To Boost Reference or not to Boost Reference?
12-27-2002, 06:08 PM
#11
Guest
Posts: n/a
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!!!
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!!!
12-27-2002, 08:21 PM
#12
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!
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!
12-27-2002, 11:08 PM
#13
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.
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. 
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.
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.
12-27-2002, 11:16 PM
#14
Platinum Member
Platinum Member
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.
Thanks
Roger
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.
Thanks
Roger
12-27-2002, 11:44 PM
#15
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.
12-28-2002, 06:57 AM
#16
Registered
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
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
Last edited by RumRunner; 01-06-2003 at 12:34 PM.
12-28-2002, 10:05 AM
#17
Guest
Posts: n/a
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!!!
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!!!
12-28-2002, 10:08 PM
#18
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.
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.
12-29-2002, 12:53 AM
#19
Platinum Member
Platinum Member
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
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
12-29-2002, 07:29 AM
#20
Registered
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
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
