I6 to V8 Engine Swap - Vintage Mustang Forums
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post #1 of 49 (permalink) Old 09-09-2019, 09:39 PM Thread Starter
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I6 to V8 Engine Swap

I have 67 Mustang Coupe with the original inline 6 200cc engine. I have owned the car for a few years and have done quite a bit of work. Overall the car is in good shape, not great and not something that is super valuable. My 14 year son and I are rehabbing the car.

This summer I started having engine trouble. I lost compression in the 3rd cylinder and had oil pushing back through the breather cap. I tried a bunch of different things and then ended up calling in a few experts to help diagnose the problem.

I now have removed the engine head, had it pressure tested and looked over for cracks. The head is all good. All the seals are tight and no cracks. That means I have a problem in the small block

My question:
Remove the 6 cylinder engine and rebuild the small block myself or find a replacement 289 V8 engine ?

Any recommendations ?

How do I find a replacement engine ? What will fit in this car. 289 or 302 ? Can I keep my 3 speed transmission ?

Any help would be appreciated

thanks
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post #2 of 49 (permalink) Old 09-09-2019, 09:46 PM
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You'll need to replace the bell housing. You'll need to upgrade the front suspension. And you'll need to replace the motor mounts. The clutch linkage (I'm pretty sure) would need to be changed as well.

69 Convertible, 351W, T5, E-Brock Performer 351-W intake, Performer Plus cam, Holley 4160, power assist, dual exhaust, 4-wheel manual drums.
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post #3 of 49 (permalink) Old 09-09-2019, 09:55 PM
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It all depends on what you are comfortable doing. You can pull the six for a rebuild or purchase a remanufactured short block and reinstall your cylinder head.

You can also remove the six and install any of the Ford small block (221-260-289-302-351W-351C-400) or FE (332-352-390-406-427-428) V8 engines as well as the 385-series (429-460) with a bit of modification.

Note that the swap from the six to ANY of the V8's is going to mean substantial expense and work in the area of radiator, radiator brackets, engine frame mounts, throttle, clutch and shift linkages, fuel lines, front and rear brakes, springs and shocks, rear axle housing and differential, underhood wiring, starter motor, accessories and brackets (alternator, power steering pump , etc.).

As far as transmissions, you'll need the appropriate manual transmission bellhousing and the '67 3.03" 3-speed will be satisfactory for most any of the V8's, provided the correct size input shaft is used for the engine application.

In short.... unless you have lots of time AND money, stick with the six. If you're looking down the road to doing any further modifications you can look to swap in a later 200 six (aka 3.3 liter) from a late seventies/early eighties Fairmont, Zephyr, Mustang and a few other models.. they have bellhousing pattern compatible with the small block V8's so transmission choices are much greater, including the T-5 without as much "fuss" as behind the small six bell, larger clutches, better starter motor choices, larger diameter intake manifold, etc.

Visit fordsix.com to get "into" the six bangers more.
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post #4 of 49 (permalink) Old 09-09-2019, 09:58 PM
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Quote:
Originally Posted by FrankieThe69Kid View Post
You'll need to replace the bell housing. You'll need to upgrade the front suspension. And you'll need to replace the motor mounts. The clutch linkage (I'm pretty sure) would need to be changed as well.
...and the front brakes, and the front steering, and the rear axle... it can be a LOT of work and expense. If the super 6 was enough before, a good rebuild OR a replacement 250 will bolt right in, and when properly cared for the 6 can run virtually forever. There are lots of power enhancers for the 6 now, but it's hard to beat adding 50 cubic inches then adding the power enhancers ! ! You can always add the V8. It's just a lot more involved.

My 1st car...
'66 Tahoe Turquoise/ Aqua coupe
•289 / 4100 •C4 Auto •Disc Brakes
•Dual Exhaust •Quick Manual Steering
•Rally Pac •Console •Deluxe Belts
•LOTS of Rotunda accessories

Older son's 1st car...
'66 Emberglo / Parchment deluxe coupe
•289 / 2100 •C4 Auto
•Dealer A/C • Console
•Dual Exhaust • Power Steering

Younger son's 1st car...
'66 Nightmist / Blue & white deluxe coupe
•289 / 2100 •C4 Auto
•Factory A/C •Console
WAITING FOR RESTORATION

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post #5 of 49 (permalink) Old 09-09-2019, 09:59 PM
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Let’s cover a few terms first. You don't have a V6. You have a staight six often called a L6 or I6. When you remove the head the remaining engine is called the Short Block. The V8 engines are referred to as Small block or Large Block depend8ng on the family.

260/289/302/351. Small Block
427/428/390/429 Large Block.

Your car can fit either a small block or large block. In 67 you could order the car with a 200, 289 or 390.

To move to a V8 though you need to replace A LOT. The transmission, rear end, front suspension, steering, wheels, etc. All doable, but if you don’t have a donor car it gets expensive fast.

The 6 cyl engines are easy to find and often cheap. There is one for sale on VMF that is a fresh rebuild. Look on Craigslist people upgrade to V8s sell them all the time.

As for your current engine. Do you know it’s bad? It could be something as simple a blown head gasket.
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68 289 convertible Candy-apple red & white
66 200 coupe Blue
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post #6 of 49 (permalink) Old 09-09-2019, 10:02 PM
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I knew they'd be more... just wanted to hurry up and get the first word in on this one At least, nothing I said was incorrect. Chalk one up for "the kid"

69 Convertible, 351W, T5, E-Brock Performer 351-W intake, Performer Plus cam, Holley 4160, power assist, dual exhaust, 4-wheel manual drums.
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post #7 of 49 (permalink) Old 09-09-2019, 10:03 PM
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V6
Your local pick a part has a GT40P 5.0 waiting for you . But you'll need different brakes ,suspension ,transmission ,rear axle and various other V8 tidbits


Brad
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post #8 of 49 (permalink) Old 09-09-2019, 10:42 PM
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Stay away from a 250, its a lot of work, more work than a V8 swap.

I have a 67 with a 200/C4. Swapping to 5 lugs is pretty simple. No spindle or steering swap required. Driveshaft and u-joints work.

Upgrading to front disc brakes with Ford parts is simple.

A mild cam, more compression, a 68+ carb and distributor and a better flowing exhaust will really wake up a 200 in a 67, especially with a 3 speed.

200s are light, making power steering unnecessary.

Buy the Falcon Six Handbook. A comp Cams kit from Summit, flat top pistons, header and a 2V adapter with a Weber will almost double your rear wheel hp. The Weber will not give you much in the hp department, but the car will idle and run better and tune much easier.



1967-68 Mustang 6cyl to V8 Conversion - Average Joe Restoration


1965 Mustang Coupe 289/C4
1967 Mustang Coupe 200/C4
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Last edited by bmcgc; 09-09-2019 at 10:45 PM.
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post #9 of 49 (permalink) Old 09-09-2019, 10:51 PM Thread Starter
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Thanks everyone for the input. It sounds like the swap from a V6 to V8 is a much bigger deal than I am thinking. I just want to get this car running again with no issues. I am not looking for more power.

Here is my issue. Low compression in my third cylinder and oil blowback out of my breather cap. This was causing oil to drip on the engine and smoke me out inside the car.
I checked the PCV valve, no issues.
I ended up removing the head and had it checked out. No cracks and seals are all good.

I am not sure what is wrong at this point. I think it could be a bad piston or ring.

Should I pull the engine and do a total rebuild of the short block or try to remove one single piston and check the rings.

thoughts ?
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post #10 of 49 (permalink) Old 09-09-2019, 10:57 PM
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Yeah, the V8 and Inline 6 Mustangs were very different cars.

A fresh and well-tuned I-6 will pull like a mule and cruise at 80 MPH all day. Install and overdrive trans and it will do it effortlessly, quietly and use less gas doing it. Great cross-country cruiser!

As mentioned, you can even wake up the 6 a bit. Deck the block and mill the head to boost compression. Install a better cam. Calibrate the distributor. Install headers and nice dual exhaust. Find a better carburetor. This will be much easier, much cheaper and much more fun than PROPERLY converting an I-6 Mustang to a V8 Mustang.

My take is if you want a V8 Mustang, buy a factory V8 Mustang. It's not like they're in short supply. One exception would be if you're building a very high end custom Mustang will all aftermarket parts. In that case, you'll be replacing everything anyway, so starting with an I-6 Mustang doesn't make any difference.

Have fun!

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post #11 of 49 (permalink) Old 09-09-2019, 11:05 PM
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CL, Facebook marketplace and VMF classifieds turn up good running 200s pretty often. Lots of V8 swaps still going on.


1965 Mustang Coupe 289/C4
1967 Mustang Coupe 200/C4
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post #12 of 49 (permalink) Old 09-09-2019, 11:14 PM
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CL, Facebook marketplace and VMF classifieds turn up good running 200s pretty often. Lots of V8 swaps still going on.
A lot of these swaps aren't being done properly. One of my coworkers bought an I-6 Mustang with a V8 a few years ago. The PO had installed a V8 and C4 into the car and had done NO OTHER CHANGES. My coworker said he bought it for his wife. I politely recommended he properly convert the car before he let his wife drive it. Apparently, he eventually figured out the issues because he soon sold it.

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post #13 of 49 (permalink) Old 09-09-2019, 11:18 PM
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Your answer is waiting right here..

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66 200 coupe Blue
94 GT convertible Red & black
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post #14 of 49 (permalink) Old 09-09-2019, 11:30 PM
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I say rebuild your six and get back out there cruisin' and think about the V8 swap later. A V8 swap is doable but it is involved - no matter which way ( stock or hightly modified) you want to go. Plan that out well if you are going there. If you are going to rebuild your existing block, might I suggest you look at VINTAGE INLINES https://www.vintageinlines.com/ for a new head and intake manifold. There was an interesting article in MM a short while back although I'm not sure I have seen the dyno results on their I6 rebuild. Vintage Inlines' head setup seems light years ahead of the OE head with cast-in manifold. GOOD LUCK no matter which way you go!
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post #15 of 49 (permalink) Old 09-10-2019, 08:07 AM
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You probably just need new piston rings.

I've seen them break on this engine and you'll lose some compression and it will cause lots of blow-by but it'll just keep driving along.

Drop the sway bar and the oil pan and you can start taking pistons out. Just remove the caps, be careful with the bearings, and pop the pistons right out the top.

Since you haven't noticed any huge gouges in the cylinder walls or holes in the pistons the rings are likely your problem. You've almost got the engine torn apart enough to replace them so it should be a quick and easy fix.

Once it's back together check your timing too. It could be that the rings failed just because they're old, but if you're running the wrong carb/dizzy combo or pinging all the time that could be contributing to their early failure.

Last edited by Magnus; 09-10-2019 at 08:36 AM.
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