Here are the gear ratio of some other performance cars…
Ford GT- 6th .625 with a final drive ratio of 3.36 (265 mph)
Dodge Viper. 6th .50 with a 3.07 final drive (318 mph)
Chevy Corvette 6th .57 with a 3.42 final drive (244mph)
None of those cars will ever be able to reach the speeds that the gearbox ratio is capable of. So why did Ford, Dodge and Chevy waste time and money setting them up to run that way?
Why don’t you go and get a job at one of the big three? It seems you know a lot more then their engineers do. At least you should give them a call and tell them how much you and Lloyd are laughing at how stupid they are, maybe then they will fix their flawed gear ratios.
Or maybe you don’t really have a clue after all. Did it ever occur to you that large V8s (and V10) don’t like high rpms? Did it ever occur to you that cruising on the highway at over 3000 rpm is not very desirable for v8s? Apparently it occurred to Ford, Dodge, and Chevy, but I guess that fact is still eluding you, which is why you’re not working for them.
Just out of curiosity what trans and ring and pinion are you running in the cobra in your sig? Hopefully it’s not one of the Tremecs with that big overdrive 5th (or 6th) otherwise you might get labeled as a hypocrite.
Just so you know if you cant tell by the tone of my post I think your post was a little rude to Spyder Mike…
You raise some valid questions.
The big manufacturers put massively tall gears inside their transmissions because they are deeply concerned about fuel economy. The government has CAFE (Corporate Average Fuel Economy) standards which they, as a corporation, must meet. Recall that GM puts skip-shift in their manual transmissions, even in the Corvette, where they will automatically shift directly from 1st to 4th gear unless the computers sense a certain level of throttle demand. This is another instance where the engineers have introduced a horrible idea (from our perspective, as performance drivers) and sacrificed driver control to meet bureaucratic necessities. Does anybody here really think that this is a good thing, and would you want your GT40 to be equipped with this GM-engineered ‘feature’?
Too, many new car customers like to cruise long distances at extremely low rpm, so a tall highway cruising gear is pretty much standard equipment on most cars now. In most cases, there is a HUGE jump between the first four (or five) gears and the single, tall overdrive top gear. Too, they tend to put extremely low gearing on the lower gears, so that the car will be able to get out of its own way when it is launched. My first experience driving such a car was with a 5.0 Mustang; first gear was so deep that you had to shift before you got halfway across the intersection, yet fifth gear was so tall that you could get decent gas mileage, and cruise on the freeway at 2000 rpm or so. It was far from optimum for performance driving, but it worked okay on the street.
It felt pretty weird to me, as most of my driving experience was with Panteras (my Pantera was my first car, purchased as a beater at age 22; prior to that I had only ridden sport motorcycles, which may have shaped my opinions too). Both the Pantera and the motorcycles had close-ratio transmissions.
Big V8s don’t like “high” rpms, but 3000 rpm isn’t “high”. In fact, most aggressive camshafts don’t even ‘turn on’ until something above that number. Remember too that during the 1960s, most musclecars were equipped with 4:11 ring and pinion gears, and a 1:1 top gear. They were engineered to last forever spinning quite a bit faster than 3000 rpm on the highway. It wouldn’t necessarily be pleasant on the freeway, but that wasn’t their mission.
When I bought my GT350 clone, it was equipped as Shelby had built them, with a 3:89 rear end and a four-speed toploader with 1:1 4th gear. It ran great, but it did drive me a bit crazy, and as I intended to do a lot of long-distance driving in it, I changed it to a 3:25.
It has a close-ratio gearbox, which made the idea of launching from a standing start laughable at that point. Until it gets rolling, it really doesn’t go anywhere in a hurry. The tall rear end also screwed up its racetrack performance; I found that at Sears Point, Laguna Seca and Thunderhill, I would normally be one gear lower than anybody else on the track in any given corner, and they would kick my butt on corner exit even though I had decent horsepower. However, it was a compromise I was willing to make because I drove so many freeway miles in it.
In retrospect what I really should have done was convert it to a 5-speed and kept the 3:89 (or perhaps a 3:50; I haven’t really considered the question carefully yet), since I took it to Europe for a few years and ran it on their tracks (Spa, Nurburgring etc.) which are typically much longer and faster than ours. I found on the slower bits I was faced with the same performance problems as I was in the USA, but I would still hit 6000 rpm in 4th gear on the straights and then just buzz along, needing more/taller gears. But if I did put a five-speed in it, I would not keep the stock T5 gearing (with a super-tall 5th cruising gear), opting instead for something in the .080 range so it would be a useable gear on the track.
The point I’m making is that I know first-hand about making compromises in gearing choices, and in fact I have suffered to varying degrees because of the choices I have made. My goal here is to keep people from inadvertently doing the same thing.
You asked about my Cobra replica—it has a close-ratio toploader and a 3:54 rear end (it came to me that way). It has a 569 hp 427 side-oiler, and spins about 3500-4000 rpm when I’m cruising with freeway traffic—arguably too high. It is top-speed limited by the low-ish gearing (which, by the way, is exactly the same gearing they originally came with). However, it is positively electrifying on a back road or a race track. I think I get up to about 5500 rpm in 4th gear at Thunderhill on the front straight—perfect for a big block. And it’s pretty damn snappy on the freeway too; no need to downshift that puppy, just flex your ankle and you’re GONE.
Gone, that is, until you reach 130 mph or so, and then you’re just making noise on the rev limiter while the Mercedes or whatever whooshes past you. :>)
My Pantera (and thus ZF) track-driving experience is limited; even though I’ve owned it 17 years it’s been in bits for most of that time. I have only driven it on one track (Spring Mountain, in Pahrump NV), which is very tight and technical, mostly 2nd and 3rd gear; I only got partway through 4th gear (with a 4:22) once per lap, and that track is strictly a 2nd/3rd gear proposition if the gearbox had a 3.77 in it.
With respect to the SPF cars, by looking at my initial and second posts you will note that I originally failed to realize that 1st-3rd gears were considerably lower than original, which would restore much of the performance that would otherwise be lost by fitting a 3.77 ring and pinion. Too, a 500+ hp big block can tolerate taller gears than a smallblock can.
I’m sorry if SpyderMike took offense at what I wrote, or if anybody else thought I was being rude. I meant no offense or insult to any individual; I’m just offering a bit of a reality check about gears. When I consider a GT40, I tend to think of it strictly as a driving, performance car, i.e. an open track or backroads car. I recognize that other people might have other thoughts in mind for theirs, i.e. long-distance touring, or just cruising to the local hot rod café, and if that’s the case, then for them, gearing which provides relaxed highway cruising is a higher priority than outright performance.
So let me qualify my earlier statements and say that IF you are primarily looking for supreme dominance on an American racetrack, or IF you bought the car principally so you could enjoy driving it on twisty mountain roads, and IF your engine is capable of spinning to, say, 6000 rpm, and IF you are equipping it with standard-height (26 inch) tires, then you would almost assuredly be better off and happier with a Pantera-spec gearing setup, i.e. 4:22 rear end, and a closer spacing of all five gears with a 2.23 1st and a 0.705 5th
But, if you are putting 24-inch tall 345/35-15 tires on the car, or if your big block runs out of puff (or wants to come apart) at anything about 5000 rpm, or if you plan on driving hundreds of freeway miles on a routine basis, or if any number of other variables, then perhaps more relaxed gearing would suit you better.
Ultimately, I hope that everyone will consider the question carefully, and actually get the kind of gearing that suits THEM and their individual needs and desires, rather than just going along with the herd. If you haven’t already purchased your gearbox, take my advice, and Dennis’ advice, and Lloyd’s advice, and spend some time with the gear calculator program, and consider the performance characteristics of your chosen engine, then YOU make the decision that’s best for YOU. That way, you can guarantee that you’ll be as happy as can be, and you will enjoy your car to the maximum extent possible.
And isn’t that what it’s all about?