Sticky: I6 to V8 conversion

Rusty67

15 Year Member
Dec 3, 2002
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I6 to V8 conversion

Ok, since we get asked this question about 9 times a day, I talked to the mod and got permission to start a sticky thread for this.

What will I need to convert my 1964 1/2 to 1970 Mustang to a V8 ?

Power Plant:
You are going to need a complete engine. This means:
All of the accessory brackets
Front sump oil pan
Flywheel or flexplate for the correct transmission
Motor mounts
Motor mount frame brackets for the type of V8 you are installing (big block or small block)

Cooling system:
You will need a new radiator, that I6 on is not going to cool your new V8 engine. Upgrade to a 4 core copper or a 2 core aluminum (aluminum cores are 2x the size of copper cores)
New radiator hoses
I recommend to run a seperate trans cooler if you have an auto transmission (as I live in a hot climate)

Transmission:
You don't technically NEED to change from your I6 trans, you could just change the bell housing on the transmission BUT believe me when I say that the your I6 trans will not survive long behind your new V8. The 250 and 300 straight sixes have the same mounting pattern as the small block V8 so if you have one of these motors in, you can bolt your existing trans right to the V8 (Info provided by Hack, also see tjnavyblue's comments a few posts down). I still highly recomend geting a V8 trans to use !

If you have an auto and want to upgrade to another auto there are a lot of options. Ask around and ask us and we can talk about what kind you want/need. Same goes for a car that will end up with a manual trans.

Rear End/Driveshaft:
You need to change your entire rear axle assembly. People have got away with not changing this out in the past but just like an I6 transmission, an I6 rear end is definately going to brake. It was not built to handle the torque of a V8 motor. You can easily upgrade to an 8" or a 9" rear end (9 inch will cost more and may not be worth it for you). An 8.8" rear in is also possible but it is a lot of trouble and for the same or little more money you can have a 9".

As for the drive shaft, you are going to want a brand new one. Most of the early drive shafts were 2 piece units and they are not reliable and should be replaced ASAP. Stuff like that always brakes at the most inconvienent times.

Front suspension:
You are going to need to change the front suspension for a couple reasons. Your rear end now has a 5 lug wheel pattern and your front has 4, matching is a good thing. Also, the old 4 lug stuff isn't strong enough to support that new V8. You will need to change your:
Front spindles
Coil springs
Shocks
Upper control arm (not sure)
Lower control arm (not sure)
Strut rods (not sure)

Rear suspension:
Leaf springs
Shocks

Brakes:
Hopefully the V8 spindles you get will get will have brakes with them. If not you are going to need to put some brakes on them. You can get drum brakes for the front but DON'T. There are a myriad of brake options for the front of these classic Mustangs so put on something that will stop the car well. This isn't the place to discuss brake upgrades. Maybe we will make another sticky for that later ! Just make sure you put on adaquite stoping power for you new motor !

As for the rear brakes, a lot of people feel that drums are fine. I'll be puting discs on my rear soon, I don't like the way drum brakes react and they are a pain in the butt to service.

Steering linkage:
More stuff to change ? Thats right.
Inner tie rod
Outer tie rod
Drag link
Idler arm

Exhaust (added at 65fastbackresto suggestion):
Your I6 exhaust system is not going to work with your V8. You are basically going to need an entirely new exhaust setup. It is more expensive, but PLEASE try your best to get a mandril bent exhaust instead of a crush bent exhaust. They look better and perform much better.

Misc.
On a 64-66, the gas pedal will need to be changed (added at 65fastbackresto suggestion). I'm not sure about other years.

Now, I don't claim that this list is 100% complete or 100% accurate. Little things vary by year and I might have forgot stuff. As people post more or PM me information I'll edit this post to make it more complete and accurate. Something we didn't cover in here ? Post it in the forum !
 
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Hack

15 Year Member
Mar 23, 2004
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Good post, but it's already stickied in the FAQ in classic talk.

edit: I see that the link in the FAQ currently isn't working. Hopefully it can be fixed.
 

65fastbackresto

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Apr 13, 2007
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2 piece drive shaft?

I`m doing a I-6 to V-8 conversion, but I got a one piece drive shaft, but....I have found other evidence that a V-8 has prob been in this car in the past.

I guess if it was 2 pieces it would be pretty obvious? LOL

OH, dont forget the exhaust, I`m looking at almost $1000 for quality headers, x-pipe, and exhaust pipes, this was one expense I underextimated big time. I could do it cheaper.....but I`d be cheating my motor outta what its capable of.
 

geostang351

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Mar 30, 2005
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OH, dont forget the exhaust, I`m looking at almost $1000 for quality headers, x-pipe, and exhaust pipes, this was one expense I underextimated big time. I could do it cheaper.....but I`d be cheating my motor outta what its capable of.
:eek: :eek:

You may want to price this around if this is the cost you're looking at.
 

65fastbackresto

Active Member
Apr 13, 2007
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headers and stuff

Headers are $526, x-pipe is $100, rest is pipe work. After spending 4k on the motor SO FAR, and it aint done, want all it`ll make, quality headers are the biggest expense, but good ones should outlast the motor I hope.
 

Hack

15 Year Member
Mar 23, 2004
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Since this is being stickied..

You don't always need to change the bellhousing for a 6 to 8 swap. The 250 and 300 straight sixes have the same mounting pattern as the small block V8.

As you have said though, the motor brackets and mounts are different.
 

Rusty67

15 Year Member
Dec 3, 2002
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Seattle area, WA
Good to know, I'll edit the first post.

Would the 250/300 trans hold up to the abuse of a V8 or are they as week as the 200 motor's trannys ?
 

tjnavyblue

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Feb 21, 2007
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While a 300 will bolt up to a v8 bellhousing this is not a big help for Mustang owners. 300's never came in mustangs and are in fact harder to install than V8's due to overall height and length. Over at Fordsix.com they have a few, but they are labors of love and not something the average joe would want to install. Some 250 bellhousings will work after some point in the 1970's. Again, www.fordsix.com is a great place for mustang six information. Their FAQ page has all of this information.
 

65fastbackresto

Active Member
Apr 13, 2007
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Heres another item you can add to the list

Throttle assembly is different, all the way from the gas peddle to the carb needs replaced.

Found one though, YEA.
 

57fairlane

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Apr 2, 2005
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my cent and half to add is that the inline six throttle linkage is shorter and operates on the passenger side of the motor where as the v8 setup is taller and on the driver side. You can weld something up but is much easier to use a v8 throttle linkage.

I also had to add an extension plate for my transmission linkage when using the column shift and longtube headers.
 

65fastbackresto

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Apr 13, 2007
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Transmision linkage

if you have a floor shift, save the old shift linkage from your 6 cyl tranny, have it put into your v-8 tranny, there are a bunch of different kinds of these apparently. My tranny guy pretty much insisted I bring him the old tranny so he could change this part out.
 

65fastbackresto

Active Member
Apr 13, 2007
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You can add pitman arm

to the steering section. yea, I just crossed this bridge.

Soaring 1, as to your comment on "this sounds expensive". I did pretty much everything on this list at it was pushing 14K with all new parts (cept for motor from salvage year).. I could have saved a little money here and there, but I couldve spent alot more here and there to. If your gonna do a 6 cyl to v-8 conversion and do it right you better have a fat wallet.
 

65-Fstbk

Active Member
May 20, 2007
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Not That Bad

I really don't think the I6 - V8 conversion is that big a deal. The key is your time frame and whether or not you can do the mechanical stuff yourself. So far for me its been a pleasant experience.

If your restomodding one of these cars keep in mind there are a few constants whether or not your doing the I6-V8 conversion.

You will be building a new engine anyway. I picked up a complete 289 with original bore from a 67 mustang for dirt cheap.

I picked up Granada spindles complete with outer tie rods and proportioning valve for $75.00.

Stock 8" Mustang 5 lug rear $100.00. (You would probably re rebuilding the third member anyway on you V8 car)

Restomod exhaust will need to be redone whether it's a I6 conversion or a stock V8 car.

I will be putting in a WC T5 trans (rebuilt with upgrades $750.00)

Complete steering parts from Pittman arm through tie rods...$380.00 new.

Not that bad if spread out. My advice, take your time and have fun with it.
 

2+2GT

Well-Known Member
Apr 25, 2009
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Cooling system:
You will need a new radiator, that I6 on is not going to cool your new V8 engine. Upgrade to a 4 core copper or a 2 core aluminum (aluminum cores are 2x the size of
I recommend to run a seperate trans cooler if you have an auto transmission (as I live in a hot climate)
A 3-row brass radiator is about 90% as effective as a 4-row. Use a fan shroud and thermal clutch fan to improve this. Radiators have built in trans cooler, which doubles in winter as a trans heater. Figure where and when you drive, and decide.

Rear End/Driveshaft:
You need to change your entire rear axle assembly. People have got away with not changing this out in the past but just like an I6 transmission, an I6 rear end is definately going to brake. It was not built to handle the torque of a V8 motor. You can easily upgrade to an 8" or a 9" rear end (9 inch will cost more and may not be worth it for you). An 8.8" rear in is also possible but it is a lot of trouble and for the same or little more money you can have a 9".
If you worry about the 8", don't. It was an 8" version of the 9", even used the same 28-spline axles. If you get a four-pinion Traction-Lok™, or similar aftermarket diff, it'll be as strong as a 9", except the 31-spline version.

As for the drive shaft…
The 64-66 V8 was never 2 piece, and would be fine. The 2-piece was often used on big engine Mustangs and Shelbys, I've never even heard of one failing. A new one-piece is the way to go if you don't have a nice used one handy.

Front suspension:
You are going to need to change the front suspension for a couple reasons. Your rear end now has a 5 lug wheel pattern and your front has 4, matching is a good thing. Also, the old 4 lug stuff isn't strong enough to support that new V8. You will need to change your:
Front spindles
Coil springs
Shocks
Upper control arm (not sure)
Lower control arm (not sure)
Strut rods (not sure)
No! The spindles need only be changed on 64-66 cars. Struts, upper and lower control arms were the same on 200 cid through 428 cid.

As for the rear brakes, a lot of people feel that drums are fine. I'll be puting discs on my rear soon, I don't like the way drum brakes react and they are a pain in the butt to service.
Shelby dominated SCCA B production with 2.5" rear drum brakes. How bad could they be?

Steering linkage:
More stuff to change ? Thats right.
Inner tie rod
Outer tie rod
Drag link
Idler arm
Only on 64-66. 67-up these were the same.

On a 64-66, the gas pedal will need to be changed (added at 65fastbackresto suggestion). I'm not sure about other years.
67-68 also. Beware, if you are using a 390/428 and automatic, this throttle lever was different than the 289/302 item.
 

68Blue302Coupe

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Jul 30, 2005
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Regarding the suspension and steering, I thought the upper and lower control arms, tie rods, and spindles for 1967-68s were the same regardless of I6 or V8. I know they ARE different for the 19641/2-1966s. However, you'll probably want to replace most of that anyways if its original since it will most likely be pretty worn out.

I believe the fuel line will also need replacing?
 

BA Mustang

New Member
Jan 10, 2009
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Regarding the suspension and steering, I thought the upper and lower control arms, tie rods, and spindles for 1967-68s were the same regardless of I6 or V8. I know they ARE different for the 19641/2-1966s. However, you'll probably want to replace most of that anyways if its original since it will most likely be pretty worn out.

I believe the fuel line will also need replacing?
They are the same.
 

D Durden

DEEP FAT FRY
Founding Member
Mar 9, 2000
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Has anyone done a cost justification to compare the cost of putting a V8 in an I6 Pony versus selling the I6 pony and buying a V8 car? Just curious to see which one would be the better choice.