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67 390GT, what are they like?

2K views 20 replies 12 participants last post by  sdcohe 
#1 ·
So I bought my 67 390GT 6 years ago from CA and brought it back to the UK.

In this time it’s been stripped to its shell and being built back up. Nearly finished

I’ve never driven a Mustang let alone a 390 but what are the common complaints about the 390. People I have spoken to don’t rate them, is that because they don’t have one? Or is it because they’re too big for the engine bay meaning they’re a PITA to run and maintain. ?

Sneak preview as it’s not yet finished.
 

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#3 ·
I hear that it will pass everything but a gas station.
Partly why this winter I'm installing a 22 gal tank and a TKO, plus an Edelbrock.
As far as driving, it has enough torque to pull down a building and is a blast to drive, but don't expect Lotus-like handling!
And nothing, absolutely nothing, sounds like an FE.
 
#5 ·
As you see by my signature, I own an orig 67 GT factory 4spd, tried to keep mostly stock. And because I could, just to make it over the top I added tri-power. Being a 4spd it's a blast to drive. Since it's a weekend car, don't care about gas mileage. I can say driving it back from Carlisle PA to NH doing about 65 I got 16 mpg.
So as you build your car, take time, use quality parts, pay attention to details and it'll treat you right. In 14 years on the road, it has been very reliable. My engine was a mild rebuild because of tri-power and chassis Dyno put my torque at 425 foot lbs torque.
 
#7 · (Edited)
They're amazing for making tire smoke, but they do poop out pretty fast on the top end of revs. GPM are incredible. (grins per minute) - especially the sound.

Spark plugs and exhaust manifold bolts are a pain to get to. Even with the Shelby mod and beefier GT suspension, they feel pretty nose-heavy, and want to understeer, although I am used to my smallblock, so maybe that's bias on my part. Great in a straight line, but not as much for going through corners, although steering with the throttle is AWESOME if you can afford more tires.

If you use aluminum parts (heads, intake) it makes a tremendous difference in both handling, and the way they rev. The factory exhaust is restrictive as well, but then, given that it has to hang straight down to fit between the fenders, what else can you do?

Absolutely dead-on reliable. Not even very stressed, in a stock state, will run forever with proper maintenance. Just make sure the carb is doing what it's supposed to, mostly, to keep them happy.

Keep in mind, the cost of parts for this engine are why it's got the name FE. "Freaking" expensive. =)
 
#12 · (Edited)
With patience, flexible ratchet extensions and normal sized hands, spark plugs aren't a problem. Those look like tall valve covers, so it might help to pull them first to give your hands a bit more room. The engine most definitely stays in place.

How many times do you need to change plugs anyway? With a good ignition system and carb tuning, modern plugs will last years.

The 390 wasn't Ford's best performance effort in its day, but it is an FE so it has performance potential and options (427/428 parts, aftermarket, etc). I see you've already lost the anything-but-light intake and exhaust manifolds, so you're off to a good start.

Since the engine isn't a rev monster, concentrate on tuning that makes it responsive (don't over cam or carb it, dial in a nice timing curve, a small spacer under the carb, etc) will make it snappy and a joy to drive for sure!
 
#9 ·
Nice!!!

And the Shelby Mod is a simple relocation of your upper control arm where it bolts to the shock tower. The factory steering geometry for these cars was designed to cause understeer. If you go into a corner too fast, you'll find that the car just continues on right into the ditch, regardless of you turning the wheel.

This was a 'safety feature' inspired by the insurance companies as much as anything. Oversteer is fun. When you go into a corner and hang the tail out, that's loads of laughs. Plonking your car's front end into a fence or tree is not. So, car manufacturers put the top control arm at an angle. When the suspension compresses, the top of the tire leans out, rolling you off your treads onto your sidewall, and causing a loss of traction. BAM. Understeer.

The Shelby mod levels out this upper control arm's angle, allowing you to keep your tire tread planted square on the road as you go through a hard turn. It usually lowers the front end ride height by around 1/2 to 3/4" as well, and assists in preventing body roll.

All in all, the Shelby Mod should probably be the first performance improvement to any early Mustang or Cougar. And, it's free! You can find templates for where to drill the holes on a million different places. Print one out, drill the new holes, bolt your upper arm back up to them, get it aligned, and you're done.

Oh! While you're getting your alignment done, make sure you use modern specs for radial tires. The original bias-ply alignment numbers are terrible. Your car will return to center much better, have less of a 'wandery feel' and will handle with confidence if you have things done right.
 
#10 ·
Forgot to mention, having the Ford tri-power set-up, another plus is the intake in aluminum. I also have Edlebrock aluminum heads (name milled off, painted blue) so save a fair amount of weight. As for spark plugs they'll be the smaller 5/8" socket shaved down. That with 3/8" drive and swivel, pretty easy to change. But only driving 1-2k miles a year. Be awhile before I have to even worry. I did not want to use headers, not racing. But since the aluminum heads have different exhaust bolt pattern, I found a set of original SCJ exhaust manifolds that bolted right up. Bit larger tubes than 390 so flow better.
 
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#11 ·
Don't be skeered to change plugs, eh?
I can have them out and back in under 20 minutes.


Key is a swivel head 3/8 drive ratchet wrench and just a sparkplug socket.


You may want to consider removing the CA emissions equipment and plugging the holes in the manifolds.
Then re-jet the carb to the non-emissions jet size ;)
(I swapped out old/incorrect carb for the non-emissions Holley)
 
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#13 · (Edited)
I’ve never driven a Mustang let alone a 390 but what are the common complaints about the 390. People I have spoken to don’t rate them, is that because they don’t have one? Or is it because they’re too big for the engine bay meaning they’re a PITA to run and maintain. ?
Other than a slight difficulty getting to four of the spark plugs, just as maintainable as any other. Mileage is surprisingly good if the tuning of the engine is properly set up.
The Shelby mod levels out this upper control arm's angle, allowing you to keep your tire tread planted square on the road as you go through a hard turn. It usually lowers the front end ride height by around 1/2 to 3/4" as well, and assists in preventing body roll. Besides, you've taken maybe 100 pounds off the engine.

All in all, the Shelby Mod should probably be the first performance improvement to any early Mustang or Cougar. And, it's free! You can find templates for where to drill the holes on a million different places. Print one out, drill the new holes, bolt your upper arm back up to them, get it aligned, and you're done.

Oh! While you're getting your alignment done, make sure you use modern specs for radial tires. The original bias-ply alignment numbers are terrible. Your car will return to center much better, have less of a 'wandery feel' and will handle with confidence if you have things done right.
The Arning Drop [AKA Shelby mod] was developed by Klaus Arning for the IRS project, and is nothing short of transfomational.
https://cdn.website.thryv.com/7fc8b09813234ba0b3c5e3c0a1b8c109/files/uploaded/ArningShelby%20Suspension%20Drop.pdf
Great thanks.
I heard they are a heavy lump thus understeer.
Not really. Most would agree the 5.0 Mustang of the 80s-90s handled very well. It has the exact same F/R weight bias as the 67-70 BB Mustang. Put in a high-quality export brace, 1" front sway bar (be careful, you need one compatible with the BB engine) and the Arning Drop, and you wouldn't know it was the same car.
With patience, flexible ratchet extensions and normal sized hands, spark plugs aren't a problem. Those look like tall valve covers, so it might help to pull them first to give your hands a bit more room. The engine most definitely stays in place.

How many times do you need to change plugs anyway? With a good ignition system and carb tuning, modern plugs will last years.

The 390 wasn't Ford's best performance effort in its day, but it is an FE so it has performance potential and options (427/428 parts, aftermarket, etc). I see you've already lost the anything-but-light intake and exhaust manifolds, so you're off to a good start.

Since the engine isn't a rev monster, concentrate on tuning that makes it responsive (don't over cam or carb it, dial in a nice timing curve, a small spacer under the carb, etc) will make it snappy and a joy to drive for sure!
I must say I haven't changed the plugs in either of my classic cars in over 10 years.

The street performance of the 390GT is excellent, its reputation for weakness is borne out of NHRA drag racing, where the 67-68 Chevy 396 held a slight edge. This flipped in 68 with the introduction of the 428CJ.

Tuning of these engines is critical. Often overlooked is the advance curves of the distributor. Must be professionally set, preferably in a Sun distributor machine. A difference of only 1°-2° on either centrifugal or vacuum can transform the engine from dog to tire-ripper.
 
#14 · (Edited)
Whether it's in a truck or a Mustang, the 390 is the engine equivalent of Chuck Connors. It is a mean old buttkicking man that can take a lot of abuse and never complain. It always delivers, and has plenty to get the job done.

In Mustangs, they get 'tinkered with', and when the timing and fuel delivery is off, they can get fouled or burnt, but in comparison with most engines, they are very tolerant.

I had a friend with a much-abused 390 in his late 60s Ford farm truck that was burning quite a bit of oil. It started right up, ran okay (if a little noisy). Was down on power, and it seemed like the rings were just shot. We decided to rebuild it.

When he pulled the pistons out, all the pistons were badly damaged. Three of them were completely shattered. They literally fell to pieces once they were pulled out, and it was still *RUNNING* when he shut it off. Is that a good testament to the engine's toughness? I don't know, but it was sure impressive to me. We bored it .030, put it back together, and as far as I know, he's still driving it. I fixed his timing so hopefully they're not blown apart again.
 
#19 ·
Whether it's in a truck or a Mustang, the 390 is the engine equivalent of Chuck Connors.
I don't if many people here are old enough to remember Chuck Connors. Maybe you meant Chuck Norris. I think they were equally "He-man" types. But, I agree about the 390. Before I got my 67, I had a 68 "S" code/four speed Mustang that I had bought from a cousin of mine. The trans had a bad first gear, so I had take off in second. With 3.00 gears and the stock Holley carb, I could still spin the rear tires with little effort. It was a blast!
 
#15 ·
The neat thing about a 390 Mustang is they are quite rare. But stock they will not hang with a modern car. With mods they are better but still not a modern car.

I am likely to get some flames with this but facts are facts. Cars and engines have come a long way in 50+ years. Crap, they have come a long way in 25 years. It blows my mind that the 2.1 liter 4 banger in my Mercedes SUV has 204 horsepower and 369 ft/lbs torque and gets 44 US mpg. My 1994 F250 has 190 hp, 370 torque and not many mpg out of 7.3 liters.

We can be romantic about our old Mustangs but the facts are they are old technology.

I love my 65 for what it is: a beautiful old car.
 
#16 ·
Well, pprince, you're not wrong about most of that. But I disagree that they 'won't hang with a modern car'. It takes a lot of work, especially when it comes to updating the handling on these. With the exception of mileage (which is easier to get with a tiny 4V motor, slippery aero body and a turbo), they can be a match for just about anything.

Maybe it won't inflate your lumbar support and drive you to work automatically. But there's a reason people still love and drive these cars, even so many years after they were first built.

But these cars do one thing much better than any modern car will. They last. They can be worked on, rebuilt, and improved on. They don't have wiring you can't get to, or unobtanium computer controllers that will be dead in 10 years with no available replacements - even if you could find the circuit that's not working.

There are some cool things about modern technology. I love the new AFR heads, and carburetor-style fuel injection systems that are out now. I don't think it's wrong to put better brakes on an old 'Stang that you drive either.

I *love* that these cars are worth keeping, that they can be enjoyed by us, and by our kids, and maybe even our grandkids someday - even if they're bone stock.
 
#17 ·
My orig 67 390 vert besides huge "fun factor and sound", and having won many trophies, been in a music video, numerous magazines including Mustang Monthly. I can't say any of that will ever be true of my modern cars/truck.
Very few new cars that are affordably can be bought with a standard shift. I love my 67 with many trans, won't have it any other way!!!
 
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#21 ·
I own a 67 S code hardtop that I bought used (and abused) in 1974 when I was in high school. I daily drove it for about 15 years and turned the odometer over multiple times. I drove it all year round through the rain, mud, snow and salt. I still own it today but only drive it on nice days and to shows. Too bad as it is probably a better driver now than it was in the 70's and 80's.

Changing the spark plugs is a chore compared to the small block cars, but is still very doable. An old Ford mechanic saw my 1st ever attempt at changing the plugs and let me borrow a 1 inch extension that he said would help me reach all the plugs. He was right and I immediately went out and bought one for myself. That was with the stock valve covers. With the taller pent roof valve covers it is still possible, but removing the valve covers makes it easier. I did plug changes twice a year for the entire time I daily drove the car. So I've done it quite a few times although I'm way out of practice now.

In all the time I daily drove the car I thought the handling was just OK at best, but not really that great. I could always out handle my friends in their mid and full size cars, but none of our cars really handled all that well back then as they were all used and well "broken in" muscle cars, not new cars. Of course for me that was on bias ply tires and some poorly done "professional" front end alignments. With radial tires, sorted steering and suspension, and a proper front end alignment I feel that the car actually handles fairly well now. People who ride in my car are usually surprised at how well it rides and handles, especially for a 52 year old car.

As to the big block, I like all the Ford engines, but I have a special fondness for the FE big blocks. My best friend in high school had a Galaxie with a 390 that we rode around in all the time. And all that torque in a light Mustang with a manual transmission was (and still is) tons of fun. With a fairly stock engine you can putt around town and in traffic at low RPMs with no problems, but easily break the tires loose if you want to get squirrely. I managed to surprise a number of people, especially the ones who didn't believe a Mustang could have a big block under the hood.

Thanks for letting me reminisce. Can't wait for the show season to start so I can get out and drive!
 
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