posted by
someone claiming to be drew b.
on
Sat May 24 06:09 CST 2008 [ RELATED]
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For what it's worth, the large tach in my 93 automatic shows idle with a/c off at about 800-900 rpm. 50 mph is right around 2000 rpm (overdrive on). This is consistent with what I've seen in my father's manual 850 in fifth gear, 2000 rpm = 50 mph. Though, I guess I probably have a different rear end ratio than you, and of course no fifth gear.
650 rpm sounds low for idle speed to me. My large tach has three screws on the back that I always assumed were for adjustment, does your 52mm tach have that? I couldn't begin to guess how you would go about calibrating it. My 1983-vintage electrical/instrument greenbook makes no mention of adjustments to the tach.
Furthermore, shifting at 1500 rpm seems way low to me. I was always taught to shift around 2500-3000 rpm. It would take forever to get to highway speeds if you constantly shifted at 1500 rpm, I would think. My automatic shifts around 2750 rpm or so, depending on acceleration, right about when the engine sounds like it should be shifted in a tach-less car.
Drew
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Seems pretty close... that's about what my '90 w/M47 does... What size are your tires?
The shift light does indeed want you to upshift stupid early. It's more of a "fuel economy" light, and less of a "fun" or "happy car" light.
As for the differences in tachs, are you talking about the "needle" or the "red line" being different? Oh wait, I see... hmmm... check the date codes on the gauges. That might be something...
The one with the redline at 6500 is the older one, for the B21 and B23. I guess Volvo lowered the redline for the B230.
-Ryan
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Athens, Ohio
1987 245 DL 314k, Dog-mobile
1990 245 DL 134k M47, E-codes, GT Sway Bars
1991 745 GL 300k, Regina, 23/21mm Turbo Sway Bars
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While it may not be dead on, you are probably expecting a lot higher RPMs than you should. Before I got a tach I would wager I never took the car up past 4000rpms. Given the sound of the engine, I was afraid it would blow!
After my tach install I realized how low and lazy the engine idled, especially with the stock M cam. Now that I have the A cam and actually CAN take the engine beyond 5000rpms, I have taken it up to just past 6000 on several occasions, and routinely let it run up to 4500 while I'm accelerating. The AW71 with higher stall torque converter I now have helps with that.
On the highway, with my automagic, my tach tells me I'm doing 3000rpms at 80mph in overdrive, and actually only creeps up to about 3.5k at 90mph.
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'93 244: 'A' cam 4 deg. advanced, 25/22 sways, custom heim endlinks, poly bushings, and a lot more styling customization than I care to recount.
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I've got a 245 with M47 and 3.31, and my tires are 205/60-15. In 5th gear, I get 26.97 mph/1000 rpm (calculated).
What trouble me about your tach is that you're not getting a constant mph/rpm. At 60, you have 30 mph/Krpm, but at 80 you have 28.6. I would expect better agreement than that!
--
Thank goodness we don't get all the government we pay for. -- Will Rogers
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With an M47 and 3.31 gears, 5th gear gives you about 26 mph for every 1,000 engine rpm. 60 / 26 = 2.3, or 2,300 rpm. 80 / 26 = 3.07, or 3,070 rpm.
Given that your tach is only a couple hundred RPM "off" from these calculations, I would tend to believe that your speedometer is reading high, and that at 60 you are really doing closer to 55, and more like 75 when it indicates 80.
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Thanks for the explaination. Maybe the tach is totally correct and I was just expecting higher RPM. I'll try to keep an eye on things and see if the tach maches up to your calculations. I'm just running stock sized 195/75/14 tires. My 4 banger diesel runs higher rpm (yet smoother) and my 4 cylinder pickup runs much higher RPM, but has 3.73 gearing I think.
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FWIW, I've also got a small tach and my idle reads 950ish at idle, though when it was emissions tested the base idle was 750-800 rpm, so there is a bit of inaccuracy in the small gauge.
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