I guess this is for those who seriously bracket race the LT1. I bought my 94Z with the intention of turning it into a mid 12 second ocasional driver and competitive weekend bracket racer.

The car is basicly stock now, but I'm sure that my performance goals can be easily met. My main concern is with the consistency. I only have 11 passes on the car, but it has varied as much as 2/10 on back to back passes. It has also ran within two hundreths on three consecutive passes, but more often that not the ET bounces around quite a bit.

The car is an A-4 and has dead hooked on every pass but one. Is this kind of inconsistency normal for these cars, or should I be looking for tuning issues?

 

I bracket a LT1 car. I have a 160 stat and the fans come on sooner. Electric water pump. A manual switch to turn fans and or water pump to cool down between runs. Temps are critical. Water, engine oil, and trans temp. I try to keep things hot on every run. water about 170-180, eng oil 190-200 and trans 180-200. I also have consertivite, very rich, flat tune. I only have 363 RWHP but can go low 11's with a 3400lbs race weight (without me). I usually short shift and add weight to run 12.0's. Car will change .01 with 200 feet of da. Wind, clouds, and dew point will effect the ET as well. Your 60' should be dead consistant. A .1 change in 60' will make a .15 change in ET. Keep detailed data logs of each run. You can't put in enough info. I have a few more runs on my car than you. Hope this helps.

 

I also race a 94 LT1, except mines a 355, and run 7.0-7.1 in the 1/8 with a best of 6.99 at a 3400lb race weight. I run the stock pcm with a custom dyno tune, a th350 trans with 4500 converter, 4.88 gears, and 30x9 hoosier radial slicks. The car is dead on consistent if you can read the weather conditions, I ran two passes back to back this weekend on a test night and they varied only .006. Then on race day I made two time trial passes which were 7.158 and 7.157, then had to wait about 1 1/2 hrs to start eliminations and the weather changed slightly so I dialed down to a 7.14 and ran a 7.146. So as I said the car is dead consistent, but you have to account for the weather and I also keep a dedicated log book.

Randy

 

My 95 LT1 Z28 absolutely does NOT like heat in the engine at all to run it's best. It is not uncommon for the second run of a back to back run to be .2 to .3 of a second slower.

 

That's true, going from a stone cold engine to one that is heat soaked will net you a .2 sec loss, but if both passes were hot then there shouldn't be that big of difference. My car will run around .3 sec slower in the dead of summer vs the cold air of winter, but if the engine is up to operating temp it should run consistent regardless if it's fast or slow.

Randy

 

Good input, and very much apreciated! I guess my first step will be to get some aftermarket guages so I can monitor the engine and trans temps a little more closely. I already have a manual fan switch to help regulate the water temp. I also need to get a cable and software so I can start datalogging my passes. A portable weather station would probably help to. What do you guys use to monitor changing conditions?

I take it these cars are more sensitive to atmospheric conditions than I am used to. My old carbed setup would only change about .10 from time trials at 80+ degrees, to the late elimination rounds at 50 degrees. I did always try to keep the engine temp consistent, wich would sometimes require idleing for long periods during the later rounds.

I am open for any more suggestions on staying consistent. I would rather ask dumb questions now than go home early later. It seems like everyone I know is only concerned with running their fastest possible times. I don't have the bankroll for competitive heads up racing.

 

Once you get your laptop to datalog watch for knock retard. That could be whats making the difference currently. The knock sensor is very sensitive on the LT1. Either desensitize it or turn it off if you have to.

 

I have a PerformAIRE unit. You need to keep logs because sometimes just the DA is not the whole story. My car tends to change more with humidity than temps. I really don't like to "dial down". This year I'm trying not to use my weather gauget. Take notice and feel the weather changes then adjust your dial. Scarry but you can do it. Your car doesn't have to be consistent but does have to be predictible. The EFI is more sentistive than a carb car. You just have to keep better logs. My 12 second race car is look down by others on this site because its not "fast". Bracket racing is a different mentality than going really fast just once.

 

96flame, Thanks for the input. I have thought about the posibility of knock retard. Since I don't currently have the ability to check for it, I considered disabling it with a resistor for testing purposes. I have access to high octane unleaded fuel, so I shouldn't be encountering any spark knock.

kazman, Thanks again for your help. I will start keeping a log on my next trip to the track. I know what you mean Bracket Racing mentalty thing. I personally have a lot more respect for a car that can run the number time and time again, than a really fast car that takes five trys to make a clean pass. I love the strategy and competition in Bracket Racing, many people just don't get it.

 

Yeah you shouldn't experience any real knock its the false knock from loud exhaust, roller rockers etc.

 

I bracket raced my 94 heavily for 3 years. I always ran very warm. Make sure you idle long enough before the burn out to get the computer into closed loop. I also locked down my BLM's in the computer to 128 and made sure my timing tables dadnt have any large swings that could be caused by temperature differences. Mine's a stick car (not reccomended for brackets) but I could usually dial within .02. Also mine looses about .4 from best air to worst air.

Steve

 

Steve, been a long time. I see your still banging gears. I'm going to a glide over winter. I had some issues in deep staging the bird this past season. Didn't make it to the BF's I have a few Corvette races left this year and doing so so. Maybe I'll catch up to you next season.

-Jim

 

SABLT194, thanks for the input. I have been going in with the engine pretty cool, with little or no idle time before heaqding to the burnout box. I have also been running street radials, so I just clean the tires real quick and stage. It had never occured to me that it might still be in closed loop. I have a 160 degree thermostat and the fans are set to come on early, so it runs really cool according to the factory temp guage.

Before going back to the track, I will have a more accurrate temp guage installed.

 

If your car is stock, basically, it is the third gear shift that is often inconsistent. It is the same in most stock street vehicles. Try comparing the accuracy of the 1/8 splits as opposed to the 1/4 splits. A stock vehicle will usually be more consistent in the 1/8 mile if all other factors are equal. However evern where you stage can affect ET in terms of consistency due to the difference in rollout.

A small portable weather station is a good starting point and consistent 60 foot times indicate consistent launching.

 

tnthub, My car is basicly stock for now, but the UPS man is making pretty regular stops. When I get a little time off work I will be throwing some parts at it.

It's funny that you mentioned the 1/8 versus 1/4 consistency. I was looking at my time slips a couple of days ago and making some comparisons. You are dead on about the 1/8 times being more consistent. What is it about the 3rd gear shift that would cause it to be inconsistent? Would it be better to shift manually with a shift light?

I do plan on getting a portable weather station and some datalogging software as soon as I finish buying the parts for the car.

I know about rollout and do make an effort to stage the same every time. I will pay more attention to it, even though my 60' times are pretty consistent. I still have some work to do on my reaction times as well. When I finish changing parts on the car, I will figure out my the best place to launch from for my best reaction times. For now, I have been just barely breaking the beam.

I used to be pretty good at this and could regularly make it into the money rounds, if I could duck those pesky track champion types long enough. Hopefully, with help from everyone here, I will get the car and my driving sorted out well enough to be a threat again. So far I have only been hitting the T&T nights, but I have went and spectated on bracket night.