How to Modify your LS1 Bump Stop

John Huh

11 years ago

This is the first writeup in the series of LS1 free mods ( best bang for the buck mods ) that we will feature here as part of our LS1 Engine Swap Series. Up first is the ever pesky throttle body bump stop mod, which is a very common mod amongst enthusiasts as it’s free and something that a shadetree mechanic can perform at home.

The LS1 throttle body ( for those before the 2002 year or with the first year of the GTO ) is cable driven, meaning when you depress the gas pedal the cable pulls the throttle body blade open inside. Unfortunately for most of us, GM did not perfect the throttle body movement range, as Wide Open Throttle ( WOT ) doesn’t always net you the full 90° opening of your throttle blade.

That’s where our How to Modify your LS1 Bump Stop article comes in handy, allowing you a free mod that lets your engine breathe.

We’ll be performing this mod on yet another of our swap cars, with step by step directions on how to unlock a few ponies for free. The area you will be grinding away is commonly referred to as the bump stop, but to perform this mod you will need a datalogger of some sort to give you the voltage reading from the throttle body.

DO NOT PERFORM THIS MOD WITHOUT THE USE OF A DATALOGGER – You run the risk of damaging the throttle body bumpstop beyond repair if you do not use a datalogger in conjunction with this modification. This important step to How to Modify your LS1 Bump Stop, should not be overlooked.

Here’s a look at the bumpstop in a stock configuration, and you get the idea of what area you will be slowly grinding away to allow your throttle body blade to open the full 90° that GM intended. This is where knowing How to Modify your LS1 Bump Stop can come in handy.

First hook up your datalogger or scan tool and open up it’s monitor mode. The value you will want to keep an eye on is Throttle Position Sensor ( TPS ). WIth the datalogger hooked up, put the key in the ignition and turn the key to the “ON” position.

Depending on what kind of datalogger you are using it may give you the raw voltage value, or a percentage or even degrees. Push the gas pedal as far down as it will go to see what value your stock throttle body passes to the PCM. Our particular throttle body reads 82° opening, just a tad short of the 90° we are looking for,

If you are performing this job inside the car, you will have to remove the intake snorkel, Intake Air Temperature ( IAT ) sensor and any other pipes, hoses or sensors that may be in the way of you getting access to your throttle body. Remember to use tape or stuff something inside your throttle body to prevent any foreign materials from falling into your intake manifold.

Now that you have a good grasp on what part you will be grinding away, slowly do so checking after every step. It is important to take your time here, because you do not want to exceed the 90 degree opening that you are trying to achieve.

REMOVING TOO MUCH MATERIAL WILL THROW A CHECK ENGINE LIGHT. Make sure you are going slowly as to not cause an error in our How to Modify your LS1 Bump Stop guide

Take a dremel or grinder and grind down the bump stop where the throttle body butterfly touches at Wide Open Throttle ( WOT ) and don’t forget to check the voltage / reading after each grind. We like to take our throttle bodies as close to 90° as possible, but we usually never get too close as to prevent a check engine code. We stop our modification on this soon to be swapped motor at 88.2°

It’s a good idea to err on the side of caution for this type of modification.

With your throttle body freed, now is the time to put back your intake snorkel and any sensors you may have removed. It’s not a huge gain you will see from this mod, but it definitely does help!

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