Toploader and Rear Gear Questions
 

What is the best choice for a Toploader? Close or wide ratio? It seems that both have the same 4th 1:1 so why would you choose one over the other? What about the rear gears. In the ERA manual it describes the close ratio has a faster mph/rpm for all gears. Isn't that what you want or does it make it slower off the line?

Catch ya later
Ed

It's a toss as to what you prefer. The TopLoader will handle up to 1000 HP ( as I understand it ) but has NO overdrive. So the last ratio is 1:1.

If you have a good supply of power and are more into highway acceleration, you might want to keep the rear end in the 3.23 to 3.55 range. If you want to push your mate into the seat, try a 3.89 to 4.11 ( or more if you do not mind the very high Rs you will turn to drive ).

This is a "think about what you are going to do" question.

Personally I run a 3.5 Posi 9" rear with a BIO close ratio Toploader.

Just my $0.02

The close ratio has a higher low gear so depending on the torque of your motor, steel or aluminum flywheel, rear gear, etc. you may like it or you may not. The close ratio works a little better for for downshifting on short tracks the wide ratio will hit the rear tires if your not careful. It really depends on what you are going to do with the car.

Brent

You have to assess your use of the car in primary (most common) driving style. Example, with a 3.31 rear end, 50 aspect tires and 15" wheels with a close ratio trannie (I have a 2.32 Toploader), you may NEVER get into third gear until 60 MPH or so. RPMs at 30 MPH in 3rd would be a boggy 1600 and 40 MPH would be 2100.

Meanwhile, if you had a 4.11 rear with the same close ratio trannie, 30 MPH rpms in 3rd would be 2300, and 40 MPH in3rd would result in 3100 RPM. If you know your engines torque curve you can then figure out which trannie and rear end combo would get you into a sweet spot for your primary driving style.

Here in CT, I do alot of cruising on back country tree lined hilly and curvey roads and having my RPMs UP is nice and in the sweet spot of my torque (2800 to 5600) where it is flat at 435 to 485 Lb-Ft range .

Also, when you step on the gas with a 4.11 rear ratio, you just are subserviant to the massive G force. A true rush and a half. Another benefit is you get to shift up and down more. I suspect with the 3.31 rear end I would virtually never get into 3rd gear in the city or below 50 MPH.

You are probably wondering how I got that data??

There is a great program you can download called RPM.
It is located at www.gearzone.net and was written by Paul Blaccard. It is a really nice tool. He also has a great article that explains wide and close gear ratios in Trannies.... http://www.5speeds.com/ratios.html

You get to enter in your trannie, its gear ratios, Wheel size, tire aspect, tire width, rear end ratio and then by choosing a speed you see the RPMs you should theoretically experience in each gear. You can compare two different sets of data as well.

One tip, I am running 305-50-15 tires on the rear of ERA375. The program tends to not work as well with the wide tires. So I found that if I chose 205-50-15 then the results were just dandy.

I made a nice Excel spreadsheet to store the data.

Gears across the top and MPH down the side and the intersecting cells have the expected RPM.

Fun.

Here's my impression:

I run a 3.54 w CR. I really like the long 1st and 2nd (especially first, about 60 mph). As mentioned they are taller than the WR gears (hence, close ratio--all gears are more closely spaced).

With that said, if I had my choice, I would do a 3.31 with a WR. I understand the ratios work out about the same, but of course you get the benefit of a lower rpm at cruising speed.

My cruising rpm is about 3400. Something to think about.

I am thinking of ordering my ERA with a WR Toploader and a 3.07 rear.Engine will be a 428,approx. 400-425 h.p.,probably at least the same on torque.Engine will be tuned more for torque than upper end h.p.,since I don't ever intend to race it.I guess what really got me thinking this way was the posts on noisy sidepipes on long trips at cruise speeds,and the 3.07 final ratio should keep the noise down.Art,thanks for the gearzone site!Sounds like just what many of us need to help us finalize our orders.

Gary, you may want to rethink the 3.07. I think you will lose a lot of that "seat of the pants" acceleration for a few hundred RPMs reduction in cruise mode. Just my 0.02

Shaps

The advantage the CR toploader has over the WR is it has about 250 less rpm drop between gears. Keeps the engine more in the power band, but not by much.

A CR toploader with a 3.54 rear will be comparable to a WR with a 3.07 rear. Starting in 1st will be the same. In fourth, the WR will be cruising at about 400 less rpm's at 65mph.

From a dead stop, both will accelerate about the same, by seat of the pants feeling. Only while cruising in 4th, with just stepping on it, you may notice a little slower pick-up.

If you decide on the CR, get 3.54 rears. You won't be disappointed. If you go with a WR toploader, get 3.07's, you won't be disappointed. Unless you know exactly what you want, stay with these ratio's. They are good all around ratio's for a BB cobra.

Gentlemen,thanks so much for your feedback.All these agonizing little decisions to make(but half the fun!)Ed,I hope to be in line behind you real soon at ERA. Gary

Thanks for the info guys! What will be the best setup for the street & a little drag racing. I guess I am looking for what is quicker off the line. Hopefully the engine will be a 427 with a tunnel port.

Catch ya later
Ed

Tire width has nothing to do w/ final drive ratio. Only tire HEIGHT. If you're really using the calcs for a 205/50 tire, then the numbers are wrong. There's about 4" difference in height between a 205/50 and 305/50 on 15" rims.



Both would be exactly the SAME in 4th, since they both have 1:1 ratios in that gear.

Hi Wade:
Exactly. As mentioned in my previous post, I had to fudge the tire from 305 to 205 to get the "real world" number for my car. Why that is, I do not know. Nor do I know if a 205-50-15 vs a 305-50-15 has the same Outside Diameter.

Cheers

Hi Gary:
Next time you are planning to visit ERA and Connecticut, please let me know a few days in advance. If the weather is nice I can bring #375 over there.
Cheers..

Ed:
Here is a gear ratio calculator that might help illustrate what different GR's and Final Drive ratios will produce. Theoretical values only but good for comparisons.
http://www.xse.com/leres/bin/gearrat...mference=80.68

DonC

Thanks Art in CT!I just might take you up on that offer.My niece graduates from Tufts next year,and we will probably come back for that, and visit ERA at that time.I have been so busy at work that I haven't had time to finalize my order with Peter,but hope to be able to do that this week(some things in life you just can't or don't want to rush,and this is one in which I intend to thoroughly savor every moment!)Thanks again!Gary