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Discussion Starter #1
Well I am proud to say I built my 64 Galaxie XL ground up with my own two hands. I am at a fork in the road when it comes to that third member.... I rebuilt my 28 spline 3.25 gears when I though I was going to stay with the 289 sb.

but....

Engine I ended up building a 408 roller Windsor/stroked, AFR 195 cc, Eddy Air gapper, Holley 750 hp. all port matched cnc'd so maybe 480 HP/TQ to 520 HP/Torque.

Trans; A.O.D. from an 89 stang, BUT I built it up right and proper for the anticipated power range

Wheels 15' rims,

I have an overdrive tranny... I want have a nice cruiser but with massive get up, take off and go....

What would you do with your rear end, if this were yours? Do you have a similar car....
 

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Discussion Starter #3
I have a 62 galaxie with 406 and t5 and I like the 350 rear end ratio I have in it. I run 1,800 rpm at 70 mph and the 6 cylinder t5's wide ratio gives me nice take off in first.

thanks, I was theorizing towards a 3.50 posi, is that what you have or ????
 

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What size rear tires? What cam in the engine?
 

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Lets assume a 27" tire.

If it were me I would utilize the overdrive and go much lower with the rear gear, maybe a 4.11. That will give you much more get up off the line, yet still keep the cruising RPM at 2400 doing 70mph. I might even go lower than that, depending on the cam.

With the 3.50 you really aren't getting the off the line pull you'll want in the heavy car, and cruising RPM is only 2050 at 70mph which will lead to alot of downshifting to pass or on a hill. Besides if your engine is built up with that much HP it probably won't like the RPM being that low, and I'm just guessing you'll need a higher stall converter as well, especially in the heavy car.

Again this is all guessing untill we get the tire size, cam, and torque converter info.
 

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Lets assume a 27" tire.

If it were me I would utilize the overdrive and go much lower with the rear gear, maybe a 4.11. That will give you much more get up off the line, yet still keep the cruising RPM at 2400 doing 70mph. I might even go lower than that, depending on the cam.
By modern standards 2400RPM @ 70MPH is still a bit higher than I'd be looking for, remember too that depending on how fast you plan on driving the car the shorter the rearend, the closer you get to critical-RPM problems with the driveshaft.

For a 54in 3in steel driveshaft critical RPM is around 5800RPM, with 4.11 gears and 27in tires you're limited to 110mph approx before you hit critical RPM.
 

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By modern standards 2400RPM @ 70MPH is still a bit higher than I'd be looking for, remember too that depending on how fast you plan on driving the car the shorter the rearend, the closer you get to critical-RPM problems with the driveshaft.

For a 54in 3in steel driveshaft critical RPM is around 5800RPM, with 4.11 gears and 27in tires you're limited to 110mph approx before you hit critical RPM.
Its all assumptions until we have the cam and tire size, but this isn't a modern EFI engine, and probably won't like 2k rpm cruise. It's probably going to require a converter with a fairly high stall to get that 4000 lb car moving with what I'm pretty sure is a stout cam.

I do agree that he'll have drive shaft problems though if he does decide to drive the car that fast.
 

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Discussion Starter #9
What would you do with your rear end, if this were yours? Do you have a similar car....

Ok here is the total package,

Engine
408 roller Windsor/stroked- maybe 480 HP/TQ to 520 HP/Torque.
Holley Ultra 750 HP, using kick down cable

CAM
235/238 @ 50, 573/582 Lift - 112 lobe /mild

Trans; A.O.D. from an 89 stang, BUT I built it up right and proper for the anticipated power range

Stall @ 2200 converter (of course this can be changed)
Drive shaft 3'' brand new.

Wheels 27'' OD

GW approx 3800 lbs.
Suspesion; 2'' drop in front, stock height rear, 100% new.

Blood type
O Pos
Sign Torus
hanging itchy, low and slightly to the left

I have an overdrive tranny... I want have a nice cruiser but with massive get up, take off and go.... what rear end, posi, ls, 3.5, 4.11 ect. will help capitalize the top and low....
 

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What would you do with your rear end, if this were yours? Do you have a similar car....

Ok here is the total package,

Engine 408 roller Windsor/stroked- maybe 480 HP/TQ to 520 HP/Torque.
Holley Ultra 750 HP, using kick down cable

CAM 235/238 @ 50, 573/582 Lift - 112 lobe /mild

Trans; A.O.D. from an 89 stang, BUT I built it up right and proper for the anticipated power range

Stall @ 2200 converter (of course this can be changed)
Drive shaft 3'' brand new.

Wheels 27'' OD

GW approx 3800 lbs.
Suspesion; 2'' drop in front, stock height rear, 100% new.

Blood type O Pos
Sign Torus
hanging itchy, low and slightly to the left

I have an overdrive tranny... I want have a nice cruiser but with massive get up, take off and go.... what rear end, posi, ls, 3.5, 4.11 ect. will help capitalize the top and low....
Personally I would go 4.11 and a 2500 stall converter. It will get off the line great and cruise at 70 right around 2400 rpm, just below the stall/flash.

I'm not a SBF guy, so I have to use references. Your cam is just a little milder than the Comp XR288, plus the extra 50 cubes tame it down a bit more. That cam calls for a 2800 stall converter and at minimum 3.73 gears...probably in a lighter car.

Yes, the 4.11 might cause drive shaft issues at over 110 mph, so thats something else you might have to address if you plan to drive it that fast. But 3.50 is just too tall in my opinion, and the cruise will be well below where the engine actually wants to run.
 

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I have a 62 galaxie with 406 and t5 and I like the 350 rear end ratio I have in it. I run 1,800 rpm at 70 mph and the 6 cylinder t5's wide ratio gives me nice take off in first.
That 6-cylinder T5 with the short gears won't last long if you use it hard, though.

A 406 of reasonable health can break even the best (2.95 first 'Z'-suffix) T5 without trying hard.
 

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I'm not a SBF guy, so I have to use references. Your cam is just a little milder than the Comp XR288, plus the extra 50 cubes tame it down a bit more. That cam calls for a 2800 stall converter and at minimum 3.73 gears...probably in a lighter car.
You may be right about the cam.
 

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Discussion Starter #14
Damn good stuff, thanks to the gearheads who contributed. MAN O MAN, this place is great... anyone got a 4.11 or 3.7s 28 spline third member for sale, shipping to 90601 .......
 

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I might have one coming out next week, right in the middle with 3.89. Works great now, but want to check it out before I put it up for sale. Going to 4.11 in the street/strip cat with a locker and 31 spline axles.
 

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Did you lose lockup with your AOD input shaft upgrade to handle the power? I don't know your camshaft, but 2500 stall is low for any modified engine. Where did you get the 2500 number? A stock 5.0 HO converter is almost that high. However, if you are staying low-stall because you lost lockup, then you should go lower in rear gears to make-up for it.

Using juddp39532's example in post #2, his personally-satifying combo gives a 1st gear x rear gear compound ratio of 13.83. Because the AOD has a much higher 1st gear, you would need 5.57 rear gears to get the same compound ratio he has. :eek: So, you're probably not going there, but you can see how far you have to look to get some useful numbers. Is this a true daily driver?

Not to get on a soapbox here, but it would be funny if it weren't concerning where some suggestions come from. Some are because that person isn't actually happy with their setup (how would they know?), but rather they are not upset by it. Many folks have some aversion to any gears that start with the number 4 with no valid reason. Keep in-mind, factory muscle cars came stock with 4.xx gears and no overdrive. Did you pick your carb size because the CFM sounded good, or that it was actually a good fit for your application? Same here.

If it were me, I would not be afraid to give the car what it wants. Let go of the reins and let her run. My 2¢.

David
 

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Dave, i think comparing 1st gear ratios of manual and automatic transmissions are tough to compare due to the never ending variables of the torque converter.
 

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Keep in-mind, factory muscle cars came stock with 4.xx gears and no overdrive.
And they were - and are - painful to drive any distance at real-world speeds.

Grinding down the highway at 3200RPM or so while dead-stock Civics go whizzing past isn't my idea of fun. Back in the day you had folks who checked the option boxes for the short gears and the close-ratio box and then regretted the hell out of it ever after.

It all depends on how you're going to use your car and the compromises you're prepared to accept to get there. Unless every start's a holeshot 4.56 gears and a wide-ratio AOD means you're out of first by the time you hit walking speed.
 
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