Contour Enthusiasts Group Archives Forums Modifications Duratec Performance can i get a shorter (numericly larger) gear my svt?

In my humble opinion shorter gears would be a waste of time unless you were going to do some other modifications as well. The final drive is already very low at 4.06. The 4 cylinder cars are actually slightly taller, I think about 3.9.

Shorter gears are best used with engines that have greatly improved breathing including much, much, much wilder cams as well as bottom end (rods and crank, etc.)improvements that would permit raising the rev limit to well above 8,000 RPM. When cam changes and breathing raise the power band into a much higher RPM area, shorter gears help you to get into that power band quickly.

Using shorter gears without matching the rest of the powertrain can make the car actually perform worse and make it much more unpleasant to drive.

Trust me, I've been there. I once had a small block Chevy that I experimented with engine improvements and gear changes. I tried 3.00 all the way down to 5.18. I ended up with 3.70 as the best all around street usable combination with a moderate cam.

Since there is little or no availability of hotter cams and the need to move to stronger rods, I just don't see shorter gears as accomplishing anything on our Contiques. They run great the way they are with little or no modification.

Also, it was an easy thing back then to change gears. You would just find the correct ratio in a wrecking yard or swap meet complete with the entire third member differential and it could be swapped in about a half hour. Much bigger job requiring more expertise on our cars.

Jim Johnson
98 SVT

get a superchip and a 45 series tire on the stock wheel and your speedo recalibrated...you will be happy..

The manual gearbox on the Contour is a 4.06:1 ratio......that is an excellent ratio for acceleration. The automatic gearbox is 3.92:1 which is also excellent. I don't think you need a different gear. For Mustangs you can get up to 5.30:1 (for killer accleration) or all the way down to 2.90:1 (for high top speeds). But those are for highly modified ones with TONS of HP.

Hey Bret, related to what bill said about the 45 series tire..
I just used a tire calculator. Using a 225/45/16 tire & compared with 215/50/16 on the 99SVT, the tire height goes from 24.46" to 23.97". This would increase the final drive ratio from 4.06 to 4.13. That plus a bit less radius inertia should get a quicker 1/4 mile. You'll still have to shift to 4th but you'll get there quicker. Also a bit less sidewall height = less flex = a bit better handling too. Speedo would read only 2.5 MPH higher at 100MPH. Only downsides I see are a bit more fenderwell gap (.25 inches) so this would work best with lowering springs.

what if i went with like a 245/40/17 : )

where are you getting this calculator from?

I think this is a very good idea actually. I'm planning to install some 225/40-16 tires on my Cougar with some light-weight 16x7.5" rims. I was actually contemplating 205/40, but I'm afraid that their load rating is insufficient for a 3000lb car.

Glad you guys mentioned tires, as I've been meaning to post about my recent experience. I acquired a set of used 16" wheels with Yokohama A520 205/50/16. Some of you already know that the proper size for our cars is 205/55/16, so the Yoko's that I have are 3.7% smaller in diameter. This effectively raises the final drive from 4.06 to 4.21. And I will tell you, the difference is quite noticeable.

The first thing I noticed was the increased effects of engine braking while coasting in gear. This really confused me at first - the car was slowing down more quickly when coasting however when accelerating hard it felt faster. The second thing I noticed was that I could use 5th gear in city driving and have it pull smoothly from as low as 1500 RPMs (whereas before the tire change it would lug). And on the highway there is more responsiveness.

The downsides of doing this are as follows. Firstly, your speedo is going to be off (by 3.7%) however this is not that big of a deal IMHO. Just remember that your speedo is reading a couple of MPH higher than your actual speed. Secondly, since the RPMs will be higher for a given speed, highway mileage will probably go down. But, in the city it should stay the same or even improve due to greater use of 5th gear. Lastly, an aesthetic issue - there is going to be more fender gap. This is more of an issue on cars without side skirts. The remedy for this is to get lowering springs and/or install side skirts. Or just not worry about it.

By the way, the Yokos are sticky enough that I can launch @3k RPM without wheelhop and minimal tire spin. Too bad they wear so quickly!

Glad to here that this worked for you. Now I'm definitely going to have to give this a shot the next time I need tires.

Now please excuse me while I go spend the afternoon doing donuts in a parking lot

Gerald - thanks for the post.

Besides the gearing change, I'll offer up my $2(consultants .02) on another reason why you are seeing better acceleration with the tire change.

In a word - leverage.

Fact is, tires are heavy, and the energy required to change their velocity is a function of the torque moment of how far the weight is from the center of the wheel.

Make sense?

Dan

Yup, except that I don't think the moment of inertia per wheel/tire went down with the new setup, even with the 0.75" decrease in overall diameter. The reason being that the new wheels/tires weigh a lot more than my old ones. I went from the stock 15" wheels with Firehawk tires to 16" Cougar wheels with Yokos, and the 16" combo weighs around 12lbs more per tire/wheel than before. These Z-rated tires sure are heavy.

Also, I suspect that the force required to overcome the moment of inertia of the tires is not that significant when compared to the force needed to accelerate a 3000lb mass. One of these days I'm going to try some calculations..