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#1 |
Junior Member
Join Date: Jul 2002
Location: Scottsdale, AZ
Posts: 1,701
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14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Did a 160 mi trip this weekend over a mountain pass and into Eastern Washington. AC on a little while. Do I have room for improvement or should I be happy with 14.5 MPG.
Details '71 short fleet, lowered 4/7.5. Only payload was; me, the dog, a cooler, and emergency tools. Stockish unknown miles '69 350 (.030 over) 140-150 psi compression. Rebuilt Q-jet, Edelbrock SP2P intake manifold, tall open element air cleaner. 2" Ramhorns and 2-1/2" exhaust. 15 in vacuum on stock gauge at smooth idle. Running 2200 - 2500 rpm at 75. All new ignition. Summit HEI with one lighter advance spring - 14 degrees base timing. Vacuum advance can left as delivered from Summit. Tune seems good (snappy and doesn't ping) but I feel the grunt falls off above 60-65 MPH. Swap meet 700r. Lock-up doesn't want to stay locked-up after a few miles on the highway and rarely above 60 mph. I have a new solenoid to go in but that's another story. Craigslist 3.73 posi - counted the teeth to confirm ratio. 40 series 20" tires - 29" tall. New and aligned. Didn't check air pressure. Speed GPS confirmed. 87 octane 7-11 gas. After reading some posts I'm thinking a couple more MPG could be expected. What do you think?
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"I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle |
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#2 |
Registered User
![]() Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,208
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Naa .. I'd be happy with that.
10% Ethanol ? Not sure if you (or others) might benifit but: 1GL Ethanol = 12,000 btu 1GL Gasoline = 14,000 btu So, if it was the crapanol and 87 I would say you're about right. These things are not the most aerodynamic trucks on the planet. 3:55 would probably help Does it have a cam in it now or just stock through the valve train, etc. ? Do you know which heads are on it? 041 ? just thinking if it has been bored, it has probably been gone through at some point.
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Chad 1967 C10 SWB - Project Savannah - 6.0/4L80 *Currently underway* 1968 C10 SWB - TOTY 2018, 50th Anniversary Tribute Project * Sold * Pride and Joy 1986 Silverado Short Fleet - Scarlet *Sold* 1985 Silverado Short Fleet *Sold* 2022 Jeep Gladiator Mojave 2001 Jeep Cherokee XJ 4x4 - Lifted, Built 1992 Jeep Cherokee XJ 4x4 - Lifted 2013 Honda Accord EX-L v6 Coupe 6spd (wife's ride) |
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#3 | |
Junior Member
Join Date: Jul 2002
Location: Scottsdale, AZ
Posts: 1,701
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Quote:
I didn't pay attention to the ethanol question at the pump but I will next time! Cam is unknown but it seems relatively stock. Valvetrain components are all stock stamped steel rockers etc. Heads I forget the number? I recall when I looked it up they're nothing special. 76cc with 1.94/1.50 valves. I just had them off and apart for head gaskets and stem seals and everything looked ok and not messed with. Exhaust had hardened seats though so if they were didn't come with that they have been rebuilt at some point. Think the SP2P intake is helping me or hurting me?
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"I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle |
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#4 |
Registered User
Join Date: Apr 2008
Location: Md
Posts: 2,475
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
No expert here, but that sounds pretty good if you were going 70-75 mph even part of the way. At 55 you might get 17 or so. With newer set up 5.4 L and 4L60 E you might get 17 going 70. Is your avatar the way the truck looks now...Pretty sweet....More photo's ..Please.
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#5 | |
Junior Member
Join Date: Jul 2002
Location: Scottsdale, AZ
Posts: 1,701
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Quote:
I started a build thread but since I got it driving and posted some pix of my 20's I have been having so much fun driving and working out the bugs I haven't posted much. There's a few pix in this thread: http://67-72chevytrucks.com/vboard/s...=518829&page=3
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"I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle |
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#6 |
VA72C10
![]() Join Date: Mar 2008
Location: Midlothian, VA
Posts: 25,269
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
The lockup might net you a little better result on mpg's. Also you were going over a pass you said so lots of downshifting to get over inclines id assume...
I was able to average 17-18mpg in an 80z28 with a 355 and 700r4 with 373's and similar size tires to what most run on these trucks....but that camaro obviously was more aerodynamic.....and when I first had it I spent more time playing with the throttle and only was getting 15mpg (sometimes a lot less than that ![]() Posted via Mobile Device
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Looking for a 67-72 swb or blazer project in or around VA. ![]() |
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#7 |
Registered User
![]() Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,208
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Yeah, .. I think with the 3:73, slow 'er down a little and it should pick a mpg or two.
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Chad 1967 C10 SWB - Project Savannah - 6.0/4L80 *Currently underway* 1968 C10 SWB - TOTY 2018, 50th Anniversary Tribute Project * Sold * Pride and Joy 1986 Silverado Short Fleet - Scarlet *Sold* 1985 Silverado Short Fleet *Sold* 2022 Jeep Gladiator Mojave 2001 Jeep Cherokee XJ 4x4 - Lifted, Built 1992 Jeep Cherokee XJ 4x4 - Lifted 2013 Honda Accord EX-L v6 Coupe 6spd (wife's ride) |
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#8 |
VA72C10
![]() Join Date: Mar 2008
Location: Midlothian, VA
Posts: 25,269
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Seems every engine has a sweet spot for fuel economy and it can be at slightly different rpm's depending on the setup...
For example....I had a 2000 tdi beetle that got around 35 mpg in the city and 45 -50mpg on the highway....but I took trips from richmond to tidewater fairly often and experimented on cruise control speeds and if I set it on 65 exactly I could get upto 70mpg on a trip up and back. Anything over and it dropped substantially to 50 or lower. Posted via Mobile Device
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Looking for a 67-72 swb or blazer project in or around VA. ![]() |
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#9 | ||
"I ain't nobody, dork."
Join Date: Sep 2007
Location: Whidbey Island, Washington
Posts: 8,940
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
I wish I got 14.5 mpg! I's say that's pretty decent... and here in WA State... about 95% of all gas stations are E10.
Gary
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'cuz chicks dig scars... My 1972 GMC 1500 Super Custom (Creeping Death) "long term" build thread. The Rebuild of Creeping Death after the wreck Quote:
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#10 |
Registered User
![]() Join Date: Oct 2009
Location: SoCal
Posts: 815
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Sounds good to me. Hell my 03 Durango with a small v8, fuel injection and overdrive only gets 15 mpg on the freeway. So a classic truck getting what you got is great.
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#11 |
Registered User
Join Date: Mar 2005
Location: 10-Uh-See
Posts: 5,609
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
That's about right for E10 fuel. Try it again with non-ethanol 89 octane and you should get alot better. There's no reason to run any higher than 89 in that stock engine.
My old combo, which was a mild cammed 350/TH350/3.73 would average about 14mpg with 93 octane fuel. When I awitched to the 3.07 gear, I could get about 16mpg. Of course, that's with non-ethanol 93 fuel.
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#12 |
Registered User
![]() Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,208
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
SP2P meaning Single Plane / Dual Plane ? Which intake is it?
My GMC with a basically stock 350, cast intake and a 1406 Eddy. 3OTT, Nervously driving it home at about 60 mph in downtown Atlanta in the pouring rain got about 21-22mpg. I was shocked. Yes, 89 octane no ethanol will bump it up to 16+ I would bet. So the combination of slowing down a little bit (not saying Papaw slow) and maybe go to a 45 series tire out back (?) 1" more dia in the tire = more distance traveled per rotation of the tire = 3:60 or so rear ratio .. what type of plugs and wires are you running?
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Chad 1967 C10 SWB - Project Savannah - 6.0/4L80 *Currently underway* 1968 C10 SWB - TOTY 2018, 50th Anniversary Tribute Project * Sold * Pride and Joy 1986 Silverado Short Fleet - Scarlet *Sold* 1985 Silverado Short Fleet *Sold* 2022 Jeep Gladiator Mojave 2001 Jeep Cherokee XJ 4x4 - Lifted, Built 1992 Jeep Cherokee XJ 4x4 - Lifted 2013 Honda Accord EX-L v6 Coupe 6spd (wife's ride) |
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#13 | |
Junior Member
Join Date: Jul 2002
Location: Scottsdale, AZ
Posts: 1,701
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Quote:
Plugs are Autolite cheapies (#45 #25? I forget the #?). gapped to .045. (I know....) Honestly I had AC's in but half of them had cracked porcelain and I was p.o.'d and didn't buy another set. Wires are new pre-cut 7mm from ORilleys.
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"I was patina when patina wasn't cool." 1973 Cheyenne SWB Sunset Gold / Frost White / Saddle |
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#14 |
Overdrive club
Join Date: Sep 2007
Location: apache junction, arizona
Posts: 819
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
My 71 was getting about 12 at those speeds,totally stock with 3.08 gears.Try it again at 65 mph,I think you will be surprised.
Posted via Mobile Device
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1971 c-10 1951 3100 chevy 1970 chevy c-30 Sold! |
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#15 |
Registered User
![]() Join Date: Jan 2011
Location: Chattanooga TN
Posts: 6,208
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
I'd think the intake would be fine.
HEI plug gap is dead on IMO. .042 - .045 It may have been the fact you're going across a mtn pass at 70+ mph.. ![]()
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Chad 1967 C10 SWB - Project Savannah - 6.0/4L80 *Currently underway* 1968 C10 SWB - TOTY 2018, 50th Anniversary Tribute Project * Sold * Pride and Joy 1986 Silverado Short Fleet - Scarlet *Sold* 1985 Silverado Short Fleet *Sold* 2022 Jeep Gladiator Mojave 2001 Jeep Cherokee XJ 4x4 - Lifted, Built 1992 Jeep Cherokee XJ 4x4 - Lifted 2013 Honda Accord EX-L v6 Coupe 6spd (wife's ride) |
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#16 |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,500
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
14.5 mpg sounds about right. What rpm's were you turning( I'm curious because I have almost the exact same set up in a 72 swb and i am curious what I am in for. I was figuring about 15 mpg would be optimistic. I am running and edelbrock performer and a q jet, unknown "rv" cam, 700r4, 3:73's. I actually pulled a 3:07 rear out because its not going to be a daily driver and I want to be able to snap my friends neck a little when I take them for joy rides!
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#17 |
Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,218
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
My 70 steper with Goodwrench 350, 700r4, & Q-jet gets 16-18 on the highway. It has a 3.08 rear end. I think you would be better off with a 3.08 if you do a lot of highway driving with light loads. You can always pull it down a notch when it gets under heavy loads. You can still "snap your friends neck" with the low 1st gear in a 700R4.
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#18 | |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,500
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
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#19 |
Registered User
Join Date: Jun 2012
Location: Givors - FRANCE
Posts: 109
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
![]() this post is very interesting for me. my 350 is equipped with edelbrock performance heads - manifold edelbrock RPM and Holley carburetor - automatic transmission TH350 3 gears. the problem is, that the engine runs 2500trs/mn for a speed of 55 miles !!! that's very short. the consumtion is very high with... ![]() so I would like to change : 1/ Carburator to an Edelbrock 2/ final transmission ? can you explain me what is the best to get 14.5miles/gallon ??? It's difficult in france because we have to import from US so i need to order the right parts you know many thanks Laurent |
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#20 | |
Senior Member
![]() Join Date: Aug 2008
Location: Cedar Park, Texas
Posts: 7,500
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
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#21 | |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
Quote:
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#22 |
Hittin E-Z Street on Mud Tires
![]() Join Date: Nov 2004
Location: Greenville, SC
Posts: 23,090
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
I have a 350/edelbrock/700R/3.73. Going 70-75mph I get about what you got, 15mpg. If I slow it down to 55-60 I can push it to 16, maybe a hair more.
Around town is 10-12mpg. You definitely want to get that lock up taken care of, it's real easy to burn up a 700R. I know from experience... I installed the kits from Bowtie Overdrives. I used their TV cable kit. As long as you have the correct bracket I think as long as the cable is set up correctly you should be OK with the q-jet. I checked my shift pressures with a cheap gauge I bought off ebay to make sure it everything was good. I also used the BTO lock up kit. It comes with a brake switch that unlocks the TC when you hit the brakes. This is also very important. I had a kit before my BTO kit that only locked up the TC. I had a dumbass pull out in front of me and had to lock it down, and in doing so, the truck stalled because the TC did not unlock. I missed the idiot but the truck shut off on me.
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Jesse James 1967 C10 SWB Stepside: 350/700R4/3.73 1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc 1968 Pontiac Firebird: Project Fire Chicken! 2015 Silverado Double Cab 5.3L Z71 2001 Jeep Wrangler Sport 4.0L 5spd 2020 Chevrolet Equinox Premium 2.0L Turbo 2011 Mustang V6 ~ Wife's ride ![]() American Born, Country by the Grace of God ![]() 1967 CST Shop Truck Rebuild! My 1967 C-10 Build Thread My Vintage Air A/C Install Project "On a Dime" Trying my hand at Home Renovation! 1965 Mustang Modifications! |
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#23 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
i always got 15-16 at hiway speeds with very heavy loads goin long distances to swapmeet and fleamarkets at hiway speeds of 80 and higher// i had 4:10's a 2004R/350 combo
all synthetic lubrication engine tranny rear and axel bearings help ALOT
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#24 |
Registered User
Join Date: Jul 2011
Location: Mt Brydges Ontario
Posts: 181
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
67 short step, 400 smallblock with AFR 195 heads,RPM intake, 780 holley and .512 lift cam.I have a 700R4 tranny with lockup on a switch and 3.42 gears. I get around 12 mpg in the city and recently on a long trip I averaged 17.3 mpg.I think it would do a little better with a smaller carb.So these trucks can get OK mileage.A new truck doesn't do much better and won't even come close to the power.I'm building a daily driver 70 longbox now and I'm hoping for 18 mpg with a 350.
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#25 |
Senior Member
![]() Join Date: May 2002
Location: Hammond, WI
Posts: 1,804
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Re: 14.5 MPG 350/700r/3.73's at 70 to 75 MPH - Should I be happy with that?
I've got a '69 longbox with a 350/700R4/3.73 posi, with 28" tires, and get about 14mpg. I think that I might get a little more with a smaller carb, something like a 600CFM. I've got a 750CFM Edelbrock Q-Jet on there now, but it needs new brass bushings which I can't find. I've already rebuilt it with the normal kit, but it needs more.
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Mike 2001 Dakota R/T - Silver CC - 1 of 1671 •360 w/46RE •392 limited slip 1972 Chevy Suburban - Turquoise/Black 1969 Chevy C/10 - Blue LWB •350 w/ 700R4 •3.73 posi •PS PB A/C - SOLD ![]() Using your turn signal is not "giving information to the enemy" 67-72 FAQ |
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