FX transfer port mod ????????

[sigp220]

I might have missed this some where in a previous thread where folks were discussing huma dual transfer port mods.

I recently received a 30 cal barrel kit from SPAW with his transfer port mod and pellet probe mod. I stuck it in today. 

My previous recorded fps was in 924fps with the standard port. Stuck the Spaw tuned barrel in without touching anything velocity dropped to the 880-890fps range.

I was under the assumption the velocity would go up? I've seen the comments where folks just put the huma dual transfer port in with no probe modification and this is understandable, but I changed out the pellet probe too. Or did I miss something?

Thanks for helping

 

[Theman406]

What tune settings in it now?

 

[Scotaty]

I had the same effect in velocity when I modded the ports in my .30 cal. In .22 I gained up to 50 fps.

 

[cfs916]

Check ur pellet probe and make sure it’s tight. Also make sure u barrel is flushed against the rear block with only the shoulder sticking out

 

[Nathan]

So here we have the Spaw solution above, and the Huma below. Am I wrong in thinking that the Huma makes more sense?

 

[IraLite]

Do you have the new power plenum or aftermarket?

 

[sigp220]

After market plenum. Transfer port flush in block. I had that happen to a buddy.

 

[Airgun-hobbyist]

From an airflow standpoint, FPS is probably faster in your unmodified ports because the high pressure air hasn't got to turn around those extra corners of the new brass transfer port, and expanding as it does so because there's more "room" there. Airflow is more efficient traveling in a strait line and the original ports are more conducive to this end. If modified correctly, your stock parts can achieve stellar results in efficiency and ultimately speed.

If you really want to make that Impact flow with those (new) parts then you need to get a big poppet valve seat, (or at least open up that hole to 6mm), and port out the valve housing and blend and radius the drilled corners so the air moves around the corner smoothly. The exit hole of the housing should be oblong when done. (Roughly adding to 8mm dia.) The last thing, and probably the easiest, is to port the block to match the valve housing. The end goal is to get those ports to about the same size as the new brass transfer port do the HPA is flowing smoothly, without turbulence and expansions.

https://www.airgunnation.com/topic/fx-impact-valve-housing-modifacations/