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Topic Review (Newest First)

  • 01-31-2008, 12:07 AM
    scott foxwell
    Quote Originally Posted by gn7 View Post
    No matter how well you think your rings seal, the systems is dynamic, and the rings unseat or more accurately changes seats (from topside of the ring to bottom side) on the bottom of the exhaust stroke, at the very least. Pressure from this blowby mostly exits thru the oil ring expander and thru the holes in the piston and carries oil that gets trapped between the top oil rail and the scrapper ring with it. Some engine builders will actually but a receiver groove between the oil ring and scapper and drill the pin oiler in that groove. At least thats how it was explained to me by Rocky at Childs and Alberts, and read pretty much the same thing in a speed -pro tech paper when they were explaining why they don't believe in gapless rings and why the second ring gap should be bigger than the top ring. All of this really only helps the pin in the piston. Have to tell ya I never saw it that way before. And any leakage past unseated rings really moves when the pan is e-vaced. As to flow thru the pan, it's there no matter much you want think it isn't. The fact that you don't have any thing in you at the end of the day is just tribute to you baffleing and oil seperation before it leaves the valve cover. As to pump performance, I was wondering when someone would bring it up. There is no doubt that the pump with the bypass blocked couldn't make as much ultimate pressure with an e-vaced pan. wet or dry sump, however if the pump can get the set pressure and still open the bypass, you'll never see a change on the gauge. But the wet sump with bypass in the pan will open sooner than a non e-vaced motor and the pressure of both are some what effected by the fact the oil in bearings doesn't have to push against 15 psi + of to get out of the bearing. In fact it being sucked. There is way more this hole negetive pan pressure thing than most think about. wish this was shorter but this stuff is hard to explain in a few words.
    10-4 to all that. Thanks GN.

    David 519:
    Yea, you threw me when you said a short deck. I was thinking Chevy. A BBC short deck is 9.8" and what I based my comments on. The BBC truck block is a tall deck at 10.2". I'm guessing that maybe this isn't a Chevy deal...
    Standard BB Ford = tall deck GM. Stock 460 runs 6.605" rod.
  • 01-30-2008, 06:30 PM
    David 519
    Quote Originally Posted by gn7 View Post
    10.2(block hgt)-1.395(piston hgt)-2(half stroke)=6.805 hope this helps
    Yea, you threw me when you said a short deck. I was thinking Chevy. A BBC short deck is 9.8" and what I based my comments on. The BBC truck block is a tall deck at 10.2". I'm guessing that maybe this isn't a Chevy deal...
  • 01-30-2008, 06:02 PM
    gn7
    Quote Originally Posted by David 519 View Post
    If your running a 1.395 piston height with a 6.8 rod in a low deck block, you must be using a REALLY short stroke...like 3.3"
    With a 4" stroke, you can squeeze a 6.385 rod (1/4" long) and that's it.

    Edit to add...Snap, you guys may be talking about non-Bowtie stuff...If so, my bad. If that's the case, a "short deck" Ford must be pretty tall... about the same a tall deck Chevy 10.4"...
    10.2(block hgt)-1.395(piston hgt)-2(half stroke)=6.805 hope this helps



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  • 01-30-2008, 05:56 PM
    gn7
    Quote Originally Posted by David 519 View Post
    If your running a 1.395 piston height with a 6.8 rod in a low deck block, you must be using a REALLY short stroke...like 3.3"
    With a 4" stroke, you can squeeze a 6.385 rod (1/4" long) and that's it.

    Edit to add...Snap, you guys may be talking about non-Bowtie stuff...If so, my bad. If that's the case, a "short deck" Ford must be pretty tall... about the same a tall deck Chevy 10.4"...
    10.2(truck block hgt)-1.395(piston hgt)-2.00(half stroke)=6.805 hope this helps



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  • 01-30-2008, 05:49 PM
    gn7
    Quote Originally Posted by steelcomp View Post
    I don't understand how blow by helps pin oiling. Can you explain for me?
    Pin holes on the bottom of the rod end makes sense to me...that's the direction the oil's coming from.
    You mention the oil mist being sucked toward the vac pump. Again I say only if the air is actually flowing. If the engine is sealed and the vvac pump reaches a number, the block atmosphere should be at a steady state, not moving.
    I also thought about the fact that on wet sump systems, it's atmospheric pressure that's feeding the oil pump. What are we doing to pump performance when we start lowering the pressure inside the oil pan? I've never seen it as a problem on dyno runs looking at the pump curves, but I still wonder. Wet sump different story.
    No matter how well you think your rings seal, the systems is dynamic, and the rings unseat or more accurately changes seats (from topside of the ring to bottom side) on the bottom of the exhaust stroke, at the very least. Pressure from this blowby mostly exits thru the oil ring expander and thru the holes in the piston and carries oil that gets trapped between the top oil rail and the scrapper ring with it. Some engine builders will actually but a receiver groove between the oil ring and scapper and drill the pin oiler in that groove. At least thats how it was explained to me by Rocky at Childs and Alberts, and read pretty much the same thing in a speed -pro tech paper when they were explaining why they don't believe in gapless rings and why the second ring gap should be bigger than the top ring. All of this really only helps the pin in the piston. Have to tell ya I never saw it that way before. And any leakage past unseated rings really moves when the pan is e-vaced. As to flow thru the pan, it's there no matter much you want think it isn't. The fact that you don't have any thing in you at the end of the day is just tribute to you baffleing and oil seperation before it leaves the valve cover. As to pump performance, I was wondering when someone would bring it up. There is no doubt that the pump with the bypass blocked couldn't make as much ultimate pressure with an e-vaced pan. wet or dry sump, however if the pump can get the set pressure and still open the bypass, you'll never see a change on the gauge. But the wet sump with bypass in the pan will open sooner than a non e-vaced motor and the pressure of both are some what effected by the fact the oil in bearings doesn't have to push against 15 psi + of to get out of the bearing. In fact it being sucked. There is way more this hole negetive pan pressure thing than most think about. wish this was shorter but this stuff is hard to explain in a few words.



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  • 01-30-2008, 05:39 PM
    David 519
    Quote Originally Posted by gn7 View Post
    I agree, assuming I'am running a low deck, but a 1.395 piston gets me 6.800 rod which is plenty for me and just happens to fall at 1.7
    If your running a 1.395 piston height with a 6.8 rod in a low deck block, you must be using a REALLY short stroke...like 3.3"
    With a 4" stroke, you can squeeze a 6.385 rod (1/4" long) and that's it.

    Edit to add...Snap, you guys may be talking about non-Bowtie stuff...If so, my bad. If that's the case, a "short deck" Ford must be pretty tall... about the same a tall deck Chevy 10.4"...
  • 01-30-2008, 10:36 AM
    1/4 Miler
    Quote Originally Posted by steelcomp View Post
    You mention the oil mist being sucked toward the vac pump. Again I say only if the air is actually flowing. If the engine is sealed and the vvac pump reaches a number, the block atmosphere should be at a steady state, not moving.
    In a dry sump system there is a pressure gradient between the point(s) of entry of the oil (where it's higher) and the inlet side of the suction side(s) of the vacuum pump (where it's the lowest) so oil & air move between oil entry and oil & air exit. Note that a dry sump system is not totally sealed throughout: Within the motor it is (disregarding seal leakage), but, between the output side of the vacuum pump and the bottom of the reservoir it's not totally sealed (while the motor is running you open the top of a reservoir to check and make sure you have enough oil and oil continues to move through the system). Also, there is the puke tank attached to the main reservoir and it is open to the outside atmosphere.

    Another thing in the 'Purist Physicist Sense' is that nothing is really 'Sucked' in a vacuum system, it is 'Pushed' through the system by the system's internal high atmospheric pressure/depression created by the vacuum pump: A vacuum does not attract matter (the oil & air), the pressure differential created by a vacuum pump causes it, matter, to be pushed through the system. I know that probably really doesn't matter to you guys, but, it's the reality of the physics involved.
  • 01-30-2008, 08:46 AM
    scott foxwell
    Quote Originally Posted by gn7 View Post
    thar's kinda why I was saying that clearance is not the fix all. there really shouldn't be an oil issue at moderate vac levels. The real problem is that as the depression get real low the it starts to vaporize any oil thats gets "misted" coming of the crank and sucked towards the evac outlet. Oil at operating temp boils off fairly easily under that kinda vac, and the pin lives off that oil mist. I doubt very much if a flat tappet cam could survive under the same conditions, which is why nascar has gone to grooving the lifter bores, well at least before they started putting the cam in a sealed tunnel. the other reason it hard on the pins is that "blowby" actually helps pin oiling and the evac helps seal the rings better and thereby lowering the blowby. I have also have had way better luck with rods that have two holes on the underside than I have with one on top. I think this has to do with oil getting trapped in the rod web and getting forced up the rod beam on the down stroke. Don't know for sure it's just a guess. Sometimes trying to make H.P. can just be a bitch
    I don't understand how blow by helps pin oiling. Can you explain for me?
    Pin holes on the bottom of the rod end makes sense to me...that's the direction the oil's coming from.
    You mention the oil mist being sucked toward the vac pump. Again I say only if the air is actually flowing. If the engine is sealed and the vvac pump reaches a number, the block atmosphere should be at a steady state, not moving.
    I also thought about the fact that on wet sump systems, it's atmospheric pressure that's feeding the oil pump. What are we doing to pump performance when we start lowering the pressure inside the oil pan? I've never seen it as a problem on dyno runs looking at the pump curves, but I still wonder. Wet sump different story.
  • 01-30-2008, 07:50 AM
    gn7
    Quote Originally Posted by steelcomp View Post
    The reduction in piston rocking might be. Higher the pin in the piston, the more stable the piston is in the bore. One of the benefits of running a long rod. I agree about the weight savings and the rod ratio...pretty dimunitive at that point. I also like to run as close to 1.7:1 as possible. One of the secrets to Ford power.
    I agree, assuming I'am running a low deck, but a 1.395 piston gets me 6.800 rod which is plenty for me and just happens to fall at 1.7



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  • 01-30-2008, 07:40 AM
    gn7
    Quote Originally Posted by steelcomp View Post
    There's something I'm still not clear on. Is a vac pump actually drawing oil away from the pins? If so, from where, to where? For that to be happening, there must be air circulating through the crankcase, in order for the air to be moving, and taking the oil with it. If the engine is sealed properly, air shouldn't be circulating or flowing through the engine. Oil is still being thrown from the crank, right? Less atmosphere it seems, would actually alow the oil to travel from the crank more freely into areas such as under the pistons. Now I can see if there's excessive blow-by, that there would definately be a flow of air downward leaving the bottom of the piston, heading to the crankcase.
    Just my little brain thinking through this oil starvation thing. I have lots of thoughts that progress from here, just want to hear some other's thinking.
    thar's kinda why I was saying that clearance is not the fix all. there really shouldn't be an oil issue at moderate vac levels. The real problem is that as the depression get real low the it starts to vaporize any oil thats gets "misted" coming of the crank and sucked towards the evac outlet. Oil at operating temp boils off fairly easily under that kinda vac, and the pin lives off that oil mist. I doubt very much if a flat tappet cam could survive under the same conditions, which is why nascar has gone to grooving the lifter bores, well at least before they started putting the cam in a sealed tunnel. the other reason it hard on the pins is that "blowby" actually helps pin oiling and the evac helps seal the rings better and thereby lowering the blowby. I have also have had way better luck with rods that have two holes on the underside than I have with one on top. I think this has to do with oil getting trapped in the rod web and getting forced up the rod beam on the down stroke. Don't know for sure it's just a guess. Sometimes trying to make H.P. can just be a bitch



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  • 01-29-2008, 11:38 PM
    scott foxwell
    Quote Originally Posted by Sleeper CP View Post
    I know a very smart engine builder, he used to build engines for Saleen(sp) and built some Bush engines. He has never thought that running 12" of vac or less could hurt the pins. I asked him what makes him think so, He said they ran a mopar on the dyno that had a plexiglass valley pan. He said that above 3,000 rpms that oil was flying all over the place. He said he was really amazed as to how much oil was getting thrown all over the place. From the crank and rods he just couldn't see the pins getting starved

    Sleeper CP
    I think most here will agree that below 12-13" isn't much of a worry. I think the problems start when you combine more vac than that with a big shot of N2O.
  • 01-29-2008, 10:52 PM
    Sleeper CP
    Quote Originally Posted by steelcomp View Post
    There's something I'm still not clear on. Is a vac pump actually drawing oil away from the pins? If so, from where, to where? For that to be happening, there must be air circulating through the crankcase, in order for the air to be moving, and taking the oil with it. Oil is still being thrown from the crank, right? Less atmosphere it seems, would actually allow the oil to travel from the crank more freely into areas such as under the pistons. Now I can see if there's excessive blow-by, that there would definitely be a flow of air downward leaving the bottom of the piston, heading to the crankcase.
    Just my little brain thinking through this oil starvation thing. I have lots of thoughts that progress from here, just want to hear some other's thinking.
    I know a very smart engine builder, he used to build engines for Saleen(sp) and built some Bush engines. He has never thought that running 12" of vac or less could hurt the pins. I asked him what makes him think so, He said they ran a mopar on the dyno that had a plexiglass valley pan. He said that above 3,000 rpms that oil was flying all over the place. He said he was really amazed as to how much oil was getting thrown all over the place. From the crank and rods he just couldn't see the pins getting starved

    Sleeper CP
  • 01-29-2008, 10:14 PM
    cs19
    Just lurking...
  • 01-29-2008, 09:36 PM
    scott foxwell
    Tap-Tap-Tap....testing one, two...
    Is this thing on???
    Sure is quiet tonight.
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