Had a gentleman call me last night and he has a 68 XR7 with a 4-speed manual in it. Says it's the original tranny and been rebuilt once. I have never actually driven a manual transmission car that old. Just wanted to get someones impression/experience/opinion on them. The 3 speed automatics are loud and have me rocking forward sometimes to help it into 4th gear (don't know why I do that) Is having a 4th gear quiet the tranny at all? I know that they are wide ratio which of course is not ideal for muscle cars.
4-speed xr-7
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Unless you are using Gear vendors overdrive a 3 speed only has 3 forward gears in a automatic . Manual transmissions can have a gear growl if there is wear , or a dry gear . The wide ratio was intended for smoother highway driving , you can how ever change this ratio to fit the drivers needs . Rev it up and dump the clutch like you stole it .
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A lot has to due with the final ratio's - depending on which rear gears it has as to how many RPM's you are turning. "quiet" is open to a lot of interpretation too....that being said my AOD sure made a huge difference on highway comfort and brought the RPM's down to about 1800 at 65....not that my car is "quiet" with headers and performance muff's....
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My 70 XR7 4 speed makes a little bit of noise if I accelerate out of 2nd gear but way low in the gear. Noise goes away after I get firther into that gears power zone. That being said, my 2006 Z06 also has a low end growl in first gear which I found is common from other Z06 owners.
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Engine RPM (and engine noise) in top gear will be exactly the same for a 4 speed manual as for a 3 speed manual, since both have a direct (1:1) output. A 3 speed automatic (C4, C6, FMX) also has a 1:1 top gear, but because the torque converter never locks up completely, engine RPMs will be somewhat higher at a given speed than with a manual. The transmissions themselves, whether automatic or manual, should be essentially silent. Noise (other than perhaps a slight whine under acceleration) is an indication of a dry bearing, a worn gear or some other non-normal condition.
With a small block engine, the wide ratio toploader is actually preferable as a performance gearbox in most situations, as the extra torque multiplication helps noticeably with acceleration. The main exception is road racing, where its desirable to keep the engine RPMs in a high and relatively narrow band, and running steeper rear gearing than what would be acceptable in a street car is the norm.
Close ratio gearboxes also make sense behind torquey big block engines, since they don't need the extra gear multiplication. But the "big-input" toploaders used behind 427s, 428s and 429s were all close-ratio from the factory, so it doesn't sound like you're dealing with one of those.
With a small block engine, the wide ratio toploader is actually preferable as a performance gearbox in most situations, as the extra torque multiplication helps noticeably with acceleration. The main exception is road racing, where its desirable to keep the engine RPMs in a high and relatively narrow band, and running steeper rear gearing than what would be acceptable in a street car is the norm.
Close ratio gearboxes also make sense behind torquey big block engines, since they don't need the extra gear multiplication. But the "big-input" toploaders used behind 427s, 428s and 429s were all close-ratio from the factory, so it doesn't sound like you're dealing with one of those.
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