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Old 03-27-2008, 09:10 PM
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Need help tuning a SBC blower motor

Just got done with my new project. I installed a 4-71 blower on a SBC with 8:1 compression, Brodix heads, and a single Holley 950 blower carb with manifold referenced pv. The car started on it's first start and ran for about 40 minutes at 180 degrees temp. While running I set the total advance to 32 degrees and set the 4-idle mixture screws to the highest vacuum reading. It has a TH350 and in Park it idles at 1000rpm with 10"-inches of vacuum and 5"-inches of vacuum at idle in gear. I put her back in "park" and revved the motor several times then turned her off. Perfect!!!! I walked away and let her cool down, so I went indoors and got a "silver bullet" for myself. The problem started when I went to restart her. The car fired up and blue clouds of smoke blew out of both exhausts!! I revved it to clean her out but more clouds of blue smoke shot out the exhaust. *** Put the car in gear and the car died. Tried starting again, again, and again, but nothing. I pulled all eight plugs and they were black and oil soaked. What happened !!! Did all the oil get sucked up the PCV and into my carb, did my intake manifold gaskets fail, is my 50cc squirter to rich ???? Any ideas?????

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Old 03-27-2008, 09:19 PM
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Check the PCV and transmission modulator hoses for fluids. I use clear hose for testing either one while running. The Corvette in my pictures had a huge oil consumption problem with the PCV the first time I worked on it, It had standard height valve covers which I replaced with a tall set to solve this very same problem.
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Old 03-27-2008, 09:24 PM
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You need to do a compression check, oil soaked plugs isn't good. Do you have forged pistons or? And...what was your ring end gap? I'd hate say you may have broken rings, that's pretty drastic; were all cylinders oil soaked?

If it were me, I'd like what carsavvycook thinks. My thoughts are worst case.

Good luck, Larry
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Old 03-27-2008, 10:10 PM
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Thanks for the info Larry!!
I did a compression check and all cylinders are ok. The pistons are all SRP forged blower pistons, but i don't remember the ring gap. All my 8-plugs were lightly oiled and black fouled. My MSD 6btm couldn't light 'em up.
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Old 03-27-2008, 10:20 PM
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Quote:
Originally Posted by carsavvycook
Check the PCV and transmission modulator hoses for fluids. I use clear hose for testing either one while running. The Corvette in my pictures had a huge oil consumption problem with the PCV the first time I worked on it, It had standard height valve covers which I replaced with a tall set to solve this very same problem.
Thanks Carsavvy!!! I will try to raise my PCV as I have low rise Brodix valve covers with no baffles and I need a new set of plugs.
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Old 03-27-2008, 10:24 PM
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Quote:
Originally Posted by tubbedz
Thanks for the info Larry!!
I did a compression check and all cylinders are ok. The pistons are all SRP forged blower pistons, but i don't remember the ring gap. All my 8-plugs were lightly oiled and black fouled. My MSD 6btm couldn't light 'em up.
MSD Ignition @ your compression ratio runs at it's best with a medium heat range plug gapped at a minimum of .050 to a maximum of .060
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Old 03-27-2008, 10:46 PM
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Quote:
Originally Posted by tubbedz
Thanks Carsavvy!!! I will try to raise my PCV as I have low rise Brodix valve covers with no baffles and I need a new set of plugs.
Get a taller set of valve covers. It will solve your aggravation from consumption.
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Old 03-28-2008, 11:39 PM
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Quote:
Originally Posted by carsavvycook
Get a taller set of valve covers. It will solve your aggravation from consumption.
I pulled the PCV and it was full of oil. Also, the hose from the PCV to the base of the carb was filled with oil, so was the base of my carb and the top side of my blower. My vacuum gauge line also had some oil in it. I dumped the PCV and hose and instead added another breather. Next I installed new plugs with a step up in heat range. That should do it, but I know I will have a smoke show when it starts because of all that oil my blower sucked into the cylinders. Wish me luck!!
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Old 03-30-2008, 12:13 AM
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Other PCV locations???

Quote:
Originally Posted by tubbedz
I pulled the PCV and it was full of oil. Also, the hose from the PCV to the base of the carb was filled with oil, so was the base of my carb and the top side of my blower. My vacuum gauge line also had some oil in it. I dumped the PCV and hose and instead added another breather. Next I installed new plugs with a step up in heat range. That should do it, but I know I will have a smoke show when it starts because of all that oil my blower sucked into the cylinders. Wish me luck!!
I've been thinking about my pcv problem. I have custom polished low profile aluminum valve covers that I don't want to discard. My options are: 1) buy valve cover spacers that would raise my covers 1 1/4" higher and run a baffle and PVC 2) since my electric fuel pump is in the rear of the car, I could place a screw in PCV valve into the engine fuel pump block off plate and run a hose to the carb base "easy and cheap" 3) install an oil catch can that I can make out of an air compressor filter or just purchase a fancy aluminum oil catch can "lotsa work". What do you guys think/prefer ??
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Old 03-31-2008, 02:22 AM
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Blower guys??? Whatcha think?
1, 2, or 3 ??? I've seen supercharged Fords with alot of creative PCV solutions. I've also seen alot of blown, Flat Head Fords with ingenious PCV solutions. What's best for a blown SBC ? I value anyone's input into this situation as more information shared with other Rodders is better than none.
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Old 01-07-2010, 10:37 PM
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Quote:
Originally Posted by tubbedz
Blower guys??? Whatcha think?
1, 2, or 3 ??? I've seen supercharged Fords with alot of creative PCV solutions. I've also seen alot of blown, Flat Head Fords with ingenious PCV solutions. What's best for a blown SBC ? I value anyone's input into this situation as more information shared with other Rodders is better than none.
Just weld ali tube to covers and use breather cap with pcv built in works great
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Old 01-08-2010, 01:27 AM
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I think you'd pick up a lot of oil from the fuel pump cavity. The catch can idea is an option, but as you said, lots of work when there are simpler, easy fixes. Have you tried the baffled grommets? What about running an evac system to the headers? Just some thoughts.
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Old 01-08-2010, 11:38 PM
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The oiling condition that you have experienced is caused by the high depression generated by the supercharger. The blower pumps air all the time and with the throttle closed this creates a high level of depression (vacuum or pressure differential) between the carbs and blower, guess where the PCV is?, especially when you zip the throttle and snap it shut. The catch can is a good option, you will have to monitor the oil level and drain it every so often, also use the right PCV valve. I've been working with GM for several years and have privy to the flow specs for the common PCV's. I don't have the specs on this computer, but can recommend a low flow part number if you need one. Its possible to have too much flow, this will aggravate this condition. You are on the right track by bolstering the baffles and and redesigning the physical layout of the valvecover. Depending on the application sometimes I will just use a pan evac system coupled with a low flow PCV.

Regards, DrHP
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Old 01-09-2010, 12:42 AM
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Quote:
Originally Posted by DrHP
The oiling condition that you have experienced is caused by the high depression generated by the supercharger. The blower pumps air all the time and with the throttle closed this creates a high level of depression (vacuum or pressure differential) between the carbs and blower, guess where the PCV is?, especially when you zip the throttle and snap it shut.
WHAT???

tubbedz, get the publication "Street Supercharging", by Pat Ganahl, SA Designs, read it, and whatever else you can get your hands on.

Then listen to some of the hands on blower guys here, weigh what you hear, and I mean from everybody, with basic common sense and go from there.
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Old 01-09-2010, 07:35 AM
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DRHP has it right.

I ran into the PCV problem right away when I put the blower on late last fall. We put vacuum gages on both the manifold and under the carb. I don't remember the numbers as it's been a few months but there was a huge difference between NA and blown. As was noted there is always vacuum under the carb with the blower. I have 2 750 DP on a 355. I already had tall valve covers with baffles and still pulled oil into the PCV. I added a secondary baffle which seems to have cured it. I only run the PCV to the rear carb. Coasting down from a charge down the highway I can get 21 inches of vac. My 89 T-Bird Super Coupe used to get even more vac. It ran over 200k miles with very few problems. 100k on a set of plugs. Possibly a PCV from one of these might be a good choice. I'm going to check it out.

We just took the motor out and lifted the blower off. There was no oil in the manifold, in fact it was very clean. The plugs however were pretty black but they have been in since I first started this motor with the RPM manifold and single vac sec 750.

The few times I checked the plugs while running the blower after making a few hard passes on the road they seem to clean up pretty well but get black quickly just idling around. I run pretty rich at cruise 11.8 to 12.2 AFR at the last of the year. If you really jump on it at 2000 rpm or less it will puff some black smoke. Sometimes it's hard to tell with the tire smoke. haha

I was cleaning things up yesterday and noted that there was no oil in modulator line or the power brake line. Both are quite long and I hung them over a clean paper towel. so far nothing is dripping out.

Got a new pulley from the kids for Christmas so I'll be moving on up to "big boy" class now haha.

Just a thought, It's possible that the blower front cover seals have gone away and you are pulling gear oil in. We used to run Bakers AAA Castor oil in the blowers on the race cars. My son says they still do. You can sure tell if there is a leak as there is a very unique smell to burning Castor oil. You may have a pressure relief valve in the blower front cover near the top of the case. You should not relieve the pressure unless you are storing the blower for a long time. These lip seals keep the oil in and if you release the pressure they can leak. I took the valve out and installed a pipe plug before I ever put the blower on. My blower has been sitting for 6 weeks now and there is not a drop of oil inside of it.
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