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Old 07-07-2010, 06:31 PM   #1
Frank The Plumber
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Default Vacuum question on a 351W?

Proper vacuum would be what on a 351 w, 20? Pretty stiff cam, .541-.544 240-246 duration. 9.8 -1 compression
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Old 07-07-2010, 06:54 PM   #2
George/Maine
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Default Re: Vacuum question on a 351W?

I still have the same problem with my 302 It has 14 lbs and wouldn,t idle good.Less then 16 is low, may have power brake problems.
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Old 07-07-2010, 07:05 PM   #3
Frank The Plumber
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Default Re: Vacuum question on a 351W?

Im trying to put a final tune on her, for some reason she just became very unhappy, started running really rich and is enjoying fouling plugs, I hope I dont have to rejet her because of air oxygen content in the summer, that would be a case of the roids to have to be a meteorologist over her. I don't want to be tuner dude on two lane black top.
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Old 07-07-2010, 07:14 PM   #4
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Default Re: Vacuum question on a 351W?

It seems that initial timing on a 302w- 351 w is 13-16 degrees initial 32-34 final, if you plug all the carb vacs, you could see what you get, I was bumpin around on you tube, I went to the comp cams site, the msd site, and the edelbrock site and holley site, lot of good tutorials, figured out I put my trans solenoid vac on the wrong port. That explained the bang engaging of my tranny, didnt get full vac till 2500, maybe you are pulling your test gauge vac off the same vac port as me, sit down with a frosty brew and watch some videos.
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Old 07-08-2010, 07:22 AM   #5
Ole Don
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Default Re: Vacuum question on a 351W?

With a cam like that, you take what you get. It should give you 17 to 19 at warm idle. If it was OK then suddenly went rich, check the power valve. Make sure the air cleaner isnt holding the choke part way closed. Is the float level right? Let us know what you find.
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Old 07-08-2010, 01:28 PM   #6
Frank The Plumber
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Default Re: Vacuum question on a 351W?

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So the cam guy says 11 for that cam, I somehow thought I had 20, blindness is not fun, in order to get the c6 to shift happy it needs a boost can. George is this helping you?
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Old 07-08-2010, 03:03 PM   #7
Frank The Plumber
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Default Re: Vacuum question on a 351W?

According to comp cams the power brake booster needs 14 vac,minimum, theres two ways to go, there is a vacuum cannister which I will try but doubt will work for me or an electric vacuum pump, My c6 needs a vac of 10 to be happy, then again the guy on the phone kept changing the number, first he said 12, ooyyyy, I have a bad feeling that Im going to end up with another freakin gizmo on this one.
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Old 07-09-2010, 01:35 PM   #8
Ole Don
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Default Re: Vacuum question on a 351W?

Summit carries a vacuum canister that I bought to make the power brakes work. It was not expensive, and solved more than one problem.
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Old 07-09-2010, 03:27 PM   #9
Frank The Plumber
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Default Re: Vacuum question on a 351W?

I think a vac canister may work, the trick is capturing the vac when its available, you then have to see how you run when you use it up, at 1100 rpm I have a vac of 11, at 2800 rpm I have a vac of 21, brakes with a booster need 14, a c6 automatic trans requires 12 solid. I plan to fab up a 1 gallon air vessel, I will place a full size vac tube from the intake to the vessel and try to insert a check valve into the line with a very low trip spring rate, I will pull 2 small vac feeds off the vessel to the brakes and trans, the big test will be how much vacuum will I be able to store as residual compared to what I require to operate, stop and go driving will be the test, regardless of how I fare I will need a storage vessel, if I cannot get to a balanced vac then I will resort to a negative pressure pump system.
The problem I am trying to resolve is a dumping of vacuum when the brakes are applied and the transmission shifts, with such a low vacuum on the engine it has no buffer to absorb the required vac being pulled off and goes to a rich burn cycle and stumbles, the initial timing suffers as it drops from 16 to 6 degrees and the rpm drops from 1100 to 600 will stumble and eventually die as the spark is not being discharged at the prime time. I think George needs the canister, at 14-16 vac he should have enough residual to not require the vac pump.
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Old 07-11-2010, 02:13 PM   #10
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Default Re: Vacuum question on a 351W?

All of a sudden rich means your're dumping fuel and depending on carb type would suggest a blown power valve or a float problem.Losing your vac advance may also cause it to run fat.

Something you can try is to install a set of Rhoads lifters to get your vac pressures up. They bleed off some of the oil in the lifters at idle and pump up as rpm increases. Makes the big lift cams think they are a lot smaller and gives you a milder idle, higher vac but full cam specs when wound up.
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