Rich-L79
May 9th, 02, 1:12 PM
I've toyed with the idea of swapping my 3.31 gears for 3.73 gears for some time now. In the end, I've always justified NOT doing so because I don't want to zing the engine on longer drives. With my non-stock sized tires (shorter) I've always been curious how accurate my speedometer and tach REALLY are so I can more accurately determine what I'd be doing to the engine. Years ago I swapped out the speedo gear in the trans to match the tires I run on the street the vast majority of the time so I've always assumed it was fairly close but never really sure.
The car has 3.31 gears and rides on 235/14's. At 60mph the tach reads right at 3000, maybe just a touch below it. I've asked friends I've caravaned with how fast we were going at various times and things seemed to be pretty much on target on the speedo side assuming THEIR speedo was accurate to begin with. This led me to believe 3000 at 60mph seemed high.
The other day while in the Chevelle I approached an awful intersection that has been the site of numerous accidents, many fatal. Now they have set up a sign with radar that shows you your speed and flashes it at you if you are speeding (speed limit 45). Theoretically to allow you the chance to get down to or below the limit before you reach this semi-blind steep down-hill approach to the intersection.
Anyway, if this radar sign can be believed, my Chevelle's speedo dead on with these tires and gears. More accurate than either my truck or my daily driver MR2. I passed through this area about 3 times and every time it was dead on to the radar sign.
Assuming for the moment that this sign is NOT set to overstate speeds to get folks to slow down even more, I have to now assume my tach is off (not surprising) since by using an on-line calculator, my RPMs with this combo should be more like 2650. Even on these crappy 64/65 factory tachs I should be able to clearly read a distinct difference between 2650 and 3000 RPMs.
Okay, I could buy an aftermarket tach to use and test with but I really don't want such an item in my stocker. In the end, is there any way to adjust the accuracy on the factory tach?
Funny thing is, at idle speeds and a little above, the factory tach is pretty accurate to my tach/dwell meter readings so the tach's inaccuracy isn't consistant so maybe I should just leave well enough alone! Of course, this is assuming my tach/dwell meter is correct. Man, what can I trust?! Unfortunately the tach/dwell only reads up to 2000 or I'd hook it up with longer leads and go for a drive and see how things match up.
AND, would running at nearly 3000 rpms at 60mph with the 3.73 gears be unnecessarily rough on my short strokin' 327?
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NCOA member #220 ACES member #1670
Team Chevelle #998 YesterYears Chevys #52949
American Muscle Car Association #142
Rich's 1965 Malibu SS Restoration Project Progress Page (http://www.geocities.com/ticklewiggle/)
The car has 3.31 gears and rides on 235/14's. At 60mph the tach reads right at 3000, maybe just a touch below it. I've asked friends I've caravaned with how fast we were going at various times and things seemed to be pretty much on target on the speedo side assuming THEIR speedo was accurate to begin with. This led me to believe 3000 at 60mph seemed high.
The other day while in the Chevelle I approached an awful intersection that has been the site of numerous accidents, many fatal. Now they have set up a sign with radar that shows you your speed and flashes it at you if you are speeding (speed limit 45). Theoretically to allow you the chance to get down to or below the limit before you reach this semi-blind steep down-hill approach to the intersection.
Anyway, if this radar sign can be believed, my Chevelle's speedo dead on with these tires and gears. More accurate than either my truck or my daily driver MR2. I passed through this area about 3 times and every time it was dead on to the radar sign.
Assuming for the moment that this sign is NOT set to overstate speeds to get folks to slow down even more, I have to now assume my tach is off (not surprising) since by using an on-line calculator, my RPMs with this combo should be more like 2650. Even on these crappy 64/65 factory tachs I should be able to clearly read a distinct difference between 2650 and 3000 RPMs.
Okay, I could buy an aftermarket tach to use and test with but I really don't want such an item in my stocker. In the end, is there any way to adjust the accuracy on the factory tach?
Funny thing is, at idle speeds and a little above, the factory tach is pretty accurate to my tach/dwell meter readings so the tach's inaccuracy isn't consistant so maybe I should just leave well enough alone! Of course, this is assuming my tach/dwell meter is correct. Man, what can I trust?! Unfortunately the tach/dwell only reads up to 2000 or I'd hook it up with longer leads and go for a drive and see how things match up.
AND, would running at nearly 3000 rpms at 60mph with the 3.73 gears be unnecessarily rough on my short strokin' 327?
------------------
NCOA member #220 ACES member #1670
Team Chevelle #998 YesterYears Chevys #52949
American Muscle Car Association #142
Rich's 1965 Malibu SS Restoration Project Progress Page (http://www.geocities.com/ticklewiggle/)