Slow Acceleration - Ford Forums

Mikestang · 04-10-2002, 17:26

I have a 1965 Mustang Fastback 2+2 GT 350 replica and it is great other than it accelerates really slow when feathering the clutch. It seems as though it just won't grab. Once the clutch is all the way out it runs perfect but starting from a stop it is terrible and almost difficult just to go without stalling. I was wondering if this is normal for older small block mustangs or is there something wrong with it? My dad's old 69' Mach 1 428 CJ did not have this problem and I have driven many newer standards and they grab MUCH MUCH easier. What could be the problem? If I took this car to the track I would be embaressed off the line!!

tyrantX · 04-11-2002, 22:02

Sounds like those ridiculous highway geared axles that way too many early Mustangs were equipped with is the main cause of your problem. Put in a 9" with a 3.89 ratio like the early Shelby and your car will wake up off the line. A performance clutch and pressure plate next time would be good too. You didn't mention how the motor's put together. I hope you're not using a single plane intake, also if you have headers, don't delete the H pipe, it helps low rpm torque.

Mikestang · 04-12-2002, 09:47

Thanks for the info. Right now it's got 3.00:1 gears in the rear and I don't know what we are lookin at for a clutch but a new rear end would work. I wasn't sure if it was something wrong with the engine or not. The original engine was a 289 A but it's got a '66 289 type unknown in it now. It has solid lifters so I'm hoping it is a hipo but don't know and can't find the serial number. Like I said, it works great once you get going but off the line there are some real problems. You have to really feather it. We are getting headers too and I heard that plain headers are better on older Mustangs than hookers or something like that... True?

Are 3.89:1 gears good for the track and the highway?

I will be sure to inquire about the H pipe when installing the headers.

04-12-2002, 18:45

Ok, my 1/50th of a dollar...

I have a very warm 289 with a 4speed top loader, 9in rear and 3.89 gears. I think if I were doing it again, I would do 3.50. I can sometimes chirp top gear, but in 1st I have to be very careful or I will roast the backend off the car. I don't hardly get any use of first with street tires, they just spin. 4000rpms is 80mph on the highway. Gets really bad trying to drive anywhere!

Clutchs!! first off, don't use autozone or discount auto remanufactured units. They are a waste of time and money. Go for a performance clutch, I use ram. I upgraded to a 10.5 inch clutch (don't remember all that it takes, I did mine 10 years ago, but its just a different clutch and flywheel I think). I also use a steel ford motorsport flywheel, I think they last much better than the iron ones.

Mikestang · 04-12-2002, 20:59

mfp, do you think the gears are the cause of my problems then? Have you seen this before? I wouldn't mind being able to chirp the top gear too!!

Gearhead99 · 04-13-2002, 07:36

Rear gears will surely make a BIG difference.

One more though. Where is you initial timing set??

tyrantX · 04-13-2002, 16:16

That's a good point about the timing, I forgot about that. My 351W is stock 6 degrees initial if memory serves, and I've heard of 12 degrees initial with 24 degrees in the distributor, but that is not very streetable. It moves the torque curve up too high in the rpms. The Shelby type tri-y headers don't breathe as well as conventional 4 tube ones. Hooker headers are expensive for reasons that escape me. There are some nice aluminized brands on the market. Compare prices and fit. It really bothers me when the collector flanges aren't welded with the flat portion of the triangle parallel with the ground, it's worthwhile to open the box and look. You may have a hipo 289, check the spotters guide I posted in the "GTA or not thread". Another thing about axles, get a posi(traction lok in Ford lingo) if you go with stout gears, a regular open axle(just one wheel driving) will spin the tire far too easily. I had a problem with an old 289 4spd 66 fastback that used to have bad axle hop from weak rear leafs. Traction bars can help, but I've seen them break a leaf over time. Weak springs like that need to be changed to stiffer ones having an extra leaf. A mideye type to drop the back 1" is nice if paired with stiffer drop coils in the front.

04-16-2002, 09:49

I think the gears will make a difference, but are not the source of your problem. Timing seems like a good place to start. Timing came make a car a bear or a mouse depending on how its set. BTW, if you get enough power and enough gear you will not get 1 wheel tire fires. Instead both of them will rip loose all the time, let me tell you it sucks! Drag radials coming soon!

Mikestang · 07-06-2002, 14:03

Thanks for the input, I fooled around with the timing and it seems to be working a little better but still a little mopy off the line. I know that I am going to get some 9" 3.50:1 gears with pausy trac for the rear now and I want to get tri-y headers and exhaust that come out in front of the tires but i heard that makes the car sound pingy and awkward. Is this true or is it not a big deal? I would also like some info on air breathers too (KM, cobra?).

If you can't tell, this is my first project :o)

07-09-2002, 09:37

Mike, just to make you feel better(or worse depending on how you look at it) my 67 was my first project too. 12 years later I am still working on it! I really think you will also see a big difference in a good performance clutch. If you drop the clutch out just a little bit on mine it will bite good. I can let it just touch and it will grab the tires. They also last a lot longer and handle a bunch more punishment. Clutch adjustment may make a difference too. Most clutches will hold once they are all the way out, but its the in between times that it shows. also with a 3.00 vs a 3.89 the clutch is having to work harder because of the lack of mechanical advantage. Does that make sense to you?