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67 Mustang 351Cleveland engine change

My son has a 67 Mustang and wants to put a 351C engine in it. We thought it had a 302 but there is a tag on the intake that says 289 so we are not sure. Assuming it is a 289, is there a need to change the transmission? Is there a need to change the differential?

I know the 5 speed manual put in Mustangs in 1971 would match the 351C better, but is there any reason why he couldn’t leave the tranny and differential in the car and just put in the 351C?

The input he has gotten to date says the tranny will work fine. Today, some auto parts store guy said that he needed to put in the 5 speed because he would end up damaging the tranny that is in the car now. He is fit to be tied with this question now.

Any help would be most appreciated.

The tranny and the rear end should be OK…But there will be lots of little surprises. The Cleveland engine is physically larger and heavier than the original 289…The fan will probably hit the radiator unless the very short 289 water pump will fit the larger engine…The exhaust manifold on the left side will be very close to the steering…There will be other surprises…

The standard motor in '67 was the 289. The 302 came along a year or two later. There is lots you can do with a 289 and it is a great motor so I’m not sure why he is so hot on changing it out to a 351.

The engine compartment isn’t that big and the big block Mustangs didn’t come out until a few years later in the model run. At one point you had to undo a motor mount and jack up the motor to change a couple of the spark plugs on the big block motors.

Changing to a 351 will actually reduce the value of the car, since the OEM motor is a 289. I’d either work with the 289 you have in there now, or get a 72 Mustang that can handle the bigger motor.

At least you don’t have electronics and pollution controls to deal with. If he can make it fit, it should work. The 289’s came with a 3 speed stick or 4 speed. They were OK trannys but perhaps not robust enough to handle a hopped up 351. If he expects the 351 to put out 400 hp and is headed to the drag strip he’ll need a stronger tranny.

This is a doable swap for the most part. A couple things to consider. If you don’t already have the engine, a 351W will swap in easier and be cheaper to obtain. 351C’s command a higher price and aren’t as plentiful. IIRC The 1971 Mustang did not come from the factory with a 5 speed. It would probably have a 4 speed manual. You really can’t gauge a transmissions strength by the number of gears is has, so I’m not sure what the auto parts store guy was going for. What transmission does the car have in it now? You may be okay with the stock rear axle. If it’s the venerable 9 inch then you’ll be fine.

He can work a 289 as much as needed. GRANTED, the Cleavland can handle much more power output and hold together compared to the 302. No comparison in durability at higher power output.

There were no OEM 5 speeds in a passenger car at that time. Maybe a heavier truck (in the 1.5ton class or higher).

The fact that he’s looking toward the engine and wanting to keep the much cheaper components kinda tells how the funding is for this project. I’d go with the working of the 289 or getting some crate 302. Easy bolt on power is available and only limited by his credit card limit in the Jeg’s catalog.

btw- don’t have him order ANYTHING from Jeg’s on line. Assemble a list of IDENTICAL parts from Jeg’s and Summit and play tag with a live customer service person. They get commission on those sales and WILL compete on IDENTICAL ITEM FOR IDENTICAL ITEM head to head. “Why should I buy this from you? Jeg’s will give me the same price”.

The listings are only what the vendor agrees to advertise the given products at. If it were fixed, that would be illegal. Naturally they’re not going to cut you much on $100 …but on the (former) “dying to blow my home equity on a geezer boy toy” type that’s spending $1500 at a clip …absolutely.

Your son will be far better off with the 289. The car will handle better and the value will stay with the car. I’m basically a Chevy guy but the 67 Mustang GT Fastback holds a special place in my heart.

While I agree with the others that going with a 302 opens up many, many more options for tuning, keeps it much more original, and will be much easier to work on, a good number of 351Cs must have been put in '67s, you need to find a Mustang forum and find folks that have done exactly what you’re considering.

The parts store guy is wrong of course by making such a statement. The only issue I could see, other than doing away with originality, is possibly some hood clearance issue as the 351C has a taller block deck height than a 289.

These cars were available with an FE series 390 though.

If the conversion is done I would strongly advise hanging on to the original motor.

You’ll want to check that the 351C is the ‘4V’ M-code version, it has higher compression and better heads than the ‘2V’ H-code 351C.

Thank you everyone for your quick responses. It sounds like the consensus is that the OEM tranny will work fine. He already has the 351C engine in the garage. It is big!!

Again, thanks for all your input. I very much appreciate it.


As I mentioned, the 351 has a much taller block deck so a careful measurement from the engine mount through bolts to the top of the air cleaner is in order.

There’s a possibility anyway that the hood will not close. Now you know why some of those hoods are induction style hoods, have scoops, etc.

The 390 GT came out in '67…It was a nose heavy slug compared to a 289 Hypo powered car.

The GREAT thing about the 289 was its bore and stroke ratio. I think the stroke was only 2.87 inches with a 4" bore…This arrangement made for a quick reving, high reving engine.

The standard 289’s came with a cast iron crank and rather flimsy valve gear. The High Performance variant at 271 hp corrected all this, but today, these parts might as well be Gold. The 225hp 4V engine can be tweaked quite a bit at low cost and will maintain the value of the car…Cobbing in a 351C is loves labor lost…