Just curious to see who bracket races with fuel injection, and things they've learned to keep the car consistent. Don't mind my ego, but I can cut a light lol. First pass ever in the Lumina since the Firebird was down, I went -.008 red. After 3 weekends of points racing, I'm consistent .00x-.02x. The car moving 2 tenths from round to round kinda ruins the package though. This is just a stock street car though, the Firebird I have the ability to tune. It seems like the first strike would be to change the temp variables to keep everything the same no matter how much the temperature changes.

Anyone have any other tips? Other then the normal car checklist like tire pressure, temps, etc.

 

You know my thoughts on this. My car has been very consitant when the air is the same. Enthalpy. IF I DONT keep messing with the tune.

Your on your way once you dial in the car with the tune. I ran a 13.08 when it was sunny and hot out that other weekend, then went 13.07 on that break out when it was cool out. This should show you that if your 60 ft times are consistant, and your car is tuned very well you will be able to be deadly in it. When I look at my 60 ft times on the .08 and .07 run they were damm near identical to the thousands and so was the 660ft time to the hundreths. The only reason I was picking up was leaning out down track since it was cool and my tune is rich.....on purpose.

Now if your car is stinking rich and then you race in the day time(heat) it makes it slower. Then at night when its 20* cooler and the air is more dense, you lean out and go faster. The key is to dial in those afrs as best as you can because you can not control the air density and when you in open loop you can only tune so much. Even Carbed cars move arround a tad. Im not sure how much control you have over afr vs temps in open loop on your mask let alone the ole 165 ecm.

Ive got some crew chief software if you wana try that on the laptop. It works well but still it doesnt take in account for your launch and 60ft time being the same or different each time.

 

im thinking an efi car should be more consistent than a carb since it has the ability to adjust itself for whatever atmosphere you might be running in. if the car is moving 2 tenths between rounds, there is something else going on, imo. my car with a megasquirt was running within .05 over 4-5 passes in an evening.

 

Coolant temp and intake air temp are the most important things to keep in mind for consistency with fuel injection. Keep them the same, and the car will run the same numbers. When tuning, I just set the temperature correction tables the same from 120 to 190 degrees. You can do the same thing by unplugging the pcm's temp sensor and using a potentiometer or resistor to trick the pcm. Just keep in mind you need manual fan control.

These are a few years old, but I had pretty good luck with efi.

 

The biggest inconsistency with a street car is traction. If the class allows it, put on some slicks even if you're only running 15 second 1/4 mile. The less you spin off the line, the more consistent the car will be. Traction at the dragstrip is not the same as traction on the street. Just because street tires work good on the street doesn't mean they'll hook up at the track.

The EFI system should provide very similar ET's if you can eliminate or reduce the other variables.

I like the resistor trick for the PCM. Too bad I don't race EFI any more.

 

The 2 tenths in the Lumina was a slight exaggeration, but close. Round 1 went 16.55, round 2 went 16.38 lol. I account that to weather change, being that the rounds were probably about 2 hours apart. But that's what I'm looking to get away from. I can work with it moving a few hundred. But its hard to close a good package when the car isn't consistent. Playing the stripe only goes so far. As mentioned above, its the computer compensating for changes in air condition, but honestly I'd prefer if it didn't lol. I agree with reducing the variables, that's what the goal is of this thread. I suppose I've been posting a false argument, seeing as I'm talking about my experience with the Lumina, when the Firebird is my bracket car. But as a driver, I do nearly everything I can to be the same between runs. In the Firebird, I burnout the same, stage the same, get up on the converter the same. Also have aftermarket water, trans, and oil temp gauges, as well as a manual fan switch and manual electric water pump. I check tire pressures as well. I'll have to see how consistent it is this year with the new setup before I talk too much about inconsistency, but consider it a precaution lol.

I've seen that pic before Matt, I'm jealous lol. Oddly enough, the one night, my Lumina went 6 passes in a row of 10.87-10.88 1/8th mile. I dunno why it won't do it in the 1/4 though. Its only been that consistent once lol. Thanks for the replies everyone.

 

If all else fails and the car is inconsistant.... learn how it runs with the exact same air. F

I cant stress enough how important the tune is for consistancy exspecially when the engine is modded so hard that the tune is very very far away from stock.


Good luck bud!! Keep up the RTs and you be a beast in the car.

 

I dont know if EFI is more consistent to a carb for me. I have never had a carb throw my times off at all. Been spot on pass after pass. But with EFI, i know there are heat sink issues on some that can cause issues. Different cars will act different with different injection EFI setups im sure.

I know if you could watch IATs and what not, that would really be able to help figure out if that is a issue. Just my 2 cents.

 

There is 2 wires in the iat sensor plug you can jump with a paper clip to make the car think its running in the same temp air all the time.

 

.....but if the air is different, the air is different. there is more variables than just temp...

 

Same car, same engine, same track and lots of passes that I logged. With the miniram, my time would really drop as we went through eliminations on a Friday night (2 tenths many times and sometimes more). With the carb setup, it has never dropped 2 tenths on one night. But, as was mentioned above, if you log enough passes you whould know where it is heading regardless if it is carb or injection.

 

fast eddi currently has this issue on his turbocharged v6 turbo cars are notourios for not being consitant as the weather changes.

whats happening with his car is as he does his time trials / 1st round run the air temps are high

then come the later in day rounds as it cools off the engine is leaning out due to the cooler denser air and picking up power

the easy fix fix for this is to log the afrs carefully and then adjust the ait correction table so that afrs stay constant over a wide range of temperatures

i will say his car is dam consistant for a turbo car im sure he will chime in but during tt and 1st round i think his car only moves around about .08 at the most last outing i think he went 13.07/13.08 then broke out by a bunch in first round with a 13.08 dial

car wants to go alot faster in the cooler part of the day

 

maybe it depends on the setup.... and i never ran my car over the course of an entire day, just evening/night. but i could put a 100 shot in it and it would run 6.10-6.12 in the 1/8 5 or 6 passes in a row with the megasquirt/sbc/nitrous combo.

maybe i shudda bracket raced it? lol

 

I think it does depend on the set up. Leaning out or being too rich in the heat of the day is what makes fuel injection inconsistant considering the driver knows how to smack the same 60ft time each run. I can say on average, when I knock down the same 60 ft times and lauch the exact same.... the car only moves about .1-.12 though out the day. Thats considering a hot mid day run compared to a turbos dream of a cool 50* first round. I dont think its too horrible but obvously it needs to get better.

My car is pretty darn consistant though. Im still working on the afr consistance. When your jaming in that much air and the afr goes .3 this way or the other its good to pick up or loose a tenth or 2 at time. But if phonenix(andew) gets that car started up and really works hard at tuning it I feel he can be somewhat consistant or at least learn how the car reacts if he cant control the afrs the best.

It all comes down to are you doing all you can do to make the car consistant?? If you are and its still moving 1-2 tenths then you just have to learn the car well and document it to the fullest.