Mark Houlahan
Tech Editor, Mustang Monthly
January 28, 2014

Not So Good Vibrations

I have a 1985 Ford Mustang LX convertible that originally was a 3.8L V-6 with automatic transmission. When I bought it, a previous owner had already installed a 5.0L V-8 with a C4 automatic. The C4 was leaking fluid in reverse, so I installed a T-5 five-speed, which was something I planned to do anyway. I assumed (wrongly) that the engine was an early- to mid-’80s vintage, so I used a flywheel from an ’83 Mustang GT that had been junked. I ended up with a vibration in the engine that wasn’t there before the transmission swap. I eventually learned that the engine is a ’79.

A friend told me the older 302 V-8 used a different flywheel, so I am guessing that is where my vibration is coming from. Here is my question is regarding the ’79 engine: Is there a difference between the passenger car and light truck engine when it comes to the flywheels? I’ve been looking at flywheels online for a ’79 and some indicate that there would be a difference between a car and an F-150, both with a 302. The casting number from my block is D90E-6015-E3A. Is there any way to tell if this engine is from a passenger car or light truck? It seems to me that they would be the same, but I want to double check before I get another flywheel.

Lew Stark

Via the Internet

What you are dealing with here is Ford’s now famous switch from 28 oz-in balanced 289/302 small-blocks to the 50 oz-in balance 302 in 1982. The block casting for a ’85 Mustang would be E5AE-6010-HA, indicating the new roller cam block. Your block casting indicates the earlier 28 oz-in small-block, probably from a ’79-’81 passenger car. The ’83 Mustang flywheel is the incorrect 50 oz-in balance and is causing your vibration. Unfortunately, this is an all-too-common occurrence. The fix is to simply replace the 157-tooth flywheel with one that has the correct 28 oz-in balance. The reason you are seeing different applications for truck versus car is that most F-series trucks use a larger bellhousing and thus a larger tooth count—164 versus 157. Stay away from the truck flywheels, as they won’t even fit inside your bellhousing. You can find 157-tooth 28 oz-inch flywheels, many with dual bolt patterns to fit different clutch sizes, from several sources, including Centerforce, Ram, McLeod, Ford Racing (shown here), and others. Swap out that flywheel and you’ll have smooth sailing, er, driving.

S197 V-6 Dual Exhaust

I’ve owned eight vintage Mustangs over the years, all V-8s. I am currently restoring a ’66 hardtop and I’ve been giving some thought to buying a ’05-’10 Mustang as a daily driver. I feel the GT is kind of pricey and I’m considering the 4.0L V-6 instead. I’ve never seen an article on installing dual exhaust systems on the ’05-’10 six-cylinder cars. Is that because there is no advantage, performance or sound-wise, or have I just not been looking in the right places?Also, what’s a good source of information on any problems associated with late-model Mustangs? I’ve read that the ’05 tended to leak and others required expensive engine repairs.

Bob Atchison

Via the Internet

While the ’05-’10 Mustang’s 4.0L V-6 suffers from a little performance anxiety when you compare it to the newer 3.7L DOHC V-6 that replaced it, the 4.0L is far from a slouch and moves the S197 along quite nicely for daily driver duties. The 4.0L is a sound engine that has seen many updates over the years (the 4.0L in my wife’s ’02 Explorer Sport Trac has 215,000 miles and runs like the day we bought the truck!). Several manufacturers offer dual exhaust conversion kits for the S197 V-6 Mustang. You’ll find semi-axle-back kits as well as full dual conversions that start at the exhaust manifolds. Exhaust note is very subjective, so your best bet is to visit manufacturer websites and listen to their exhaust recording samples to determine what sounds best for you. You’ll find kits from Mac, Pypes, Ford Racing, Bassani, and others. Most, if not all, require minor trimming of the bumper cover for the driver’s side exhaust tip. This can easily be handled with small rotary tool or hot knife. For tech info, you’ll usually find an S197 sub-forum at your favorite Mustang website, such as,,, and others.

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