Gear change comparisons

[Steve 00RT/10]

I know this subject has been well covered and I have read most of what's been posted.......but is there anyone who could, through formulas, post a graph of gear ratios(3:33,3:45,3:55)on a Viper going from 0-150 MPH similar to the web page listed below? Even better if time could be included. From what I've recently read, it seems the most bang occurs up to about 65 MPH. Then the stock rear end starts to approximate the lower rear end. That is what the below information seems to say.
Gear chart

How would an individual car's HP & torque be factored into the equation? I'll be swapping mine out in a couple months and am still a little confused about the best way to go. 1/4 miles are not the ultimate goal. Xcrossing and track stuff appeal to me more...along with dusting a few cars in everyday driving.

Steve

 

[GR8_ASP]

Steve,

Look at the graphs below. Is that the type of info you want? If so I can modify it for your dyno curve and data without too much problem.

The curves are for the SRT and the tire diameter is the biggest difference. Your cars performance wasn't that much different. The graphs were from my dyno test in the spring before I changed out the exhaust.

 

[Steve 00RT/10]

Hi Ron,

Yes, I believe that's part of what I would like. I'm also wondering which ratio gets to 100MPH first...and on up to 150..first? The web page I referenced seems to show the lower gears dropping off in performance after 65 or so. I don't quite follow that.

Do you have my dyno runs from last spring? I got a floppy that day, but was never able to make it work. I can send you a copy of the sheet. I topped out at 438&480

Thanks--Steve

......snowmobiling tomorrow.

 

[GR8_ASP]

I don't have your runs but if you still have the file you can email it to me.

And yes you can calculate time to distance and all of that. Since I have 1/4 mile data on my car in the same state that the calculations are from it is straight forward to compare and make adjustments. If only I had enough time to do everything I want to. But given the snow and cold I may have more time on my hands then I wanted.

 

[Steve 00RT/10]

I recently rediscovered a software program which I had played with many years ago in a DOS format/demo version. I found the site again and this time bought the program. Assuming the model is correct, it basically answers anything you want to know about gear ratios,ET's, top speed..the list and combinations of what you can do is endless. There are over 1400 cars(and 50 road race tracks to play on) in the initial database including several Vipers. You can do side by side comparisons with as many cars as you like. You can add your own car and input about 50 different car specific parameters. You can also plug in your own HP and torque numbers in 500 RPM increments. I created cars with my dyno numbers and several different gear ratios. Interestingly enough, the standing start acceleration numbers bear out the info from the David Atkins chart above. 0-150 times are within a couple seconds of each other. Where the difference occurs the most seems to be in 2 places. The time it takes to achieve top speed and runs up from specific speeds in various gears. Here is where the lower rear ends have an advantage. Especially time to top speed. You can have the program optimize your launch RPMs per your car specific parameters. It can also recommend optimum shift RPMs in each gear based on your cars info. There's lots of other 'stuff' you can do with the program in addition to the above.

Has anybody else tried this program out..and/or have an opinion on it?

Steve


Car Test 2000

 

[BruceW]

These graphs don't agree. If a stock rear (3.07) car is doing about 3,000 lbs in first then a 3.55 rear will give about 3,470 lbs (not over 3,700 as the second graph shows).

 

[Big Medicine]

I thought they were measured thrusts.

 

[BruceW]

If they are measured thrusts then this is saying that the 3.55 gear has a significantly lower torque loss. I find that hard to believe.

 

[Steve 00RT/10]

These graphs don't agree. If a stock rear (3.07) car is doing about 3,000 lbs in first then a 3.55 rear will give about 3,470 lbs (not over 3,700 as the second graph shows).

The above charts are not the program I'm using. Looking at that same criteria in the Cartest program, and with my numbers plugged in for HP&torque, I show the 3:07 gearing at 3657 and the 3:55 ar 4236

Steve

 

[BruceW]

Those numbers make sense.

 

[GR8_ASP]

Bruce good catch. I just checked and when I quickly made the 3.55 I left out the efficiency differences between gears. 4th gear would be the same but others were off. I have corrected them and will try to change to graphs (originals).

 

[GR8_ASP]

Couldn't change the originals so here they are. Sorry for the confusion.

 

[jrkermode]

Steve00RT10,

If your goal is road racing or autox, you'll want to be more focused on when shifts occur rather than overall acceleration. You don't want to be shifting during corner exit. It would also be nice to avoid an extra shift just before a braking zone. So, your gear selection will be based more on the track specifics, than some theoretical "best".

 

[Steve 00RT/10]

If your goal is road racing or autox, you'll want to be more focused on when shifts occur rather than overall acceleration. You don't want to be shifting during corner exit. It would also be nice to avoid an extra shift just before a braking zone. So, your gear selection will be based more on the track specifics, than some theoretical "best".

Your point is well taken and presents a conundrum of sorts. You can't have it all ways. I think for Solo 2 xcross stuff, a 3:45 would work well. I know the lightened flywheel did for that purpose. However for road race tracks, you are definitely at..or past.. the shift point into 4th, at least the 2 tracks I've been on. I played with the software program I bought on several tracks, from tight ones to longer ones, there appears to be no distinct advantage to the different gear sets on a road track--at least for a novice like myself. As I will only ever see 1 or 2 tracks per season, but will likely do several xcrosses per year, I am leaning toward a rear end mod this spring. I think I would buy the entire assembly. This would allow me to swap out rear ends relatively easily.

Thanks for the input.

Steve

 

[joe117]

How fast do you go in a typical autocross these days? Do you need to shift at all?
I haven't done an autocross in more than 40 years but I remember them being tight courses where they tried to make sure folks didn't get going too fast.

I changed to the 3.55 from stock just so I could use all the gears. The bottom end of 6th was just too fast for almost all of the driving I do. No big highways within quite a distance.

I don't like to see the engine at much less than 1500rpm and that was about 80mph with the 3.07 rear. Others might lug around at lower rpm but I don't like it. If I take a trip on a highway and folks are going 80-90mph, I still find 6th to be a very comfortable gear with the 3.55.

 

[Steve 00RT/10]

How fast do you go in a typical autocross these days? Do you need to shift at all?

I think the rule of thumb for many xcross courses is that 2nd gear pretty much works most of the time in a Viper. That's why having a little more grunt with a lower gear should be helpful when coming out of a sharp corner. I have tried it both ways and found it easier to be smoother in only one gear. I did do one this past fall that had a very sharp corner followed by a right angle corner that you exited at about 10MPH. I did go to first there. The airport runway we used the last couple years would get me up to 85 or so crossing the finish line. That was at the shift point for the stock gear.

Steve