gmnhra

made some minor repairs last week (replaced dead msd coil) and took boat out for a test ride yesterday...540cid bbc with carbed whipple blower....

i swear that "before" the boost gage would read 4-5psi after about 4500rpm and on up to 5500....
yesterday the gage would read 7-9psi when accelerating and would read 3-4psi at 3500rpm....

no other real symptoms..it idled o.k., etc...maybe my perception but it felt a little down on power...???

is there any mechanical scenario (i.e. valve train, timing, etc.) that could cause this phenomenon????

thanks

gm

Turbojack

The boost gauge should be in the intake after the blower. When motor sees boost such as having throttle wide open you will see at or close to max pressure on gauge. When you are crusing at part throttle the gauge will be showing vacuum or boost based on engine load. When you have an engine problem (lets say plug wire off0 the throttle will have to be further open to maintain the same RPM as before (all plugs firing) thus the greater boost reading.

I have a procharged 540BBC & sometimes it is hard to tell if I am down on power. In my boat I know when I am crusing at 2400 rpm at aprox 30 mphs boost gauge should be about 6" vaccum. If it is not close to that I know I have a problem somewhere

So yes, if you see higher boost at same cruse RPM as before than you have a motor problem.

CFD12

Earlier this year my 454mag/B&M 174 was showing high boost. We then realized the cam was wiping out. Valves not opening/closing properly is going to increase boost readings.

FindMe

Not true... A whipple Supercharger is a positive displacement "Blower", or actually an air compressor that is designed using the twin screw design, which means it compresses air internally as well as compressing it in the manifold. Because the screw compressor compress’s the air inside the case, air enters into the pressurized environment with very little leakage or energy loss. A roots-type supercharger sweeps atmospheric air into the manifold and is compressed in the manifold only. With manifold pressure, air leaks back through the rotors causing air to be heated, lowering it's effectiveness. Roots-type blowers use Teflon to attempt sealing the rotors to the case, but touching tolerances cause more frictional heat and greater parasitic losses. Marine roots-type superchargers have more tolerances between the rotors and the case so they will live longer, but this causes more leakage back through the rotors, and loss of pressure to the cylinders. A screw compressor has very tight tolerances between the rotors, and the rotors never touch, eliminating many of the problems that are inherent with common roots type superchargers.
With a Whipple, you should reach maximun boost somewhere around 2000-2400 rpm, as the twin screw design doesn't need to "spool up" like roots type blowers, dependant on the velocity of air going through the motor. I have installed somewhere in the range of 20 plus Whipplechargers, and do the diagnostic work in Nor Cal for Dennis @ Whipple, which if you know Whipple and had a problem or question, you know Dennis. Volumetric efficency is the reason for your boost gain, and much too complicated to get into on this board, and is the only thing that will affect how efficiently a motor can utilize boost. Also, boats rarely (if ever) see vacuum, except at idle as they are always under a load (ever see a boat coast downhill?) and with a Whipplecharged motor, you should be showing boost at ALL TIMES due to their design. Basically with a weak ign system, your volumetric effeciency will be considerably lower and make the engine weak, unable to utilize the advantages of a positive displacement supercharger. Don't be fooled... you are right where you want to be... Fail safe boost levels out of the box from Whipple are approx 7psi and ok to 9 psi if no detonation is heard, depending on many variables, camshaft, head design, piston dome design and compression etc. Call Dennis and ask him!(559) 442-1261

The 3 phases of a Wipplechargers operation...

Inlet Phase - The male and female rotor's rotate counter to each other. As the lobes of each rotor travel past each inlet port, air is trapped between consecutive lobes and the cylindrical casing. The air moves axially (forward)throughout the case towards the discharge port.

Compression Phase - Once each trailing lobe seals its cell, the air charge is swept around the casing until the leading lobe uncovers the discharge port. At the same time, the male and female lobes will intermesh in such a way so that the volume formed between them, and the apex where the twin cylindrical walls meet, is progressively reduced in an axial direction from the inlet port end to the opposite discharge port end.

Discharge Phase - Once equalization of pressure between the existing charge in the manifold and the charge being moved into the discharge port occurs, then any further rotation of the rotors displaces the charge positively into the manifold until the volume between the intermeshing rotors and casing walls in the discharge port region are reduced to ambient pressure again.

Turbojack

FindMe-I do not have a whipple charger. I only know turbos & prochargers, both from having them for the last 28 years in boats.

I have been told that whipples have a bypass valve so when motor is crusing at light load the blower is going to bypass the extra pressure, thus reducing load on blower. Is this not correct?

As I said I do not know whipples but I can cruise up to about 3200 rpm & my 540 will be in vacuum. Only after that will motor start seeing boost. I am not talking with throttles hammered, but partial throttle. I am taking gmnhra's questions as to be at cruse not full throttle.

FindMe

There are no valves, bypasses or anything else to alter boost on a Whipple at any load or rpm. I find it very interesting that you are seeing vacuum at that speed, are you positive you aren't hooked to ported vacuum with your gage? Manifold vacuum has to come from under the throttle plates on a naturally asperated engine, and on a blower it's best to tap into the intake plenum or at the base if bolted to the manifold like Whipples, but considering the type of blower you are running, a proper source for getting a true reading may be tricky. You just need to be able to see the pressure change that occurrs before entering the cylinders. In a boat you are displacing water constantly, thusly always being under a load.... and I have never seen any type of boat cruise above 2-5 hg of vacuum at ANY speed, that being extremely rare. You should investigate the source for you gage, as it sounds to me that it's possible you very well may be making more boost than you are seeing, and the vacuum is not "real" manifold vacuum, also remember that a Whipple is actually an air compressor, producing positive pressure under all conditions which operates under different principals than your type of blower. Is your unit plumbed like a Paxton, or similar to a turbocharger? With Whipples being bolted to the manifold, getting a reliable source for boost and vacuum is easy, but wherever you hook up a gage, it must be able to read both. I won't say you are wrong by any means, but I would be staggered to see a boat of 5000 lbs or more produce vacuum @ 3500 rpm... but hey, stranger things have happend right? I am interested in how you are achieving vacuum none the less, cause if you are...You da man! I am always open to learn something new, so I will never discredit what you are telling me (as long as you share your secret with me)... lol Any more info you are willing to share would be greatly appreciated... Hell, it's all good dude!

gmnhra

thanks for the inputs so far....

i got the boat into rudy and gary at gt performance today and they will be looking at it tomorrow.....

findme...lots of great tech info....dustin actually emailed me today and explained some of what you posted but he did say that i may have some valve train issues also that are causing some back preesure...we will see...
as i may have said...i just have not seen the boost gage go above 5psi before...
maybe a block in the gage line and now it is actually working correctly!!!! that would be tooooooo easy!!!!

i'll post results after teaque and company check it out.....

gary

FindMe

Thanks bro... we can never know too much heh? Restrictive valve trains are a problem with superchargers for sure, but don't assume the worst, and lets hope for the best! Thank you too for the info...

mcollinstn

The boat that I got my prochargers off of also showed vacuum at cruise. Not alot, but around 3 to 5 inches. Was pulleyed for only 5psi WOT. Blow thru application. Vacuum/pressure gauge plumbed into the intake manifold beneath the carb thru a big ole port nearest to the #7 intake runner.

Would assume a positive displacement setup would behave similarly at cruise speeds. Can't see why it would not. Motor needs would be similar unless the positive displacement setup had far greater parasitic drag, which I wouldn't figure on either.

Turbojack

The procharger setup is different than the turbo setups I have had. The Turbo setup had the carb upstream of the turbo, thus suck thru. The procharger setup is a blow thru setup, carb below blower. In both setups I could see vacuum at cruise. The boost/vacuum gauges in both setups are plumbed into the intake manifold downstream of the carb.

I will say that a friend of mine has a turbo setup with a turbo 400 trans & v drive. I was amazed that his motor was in boost almost all the time once off idle. I first could not understand why but then figured out that motor was under more of a load at the low rpm than mine thus boost instead of vacuum.