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Discussion Starter · #1 ·
Although my first post I've been visiting the FFcars for sale for some time looking for a cobra already built. That said I recently found a very nice (non-doner) MKIII for sale locally within my price range. It was powered by 347 stroker EFI (according to the seller close 500hp) connected to a tremic trans, and 3.73 rear end. It started and idle nice, and sounded great. My surprise when driving was how twitchy it was. There was no horsing around with the throttle at all. It would literally spin the rear wheels at virtually any speed or in any gear and go sideways. I never used more than 1/2 throttle. Is this just typical for these cars and I’m wondering why anyone would put more than a 350hp power plant in one of these cars. My serious question is if I were to acquire this car is there anything I could do to make it more well-mannered? My first though is gearing? Any though would be appreciated.
 

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Others will contribute here, but a car with a 347 & 500 HP doesn't need 3.73 gears, more like low 300's. Also, what tires are on it? These two items could make a huge difference. How the rear end is set up is another possibility.
 

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Billy,
500hp with EFI(or any other set-up) is alot of hp for these little cars! . What has been done to the 347 to get that much hp? Maybe a cam change to tame it down some? 347s have alot of TQ, a gear change might help with the manners a 'lil? Need more info so others can give their ideas--
hth
Butch
 

· FFCobra Owner
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:cool2:Hey, Billy.
Someone has to be the first for reply so here I am.
First, I have a 550 Hp car with 373's. It is a great ride but if I were to change anything, that would be it. Go with 355 or 340 something and it will give you a better 1st gear and help a bit. Next, if you have a lot of torque, I have same 550, it is tougher to mellow it out. Yep, twitchy, nasty and just a lot of fun.....but you always want to be squarely focused on your surroundings. Things happen on roads but with these cars it happens faster and not as agile to dodge danger unless you are prepped! The boys here will offer some other thoughts, but they all will have one common thread.......respect the car and the power it presents and never ever take it for granted .....even when you think you have it wired!! Trust us......you don't!
have fun, bud. :cool2:

fred z
 

· FFCobra Master Craftsman
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I have a 5 Litre straight from the Mustang GT donor car and it is very pleasant and predictable. I've never been in a situation where the car got away or surprised me. Based on what I'm reading here, I'm glad I got what I got.
 

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I have a 5.0 Explorer motor and am very happy with the power level. It is very fast yet easy to control. Full throttle spins the tires in first and second, but the tail only wags a little. It's not twitchy or scary. If this is the car you want you should consider buying a mild 5.0 and either saving the 347 for another time or sell it to someone with the power bug. Good luck and welcome to the forum.

Jeff
 

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The first thing I would look at is the throttle pedal. If its the stock mustang unit, I would switch it out. Next, I would try 2:73 or 3:08 gears. The F cam really is aggressive for street use. Cars with a lot of horsepower can be a bit of a handful, but your experience seems a bit extreme. There could be some suspension or tire issues with it.
Mike
 

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My experience is good , not twitchy with 560tq and 580hp. I use drag radials 315x17 on the rear , I have the suspension in the rear set to provide the longest (farthest forward) instant center , and I use a 3.27 rear gear . There are adjustments , for the suspension , larger (taller) tires will help as will sticky drag /road race tires. Did you say F cam and 500hp ? I'm guessing that cant happen without a power adder . Hopefully someone who knows for sure will chime in . Even so it sound like fun to me B ob
 

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The actual number is not important. 400, 500, 600... too much is too much. Tires (and tire pressure) can make a lot of difference. How the rear suspension is set up can also influence throttle induced twitchiness.

Sean



Sent from my Autoguide iPhone app
 

· FFCobra Craftsman
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My 2 cents.

You have 2 distinct issues here. Power/traction & front end handling/twitchiness.

Firstly, have it dyno'd. What margin of error is there in 'close' to 500 HP. Most 347's have about 450 HP (at the flywheel). Stock 302/5L blocks start to fail around 500HP unless they have stud girdles and valley supports (from what I have read). But regardless, that is just a number and whatever it is, that car has a driveability issue.

Gearing is a substitute for TQ...and strokers produce lots of TQ. That car does not need 3.73s (unless you want brutal off the line or intend to drag race the car.

Along with the gearing, what brand of tires does it have. There is a huge difference between a harder tire (BF Goodrich, etc) and a sticky or even drag radial. You will not get the same wear/tire life out of the sticky tires, but that is the tradeoff. The size of the front tires is a factor too. I have heard of twitchy front and wandering from cars with 275s up front. a 235/245 will reduce that.

Lastly, you have to look at the front end. What is the alignment (especially the toe & caster)? A properly set up and aligned front end makes all the difference in the world. Also look at the components, bushing and set up. That can also contribute to twitchiness.
 

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There are definitely some things can help settle it down. I would agree that 500hp is overkill in these cars, that being said I wouldn't turn it down. Like Mike said above, I would look at the throttle pedal. I have the stock pedal, but I changed the pivot point to slow down the throttle opening. I may still replace it at some point. The buzz from everyone with the Russ Thompson pedal available from Breeze is that it is night and day. I agree that 3.73 gears are definitely overkill, especially with 500hp. I've got 3.73's with about 350hp and I think it's something I'll be looking to change. I can light the tires pretty darn easy so I can't imagine with another 150hp.I would consider 3.08 or maybe even 2.73 with that much torque. I like to be moving quick without making it known for 2 miles.Tires and suspension are next, as mentioned. Pressures, brand (stickiness) and size matter. I think Jeff had the best suggestion though. Buy this car and swap in a milder motor. Won't cost you a dime. Just bring it to my house, I'll do the labor and you'll have a fresh 350hp 306 with less than 50 miles :) Problem solved.
 

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I'm running a 347 (450 HP) with Holley 670 street avenger-IRS-and 3.27 rear with 3.15 rear meats. this is perfect for me-I get 20+ MPG all the time-till I nail it-2nd and 3rd happen real fast and it stays straight. I chose the 3.27 gears cause I know with this kinda mileage (better than my trucks) I'll drive the snake lots more (and still put a grin on my face with the acceleration)-my buddies 427 always launched straight (it just didn't turn too good)-it's set up that makes a big difference in how the car reacts.

Bob
 

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I am perfectly happy with 350 hp I have. Does everything I want it to when I want it. Unsure of what you paid or are thinking of paying. But making big drastic changes may put the car out of a price range that is re-sellable or makes another choice of car more affordable.
Heck there are plenty of us going into Storage Depression having to put cars away for winter.
You never know where you could strike up a good deal :)
 

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Discussion Starter · #16 ·
I appreciate everyone sharing their experience and recommendations. I’ve driven cars with big HP before but I guess in nothing this light. I think I agree with Michael at some point the increased HP has diminishing returns. Well I may pass on this one but I’m definitely in the market. Definitely EFI 302 or 4.6L.
 

· Pro FFR Builder and Moderator
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Setup is everything. We have 650+hp cars that drive straight, true and predictable.
 

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My surprise when driving was how twitchy it was. There was no horsing around with the throttle at all. It would literally spin the rear wheels at virtually any speed or in any gear and go sideways. I never used more than 1/2 throttle. Is this just typical for these cars
No, this is not typical. No offense meant to the builder, but as the others have said it sounds like there are setup issues. That amount of power is managable without the twitchyness. That is just dangerous.
 

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Tires and gears!!! I had a 350 HP cobra with bad tires (BF Goodrich) and I could spin the tires anytime I wanted in 1st, 2nd and sometimes third. I now have a different cobra with around 500HP and have had a few tire combinations on it. On this more powerful machine I have had a set of mickey thompson tires and they spin in 1st and 2nd. The tires I have on now are super sticky and literally grab and go after first. As others have said, gears do play a role in this as well, I'm running 3.55. The twitchiness sounds like an alignment issue to me. Overall with the right tires and alignment you can make 500HP very controllable and still spook you when you want it to. I would never tame down a motor but that's just me.
 
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