Does bigger valve seat give more fps on impact?

Is there anyone in here who has an FX Crown? I have a Crown Continuum .25 cal and I have done the port, probe and hammer. I have ordered but not yet received a 6.35mm valve seat. I am wondering how much improvement stands to be gained by going from the 5.5 to 6.35 in .25 cal? I have brought my FPE from 55 to 69 so far (at 160 bar), and I am hoping to hit 80 FPE...if I can keep the reg in the same place that would be good because I will not need to replace the spring washers for stiffer ones.

What do folks reckon are my chances of hitting 80 FPE by replacing the last airflow constraint that remains in my system?

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FWIW the 5.5mm supports porting up to 4.32mm and the 6.35mm supports up to 5.35mm porting...the power difference between the two (depending on caliber and a few other variables) is roughly 15% so it is possible, provided you port upwards of 5.35mm forward of the new 6.35mm valve seat...



This is provided the stem in throat is 3.175mm...if you reduce the stem od in the throat area, one can achieve the same effect, its quite safe to go thin down the stem to 1.9mm (only in the area the stem resides in the throat at rest and while at max lift), doing so allows one to run the 5.5mm seat with up to 5mm ports without requiring more hammer to open the valve...or you can run a thinned stem, and 6.35mm seat and run porting upwards of 5.85mm, which would provide a lot of benefit..but you'd have to make sure the probe area isn't restrictive running ports this large. HTH


Porting beyond 85% or so of caliber takes a lot of care to not go too wide on the barrel port so that pellet damage occurs upon loading, most run oval ports when going beyond 85% of their bore OD.

@CFS916 I already did add a hammer weight. I am running at 160 so the spring tension is dialed back quite a bit, but the hammer weight is already in there and ready to go for when I change the VS. If I get another 40 FPS that would be great as it would bring me up into the 75 FPE range and then it would only be a little reg tweak to get me to 80 FPE.

@ackuric Thank you for the insights. I imagine you must be using that amazing PCP performance spreadsheet you have been developing to come up with these numbers. I look forward to seeing future posts on that. 

I most likely already ported above and beyond what is optimal. I have no idea what you are talking about when you are talking about the stem. Is that an Impact thing, or does it apply to Crown as well? I have ported both a standard round port and I ported that a bit above the .25 cal diameter, and also I re-worked a split port that I got from Stu Wrycraft. I lengthened the ports a bit, widened them a bit and rounded them for air flow. I also hollowed out the top side of my probe and took out the top and bottom part of the terminal ring, so now I just have two bits (one on each side), and each of them is maybe 3 mm. With all of this I most certainly brought my power levels up. It may be that I can improve them by porting another TP but slightly smaller. I was not sure what size to go with and I went a little wild. I think I ported to a 6.3mm diameter (externally), and the internal I am not sure how much the internals are...I just tried to make a nice transition but there was not much space to open it much. I have had zero problems loading ammo and everything works fine so that is something! 

When I switched to 6.35mm VS, I got around 40fps. That was on my crown .30cal so just thinking you’ll get similar results. 

@ackuric Porting beyond 85% or so of caliber takes a lot of care to not go too wide on the barrel port so that pellet damage occurs upon loading, most run oval ports when going beyond 85% of their bore OD.

Are you saying that I should keep my porting down to 5.4mm and no more to be safe? Also, is that saying that the width cannot be more that 5.4, or the length, or both, or is it that the area should not be more than the area of a 5.4mm diameter? I have seen some people go a lot longer than they do in width. I can certainly understand not going too wide, because the pellet is more likely to drop in. 

When I switched to 6.35mm VS, I got around 40fps. That was on my crown .30cal so just thinking you’ll get similar results.

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That is good to know! Fingers crossed. It will be interesting to see how it compares, you with a greater diameter but also more mass...hard to say if I should get more, less or the same.