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525sc dominator 1050 carb question

Old 06-17-2012, 06:21 PM
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Originally Posted by MILD THUNDER
That works ONLY if its boost referenced. The standard 525SC merc is not. Like griff said 6.5PV.

If you wanna be safe, you can put a 8.5pv. Only way to really check is either have a vaccum gauge under carb, but on top of blower. This is where the PV gets its signal from.
Mine is NOT boost referenced and this procedure works perfectly. My vacuum/boost signal is taken off the back of the intake under the carb, stock 525sc location. How do you check vacuum under the carb but on top of the blower? That makes no sense. I have stock 525sc top end and know my method works. You always need to check using this procedure when making any major changes like going to a 250cfm blower from a 177. To just tell him to run the stock 525sc 6.5 PV (or to even change to an 8.5) without any data of the engine running is going WAY out on a limb. Checking vacuum and a/f is imperative.

Last edited by blue thunder; 06-17-2012 at 06:53 PM.
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Old 06-17-2012, 10:13 PM
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Originally Posted by blue thunder
Mine is NOT boost referenced and this procedure works perfectly. My vacuum/boost signal is taken off the back of the intake under the carb, stock 525sc location. How do you check vacuum under the carb but on top of the blower? That makes no sense. I have stock 525sc top end and know my method works. You always need to check using this procedure when making any major changes like going to a 250cfm blower from a 177. To just tell him to run the stock 525sc 6.5 PV (or to even change to an 8.5) without any data of the engine running is going WAY out on a limb. Checking vacuum and a/f is imperative.
Hold on a second there big guy. You CANNOT tune your power valve based on the manifold vacuum, IF the power valve is not boost referenced. Other wise, WTF is the point of boost referencing. The entire purpose of boost referencing is so that the PV signal is based on the intake manifold vaccuum.

On a 250 blower carb plate, there is a fitting that you can install a vacuum gauge. If the pv is not boost referenced, you can install a vaccum gauge in that port, and it will show what vaccum the non referenced PV sees. The vacuum directly under the carb is what a non Referenced PV sees. Makes total sense to me. Oh, and the 420 B&M blowers have this too.

He asked what the stock PV size is in a stock 525SC, and I told him. Back in the day before boost referencing was popular, holleys supercharger carbs came with 10.5PV non referenced.

Ive ran 177's, 250's, and 420's on my engines. I think before you go telling me I don't make any sense, stop by a Border's or Barne's and Noble and get yourself a book on Carburetors.
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Old 06-17-2012, 10:22 PM
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Oh, and BTW, I ran a 1050 dominator on a 454 with a B&M 250. 6.5PV's, non referenced. By telling him he can install a 8.5 to try, it would only make it open sooner, and be fatter. It would not, cause him to lean his engine out. Its not as if I said install a 2.5PV and go boating.
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Old 06-17-2012, 10:29 PM
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Ok guy i have not test my vacum this week end but i have tested my A/F. The A/F that i read at cruise is 11.2 just on the 4 barel opening got 10,5 and WOT 11.5. I am jeting 104 4 corner and i have 6.5 pv (stock 525sc). I think that i have the right pv but litle rich on the primary side at cruise.
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Old 06-17-2012, 10:35 PM
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You need to watch the front cylinders on a single carb 250 setup. While your AFR can read within spec, youll find the front cylinders can be lean. The blower will push fuel to the rear. Dual carbs much better on this setup.

AFR is great, but fuel distribution can be a issue, so watch your plugs, ESP #1 and #2 cylinders.
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Old 06-17-2012, 10:37 PM
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Originally Posted by MILD THUNDER
Oh, and BTW, I ran a 1050 dominator on a 454 with a B&M 250. 6.5PV's, non referenced. By telling him he can install a 8.5 to try, it would only make it open sooner, and be fatter. It would not, cause him to lean his engine out. Its not as if I said install a 2.5PV and go boating.
Mine is NOT boost referenced and this procedure works perfectly. My vacuum/boost signal is taken off the back of the intake under the carb, stock 525sc location. How do you check vacuum under the carb but on top of the blower? That makes no sense. I have stock 525sc top end and know my method works. You always need to check using this procedure when making any major changes like going to a 250cfm blower from a 177. To just tell him to run the stock 525sc 6.5 PV (or to even change to an 8.5) without any data of the engine running is going WAY out on a limb. Checking vacuum and a/f is imperative.

No matter with that i realy apresiated every people setup idea . I am new on performance boating but i have alwase do mecanic on deferent engine, but this is my first time on BBC boat engine.
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Old 06-17-2012, 10:38 PM
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Originally Posted by blue thunder
Mine is NOT boost referenced and this procedure works perfectly. My vacuum/boost signal is taken off the back of the intake under the carb, stock 525sc location. How do you check vacuum under the carb but on top of the blower? That makes no sense. I have stock 525sc top end and know my method works. You always need to check using this procedure when making any major changes like going to a 250cfm blower from a 177. To just tell him to run the stock 525sc 6.5 PV (or to even change to an 8.5) without any data of the engine running is going WAY out on a limb. Checking vacuum and a/f is imperative.
blue thunder,it makes no sence to you because you cant comprehend how a carb works.mild thunder is dead nuts on the money,a non boost referenced carb gets its vaccume signal from above the blower,not from the intake manifold.think about it,it is not that hard to understand.
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Old 06-17-2012, 10:42 PM
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Also for vacum pick up the dominator 1050 have a plug on the primary side under the carb. i think this a good place if you can't plug it on the carb plate.
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Old 06-18-2012, 06:50 AM
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Originally Posted by mike tkach
blue thunder,it makes no sence to you because you cant comprehend how a carb works.mild thunder is dead nuts on the money,a non boost referenced carb gets its vaccume signal from above the blower,not from the intake manifold.think about it,it is not that hard to understand.
You select the PV with an a/f gage. The vacuum gage is used as a reference for when you need to enrichen the engine. We are tuning an engine right? If I ran 8.5 pv in my 1050s w/177 I'd be way too rich in the mid range and wash the cylinders down. You need enrichment at the right time, not early or late with a blower motor. The OP asked just that, how to determine the correct PV size, not what comes on a stock 525sc. Why do you guys always try to start a pissing contest? It really detracts from this site.
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Old 06-18-2012, 09:24 AM
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blue thunder,its to bad that you have a problem when you are corrected,mild thunder explained some facts,and you dispute it,because you dont understand it,then i tell you he is right,and you think its a pizzing contest.mild thunder,and myself were just sharing information,and because you dont understand you get an attitude,dude,i could care less if you take good advice or not,but i will continue to put it out there for those who can understand it.i guess because you think you know everything,you dont need to listen to anyone,so,CARRY ON and have a nice day.
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