OK, I'm a nerd... But what do you think re: actual RPMs vs expected

[Tubo]

GAh!!!!

I'm like a kid on Christmas Eve... It's all I can think about

Summit is good about swapping parts, even after a period of time has passed since the purchase. So No pressure bout picking a gear right away.

Now when iz that rascall getting the new tranny and out of the shop??

Ok tech question. What shifter are you using for the trans??

C-4 shifter w/rod linkage?? Or an aftermarket shifter?? Or what I found to be good, modify a 86-99 Mustang cable shifter??

 

[CZ-75]

Good question on the shifter... I'm going to try to use the existing shifter, and just let the tranny go into OD when it wants to.

I think I have the right adapters/cables to be able to use the same shifter. I have a Lokar "Universal" AOD linkage adapter, and I'm hoping that will help. Also have their TV cable and brackets.

I spoke to teh shop this morning, and they haven't ven had a chance to take the AOD out of the shipping crate yet.

I'm pretty confident I found the right shop, though. When I dropped off my '73, there was a 1970 fastback on the lift with an AOD installed. It looked to me like it also had Lokar cables.

 

[Mister 4x4]

You have no choice about putting the AOD into OD - there is only "1-2-D" - there is no selectable "OD." When the transmission hits "D," it will go into OD on its own volition.

The stock Mustang shifter will need some adaptation to work with the AOD shifter cable, since it uses hard linkage to change the selector on the FMX transmission. The stock Mustang shifter also uses a "bolt-through" method with the linkage, whereas the AOD shifter cable uses a 'ball & socket' fastener on the end of the cable-to-shifter lever junction, and has a fixed mounting point for the cable 'sheath' (since the cable itself moves, not the whole thing - you'll find the same thing on the 'transmission end' of the cable). The shifter cable also comes in from behind the shifter itself (as opposed to from the front, like the linkage), which is one reason one must 'flip' the gear selector on the transmission itself (depending on the shifter configuration from the donor vehicle).

This is going to be pretty consistent whether you use the AOD cables, or an aftermarket cable/shifter solution (Lokar, B&M, Hurst, et al).

You can go to Summit Racing and d/l the Installation PDF for any of their shifters to see what I'm talking about. I was interested in the B&M Megashifter, so I d/l'd the Installation PDF for it. B&M's Installation PDF outlines the things you need to install their cable shifters, with many different applications spelled out (included for Ford: C4, FMX, C6, and some AODs).

 

[wwhite72]

Not sure if this helps but my 351c 2v had 2.75's in it from the factory. After engine work i was very happy with the improvement, but when i stuck the trutrac and 3.25's in the car changed dramatically. I can actually get on the cam and feel the engine wake up in my normal driving. Then i had a 2500rpm stall converter installed and now launches are quicker (a bit louder out the pipes also) and the rpms climb very quickly. Feels like the whole car works better now. The 2.75's were killing the car. The 3.25's are great on the highway as well since i dont cruise at 90mph all day with the top down.

 

[sdstang]

Not sure if this helps but my 351c 2v had 2.75's in it from the factory. After engine work i was very happy with the improvement, but when i stuck the trutrac and 3.25's in the car changed dramatically. I can actually get on the cam and feel the engine wake up in my normal driving. Then i had a 2500rpm stall converter installed and now launches are quicker (a bit louder out the pipes also) and the rpms climb very quickly. Feels like the whole car works better now. The 2.75's were killing the car. The 3.25's are great on the highway as well since i dont cruise at 90mph all day with the top down.

Glad to hear this! I have a rebuilt engine in my car but it seems like a dog. I'm going to an AOD and 3.50 gears, maybe 3.73 though i'm a little worried about the 3.73 might be too much?

 

[Don65Stang]

Glad to hear this! I have a rebuilt engine in my car but it seems like a dog. I'm going to an AOD and 3.50 gears, maybe 3.73 though i'm a little worried about the 3.73 might be too much?

How tall are your tires and what is the end goal?

 

[CZ-75]

With the Overdrive in the AOD, each 1" in tire size equates to approximately 130 RPMs.

25" tires with 3.7 rear end would be right about 2,330RPM at 70MPH. Go to a 26" tire, and RPMs drop to about 2,200.

I think 2,200 - 2,300 is fine for highway speeds.

Going to a 3.5:1 rear would droop each RPM reading by about 100 or so... So 2,200 and 2,100 respectively.

 

[wwhite72]

With an aod im sure 3.73 would work, as would the 3.50. But the 3.50 would work well before you spent the money on the aod. Perhaps you might try the gear change before the bucks on the trani swap? And the stock, out of the yard used aod trani might not be as stout as the FMX or C6 under heavy load. Unless you are buying a new aftermarket unit? Im by no means a trani specialist but i know the factory had been matchin the FMX to performance mills for a while before they decided the C6 was needed for top torque engines. But AOD fans would know better. Maybe from a Country Squire with a 460 or something?

 

[Mister 4x4]

He's already in the process of getting an AOD installed (w/4R70W "wide ratio" guts in it), so his set-up should be a bit stouter than my plain-old stock AOD.

But honestly, what kind of 'heavy loads' can we really expect our cars to be enduring, anyway? Short of some occasional spirited driving, the stock equipment should be just fine for most people. When you're talking about racing on a more-than-occasional basis, then yeah - need something a little stronger to endure (but most racers tend to build their stuff accordingly).

 

[CZ-75]

What I'm looking for is a sweet spot between casual fair-weather driving and the occasional desire to burn rubber, especially when a tweaker gets all froggy at a red light in his Accord coupe with fart pipes on it.

Going with the wide ratio and 3.89 may, in hind sight, be a bit over zealous... We'll see.

 

[Mister 4x4]

What I'm looking for is a sweet spot between casual fair-weather driving and the occasional desire to burn rubber, especially when a tweaker gets all froggy at a red light in his Accord coupe with fart pipes on it.

Going with the wide ratio and 3.89 may, in hind sight, be a bit over zealous... We'll see.

I'm wanting the same thing, but I'm overcoming any issues with the 3,00s with more power. I think the 3.50s are what you'll want. 3.25s are starting to get into highway gears. Although, your wide-ratio gears will afford you a little more low-end than mine.

Can't wait til you get yours on the road so you'll know for sure!

(Did what I say about the shifter & cable make sense? It's not a show-stopper... just something to think about. The shop doing your conversion should be able to get it squared away... especially since they already had that '70 in there)

 

[CZ-75]

Yes, it made sense. I know that the AOD shift cable comes in from the opposte angle. The guy at the shop was like: "Don't worry about it, we'll get it right for ya. I'll call you before I buy or fabricate anything expensive."

I am hoping to get satisfaction off the line without having to dive into the engine any more than replacing the intake, carb and distributor. And I definately wanted overdrive regardless... so wide ratio made sense to me.

On the other hand, I am nevous about NOT doing a valve job... I have heard a lot of bad press about teh 351's 2-piece valves. And if I'm going to do that, then maybe a new Cam, lifters, rods, pistons, etc... bring compression up a bit... I think the 73' had like 8.5:1 CR. One would think it pretty easy to get a lot more out of the '73 engines without over-building them.

 

[Mister 4x4]

Yeah, the two-piece valves are about the only thing I didn't replace. The machine shop said my valves were just fine, so I didn't give it a second thought (at the time).

I pretty much had no choice but to rebuild everything, so I decided to build-in some more power. So far, it seems to be a solid combination - even though I haven't actually had a chance to run it to see what I actually have. I based my build loosely on Doc's (73vertproject) rebuild - same cam - and had planned all along for "balanced & blueprinted," 3-angle valve-job, 9.5:1 flat-tops, roller everything, Edelbrock intake/carb, and long-tube headers.

Going with a new intake, carb, and dizzy will definitely wake-up what you already have... but you'll probably want some more after awhile.

 

[CZ-75]

Yeah... although the budget needs a year to recuperate before I do any extensive engine mods... unless I win the lottery soon.

 

[Tubo]

DIY AOD shifter, made from a 86-98 Mustang shifter. They are all variations of the same parts.

The shift detents will match the AOD. When using a C-4 shifter with rod linkage, it doesn't quite hit exactly right.

This is the basic shifter, with the base de-constructed. You take the cable bracket, and install it in the tunnel, though in the same relation as it origionally was to the shifter mechanism. It works just like the Ford intended.

This is the ct out Fox base compared to a C-4 shifter. This assembly was used in the 2+2. I used the same principal to maake a shifter for the 73 Vert and 4R70W. Again same detents as AOD.

returning to your rear gear selection. The reason I have suggested the 3.55 over the 3.89 is the wide ratio gear set.

The AOD's 1st gear is a 2.4, where the 4R70W's is 2.84

So if the AOD 1st sees a 3.25, the same 3.25 rear gear would be as a 3.89 to the 4R's lower 2.89 1st gear.

Use 3.89 and that 1st gear gets super low.

 

[sdstang]

Glad to hear this! I have a rebuilt engine in my car but it seems like a dog. I'm going to an AOD and 3.50 gears, maybe 3.73 though i'm a little worried about the 3.73 might be too much?

How tall are your tires and what is the end goal?

25" currently. "My goal it to feel something in the seat of my pants and not of the jail house variety".

The PO rebuilt the engine 11k miles ago but not much in the way of performance increase. (Carb, intake, RV cam and headers so maybe 220HP). I was hoping that if I could get by for a few years with an AOD and gear change.

Thanks for any input!

 

[CZ-75]

DIY AOD shifter, made from a 86-98 Mustang shifter. They are all variations of the same parts.

The shift detents will match the AOD. When using a C-4 shifter with rod linkage, it doesn't quite hit exactly right.

This is the basic shifter, with the base de-constructed. You take the cable bracket, and install it in the tunnel, though in the same relation as it origionally was to the shifter mechanism. It works just like the Ford intended.

This is the ct out Fox base compared to a C-4 shifter. This assembly was used in the 2+2. I used the same principal to maake a shifter for the 73 Vert and 4R70W. Again same detents as AOD.

returning to your rear gear selection. The reason I have suggested the 3.55 over the 3.89 is the wide ratio gear set.

The AOD's 1st gear is a 2.4, where the 4R70W's is 2.84

So if the AOD 1st sees a 3.25, the same 3.25 rear gear would be as a 3.89 to the 4R's lower 2.89 1st gear.

Use 3.89 and that 1st gear gets super low.

Thank you!!! :goodpost:

Glad to hear this! I have a rebuilt engine in my car but it seems like a dog. I'm going to an AOD and 3.50 gears, maybe 3.73 though i'm a little worried about the 3.73 might be too much?

How tall are your tires and what is the end goal?

25" currently. "My goal it to feel something in the seat of my pants and not of the jail house variety".

The PO rebuilt the engine 11k miles ago but not much in the way of performance increase. (Carb, intake, RV cam and headers so maybe 220HP). I was hoping that if I could get by for a few years with an AOD and gear change.

Thanks for any input!

With 25" tires, a FMX/C4/C6, and a stock 2.75:1 rear-end, you will be around 2,600 RPM at 70MPH, maybe closer to 2,800-2,900 if your tranny is like my FMX, and the torque converter never really locks up.

Switching to the AOD with 3.7 rear-end, will net you just north of 2,300 RPM at 70MPH, which in my opinion, is perfectly fine. And in first, you rfinal gear ratio will be 8.9:1 which is going to be a LOT better than the 6.6:1 you have now (assuming a 2.75 rear end).

With a 3.5 rear end, your RPM will drop by approximately 125 at 70 MPH, and in 1st your final gear ratio will be 8.4:1.

 

[Mister 4x4]

DON!!! Where's that "smilie head that shivers then explodes" I asked for a few weeks ago?!

 

[Don65Stang]

With 25" tires, a FMX/C4/C6, and a stock 2.75:1 rear-end, you will be around 2,600 RPM at 70MPH, maybe closer to 2,800-2,900 if your tranny is like my FMX, and the torque converter never really locks up.

Switching to the AOD with 3.7 rear-end, will net you just north of 2,300 RPM at 70MPH, which in my opinion, is perfectly fine. And in first, your final gear ratio will be 8.9:1 which is going to be a LOT better than the 6.6:1 you have now (assuming a 2.75 rear end).

With a 3.5 rear end, your RPM will drop by approximately 125 at 70 MPH, and in 1st your final gear ratio will be 8.4:1.

CZ, I agree with everything you said except for your first gear calcs for the AOD. The "target" first gear ratio is between 9.5 and 11 with 10 being optimal (in my opinion) but there is wiggle room depending on tire height, amount of engine torque available and when.

I get the following first gear ratios:

FMX w/ 2.75 rear: 6.60:1 - a VERY slow start like a slug.

FMX w/ 3.25 rear: 7.80:1

AOD (4R70W) w/ 2.75 rear: 7.81:1 - beginning to see a difference in the take off.

AOD (4R70W) w/ 3.00 rear: 8.52:1 - brings a smile maybe.

AOD (4R70W) w/ 3.25 rear: 9.23:1 - pretty darn good 1st gear ratio.

AOD (4R70W) w/ 3.50 rear: 9.94:1 - perfect IMHO.

AOD (4R70W) w/ 3.73 rear: 10.59:1 - another pretty darn good ratio.

AOD (4R70W) w/ 4.11 rear: 11.67:1 - approaching dump truck granny gear territory but still OK for an aggressive setup.

Dang, I typed all that and noticed you were addressing sdstang who has an AOD and not CZ. Well then since I've come this far... here's the AOD ratios:

AOD w/ 2.75 rear: 6.60:1 - accelerates just like a slug.

AOD w/ 3.25 rear: 7.80:1 - accelerates just like a turtle.

AOD w/ 3.50 rear: 8.40:1 - getting better.

AOD w/ 3.73 rear: 8.95:1 - pretty good ratio.

AOD w/ 4.11 rear: 9.86:1 - approaching perfection.

I need to clean up and put my Transmission and Rear Gears spreadsheet on here.

 

[Mister 4x4]

Yeah - I'm not convinced that data is correct (VERY slow start like a slug).

Why? Because I remember seeing a couple of videos of Doc's car (FMX w/either 2.75s or 3.00s - can't remember which) accelerating unbelievably from zero-100 in about 8-9 seconds, while not even catching 'D' (i.e. only 1st & 2nd). Or was I imagining things?