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#1 |
Registered User
Join Date: Sep 2002
Location: Davenprort, Iowa
Posts: 18
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My 70 Screeeems at crusing speed. I don't have a tac since I have an automatic. I'm guessing 25 or 30 thou. What is the best way to slow the RPMs without messing with the speed?
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#2 |
Registered User
Join Date: Aug 2001
Location: escondido, ca 92026
Posts: 1,222
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change the gearing in the differential (by lowering it numerically) or install an overdrive trans..
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'72 short step, 350, 700R4, tilt, ps, pdb, a/c, lowered coils, etc., other work in progress... San Diego, CA 72 Stepside Project Last edited by bigvinnie; 03-25-2004 at 10:46 PM. |
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#3 |
Cause the Chicks DIG IT!!
Join Date: Nov 2003
Location: Beaufort SC
Posts: 509
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Yep just like he said. You probably got 3:73's thats what i had and i changed em because i drive back and forth from NC to nebraska and going down the interstate doing 80 mph with some 255 60's just works the dog piss out of the motor. It cruised along at about 3500 to 4000 rpm. I dropped down to a 3:40 here lately and now cruising at 70 is about 3,000 rpm. Either that or get you a 700R-4 thats the one with the overdrive. YOu hear all kinds of stories with them about reliability though so beware.
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#4 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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If you have a small block and an automatic, then you probably already have a 3.07 gear, which should get you about 60 at 2500 or so RPm...no too bad really. You'll have a hard time getting anything lower, so if the RPMs are too much for you, an over drive tranny is about your only option.
Just remember, reducing the RPMs, does not always mean better MPG. I've seen plenty of OD conversions that net 1 or 2 MPG better, and that'll take the life of the tranny to make up the difference in cost. |
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#5 |
Registered User
Join Date: Jul 2003
Location: Cypress, Tx
Posts: 4,005
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You know I Love ya Longhorn Man, your my idol, but if you figure 2 mpg better at 1.50 a gllon for gas, and about 750.00 for a 700r4 tranny, your looking to make it up the cost in about 2 1/2 years. I figure it like this:
10 mpg x 20 gallons per tank = 200 miles per tank, at 1.50 per gallon = 30.00 per tank based on a 12,000 mile a year, that works out to 1800.00 per year on gas. Now at 12 mpg x 20 gallons per tank = 240 miles per tank, at 1.50 per gallon = 30.00 per tank based on 12,000 miles per year that works out to 1500.00 per year on gas. A savings of a mere 300.00 per year, but figure you can sell the tranny you have now for a little green, and you could easily pay for a 700r4 in 2- 21/2 years. Of coarse I'm not includingthe driveshaft replacement either. ![]()
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1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE |
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#6 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Hmmm, your numbers look good, I never bothered actually doing the math.
Good point. However, if I am your idol...you have issues...no, you have ISSUATIONS ![]() Thanks for pointing out my oversight. |
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#7 |
Registered User
Join Date: Jul 2003
Location: Cypress, Tx
Posts: 4,005
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By the way Longhorn, why are we up this late?!?
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1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE |
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#8 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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I don't work on Fridays, so I can stay up as late as I want. (BTW, it is one hr later here)
I normally don't turn in untill 1 in the am or so...even on work nights. BTW, I got your check today...your light will be going out tomorow. |
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#9 |
Registered User
Join Date: Jul 2003
Location: Cypress, Tx
Posts: 4,005
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Cool Thhanks for the news. I'm off tomorrow too. The wifes out of town anyway, and I can't sleep when she's gone for some reason. I'm driving to Dallas tomorrow morning, so I better get some rest soon.
Back to the thread at hand, sorry kecah04. ![]()
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1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE |
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#10 | |
Watch out for your cornhole !
![]() Join Date: Jun 2003
Location: Azle, Texas
Posts: 14,162
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Quote:
![]() ![]() ![]() ![]() Seriously though, lower your cruising revs for your engine's health too. As RPM increases, the stress on the engine increases incrementally. An engine turning slow speeds is a much happier engine.
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I'm on the Instagram- @Gearhead_Kevin |
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#11 |
Registered User
Join Date: Jan 2000
Location: ca
Posts: 1,110
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gears need to match the cam also. i'm thinking about changing my 3.50s for 3.70s because i think with the overdrive the engine is bogging down.
1.50 for gas? i wish i lived there. its 2 bucks here.
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68 short step, 406/700r4, 9" w/discs. |
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#12 | |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Quote:
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#13 |
Registered User
Join Date: Jul 2003
Location: north of Phx AZ about 30 miles
Posts: 698
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Put on as tall a rear tire on it as you can. Get a tach, even a temporary tach, so you know what rpm you are turning. Change rear gears. Install new OD trans. Install gear vendors overdrive unit.
New tires $250 New rear gears $500(shop doing the change) New tranny $1000 OD unit $2000 Compare these prices to a new GM crate engine @ $1200 in 100,000 miles. IMO over rev the engine, wastes a little fuel, that is about it. BTW I have a TH400 and 4.11 rear end.
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Andy,Phx AZ '67 C-10 (Ahhh, done at last. Well there is that disk front end I want to put in and...) "23 C-Cab-sold '48 Ford 8N tractor(still working) '67 Scout(Now on the road) '70 MG B.-sold |
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#14 |
C10 now is a GMC
Join Date: Jun 2003
Location: Modesto, Ca
Posts: 740
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Hmmm, now you got me wondering what gears i'm running. lol
![]() She does 2,500 RPM @ 60 mph, what's a good site to plug in a RPM calculator online? ![]() David
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*1962 C10 swb fleetside, big window, custom cab 350/TH350 combo...Hot Rod *1963 C10 lwb fleetside, small window 230/4 speed...Blvd Cruiser *1931 Ford 5 window coupe (soon to be Hot Rod)... Father & Son project |
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#15 |
Registered User
Join Date: Oct 2003
Location: San Jose Ca.
Posts: 3,335
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Try this one.
http://www.angelfire.com/fl/procrastination/rear.html For me 3000 gets me 70mph. Cant wait to get the 307s in.
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RIP to my son Dylan. 5/17/2002 - 8/18/2018 If you want to know more about rare forms of pediatric cancer or if you want to help fund pediatric cancer research, please check out the website for the non-profit I started. https://slothforpedcancer.org 68 build thread http://67-72chevytrucks.com/vboard/s...d.php?t=223234 |
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