Question for Roadster owners

[billy2guns]

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.

[CapeCoralCobra]

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.

[Butch B]

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

[Fred Z]

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.

fred z

[DMW]

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.

[Michael Everson]

I've said it before and will say it again.. The most enjoyable cars are the ones with the stock drivetrain. 225 horse, no drive ability issues, and a smooth shifting T5. 500 horse is a waste of time and money.
Mike

[billy2guns]

the CAM is a Ford F303, I consider changing the CAM but was hoping for an less drastic solution

[Silverstreak02]

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

[Michael Everson]

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

[Bob Taylor]

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

[canuck1]

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

[KC Wildcat]

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.

[SeanHM]

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.

[bobcat]

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

[Dr Stebo]

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

[billy2guns]

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.

[Gordon Levy]

Setup is everything. We have 650+hp cars that drive straight, true and predictable.

[dallas_]

Originally Posted by billy2guns

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.

[bcw]

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.

[KEITH T.]

Originally Posted by Gordon Levy

Setup is everything. We have 650+hp cars that drive straight, true and predictable.

Gordon is wright I have a 552 in mine and I use it! Even with tire spin it goes straight. But tires are a factor also.

[RE63]

Originally Posted by Michael Everson

I've said it before and will say it again.. The most enjoyable cars are the ones with the stock drivetrain. 225 horse, no drive ability issues, and a smooth shifting T5. 500 horse is a waste of time and money.
Mike

ditto, although I do really like the 320 HP 4.6 DOHC cars.

My car has 30K miles on it and is a 225 stock 5.0 plenty for me and a blast to drive and enjoy.

to more than double that is a little overkill in my opinion.

[Jack Wojack]

Like I just said on the DOT tire thread: I also have a 347 that was dynoed at 360hp at the rear wheels ~= 426 bhp & 3.73 gears. The car scaled out at 2,270 lbs with ½ tank of fuel. The car is a HOOT to drive. Fast but predictable…with 3.73 gears, aluminum flywheel, al. drive shaft the R’s come fast and I haze the tires but the car stays strait or in my line. I’m feel the Detroit TrueTrac has a lot to do with the handling as does the SIA mod and the tuned AGR power steering rack and the super flat torque curve. My passengers do say it’s scary fast but from my perspective the car has excellent street manors. It will wag the tail a bit but I have never felt out of control.

I would not want any less of a tire...and i swear by that TrueTrac.

It ALL come into play in a 90 inch wheel base 2,300 lb car...including the driver.

Jack

[mrmustang]

Originally Posted by Michael Everson

I've said it before and will say it again.. The most enjoyable cars are the ones with the stock drivetrain. 225 horse, no drive ability issues, and a smooth shifting T5. 500 horse is a waste of time and money.
Mike

X 2 in a car that weighs less than 2,200lbs.



Bill S.

[Thomas W]

First of all, I highly doubt the car you drove is making 500 hp (flywheel) with an F cam without a power adder. Sounds like the car has some things that need to be addressed which may be as simple as tires and gear change. When I first got my car, it made around 420 rwhp (close to 500 hp flywheel). It had no tire spin in 1st if you rolled into the throttle on the street. I run way more hp than that now (but I now have to modulate 1st gear). It's all in the setup. Cheers.
Thomas

[seansipes]

Did I miss what the suspension was? I will soon ( hopefully!) Be driving a 500ish 347 W/ 3.73 gears, Levey 5- link, Stock Throttle. Interested in any other commits. Especially about the throttle.

[Dr Stebo]

I should also add that my 350hp Roadster was very unpredictable to drive at one time also. Set up, making sure the suspension is moving free through it's travel range and bump steer corrections have made mine a totally different car. With help of some of the vendors here I have a renewed enjoyment in driving. There is a great wealth of knowledge here to help you through what may seem to be an impossible situation to correct.

[Big Blocker]

12K on a basically stock EFI 302 . . . GT-40 upper and lower and an "E" cam give me all the "WHOO-HOO!" I need. Car is very predictable, goes where I point it, smokes tires (hard BF Goodrich TA's) into 3rd, corners hard, brakes hard and is an absolute pleasure to just cruise around all day in.

The rear end is 3.73's with 315 x 17" and 3-link. Setup is critical on these cars, both front and rear. Too little caster and the front end wants to wander. Some tread patterns will "tram-line" out on the open road (follow the grooves in the surface). Toe-in plays an important part of the front end drive ability, as does too fast a rack-n-pinion ratio.

Find out more about the car you are interested in and post the particulars here and we will be able to better get you going in the right direction.

This forum is filled with an enormous amount of talent and knowledge . . .

Doc

[CraigS]

Don't pass on it. It can be tamed. Gas pedal,rear spring and shock rates, front alignment, rear gear. None of these is too expensive to do and if you are still not happy, I'll trade you for my 400hp 351.

[tirod]

This brings up issues I see repeatedly.

First, the choice of final drive ratio. I'm definitely in the 3:55 camp, drive one daily - in a 4WD. With the underwhelming power, it helps to get it up to speed in traffic nicely. On the other hand, if it had 200 more hp, it would become the monster the 427 was accused of being, twitchy, uncontrollable, and hard to race. It's a fact the 427 Cobra with all it's torque would barely post a second quicker lap times over the 289, even with the supposedly superior double A arm suspension.

Uber hp to weight ratios mean a lot more development, sorting out, and tuning needs to happen, and the car as described by the OP is certainly one that may not have gotten it. Building the car is the first 5%, the factories then spend months on test tracks getting it to perform with manners. It didn't happen with the 427, and lots of kits never get it, either.

The comment about detuning the cam is relevant, as abhorrent as it looks a first glance. What we're dealing with is too much hp getting dumped on the tread to asphalt interface. There's only so much friction, apply it too suddenly and whiz! your burnin' rubber!

Let's start with 3.73 - what rpms does that give you at 75mph? Way too many, well over 3,000 at cruise. Modern cars with that kind of hp don't need to spin that hard. Goes to being a street/strip ratio, and it always has been. Even 3.55 is high for a daily driver unless you're running them at low speeds in tires taller than 27" - think rock crawler.

Cam selection is important, too. Big overlap cams with horrible low rpm performance forces the driver to spin the motor up to get smoother performance - putting the torque curve suddenly 150 ft lbs higher. That dumps on the tire grip, and things start spinning.

Throttle linkage opening rates - we frequently use donor parts designed for sporty, smooth performance, but on a car with nearly ten pounds per hp less, plus a peaky cammed motor, it's not correct. Opening the throttle blades too fast is exactly what contributes to the hp dump. Again, my daily driver does that - notoriously either power on or power off at low rpms. With its mundane output, nothing much bad happens, but it could still be a lot less geometric. Throttle linkage on carburetors used to get a lot more discussion in the day, and lots of catalogs had parts to modify the opening curve to get better responsiveness. We likely need to slow that down now, as we make a lot more hp these days.

I'm reminded of a video from a few years ago, a street event where strip cars were doing burnouts at a parade event, and one got away into the crowd, killing bystanders. Are we doing the right thing by using deep ratios, fast acting throttles, and dry tires with high grip? Sure, it's a hoot. It's also a one dimensional car, all smoke and very little finesse. Some do tame them down, but the constant testosterone measuring that goes on in forums keeps pushing an agenda that too much is not enough.

Hence, the car the OP drove. Most responding here don't accept it's handling as safe, and say they've done better, but there's still an undertone of "Man up and learn to drive it." Well, seeing the videos of other people putting roadsters thru the garage or into a neighbor's car, is that the standard we need to promote?

The 289 made Shelby's reputation, the 427 killed off the business. Harsh historical fact is that the average car buyer won't put up with a car that can't be trusted. The factory takes the time to make their supercars user friendly enough your teenage daughter can drive home without incident. Is yours?

[NiceGuyEddie]

first, billy2guns a freaking amazing handle, and it's what drew me to this thread!

second, look how many people eagerly chimed in!

third, Gordon Levy nailed it - setup is everything, and you can dial in most of it yourself.

nobody has asked if the car has power steering - if equipped, the car may not have the caster maxed out, which helps the car right itself if it gets squirrely. ask me know I know.

driveshaft pinion angle is directly related to wheel hop and bite, maybe it's not set up correctly. ask me know I know.

tires are make/break (pun intended) when shifting, ask me how I know!

I'd highly recommend budgeting about $500 to change your rear gearing. I also have a 347 stroker, loads of low-end toruqe. I don't like my 3.55 because it loops out too quickly. I wish I had lower/taller gearing, maybe 3.27

bottom line here is don't let what you experienced scare you off - it can be easily changed.

cheers,