Opinions on 3.89 gears or ??

[winr1]

29" tall rear tires .. 3.89 gears
MPH         RPM
30-------- 1388
40-------- 1851
50-------- 2314
60-------- 2777
65-------- 3008
70-------- 3239

I think this is the ratio gonna put in my 65 F100
Not gonna go far from home, cruise ins an car shows , puttin around
Cant seem to make a decision anymore bein old an such

It is 200 lbs lighter at the moment, gonna remove another 3 or 400

Tube cross member with engine mounts, F1 front axle with coilovers

1 x I-beam with spindle is 5 lbs lighter than the F1 axle with both spindles

The factory crossmember, I-beams, coil springs, radius rods are real heavy

Alum. radiator, bedsides only, tailgate will be a shell, mustang tank in rear

Building a light weight bench seat around 30 lbs lighter than factory

DeWayne gave me a C4 pan fill case so I can swap the innards out of my C4 case fill

Will fit JPT bell I have an save around 30 lbs


Thoughts ??



Ricky.

[Thumperbird]

What's the engine combo./hp behind this and expected low end torque?
Rear tire width?

[Falcon67]

I run 4.56 and a spool with 28" tires - all depends on what you want.  If you are just showing, cruising and using a 11" performance converter that stalls in the 2000~2200 range, then 3.50~3.70 would be a good balance.  Those RPMs are theoretical anyway because of converter slip/lockup, actual tire diameter under load, etc.

[BattlestarGalactic]

I run 3.89 in my black car with 275/60/15 BFG radial TA's.  Nice all around gear.  Approx 3000 rpm at 65 mph.
I do run 4.56 in my pickup with 29" tires.  It spins the old 428 pretty hard on the highway, but it doesn't seem to care.  Approx 3500 rpm at 65 mph.

Neither have accurate speedometers, so it's just a close guess running with traffic.

[cjshaker]

I run 3.89 in my black car with 275/60/15 BFG radial TA's.  Nice all around gear.  Approx 3000 rpm at 65 mph.

Same here. I ran that combo in my Mustang for years. A good compromise between performance and streetability. That was with a stock stroke 427 though. If it was a big stroker engine with lots 'o torque, something in the 3.70 range would probably work good.

[winr1]

Sorry... should of added mill/trans heh 

.040 390/428 crank// D2 heads/ bowl port/CJ valves.. ported Performer intake

Also have Ed. 2x4 and Ed. old style 3x2 intake

C4 or C6 with 10" or 11"  convertor .. 2200 or so stall

Rear tires are 255/70/15... not real wide 



Ricky.

[Falcon67]

10" is going to be way more than "2200" - more like 3K plus. 11" is usually in the 2200~2500 area.  The thing to watch for is when "cruising RPM" is below converter lockup, that's when you can be building heat in the trans due to slippage. 

[plovett]

10" is going to be way more than "2200" - more like 3K plus. 11" is usually in the 2200~2500 area.  The thing to watch for is when "cruising RPM" is below converter lockup, that's when you can be building heat in the trans due to slippage.

That is true, but remember that a converter doesn't have a set lock-up rpm.   It depends on the load.  At high rpm (power) and high load, it will stall higher.  At lower rpm and lower load it will stall lower.   What  I am getting at is that it is possible to cruise under the rated stall speed without any problem.   If the throttle is barely open and you are not accelerating, the converter will slip less. 

Torque converters are an amazing device.   They can multiply torque under high load and reduce stress on the drivetrain while maintaining similar cruise conditions.  They are certainly less efficient in terms of power transfer and mpg. 

JMO,

paulie

[plovett]

What cam do you have in there?

paulie

[Thumperbird]

Having just gone through this, 2 cents worth here:

Depending on cam, with those narrow tires, I see no need to get too crazy with gearing or stall for that matter, no way to hook it up and you would be moderate rpm's on the highway.
Broader did a 2600 rpm 12" for me, like it a lot better than the 3200 10" I originally had, just feels right in the heavy Thunderbird at low rpm's.
Unless your fun is smoking tires which I understand can be, then seems like 3.5 to 3.7ish is enough.

For the street I look at it like this, from a brake, if full throttle launch spins them immediately thru to 2nd then no need for more gear or stall correct?
Of course there is that bug for quick and fast which will have you looking at your suspension and tires soon enough anyways so I change my mind, gear it up.

[plovett]

For the street I look at it like this, from a brake, if full throttle launch spins them immediately thru to 2nd then no need for more gear or stall correct?
Of course there is that bug for quick and fast which will have you looking at your suspension and tires soon enough anyways so I change my mind, gear it up.

This is true.  However, if more traction is in store in the future then maybe lower gears might be good.   

My Cougar spins the tires up to about 65-70 mph on 10" street radials and maybe 30-35 mph on cheater slicks, on street surfaces.  So you might think I need less gear and less stall, and that WOULD help, but even better would be me getting my suspension in order so I have the benefit of traction AND gearing. 

I have 4.11 gears with 3600 stall and 27" tall tires in a lighter vehicle with a bigger engine (I think) so different, yet same situation.  aaaahhhhhhhh, very wise, grasshopper.   Not saying I am wise, just making a "Kung Fu" reference.

JMO,

paulie

[winr1]

No cam yet...


Ricky.

[plovett]

Well, gearing, cam, stall speed, vehicle weight,  rpm range, all must match, for the best result.   The cam is a major component that affects all your other choices and vice versa.

So....what are you thinking for a cam?

JMO,

paulie

[e philpott]

my take is gearing is it's not as important as the Cam and Converter matching each other is . The  last project 71 Mustang I did the drivetrain on I finished the vehicle before his Moser ( complete 9 inch conversion 3.50 ) was shipped so we tested the manual shift Broader valve body C-4 transmission 3K stall on the 1971 429 clone, Aluminum CJ heads , Comp 294S Cam with the cars original 302 8 inch  2.75 gear axle and that Cam and Converter was fine and influenced the final decision on 3.50 gears from initially wanting 4.11 and he almost went with the 3.00 to 1 after driving the 2.75 gear , it drove that nice in town and was great on the highway with some MT 275-60-15 street drag radials and 2.75 gear

[Falcon67]

That is true, but remember that a converter doesn't have a set lock-up rpm.   It depends on the load.  At high rpm (power) and high load, it will stall higher.  At lower rpm and lower load it will stall lower.   What  I am getting at is that it is possible to cruise under the rated stall speed without any problem.   If the throttle is barely open and you are not accelerating, the converter will slip less. 
...
JMO,

paulie

Depends on the converter and how "loose" it's designed.  Most off the shelf "Saturday Night Special" 10"s will error on the tight side -at least in my experience.  The 10" 3800~4000 I had built for the 302 is not that and will get the trans to around 200F in maybe 20 minutes of very light throttle cruising.  But it's yank the front tires on the track - which is what I want, as opposed to driving around a lot.

For the street I look at it like this, from a brake, if full throttle launch spins them immediately thru to 2nd then no need for more gear or stall correct?
Of course there is that bug for quick and fast which will have you looking at your suspension and tires soon enough anyways so I change my mind, gear it up.

Sorry - this makes no sense at all.  The converter does not control the shift points - unless you have a manual valve body, those will be determined by the valve body programming and the governor.   If the converter is way loose, then I think that may be what you are saying - RPMs will "wing" and the trans will shift at whatever RPM it is set for.