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1968/67 fastback 4 speed top loader

67stang

Active Member
Hey guys, so I’m still in the hunt for another FB. And I will be looking at another in two weeks.

Specs:

347 scat balanced crank and rods, trick flow heads with 1.6 roller rockers, probe pistons,
Center force clutch roller bearings
Hooked headers
Aluminum intake 750 double pumper
4 speed top loader
9 inch with 31 spline
3 member is a nascar rear end nogular case larger carrier bearing.
455 gears

I think I understand about half of that. Lol. Car seems in good shape but does need upgrades. Only other upgrade is that the front is coil over.

Question: why the 4 speed and not a 5 speed? Is it because 4 speeds are better for launching and are stronger to support the hp?

Would this set up be difficult for a daily driver?

And can I put an EFI with this setup?

Also the instrument panel is not working. Could that just be the voltage regulator? And were would that be?

Thanks for the help I hope this is will be my last FB. .








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Midlife

Well-Known Member
Staff member
Moderator
4.55:1 rear end gear is excellent for drag racing but something along the lines of 3.25 or 3.50 is much better for the street. That rear is not for the street as it will give you horrible gas mileage (like 5-6 mpg).
 

67stang

Active Member
Is it hard or expensive to change it out to a 3.25 or 3:55?

Also if I change it from the 4.44 to a 3.55 would that drop the rpms to about a 1000k doing 70?

Or is a t5z transmission a drop in?


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kb3

Well-Known Member
I would worry about the longevity of a T5 behind that motor. T5s are rated for 350 lb ft of torque, that motor sounds like it is built up quite a bit. There are other 5 and 6 speed trans that you can put in the car, but they require trans tunnel modifications to make them fit.
 

67stang

Active Member
So would a simple solution be just to change the gear ratio? And if so going from a 444 to let’s say a 3.55 what would the rpm drop be?

So even the t5(Z)made for cobras wouldn’t work?



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67stang

Active Member
So I was mistaken it does have a 3.55 gears so at 70mph it runs about 3700. Seems okay??? Or do you think it still drink 5-6gph? I think I will need a larger fuel tank!


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Patrick Stapler

Active Member
Please take no offense to this, but it sounds as though this car might be a little over your capabilities...based on the questions your are asking...especially if you are looking for a daily driver. Based on the description of the engine and rear, it doesn’t sound as though this car is intended to be driven on the street. The carb is way too big, the rear gear is way too high (numerically).

Why the 4 speed, because they are better.

Why do you think it needs EFI?
 

Midlife

Well-Known Member
Staff member
Moderator
That 3.50:1 rear and 3700 rpm at 70 mph will give you awful mileage on the freeways, as well as being very loud with that high an rpm. That rear gear will be great for stoplight to stoplight though.
 

Patrick Stapler

Active Member
Well..I’m not buying that it has 3.55’s with the Toploader. My car has that exact setup and it turns 3000 RPM at 70 MPH, and that’s with a 24.2” tire.
 

67stang

Active Member
Well unfortunately the seller backed out. I appreciate the comments. His mph was off because he never changed out the correct gear on the cable (edit sorry for the confusion) so the 3k at 70 is about the same.



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Horseplay

I Don't Care. Do you?
I think you are very lucky that this deal didn't happen. You have some errors in your description but even after trying to translate it all correctly I get the feeling that car is not a good, well done build. Probe pistons haven't been made in a while and were never great to begin with. I'm not a fan of SCAT stuff either (my opinion) and it just reads like a compilation of stuff that doesn't work well together but might sound impressive. Sounds like someone bought a Coast Performance "balanced" assembly and bolted stuff together to me.

Like Patrick said, that is WAY too much carb. There are lots of Trick Flow heads out there as they have been around a while. Not all are good. They had to do some learning along the way. Don't settle for the brand name you want to know the model of heads in the future. For all you know those could be first generation heads that have been bought, used and sold three times over.

You can build a T5 to take everything a 347 can throw at it but a T5z isn't enough if you hook with a slick. On the street it will be fine if you stay away from slicks and don't hammer it all the time. The beefier "stock" manuals like a TKO 500 require a little extra room up top in the tunnel to fit. Some will tell you they don't but they really do need it to fit well. A toploader is a really strong trans but without an overdrive gear not nearly as streetable. Running a .67 or so 5th gear and a 3.80 rear gear I can cruise all day at 70-80 mph on the highway and the engine never comes close to 3k rpm.

Find yourself a nice car with a 302 or 351W engine that has been mildly built with either a modern overdrive auto or a 5 speed with a 3.55 rear gear and you'll have a really fun, reliable street car. Cars with even well built engine like this one purported to be require an owner who knows how to fix things...because things will break when you push the edge like that. One of the new self-learning EFI systems can work on any engine. Personally, when I do it again I will go to a port injected set-up that can be tuned off a laptop as opposed to a generic handheld piece. Much easier to get it all dialed in that way.
 
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