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IAG Spec PPG 1st - 4th Straight-Cut Synchro Gear Set for 2004-21 Subaru STI

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IAG Spec PPG 1st - 4th Straight-Cut Synchro Gear Set for 2004-21 Subaru STI

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IAG Spec PPG 1st - 4th Straight-Cut Synchro Gear Set for 2004-21 Subaru STI


IAG Spec PPG 1st - 4th Straight-Cut Synchro Gear Set for 2004-21 Subaru STI

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  • IAG 6 Speed Synchro Set 1st - 3rd Brass / 4th - 6th Carbon Faced - Brass for 08-21 STI

IAG Spec PPG 1st - 4th Straight-Cut
Synchro Gear Set for 2004-21 Subaru STI

The Weekend Warrior

Gone are the days of blowing up stock six speeds, or having to resort to race-only solutions to support the high power levels that built Subarus now produce.

The IAG-Spec PPG Straight-Cut 1-4 Synchro Gear Set is designed for weekend racers (and weekday racers for that matter) who prefer the streetability of a synchronized gearbox which is suitable for daily driving. The kit features strong, straight-cut gears (vs. traditional helical gears) which provide maximum performance and durability for high horsepower Subarus and can be safely driven on the street.

Straight Cut For Extra Strength

The OEM gear shown on the left is cut in a "Helical" Style. Notice that the shape of the teeth are designed to wrap around the gear. Helical gears are used in most OEM transmissions due to their quiet operation and easy engagement. The teeth are much thinner and weaker than the IAG PPG gear on the right with "Straight-Cut" teeth due to the helical style.

Eliminate Extra Shifts

Our engineers worked directly with PPG to specify custom gear ratios which allowed us to increase top-speed in 1st and 4th gear. This change will prevent extra shifts while drag racing. Additionally, the gearset is designed to utilize the OEM 5th and 6th gears for quiet highway operation and maximize streetability.

While the synchronizers improve drivability for the street, the taller 1st and 4th gears are the stars of the show when it comes to racing and all-out acceleration. A 1st Gear Ratio of 3.077 results in an 8-10 mph increase vs. OEM (years vary) while the new 4th Gear Ratio of 1.042 will ensure that you finish out your quarter mile pass without shifting to 5th.

Gear Ratio Final Ratio Min Spd Max Spd

1st Gear





2nd Gear





3rd Gear





4th Gear





5th Gear





6th Gear





* Chart reflects a 9000 RPM redline with a 26" tire. Speeds are shown in MPH.

IAG+PPG = A Combination You Can Trust

Sub 10-second street Subarus are all the rage right now. The partnership between IAG and PPG combines our experience to offer a robust but versatile combination that appeals to those who want the strength of a built transmission, but don't want to give up driving the car on the street. Pfitzner’s legendary strength and durability paired with IAG’s insight on gear ratios and specifications has resulted in a product that we know will be a game changer in the Subaru community.

What's Inside?

IAG Spec PPG 1-4 Synchro Gear Set Includes:

  • (1x) Input Shaft
  • (1x) 1st Straight-Cut Output Gear
  • (1x) 2nd Straight-Cut Output Gear
  • (1x) 3/4 Straight-Cut Cluster Gear
  • (1x) 3rd Straight-Cut Input Gear
  • (1x) 4th Straight-Cut Input Gear
  • (1x) Clutch Input Shaft
  • (1x) Reverse Idler Gear
  • (1x) Input Shaft C Clip
  • (1x) Retainer Key

Power Rating

IAG Spec PPG 1-4 Gear Set is designed to support vehicles up to 1000 BHP

Dogbox vs. Synchromesh Gear Sets:

Dogbox vs. Synchromesh

As turbocharged Subaru power levels have increased to new heights, so has the demand for a more balanced transmission solution for the masses. The IAG/PPG gearset improves strength over OEM transmissions while also maintaining the mannerisms of factory synchromesh for those drivers that like to have their cake and eat it too.

Pfitzner’s 'Dogbox' drag racing gear set is featured in nearly all of the world’s fastest and quickest Subarus. The strength and reliability of dogboxes have positioned them as the go-to 6-Speed option for years, but their drivability and required service intervals limit their use to only the most serious race applications.

The IAG PPG Gear Set is known as a Synchromesh Gearset. This works similarly to the OEM Subaru transmission. This type of gear is engaged using cones to match the speed of the gears and then held in place with multiple ‘teeth’. The load on the teeth prevents play when in gear. Because of the load on the teeth and the fact there is not much space the speed of the gears needs to match almost exactly in order to engage. This is what the cones do - they match the speed of the gears to provide smooth engagement. A clutch allows the gears time to align during downshifts without load from the engine.

On the other hand, a 'Dog' gear set is typically only used in racing applications. A 'Dog' gear usually has 3-6 ‘dogs’ on each gear, leaving a lot of free space for them to engage. This free play can make the dog box challenging to drive on the road and create bucking, especially at low speeds. However, this space between the dogs is necessary to allow up to a 900 rpm difference in gear speed during shifts at slow speeds. This is not an issue when driving fast, as you are pushing on one side of the dog for acceleration or braking rather than hovering in the middle.

Due to the free play in the dogs you do not need the clutch. In street applications damage to the dog teeth can easily occur when shifted improperly (as seen in this photo.) The IAG PPG gear set provides much of the strength of the PPG dog gear set without the potential for damage during shifts while street driving.

Installation Instructions & Notes

Product Notes:

  • The IAG-Spec PPG gear set suits factory 2004-2021 STI transmission cases and requires professional installation.
  • Additional components required for installation include synchronizers, bearings and more. Transmission should be professionally torn-down for inspection and evaluated before determining additional components needed for proper installation.
  • Due to the straight cut gear teeth an audible whine while in gear is to be expected and is normal.
  • PPG Recommends Motul Gear300 75w90 Gear Oil which should be changed at 3000 mile intervals.
  • Please Note that this product carries only the manufacturer's limited warranty. More details can be found here:

PDF Instructions

Model Year & Fitment

  • 2004 Subaru STI
  • 2005 Subaru STI
  • 2006 Subaru STI
  • 2007 Subaru STI
  • 2008 Subaru STI
  • 2009 Subaru STI
  • 2010 Subaru STI
  • 2011 Subaru STI
  • 2012 Subaru STI
  • 2013 Subaru STI
  • 2014 Subaru STI
  • 2015 Subaru STI
  • 2016 Subaru STI
  • 2017 Subaru STI
  • 2018 Subaru STI
  • 2019 Subaru STI
  • 2020 Subaru STI
  • 2021 Subaru STI

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IAG will repair any IAG Manufactured Product that proves to be defective in materials or workmanship within the warranty period. If a repair is not possible, we will either replace your Product with a new Product of similar composition and price, or refund the full purchase price of your Product, at our sole discretion. There is no charge for inspection but the buyer is responsible for shipping charges.

IAG Performance Engine Warranty

For more information concerning our engine warranty please visit IAG Performance Engine Warranty Page

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Products not manufactured by IAG are subject to the individual manufacturer warranties which may apply. If you have questions concerning the fitment, appearance, or performance of your item, please contact a member of our customer support team for assistance.

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