[Driver72]

OK, so here's the deal.
I went out to my car today and noticed that the tire pressure on all the tires were at 37-38 psi.
In the door jam, it recommends 32 psi.
Hmm, well that could have a small effect on my 1/4 mile runs, specifically traction.

So I decided to go out to the exact same desolate highway I have used many times before and used the other day when I did the tests in the link below to see if I could better the times:
1 4 mile runs....on the street...stock SRT Hellcat Forum

All the same disclosures apply.
Car is still completely stock, not a performance mod, weight reduction mod, and no race gas in tank, nothing.
Stock car, stock summer Pirelli tires.

The differences this time:

Car now had 675 miles on odometer (not even 100 miles more since last test).
Tires were set to 32 psi rear, 34 psi front.
I had just over 1/4 tank of the same Shell 93 Octane I had a few days ago. Then I had just under 3/4 tank, so I had about 6-7 gallons less fuel this time.
The temps then were 70 degrees with 91% humidity and a DA of 950 or so feet.
The temps this time were 65 degrees with 59% humidity and a DA of 475 feet.

RESULTS:

First run:
60 foot of 2.2 seconds
0-60 in 3.8 seconds
0-100 in 7.4 seconds (improvement of .2 seconds)
60-130 in 8.0 seconds (improvement of .4 seconds)
1/4 mile in:
11.7 @ 129.0 (same ET but trap went from 127.4 to 129.0)

2nd complete run:
60 foot in 2.1 seconds
0-60 in 3.7 seconds
0-100 in 7.4 seconds
60-130 in 8.0 seconds
1/4 mile in:
11.6 @ 128.5

3rd complete run:
Basically same as 2nd run but 1/4 was
11.6 @ 128.0
**a bit of heat soak was kicking in. I did these passes almost back to back.
I'd pull over on the side of the road and turn off engine for 2-3 minutes a couple times if I saw headlights coming from a mile or so away, but I also had 3-4 busted runs in between where I spun too much, stopped, and then went right away again seconds later.
So without proper cool down the traps began to drop with the heat soak.

So, dropping my tires to the 32 psi did nothing for better launch.
On the street on the stock summer tires, inflated to factory recommendations, it may be hard to get a better than 2.1 60 foot time.

But the better DA clearly came into play and showed how low DA's help a lot.
best ET is now 11.6
best trap of 129 mph.

I think my predictions of 11.5 on the street stock is real, with a sea level DA.
And I'm super stoked about the 129.0 trap speed.
With sea level DA, I'm hoping for 11.5 at 129+

On a side note, anybody who may be thinking they would discount these times as it's not a drag strip, I'd say, well then you better discount nearly all automotive journal/magazine's (like Motor Trend and Car & Driver) times you read then too, as I'm using the exact same GPS based VBox performance meter nearly every one of them use. The industry standard really.
One could also argue that drag strips are no more accurate as you are relying on their timing lights being accurately set up and spaced, and maintained, and they use VHT chemicals and heat to make the launch pad sticky, which always helps ET's. Plus some drag strips run a bit uphill or even downhill, NHRA accepts a bit of variance. The road I'm using is dead flat, you can see it, and verified on Google Earth. I either video taped or took photos of the VBox for verification too.

I will be taking the car to the drag strip soon too. But in the past when I've compared the VBox to the drag strips, they are almost always within .05-.075 time and within .5 mph of each other, sometimes basically dead on.
Good times and was stoked with the results. Car is a beast and it's not even fully broke in yet.

 

[Doug Redd]

That is a great mph, how was the traction?

 

[Driver72]

That is a great mph, how was the traction?

Not great.
Had to launch in 2nd gear and even then had to feed in the throttle gently, but swiftly.
On several runs, if I fed in the throttle too hard it would start spinning, even at 30-40 mph. So I'd just let off the throttle and go again.
Getting better at knowing the amount I can feed in on the street tires on the tarmac, launching as hard as I can and feeding in the throttle just enough to keep the tires from breaking loose all the way through 2nd gear. Not sure at what speed I was able to go full throttle, but I know I was still in 2nd when I did, and then it would run to redline and shift hard into 3rd.
But still, I can only imagine what the 0-60 time would be IF we could get even 50% better traction on a 2nd gear launch on the street.
As we all know, the car should of come with 20 x 10.5 inch rear wheels on 315/35/20 tires.
It would make a noticeable difference.

 

[B5 Blue]

129 heck 128.5 is great. Get her to the track to verify, mine is flat.

 

[Driver72]

I will hopefully be hitting up the drag strip next Wednesday.
But right now the forecast is showing a 30% chance of rain and temps warmer than yesterday.
So I won't be surprised if at the strip I don't have a great DA.
But I've gone to this same strip before with my VBox attached and have done many runs.
The strip times and my VBox times often time overlap each other so they are very close to being the same.
But again, I never know which one to believe in that regard, since set up of those timing lights can have human error, and even though it's a NHRA certified track, there is room for error in NHRA rules, so there is some wiggle room if they are a tiny bit off if they aren't calibrated just right.
Who knows.
If weather permits and my schedule doesn't change, I'll give it a go and see what I can do there too.
But knowing my VBox is really accurate, I'm quite happy with 128-129 mph traps.

 

[Cerino2000]

The key to getting the launch control to work is knowing that the car expects a certain amount of pressure on the brake pedal. When you have it right you will be able to floor the gas and the car will hold the desired rpm without burning tires at all and when you left off brake you will notice it cutting power. Its very noticable. I have a thread with vids somewhere on here. I had to search out why mine wasnt seeming to work and it was the brake pedal pressure.

 

[Driver72]

The key to getting the launch control to work is knowing that the car expects a certain amount of pressure on the brake pedal. When you have it right you will be able to floor the gas and the car will hold the desired rpm without burning tires at all and when you left off brake you will notice it cutting power. Its very noticable. I have a thread with vids somewhere on here. I had to search out why mine wasnt seeming to work and it was the brake pedal pressure.

Good to know, thanks.
I'll have to give it some test time in the near future.
I'll look for your vid to see as well.

 

[JeKo]

Im wondering how you are hitting such high traps and not having faster ET's??

 

[Hemi Dave]

Im wondering how you are hitting such high traps and not having faster ET's??

Lack of traction....................

 

[DGatzby]

Very high traps to indicate some high horsepower on that unit. I am getting those 0-60's but those traps are 5 mph over my street traps. Our D/A in Minneapolis yesterday was 1250' with a beginning elevation of 980' It was low 60's dew point was 32 degrees - nearly ideal except we need some pavement heat. Best I have is 124 (yesterday), but we needed to add about 420 lbs for two people riding including myself, that may be the difference. That calculated to about a 750 hp to the wheels which is a leap of faith, we figured too much weight was throwing the equation off a bit. Your trap with 4650 lbs (say 4450 plus 200 lb) calc's to about 780 hp at the rear wheels FYI. That is pushing the expectations I think. Or do you weight about nothing? Calc with 4450 is 750 hp, still high.

Also, that relative humidity calcs to a dew point of less than 20 to get those D/A's. Relative humidity takes the equation RH=100-5(T-Tdp) where T=temp in C Tdp is the dew point which you need to calc D/A. Are you in the Nevada Desert on a 70 degree day? Or basically on the coast on a very dry day?

JeKo, we know you are less or about 100 lb.... lucky, nice work, my money is on you! That car is going to be quick and have a high trap. Plus you are shifting real well, again congrats on your times.

 

[Driver72]

Im wondering how you are hitting such high traps and not having faster ET's??

Lack of traction....................

That's often times the case.
Lower ET's often translate to lower trap speeds
Higher ET's often translate to higher trap speeds.

The more traction you get off the line, the faster your car jumps forward, you get to the 1/4 mile line faster, but your car has less time to build speed.
If you spin off the line a bit, you get to the line a bit slower, but your car has a bit more time to build speed.

Then there is just individual cars. Each engine will make slightly different power. I've organized some Dyno Days back in Los Angeles, where 10-15 of the exact same cars would show up and we'd have a BBQ and dyno our cars then put a tune in, and redyno.
On the stock cars, it was not uncommon to see 10-12 hp variance. And this was on cars that were putting down on 250 rwhp stock.
On cars like the Hellcat, I'd be willing to bet, we could get 20 Hellcat's together on the same day, same dyno, all stock.
We'd see dyno results that varied by 15-18 rwhp.
Some will run strong, some will run a bit weaker. Can depend on how many miles are on the car, but not all the time. Some cars with low mileage can outperform cars with a few thousand. Can depend on break in procedure, but again, not necessarily.
Can just be luck of the build. Just like with anything you buy.

 

[DGatzby]

I agree. Would bet your car has a favorable dyno run.

 

[Driver72]

I don't know, maybe, I always go in feeling my car is average, this way I'm not disappointed if there are more powerful ones and know that there is more than likely ones that aren't quite as strong.
I remember on a dyno day we did for the first 20 people that got the first tunes ever on a 335i, my 335i was the 3rd most powerful stock of the 20. One was 1.5 rwhp more and the other was like 2-3 rwhp more. The other 17 were anywhere from 2-8 rwhp less than mine.

The traps I got were probably a combination of slightly slower ET's, allowing the car a couple tenths of a second to gain an additional mph or so, as well as actually being near sea level (though my DA was like 450 feet, the road I'm on (well the who city and region I'm in, is between sea level and 20 feet above it.
You can drive 50 miles and only change elevation by 20 feet. I Googled the road and it shows like 3 feet above sea level, for miles in both directions, occasionally going up a foot or two, but that's over the areas that have water canals running below.
I of course don't do the runs over those small inclines going over the canals.

We had great weather this past Wednesday (high was 67, low was 59) nice air, and the drag strip was open that night for test and tune (probably low 60's that evening) but of course, I had to work.
Now it's low 80's again during the day (so at best 75 degrees by 10 pm when the track closes).
May not get a chance to have good weather again for drag strip runs until fall.

 

[#GRRRR]

Great times with your car, I'm struggling , best I've peeled off is a 12.5 :/ , tonight raced a gt3 Porsche , and it got me out the hole and not enuff road to pass him, 0-60 was 5.6!!! And 12.9 1/4 @ 115 clearly I'm doing something wrong, albeit it was awful road very dusty no traction ..

 

[Driver72]

Great times with your car, I'm struggling , best I've peeled off is a 12.5 :/ , tonight raced a gt3 Porsche , and it got me out the hole and not enuff road to pass him, 0-60 was 5.6!!! And 12.9 1/4 @ 115 clearly I'm doing something wrong, albeit it was awful road very dusty no traction ..

Start in 2nd gear.
You can leave the transmission in D if you want.
Transmission in Track
Stability in Sport
Suspension can be Street or Sport
Once you come to a stop and are ready to go, just hit the + paddle up so you see that you are in 2nd gear.
Then ease into the throttle at launch pushing it down quickly but don't jab it down.
If you feel the tires starting to break loose, back off the throttle a bit then ease back into it again. But at that point the run is a bust anyway and you wont have a great time. But if you are doing a little stop light run, either abort or let off a bit, then get back into it and play catch up if you can. If you start to spin yet again, just abort, chalk up the loss to a bad run.

You'll get a good time if you can get into the throttle quickly and smoothly, pushing in down progressively with little to no wheel spin. You should strive to be right on the edge of breaking the tires loose. Then you know you are accelerating as fast as you can with the grip you have.
A tiny bit of chirp chirp chirp is ok thats how you know you are right edge of breaking loose

 

[Hubbs]

I'd like to know how the car's stats compared to the VBox during those runs. 128-129 are incredible traps...congrats!

 

[B5 Blue]

Start in 2nd gear.
You can leave the transmission in D if you want.
Transmission in Track
Stability in Sport
Suspension can be Street or Sport
Once you come to a stop and are ready to go, just hit the + paddle up so you see that you are in 2nd gear.
Then ease into the throttle at launch pushing it down quickly but don't jab it down.
If you feel the tires starting to break loose, back off the throttle a bit then ease back into it again. But at that point the run is a bust anyway and you wont have a great time. But if you are doing a little stop light run, either abort or let off a bit, then get back into it and play catch up if you can. If you start to spin yet again, just abort, chalk up the loss to a bad run.

You'll get a good time if you can get into the throttle quickly and smoothly, pushing in down progressively with little to no wheel spin. You should strive to be right on the edge of breaking the tires loose. Then you know you are accelerating as fast as you can with the grip you have.
A tiny bit of chirp chirp chirp is ok thats how you know you are right edge of breaking loose

Second gear start kills my 1/8 to 8.25 but is consistent however I've learned how to launch all seasons in first and pull 7.95 hot engine 7.75 cooled down some.

 

[Driver72]

I'd like to know how the car's stats compared to the VBox during those runs. 128-129 are incredible traps...congrats!

When I went to the drag strip, I had my Vbox hooked up and the ET's matched exactly. And the trap speeds were within .75 mph each time. On one run, the VBox actually read .4 mph slower than the drag strips results.
I've done this on many cars and the VBox is pretty dead on, especially with the ET's. Since the VBox rounds its figures it's hard to tell exactly how close it is but if you get a 10.951 on the strip, the VBox will show an 11.0
And with the trap speeds, the VBox reads to the tenth.
So on the strip if you got a 126.55 mph, the VBox may show 126.6, or it may be 126.9 or 125.9
Every time it's always pretty close. Close enough that it could actually be the more accurate of the two (compared to the timing lights at the drag strips) depending on how accurate the lights at the strip were set up.
And yes, 128-129 traps are fast.
But keep in mind, that was on the street.
You don't have all the friction and grip of the drag strips, which rob you of a bit of trap speed. Great for ET's but whenever you are rolling on glue, you aren't going to roll as fast. When you are at a drag strip, when you just drive on it, you can hear your tires sounding like they are driving on glue, because that's pretty much what the VHT they throw down is. LOL
So traps on the street will always be a bit higher than on the drag strip.
On the strip, my bone stock Hellcat did 126's with a DA of 1670 and only like 1,300 miles on the odometer.
At sea level in great air, it probably would of been 127's maybe low 128's
That's a higher trap than even Dodge/SRT got with their professional drivers with a stock Challenger Hellcat, and they were definitely in prime air with a well broken in Hellcat.

 

[Driver72]

Second gear start kills my 1/8 to 8.25 but is consistent however I've learned how to launch all seasons in first and pull 7.95 hot engine 7.75 cooled down some.

I got 7.4's in the 1/8th starting in 2nd.
Again, not ideal conditions at all, and with only 1,200-1,300 miles on odometer if I remember correctly.
So I'm sure 7.3's, maybe even 7.2's on a bone stock Hellcat would be possible with a bit more break in miles and sea level DA's.
I have summer PZero's

 

[Hemi Dave]

How did the SRT performance pages compare to the V Box?