jpc calculator....How accurate is it?????

[396_WAYS_TO_SPIT]

Ok heres the deal. I went out yesterday and ran my boat with a fresh pump and different impeller. I was spinning a bronze "A" impeller to 5100 rpm's. I looked at my gps and it read 81.7 mph. I was shocked on how fast I was running with full tanks of fuel. My last speed before the rebuild was 74.9 with a tore up berkley "b" aluminum impeller. When I plug in my numbers in the jpc it shows the following.
with a agressor bronze "ab" @ 5100 =458hp
with a american turbine bronze "ab" @5100 = 386hp
I know for a fact that I have way more than 386 hores :confused: :confused: Any ideas????? I am going to cut my impeller down some more to a "B" cut to get my r's up so I can spinn the r's where my motor makes the most hp.
396

[SmokinLowriderSS]

As far as I understand, all JP Calk really has is the impeller cut RPM/HP charts electronically accessed. That and a calculation of speed relative to RPM per cut. It should be as accurate as any of the impeller charts. I'm waiting to see LVJetboy chime in on it tho as it is his program.
It seems to be right on in my case. My engine is turning about 350 HP accordign to Desktop Dyno ( I have tried to be as accurate as possible with it) and the RPM I am spinning my berk "A" fits 349HP, 4800 RPM. I will see what next spring brings as my headers should put me right at 400HP and 5,000 RPM.

[396_WAYS_TO_SPIT]

Anyone??? :confused: :confused: I know I have waaayyy more hp than 380 :confused: A 12.5-1 compression motor better have more hp than 380 :confused:

[Oldsquirt]

Michael, the JPC is telling you what HP you have at 5100 rpm not necessarily what your peak HP is.
Why are you referencing two different AB cut impellers if you have an A ?

[steelcomp]

Michael, what are you basing what you're saying on??? Why do you think you have more than that? JPC is accurate. You may have way more HP than that, but appearantly not at 5100. Big cams, high compression, tunnel rams, etc. all don't automatically make HP unless carefully matched combinations. If you have the wronmg cam for your combination, you could be giving up 100+ hp, and building the hp you do have at an unusable level.

[cyclone]

are you sure your tach is accurate?
I think the jpc is a good tuning tool but i wouldnt rely on it as the absolute on how much power your engine is making.
81 mph is pretty damn good. i wouldnt worry about what the computer says. if you are happy thats all that matters.

[396_WAYS_TO_SPIT]

Michael, the JPC is telling you what HP you have at 5100 rpm not necessarily what your peak HP is.
Why are you referencing two different AB cut impellers if you have an A ?
I am just throwing out ideas. I have a bronze "ab" cut impeller and I dont know what brand it is.

[396_WAYS_TO_SPIT]

Michael, what are you basing what you're saying on??? Why do you think you have more than that? JPC is accurate. You may have way more HP than that, but appearantly not at 5100. Big cams, high compression, tunnel rams, etc. all don't automatically make HP unless carefully matched combinations. If you have the wronmg cam for your combination, you could be giving up 100+ hp, and building the hp you do have at an unusable level.
Very true. My boat pulls real hard and runs great but when I get to 5100 r's @ 81.7mph it feels like it wants more but the impeller is restricting it. I am going to cut it to a "b" cut and bring up the r's. The only thing is that I dont know if I really want to go any faster than that :eek: My motor was built to spin between 5900 and 6100. My mill is similar you your scott. Im not saying identical but very similar. 12.5-1 comp,258@.050,108 lobe,solid lifter,tunnel ram,holley 750's, ported iron heads. I know I need more r's but damn, this boat is getting scary fast really quick.

[396_WAYS_TO_SPIT]

are you sure your tach is accurate?
I think the jpc is a good tuning tool but i wouldnt rely on it as the absolute on how much power your engine is making.
yup, All of my guages are new.
i wouldnt worry about what the computer says. if you are happy thats all that matters.
I am happy;) But its getting faster and faster everytime I change something. The only bad thing is, how much speed can this kachina handle?? I sure and the heck dont know. Mike, are you going to firebird this year for the finals?? If so I would like to se your boat and meet you in person;)

[DeputyDawg]

originally posted by 306_WAYS_TO_SPIT
My mill is similar you your scott. Im not saying identical but very similar. 12.5-1 comp,258@.050,108 lobe,solid lifter,tunnel ram,holley 750's, ported iron heads. I know I need more r's but damn, this boat is getting scary fast really quick.
Um, do you have any idea just how different your motor actually is than steelcomps? Other than the fact that they are both Chevys they are night and day different. I am in no way knocking your motor, and 80+ is hauling ass in a jet like yours. Do the leading edges of the front side of your impeller blades come all the way out to the lip? If they do it is probably an Aggressor. I don't have any experience with Aggressor impellers but Duane at HTP told me that the the blades on them go all the way to the lip. Nice boat by the way.

[396_WAYS_TO_SPIT]

Um, do you have any idea just how different your motor actually is than steelcomps? Other than the fact that they are both Chevys they are night and day different. I am in no way knocking your motor, and 80+ is hauling ass in a jet like yours. Do the leading edges of the front side of your impeller blades come all the way out to the lip? If they do it is probably an Aggressor. I don't have any experience with Aggressor impellers but Duane at HTP told me that the the blades on them go all the way to the lip. Nice boat by the way.
I know scotts motor is way different than mine. Im not saying that I am making 800hp. I know damn well I am over the 500 range though.

[Squirtcha?]

how much speed can this kachina handle??
I guess that kinda depends on your setup Michael. When you drove mine at that same speed, you mentioned that it handles differently than yours. How's yours handling at that speed? If it's at all squirrelly you might want to play around with your setup some. As you know from driving it, mine's real stable at 80 mph, but I've done some work to it to get it that way. It's still cool at 85 mph too so you should be fine to that point. Can't say with any degree of certainty after that though since my best gps reading was only 88.9 mph.
In the process of tuning things, I definitely hit on some combinations that weren't so great, and got a little scary.
Anyway.........long story short, I think you'd be fine up to mid 90's if the bottom is straight, and it's not doing anything weird.
Let er rip skip.

[kachina_labala]

how does weight of the boat effect the numbers of the JPC calculator?

[cyclone]

yup, All of my guages are new.
I am happy;) But its getting faster and faster everytime I change something. The only bad thing is, how much speed can this kachina handle?? I sure and the heck dont know. Mike, are you going to firebird this year for the finals?? If so I would like to se your boat and meet you in person;)
Firebird isn't in the plan for me yet. i havne't made a decision yet on whether or not i'll run there. For now I plan on running the njba race at lake ming in two weeks.

[Squirtcha?]

how does weight of the boat effect the numbers of the JPC calculator?
Obviously Jer would be the best one to answer the question. I'll give it a go though. I'm pretty sure the weight of the boat doesn't affect the JPC. I don't think the program really cares how much your boat weighs, only the rpm, and horsepower at maximum speed, and what impeller type and cut it has.
However, I think the boat's weight will ultimately affect the outcome of the program, as a heavier boat won't obtain the same maximum speed numbers of a lighter boat with the same horsepower at the same rpm.
Does that make any sense at all?
Haven't seen Jer post in a while. Maybe he'll drop in and straighten me out.

[kachina_labala]

I was wondering because it asks for observed speed and rpm to calculate the ponies, but the weight of the boat and setup will effect the speed and i would guess the HP calculation.

[Squirtcha?]

That's my take on it too.