28/08/2026
I have available some Gen2/3 NA thick wall 306 stainless exhaust sleeves.
After recently seeing a YouTubers post as he’s now beginning to head in the right direction with his 26b build showing effects of exhaust verlosity has on the power band. I thought it might be time to show some detail pics and explain why I gone into so much effort in this area with my sleeves.
The Facts.
Note. These sleeves were not designed with a coffee in one hand and mouse in the other to what looks good on the laptop screen!
If you’re one of those tyre kicking idiots thinking about asking me for data, I suggest you continue shopping with your companies that share their hard earned IP on social media.
These have been designed with passion for my own personal projects and have only recently decided to sell to the serious NA players.
This is not the first time I’ve been down this rabbit hole either with the last time being 30ish years ago racing/winning Pro7’s.
Starting with clay on the flow bench the old fashioned way, I quickly discovered that the optimal shape changes with the flank positioning in the stroke and just how turbulent the flow was as it transitioned from the ware surface to a round pipe. (This was going to be like fitting a square peg into a moving round hole) I then decided that the optimal flank position to focus on was in the closing area, however I could be completely wrong but time will tell!
I look at this simulator to the short side radius of a port, most commonly used term would be the closing edge/radius/lip etc. In my opinion this should be straight across side to side not with an arch as many people often do. With 28 data points per test and something like 80 test sleeves printed plus the initial set up, this soaked up hundreds of hours!! Luckily designing the optimal 13b PPort housing has been one of my hobby projects! I’ve done a lot of porting and fabricated more headers than I can remember over the years and I can say that the airflow through the rotary is unlike anything else I’ve experienced with its moving combustion chamber. I should also state here that all my testing is done using GSL-SE housings as I only use them in my builds. The Gen2/3 sleeves I have available here have been modelled from my GSL-SE sleeves. To give you a number, the maximum gain I’ve seen @ one flank position is 18% increase in flow. I will also state, 44mm pipe at the beginning of the fl**ge to housing and that overlap is not our friend in my experience. Your equal pipe volumes are a critical factor same goes for there length. Remember bigger isn’t better 2” is big on pump fuel
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