Lets talk about the Exhaust Slash Cut method...

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Lets talk about the Exhaust Slash Cut method...

By teal_dx
- Tue Apr 24, 2007 6:35 pm #6497 (For anyone unfamiliar with this setup, the idea is to create vacuum to vent the crank case and valve cover. When done correctly, a 45? slash cut tube placed in the exhaust will create vacuum by the Bernoulli Effect )
I'm looking into this setup and having a hard time finding good info on it...

I've read about it but want to be sure I have all the details right before I attempt... Here's a drawing:

Image

And Here's what I've read:
- the metal "slash" tube going into the exhaust should go straight into the down pipe at a 90 degree angle.
- the slash should be at a 45 degree angle away from the exhaust flow.

I'm unsure of how far the tube should go into the down pipe?

What do you guys think about this setup?
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By asianrob
- Tue Apr 24, 2007 7:13 pm #6502 i dunno about that my bro put a catch can on but he didnt do that.... on the intake arm there is a spot for a tube from the arm to the crank case vent port....thats stock... you can put breathers on it too....
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By teal_dx
- Tue Apr 24, 2007 7:54 pm #6506 On a NA motor that setup will give you a vacuum. On a boosted motor, you'll be forcing air back into the crankcase & valve cover. A check valve will prevent this from happening by blocking air from going back in under boost, but then pressure can't be vented from the valve cover or crank case.

Also you don't want blow by residue to be sucked back into the intake and gunk up the inside of your manifold I combustion chamber, leading to detonation.

Exhaust slash cut method avoids all this by using the exhaust flow to vent the crank case & valve cover. It's just harder to setup.
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By Jsa-SIR2
- Tue Apr 24, 2007 10:19 pm #6515 iv not herd much about this, whats to gain useing this setup??
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By Jsa-SIR2
- Tue Apr 24, 2007 10:22 pm #6516 oh, just read the last bit. is there any gain on NA motors?
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By ohDirka
- Wed Apr 25, 2007 12:51 am #6533 this is basically how our drag car is
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By teal_dx
- Wed Apr 25, 2007 1:30 am #6539 what dia. tubing did you guys use on your drag car? i read one place that it needs to be 1" to work, and then I read somewhere else that 5/16" tubing worked :?
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By LaMbErT*
- Wed Apr 25, 2007 1:45 am #6542 Yeeah erm, ill stick to level one mechanics :o :eh:
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By ohDirka
- Wed Apr 25, 2007 2:00 am #6543 i think it was like 3/8 or something ill double check with my dad he did all the fab on it
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By vtec_gloucester
- Wed Apr 25, 2007 11:18 am #6559
LaMbErT* wrote:Yeeah erm, ill stick to level one mechanics :o :eh:


LMAO :lol: +1
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By york62
- Thu Apr 26, 2007 2:29 am #6617 any new news on this teal, i woudl love to try it my self.
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By york62
- Thu Apr 26, 2007 4:58 pm #6647 ok well i noow knwo that i DO have quite a bit of blow-by, i was told by another guy on another forum to find this out you start the car, let it idle, pull the dip stick out just a little bit and see if it smokes out of there. if it does the your have too much pressure in the head, if not you dont i guess. so now i wanna figure out which method i am going to use for venting.
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By teal_dx
- Thu Apr 26, 2007 6:14 pm #6653 if there's smoke coming from the dipstick hole, I'd think that would mean too much pressure in the crankcase too.

I've seen heavily modified DSM's that had soo much pressure in the crank case that the dipstick was always popping out on it's own. So they had to put a tiny hose clamp on it to make it stay in. An example of very poor venting of crank case fumes, had to be hard on the rings + internals to operate with that much pressure under boost :death:

Right now you guys know everything that I do... I'm still trying to figure out the right size for the tubing.

I'm guessing for it to be effecient, You'd need a bigger tube ( say 1") going from your catch can to exhaust, if you had two 1/2" tubes going into the catch can :?
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By york62
- Thu Apr 26, 2007 8:14 pm #6664 well i have more than just a seal problem and i think its just from all the oil going around my plugs and wires i think its fucked them up, i seem to have no power like i used to + blow by i figured it coudl be rings.

so i did a compression test today and i dont need rings but i have some weird numbers.

190-110-120-150

but the weird numbers coudl be from some of the oil that got into the cylinders when i took the plugs out.

and yes teal i knwo what you mean it woudl make sence if you had to 1/2" lines that your cut out line would be 1" inch but the more i think about it i think it woudl have to be smaller than your feed lines to the catch can, so the vacuum in the smaller line will be much greater than in a a big line. if you knwo what i mean
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