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12-04-2014, 10:15 PM
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#1 |
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Registered User
Join Date: Sep 2013
Location: North Tonawanda, NY
Posts: 236
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250 Straight 6 Auto or Manual
I have a 1971 C20 Chevy pickup with a 350 V8 and an automatic transmission. I am thinking of pulling the 350 out and putting a 250 straight 6 in for better gas mileage. I have a line on a 250 engine from a 68 Nova that had a manual transmission. Are there any modifications I need to make to this engine or will it bolt on the auto transmission in my 1971 C20 truck?
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12-04-2014, 10:19 PM
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#2 |
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Registered User
Join Date: Sep 2013
Location: Gonzales, La
Posts: 1,441
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Re: 250 Straight 6 Auto or Manual
Your gas milage will depend on the rear gear. I have a truck with a 462ci with turbo 350 tranny and 3.08 rear gear that gets 10 mpg and I have another trick with a 250ci with 3 speed manual and 3.73 rear gear, guess what it get 11-12 mpg. Not much better. And the 3.73 geared truck turns high RPM's on the highway.
I wouldn't change it out thinking I'd be getting a huge change in mpg.
__________________
MyToys: Goldilocks the "Ol School Survivor" 1968 C10, SWB Stepside, 08/15 TOTM, 250 CI 6 cylinder, 3 on the tree, 3.73 rear, 3/5 static drop, 23,500 original miles. Samson the 1970 CST10, LWB, 462Ci, Turbo 350 tranny, 3.08 rear gear, PB, PS, A/C, AM/FM, 2/4 Drop. Brutus the 1998 Camaro Z28, 33,500 original miles, LS1, 519 RWHP/497 RWTQ. Member of the Louisiana Classic Truck Club, LCTC Member of the Louisiana C10 Club Member of the Baton Rouge Drifters Car Club Last edited by CST10; 12-04-2014 at 10:19 PM. Reason: Typo |
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12-04-2014, 11:04 PM
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#3 |
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Registered User
Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,207
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Re: 250 Straight 6 Auto or Manual
It will bolt right up to your presant trans. I'm with CST. You would be better off putting a 700R4 trans. in it. Then drive it real slow & sluggish like you already have a 250 in it. You will get as good as or better mileage.
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12-05-2014, 06:32 AM
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#4 | |
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Registered User
 
Join Date: Sep 2013
Location: iredell county, nc
Posts: 77
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Re: 250 Straight 6 Auto or Manual
Quote:
Yes it will get better mileage Yes it will be gutless above 40mph But at least there will be something cool about it
__________________
Real trucks have a clutch. Please inform automakers.  1972 GMC, K25, 383 stroker, SM465, NP205, Eaton HO-72 |
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12-05-2014, 12:30 PM
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#5 |
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Registered User
Join Date: Mar 2014
Location: Comox B.C.
Posts: 46
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Re: 250 Straight 6 Auto or Manual
When I was in my 20s, I had a 65 c10 fleetside with a 250 and single downdraft rochester. I got 12-13mpg in the mountains, valleys ...pretty much everywhere I drove. Last year I picked up a 70k10 short box stepper with 350, 4" lift, 33s, and the same 373 dif and 4spd. I drove that over the Coquihalla (google it) in November and got dead on 16mpg. 250s are cool but no gas savings there...
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12-05-2014, 12:40 PM
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#6 |
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Registered User
Join Date: Mar 2012
Location: paducah Ky
Posts: 46
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Re: 250 Straight 6 Auto or Manual
I'm on board with everyone else. Over drive or a gear swap or even both. I have been really thinking about a 200r swap. But I have a line on one I can pickup almost free.
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12-05-2014, 12:48 PM
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#7 |
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Registered User
Join Date: Jun 2013
Location: Hemet,Ca.
Posts: 89
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Re: 250 Straight 6 Auto or Manual
I am installing a 700r4 with my 250 six.
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12-05-2014, 12:53 PM
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#8 |
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Registered User
Join Date: Sep 2013
Location: North Tonawanda, NY
Posts: 236
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Re: 250 Straight 6 Auto or Manual
So then the bolt pattern is the same as the 350 to my TH350 auto trans?
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12-05-2014, 01:05 PM
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#9 |
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Registered User
Join Date: Jun 2013
Location: Hemet,Ca.
Posts: 89
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Re: 250 Straight 6 Auto or Manual
Yes it is.
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12-05-2014, 01:15 PM
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#10 |
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Registered User
Join Date: Jul 2005
Location: AL
Posts: 1,828
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Re: 250 Straight 6 Auto or Manual
I have had both 6 cyl and "for-kid" eights in these trucks. There is no way I would go in this direction. The 6 cyls I had got less gas mileage and not nearly as much power.
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12-05-2014, 01:19 PM
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#11 |
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Registered User
Join Date: Jun 2013
Location: Hemet,Ca.
Posts: 89
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Re: 250 Straight 6 Auto or Manual
Well I had work done to my six so its at 400 horses now.
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12-05-2014, 08:21 PM
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#12 |
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Registered User
Join Date: Sep 2008
Location: Mobile, Al.
Posts: 687
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Re: 250 Straight 6 Auto or Manual
I pulled the 700r4 out of my truck, I'm running a 250 and it never was in it's power band. I went to a 3 sp manual trans. Mine is stock, I'm sure if you get the HP up it will be fine but going to a 6 for MPG is not going to happen.
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