How slow will a rear end ratio make your car?

[stephen4785]

Ive got a 65 GT and I rebuilt the motor.I put all kinds of stuff in and on the motor and its still not very fast.Whats the stock rear ratio's that came in the 65's and if Iv got the craspiest ones will that make my car pretty slow.The motor runs great and everything.Im just thinking since ive got a 2600 lbs car and at least 250 hp it should be faster than a Z28 or newer GT.I dont have any track times or anything just a SOP feel.This is the stuff I have done on my car.
1968 302 block bored .040
stock 84 Stang crank .010 under
Speed pro Hyper. coated skirt flat top pistons
Total seal Claimer series gapless rings
Cloyes double roller timing chain
Comp cams 280H Flat tappet hyd cam(280 intake-512ex)
Comp cam hyd lifters
Comp cams 1.7 roller tipped rockers
comp cams double valve springs with shims
1968 351 W heads with 3 angle valve job
Weiand Xcelerator intake manifold
Edelbrock 650 carb
Mallroy Unilite Comp 9000 distributor
Mallory wires
Ford motor sport coil
Autolite platinum plugs
K&N air filter
home made H pipe and super turbo mufflers
Stock C4 tranny
Stock rear end
Stock exhaust manilfold
Iv got a Holley 670 street avenger carb to go on it.I know I need headers and tranny work and a new rear end and all of the other stuff that I dont have money for right now.

 

[crushnut]

Most likely 2.79:1, those dont really help performance. But they are great on the highway

Check the tag on the rear diff. to be sure

 

[88 Fox GT]

Yeah, check the tag on the rear end. I found out mine was a 2.80. I figured it was pretty high considering the fuel mileage I was getting and the crappy low end acceleration it didn't have.

 

[stephen4785]

mine doesnt have a tag on it anywhere.I turned the pinion by hand and counted the revolutions of one of the tires.It was under 3 so its probably a 2.8 or some crap.Will that make exceleration that crappy?

 

[69fb00GT]

you'll notice a nice SOTP improvement with a 2000 rpm stall converter and 3.50 gears

 

[69Rcode_Mach1]

This may be kind of off topic but i have the same cam that you have awaiting an install. How does it feel?? Does it really pick up in the mid rpms and how does it fair on off the line. Also rear gears will do wonders for that car especially with that cam. You can go with 3.55's if you want a nice mild driver. For that cam you want 3.73's-3.89's those would be the best. As you can see im running 2.75's and switching to 3.73's will be a big difference and it would be perfect for your setup. May be rough on mileage though.

 

[69Rcode_Mach1]

Another thing that would really help your setup would be a set of headers. Headers make an amazing difference on driveability and power on a car. Get yourself a 2 1/2" exhaust and some rear gears and youll whoop any z 28's coming your way.

 

[stephen4785]

I really like the cam.I hear alot of people say its way to big but mine doesnt stall its got a good lope.The only draw back is it doesnt lanuch real hard(probably cause of gears)but once the rpms pick up it starts pulling and doesnt stop untill it shifts.I plan on putting on some headers soon.And I work in an exhaust shop so theres no problem in installing anything or making anything.Im planning on installing a 9 inch with 3.73's.But I dont give a crap about gas mileage or highway.I want mine to say bye bye to my girls 01 WS6 at a light or the track and thats my only goal .Iv got lots of plans for it but thats the ultimate goal.

 

[69Rcode_Mach1]

Sweet man that is a cool setup. Get that exhaust in and some 3.73's youll be set. Im really excited to get that cam in there once i get the heads. Unfortunately i won't have money for heads and gears till thanksgiving or so cause im paying for a paintjob right now. I plan on doing what you are doing right now. I was hoping to run the cam without a stall converter and you have assured me ill be okay until g-force t5. If you want to get in the upper 300's a nice set of heads won't hurt. If you get a set of afr 165's or 185's you will fly and be able to keep up with cobras maybe and probably beat sti's. Also whats your shift point rpm?? How high does that cam make power upto?

 

[stephen4785]

well my car doesnt have a tach in it so I cant tell exactly but I think it shifts around 4000 or so.I could be way off though.I do plan on getting some AFR 185's.I want to replace all of the suspension with a American pony real big kit or comprable,9 inch rear with 3.73's,rear disc,a AOD swap,stall convertor,and install the a/c stuff soon as I get a chance.My friend gave a complete setup out of a 67 caoupe.

 

[SadbutTrue]

with a stock displacement 302, AFR 165s would be abetter bet. I would actually go for somethign cheaper, like Performer RPMs or Trick Flows... they'll flow as much as you need and probably cost half as much.

 

[69Rcode_Mach1]

i would agree with sadbuttrue. the 165's would be the better choice for your setup unless you plan to go stroker.

 

[69Rcode_Mach1]

Also your probably revving a lot higher than 4000. That cam makes power all the way upto 6000-6200. If that is indeed where it is shifting at you are missing a lot of power.

 

[stephen4785]

Well I hooked up a temporary tach and thats what its shifting at.It barly hits 4000 then shifts.

 

[69Rcode_Mach1]

Whoa thats really low for that cam. Try throwing on another 2000 rpm on that shift. Youll need to adjust the vacuum modulator on your tranny. Try manually shifting it and seeing the power gains first though. Cause that is way too low for this cam. Have you taken the car to a dyno? A dyno will do wonders in tuning and setting the car up for maximum power and then youll know all your stats and where you hit your peaks.

 

[MrBobMarley]

I agree with 69Rcode, check the modulator and try manual shifting. When I shifted my c4 on my bone stock 65 coupe w/289, it used to make the dash cover/pad fly off. Everyone used to get a kick out of it. Also, have you looked into a stall converter? How about a set of longtubes?

 

[ratio411]

Headers are a must.
I would be suprised if you pick up much power over 4k without them.
They help throughout the entire power band too... so bottom end will improve some.
Gears and headers is what you need. After that you will come to us wanting to know how to keep the car from going sideways all the time.
You still have a good shot at the LS1, even with traction problems because they are terrible about hooking too.
Dave

Btw: Auto LS1s make less power, but hook better.
M6 cars put more to the ground, but the driver has to be top notch to use it.
When dealing with an LS1, go from a stop... If you are taunting an LT1 car, go from a roll.

 

[69Rcode_Mach1]

ratio 411 brings up a good point. For your power to really kick in at the higher revs you need the headers. Ronstang is helping me with my build and i just put them on and they make a big difference. He said that they would shine a lot more when the whole combo is put together. Its probably holding you back a lot. Think about it as a human runner, a runner who can inhale a bunch of air will be amazing but if he can't exhale it easy enough its useless all his energy will be wasted.

 

[stephen4785]

well Iv got plans for headers gears convertor and heads.As far as the LS1 hook?I was driving the bird the other night to shut up this guy at my old work(hes got a 99 Auto SS).We raced about 6 times and every time I always had him off the line.And yes I beat him. 5 out of 6 times(missed 3rd gear,clutch got hot and wouldnt shift).My next future mod after replacing my flexplate is the converotr cause I have to change the flexplate then headers then gears(8.8 or 9 in ).

 

[stephen4785]

P.S. The birds going down soon!!!!!