68 Mustang Engine Options

I am exploring what options there are for improving the performance of my 68 Mustang.

Currently I have a 200 Cubic Inch single barrel straight 6 backed by a 3 speed.

My understanding is if I want to upgrade to a v8 say a 289 that I would have to upgrade the whole under carriage (rear end, drive shaft, leaf springs, engine mounts, a-frame, springs, suspension, front end etc - $$$$

Other option is to look at staying with a 6 cycl looking at one that is bigger or just rebuilding the one I have. Also is it possible to attach a 4 speed to a 6 cycl or is that just over kill.

Thoughts on this?

Only serious option is to replace the 200 with a 302. There are some performance parts for you 6 from Clifford:
But the results will be pretty limited. As for a 4 speed, I had one on my 170 cid '65 Mustang. A little better, but it doesn’t really change the performance much.

The conversion parts for you Mustang are readily available (much more than just the engine, as you said), but the easier (and probably cheaper) route is to just sell yours and buy one with a V8. LOTS of them out there.

Six cylinder and V8 Mustangs of that vintage were VERY different cars… Your understanding is correct. The suspension, steering, brakes, running gear are all different. 4-speeds were in great demand and were seldom found in the six cylinder cars. I think they were only available in the V8 cars…You would gain little by installing one…

What limits the performance of the Ford six is the cylinder head with it’s cast in intake manifold. That head/manifold simply does not breath very well. However, aftermarket heads were made for that engine and a few hot-rodders would cut off the “log” and with some fancy welding and machining, install 3 Weber side-draft carbs along with other head work… These engines found their way into USAC Midget race cars of that era.

It was a lot cheaper then and now just to buy a V8 powered car than to spend a lot of money on improving the six…But the six is a better balanced car and they handle better everything else being equal.

I found this in WiKi…Looks like someone is making a trick aluminum head for these engines…

“The 250 cu. in. Inline Six was an engine option offered in 1969 in the Mustang, and 1970 in medium-sized Ford cars (Maverick). The 250 was a stroked 200, made by changing the stroke from 3.126” to 3.91". Output was 155 hp (115 kW) in the Mustang, and became the base engine in 1971. Power was re-evaluated at 98 hp (73 kW) for 1972 (due to power rating changes) and 88 hp (66 kW) the next year. The last year of production for the 250 was 1980. This engine had seven main bearings, and can be identified by the five freeze (core) plugs on the side of the block. The block uses a low mount starter and six bellhousing bolts, sharing its bellhousing with the Windsor V-8s 302-351W, late (1965–68) 289, 351 Cleveland, early 4.6, and the 240-300 CID Ford Six.
Restoration and restomod status

The rising cost of fuel has increased the interest in the Falcon six design, and the engines have been gaining in popularity in recent years. Many Falcon and Mustang owners who used to replace their car’s original I-6 engine with a V8, are now keeping their inline sixes for the better fuel economy the inline six motor offers. A number of restoration and performance parts vendors now stock parts for people restoring their inline six motors.

Due to increased popularity of the Falcon I-6 engine, the desire for improved performance, and difficulty in finding good quality used parts for an engine that has been out of production for 25 years, in 2005 the company Classic Inlines designed a modern aluminum head based on the Australian 250-2v head but with raised intake ports, high swirl combustion chambers, and larger valves. One of the features of the new head are pads cast into the top of the intake runners, which allows owners the ability to machine the head to accept modern electronic fuel injectors for direct port fuel injection.

Not only does the new head improve power output, but also the high-swirl design improves fuel mixing in the cylinder for a more complete burning of the air fuel mixture, resulting in reduced emissions output.

That six wasn’t a bad engine. The block is fine, but it was tuned for smoothness over power. As @caddyman indicates there are lots of opportunities to get more performance. Adding some zip to the six in there now is going to much cheaper than dropping in a V8 and making all the other needed modifications that go with it.

You need to increase the breathing of the six; which means better heads with larger valves, better intake manifold, bigger carbs, and less restrictive exhaust. All parts are available to do these things. The exhaust note isn’t too bad from these motors either with a good exhaust system. A different cam will make a difference to if you want to get deeper into the motor. In the end you’ll give up some idling smoothness, and you won’t get all the torque of a 289, but once the revs are up a bit it should be a pretty zippy fun ride.

put electric drive on the front wheels…recharge once in a while.

I’m not so sure it’s much cheaper to hop up the 200, looks like just a new head (needed to get better breathing) and carb is about $2,000:
Then come the cam, headers, etc, etc. But it would be a fun project, something unusual. Just remember, the more the mods, the lower the mpgs.

Here’s one example of what it could look like:

I’m not real sure that yo have to do all those mods for a 289 conversion. The 289 was a fairly light engine for a V8, but you course you will have to deal with the additional torque. The thing was that in 68, you could get a 390 and that was a heavy, high torque engine that would require all those mods.

If you don’t build up the 289, just use a stock 2 barrel 289, the I6 chassis might be able to handle it. I believe the real issue will be the torque, not so much the weight of the engine. The rear end might not take it for long and if the 68 had leaf springs in the rear, you may need to add some light weight traction bars to keep them from hopping on you.

@keith - I’m not sure about the '68, but I know that the '65-'66 Mustangs with the 6 (like mine) had MUCH weaker brakes, 4-bolt wheel hubs, weaker springs, rear axle, etc. All were significantly stouter on the 289 version.

texases, I am not doubting that the 68 Mustang with any V8 probably had the beefier stuff, but I am saying that IF he sticks with the lower power version of the 289, I think he can get away with it. Before Ford made the 302 an option in the Maverick, people were putting 289/302’s in them. When Ford made it an option, they also beefed up the car as well.

Now if someone got real serious about the 302 in an early Maverick, like using the Boss version or better, then they had to do some serious mods to the rest of the car as well. But for the Saturday night red light Grand Prix, a simple 289/302 conversion in an early Maverick was a cheap thrill.

But have you seen the puny 4-bolt hubs and tiny brake drums on the 6 (I checked, the '68 also had the small hubs/drums)? They were marginal in '65 for the 6, much less in today’s traffic with a much faster V8. I’d want the disc brake upgrade, really for either the 6 or the V8.

Good brakes? That’s a different issue all together.

Upgraded (V8 style) brakes are a major part of the V8 conversion, they require the new rear axle and front spindles, I think. Once you’re in that far, the other parts aren’t much more work.

A '68 Shelby 500 had a 428 super Cobra Jet with about 360 HP. Try one of those.
My son put a Daytona 427, 600+ HP in a '68 but it took some cutting and welding.

Have personally seen a 68 Mustang with a 390 coded car and factory installed 4 lug suspension. Only issue that car had was fractures in the front shock mounts which I understand was present on all 390 cars. I’m not sure all suspension mods will be necessary just to change over. If trying to pass as a real V8 car from the factory then it will be needed.

Thanks for all the great responses.

Based on all this info I am going to go down the road of fixing up the 68 mustang - new dash, radio, front seats and front end (handles like crap), keeping the I6 and 3 speed. And then keep an eye out for a 65 - 69 V8 mustang or 67 - 69 V8 camaro in my price range. And to offset the cost sell the current 68. Might explore some of the options about having the engine breath better - and see if it really is worth it and how much I can do myself.

FYI, the pittman arm on these Fords tend to get very sloppy with age and can be the source of really bad handling, even after the shocks are replaced. Don’t overlook it.

I had a '67 Mustang 289 2 bbl with 3 speed stick. It had non power brakes and it came with 5 bolt wheels and the only option was the wide oval tires. I’d don’t believe a factory installed 390 came with 4 bolt wheels. Something fishy there.