To Boost Reference or not to Boost Reference?
 

I am hearing reports from various members and shops as to the pros and cons of Boost Referencing my Nickerson 1050 Dominator.

Nickerson says send it back as they have an upgrade for my carb. They say Boost Referencing is "old technology". What is Nickerson doing that eliminates the need to boost reference?

Others say that after their carb was boost referenced, it ran like it was fuel injected.
I am looking for low speed and idling performance.
Any suggestions?

Hi RLW,
I have tried Nickerson and almost every other carb known. They have never worked to my satisfaction without boost referenced power valves. The problem is, the signal from the plenum under the carb sees blower vacuum signal, the engine, the important part, sees a different signal and IT gives the signal you want to control your fuel mixture!!!
Usually, a carb must be set up rich in many situations so it cannot go lean and destroy parts. This causes too rich a mixture at some throtle/load situations. The referenced power valve solves this problem. The same reason you need a power vavle to start with is the same one it needs accurate feedback from the ENGINE.

I am no expert but I agree with blown1500. A good basic explanation as to what is going on below the carburator. I do run a 1071 blower with 2 850 carbs that are referanced. I like to tinker on my stuff and set the carbs up myself. Idles all day and will not load up. :D

IT NEEDS TO BE BOOST REFERENCED ,PERIOD
IF NOT YOU HAVE MAKE IT SO RICH IT WON'T LEAN OUT AT PART THROTTLE ,ON TOP OF THE BLOWER THE CARB ALWAYS SEE'S A VACUM RIGHT ?? EVEN IF MAKEING BOOST ,BAD DEAL :( :(

I bought my 750 Holley carbs from Teague and told them I was putting them on 454's W/ Whipples. I told them I wanted them boost referenced and was advised that I didn't need to boost reference but they did a blower upgrade for $85.00. They put on larger primary pumps and installed 10.5 power valves, 80 primary jets and 90 secondary. The motors smoked black and fouled the plugs after ten minutes idle time. I ended up switching to 6.5 power valves 74 primary and 90 secondary jets. Is boost referencing different than changing power valves and jets? If I run the exhaust thru the props at idle it still wants to foul the plugs. Other than that it runs great.

Roger

Quiet Storm,

I have Whipples with 850 Holley carbs setup by Gary at GT Performance and they work like a dream. Out of the box there was no loading up and the engines responded and revved clean from idle to the rev limiter. I increased the jets one size for safety as the plugs looked a little too perfect.

Ian T.

The consensus seems to be that Boost Referencing is the most accepted way to address low speed operation for Roots style blower packages.

According to Nickerson my single 1050 is equipped with:
4.5 Power Valves front and rear.
#96 Main Jets all 4 corners.
CFM has been increased to 1170.

How will a qualified Carb Shop know what to do if I ask them to Boost Reference the carb?
Will it be "Flowed"? Is this correct terminology?
What questions would I expect to hear from them?
Are there internal modifications that were done by Nickerson that have to be reversed or addressed?
I just don't want to say, "Here is my carb, Boost Reference it for me."
Thanks for the replies and still looking for direction.

JUST TELL THEM TO REF. THE VALVES IT WON'T AFFECT ANYTHING .
THEY CAN FLOW IT NO PROBLEM IF YOU WANT I CAN INDEX ONE FOR 20 BUCKS AND RETURN IT THE SAME DAY IF NEEDED
IF YOU WANT IT FLOWED I CAN DO THAT ,,,JUST PM. ME
THANKS ,JUST GET SOMEONE TO DO IT PLEASE

CayFomula,
I've heard so many people say the same thing that you did. I took them out of the box with no problems at all. I wish I could of said that. I went through four sets of plugs before it settled down. I will change them again in the spring.

Maybe I should pull the carbs and send them in for boost referencing anyway. I'm just a little afraid to touch them because I don't want to start the process all over again.

How's the weather there?

Roger

Yes boost referencing requires plugging the port for the power valve signal at the base of the carburator and running an external line to the intake manifold. Instead of getting reference (vacuum) from under the carb it will get a signal from the manifold. Under part throttle operation it is very likely you will see a vacuum under the carb and boost in the manifold. This causes a lean condition and TROUBLE. Power valves would be closed when they need to be open.

Right on Paradigm Shift,
I have seen many broken parts caused by lean conditions from not boost referencing the carb(s). No matter whose carb you use, you should expect to have to change at least jets. Even seasonal changes require jet changes because air density changes and the carb just doesn't understand! I have never seen ANYBODY'S carb run correctly with a blower of any kind using draw through set ups without BOOST REFERENCE!!!!
This is not too difficult to do and Bobby Daniels has a great deal to get this done. If the carb was not too far off to start with, it will be easy to tune after the work-and no moore fouled plugs and black transoms!!!:D

You can get away from boost referencing the power valve(s) if you change the power valve opening point to the vacuum you see under the carb at a little above your high cruise rpm.

If you cruise at 50 mph, and you have a vacuum of 8 in. And at 60 mph the vacuum is 7 in. Go out and buy some 7.5 power valves. Then when you go under 7.5 in. the carb goes richer and you don't cook the motor.

This is boat and prop and load specific. You need a good vacuum gage hooked to the manifold.

If you want (need?) the power valve to trip open based on under blower vacuum (boost referencing), read your boost gage (if it reads vacuum), and set it the same way as above.

I have two blower motors with 400+ hours in a Topgun without motor problems. Can't say the sameabout the drives!

JohnB nice ride I should be so fortunate one day! I would suggest if any one is going to do this themselves you should hook up a vacuum gauge to base of carburator(s) and a vacuum boost gage on the manifold so you can see what is happening above and below the blower. Could use a temporary gauge set up under the carbs if you want. Just my opinion again.

John how do you you keep the motors from running lean at higher throttle not just at cruise. My set up at 3500 to 4000 rpm runs a high vacuum at base of carbs and depending on trim settings etc around 0 to 1.5 psi boost at the manifold. I can even run it up to 5000 rpm and still see a high vacuum under the carbs. Manifold boost goes up a bit of course. I am running a 525ci with a 1071 at 6% under driven. 400hrs so you must have your set up dialed in I just would like to know more about your motors not just the carbs. I am always curious of how others make there motors live. I tend to run mine pretty hard so it shortens the life. :rolleyes: I still think boost referenced is the way to go. I tried without them referenced and had trouble until I finally gave up and referenced them. I have no lean or rich conditions from idle to WOT now. :)

Okay, now I’m concerned. When I received my Holley carbs, they didn’t have a place to hook up the hose from the boost bypass valve on the Whipples. I thought that was strange because I specifically told them it was a Whipple installation. I found a 1/8” NPT plug on the base of the carb and figured that must be the place. After quite a search I found a barb fitting that would attach the hose to the base of the carb.

Was this the wrong place to attach the hose? Was the hose for a vacuum gage?

I’ve had a couple of mechanics look over the installation and adjust the carbs. Neither said it was hooked up wrong.
:confused:

Thanks
Roger

Roger sorry did not mean to confuse anyone. I am not real familiar with whipple set up and boost by-pass. Someone will probably know or Dustin might drop in. If not call Whipple direct just so you have that comfort feeling. My guess and that is exactly what it is a guess but I think that you are probaly OK. The boost by-pass on a whipple system is different than boost reference of power valves for carb tuning. If your not sure call Whipple they seem to have great support.

Roger:

That doesn't sound right. You can trace the path by taking the carburetor apart. When most people boost ref. a Hooley it is done through a tube in the metering block, A Demon is done through the baseplate. If you take your carb apart, first locate the Power Valve in the metering block, now look at the cavity (in the mainbody) where the PV gets its vacuum, this cavity needs to be sealed to the boost ref. port, in a standard application it will be open through a hole in the baseplate to intake manifold vacuum. If you're not sure you can give me a call at the office and I can go over it with you in more detail.


Doug
Tech @ Barry Grant, Inc.
(706) 864-8544 Ext125

Boost Referencing power valves
 

Hello Guys,
Any time you don't reference power valves, you can find some setting for the throttle and some scenario where the mixture is wrong because the carb cannot communicate with the engine. It does not matter what the signal is between the carb andf blower, just what the ENGINE wants. I say again, mileage and safety from meltdown are available ONLY by connecting the carb mixture controll(power valves) to the ENGINE!!!! Whipples or roots both need the same treatment, though the Whipple system does have a bypass and does do a better job untill vacuum is very low. You usually only get one chance at too lean!!!

The above information is all correct. It's best to hook up two vacuum gages. I also ran a pyrometer in each tailpipe and knock sensors.

Take the boat out and plot the following as you increase speed:
RPM, boat speed, vacuum under the carb, and vacuum or boost under the blower. Trim and tabs should be as you normally run at the speed your running.

If you have a pyrometer, record the exhaust temperatures.

Cruising temperatures should be around 1200+- 100 depending on where your probe is. Max WOT should be under 1450.

Develop a graph of the data and it should be apparent if and when you should add fuel, and how much, if you can record exhaust temps. The temps should also give you information for proper jetting.

Many dominators (big holleys) don't have power valve circuits from the factory. These have to run rich all the time or you will burn up the motor. Special metering blocks are available to convert these. It's best to let a pro do this.

Let's say you need about 20% more fuel/air ratio when floored than cruising to optimize the operation. The power valve curcuit allows this additional fuel when you or someone tells it to open. This is the setting (number) on the power valve body.

You should want to be lean at low speeds up thru cruise speeds and go rich when you get on it up to WOT.

I personally would not run any supercharged engine without a pyrometer or a detonation sensor. Failures are just too expensive.

I hope this helps, my first supercharger experiment was in 1976, and was successful. Lost one stock head gasket in 84.

RumRunner
Thanks for the offer. I won't see my boat untill March, but when I do, I'll check out what you said and then contact you. Untill then I'll call Teague and find out exactly what they did to the carbs. I'll talk to Dustin also.

I do remember a port being blocked with blue silicon sealant from the outside. When I changed the power valves I didn't notice anything going on inside but I wouldn't know what to look for anyway. I put about 30+ hours on the motors last year and didn't break anything that I know of. I know it still dosen't mean everything is right.

paradigm shift
No problem, I'm in a constant state of confusioin any way but its getting better.

John B
Thanks for the advise. I will speak to the mechanic that set up my carbs and find out his procedure for determining the size of power valves and jets. Make my own chart also.

RLW
I'm sorry that I butted in here but your question has been on my mind for a long time. I also wondered why my carbs didn't work better out of the box. I think we both learned something here.

Thanks
Roger

Roger:

From the way you described your carburetors, and knowing Bob what you have are most likely not boost ref. carbs. He takes the standard vacuum fittings out and silicons the holes. He does this so that if you have a backfire it doesn't blow the cap off. I generally try to tune the stuff so you don't get a backfire. Once you look at what you have let me know, we do a lot of carbs for Whipple systems.

Doug

You definately want your powervalve boost referenced if your setup is a drawthru system. You self doer's need to look in the HOLLY book under ...Carb mods for Turbo draw thru systems.It requires drilling a hole in the carb body and pluging another hole in the powervalve chamber. I did both carbs of my carbs 18 yrs ago epoxy still holding. Hope this helps.. HAPPY NEWYEAR OSOERs.

The pic is of my 1050 Dom that was also originally a Nickerson carb, that shows the now boost reference port. It appears that it was originally set up the same as RLW's. Boat would not idle more than a couple of minutes and the transom was always pitch black. I sent it to Bruce Dudley to have it boost referenced. He replaced the metering blocks as the originals were modified too much for use. (This was appearent to me from the grinding of some of the passages) The response and idle characteristics from the change over was unbelievable. AND, the transom has always been white. I could not believe the change. The statement "runs like a fuel injected" came from me. By no means knocking Nickersons work, it just did not work for me.

How about this. I found out the carbs I got from Teague are wrong. There was a communication problem about my setup and they are going to trade the 750’s for 1050 Dominators. I’ll pay the difference of course. I think this time I will send them for referencing.

RumRunner
If Teague does there normal modification will it cause a problem to have the 1050's boost referenced. I do have problem with backfires now if the boat isn't started for a week or more.

Roger

Roger

If they boost ref. the carbs it shouldn't have any affect on having problems.

The only reason you should be backfiring through the carb is being too lean or your timing being off. Since this only happens when you let the boat sit for more than a week you're most likely looking at either fuel leaking out of your 750's into the motor, or evaporating. Try to crank your engine over until you have oil pressure (so the carburetor is sure to have some fuel) before you try to start it. That should eliminate that problem.

Doug

Hello Guys!
I just remembered something:eureka: Remember when Detroit built carbureted draw through turbo sustems? True, this is not exactly the same as roots or Whipple, but it is the same principle.
GM indexed the power valve on their Q-Jet on the turbo Buick V-6 and Ford did it on the turbo 2.3. The Q-Jet was a pain to do, but they spent the money and did it anyway! Boats are different than cars, but there is NO fuel curve that can account for every situation without INDEXING THE POWER VALVE!!!:D

blown1500
Interesting they boost referenced a Qjet. I've seen cars set up with a blower and Carter AFB/Edelbrock carbs. Has anyone seen one of these carbs boost referenced?
Gary

Mr. Anderson,
I have boost referenced almost every carburetor there is and a Carter or Edelbrock is a pain to do, but it can be done. It is like doing 2 Q-Jets. The carb body must be drilled below the power valve to connect a vacuum hose and the hole in the cavity now must be plugged. The other thing you must do is use a valve that will close off the boost reference hose when no vacuum is present. I used to have a NAPA part number for one, but I don't remember it and can't find my note. It was a Ford part for evaporative emissions I think. If you will pm I'll try to help.
I can boost reference for you if you need it.

blown1500
Thanks, I was just curious. From your description the port at the bottom of the piston needs to be plugged. I wasn't sure if there was room to drill a new port below the piston though. That's the hard part, right?
Is the function of the valve you were talking about to prevent the positive blower pressure from leaking around the piston or blowing it out? That piston does not seem to have an air tight seal around it.
Gary

Mr. Anderson,
The power piston can be plugged in the bottom and a hole drilled
CAREFULLY from the front of the main body very near the bottom of the piston bore. I generally drill the hole and insert a 3/16" piece of steel tubing on each side.
The piston is not a perfect seal on this carb or a Q-Jet and any boost will leak past the piston and wreak havoc in the float chamber!! That is the function of the valve. The NAPA part number for a compatable valve is 207449. I believe these are good carbs, just annoying to tune or boost reference-but worth it.
If I can further assist, I will give it my best effort. pm if you want my number and we can talk:D

blown1500
Thanks for the info. I know where to send it now if I want to try this. I dont think I would want to try to drill it myself. There doesn't seem to be much clearance for that hole.
What is used for a check valve. Is it a specialty, custom made piece or is something like a small PCV valve available?
Gary
BTW, This board is great for learning some of this stuff that's almost impossible to find out elsewhere!

Did anyone try this?
 

If you really want good midrange fuel distribution try mounting the carb sideways. Can you guess why this works better?

BTW any method of power valve referencing, or any type of power valve has nothing to do with idle quality unless the fuel is bypassing a blown diaphram (ie. blown power valve). Think about it!!!!

Also remember a power valve is stupid, it only opens, to allow more fuel into the main metering system (bypassing the jets), WHEN THE VACUUM IS LESS THAN THE (powervalve) DESIGN.

Light boats may need below SC refrencing, heavy boats shouldn't.

BTDT, JB

Picture for above post
 

Carb mounted sideways= great fuel distribution in the midrange, because throttle plates can't direct fuel to their backside until they are open 90 degrees. Found this during part throttle dyno tests.. Think about where the fuel hits the rotors in either position. Standard position = end cylinders run lean!! at less than full throttle. Hummm

Mr Anderson,
The check valve part number from NAPA is 207449.
There are others, but this one works and is usually readily available anywhere. Good Luck!!!!!
No matter what boat you have, there are times when the power valve is needed, no matter the size or weight unless it is a pure RACE piece, IT NEEDS POWER VALVE INDEX!!!!!!
We also try to run the carbs sideways except on Whipples which don't care which way the carb is.

I'm going to chime in here, even though I'm in the minority. Teaque has set up 6 750's for me, all running on blown 502's with B&M 250s. They are not boost referenced, although I don't know exactly what they do to them. They don't load up, they idle great, minimum black on the transom, I've never even had to rejet the carbs. Maybe my engine combinations are just good for whatever they do to them, but they work great for me.

All of the carbs that I have seen are boost referenced on the primary side only.
Is this because everyone is running a p/v plug on the secondary side?
Just curious because I'm going to try to set-up a HP 1000 cfm carb to run on top of a 250 powercharger on my 502.
Any base line jetting recommendatios?
Thanks,Jeff

Yep, my sec. is plugged. Can't recall jetting, but they are around 112-115 all four corners. 1050 Dom, 250 blower, 502

If your carb came with two power valves, I would run them and have both ends boost referenced. If you do plug the secondary power valve, be sure to adjust your jetting properly and maybe do some metering block changes (Air bleeds, maybe?) or you will get a surprise!!

I`ll jump in here also. When I first bought my Top Gun, with 750 Hawks, the carbs were sooo rich that just the short no wake from my house to the lake I`d foul the plugs badly, soaked with gas. Last April, I had sent all 4 carbs to Nickerson Performance. He had reworked the carbs and flowed them and ran all of them on a blower motor similar to mine on his dyno. I could not be happier with the results. The black transom problem is gone, I can idle all day, no problems and have not fouled a single plug in over 100 hrs. They are NOT boost referenced and my plugs look perfect throughout the entire rpm range.

How was this achieved without needing to boost reference????

Kurt.

I'm also running Nickersons on my blown 572s. Rejetted them slightly after dyno runs, but otherwise they work fine. Not boost-referenced.

Okay, sp far we've been talking about DRAWTHRU setups. The need for boost-referencing is obvious for these applications.

Maybe I'm off topic here, but I'm curious as to what mods are useful in a BLOW THRU (carb box) application.

I know: floats must be "crush resistant".
power valves must be sized differently.
That's all I know of.

Surely there is a host of setup info applicable to a 502 8.5:1 Crane 731, rect port, 6 psi Procharger Stage 3, CMI Etop, holley 4150HP 950cfm...

Who does the best job on these setups? What is the appx cost? Does anybody know if the carb itself is modified (powervalve feed circuits, etc..) or if it is just a matter of proper air bleeds, powervalve sizes, and jetting??

Comments? RumRunner??