What Causes Blower Motor Surge
 

When some blower motors are idling, there is a significant RPM fluctuation.

What causes that fluctuation ?

Running rich causes it. Leaning it out to make the Air/Fuel ratio correct will stop the surging.

Yup, exactly:D

I like that sound.

:drink::D:D

http://media.putfile.com/388MOV04062

Best sounding blower setup EVER.

http://www.sorcererboating.com/images/new.htm

The sound of pure evil.

Rodney's Skater sure would get the vote for the most baddest azz sounding powertrain. As bad azz as it sounds, I'd sure hate to have to do the maintenance on it. :eek:

With carburetors, a balanced A/F ratio at idle,when RPM comes off idle, does the risk of lean increase vs. fat idle ?

At idle, the throttle plates are closed and very little air is passing. Therefore, as the engine surges,does high pressure transfer from the bottom of the rotors to the top of the rotors ? If yes, how much gear and rotor slap is occurring ? With those questions asked, would a flapper or blow off valve connecting the top and bottom of the case seem prudent ?

Also, at high RPM,when the throttle is closed and inertia is at work from the drive train, is there enough A/F turbulence to encourage detonation as the throttles are reopened ?

My motors have a pretty big surge, 800-1200RPM's. But with Bravo style drives, this actually helps me shift easily into gear. I simply wait for the downside of the surge and it clicks into gear. If I want to shift them at the same time I rev the motors a bit and it will syncronize the surge and when the revs fall ckick they go.


Darrell.

Leaning will smooth the idle, but if you lean them too much, the engines will die easily when shifting into gear.

LE could you use a bypass valve assembly like Whipple's? See their web site. I believe that their carb blower setups idle good with the bypass.
JE

JE, I'll look at whipples web site....Are you familiar with the valve ?

Thanks, LE

PS: We have found a highly engineered valve for holding vacuum on a dry sump motor. Kind of a must have. Might work for bypass on the blower.

Tommy at Chief Engines has a cure for that surging idle that involves a vacuum line to the metering block.

Damn, that sounds cool.

It does sound cool but it's rough on tranys' and drives, depending on who's on the sticks.

Ron Potter has a good set up, his motors don't seem to surge nearly as badly as most.

AS to the root cause, I'll leave that to the engine gugrus'.

If you take the time to set them up it is possible to get a strong smooth idle. Get all the shutters even and make it run on the idle circuits.

I wonder if our motors have that. We have minimal surge compared to others who have blower motors.

I have zero surge with only a slight hunt when shifting into neutral but that's normal for a blower motor.

The surging is caused by fuel puddling in the intake. The line that goes to the metering block is most likely a boost reference line...this has been done for years.

EFI fixes that! :D

Me Too!!!

Easy work-around. Warm your motors up in neutral. Shut them down and restart in gear.

Talk to Dean Nickerson in PA.

Chris, what good is it if you can't count on your motor to shift and stay running? Are you kidding?

Amen,

Or have to replace starters once a month.... :eek:

Most of them can be set up correctly...if not, they belong on crash boxes with dual starters. :drink:

Is it possible, the following influences some amount of surge ?

1. Blower shaft pulley to engine crankshaft pulley ratio.

A. When the blower pulley is smaller than the crankshaft pulley,the ratio is said to be over driven. Therefore,the more the ratio is over driven,the engine and blower will have a greater RPM differential. Subject to lowest idle RPM, the blower will be least efficient,fuel puddles, fuel ignites,RPM increases and blower increases efficiency. The excess fuel is used and RPM decreases....so goes the cycle.

B. The Bypass valve should equalize pressure at the top and bottom of the blower case and therefore reduce fuel puddling.
Subject to puddling, the spark plugs may stay cleaner. The Bypass valve may be most beneficial on the over driven ratio.

2. The more timing is advanced the more vacuum will fluctuate.

3. The more cam overlap is increased the more puddling is encouraged.

4. Subject to inter cooler fin count per square inch,corrosion and tube arrangement, puddling may increase.

5. The blower case size (8-71 vs. 14-71) , design,condition and etc. may encourage puddling/surge.

6. The flywheel weight may encourage/discourage RPM fluctuations,spark plug condition,puddling and dock manners.

There are several other factors that are of consequence.

What is your opinion ?

Simple, lean the idle.

This is true in a race car application, but with a giant boat, huge blower and bending hoarspower a couple of times it is a little more complex than a lean issue..........

If it was simple everyone would be duing it RIGHT>>>>>>>>>>>>