Unabomber's Manifesto - TGV Deletes FAQ

Pick a FAQ:

The primary purpose of a TGV delete is to remove the divider bar and butterfly valve inside the TGV assembly to improve airflow to your engine.

HP gain is 12 HP. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods.

What is the purpose of TGV Deletes? The are meant to reduce cold idle emissions. Nothing more, nothing less. Once your vehicle is warm, the butterfly valves open fully and remain that way.

Which manufacturer is best? This topic is highly debated with no real winner in terms of performance. There are several companies that offer the TGV delete service as well as purpose built units or Japanese models which are, in essence, hollow units.

Japanese model, what is that? TGV internal assemblies are only used for cold start emissions on US cars. Hence, the Japanese TGVs do not have the divider plate or butterfly vavles. Some models are one piece intake manifolds with longer runners that make up the TGV portion and other models are just like their US cousins with no internal plates or butterfly assemblies. Neither units have the associated TGV external motor controllers as well.

Which TGV Delete has the best gains? There is no irrefutable evidence that any TGV Delete option has better gains than another. The consensus, if there is one, is they are all within 5HP or less, gain wise, of each other.

Do TGV Deletes cause a CEL? Yes. By removing the TGV motors, it will throw quite a few CELs. The bad news with this, is the TGV CELs will throw your car into limp mode, meaning unlike some other CELs that you can still drive around with and have no fear, the TGV codes limit boost/RPM operation meaning they must be taken care of in order to drive your car for any reasonable distance.

How do I fix the TGV CEL? You have three methods:
1. Normally, you remove the TGV motors and the rod that holds the butterfly valves in place. You could leave the rod in place (sans butterfly valves) and reinstall the TGV motors. This would allow them to actuate normally making the system think everything is working correctly.
2. APS makes a block that you attach the TGV motors to, this allows them to actuate normally making the system think everything is working correctly. These are not sold separately though, but can occasionally be purchased in the Private For Sale Forum or on eBay.
3. Various engine management systems can remove the associated CELs.

Do I need to perform the CEL fix? Yes. The TGV CEL codes will throw your car into limp mode. This will limit boost/RPM seen by your vehicle. It will still drive, but it should only be driven a short distance with the TGV CEL. Meaning you can drive it across town or a few short trips, but by no means should you drive it as a daily driven car for weeks on end until you get the proper fix.

Are there any downsides to TGV Deletes? No. As long as you account for removing the associated TGV CELs, there are no known downsides to this mod. Depending on the user, some see a wandering idle on cold starts which isn't so much a downside as it's stated in case this should happen on your particular vehicle....it happens to some cars and not others, so you may or may not see this. Once the vehicle is warm, this goes away and most users report this for just the first few seconds of starting a cold car.

Is there anything to be careful about when buying TGV Deletes or using a TGV Delete service? WRX and STI TGVs are not interchangable, so you must state your year/model car with the Vendor to ensure you get the right kind as the JDM TGV varieties are complicated. For the US varieties:

2007 STI are topfeed
2004-2006 STI are sidefeed
2002 WRX are topfeed

Yes you can convert your car from top to sidefeed or vice versa, but unless you want the additional time/trouble/expense, it's best to get the right TGVs in the first place. Top or side feed refers to the injector type/seating surface as they are different as are the associated fuel rails. So you must use all the components of either type if swapping TGV styles.

Where do I buy a TGV Delete? For purchasing, support your NASIOC Vendors. You have four options for TGV Deletes though:
1. Do it yourself
2. Use a TGV Delete service
3. Purchase APS TGV Deletes from APS or one of it’s Vendors.
4. Use a Japanese intake manifold/TGV assembly

So which route should I choose? It depends on many factors, but they are highlighted below:

DIY: Can be done while your car is down or with an extra set. Deleting can be accomplished in one afternoon with the proper tools (air tools and carbide bits) or over the course of a week with less than proper tools (Dremel). This is definitely the cheapest way to go and as long as you take your time, the quality and flow can/will match the best porting service.

TGV Delete Service: Probably the easiest solution as you can either send yours in for porting or most places offer a core charge service where you obtain $XXX back when you send in your OEM units. Most offer commercial grade painting and/or thermal dispersant coating.

APS TGV Deletes: These are a very expensive option as they were manufactured with a purpose built CEL fix as well as designed to accommodate extra fuel injectors. So if you plan on extra injectors, these may be the route to take first. Otherwise, they are a rather poor choice mainly due to their internal fit and finish as they are not port matched to the engine block and create a restriction at that junction compared to DIY/TGV Delete Service models. So yes, you can/should port the APS units for best flow.

Japanese: These can be used as well, but you have to do some research with a trusted vendor. The reason for this is you have to ensure that you have the right Japanese manifold for your vehicle due to JDM/USDM differences in injector type and throttle body type. Using these is fine, but you cannot use the TGV CEL fix #1 as detailed above with them as they have no rods to do this with.

Can I gut my TGVs myself? Yes. NASIOC instructions can be found here, here, and here.

If I gut my TGVs myself, how should I fill up the hole where the rods were? You can either have it welded up (probably the preferred method) or many have successfully used various bolts or epoxies to fill them up with great success.

If I gut my TGVs myself, should the inner surface be polished or have a slight texture? The easiest way is to use a light abrasive to smooth over your rough porting work to leave a slight textured finish. While the smooth vs. rough debate has and will wage for years to come with internet fluid dynamics specialists, it probably matters not but to say it's 100% easier just to leave a smooth, but textured finish.

What about external coatings for TGV Deletes? While thermal dispersants would be most beneficial, the benefits would be very hard to measure. But, for some this would be considered the “best” option. Most are happy enough to color match them with spray paint to their car’s color scheme or leave them unpainted. To paint them, simply clean them very well, tape off the top and bottom mating surfaces, and use a quality high temp spray paint.

How will leaving the rods in affect me vs fully ported options? The rods are actually quite large in diameter for what they do. You can grind them down in profile so that when they are in their open position they block less flow. Leaving them in untouched is an option as well. They do present a blockage in total flow, but it's impossible to say whether they would present a loss in HP on the dyno vs. the no bar options. In the perfect world, you'd remove them totally and fix the associated CEL through engine management or the APG TGV delete motor "cheater blocks" vs. leaving the rods in.

What about phenolic gaskets? These are plastic based gaskets that limit the thermal conductivity between the hot engine block and the TGV/Intake Manifold. As with external TGV thermal dispersant coatings, phenolic gaskets are the best to use, but their benefits are nigh impossible to measure on a dyno. Most users just consider these a “must have” and get them with little thought though. Some use OEM gaskets, some OEM and phenolic, some have reused OEM and/or phenolic gaskets….unlike some Subaru junctions, the TGV/motor junction isn’t particularly prone to leaking. This isn’t carte blanche to re-use gaskets akimbo, but re-using gaskets here isn’t a deal breaker like it can be in say the exhaust side of the house.

How hard is it to install TGV Deletes? Allow around six hours for install time. Professional installation, depending on your area, is around $400. This is one vehicle modification that is fairly complicated and should only be tackled by those with extensive Subaru experience.

How do I install TGV Deletes? Refer to the TGV Delete manufacturer's instructions. For those without instructions, below are links to some of the better known TGV Delete installation instructions:
Grimmspeed's Instructions
Scoobymods.com instructions
Scoobymods.com instructions on how to align the stock TGV rods or APS blocks can be found HERE.
Meatys DIY TGV Delete Guide

What are the TGV delete CEL codes I need to turn off?

2004 STI, the TGV codes are called "Tumble Generated Valve" codes and they are codes P1086-P1097
2005 STI, the TGV codes are called "Intake Manifold Runner" codes and they are codes P2004-P2022
WRX, the TGV codes are P2004, P2005, P2008, P2011, and P1086 though P1097 Tumble generator valve and valve circuit codes.

This information is somewhat outdated for the later models though, so if you see something has changed with later models or other models, please post up.

There's a hose sticking of my driver's side TGV that I don't know where it goes....will my car explode and kill everyone within 500 miles? No, that's just a vent hose and goes to nothing, leave it alone.

Do I need engine management with a TGV Deletes? Actually no. Having TGV deletes on a stock ECU or aftermarket tune causes no issues. While it is always better to have a mod tuned for, this is one modification that could be performed with no future tuning if you so desire.

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.

Editors Note

This post was created because I wasn't able to find a good TGV Deletes FAQ. I came up with the text based on LOTS of searching here. It was also created to be intentionally brand neutral so that it serves as a stepping stone for further research. Upon reading this you should have an idea of which TGV Delete best suits your needs. The manufacturer is up to you.