350 to straight 6 conversion... - The 1947 - Present Chevrolet & GMC Truck Message Board Network

fade94 · 08-05-2005, 10:45 AM

I have a 6 cyl out of an old parts truck that I want to put in my 71 while I have the 350 out. I have the motor mounts that were on the motor, but not the frame mounts or towers. What do the frame mounts look like? I have a set of V-8 mounts from a 72 I would trade locally for the 6 cyl frame mounts if this is what I need. I am pulling the motor to clean it up and replace the gaskets and do some engine bay detailing. But, I still need to be able to drive the truck, and let's face it, gas ain't cheap. The six "should" get better mileage...

71meangreenc10 · 08-05-2005, 11:30 AM

Yes and no,
My 250 only gets 13mpg at the moment, my 283 probably will do the same or better since I regeared the rear end. I wont know till she is running soon. Ill take a picture of my mounts for you today. Remember that if your truck was a stock eight (check the vin for a cs=6, ce=8) youll will have to move everything to the rear for the 6 to fit, also is yours a 3 speed or auto, the 3spd crossover mount is different for each engine, auto shouldnt be hard to move, the drive shaft will need to be shortened (maybe) if its swb truck. I have converted mine from a 6 to 8 and made it look like stock, (no half assing) all the parts were changed. 6 has a different fan shroud too.

Let me know if I can be any help

Bottom line, if gas is the reason, you can get more mpg out of the eight if you change the trans or regear the rearend, youll have to give and take, the 6 will be less hp and torque, but if the drivetrain is not changed youll only gain a couple of mpg.

Smitty

fade94 · 08-05-2005, 11:37 AM

Truck was factory 6 with 3 spd. Now has 350/350 with 3.08 rear. I WISH it was a short bed, but it's a long. No shroud on it. I have dual electric fans. I don't want to change the trans or rear gear on this truck. Not concerned about HP and Torque since I also have an 01 Dodge Diesel that will pull whatever I hook to....FOR SALE...
My work drive in only 8 miles round trip. The motor that is in now seems to really be a gas hog so the 6 HAS to get better mileage. Of course, a lot of the problem is my right foot.

matt67350 · 08-05-2005, 01:50 PM

I have a set of I-6 motor mounts, will trade for the v-8 mounts

dave666693 · 08-05-2005, 02:01 PM

what rear end gears do you reccomend for the best mileage?

fade94 · 08-05-2005, 02:17 PM

Quote:

Originally Posted by matt67350

I have a set of I-6 motor mounts, will trade for the v-8 mounts

Are you going to be on this side of the metroplex this weekend? I should have pulled the frame part of the mounts off of the truck I got this out of, but I thought my brother was going to use it for a horse walker. Since he doesn't need it, I though I would stick it in to up my mileage.

HeavyD · 08-05-2005, 04:44 PM

You want to put in a 6 just temporarily? IMO it isn't worth the hassle of switching it all around. Mileage won't increase by much if any, since the old sixes are not like a fuel injected 4.3 of today. I have a 250/3 spd in my GMC and it is not good on fuel at all. You might be better off seeing if you can get any V8 (267, 305) real cheap to throw in there for the time being.

68speedalert · 08-05-2005, 06:58 PM

Heavy D is right. I've got the same truck and gears in my '68. When I ran the 350 with 4v, it was a gas hog. When it popped, I 'temporaily' put in a '77 305 with a 2v. It now does better on gas than anything I own (sad part) and ain't bad on performance. It runs so well I haven't touched the 350 and it's been almost 5 years now.

The six is REALLY gonna suck gas when you try to make it run like the 350 did. Those sixes were never know for their economy.

LUV2XCLR8 · 08-05-2005, 07:01 PM

Hmmmm, I had a 70 w/ a 250 mated to a 350 turbo, 4:10 gears, and got 20 MPG

wichitawings · 08-05-2005, 09:01 PM

I changed from a 250 6 cylinder to a 350 and I didn't have to change the motor mounts (I was able to use the 6 cylinder mounts). The 350 was pretty close to the firewall but it worked and everything lined up (I didn't have to get a new driveshaft or move the transmission even.

I did get the v8 mounts later and move the engine/trans up and got a lengthened driveshaft.

But I had an automatic and a shortbed.

By the way my 350 gets the same mileage as the 6 cylinder which was in good shape still

71meangreenc10 · 08-05-2005, 09:29 PM

I m running 2.76 in my truck (came with 3.73), I want to change it to 3.08, 2.76 is great on the highway, engine runs smooth and low rpms at high speeds but it has no take off with that range, I may put in 3.08 and see if that helps with some torque. A 2bbl would give you better mpg but would have less hp,,,you have to pick your poison also 2.76 will through your speedo off, thats why im using dakota digital, i can run anything and recalibrate my speedo.

Smitty

68speedalert · 08-06-2005, 08:42 AM

Quote:

Originally Posted by LUV2XCLR8

Hmmmm, I had a 70 w/ a 250 mated to a 350 turbo, 4:10 gears, and got 20 MPG

You're supposed to divide the MILES by the GALLONS, not the other way around!

Seriously, that's amazing. The only time our kind of trucks get into the 20's is by being towed for half the miles!

08-05-2005, 10:45 AM	#1
fade94 Registered User Join Date: Mar 2005 Location: Melissa, TX Posts: 799	350 to straight 6 conversion... I have a 6 cyl out of an old parts truck that I want to put in my 71 while I have the 350 out. I have the motor mounts that were on the motor, but not the frame mounts or towers. What do the frame mounts look like? I have a set of V-8 mounts from a 72 I would trade locally for the 6 cyl frame mounts if this is what I need. I am pulling the motor to clean it up and replace the gaskets and do some engine bay detailing. But, I still need to be able to drive the truck, and let's face it, gas ain't cheap. The six "should" get better mileage... __________________ 68 short bed driver (71 clip on it now, swapping to 68 when weather cooperates) 67 short step project (will get SWB from the 68) 67 Camaro, #'s matching (my wife's) 03 Dodge Ram 2500 4x4 diesel 5 speed 4.10 rear Last edited by fade94; 08-05-2005 at 11:32 AM.

08-05-2005, 11:30 AM	#2
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,179	Yes and no, My 250 only gets 13mpg at the moment, my 283 probably will do the same or better since I regeared the rear end. I wont know till she is running soon. Ill take a picture of my mounts for you today. Remember that if your truck was a stock eight (check the vin for a cs=6, ce=8) youll will have to move everything to the rear for the 6 to fit, also is yours a 3 speed or auto, the 3spd crossover mount is different for each engine, auto shouldnt be hard to move, the drive shaft will need to be shortened (maybe) if its swb truck. I have converted mine from a 6 to 8 and made it look like stock, (no half assing) all the parts were changed. 6 has a different fan shroud too. Let me know if I can be any help Bottom line, if gas is the reason, you can get more mpg out of the eight if you change the trans or regear the rearend, youll have to give and take, the 6 will be less hp and torque, but if the drivetrain is not changed youll only gain a couple of mpg. Smitty __________________ 71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 69 C30 Former Motor Home, Flat Bed time 70 G20 Red-E-Kamp Conversion "I'm your Boogy Van"

08-05-2005, 11:37 AM	#3
fade94 Registered User Join Date: Mar 2005 Location: Melissa, TX Posts: 799	Truck was factory 6 with 3 spd. Now has 350/350 with 3.08 rear. I WISH it was a short bed, but it's a long. No shroud on it. I have dual electric fans. I don't want to change the trans or rear gear on this truck. Not concerned about HP and Torque since I also have an 01 Dodge Diesel that will pull whatever I hook to....FOR SALE... My work drive in only 8 miles round trip. The motor that is in now seems to really be a gas hog so the 6 HAS to get better mileage. Of course, a lot of the problem is my right foot. __________________ 68 short bed driver (71 clip on it now, swapping to 68 when weather cooperates) 67 short step project (will get SWB from the 68) 67 Camaro, #'s matching (my wife's) 03 Dodge Ram 2500 4x4 diesel 5 speed 4.10 rear

08-05-2005, 01:50 PM	#4
matt67350 Registered User Join Date: May 2001 Location: Benbrook, TX Posts: 1,060	I have a set of I-6 motor mounts, will trade for the v-8 mounts __________________ 69 swb stepside, rebuild and upgrade in progress

08-05-2005, 04:44 PM	#7
HeavyD Senior Member Join Date: Sep 2004 Location: Wakaw, Sask, Canada Posts: 3,180	You want to put in a 6 just temporarily? IMO it isn't worth the hassle of switching it all around. Mileage won't increase by much if any, since the old sixes are not like a fuel injected 4.3 of today. I have a 250/3 spd in my GMC and it is not good on fuel at all. You might be better off seeing if you can get any V8 (267, 305) real cheap to throw in there for the time being. __________________ "You can take the man out of PA, but you can't take PA out of the man"

08-05-2005, 02:01 PM	#5
dave666693 Registered User Join Date: Jul 2005 Location: Edgewood, WA Posts: 901	what rear end gears do you reccomend for the best mileage?

08-05-2005, 06:58 PM	#8
68speedalert Semi-Senior Member Join Date: Feb 2003 Location: Washington, MO Posts: 390	Heavy D is right. I've got the same truck and gears in my '68. When I ran the 350 with 4v, it was a gas hog. When it popped, I 'temporaily' put in a '77 305 with a 2v. It now does better on gas than anything I own (sad part) and ain't bad on performance. It runs so well I haven't touched the 350 and it's been almost 5 years now. The six is REALLY gonna suck gas when you try to make it run like the 350 did. Those sixes were never know for their economy. __________________ '68 50th Anniversery LWB Custom Fleetside, '77 305 v-8, turbo 350, factory speed alert (still works), '71 drivetrain w/front discs. Some call it ugly yellow, others call it Ochre '83 Jeep CJ-7, <80,000 miles, original owner '04 Chevy Suburban, 4x4, 2500, 6.0 ltr, Predator Diablo programmer '95 GMC K1500 Extended cab

08-05-2005, 07:01 PM	#9
LUV2XCLR8 The LuvShack Garage Join Date: Jan 2004 Location: Maple Grove, TN (West Side) Posts: 30,474	Hmmmm, I had a 70 w/ a 250 mated to a 350 turbo, 4:10 gears, and got 20 MPG __________________ Owner/Op: "TN Classic Transport Carriers" The Toy: "Square Vette" 72 Hybrid Blazer Toy Barn: "LuvShack" 40 x 60 x 20 Shop Tow Piggy:"Maddy" 88 Silverado 3500 Hauler: "Feathers" 14 Aluma 8218T

08-05-2005, 09:01 PM	#10
wichitawings Registered User Join Date: Jun 2005 Location: wichita, ks Posts: 6	engine conversion I changed from a 250 6 cylinder to a 350 and I didn't have to change the motor mounts (I was able to use the 6 cylinder mounts). The 350 was pretty close to the firewall but it worked and everything lined up (I didn't have to get a new driveshaft or move the transmission even. I did get the v8 mounts later and move the engine/trans up and got a lengthened driveshaft. But I had an automatic and a shortbed. By the way my 350 gets the same mileage as the 6 cylinder which was in good shape still

08-05-2005, 09:29 PM	#11
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,179	I m running 2.76 in my truck (came with 3.73), I want to change it to 3.08, 2.76 is great on the highway, engine runs smooth and low rpms at high speeds but it has no take off with that range, I may put in 3.08 and see if that helps with some torque. A 2bbl would give you better mpg but would have less hp,,,you have to pick your poison also 2.76 will through your speedo off, thats why im using dakota digital, i can run anything and recalibrate my speedo. Smitty __________________ 71 C10 283/3SPD Full Resto 71 GMC 1500 Sierra Grande http://67-72chevytrucks.com/vboard/s...d.php?t=518599 70 C10 Suburban Former military GSA truck. 72 Chevy Blazer 4X4, Sloppy Jo, Mountain Climber. Wife says no more trucks. http://67-72chevytrucks.com/vboard/s...d.php?t=707378 72 GMC 1 Ton Motor Home, wife said no more trucks until she saw this one. Gen 3 6.0/4L80E 4.10 http://67-72chevytrucks.com/vboard/s...d.php?t=761110 68 GMC Suburban was 3/4 ton, now 1/2.Wife shook her head 71 C30 Wrecker 71 C20 Scott-Bilt As weird as it gets..BB Cheyenne AC Truck 68 GMC Long Stepside. They keep following me home 69 C30 Former Motor Home, Flat Bed time 70 G20 Red-E-Kamp Conversion "I'm your Boogy Van"



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