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I was thinking of doing the same kit (121-125 VVT delete). Dealer had a good promotion going on stage kits. The difference in labor between the 125 kit and the 135 kit was 1 hour, not much at all. But the price of the kit was about $2500 more.
I actually schedule this install but after some research I decided to wait for now.
Keep us updated on how this project goes.
I simply cammed it and kept the 121 VVT in tact. (Details on the dyno sheets).
The results are plenty for me as I'm a 2500 - 5500 rpm type rider.
Rarely do I ride above 5500 unless it was a missed shift or something.....lol.
Remember to watch where the peak hp & tq hits and be sure your it aligns with your sweet spot otherwise most of us would be wasting our money on the hype.
I simply cammed it and kept the 121 VVT in tact. (Details on the dyno sheets).
The results are plenty for me as I'm a 2500 - 5500 rpm type rider.
Rarely do I ride above 5500 unless it was a missed shift or something.....lol.
Remember to watch where the peak hp & tq hits and be sure your it aligns with your sweet spot otherwise most of us would be wasting our money on the hype.
Did you upgrade the pistons? I've been reading a lot about the cast pistons being too thin between the top ring and the top of the piston. Something about putting too much timing in the tune. Some tuners refuse to tune the 121's without upgrading the pistons.
Last edited by Scurv87; Feb 24, 2026 at 03:01 PM.
Reason: Spelling error
I'm probably going to wait to save up some overtime to do the 135. See if I can save enough to do the crank too. Then I won't have to worry about that breaking.
You might want to check with GMR Performance, they are working with the Impact a lot. If I remember correctly there is a video around that shows a vvt delete kit, can’t remember who made the video though.
GMR is an employee for Impact and has been for several months. He still does side work but since he closed down in Texas and moved to Iowa he has been an employee.
Last edited by Steve Cole; Feb 24, 2026 at 03:33 PM.
From what I've been reading, I don't think it's a good idea to just do the cam without upgrading the pistons on a 121 to go from cast to forged. I had a short text conversation with Ben from IWS and he said it's probably a good idea to upgrade the pistons before doing the cam. I like all the upgrades on the 135 kit, except I don't need the header. I have a Khrome Works head tube already.
You can buy the 135 kit from HD and get everything you need at one time or you can do the 125 kit for less money but still be missing the rest of the performance. Your choice, your money. Remember that when installing an aftermarket ECM your going to loose features that your bike came with, Factory traction control system is out the window along with the brake and cornering safety functions that require the factory ECM to be in place. IMU, EHCU, BCM modules no longer work properly because they are missing the factory ECM as they all need to work together, for things to work properly.
GMR is an employee for Impact and has been for several months. He still does side work but since he closed down in Texas and moved to Iowa he has been an employee.
You sound kinda bitter Steve.. I still talk with Steve (GMR) and he's advising on my next build.. He's still very much open and GMR is still going... He does tuning and testing for several manufacturers and not tied to just one..
You can buy the 135 kit from HD and get everything you need at one time or you can do the 125 kit for less money but still be missing the rest of the performance. Your choice, your money. Remember that when installing an aftermarket ECM your going to loose features that your bike came with, Factory traction control system is out the window along with the brake and cornering safety functions that require the factory ECM to be in place. IMU, EHCU, BCM modules no longer work properly because they are missing the factory ECM as they all need to work together, for things to work properly.
With the IWS ECU you keep all of the functionality of the original ECU.
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