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Old 09-26-2004, 05:31 PM
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Designing a turbo setup need help

Okay this isn't as basic of a questionas you may think.

First off here is my proposed setup.

4cyl
390cfm 4bbl
Draw thru turbo

Carb will be adapted to the turbo and sit about level or a little higher then it would sit on the manifold normally. The elbow to the turbo will be a smooth bend, no more than 90 degrees.

Now onto the question.

I was thinking about the limits put on draw thru turbo systems to have a carbon seal on the compressor side to protect the turbo oil from getting sucked out under high vacuum when the throttle plates are closed...

Well I have an idea that I think will work.
I want to add a bypass runner from the elbow beneath the carb down to the intake manifold with minimal bends... It's a 4cyl motor so I can add the exit for the bypass at the rear of the manifold allowing for any air/fuel mixture that is sucked thru the bypas to be distributed evenly.

The valve supporting this system is a PCV style valve, closed under boost pressure and opened under vacuum.

Will it work?
And will this allow me to pic other turbos that don't have the seal?


- Thanks
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Old 09-26-2004, 06:56 PM
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Okay I found somehting that might help me...

BALL STYLE CHECK VALVE

Problem is the operation temp of the valve might cause it to fail.


I was also wondering more about the vacuum situation...
Will vacuum be created more between the carb and the compressor or the compressor and the valves?

I guess my idea isn't going to work if vacuum is more on the carb compressor end.




yay, I found a valve i can work with
http://www.wordsun.com/pip140.html

looks nice, 550 degree F, stands up to 206 BAR

I'll add in a male pipe but ported to flow better, just to cover up those threads inside the body of the check valve



hmm, I may just rig up a second trottle plate that only opes when the thotttle is closed... it could be vacuum operated but without some mechanical link it may force it's way open under boost and that'll mess things up.

I'll give the carb the short end of the lever so the throttle plates on the carb will only have to move slightly... and the longer end of the lever will have more rotation cause it's further from the pivot point opening the bypass throttle plate more.

This should keep the bypass from operating under part carb throttle.

urr i may have to rethink that, i can already see a few problems.

Last edited by Carb_kid; 09-27-2004 at 12:21 AM.
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Old 09-27-2004, 06:32 PM
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Make yourself some reed valves so it will bypass the turbo and under boost the pressure will close the valves.
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Old 09-27-2004, 08:26 PM
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I dont think any sort of bypass valve will prevent the turbo from being exposed to engine vacuum.
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Old 09-27-2004, 09:42 PM
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Depending on just how much boost you were going to run you could just place a second butterfly after the turbo.
Let it close and open just before the carberator and it shouldn't be a problem.
The closed butterfly will keep engine vacume from increasing to the point of sucking oil from the turbo bairing.
As for any blow by at this new butterfly you shouldn't have to worry about it unless you push pass 15# of boost. A seal on the butterfly shaft SHOULD keep any fuel/air mix from getting past.

Then again once your past about 10# of pressure you shouldn't be worrying about any bends in the pipes.

If your not going past 15# of pressure I don't think you'll need a drawthough system and a blowthough system should be able to handle it. With the proper fuel pump.

This is all from memory on my part. I did a lot of reading on turbos when I was rebuilding an old Yamaha Seca.
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Old 09-28-2004, 06:30 AM
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just get you a dam good boost regulator, don't go cheap because the cheap ones tend to spike and from my own trials you will be buying or rebuilding the turbo sooner that you expect.

have a 92 talon AWD 5 speed, with a big 16G turbo pushing 18lbs of boost with 550 injectors....make sure your getting enough juice to the carb or you will blowing the head of that thing.
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Old 09-28-2004, 05:40 PM
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Or, you couls just use a blow-through system. It would help with keeping the air/fuel charge cooler abd thus more dense which equals better power. Just my $.02.
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Old 09-29-2004, 11:02 AM
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I think that it might just work, but finding the right range for the actuator will be key. I would look into using a BOV with a low pressure setting. Tuning it will be key.

Another thing to consider is that while drawing air/fuel through the turbo and compressing it you are introducing fuel to the oil in the bearings since there is not carbon seal to prevent it. It is my understanding that this is an REAL bad thing........think about it.

Chris
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Old 09-29-2004, 12:29 PM
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I agree with TurboS10 never happen drawing thru the carb.
What about the waste-gate, intake,oil system, ignition do you plan on running ?
What type of block & head are you using ? How much HP are you planning on having? Just curious .
That blowoff valve will have more than just air in it, how about that nice big cloud under the hood waiting for a spark.
You may want to think this one out a little more.
A blow - thru carb would be better. my $.02 1/2 worth
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Old 09-29-2004, 01:10 PM
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I have seen a reed bypass on a small block ford before. Basically it looked like a 4" spacer. The top 2" was separated from the bottom. On the side of the top 2" was a 1/1/2 pipe that fed the intake of the turbo, the bottom half was fed back from the compressor outlet of the turbo. In the section that separated the top and bottom there were holes that were covered by reed valves. When the engine wasnt under boost it would draw straight through the reed valves. When the turbo spooled up the boost pressure would push the reed valves closed.

Buick used a draw through setup for awhile, but that turbo might be a little too big for your application.

John
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