06-20-2008, 05:15 PM #1
concord 15/21 on a 15f with bolt ons
has anyone tried the 15/21 concord on a 15f with an rpm kit and a couple of other little things ?? riva says 14/21, just trying to get some feedback if anyone knows what rpms turn with this prop and how much loss in low-mid range and gains on top if any
06-20-2008, 05:45 PM #2
this is way too much for an rpm kit w/ a couple extra mods. i'm running the 14/21 and it works great! my highest GPS speed is right at about 69MPH and i have some more things i wanna try. runs good rpms and keeps low and mid.
06-20-2008, 07:36 PM #3
i recall you saying u had the stg. 1 impros. i have the same and i am not completely happy with it. i am looking for something to pull a bit harder out of the hole. the top end gain is not much to brag about either.
how is the low end acceleration on the 14/21 ? and what gains did u notice on mid and top with this prop compared to the stg 1 prop.
06-20-2008, 08:06 PM #4
the 14/21 is a taller impeller (compared to impros 13.5/20) and will give more top end, less accel, and pull less RPM than the impros spec.
I have the impros spec impeller and factory exhaust, and my friend has the 14/21 with the riva exhaust. I turn about 125-150 more RPM than him. I get about 4-5 ski lengths ahead (i'm also 30-40lbs less weight) but he always reels me in on the big end. He has about 1 mph on me on the top end.
I have since had my impeller tweaked with a 2mm kick to the trailing edge and the accel in AMAZING! The rpms are up about 200+ and it has tremendous grunt. The top speed has gone down 1 mph, probably due to running just past peak hp. On holeshot it never bogs down, just hits and the rpm's stay spiked without that bog just after you get on plane.
If you want more accel, more rpms and more top end then you're just gonna have to make more power. There's no other way around it. A tweak will help accel but top end will suffer if rpms go past peak power. A taller spec (15/21) will probably make the ski very slugish on holeshot and run at the bottom or below it's peak hp curve so it won't even pull on the top end. Ideally you pitch an impeller to run on the high side of the hp curve. That way it accelerates as hard as it can and can pull the impeller at high speeds too.
Last edited by AaronC; 06-20-2008 at 08:18 PM.
06-20-2008, 08:21 PM #5
has anyone tried the 13/19R skat or repitched one? am curious to see how this prop does
06-22-2008, 08:00 AM #6
06-22-2008, 07:14 PM #7
im looking for top end, i dont want to lose a huge amount of low and mid, but i'm willing to lose a little bit to get that extra 1 mph on top end. its all a personal preferance, bit if you look on my 15 project thread, the goal was 70 mph w/ a N/A, non-enduro engine and to keep it under 2k. liner911 has got 69.8 mph and i noticed a 1-1.4 mph loss on top end w/ the spec. sorry for rambling, its a GREAT impeller, just not what i'm lookin for, thats why im goin back to the 14/21
06-22-2008, 07:49 PM #8
06-22-2008, 10:23 PM #9
i think it might pull a little harder, especially in the middle of summer when its 95 degrees and 100% humidity, and 85 degree water temps.
06-23-2008, 01:10 AM #10
The impros spec has more accel, but less top end. I have the impros, my buddy has the 14/21. He pulls me on top end everytime despite my 4-5 boat length hole shot.
I will be getting a 14/21 for the 2nd pump I have and use it on the days I ride solo. I find the impros spec with a 2mm kick perfect for bouey racing, riding 2 up, or short drag races. For top end the 14/21 is the way to go.
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