All you guys with factory tach's - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**'70_402** · 04-11-2005, 05:03 PM

So do you guys just guess what rpm you are @ above 5,000..... to me that would be the most important time to know what rpm you are running..... and i know if my big block will turn 6,000 rpms then those small block have to push that much if not more....

just one of those questions that i have always had but always forget to ask...

Rick

Jason915 · 04-11-2005, 05:10 PM

that's the lame thing about factory tachs, I have seen some on e-bay that relocate the tach where the gas gauge goes and reads to 7K.

junkyardjohn · 04-11-2005, 05:28 PM

ALOT OF PEOPLE THAT PLAN ON SPINING THEIR MOTORS FASTER THAN 5000 RPMs USE CAMARO TACH CONVERSIONS (I THINK THEY GO TO 7000) OR LIKE ME... I ALWAYS PUT AUTO-METER GAGES IN MY OWN TRUCKS.

JOHN

LUV2XCLR8 · 04-11-2005, 05:36 PM

NEVER NOTICED, I GUESS I'LL JUST SHIFT IT WHEN IT'S BURIED

Idaho68 · 04-11-2005, 05:36 PM

Quote:

Originally Posted by junkyardjohn

ALOT OF PEOPLE THAT PLAN ON SPINING THEIR MOTORS FASTER THAN 5000 RPMs USE CAMARO TACH CONVERSIONS (I THINK THEY GO TO 7000) OR LIKE ME... I ALWAYS PUT AUTO-METER GAGES IN MY OWN TRUCKS.

JOHN

Hmm that is something I am looking at doing with mine, any chance on getting a how-to post?

neonlarry · 04-11-2005, 06:01 PM

http://67-72chevytrucks.com/vboard/s...threadid=82148
http://67-72chevytrucks.com/vboard/s....php3?t=137155

70 shorty · 04-11-2005, 10:01 PM

Yeah, Camaro tachs go to 7 grand. Of course in my Z28 7 grand would probably be about 1500 rpm past "Your engine is now toast"

Longhorn Man · 04-11-2005, 10:22 PM

in all reality, even when these tachs were new (talkin the camaro tach here too) they were never very acurate.....fast forward 35 years...or 25 for the camamro deal...and it is even less acurate.
All a factory tach is for is looking neat nad saying look at my options. It is pretty much crap if you plan to push your motor...actually, since it doesn't even go to the small block red line of 5500 RPM, (and I suspect it was the same for truck big blocks and inlines) then it is totally worthless if you plan to push it.

powell72 · 04-11-2005, 11:47 PM

I'm a sissy and I don't take mine over five.

avejoe · 04-12-2005, 12:08 AM

Mine would fall apart.

Idaho68 · 04-12-2005, 01:52 AM

Quote:

Originally Posted by powell72

I'm a sissy and I don't take mine over five.

LOL on mine that engine is so tired it would likely go kerblewey

in a big way if I revved over 3500, wonder why, it only has something close to 500k on it without a rebuild, hmm reminds me, gotta get the brute to the shop, so I can tear into the engine and drive axle....

**special-K** · 04-12-2005, 07:37 AM

Since these are trucks,I think the intended use was more to maintain a constant engine speed(driving your tach)and to watch your revs when hauling/pulling in a lower gear.

junkyardjohn · 04-12-2005, 09:51 AM

Quote:

Originally Posted by special-K

Since these are trucks,I think the intended use was more to maintain a constant engine speed(driving your tach)and to watch your revs when hauling/pulling in a lower gear.

VERY FEW OF THESE TRUCKS ARE USED AS THEY WERE INTENDED TO BE 40 YEARS AGO.

Longhorn Man · 04-12-2005, 05:38 PM

it doesn't matter if you are in first gear pullin 5000 pounds doin 5500 RPM going up a 15% grade, or if you are in 4th doing 120 MPH....600 RPM off, is still 60 RPM off, and at 5500 RPM, that would make it more like 6100 RPM !!!

That's enough to scatter a stock engine if you are holding it there.

Another reason I think these stock tachs were kinda stupid...even back in the day when the truck was being used as a truck... you get a 4.10 or a 4.56 geared 3/4 ton, and your going down the freeway at 70 MPH, (typical early 70's speed limit) what kind of RPMs you turning? (can anyone pull that up for me for argumentitve reasons?) What if you were passing some one and wound it up to 90? I'm sure there were some states that actually had 80 or even 85 MPH limits....Montana comes to mind. If you were used to spinning 5000 RPM just to keep up with traffic, and had to spin it higher...you wouldn't know where you were.
IMO, they are just ornimentation. Eye candy if you will.

72moneypit · 04-12-2005, 05:49 PM

Quote:

Originally Posted by Longhorn Man

you get a 4.10 or a 4.56 geared 3/4 ton, and your going down the freeway at 70 MPH, (typical early 70's speed limit) what kind of RPMs you turning? (can anyone pull that up for me for argumentitve reasons?)

When I'm going 70 MPH, my tach reads about 3800 RPMs with 4.11's and 28" tires. I can't bear to drive faster than 75... the engine's wound up so high it sounds like it'll blow!

67chevemall · 04-12-2005, 08:57 PM

^ I second what he said ^

mr402 · 04-12-2005, 10:37 PM

One good use for them though. If you haven't gotten around to lubing that speedo cable then it might help you figure out how fast your going while that needle bounces all over the place.

687980chevy · 04-13-2005, 03:36 AM

Quote:

Originally Posted by Longhorn Man

Another reason I think these stock tachs were kinda stupid...even back in the day when the truck was being used as a truck... you get a 4.10 or a 4.56 geared 3/4 ton, and your going down the freeway at 70 MPH, (typical early 70's speed limit) what kind of RPMs you turning? IMO, they are just ornimentation. Eye candy if you will.

That enormus gas gauge is also kinda stupid.....until you run out of gas. I would rather have a tach off a couple hundred RPM's than a gas gauge off a couple gallons! The same fellows designed all of the gauges in our trucks. Don't think it's gospel on any of them!

jtminton · 04-13-2005, 11:00 AM

Quote:

Originally Posted by Longhorn Man

Another reason I think these stock tachs were kinda stupid...even back in the day when the truck was being used as a truck... you get a 4.10 or a 4.56 geared 3/4 ton, and your going down the freeway at 70 MPH, (typical early 70's speed limit) what kind of RPMs you turning? (can anyone pull that up for me for argumentitve reasons?)

Here is a chart I got off of smokemup.com for my truck. I have a 4 speed with 4.10 gears and 265/75/16 (31.5 inches) tires:

Transmission Ratios:
1st: 6.55 2nd: 3.58 3rd: 1.7 4th: 1

Tire Diameter 1: 31.5 inches
Rear Gear Ratio 1: 4.10:1
MPH
RPM 1st 2nd 3rd 4th
1000 3 6 13 23
1500 5 10 20 34
2000 7 13 27 46
2500 9 16 34 57
3000 10 19 40 69
3500 12 22 47 80
4000 14 26 54 91
4500 16 29 61 103
5000 17 32 67 114
5500 19 35 74 126
6000 21 38 81 137
6500 23 41 87 149
7000 24 45 94 160
7500 26 48 101 171
8000 28 51 108 183

04-11-2005, 05:03 PM	#1
'70_402 Senior Member Join Date: Dec 2003 Location: Pampa, Texas Posts: 1,554	All you guys with factory tach's So do you guys just guess what rpm you are @ above 5,000..... to me that would be the most important time to know what rpm you are running..... and i know if my big block will turn 6,000 rpms then those small block have to push that much if not more.... just one of those questions that i have always had but always forget to ask... Rick __________________ https://www.ebay.com/itm/295742064443

04-11-2005, 05:10 PM	#2
Jason915 Registered User Join Date: Jan 2005 Location: Colorado Springs Posts: 693	that's the lame thing about factory tachs, I have seen some on e-bay that relocate the tach where the gas gauge goes and reads to 7K. __________________ 1971 GMC K1500 SWB Fleetside, 4" skyjacker softride and, 14 Bolt FF, HD Dana 44 4.10's 1970 K5 TBI conversion lifted etc SOLD 1968 C20 camper truck SOLD “To ban guns because criminals use them is to tell the innocent and law-abiding that their rights and liberties depend not on their own conduct, but on the conduct of the guilty and the lawless.” Jeff Snyder

04-11-2005, 05:28 PM	#3
junkyardjohn Registered User Join Date: Aug 2001 Location: SOMERSET KY. Posts: 6,427	ALOT OF PEOPLE THAT PLAN ON SPINING THEIR MOTORS FASTER THAN 5000 RPMs USE CAMARO TACH CONVERSIONS (I THINK THEY GO TO 7000) OR LIKE ME... I ALWAYS PUT AUTO-METER GAGES IN MY OWN TRUCKS. JOHN __________________ junkyardjohn 69 1 TON TOW TRUCK // 84 4WD CUCV BLAZER// 85 1 TON 4WD STAKE TRUCK// 86 M1031 5/4 TON 4WD CUCV// ALOT OF OLD TRUCKS FOR ONE OLD MAN TO DRIVE. THERES ROOM FOR ALL OF GODS CREATURES RIGHT NEXT TO MY MASHED POTATOES// LIFE MEMBER OF P.E.T.A (PEOPLE EATING TASTY ANIMALS) DON'T RENT U-HAUL ALWAYS TELL THE TRUTH IT WILL AMAZE PART OF THE PEOPLE & ASTONISH THE REST

04-11-2005, 05:36 PM	#4
LUV2XCLR8 The LuvShack Garage Join Date: Jan 2004 Location: Maple Grove, TN (West Side) Posts: 30,470	NEVER NOTICED, I GUESS I'LL JUST SHIFT IT WHEN IT'S BURIED __________________ Owner/Op: "TN Classic Transport Carriers" The Toy: "Square Vette" 72 Hybrid Blazer Toy Barn: "LuvShack" 40 x 60 x 20 Shop Big Piggy: "Goliath" 07 Kodiak C4500 Lil Piggy:"Maddy" 88 Silverado 3500 Hauler: "Feathers" 14 Aluma 8218T

04-11-2005, 06:01 PM	#6
neonlarry Registered User Join Date: Feb 2002 Location: Vacaville, CA Posts: 2,746	http://67-72chevytrucks.com/vboard/s...threadid=82148 http://67-72chevytrucks.com/vboard/s....php3?t=137155 __________________ 70 C/10 Light Red 350/TH350, HEI, Duals w/40 series Flows, 91 seat, LED taillights 99 Pontiac S/C GTP, SLP Ram Air hood, GMPP Konis & springs 95 Neon ACR, MP PCM, AFX UDP, 3.0 CAI

04-11-2005, 10:01 PM	#7
70 shorty Where's my beer? Join Date: Oct 2004 Location: Glen Allen, VA Posts: 1,768	Yeah, Camaro tachs go to 7 grand. Of course in my Z28 7 grand would probably be about 1500 rpm past "Your engine is now toast" __________________ 70 C10, shortstep, .30 over 250,Hurst shifted 3 spd parts hauler. Holley 390, Clifford Intake, Header, ported cylinder head, unknown bigger cam. 79 Corvette L82, 4 spd, black, red interior, headers, flowmasters, and unkown bigger cam. '03 Grand Cherokee Laredo, 4.0 4x4 daily driver. 165K miles, and runs great '08 Tahoe LTZ 4x4 155K

04-11-2005, 10:22 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	in all reality, even when these tachs were new (talkin the camaro tach here too) they were never very acurate.....fast forward 35 years...or 25 for the camamro deal...and it is even less acurate. All a factory tach is for is looking neat nad saying look at my options. It is pretty much crap if you plan to push your motor...actually, since it doesn't even go to the small block red line of 5500 RPM, (and I suspect it was the same for truck big blocks and inlines) then it is totally worthless if you plan to push it.

04-11-2005, 11:47 PM	#9
powell72 Senior Member Join Date: Jan 2005 Location: Loveland Co. Posts: 3,098	I'm a sissy and I don't take mine over five. __________________ Chris 74 Custom Deluxe SWB 350/350/3.73’s 99 2wd Silverado RCSB 5.3/4L60/3.90’s http://www.classictrucks.com/feature...short_bed.html

04-12-2005, 12:08 AM	#10
avejoe Custer had a plan too. Join Date: Dec 2003 Location: No. California Posts: 344	Mine would fall apart. __________________ 72 K15 GMC (aka Big White) Performance Rockers, Cab Corners, and Floors Fossil Fuel Glutton Neighborhood Nuisance 98 BMW 540i for Speed (Sold ) 05 Subaru Outback for mileage

04-12-2005, 07:37 AM	#12
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,863	Since these are trucks,I think the intended use was more to maintain a constant engine speed(driving your tach)and to watch your revs when hauling/pulling in a lower gear. __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

04-12-2005, 05:38 PM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	it doesn't matter if you are in first gear pullin 5000 pounds doin 5500 RPM going up a 15% grade, or if you are in 4th doing 120 MPH....600 RPM off, is still 60 RPM off, and at 5500 RPM, that would make it more like 6100 RPM !!! That's enough to scatter a stock engine if you are holding it there. Another reason I think these stock tachs were kinda stupid...even back in the day when the truck was being used as a truck... you get a 4.10 or a 4.56 geared 3/4 ton, and your going down the freeway at 70 MPH, (typical early 70's speed limit) what kind of RPMs you turning? (can anyone pull that up for me for argumentitve reasons?) What if you were passing some one and wound it up to 90? I'm sure there were some states that actually had 80 or even 85 MPH limits....Montana comes to mind. If you were used to spinning 5000 RPM just to keep up with traffic, and had to spin it higher...you wouldn't know where you were. IMO, they are just ornimentation. Eye candy if you will.

04-12-2005, 08:57 PM	#16
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	^ I second what he said ^ __________________ 1968 Chevy C10 307 3ott fleetside 1967 Chevy C/10 V8, 3spd, fleetside lwb.Sold 1967 Chev C/10 step, 383, M21. SOLD

04-12-2005, 10:37 PM	#17
mr402 Registered User Join Date: Jan 2004 Location: Elmira, Oregon Posts: 449	One good use for them though. If you haven't gotten around to lubing that speedo cable then it might help you figure out how fast your going while that needle bounces all over the place.



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