Lower Rev'ing Vipers, Shorter Power band?

[Marv S]

Re: Lower Rev\'ing Vipers, Shorter Power band?

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It is a bit tough to pull 7,500 rpm in an 8.0 litre motor when it has to **** air through straws.

 

[BigsViper]

Re: Lower Rev\'ing Vipers, Shorter Power band?

MARV!!! Buddy!!! What is THAT??!!! You have always been a great help to me and everyone else on this board, but I had no idea what you were hiding under the hood! Details please!

 

[jcaspar1]

Re: Lower Rev\'ing Vipers, Shorter Power band?

Mellow Yellow,
As HP is a function of rpm the only way to have your HP curve remain flat is for your torque to drop off with rpm. As the Viper has a pretty flat torque curve between 3k and 5k the HP continues to increase with rpm, not remain flat as would happen with a car which had reached its torque peak and was falling off.
I would be interested in seeing the dyno curve of a Corvette to compare, can you post your results?

 

[phiebert]

Re: Lower Rev\'ing Vipers, Shorter Power band?

See my thoughts inside your quote...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by MelloYellow:
...but I notice it rev's fairly low and the powerband falls off very fast near 6k.

Is there any downside to this?

[I'm not sure I understand the question as to what would be a downside. You are working with different rpm ranges on different cars but generally the bigger the engine the more torque at lower rpms so you actually have an advantage because your range of power starts lower and you don't have to wind up the engine so high to get the effects.]

I guess you just shift faster and more often?

[Not really, just in a different range. For example, in my Viper with the Nitrous on during drag racing. I am getting maximum torque around 4,000 to 5,500 rpm (a little higher without Nitrous) so I just shift when it hits 5,500 and I stay right in the maximum torque range. Not unlike you shifting at 7,500 to stay in your best range.]

How is gearing in 5th and 6th?

[I can't remember the exact ratios, they are posted in another thread I read somewhere recently though. 5th is your maximum speed gear though. 6th is more for cruising efficiency. If the engine had the power to pull 6th at maximum rpm you would be going over 300 mph, so that's why 5th is the top end gear to use.]

Anyone want to compare this to higher rev'ing cars?

[I sold my Porsche Turbo Cab when I got my Viper. Obviously these two cars power ranges are infinitely different. With the Porsche you need to be much, much more aware of your RPM's at all times to make sure you are in a range of power. With the Viper's massive torque, even at lower rpm's, it's much more forgiving. Although my Porsche was very fast, it wouldn't have stood a chance (except for handling) against the Viper in a slow rolling started street race. For example, in my Porsche I could be beat by a Supra or something like that if I was caught off guard by a guy coming up beside me. That is, if I found myself jsut cruising along at low rpms, by the time I got myself into the power range it was too late. With the Viper, it's much harder to surprise. I can be cruising along at 2800 rpm and if someone sneaks up beside me and punches it, I don't have to even shift to beat him.]


Where are you shifting at and where do you fall in your powerband in the next gear?

[For seat of the pants feel (not necessary true dyno numbers represented in this comment) I find that you can start feeling the serious V10 power at around 3000 to 3500 rpms. I usually don't go above the high 5000's because the rev limited cuts in at 6200 and that is something I try to avoid hitting! So in a usual fun take off I'm shifting at around 5000 and that puts me in the next gear somewhere just under 4000. When I'm in serious drag racing competition trying to get the most out of the car I try to keep the rpms between low 4000's and mid 5000's for peak HP and torque.]

Looks like my new engine may give me some advantage there being able to shift at 7k and land at a nice high flat point on the power-band for each gear. Was doing some comparisons to Viper dynos. My new powerband should stay near flat at 460rwhp from 5.5k-7k.

[If you have a flat power band giving you 460 RWHP you will find yourself very competitive with a stock Viper. The two of you will just be shifting at different RPMS. And I guess some may say that the Viper engine will outlast yours because it is revolving at 70% of the speed on average.]

Thx!

<HR></BLOCKQUOTE>

 

[Marv S]

Re: Lower Rev\'ing Vipers, Shorter Power band?

Hi Don,
That is a factory GTS-R race car that was owned by Az Racer Muzzy earlier this year. He won his class at Phx Grand Am race last spring, co-driving with Erik Messley. Beat out the Saleen and Vettes.

It's an example of a BIG restriction placed on the Racing Vipers.

 

[jcaspar1]

Re: Lower Rev\'ing Vipers, Shorter Power band?

Mellow,
Check out this site . It will calculate the best shift points based on your gearing and dyno curve. I think I remember running my numbers thourgh it once and it suggested shifting at redline in each gear for my car.
Sounds like you will have a sweet machine when all is done!

 

[BigsViper]

Re: Lower Rev\'ing Vipers, Shorter Power band?

Awesome Pic! Especially for those of us not too experienced with race-preped Vipers! Are those trumpet-looking tubes a restriction placed on the car by the sanctioning body? How about that intake plenum and the different ignition set-up. WOW!!Thanks, Marv!