FPS drop with new motor

Hi all!

I have a LDT HK416D and am getting 280avg fps. I purchased a higher torque motor and swapped out the stock motor and suddenly my fps drops to 200. Swap it back to stock motor and fps back up to 280.

Anyone have a clue why the drop in fps with just a motor change?

Could it be as simple as the motor has higher rpm and not letting the nozzle seal the tpiece or perhaps picking up the cylinder “early”?

Cheers peeps!

Could be. How does the fire rate change? How many shots per minute with either motor?

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I cant find any details on either motor but the new one is definitely faster. Chrono details below, with same 7.4v battery, ausgel greens and mag.

Full auto rpm:
Stock 550rpm
New 850rpm

However, single fire also suffers the fps loss.

Theoretically, the motor can have no effect on FPS… The FPS is only changed by the main spring and the quality of the seals from the main piston seal, the seal of the nozzle on the cylinder head, the cylinder head to the cylinder… and the nozzle to the barrel…

The motor only affects rate of fire… :thinking:

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Thanks all for your input and being a sounding board for me. It’s much appreciated - thought i was going insane!

Turns out the custom sector delay chip that i made to fix my feeding issue, was now the FPS drop issue, being that it worked for the stock motor, but the new motor being a much higher RPM, the timing was now out. I believe this had the effect of activating the tappet before the springs full extension and created the air gap between nozzle and tpiece.

I have remodled my delay chip and FPS is now back to normal and maybe a little higher! Full testing to occur tomorrow. To show the difference in order to help anyone else out, I’ve attached 2 pikkies to view.
1st mod is RHS [no cylinder visible]
2nd mod is LHS [cylinder and piston visible]

Again, thank you very much!

Check to see if your piston head is pulling a vacuum

and adding to what Hamish said if it’s pulling back swap prison head to a 6port alloy one so that was it can still be retracted with backpull

or take to the one you have with a 3mm drill bit ENSURING you don’t mark up the rear surface in any way.

Thanks @zeHamish and @Mr.milkman - ran it through a night game and worked quite well, though strangely the accuracy has now suffered but still great for cqb.

I do actually have a ported plunger [6 or 8 cant remember] and i have opened up the ports slightly from stock. I did a vacuum test to make sure I can retract plunger, but perhaps I can test it further to remove any vacuum that may still be there. Is there a limit, other than the physical restrictions of the plunger, that would determine the size you can open to? Or is it a case of bigger is better?[quote=“daegis, post:9, topic:1365, full:true”]
Thanks @zeHamish and @Mr.milkman - ran it through a night game and worked quite well, though strangely the accuracy has now suffered but still great for cab.

I do actually have a ported plunger [6 or 8 cant remember] and i have opened up the ports slightly from stock. I did a vacuum test to make sure I can retract plunger, but perhaps I can test it further to remove any vacuum that may still be there. Is there a limit, other than the physical restrictions of the plunger, that would determine the size you can open to? Or is it a case of bigger is better?
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