I think a gear change is needed

Mstng93SSP · Apr 27, 2021

My 93 coupe has 3:73's in it. and an AOD with a 2500 converter and silver fox valve body. Now that I have installed the On3 Turbo I feel like the 3:73's are too much. The car just gets up into the power band too fast and I am always having to get off it. I know my right foot has a lot to do with it but I feel like 3:27's might be better. Opinions?

CtCarl · Apr 27, 2021

I love the 3.73s in my '87, but I've got a World Class T-5 Z with the taller 2.95 first gear. A buddy of mine who bought his notchback in '87 had 3.27s with his AOL from the factory.

Personally, I always thought 3.55 was a good compromise for the AOD. But it's hardly worth switching out 3.73 for 3.55.

Mstng93SSP · Apr 27, 2021

I love 3:73's too, but they are not ideal with the turbo.

slow84lx · Apr 27, 2021

I think that you are experiencing what many do after putting on a turbo. There is a need to get the gearing more suited to the new power curve. It's common to revert back to original equipment comparable ratio's with 3.27's being one of the more popular. Your car with the new power curve will likely respond well.

...but, this summary isn't from personal experience, I've never owned any car with a turbo, although, I've followed along on the forums thru a lot of conversions and gear discussions. I think that you are on the right track.

CarMichael Angelo · Apr 27, 2021

I have 3.73’s...and a pretty wild power band that comes on late compared to yours...The thing to consider isn’t how quickly it goes through the 1,2,3....it’s what happens when it goes into OD, and you lock up the converter.
if the interstate and the speed/rpm it cruises at are even remotely a consideration, you need to see where it is at 70 mph locked up...for me that’s about 2200 rpm...if you put a 3.27 in the rear, the rpm on the highway will be so low that the engine may be too lazy to get decent gas mileage. But that’s all relative I guess..especially if you don’t care about the cruise.

Mustang5L5 · Apr 28, 2021

I've always had the notion that as your power levels go up, your gear ratio needs to go down the other direction towards lower numerical gears to keep the engine in the powerband more. Of course, what gear to go with depends on many other factors.

But the whole "don't fear the gear" movement seemed to be during a time when bolt-ons were the most common mod and a pair of decent heads was not as common as it is today along with plentiful turbos for everyone. We almost needs to rethink that.

In your shoes, i would definitely be considering 3.27's, 3.31's or even 3.55's although i don't think the jump from 3.73 to 3.55 is worth it.

Ryuk · Apr 28, 2021

Mustang5L5 said:
I've always had the notion that as your power levels go up, your gear ratio needs to go down the other direction towards lower numerical gears to keep the engine in the powerband more. Of course, what gear to go with depends on many other factors.

But the whole "don't fear the gear" movement seemed to be during a time when bolt-ons were the most common mod and a pair of decent heads was not as common as it is today along with plentiful turbos for everyone. We almost needs to rethink that.

In your shoes, i would definitely be considering 3.27's, 3.31's or even 3.55's although i don't think the jump from 3.73 to 3.55 is worth it.

I like the inverse of this logic. My car has 2.73's, therefore I need more power.

a91what · Apr 28, 2021

I went from a 373 to a 308 gear when I had the blower setup on the car... it was violent with the 373 gears the 308 calmed the car down quite a bit

Hoytster · Apr 28, 2021

Pretty typical from my experience, most people switch back to a lower gear ratio when going turbo. Are you blowing the tires off in the lower gears (1,2,3?). Lowering the gear ratio will help with that as well as put more load on the engine in the lower gears, which helps with spooling and power delivery on a turbo car. It's a balancing act though, you don't want so low a gear it takes forever to get into the boost. 3.27's would be a good start imo.

Mstng93SSP · Apr 28, 2021

Yeah, that is one of the issues I have. If I get on it the tires just light up and I can get sideways way too easily. I have 275/35/17 BF Goodrich tires so they should grab but nope.

deathb4dismount · Apr 28, 2021

Mstng93SSP said:
Yeah, that is one of the issues I have. If I get on it the tires just light up and I can get sideways way too easily. I have 275/35/17 BF Goodrich tires so they should grab but nope.

Sport Comp 2s?

Mstng93SSP · Apr 28, 2021

deathb4dismount · Apr 29, 2021

Mstng93SSP said:
Yes

Not that it will make a difference in your gear choice, but IMO those tires leave something to be desired. When new they were pretty good, but after few seasons, meh. Mine still have about 70% tread left, and I can get loose on 2-3 shift with a mild h/c/i car. Those tires arent grabbing anything.

Monkeybutt2000 · Apr 29, 2021

You're gonna need a drag radial, the ET street ss have worked well for me.

Mstng93SSP · May 19, 2021

Spent my day doing this. What fun!

I picked up an 8.8 from a friend. It has 3:08 gears. He also gave me a set of 3:27s. I installed the 8.8 in the car with the 3:08 gears to give it a try. So far I kinda like it. Cruises smooth and I can roll into boost without the back end skating all over the place.

CarMichael Angelo · May 19, 2021

While I understand the justification for the gear change, going from a 3.73 to a 3.08 just cost you the race. What would be the point of upping the power only to throw away the acceleration because traction is the issue? Dumping the gear isn’t the fix, putting a tire on it that hooks is.

The only time a gear change is mandated would be when target RPM is out of the range you‘re trying to be in ( i.e. cruising RPM in high gear/ engine RPM at trap speed). Now that you’ve dropped that gear so far, I think you’ll absolutely hate it when you put a drag radial on it again. Granted, a 3.08 will calm it down dramatically, but calm and slow now go hand in hand.

Im changing the gear in my car from a 3.73 down to a 3.31 only because i’m swapping a transmission. The 2.48 first gear in my current auto, ( 4l80) will go up to 3.78.

Mstng93SSP · May 19, 2021

There is no trap speed on this here little "rock" where I live. We have not had a track here in the last 20 years. And to find a track would require a boat and a hefty shipping charge. 3:08 were already installed so that's what I went with for now. I can always gear up...but not 3:73's.

Monkeybutt2000 · May 19, 2021

If I were a betting man I would bank on the 3.27s. Once I get my car back together,gonna decide on a gear swap or no. With the TKO and it's gear ratios,the 3.73s weren't that bad. However,I've been told the lower gear numbers will allow the turbo to build boost more efficiently. We'll see.

Mstng93SSP · May 19, 2021

I just felt with the 3:73's it was like an on/off switch. When it hit boost it would hit hard. So far I like the 3:08's as it seems to get into boost in a slightly less aggressive manner. If it gets boring my engine is built for boost so I can always turn up the fun knob...

I think a gear change is needed

Mstng93SSP

You have a nice rear end there Dave.

CtCarl

Active Member

Mstng93SSP

You have a nice rear end there Dave.

slow84lx

clean it good before insertion

CarMichael Angelo

my rearend will smell so minty fresh,

Mustang5L5

That is…until I whipped out my Bissell

Ryuk

I love your drawers

a91what

SendMeUrDataLog

Hoytster

I don't dare do that to my Knob

Mstng93SSP

You have a nice rear end there Dave.

deathb4dismount

Crap, didn’t realize my crotch was in that picture

Mstng93SSP

You have a nice rear end there Dave.

deathb4dismount

Crap, didn’t realize my crotch was in that picture

Monkeybutt2000

Mustang Master

Mstng93SSP

You have a nice rear end there Dave.

CarMichael Angelo

my rearend will smell so minty fresh,

Mstng93SSP

You have a nice rear end there Dave.

Monkeybutt2000

Mustang Master

Mstng93SSP

You have a nice rear end there Dave.

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I think a gear change is needed

You have a nice rear end there Dave.

Active Member

You have a nice rear end there Dave.

clean it good before insertion

my rearend will smell so minty fresh,

That is…until I whipped out my Bissell

I love your drawers

SendMeUrDataLog

I don't dare do that to my Knob

You have a nice rear end there Dave.

Crap, didn’t realize my crotch was in that picture

You have a nice rear end there Dave.

Crap, didn’t realize my crotch was in that picture

Mustang Master

You have a nice rear end there Dave.

my rearend will smell so minty fresh,

You have a nice rear end there Dave.

Mustang Master

You have a nice rear end there Dave.

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