Blower boost without load???

[ghittner]

Does a blower make boost in neutral or does it need a load to produce boost like turbos?? Mine doesn't seem to boost until it has a load on it, so I guess I have to test pulley changes on the water? Ron?

[repo man]

mine does.

[DMOORE]

My motors do not produce any boost at idle. In fact, My boat cruises at 3000rpm's @ 55mph and isn't producing boost at that time. It is still in vacume. It isn't until I get some load on it that it starts to make some boost.
Darrell.

[Warp Factor]

On a positive displacement blower, boost will depend on throttle position versus rpm. In neutral, you won't see boost unless you "wing" the throttle.
If you're trying to change maximum boost, there's no way to know what change you made without going full throttle under load, so yes, you need to test changes on the water.
You might be able to get a rough number by mashing the throttle mometarily in neutral.

[BOOGEYMAN]

I personally have never seen any boost at idle....eithor blower or turbo! I guess if you are running that small of a turrbo(with an extreamly small turbine housing) or run your blower that fast(LOTS of overdrive!!!!) you MAY see boost at idle.
Travis.

[ghittner]

When I mash it from idle in neutral I may get a pound or so, I was running 4 pds before on the water under load and I made a pulley change looking for 8 pds. I was looking for a difference while still on the trailer and saw none so I'll check it out in Havi this weekend. Thanks for the info.

[svt2224]

My boat makes about 15psi with a quick whack of the throttle.

[MikeF]

Boost only happens when air is available to the blower/turbo. Throttle blades closed.......no boost, throttle blades open....now air is available for consumption....now valves are the restriction, depending on how far blades are open = boost.

[ghittner]

My boat makes about 15psi with a quick whack of the throttle.
What size blower/ engine combo? How much boost are you running on the water?

[Trouble Maker]

I never see any boost pressure until I start to go past 4K rpms. Set your top end boost to what you want, then anything below that is just what it is. Remember the engine is an air pump and boost doesn't begin to build until the efficiency of your air pump begins to decrease...so not building boost pressure at lower rpms isn't a bad thing, it just means you have an efficient engine/air pump..

[svt2224]

I'm running a 498ci chevy with ported dart 360's, comp ratio is 10.5:1, the blower is a stage 4 Littlefield 8-71. I like the low static compression because it starts faster and is easier on starters and flywheels, however I have to turn the blower at the speed of death to make up for it, hopefully I will be able to move up to a 14-71 soon. Right now the boat will make 22psi@7800 rpms with a corrected altitude around 3500ft.

[BOOGEYMAN]

I'm running a 498ci chevy with ported dart 360's, comp ratio is 10.5:1, the blower is a stage 4 Littlefield 8-71. I like the low static compression because it starts faster and is easier on starters and flywheels, however I have to turn the blower at the speed of death to make up for it, hopefully I will be able to move up to a 14-71 soon. Right now the boat will make 22psi@7800 rpms with a corrected altitude around 3500ft.
You run that on alcohol or gas? 10.5:1 would be a pretty high static compression for a gas engine making 22 lbs.

[ghittner]

You run that on alcohol or gas? 10.5:1 would be a pretty high static compression for a gas engine making 22 lbs.
You ain't jokin'. I run 8.5:1 and let the blower do it's job.

[svt2224]

Its on alcohol, an important tidbit I left out.
http://image24.webshots.com/24/5/54/61/2456554610069608869lhBCaK_ph.jpg

[BOOGEYMAN]

Ahhh, makes much more sence now!!! Got any pic's?

[ghittner]

Its on alcohol, an important tidbit I left out.
http://image24.webshots.com/24/5/54/61/2456554610069608869lhBCaK_ph.jpg
Rad

[john f2000]

Boost only happens when air is available to the blower/turbo. Throttle blades closed.......no boost, throttle blades open....now air is available for consumption....now valves are the restriction, depending on how far blades are open = boost.
This is true depending on where the blades are located. Most turbos are located in front of throttle blades and thereor make boost soley depending on exhaust volume, ie if the motor is reving with enough fuel to make enough hp which is proportional to the exhaust flow required to spin the turbo.
Blowers on the otherhand are typcially located down wind of the throttle baldes (if it is a draw thru) and are dependant on having enough air but also rpm is part of the equation. They are positive displacement so its dependent on how many more cubic inches of air the blower is putting out versus the number of cubes your motor is consuming the difference if positive is boost.
I have extrememly small turbos on my truck for minimal turbo lag and it still barely shows any boost if you rev it at idle.
On my 10-71 blown 572 boat motor, again unless you were to rev it too the moon nothing shows up until its under load, but that is only set up for 5 pounds boost. The guys putting out 25 pounds will see boost at a lower rpm simply because it is positive displacement so to get 25 pounds at say 6 grand it is putting out for example 5 pounds at 2 grand. Since typically blowers dont have blow off valves for anything other than emergency situations the max boost is tied to rpm, therefore the bottom level of the boost number is as well.

[kojac]

John f2000,
I have a a572 chevy with 7.5 to 1 compression with dart 360 heads (unported) and am running a 871 BDS blower with 6#'s of boost. This is on a stealth tunnel jet with an A/B aggressor impellar. The motor is turning 5900 rpm's at 114.9 mph. on 93 octane gas. I am wondering if more boost will increase more top rpm's or just make the boost come in quicker to make more hp at the same rpm's. (Not that this would be a bad thing because the motor seems to be a little lazy.)
At what boost point do I need to run higher octane?
Thanks, Kojac

[svt2224]

Kojac,
Increasing your boost will increase max rpm due to the increased hp produced the boost will also come on quicker. Your compression ratio should be aprox. 10.6:1 with the setup that you have now, calculated using this formula (Final Compression Ratio (FCR) = [ (Boost÷14.7) + 1 ] x CR). There are a lot of other variables that come into play when trying to avoid detonation, such as, timing, heat, and octane rating. When my boat was on gas I could get away with 6psi on pump gas with a 9.0:1comp ratio (FCR 12.7:1, on vp116 I would run between 10-14psi (~17:1) with around 28deg's of timming. Boost will really wake-up your boat but if you get carried away it will get in your pockets.
J
http://www.dragboats.com/images/gallery/large/01_08_MF_3642_077.jpg

[john f2000]

I would agree with SVT2224.
Sounds like we have the same motor, but i am running a 10-71 at 8.5 to 1. Most motor builders would say that unless you are specifically tuning for a given race environment that any more boost than what you are currently running should be on race gas, plus or minus a pound or two.
I do know that if you run race gas and increase your boost to around 12 psi, you will probably gain another two or three hundred hp. So yes your top rpm will go up and yes it will be quicker down low. Remember when you increase your max boost on a positive displacement blower your boost goes up across the board from down low as well. That is different than turbos, where the bottom stays the same and just the top goes up by closing the wastegates.
John f2000,
I have a a572 chevy with 7.5 to 1 compression with dart 360 heads (unported) and am running a 871 BDS blower with 6#'s of boost. This is on a stealth tunnel jet with an A/B aggressor impellar. The motor is turning 5900 rpm's at 114.9 mph. on 93 octane gas. I am wondering if more boost will increase more top rpm's or just make the boost come in quicker to make more hp at the same rpm's. (Not that this would be a bad thing because the motor seems to be a little lazy.)
At what boost point do I need to run higher octane?
Thanks, Kojac

[kojac]

Thanks for the info. Very informative.
Another question? When I raise the boost am I required to increase the jet size or will the current jetting suffice. I know more air requires more fuel but will the increase in boost just pull more of the fuel that is needed to sustain more rpm's?
Also my timing is set at 36degrees at 3000 rpm's> Everybody I talk to says it is too high. Plugs look great and engine overheats due fuel in the exhaust when I retard it much lower. Been running it this way since 2000.
Have not tried to put more power in motor due to previous handling problems when I shut down the boat after a quarter mile run. Now I am getting that under control a little better and I am looking for more serious power and speed.
Kojac

[svt2224]

Kojac,
That is alot of timing, infact between 36-38deg's locked is what I run with the alky setup. If you plan on increasing the boost a jetting change will most likely be necessary, as will decreasing the timing. Increasing your timing and decreasing your jet size from a conservitive point will be your best bet for performance and reliability. What carbs/jetting are you running?
J

[kojac]

Kojac,
That is alot of timing, infact between 36-38deg's locked is what I run with the alky setup. If you plan on increasing the boost a jetting change will most likely be necessary, as will decreasing the timing. Increasing your timing and decreasing your jet size from a conservitive point will be your best bet for performance and reliability. What carbs/jetting are you running?
J
I am running two HP 1150 dominators with 93 jets all around. I plan on installing the edelbrock quick data computer on the jetboat to gather information on intake and bowl pressures along with speed and rpm data.
With this system I hope to make adjustments to the shoe, loader, nozzle,boost, etc and be able to verify whether the changes help or hinder my speed needs.
kojac

[svt2224]

With your cubic inches you are moving more air than I am, when on gas I was running (2) 1050's with 88's squared. Just keep an eye on the plugs or Egts if you go with the quick data and you should be in good shape. With more boost and some good fuel that thing will scream.
This is a good site for reference:http://www.blowerdriveservice.com/techcharts.php

[kojac]

Thanks for the info. I have a 572 naturally aspirated with two 1050's and also run 88 jets in the carbs. It has pontiac big chief heads with a sheet metal intake manifold, jessel roller train, 13.5 to one compression. It makes about two hundred more horsepower than the blower. I had it on my sterling jet.Took it off because I like to cruise long ways and cam 2 is not an option when fuel gets low.
kojac

[svt2224]

I now what you mean, race fuel gets expensive quick. When I ran around the lake alot on gas I used one tank for 116 and one for 91 with a high flow switch. At cruise speeds boost could be kept below 7psi (safe), if I planned on pushing it a little I would switch to the good stuff. Most of the lakes around here a pretty small and a huge range was not a problem. Your NA motor sounds like a sweet set-up, what are you using it in now?

[kojac]

I now what you mean, race fuel gets expensive quick. When I ran around the lake alot on gas I used one tank for 116 and one for 91 with a high flow switch. At cruise speeds boost could be kept below 7psi (safe), if I planned on pushing it a little I would switch to the good stuff. Most of the lakes around here a pretty small and a huge range was not a problem. Your NA motor sounds like a sweet set-up, what are you using it in now?
I took it out of the sterling a couple of weeks ago. I sold the sterling will a smaller 509 13.5 to 1motor. It had all the good stuff in it but only made 870 hp on the dyno. The 572 is on a motor stand in my boathouse just in case...
After I install the quick data system I might put it in the stealth just to see what it can do..
Kojac

[svt2224]

Kojac,
Let me know how the quick data works out, I would love to have one myself but I am not sure what sensors are the most benifical and where on the pump they should be placed.

[kojac]

Kojac,
Let me know how the quick data works out, I would love to have one myself but I am not sure what sensors are the most benifical and where on the pump they should be placed.
As soon as Ive completed the set up I will send you pictures.
Kojac