Wildchild212

I hooked up a vacuum gauge to my motor this weekend on the dyo. The program for boost on the dyno was not right. When we started to make some boost the gauge held at one then would flutter back and forth between 2 and 3 lbs of boost. Why would this happen? Is the belt maybe slipping when it starts to make boost? Or is the vacuum gauge to touchy for preasure? Also what size should the pulleys be for the crank, and the blower pulley. I want to make 5 to 7lbs of boost.
Mark

mcollinstn

Are we supposed to be Psychic? Maybe you should call Miss Cleo.

1) You hooked a vacuum gauge to your motor?
Do you mean a combo vacuum/pressure gauge?
Exactly where did you plumb it to your motor, and are you sure the hose connections are tight and secure and that the hose is not leaking somewhere? The gauge should be taking its reading from the intake manifold under the blower/carb/intercooler/whatever.. Do not take this reading from anywhere on the carb. Do not take this reading from a pressurized carb box. Take this reading from the intake plenum itself. On the flipside, if you are using a carb box, then you must reference your fuel pressure regulator to the box pressure, not the plenum pressure. Got it?

2) you mention the gauge would jump from 1 to 2 or 3 pounds (positive boost pressure, I assume) intermittently. You also mention that it was on a dyno when this occurred. Did the power output jump around in the same manner? Seems that the motor wouldn't be able to hold a steady rpm if this was occurring. Was the pull smooth or did it jump around to match the pressure spikes you were witnessing? Was the throttle wide open while this was occurring (it should have been) or was it being opened and closed for some reason (which will always affect manifold pressure)?

3) Is the belt slipping? Maybe. Maybe not. Some answers to the above questions will help determine that.

4) Is the vacuum gauge too touchy for pressure?
I don't understand what you are asking here. Question makes no sense to me.

5) What size should the pulleys be on the blower and crank - I want to make 5 to 7 pounds of boost?

Look at my hands. The blower pulley should be this big. Look at my hands again. The crank pulley should be this big. Understood?

You haven't told us ANYTHING about what motor you are running: displacement, heads, cam, compression ratio, intake, carb, exhaust style, blower style and size. All of these affect the ability of your motor to pump air. And that affects the "restriction" the motor presents to the blower. And the "restriction" presented affects the manifold pressure that a blower will make.

And you want to make between 5 to 7 pounds of boost?
Which is it?

5 pounds will USUALLY be a safe number on most setups and will allow use of pump gas when tuned properly for the application. 7 pounds is ONLY safe on pump gas when all parameters are matched to the setup.

Since your dyno operator/engine tuner does not seem to possess the ability to diagnose a slipping blower belt, I have extreme doubts about his ability to match your motor's state of tune to your boost pressure.

Please find a knowledgeable guy to help you set up your blower motor. Money spent at THIS stage (matching parts to the setup and proper tuning) will prove to be far cheaper than money spent at the NEXT stage (picking parts up out of the bilge and having the boat towed in from who knows where)...

mc

KNOT-RIGHT

MC Your Killing me.

KNOT-RIGHT

Cmon Billy Thought you were Psychic. Ofcourse Hes right.

I thought You and Tommy had Ms. Cleo tied up in the back

Its Monday AM Cant ya tell.
Look at my hands its this big.

mcollinstn

She already SAW that she was gonna escape. That's why she didn't give you any trouble when you tied her up.

She also knew how big it was. That's why she left.

And she knows how big mine is.
That's why she's ringing my doorbell. (Hang on, Cleo, I'll be there in a minute - but wait, you already know that don't you..)

See you later. I've got to go let Cleo in. I'll have the blower pulley answers to you in a little while.

mc

Wildchild212

#1 I have a 525sc all of the components of an sc, would like to know the pulley size.

#3 yes the gauge was hooked up in the right spot. could have been a fitting problem.

#4 no the motors hp did not jump around, ran great.

#5 I stated 2 to 3 lbs of boost, I would say that is positive, if it would have been negative I would have called that vacuum.

#6 sutphen, The dyno was at dts dyno. these where just some questions I came up with at night, not at the dyno room.

#7The belt is a sepentine belt.

I realize I did not give out a ton of info, it was late and I was in a hurry. Then guy running the dyno seemed to know what he was doing, like I stated earlier, these where just some questions I came up with at night.

Mc I was just asking a few questions, Sorry if my questions were not up to your standards,

X-Rated30

Dayum MC! Are we getting a little grumpy in our old age?!?

tomcat

Wildchild 212: Don't be offended, sometimes us grumpy old bastards have heard the same question too many times. MC is full of good info, and he has a PhD in supercharging. If it was a DTS equipped dyno, post the dyno sheet with boost pressure as one of the columns. We'll have you edumacated in no time.

mikes280

also that is a roots type blower you may have been seeing so blower surge we see it on the dyno when we run these type of blowers

Griff

Pulley ratio on a stock 525SC is 2:1 overdriven. That makes 5.5lbs of boost.