Intake Pressure

[bp]

I believe that a good setup should have WOT intake pressures ranging between 35 and 45 psi and should not go above 55 psi in any case ... optimum bowl pressures at WOT should be in the vicinity of 360 psi and never go above something like 425 psi. Pressures above what I've stated can lead to pump reversion and 'Blowing The Tail' ... Not A Good Thing At Speed.
but your optimums are solely based on where the pressure taps are located on -your- boat.
my suction pressure tap is at 10, about 1" down from the handhole toward the thrust bearing. my bowl pressure is at 10 (looking front to rear of the boat), opposite from the engine cooling outlet.
i crewed for a boat that had 3 suction pressure taps in the intake and 2 bowl pressure taps, all feeding a racepak system. general rule; suction pressure was always higher as you got closer to the impeller. bowl pressure is always least at the flange, and higher as you moved toward the nozzle.
while there was a lot of information there, after lots of races, all i wanted to see right after a pass would be two data points. the other info was good for analysis later on.
i like having the taps where they are because the readings are within a range where i can tell whats going on. suction pressure is the first thing i'd look at to tell me if something "blew the tail", or got close to blowing the tail, not bowl pressure.

[bp]

I was thinking along the lines of 20-40 lbs. on the inlet and 200 on the bowl (not droop) for a mild hotrod lake boat??? I never seen data on something like that so its hard to say.If you can get 50 on the inlet, go for it. On the bowl, the higher the better.
I agree with Jak when he says not to get too high on the inlet.The jet can only process so much water, now people like to say that really high inlets create lift and thats a whole different subject that probably wont get talked about here. .
Whats frys my unit is I started a thread about inlet pressure a while back and the thread tottally sucked. I was prepard to discuss everything in detail and go over my numbers Ive gotten from my data logger but none of the techie guys took the bait.A guy with a set of guages from pep boys got more replys that I did.
Im starting to believe that racer chit LVjet talks about is true.
based on where my pressure taps are located (and you know where those are), i like to see between 40 and 60 on the suction, but i'm not too concerned if i see spikes to 70 if it's really rough. on the biz, we had a tap closer to the intake, where we would see half that pressure, and it would dip to 0 first on unloads, so it was useless at that point, other than later comparisons with other data. what i want to know is how far down it's going to go, how long it stays that way, and how long it takes to recover, and to what pressure it recovers to.
like when i hit a really big hole in san diego and completely unloaded at over 100. when i hit that hole and went to the rev limiter, the boat completely unloaded, and the suction spiked to 80, then back down. i already know my setup, but it told me -how long- i lost thrust. i still ran a .92, so needed to compensate.
at marble falls, it was extremely windy and there were white caps all day saturday. if i had the tap too low, i wouldn't have been able to guage the little partial unloads that happened 5-6 times as i went down the track on Q2, and figure out the effect.
consequently, with my -basic- system, i like where the taps are located. if i had a more extensive system, i'd use it for broader analysis and evaluation, but after what i learned with the race pak, this is ok for now...

[Rondane]

but your optimums are solely based on where the pressure taps are located on -your- boat.
my suction pressure tap is at 10, about 1" down from the handhole toward the thrust bearing. my bowl pressure is at 10 (looking front to rear of the boat), opposite from the engine cooling outlet. .
I was going to ask the same question
I said "about" the best area..meaning in a lake boat that, without getting too technical, is where alot of them are placed from i notice. Besides, i'm not sure what mr. BP means by ten but i'm assuming 10 o'clock...which in you eyes mr. steelcomp, should answer your question.
rondane

[bp]

.
I said "about" the best area..meaning in a lake boat that, without getting too technical, is where alot of them are placed from i notice. Besides, i'm not sure what mr. BP means by ten but i'm assuming 10 o'clock...which in you eyes mr. steelcomp, should answer your question.
rondane
yes, that is what i meant, but that's bp, not BP...
[/QUOTE=UBFJ #454]
"but your optimums are solely based on where the pressure taps are located on -your- boat."
Actually they're not. They are based on our old setup which McClure installed (sensor locations where he typically puts them), Jim Sampica's 7.50's BGJ, Dan Nelson's Record Holding BGJ and discussions with Oblander, McClure, Nelson and quite a few others, both jet riggers and racers.
The psi's we're currently observing are quite a bit different and wouldn't do anyone any good for me to post as they are, as you pointed out, unique to our boat and the info we feel we need.[/QUOTE]
ok. so, the optimums posted were not based on first hand observations? you DID post the location of the taps on your boat, so the relationship between the psi's you're seeing and the location of your taps might actually have some relevance? as cs mentioned, having bowl pressures that high requires a great deal more hp than a lake boat is going to have, but there is that relationship.
[/QUOTE=UBFJ #454]
All I posted were general ranges of psi's that I thought would be useful to non racers realizing that specifics would vary boat to boat.
[/QUOTE]
understood, and what i'm saying is that 55psi may or may not be the stopping point, depending on where the pressure tap is. that may be WAY too high, and then again, it may not be. as i mentioned in the other post, suction piece pressure can vary widely. i think jack -tries- to tap in similar locations so there's a data relationship between different boats. however, different people do different things with different systems.

[steelcomp]

.
I said "about" the best area..meaning in a lake boat that, without getting too technical, is where alot of them are placed from i notice. Besides, i'm not sure what mr. BP means by ten but i'm assuming 10 o'clock...which in you eyes mr. steelcomp, should answer your question.
rondane
My question was to you, not bp, so his response tells me nothing about why you made your recommendation. I'm just trying to get other useful info, so go ahead, get technical. That's what this is all about. Generalities are useless without supporting info. I've talked with bp plenty, and as you can see by his response, he has good reason for where he positioned his pickups, and has lots of experience to reference to. Jack (UBFJ 454) has other ideas, just as useful to his app. I'm just wondering if you can provide the same kind of technical explaination. Why seperate lake boat from race boat when gathering data?
Thanks.

[TIMINATOR]

I BELIEVE the best places(yes two!) to put the pressure taps are as close to the wear ring that you can on the top (right up next to the hand hole 10 or 2 o'clock) and the bottom as close to the bottom as you can (the 5 or 7 o'clock position). This is because the shoe controls most of the bottom load and the loader grate controls the top load. These two pressures are quite independant of each other and should be roughly equal. Having only one tap in the middle (3 o'clock) only reads the average of the load and can't discern top from bottom. We try to keep the loads even, and low (12-20 lbs). It is much easier to run low inlet pressures with two taps. I ran my Daytona at 113 mph on the lake with the gauges reading 12-15 lbs for 3 years. It picked up about 6 mph over the setup that I bought it with, and shutdown was an easy coast like on snow. It had 50-60 lbs when I bought it, and would try to launch you over the windshield on shut down at only 80 mph. I kept removing shoe and stinger (biting end) keeping the pressures even and lowering them until no more speed gains were realized. There are many ways to do this, everyone has a favorite way, this is just one of them. TIMINATOR

[Cs19]

thats just amazing to me that you can keep your pump loaded with 12 lbs. of inlet pressure.How are you reading your inlet pressures? data logger or guages?
I saw the exact opposite on my boat, it got much faster as we started feeding it more water by keel,loader and shoe changes.

[TIMINATOR]

Mine was not a drag boat,it was a lake boat with 970 HP on the bottle. Because of this the load for acceleration on a measured LENGTH course and the load for eventual top speed at a much longer distance will not be the same. Just as gearing for the land 1/4 mile and Bonneville top speed runs will be different. Also different quality of water will affect the load needed and recorded. Water with a lot of turbulence and aeration will require more load pressure than "good solid" water. To the non racers and non pros reading,this is the most important issue on this post. Posters please relate whether you are a 1/4 mi racer or top end set-up person, this will help the less informed. TIMINATOR

[TIMINATOR]

OOPS!!! 5" gauges with tattletales. TIMINATOR

[steelcomp]

Mine was not a drag boat,it was a lake boat with 970 HP on the bottle. Because of this the load for acceleration on a measured LENGTH course and the load for eventual top speed at a much longer distance will not be the same.
Tim, I need help understanding this. (Not being argumentative) I understand the difference in engine power between long distance speed and 1/4 mi acc., but it seems that jet pump performance, weather in a few seconds, or if it takes half a minute, should be relative to intake and bowl pressures. Jets don't "create" power, they just "respond" to the water provided, good or bad.
Thanks