Reply With QuoteI think the impeller charts are pretty much in the ballpark. I'm turning an American Turbine AA at 5300-5400 rpm with just over 600HP which is right in line with what the chart says.
Wait a minute.
A few months back I mentioned those charts were pretty accurate.
Would be a good backup when questioning dyno numbers.
I was attacked from both flanks and the rear.
Never saw any final results from that deal.
Decided to just be quiet about it rather than gang fight.
I think the impeller charts are pretty much in the ballpark. I'm turning an American Turbine AA at 5300-5400 rpm with just over 600HP which is right in line with what the chart says.
please dont hurt me over this one. ok, if an "A" is turning 5500rpm, and a "B" is also turning 5500rpm, wouldnt the "A" be flowing more water? ie faster speed? im not understanding why someone builds more HP, but cuts the impeller to a "B". wouldnt you want to flow more but keep the rpms down were the torque curve is?
From what I have seen with an "AA" to "B" your not
looseing enough to worry about. You want to match the engines HP.
Last boat we worked on started with an "AA" turning 5800RPM. Went to an "A" turning 6300RPM
and it was a night and day difference in accelaration and top speed. The motor was cammed to work with more RPM.
Victor, dogs right, for maximum thrust you want maximum power to the impeller, not torque. So for top speed you match impeller to your engine's power curve, (tempered with reliability concerns and so on) whether that means picking an AA, A or B. Some engine mods shift the power peak rpm, others leave the peak alone but give you more power. So "building more hp" doesn't always mean going to a bigger or smaller impeller.
In my case, going from a 454 to a 540 shifted peak rpm and increased it by nearly 300 hp. The combination of those two shifts nearly followed the B impeller curve, so no change in size needed to match peak power. But as Daytona mentioned, a slight upsize for me may pay-off in less engine wear with no big loss in hp...that because the dyno run shows my engine's power curve fairly level from 5800 to 6200. So in my case I could go 1/2 to one size up without loosing too much top end.
Info,
Come on in...the water's fine
Ok, here's the best I can do for a Berkeley B check. This from my dyno run and lake test:
Dyno Test
6200 = 634 hp
Air Temp: 95 F
Elevation (est): 900 ft
Station Barametric Pressure: 28.84 inHg
Relative Humidity: 41%
Lake Test
6200 = 643 hp (JPC estimated for Berk B)
Air Temp: 80 F
Elevation: 1142 ft
Station Barametric Pressure(est): 28.64 inHg
Relative Humidity(est): 15%
If I adjust dyno run power to lake test conditions I get 654 hp...which compares to 643 hp estimated by curves. There are other small differences, but we're talking within 20 hp or so of curves as close as I can tell...on the high side of course. This difference I'd say is likely because my impeller is flowed. But I'd say pretty close.
jer
[ October 18, 2003, 01:59 PM: Message edited by: LVjetboy ]
About 1.2 HP per cubic inch.
Who would have thunk it?
I am running a stainless AA with inducer at 58-6100 rpm.I had my pump built at Don's pump service. 5800 was the last run of the season. My dyno curve is from 4200 rpm up to 6500 rpm.I achieved 1000 Hp at 5600 rpm.I have not tested since the low rpm near the end of the season and have since removed the valve springs for the winter.If I am Pushing 1000 hp at at 5600 how can the chart be accurate? It is a dominator pump.
Info, I was hoping for a bit more but 1.2 hp per cuin not bad considering mild compression and hydraulic rollers.
Del51, can you post or email me hp data from your dyno run between 5000 to 6500? I'm curious what you got.
A couple points. What was the measured dyno hp at 6100? JPC says "stock" Dominator AA impeller needs 922 hp. Don's flowed impeller may need a bit more. I've had pump work by Don too btw. If your 1000 hp was a corrected number, the curves may be closer than it seems?
How does dyno data conditions compare to your lake conditions? This brings up another good point. You can only compare dyno hp data to your full throttle rpm...6100...or later 5800. Not part throttle. 5600 is not a valid match point to dyno data unless 5600 is all you could get with full throttle.
And the loss in rpms from 6100 to 5800 is also a question. Was that from a change in lake test conditions? Or an engine problem that invalidates dyno comparisons?
Oh ya, and what hull are you running and how fast?
jer
[ October 19, 2003, 12:48 AM: Message edited by: LVjetboy ]
jer
1.2 per cube is good.
That is all I will guarantee to a customer for a N/A pump gas engine. They can buy from a fudge master if that is not acceptable. Their boat will not go any faster.
My comment was directed to the folks that claim 1.48 from their N/A single carb pump gas deals.
I have always stated 1.2 is about it. I am getting ready to build and test a new EFI deal over the winter. 8 stack injection might exceed that carbed CID/HP ratio just a bit?
You guys are awesome ! Can HP be loosely calculated by using the RPM ? I am getting 63 mph @ 4000 rpm , Aggressor "B" impeller, 350 sbc I keep claiming 240 hp But that was 17 years ago ! eek! I want to build 400 hp or close to see what that does for my little Tahiti ! but .... from reading this post I think I may be over my depth ! Moo
[ October 19, 2003, 07:53 AM: Message edited by: Moomawnster ]
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