
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Re: very inconsistent ET's

Postby slowgoat » Thu Sep 13, 2018 10:56 pm

Not that this is going to fix your problem but the first thing I read is you are getting various opinions. Find 1 person you trust, Listen to them and no one else. There is nothing worse in the racing community than asking 5 people the same question.
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Re: very inconsistent ET's

Postby Zeke » Thu Sep 13, 2018 11:12 pm

after down loading the runs I found that the mychron was set to celsius not fahenheit so it was up to temp about 200 on the line 305 at the end and 1300 EGT's so I probably don't have a carb problem, but now I have no idea where to look for the wide ET swings.
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Re: very inconsistent ET's

Postby RNorton » Fri Sep 14, 2018 5:46 am

Can you post a graph and incrementals of multiple run?
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Re: very inconsistent ET's

Postby WOLFRACING » Fri Sep 14, 2018 6:52 am

Zeke wrote:after down loading the runs I found that the mychron was set to celsius not fahenheit so it was up to temp about 200 on the line 305 at the end and 1300 EGT's so I probably don't have a carb problem, but now I have no idea where to look for the wide ET swings.


The starting line egt could be part of the problem. That is lean for staging. Gaining 105 during the run is not excessive, and maybe just a tad fat on the main. I suspect there are additional issues which may be able to be addressed if we look at the graphs...maybe. But getting some fuel to it at idle is a place to start. What is your staging rpm? Let's see a graph and see what that looks like. Are your staging temps consistent? Do they level off to some extent? With my 3.5, I generally don't want to stage anything over 150. Over 160 and I generally get a hickup during the run. Our 3" wanted 160 at the line or more. But 200 seems pretty high.
How does the run sound? Clean? Let's get some info and see what ideas pop up.
And IMO, ideas are ammunition. You don't have to follow one person's advice only. It's all part of learning these things. I still run into a mystery now and then and it is great to get feedback.
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Re: very inconsistent ET's

Postby 66CHEVELLE » Sat Sep 15, 2018 7:49 am

We had the same issue a few years back. The engine was a 3.5 with a 42mm and the car it was on previously would not run very well at all. We did replace a few things right off the bat, I know one thing at time but what we replaced I don't think hurt it to bad. We replaced the valve springs because not sure how many runs they had on them and also put a 33mm on it. We are in the Midwest so I think humidity played a factor in it as well but it was decent in time trials but as soon as eliminations started it was all over which was right around noon. There was a 100 lbs of weight and a old but rebuilt polar and also a driver that was new to 8.90's. Big learning curve for all but after smoking the clutch we put a new clutch on ( purple spring,15-28-22,14 grams and 34* ) and went out and with in a couple races we won the race. So sometimes what appears (parts) to be good sometimes is not and listening to your gut sometimes is just as helpful then getting advise from others ( they want to win at the end of the day also smiley-lol ).
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