THe title says it all. Looking for more power, or just want to make it quicker, it has 3.27's in both now. Should I change to 3.73's in both of my cars? They both have the borg warner rear end.

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89 Iroc 350 TPI,
Forged pistions
Comp roller Cam .510 lift 230dur
Flowmaster exhaust
Dart Iron Eagle heads 200cc runners 64cc chambers
MINI RAM SOON!!!!!
stock TPI for now 24# inj
87 Trans Am GTA 350 TPI
had engine fire
SHE NOW RUNS!!!! GREAT!!
Flowmaster exhaust
LT1 Injectors

 

Borg warner doesn't make 3.73's. You can get 3.70's for them, but they are expensive and hard to find from what I understand.

 

Again, that is no longer true!! I have 3.73's in my 9 bolt (not the 3.70). The 3.73 is stronger as it has an 11 tooth pinion vs the 10 tooth pinion on the 3.70 ratio.

I have available (ie for sale) new gear sets and new series 3 posi carriers for the 9 bolt. I currently have 4.10 gear ratios and series 3 posi carriers in stock! Yes, for the 9 bolt! I will be getting some 3.4x and some additional 3.73 ratios soon.

Miles

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88 427 Camaro
12.18 @ 113mph 1.75 60ft
Currently installing 3.73's into my 9 bolt (YES, it is a 9 bolt & YES they are 3.73's, not 3.70. I currently have 4.10 gear sets and new series 3 carriers in stock for 9 bolts )
www.koolmeister.com

 

3.73s are avaliable from TPIS for $500 with all the berrings and instal kit.

 

Better check again, they only have the weaker 10 tooth 3.70 ratios (even though they advertise it as 3.73).

I have available 4.10 ratios with install kit for much less. I will also soon have available, 3.4x and the stronger 11 tooth pinion 3.73 ratio.

Miles

------------------
88 427 Camaro
12.18 @ 113mph 1.75 60ft
Currently installing 3.73's into my 9 bolt (YES, it is a 9 bolt & YES they are 3.73's, not 3.70. I currently have 4.10 gear sets and new series 3 carriers in stock for 9 bolts )
www.koolmeister.com

 

How about precision gear. I have a old catalog of theres at work and they advertise 3.73's. Dated early 90's. 88 427 Camaro do you have any info on your gear sets?

------------------
89 Iroc 350 TPI,
Forged pistions
Comp roller Cam .510 lift 230dur
Flowmaster exhaust
Dart Iron Eagle heads 200cc runners 64cc chambers
MINI RAM SOON!!!!!
stock TPI for now 24# inj
87 Trans Am GTA 350 TPI
had engine fire
SHE NOW RUNS!!!! GREAT!!
Flowmaster exhaust
LT1 Injectors

 

I've heard a lot of people say that they have had better experience using 3.45s in thier TPI cars as opposed to 3.70s.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End with 2.77:1 Gears.

Current Mods: LT4 HOT Cam, Comp Cams 1.52:1 Roller Rocker Arms, Accel High Flow TPI Baseplate, Edelbrock TES 1 5/8" Headers, Catco 3" High-Flow Catalytic Converter, Hooker 3" Aerochamber Cat-Back System, Transgo Shift Kit, Performance Resource Chip, Accel Ignition, K&N Filters, Jet TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET: 14.32 @ 97.7mph
(corrected for elevation)

 

What do you do when your ecm(prom)is programed for 3:27?That will effect your spark advance.

 

Have you had your car dynoed? What RPM does it pull to? I dont recommend 3.70 gears for stock engines, but for modified ones like yours, sure. I have them in mine and love it.


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1991 Camaro Z28
5.7L 5-Speed (originally 305)
317 RWHP, 418 RWTQ
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Member: SoCal F-Bodies
-=ICON Motorsports=-

 

Changing gears won't affect spark advance or anything ecm related for that matter because it goes off engine rpm not driveshaft rpm.

 

Call them up and ask them to count the number of teeth on the ring and pinion (not what their catalog says), then do the math your self.

There is so much bad information floating around about the 9 bolt. It is much better than people think. And parts ARE available. They are more expensive than a 10 bolt, but much cheaper (and lighter) than a 9 inch or 12 bolt. The 9 bolt fills a void between the 10 bolt and the 9 inch in terms of cost, strength and weight.

Miles

------------------
88 427 Camaro
12.18 @ 113mph 1.75 60ft
Currently installing 3.73's into my 9 bolt (YES, it is a 9 bolt & YES they are 3.73's, not 3.70. I currently have 4.10 gear sets and new series 3 carriers in stock for 9 bolts )
www.koolmeister.com