Guest bastaad525 Posted November 1, 2003 Share Posted November 1, 2003 A friend of mine was telling me this one... Okay you know how there are breather vents on the valve cover and from the block... some people just leave them open, and some people leave them routed, stock, thru the PCV valve. Now, this guy said, a trick he's learned from 'real racers' is to instead, run a hose from each breather, tee the two together, then run that one to the exhaust? I dont know if he specified if it need to go before or after the turbo, only that it would dump into the exhuast. Also, you would use a one way check valve in the hose, so that exhaust couldn't go back into the engine that way. He says that 'real racers' do this trick and have gained as much as 20hp from this. HOW??? makes no sense to me... anyone know any more about this??? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 1, 2003 Share Posted November 1, 2003 The crankshaft is pushing around through pressurized air, which is harder to do than in a vacuum. Think of how many home runs you get at Mile High Stadium, and that's only a few in/lbs less pressure, not a vacuum. So if you run a vacuum in the crankcase, the internals can spin easier. In the How to Hotrod book they say not to put too much vacuum to the crankcase, because the rear main seal will start to suck in and create a huge oil leak. I know one Z mechanic who was claiming 20 hp on a really crazy NA buildup (don't know if I believe him), and I was considering trying this myself, and he said he never had a prob with the rear main. In fact, here's a kit: http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=1783&prmenbr=361 If you're serious about trying it, I'll go halvsies with you on it since theres 2 in the kit. I'll buy it and sell you the other half and we can split shipping. Only thing I would be concerned about in your case is the turbo. I don't know what effect that has on this. Jon Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted November 1, 2003 Share Posted November 1, 2003 Hard to believe the exhaust will create any meaningful vacuum (better plumb that baby AFTER the turbo ). I've heard of evacuating the crankcase with the intake vacuum, but of course that won't do under throttle. Better yet, run a vacuum pump, then dump the vapors into the exhaust. Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted November 1, 2003 Share Posted November 1, 2003 My buddy did this with his Hybrid '64 Skylark/GN conversion and it made his car look like a crop duster. Lost a lot of oil through the exaust. I didn't understand the theory behind it, and I still don't. All I know is it didn't work for his application. FYI, he put the connection on the down pipe. !M! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 1, 2003 Share Posted November 1, 2003 The Z mechanic guy I talked to mounted it just after the collector. The higher the exhaust velocity the more suction, so the GN guy may have had too much vacuum. You would think that it would only suck oil if the PCV was really low on the block. Maybe it would be possible to get around that by plugging the block PCV and connecting to the top of the valve cover, which has that baffle built in. I can only assume that you'd still be able to pull the pressure out of the block, but I suppose it would have to be tried to see if it really worked. I know it works, drag racers have been doing it for many years. I just don't know how well it works, and I've always wanted to try it. Jon Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 1, 2003 Share Posted November 1, 2003 You can always run your car a quart low too for less windage. Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted November 1, 2003 Share Posted November 1, 2003 You can always run your car a quart low too for less windage. Hmmm... I would rather "knife edge" the crank before I used less oil in my engine. !M! Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 1, 2003 Share Posted November 1, 2003 I know, but it does give you more HP for 1/4 mi situation. I wouldn't do it either. I like having 6 quarts. Quote Link to comment Share on other sites More sharing options...
johnc Posted November 1, 2003 Share Posted November 1, 2003 Many drag racers design the oiling sytem to pump all of the oil out of the crankcase into the valve covers by 2/3s track so there is no windage as the car goes through the lights. Its even recommended by Chevy for some of their drag race only crate motors. I posted a quote from the Chevy guy in charge of the crate motor program a few months ago somewhere on this board. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted November 1, 2003 Share Posted November 1, 2003 Or get a olds big block Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 1, 2003 Share Posted November 1, 2003 I had an idea. Maybe leave the PCV vent open, with a filter on the tube, then route the vacuum off the valve cover. It might prevent the system from drawing too much vacuum, and still use the exhaust to at least reduce the pressure inside the crankcase. Still want to try this... Jon Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 2, 2003 Share Posted November 2, 2003 wow... thought you guys woulda shot this one down in a heartbeat... yeah I was thinking of routing the hose to small pipe that comes off my downpipe, that USED to go to the EGR valve. I just cant see that creating 20hp.... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 2, 2003 Share Posted November 2, 2003 It's kinda funny Bastaad, but I've been rolling that one around in the back of my head for about 10 years or so, and I just found the kit on Jeg's website like 2 weeks ago. But the idea is sound, so don't let anyone talk you out of it for that reason. There may be other complications like the rear main thing, but the idea is a good one. Jon Quote Link to comment Share on other sites More sharing options...
TomoHawk Posted November 2, 2003 Share Posted November 2, 2003 WE do the same thing on model powerboats using weedwacker engines. We fill the holes in the pull-starter cover so the flywheel doesn't suck any air. The cylinder is water-cooled, of course, so it doesn't need any cooling air. So... that much less drag from the air gives you more Hp & rpm. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 2, 2003 Share Posted November 2, 2003 Okay so... did I have the setup right then? as far as the details of it? I'm going to run a hose from the valve cover breather, and a hose from the crank breather, tee them together, then from the tee, run one hose into the downpipe, with a one way check valve in between. It'd be a really cheap, easy mod so I can do this one real soon if you guys really think it will help. Seriously though... can someone explain to me in laymans terms just why this creates extra power though??? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 2, 2003 Share Posted November 2, 2003 It creates power because there is no air resistance in the crankcase. That's why I brought up the example of mile high stadium. Isn't it Sleeper that lives in Denver? What's the air pressure at 5000 ft Sleeper? Isn't it something like 12lb/in vs 14 at sea level (guessing here). And that 2lb/in means that the ball travels farther with the same effort. Less energy or hp in our case wasted to push the ball or engine internals through the air. Here's a totally different example. They say that open wheel cars use 80% of their hp in just pushing the car through the air. Take that same car and put it in a vaccum, and what's the new top speed? It's gonna be way higher. Because the resistance is not there. Take that same car and put it in a track that's inside a huge hyperbaric (sp?) chamber that's at 3 bar pressure. Top speed is going to be seriously reduced (assuming the engine isn't getting that 2 bar boost!!!). In the engine we're not talking about top speed, but the resistance to movement created by the air pressure inside the crankcase. Someone mentioned routing the PCV to a vacuum source. Only problem there is that you don't have any vacuum at WOT, or a lot less anyway, and that's on an N/A engine. So at the time when you have the most crankcase pressure, you have the least amount of vacuum trying to suck it out. But if you use the exhaust you would have more vacuum at higher RPM's, which is when you need it. But the crankcase is filling with blowby and air pressure is generated just from the crank spinning and pistons going up and down. This I think is the important part. When the piston goes down and there is pressure in the crankcase, it is forced to compress on the DOWNSTROKE as well, even if it is to a much lesser extent. Someone else mentioned hooking up a vacuum pump to the PCV. I suppose that might work, but the expense involved would be a lot more than the kit at Jegs, for sure. I imagine it would have to be a pretty big pump too to move enough volume to evacuate the crankcase. I haven't seen anyone else's setup (I wish I could though). The GN story made me think that hooking all of the PCV ports to the vacuum source may be a bit much. I'm thinking now of putting a filter on the pipe coming out of the PCV on the block, then hooking to the valve cover. If you felt like this was too large a hole, you could always put a restrictor inside the filter to get more vacuum and less fresh air coming through. Jon Quote Link to comment Share on other sites More sharing options...
CruxGNZ Posted November 3, 2003 Share Posted November 3, 2003 When the piston goes down and there is pressure in the crankcase, it is forced to compress on the DOWNSTROKE as well, even if it is to a much lesser extent But, as one piston goes down another goes up, so there is no change in crankcase pressure, correct? !M! Quote Link to comment Share on other sites More sharing options...
TomoHawk Posted November 3, 2003 Share Posted November 3, 2003 I would thing so, but it probably depends on the firing order. There may be more pistons goint down than up on a certain part is each revolution. Or vice versa. If there wasn't some kind of pressure equilibrium, the blocks would explode or the valve covers would pop off, of the engine probably wouldn't run at all. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 3, 2003 Share Posted November 3, 2003 Regardless of whether there is another piston going up, can we all agree that there is pressure in a crankcase? Can we all agree that it gets higher with rpms? I would think so. Anybody else ever seen a Volvo 4 cyl in a 240 or 740 with the PCV plugged? It blows oil out the valve cover, oil cap, and anywhere else there is a gasket or seal. How about a newbie hot rodder that plugs all the PCV ports because he wants to eliminate all that smog stuff. Fire it up and it leaks immediately. With this in mind, when the piston goes down, it is still compressing the air underneath it, and that air is pressurized. It may be less pressurized because of another piston going up, but it is still pressurized. And there is still the issue of wind resistance that putting vacuum to the case would alleviate. Jon Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 3, 2003 Share Posted November 3, 2003 Okay... one other point I'm confused about though How is there vacuum present in the exhaust manifold? I mean... to me it seems that the exhaust is always pressurized. So I would think that the exhaust would always be trying to push it's way back into the hose that tees off into the intake and exhaust, and if there was a check valve there, it would just always be forced shut by the exhaust pressure... wouldn't it? Quote Link to comment Share on other sites More sharing options...
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