Drag race results

[silverviper]

Ok, so I took my Viper drag racing for the first time ever (both for me and the car) at Sears Point yesterday. My results were:

12.470 seconds @ 116.09 mph

Here are my questions:

1. Is it possible to calculate real horsepower from time, weight, and distance? Or do the variables of temperature, traction, etc make this unreliable?

2. I was hitting the rev limiter in 3rd just before the finish, would it be best to shift to 4th, hold it at 6000 rpm, or something else?

3. Should I expect to go much faster with an unmodified ACR on street tires?

Cheers.

And a big thank you to Ben for his advice and coaching at the track!

 

[phiebert]

1. From what I've heard/found, the horsepower calculation is quite accurate based on the variables you have. I don't have them in front of me now but you will be pretty close. Frankly probably as close as a dyno is. They are not infallable either.

2. Shift into fourth. Don't hit limiter and get a little more torque at the right RPM.

3. Don't know, probably not with street tires. I think your times are very good. I wasn't close to that on my first time out. I've got to about 12 flat but with some exhaust and other mods and of course with drag radials. Your car is definitely more powerful than mine because I couldn't do those times with street tires.

 

[Venom Lover]

Congrats on your first time at the drag strip. Did you enjoy it?

1. An approximation of rwhp can be made from trap speed. According to a table in Tom Welch's drag racing video, with a 116 mph trap speed, your wight to power ratio would be 8.4, so if your fully laden weight were 3600 lbs (including driver and gas), then your power would be 3600/8.4 = 429 rwhp. 429 rwhp/.87 = 493 fwhp. Not bad, but I believe Welch's formula to be slightly "optimistic". With 120.5 mph trap speeds that I'm running, Welch's video claims my W/P is 7.5, so my P = 3600/7.5 = 480 rwhp = 552 fwhp. Compare that with my dyno results of 456 rwhp. Anyway, it's an approximation, but don't expect the numbers to be comparable to what you'd see on a Dynojet.

2. Phiebert is correct: shift into 4th.

3. I have seen a time as quick at 11.9 in a bone stock ACR on street tires. I forget who achieved that, but it was somebody on this board. Just keep bringing the car to the track and practice. Practice the launch, practice with shift points, practice shifting as fast as possible without letting the revs fall too much. These things all matter. What kind of 60' times were you running?

 

[silverviper]

Thanks for the info. Of course, I enjoyed it!!

I did shift into 4th on the fastest runs, just checking.

My 60ft time was 2.051s.

Seemed like the best launches were starting at really low rpms, letting the tires bite, and then giving it full throttle.

I've heard Sears Point is a "slow" drag strip, seemed like a slight uphill and headwind, so I'm hoping for better sometime.

Thanks for the tips.

 

[treynor]

Regarding Corvettes, there was one mildly-modded C5 there running mid 13s. Surprisingly, no Z06s showed up; stock Z's usually run 12.9 - 13.1 @ Sears.

Regarding HP -- calculations for Vipers should be made using MPH calculators, not ET. A roadrace car like the Viper launches much more poorly than does a dedicated drag race vehicle, primarily because of the IRS and the relative lack of weight transfer. 1/4 mile MPH is less affected by the launch than is ET, and you will get more accurate readings from it.

On the HP calculator at http://members.aol.com/fastnuf1/calc.html , I plug in 3700 lbs (my RT/10, curb weight 3460, plus hardtop and roll bar and driver) and 122 MPH and get 524 RWHP, which compares well with my 515 SAE / 530 uncorrected dyno figures.

For the ACR, I plug in 3520 lbs (curb weight is 3356) and 116.1 MPH and get 430 RWHP, which is about right for uncorrected HP from an ACR (usual SAE ~415 RWHP).

Finally regarding results -- for Sears, I'd say 12.47 is an excellent ET for a stock ACR. Good job!

 

[Venom Lover]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by illy:
Also, for Mike Pavloff. How did your rear gear swap affect your 1/4 mile times and street "Seat of the Pants" feel? I think that might be my next mod after headers. I am all about the seat of the pants value of things!


<HR></BLOCKQUOTE>

illy,

On street tires, the 3.55 gear seems to have bought me a tenth of a second in 0-60 and in 60' time. I never broke under 2.0 sec 60' time on the 3.07 gear with street tires, but I run 1.9's now. G-Tech 0-60 times showed a similar improvement.

Actually, as far as SOTP is concerned, I notice a small difference, but I would say it is not worth the $$ just for SOTP feel. But I know others have a different opinion.... Maybe it's just that my expectations were higher given what I heard others saying.

Nonetheless, it was worth it for me because of what it did for improving my launch. "I am all about lowering ET!!!"

Oh, by the way, the Corvette guys you mention must have been FOS, especially if Sears Point is a slow track. Occasionally, there are stock C5s that run in the high 12's if the driver is really good or the track is really sticky, but based on my experience at Pomona, Famsoso, and Carlsbad, a 12-sec run from a stock C5 (except Z06 of course) is very rare!

 

[Venom Lover]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by silverviper:

Thanks for the info. Of course, I enjoyed it!!

I did shift into 4th on the fastest runs, just checking.

My 60ft time was 2.051s.

Seemed like the best launches were starting at really low rpms, letting the tires bite, and then giving it full throttle.

I've heard Sears Point is a "slow" drag strip, seemed like a slight uphill and headwind, so I'm hoping for better sometime.

Thanks for the tips.<HR></BLOCKQUOTE>

A 2.051 short time is good! You should be happy with that in a stock car on street tires. Others have done better, but I never did before mods.

I agree, especially if you are at a slippery track, the best way to launch is just below 2000 rpms (if you're stock). For sure, if you start spinning and you stay in the throttle, you are done!

Good luck in the future!

 

[PhilC]

Hey Treynor:

Thanks for the link to that HP calculator. I've got a question though. I'm getting two drastically different numbers (~50hp) when using mph versus ET. MPH is higher and seems more consistant on the track. Is it reasonable to assume that I can plug times into the ET calculation until I get the same HP number and then assume I should be capable of making that ET?

Thanks in advance.

Phil

 

[jamie furman]

Not to give you a hard time treynor but 122mph in the quarter is about 425 rearwheel horse not 530, stock vipers run 120 plus and I have seen stock ones with tires run 123 in the quarter, my supercharged viper was at the dyno last week and made 569 hp on the rear wheels and it runs from 131 to 135 in the quarter depending on 60ft. Alot of the time the slow mph under 119 for a viper is the drivers shift points and how fast he shifts. My car bone stock ran between 120 and 122 consistently at the track and it made 417 rwhp at the dyno and these are all corrected numbers which probally add a couple of horsepower to boot. There are many horsepower calculators on line if you look for them and they ask you to put your cars weight and et and mph then they give you hp based on et to weight and one based on mph to weight and if you average those 2 it will get you within 10 hp of what you actually make. Before I responded to this post I went on line and did exactly that and it said my car has 564.69 on the rear wheels and my corrected to sealevel hp on the dyno was 569.9 so it was right on the money so I recommend that if you want to know your hp you do the same. But If you ever read mopar magazine evan smith ran a bone stock rt10 11.7 121 so you know that cannot be 530hp that car on a dyno would make 415 rwhp. And any guys that go to the dyno will tell you the same.

 

[treynor]

Jamie,
That's an interesting opinion. The facts are however somewhat different:

(a) I just re-dyno'd my car today (testing for problems with 91-octane gas). 515 RWHP, same as before.
(b) a stock ACR ran a best of 116 mph at Sears the same day I ran my 122 mph. His car was on street tires and weighed 150 lbs less than mine. We can assume his car was making the usual 415 RWHP. If we also assume he and I shifted similarly, then my car was making at least 70 RWHP more than his. We're still "missing" 30 HP at that point, but nothing like the 100 HP you're talking about.

Perhaps the track you run at is unusually fast, or perhaps Sears was unusually slow that day. I've never seen a stock Viper run faster than 116 at Sears, however, so the variable must lie elsewhere. Certainly speed-shifting can substantially improve your MPH, with an attendant cost to the drivetrain...

 

[jamie furman]

Well the east coast usually is faster but sears must be unusually slow, because like I said forget about what I run, the magazines, mopar performance, musclecar review and others have run 11.7's to 12.1's at 119 to 121 mph with stock cars making a little over 400 rwhp.I just think with 115 more hp your going to pick up alittle more than 1 mph.I think on this particular day your car was down on horse or the reading you are calling rwhp are indeed crank hp. Go to the site www.corral.net go to technical features then go to 1/4 mile based dyno's and if you do that you will see that 122mph is 535 hp at the crank but only 450 on the rear wheels.The last time I took my car out I went to the dyno the day before and made 569 on the rear wheels went up to the vca event in englishtown and ran 131 on a perelli pzero tire the next day, and according to the computer dyno I was making 564 rwhp within 5 of what I actually turned the drum at just the day before, so it must be pretty accurate.So I will agree with you that the facts are quite different its just your not getting the right ones.I am not trying to bust your balls but your wrong on this one.

 

[treynor]

Jamie,
I understand what you're saying, but I once again disagree.

Comparing times from different tracks on different days and trying to infer power differences from these comparisons is suspect -- obviously worse than comparing "uncorrected" dyno figures, for instance. By the logic you present, SilverViper's car must be making 350-360 RWHP because he's "only" running 116 in the traps. Similarly, the Porsche 996 turbo which ran that day (12.5 @ 113) must be defective, since C&D got 116 mph out of it in their test, and they don't even speed shift.

Now all that said, I DO agree that 122 MPH seems slow for the power my car's making. The only other time I've been at the strip since my latest round of modifications, I ran 123.8 MPH in a shakedown run (i.e. lazy launch, lazy shifts). However, that run was at Sacramento Raceway, which is usually a faster & better-prepped track than Sears. With a good launch and favorable conditions, I'd expect 125 MPH with my current power levels and weight. It'll have to be another day...

 

[jamie furman]

Well the last thing I am going to say is this, 116mhp is about 375 rwhp if there was more in the car someone left it there and different weather conditions and driver techinques can greatly change the amount of horsepower put down. So you could definately have different horsepower at different tracks thats why they break out jet kits and computers to tune cars at the track in alot of instances.If you only go 125 in the 1/4 mile you only have 500 rwhp. But whatever your mph is thats how much hp you made on that run period.And no the porshe wasn't defective but maybe the drivers abilitys were,so the car couldn't put all of its hp to use or maybe the mag used altitude corrected mph. By the way what are you ets that go with these mph numbers your giving.All the numbers I compared were corrected to sealevel not half and half.