motor mounts V-8 vs Straight six - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Stevie G · 02-07-2007, 08:38 AM

What is the difference?
I'm guessing the point that attaches to the crossmember....since the V-8 mount sits 3" closer to the front.

cooters · 02-07-2007, 09:43 AM

On a 73 to 87, a 250 mount is lower than the 350 mount by about an inch or so but is not further forward. Never did the swap on a 67-72 but same principle should apply.

Aarons72s · 02-07-2007, 10:15 AM

Stevie here we go.

The 6 cyl mounts(250) mount in the rear mounting holes and a small block will bolt right up to them so you dont have to move the tranny forward and have to have a lengthened drive shaft. But as you said the engine will be 3" back. If you have a 292 then one of the mounts will be diferent, i think it was the passenger one, and will not work with the v8 swap or a 250swap you would have to get a 250 mount for the passenger side.

The 8 cyl mounts mount in the front mounting holes. They are also alot more massive than the 6 cyl ones. Plus the engine gets moved forward for more clearance and for the stock position.

Hope this helps.

72k20+afew · 02-07-2007, 02:21 PM

never done one on a 67-72 but on a 73-87 i took out a 250 and dopped in a 350 then a big block no changes i also took a 305 out of a 88 and put a 250 in no problems

fastwillie 696969 · 02-07-2007, 02:41 PM

my 70 had a 250 in it now 350 same mounts didnt have to do anything to it

bryanw1968 · 02-07-2007, 04:05 PM

My '68 had an inline six and now a 350. The mounts are in the back holes on the frame and the motor IMHO is way too far back. I can't even get the distributor out without pulling the cap off first so I won't run into the fire wall.
I know that the farther back the motor is the better weight transfer, but I'd rather have more clearance back there.

dilling · 02-07-2007, 07:20 PM

do you just move the frame brackets and move or do you need v-8 frame brackets ?

Longhorn Man · 02-07-2007, 07:24 PM

assuming you have a 250, and not a 292, you can use the ones you have, but they are taller. if you move them forward, there *MAY* be issues one day with U-joints or something. Bellhousing to floor board issues may pop up too.
Correct small block ones can be had pretty cheap.

brak · 02-07-2007, 08:30 PM

The bottom mounting hole in the crossmember is lower in the V-8 position, so you do need the proper V-8 towers.

I noticed this over the last summer, when i replaced the motor in my truck. The PO had installed a V-8 in the I-6 position, and i figured i could just move the mounts forward. No dice.

However, it is possible, but you would have to drill a new hole in the crossmember, but IMO it's just easier to pick up a set of V-8 towers.

Longhorn Man · 02-07-2007, 09:05 PM

thanks for the correction.

71meangreenc10 · 02-07-2007, 10:02 PM

What trans are you running, I did the swap correctly and If you are running a 3 speed you will have to get a v8 crossmember for the trans, the 6 wont move up into the frame, at least mine didnt, I had a 1 piece shaft made and it has given me no problems. If you have an auto you shouldnt have any issues with the crossmember.

Smitty

Stevie G · 02-08-2007, 11:07 AM

Found a set with a pic at manes truck parts.
I may just use the frame stands from the 76 we got the suspension from.
Thanks guys.

02-07-2007, 08:38 AM	#1
Stevie G Registered User Join Date: Apr 2006 Location: Bethlehem, GA Posts: 18	motor mounts V-8 vs Straight six What is the difference? I'm guessing the point that attaches to the crossmember....since the V-8 mount sits 3" closer to the front.

02-07-2007, 09:43 AM	#2
cooters Senior Member Join Date: Oct 2006 Location: Edmonton Alberta Posts: 458	Re: motor mounts V-8 vs Straight six On a 73 to 87, a 250 mount is lower than the 350 mount by about an inch or so but is not further forward. Never did the swap on a 67-72 but same principle should apply.

02-07-2007, 10:15 AM	#3
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,670	Re: motor mounts V-8 vs Straight six Stevie here we go. The 6 cyl mounts(250) mount in the rear mounting holes and a small block will bolt right up to them so you dont have to move the tranny forward and have to have a lengthened drive shaft. But as you said the engine will be 3" back. If you have a 292 then one of the mounts will be diferent, i think it was the passenger one, and will not work with the v8 swap or a 250swap you would have to get a 250 mount for the passenger side. The 8 cyl mounts mount in the front mounting holes. They are also alot more massive than the 6 cyl ones. Plus the engine gets moved forward for more clearance and for the stock position. Hope this helps.

02-07-2007, 02:21 PM	#4
72k20+afew Registered User Join Date: Dec 2006 Location: National City Michigan Posts: 15	Re: motor mounts V-8 vs Straight six never done one on a 67-72 but on a 73-87 i took out a 250 and dopped in a 350 then a big block no changes i also took a 305 out of a 88 and put a 250 in no problems __________________ No NO NO Sir Don't Want em Can't Use em Couldn't Afford em If I Did

02-07-2007, 02:41 PM	#5
fastwillie 696969 ~Rest In Peace~ Join Date: May 2005 Location: CALIFORNIA NOR CAL Posts: 9,707	Re: motor mounts V-8 vs Straight six my 70 had a 250 in it now 350 same mounts didnt have to do anything to it __________________ is it fast ? it has a lighting bolt donut? B___H please, I can remove 90% of your so called "beauty" with a kleenex

02-07-2007, 04:05 PM	#6
bryanw1968 Senior Member Join Date: Jul 2006 Location: Leander, Texas Posts: 850	Re: motor mounts V-8 vs Straight six My '68 had an inline six and now a 350. The mounts are in the back holes on the frame and the motor IMHO is way too far back. I can't even get the distributor out without pulling the cap off first so I won't run into the fire wall. I know that the farther back the motor is the better weight transfer, but I'd rather have more clearance back there.

02-07-2007, 07:20 PM	#7
dilling Registered User Join Date: Jan 2007 Location: massey Posts: 74	so what do you need to do v8 swap do you just move the frame brackets and move or do you need v-8 frame brackets ?

02-07-2007, 07:24 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: motor mounts V-8 vs Straight six assuming you have a 250, and not a 292, you can use the ones you have, but they are taller. if you move them forward, there MAY be issues one day with U-joints or something. Bellhousing to floor board issues may pop up too. Correct small block ones can be had pretty cheap.

02-07-2007, 08:30 PM	#9
brak Registered User Join Date: Apr 2006 Location: MinneSNOWta Posts: 1,381	Re: motor mounts V-8 vs Straight six The bottom mounting hole in the crossmember is lower in the V-8 position, so you do need the proper V-8 towers. I noticed this over the last summer, when i replaced the motor in my truck. The PO had installed a V-8 in the I-6 position, and i figured i could just move the mounts forward. No dice. However, it is possible, but you would have to drill a new hole in the crossmember, but IMO it's just easier to pick up a set of V-8 towers. __________________ 2003 GMC Sierra 1500 WT 1995 Nissan Hardbody 2016 Hyundai Veloster Turbo DC2 (SW/AW) Clyde W. Harvey USN "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery" Winston Churchill

02-07-2007, 09:05 PM	#10
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: motor mounts V-8 vs Straight six thanks for the correction.

02-07-2007, 10:02 PM	#11
71meangreenc10 Its a Truck Thing...... Join Date: Dec 2004 Location: Sierra Vista, Arizona Posts: 3,159	Re: motor mounts V-8 vs Straight six What trans are you running, I did the swap correctly and If you are running a 3 speed you will have to get a v8 crossmember for the trans, the 6 wont move up into the frame, at least mine didnt, I had a 1 piece shaft made and it has given me no problems. If you have an auto you shouldnt have any issues with the crossmember. 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 71 C20 Longhorn/Ole Yellor 69 C30 Former Motor Home, Flat Bed time

02-08-2007, 11:07 AM	#12
Stevie G Registered User Join Date: Apr 2006 Location: Bethlehem, GA Posts: 18	Re: motor mounts V-8 vs Straight six Found a set with a pic at manes truck parts. I may just use the frame stands from the 76 we got the suspension from. Thanks guys.

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