Fun at the dragstrip today: 11.76 , 11.82 @ 122,

[treynor]

I borrowed's Liz's SRT/10 for a spin at the dragstrip today. Her car still has the stock run-flats on it, and I was going to get up and put on our new Purner drag wheels (more on that later), but at 6AM I decided I'd rather sleep an extra hour and give it a go with the stock tires. So off to the dragstrip I went.

The first few passes were predictably poor, as the track warmed up and I experimented with tire pressures and shift points. The SRT would spin on launch, then spin again during the 1-2 shift. I ran three passes in a row wth 2.0 60's and 12.2-.3 @ 118 1/4s, and started recording my launch RPM and shift points.

As the track continued to improve, I found that the 1-2 shift seemed to work best at 5900 RPM because the tach lagged, and the 2-3 shift at 6000 produced the highest 1/8th - 1/4 MPH gain. I finally put it all together with a launch which produced a 1.93 60 and an 11.8 @ 122 pass, staying in 3rd and hitting the rev limited just before the traps. I backed it up with a 1.90 60 and an 11.757 @ 119 pass where I tried shifting to 4th just before the traps.

Next week: returning to the dragstrip with Purner's new 18" wheel+spacer+studs package which fits over the stock rear brakes! I expect to run 11.4s

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[SMHOD]

Ben,
Great runs!!!
I have a few questions.
1. Which tire pressures did you try and which seemed to work the best?
2. Is her car totally stock in all other ways than just the tires?
3. Is there a web site for the wheels you are referring to (Parner's)?
4. Which tires are you putting on?
5. What was the tempurature?

Thanks for the help,
Scott

 

[treynor]

To answer your questions:

1. I tried 35, 31, and 27 PSI, measured just before the runs. 31 PSI yielded the best "hook", although I have only a few data points.

2. Liz SRT has some headwork from when the heads were off for the valve recall, and has a K&N intake.

3. John Purner makes the wheels that most Viper racers use. His website is at http://www.ccwheel.com/ . We're using his 18x13" rear wheel

4. ... with 345/30-18 BFG g-force Drag Radials. I used these same wheels & tires on my RT/10 to run mid-10s @ 148

5. It was low/mid 70s and sunny.

One of the keys I found was getting a decent burnout before the launch. Rather than trying to balance the gas & brakes, I would just nail the throttle and keep the revs around 4500 as the car did a rolling burnout. I'd then back up past the starting line and go.

 

[Kai SRT10]

Great numbers for a (mostly) stock car on stock tires.


What RPM are you launching at?

Thanks

Kai

 

[treynor]

When the track was cold, I was launching at 2250 RPM. As things warmed up and I started doing longer burnouts, I would launch at 2500 and then 2750 RPM. Equally it was a matter of being smooth with the clutch release to allow the engine's momentum to get the car launched without spinning.

 

[Dead President]

How about safety equipment? Does your SRT have a roll bar, five point harness, half shaft loops, etc. ? If not, I thought that NHRA rules would not allow for an 11 sec car to run without these safety items. Comments ?

FYI, I also have a DC Performance Stage 1

 

[treynor]

I'm getting 5-points installed this week. The undercarriage is sealed below the driveshaft, and no one has ever asked about half-shaft loops.

The main concern my local track has is that it has a roll bar (it does) and 5-points (it will within a week).

 

[Dead President]

Who's roll bar did you install ?

Thanks!

Frank

 

[limige]

why do vipers have such poor 60' times?

 

[treynor]

Frank - the rollbar is AFAIK just the stock hoops. They don't want convertibles there with NO rollover protection.

Regarding "why are Viper 60's so bad?":
Actually, 1.90 on stock street tires isn't terribly bad, although it's not especially good either. The general answer to your question is:

1. Vipers don't transfer weight well - the center of gravity is low and the suspension is stiff.
2. Stock SRT tires are run-flats, which means they have VERY stiff sidewalls. If you drop tire pressure to increase the contact patch, they "cup" badly and you end up riding on the sidewalls. Also, once you start to spin, they want to hop rather than hook back up.
3. Stock Viper gears are pretty tall; the SRT will do almost 60 in 1st. To get a really good 60' time you need to slip the clutch and keep the engine in the powerband, as stock it doesn't have enough thrust to produce a 1.7 60' on its own. This is one of the reasons that adding a rear gear improves the Vipers' 1/4 mile ET so much.

 

[MannyC]

I need to get some 18 inch rear purner wheels (I have the 17's which wont fit over my stop techs.) I have put two calls into John Purner, but he never has any in stock for the exchange program It's been about 2 months now. As somebody who has purchased two full sets of Purner wheels, and these would be my 9th and 10th Purner wheel purchased, I'm saddened I had to go buy some other wheels instead. They should arrive today, but I still need another rear set for road coursing so I don't have to keep swapping out my road course tires with my drag tires.

John, you listening? Hook a loyal customer up, brotha!

Manny

 

[VIPER D]

THANKS for the write up. I really got some good from you ben.


I think that the drag radials are my next buy. What do you think that 2 wheels, 2 tires and spacers ect will cost?


thanks in advance
vd..

 

[Cobra4B]

Great times.... killer MPH. What kind of head work did you have done?

 

[treynor]

ViperD - The full list O what you need to do this properly is:

Purner 18" SRT wheels with 345/30-18 BFG g-force TAs
SRT 18" wheel spacers
ARP rear wheel studs & lug nuts (got mine through Archer Racing; Purner may have a source as well)

All told, you're probably looking at just over $2K - a steal in Viper dollars!

Cobra4B - the headwork was DC performance's "stage 1", just mild porting and polishing, stock valves & everything. Our car has stock headers, stock cats, stock exhaust, and so on - in fact, you can't tell the car isn't stock, except that it picks up 30 RWHP above 3300 RPM The MPH is actually a bit low because I'm launching softly - I bet I get 124 MPH with the drag radials. We'll see in two weeks!

Manny - if it's any consolation, I think I've purchased 20 Purner wheels over the past 4 wheels. They're like potato chips - you can't get just one (set) !