xpndbl3

iTrader: (5)

I'm thinking of joining an index class next year at the track. How much faster than that index should I be capable of running, and how do you all slow your cars down to run that index based off weather changes? I'm guessing I can shave ET by timing, tire pressure, etc.

Furthermore, are nitrous cars consistent enough to run an index class or should I join a slower N/A class for the first season to have a better shot at doing better?

AlkyIROC

What kind of index class? Stock Eliminator, Super Street?

If running in stock eliminator you're basically running in a bracket race. At national and I think divisional races, you need to run at least as quick as your index to qualify. The only time you need to be a lot faster than you index is if you get paired up against another car in the same index class. Then it's a heads up race to the finish with no break outs.

Super Street (IHRA Hot Rod class) runs a 10.90 index meaning you need to run 10.90 all day long without going quicker. Your dial in on ever pass is 10.90. To run the same ET all day, you normally use a throttle stop to slow the car down. A typical 10.90 car should be able to run low 10's off the stop. That means you have a lot more HP on tap for when conditions get very poor and still be able to run the index number.

To use NOS, you need to find out if it's even allowed in the class. No NOS allowed in Stock Eliminator or Super Street.

Read up on all the rules required for a specific class. Just because you want to run in a particular class doesn't mean your car qualifies for that class. Most class racers build a car to suit a class not build a car then decide to race in a specific class.

When you get into the other sanctioning bodies for classes like Real Street, True Street, Cheap Street, etc, same thing goes. Read up on the rules first. To compete competitively it can cost a lot of money to make your car run as quick as all the other ones in the class. It becomes a money race as in who can spend the most to go the fastest in the class.

KWIK84

iTrader: (5)

When I was running a S/C car we slowed the car down by either timing, shift points, or launch RPM. Normally we used launch, and shift points though. The car would run 8.40's flat out. We were able to run consistently and be easier on parts by dropping launch RPM by 500, and bring down the shift point by 400. FWIW. I think NOS would be fine, however you are adding another variable with regards to bottle pressure and all of the other issues associated such as solenoids and the like.

mw66nova

iTrader: (13)

what index class/org are you looking to run? stock eliminators are set up alot differently than stephen said, but i honestly doubt you're putting a 416 headed 305 with all the stock goodies back in, along with a TON of other equipment. stock eliminator is a very expensive class to run. but they are basically setup with an index of "x" and then depending on variables such as wind direction and DA, they determine how far under you can run...in most cases it's atleast 1 second.

my father and i have run index classes in the NSCA for a few years now and they are set up more like a bracket class with a set index that you pick for the weekend. my father's car runs 11.7x's out the back door, so we'll slow it down using shift points and timing to run the 12.00 index. my car has been 12.3x's, so i'm running the 12.5 index. a solid .2 quicker is a good starting place.

as far as n2o is concerned. Todd Merkle ran it in the EFI class in the NSCA a few years back. car would run the 9.50 index and he had the n2o come in on a timer, much like a progressive boost controller. not sure how it would work with a carb though cause it was part of the computer for the EFI. (i wanna say he was running F.A.S.T.)

xpndbl3

iTrader: (5)

it's an index class where you need to run 12.50, 11.50 or 10.50 depending on which class I choose, Street Fighter, Street Eliminator, or Street Avenger. All makes, and models, combos are allowed as long as you run the same time over and over. I'm not certain but it looks like who gets the closest without going under wins. There's also a bracket racing class where the index is 12.99-10.50 and you choose your dial each run. I didn't know which I would really rather do or which would be easier first season out.

the site is currently under construction for the new season but it's:
http://www.imsmracingseries.com/

Trevor86TA

I think running a bracket is going to be easier but index classes would be neat to try.

AlkyIROC

Running a bracket, you change the dial in on the car to match what you think the car will run. Running a specific number means you need to adjust the car to run the same ET every time. That means, you should be able to run at least 1/2 second under the index of the class you're running in.

Adjusting the car to slow down isn't as easy as it sounds and that's the appeal to some racers who want to run an index. It becomes a heads up race where reaction time normally decides who wins since all the cars are running as close to the index as possible without breaking out.

Doing things like adjusting the timing, shift point, launch rpm will all work but are very hard to control the outcome. You could just as easily install a ballast box and add weight to the car to slow it down. As I've previously mentioned, normally you slow a fast car down with a throttle stop providing it's allowed in the class. A throttle stop controls the throttle position for a specified period of time. You need to calculate what the ratio is to determine how long to be on the stop.

The way it works is you launch at WOT or however you launch. Shortly after coming out of the hole, the throttle stop kicks in and drops the rpm down to a specified rpm for a specified period of time. It then goes back to WOT and you finish going down the track. How long the car is on the stop determines how much it gets slowed down.

An example for a 10.50 class. Numbers not exact but just used for the example.

Car can run 10.0 off the stop. Stop timer is set to come on one second out of the hole and the throttle stop is adjusted to drop the rpm down to 4500 for 3 seconds. After 3 seconds the throttle stop turns off and the engine goes back to WOT. The run is 10.6. The throttle stop was on for too long so the timer is readjusted to be on the stop for 2.8 seconds so it will run a bit quicker than 10.6 but not quicker than 10.5. During time trial runs is where you do the calculations. Elimination rounds are just fine tuning for each round.

The goal is to know how much to adjust the timer before every run since conditions change during the day and the car speeds up or slows down from the available HP it can make to match the weather conditions. Bracket racers just change the dial in on the window. Index racers need to adjust the throttle stop to speed the car up or slow it down. Having a good weather station and ET/throttle stop predictor makes it a lot easier.

On the down side, you see some extremely fast cars running in the slower classes for whatever reason. How about a 10.50 class where normal MPH should be about 125 and the car runs 10.50 at over 140 mph. You know he has a lot of HP in reserve and was on the stop for a long time to slow the car down.

As for what class you want to run in, I've already mentioned, read the rules. Each class may have specific rules that your car may not qualify for. You may have to change something about the car to fit in a specific class. Maybe you can run 10.50 with NOS but that class may not allow NOS etc. There also might be a CID/weight ratio limitation where a big engine in a light car may not be allowed. If it's "anything goes just run the index" type of racing, someone may find a way to get an unfair advantage over others in the class and dominates the class every time.

I've considered running in Super Rod (9.90 .400 pro tree) or Hot Rod (10.90 .500 full tree) but don't really care for throttle stop racing. I'd rather write a number on my windows and try to run it.

1bad406

iTrader: (1)

I run a heads up index class with my car. It's 7.00 in the 1/8th mile .400 pro tree. I use timing and shift points and a restrictor plate to slow mine down and its real consistant like that. Bracket racing would be a little harder for someone starting out because its a little tricky trying to judge the top end when you have a faster car coming on you. But if your index racing and leave at the same time, you pretty much know if your running too fast or have the advantage on the tree and can judge the top end easier. I think you'll enjoy the index racing alot better than bracket racing. Just pick the class that you can run a little fast in and go for it.

xpndbl3

iTrader: (5)

thanks, maybe i'll sign up then. Looks like it would be a fun time to see how the car reacts

sixpackmtrspts

we race in a 10.60 index class, only way we can do heads up racing since you cant go quicker than 10.60. .400 pro tree, pretty fun. we run nitrous and have it setup to activate when shifting to 2nd gear and running it out the back door, car runs right near the index every time.

xpndbl3

iTrader: (5)

do you feel that nitrous is acceptable to run in varying weather conditions? or is a n/a combo more accurate when it comes to running your index consistantly?

mw66nova

iTrader: (13)

niether n/a or nitrous will be as conistant as say a forced induction motor...

xpndbl3

iTrader: (5)

well i meant would adding nitrous to a n/a combo to run a faster index, be a smart thing to do, or is it one more headache variable that i have to deal with.

AlkyIROC

Have multiple bottles and a bottle warmer in your pit. One of our local racers has a bottle warmer that looks like a mini hot tub. He keeps 2 bottles in the warm water while using the third. After every run, he swaps the bottle for a warm one so it's always at or near the max pressure for consistency.

mw66nova

iTrader: (13)

with the progressive nitrous controllers on the market now, it's not that big of a deal anymore, as long as you're willing to do the work to make every run the exact same.