The Dodge Challenger Message Board

Oh you did get back to me did you Dave?..
Can't remember having seen that mail...Ohh well.......
The overdrive;.......best fun money can buy!!!
I was practising my "rapid fire gear exchange" all summer 2001. Of cource we went to Power Big Meet in Sweden, and quite a few other places.
With my "new" (2'nd hand) P275/55R15, and my Hijackers=liftback filled to max airpressure, I managed to ruin my limitedslip. Suddenly only one tire were smoking, when doing piruettes with the car all filled up with people.
I managed to persuade my wife, to spend an afternoon getting "new" parts, on our honeymoon when passing San Francisco early this year.
I still regret using all that money (parts/work), just so that BOTH tires will be smoking next time I get the chance to use car.
2 years until next time........

OVERDRIVE details...
I've got a few pictures of how it looked after the installation....used an angle grinder on the OD to get a few more mm clearence,...and just to be on the safe side, I used the hammer on two places on the car itself.
Apart from the INSANE sound of the 440 running through the gears like a motorbike, the noise level at cruising came down A LOT. And of course,....whenever passing a car,...you can shift down twice (even 3 times..)
OOhhh what a nice sound.........
I still have'nt been able to measure the fuel consumption after the installation.....
Too many people are quite off the target, when discussing fuel consumption. There are MANY things to consider, and unless you have the correct tire size, gear-ratio, to go with your odometer, you can really be far FAR from the truth.
"The more power you have, the more you use" rule also applies.......
I've heard comments like "Those wide tires of mine are increasing the air-drag so much you will not believe the impact on the fuel consimption"......If you try to explain the difference on tire diameter,...they don't believe you......He he...
My suggestions to those of you who have a "friend" bragging of how little fuel his ride are using,......Go cruising together (in seperate cars).....fill up before you start,....and after you've finnished.......THEN COMPARE !!!
Of course,....if you want to win this little competition,...stay off the accelerator,....and make sure your tire pressure is 'up there"....
5 km to 1 litre?!?......acceptable to me !!!!
By the way,....I have a REALLY nice picture of a car-wreck I spotted in Washington State,....not a Chally,...but a MOPAR still....wanna see it?

NO! I don't want to see a wreck. Unless it is funny in some sick way.

How much power does the manufacturer say you can safely put through one of these overdrive units? Will it take 550-650 horsepower?

You get best fuel consumption figures from any engine trans combination at the same rpm as peak torque. That is physics. You can't change that.

With the overdrive unit you cover more miles per rpm that is true. But if your engine produces little torque at the lower rpm you are running at it is actually possible to get worse fuel consumption!

However in the case of a stock or near stock engine (like yours) it will be a great benifit as peak torque will be around the 2800 to 3200 rpm mark and it drops off over that speed.

My engine makes HALF the torque at 3200rpm than it does at 4400rpm. So if I was not careful I could find that the advantage of getting more miles per rpm is outweighed by the increase in fuel consumption at that rpm.

It would be a pain to work out if there was an advantage in a case like mine or not. But far from impossible. There are many factors to take into account. And anything that could make getting to a race track cheaper would be welcome. But not if it broke as soon as the slicks go on.

In real life, you also have to consider that different cars have different drag coefficient....
(I am not an expert in this field, but I think you know what I am getting at, Dave.)

And Challengers have HUGE drag. BIG vaccumn at the rear lights trying to suck you back. The T/A style spoiler in fact helps reduce the drag at the rear quite a bit.

The 1970 model in particular had a lot of front air resistance and lift at speed because of the air pressure in that grille area under the front of the hood. You can feel the steering getting lighter the faster you go. The later more flush style grille was much better.

Fat tyres create rolling resistance. The lower the air pressure in them the worse it is. Skinny hard tyres are best for good mpg figures. Put the slicks on my car (only 10lbs of pressure in them) and try to push it along a flat road. It is twice as hard to get (and keep) rolling. But I would say that pressure is more important than width when it comes to drag. So I use 33lbs in my fat tyres on the road at the moment.

Hi Dave. Check out all the coverage in different magazines on the manufacturers home page... http://www.gearvendors.com/articles/

I quote..."and in standard form can handle 1,200 horsepower, or modified up to 2,000-plus horsepower. "

Regarding fuel consumption....
Don't forget...The efficiency curve (hook-curve) for an engine,.... your rigth that it coinside with the peak torque RPM.
However, the values for your Torque vs RPM are mostly given at WOT (Wide Open Throttle).
What is needed, is comparison BETWEEN DIFFERENT throttle settings (not RPM settings),...when generating a spesific torque....the torque needed to keep your car cruising at YOUR SELECTED speed.
I prefer to go on the fast side of 100 kmh....
To force your RB engine to operate at high RPM with the throttle only a tiny bit open,...don't appeal to me.....Don't think I've ever come across anyone that would NOT swap for a 2.73 ratio if it was'nt for the lack of acceleration it would lead to......
In any case,..I hope you get one of these toys....The sound of a big V8 running through 6 gears as rapid as a motor bike....PRICELESS !!!
Better performance, less fuel, less wear on engine...(Ooops...I think I was repeating the propaganda here...he he...)

How aboat making this a "technical" chapter on Overdrives to go on this board?
Anyone else with experience on using the Gear Vendor OD ??

I Loooove it !!!!!
I must however, admit it kicks harder than the shift kit tranny,....as you engage the thing at WOT.....
Yes..it IS designed to shift at WOT....

kW I meant, not Torque.....sorry..
The kW needed to keep your car at cruising speed...(some more kW will be needed at higher speed due to drag et...)
With reference to my last mail,...what one should have is a hook-curve for same kW, at different RPM settings....(requiring different trottle settings as well to keep the kW=hp at same level)
I feel pretty confident that such a curve would NOT favour any engine operating at high RPM with the throttle "closed"....to the same engine operating at lower RPM with the throttle more open.......ofcourse race engines are a bit of a special case....
How I would LOVE to see some comparable curves...

Yes folks. He does have a degree in mechanical engineering. How jealous am I? Very!

I just checked out their web site. Very impressive. I want one!

But too expensive!

$2500 is a LOT of money. For that I could fit a procharger and run 9s on the strip and sod fuel economy.

But it does make a lot of sense to use one. I could run 4.10 rear gears to improve my 60ft times and still have a higher top speed. 6 gears eh? Mmmm.

How do you shift gear in your particular application Johannes? Do you use a manually operated electronic switch or some form of automatic device?

Well, Dave..... when ordering the OD, they ask for your rearaxle ratio, and tire size....
You get a little device that goes between the original speedo cable, and the small extension cable they supply.
It's an speedo RPM pickup, and gives signal to a small box you place somewhere under your dash.
This boxed is tuned for your automatic upshift.
This box also connects to a switch for manual operation (I selected the most commonly used type....the headlamp-dimmer-type switch="ligth switch"...) I placed my "ligth switch" on a bracket that used to have a foot pump for the windscreen washer fluid....
Why did my Chally have that footpump in the first place???? Perhaps it came with such a pump??? I did'nt see the pump before I started looking for a place to put the "ligth switch".....

A nice little "control panel" with ligth indication (OD engaged/disengaged) also has a switch....AUTO/MANUAL.
Everything so fare is included,.......a standard splined yoke to fit the OD is also supplied

You need to have your prop-shaft shortened,....and you must then fit the NEW splined yoke to the shortened shaft.
This requires a new fork(?) and a new (bigger)U-joint...NOT SUPPLIED.

When driving in AUTO mode....MY car goes
1,2, 2'nd over, and 3'rd over (4 gears)
Down shifting can be a bit rough.....in auto mode.

In MANUAL MODE, the OD is ALWAYS disengaged when you start driving. You can then engage/disengage the OD by pressing the "ligth switch".

The "ligth switch" INSTANTLY changes OD (on/off).....so if your gear-upshift is a bit slow,.....it gets HARD to correctly time say 2'nd over-----3'rd.....
If the OD downshifts before the 727 upshifts....you go from 2'nd over to 2'nd.......
an increase in RPM by 22% (Or was it 28%)

Read the articles in Gear Vendor's homepage....

ANYWAY....the "Over Drive" stickers supplied by Gear Vendor,.....are not so cool......
If ANYONE can think of any OverDrive-badges/stickers that can match the rear of the Chally,...PLEASE let me know...........The badge on a TRIUMPH SPITFIRE is nice,.....but the letters are a bit large....

Thanks for that info mate. I must admit to being very interested. If only it were cheaper.

As for that foot water pump. That is because your car came with the standard dash. Us people with real 440 R/T cars got the rallye dash as standard which has an electric windshield washer on the wiper switch.