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mender

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Everything posted by mender

  1. mender

    Statistically Speaking, Fuel Capacity

    For 500 point cars, it seems that it's all about the free parts - which makes sense because that's all they can use unless they want to get laps (which is a choice that I think is worth considering). For the low VPi cars, it's about the combination of what we can get for our points, and leaving out one of the parts of the endurance racing equation puts a limit on how equal we can make our cars with points. At some point, more points via a lower VPI doesn't make up for the free parts and/or fuel capacity difference. For low VPi it's about the selection; for high VPi cars it's about the free parts.
  2. mender

    Statistically Speaking, Fuel Capacity

    If fuel was on the table for points, teams like Good, Bad and Ugly would have to choose between going fast and going long. And unlike all the freebies for the 500 points cars, the fuel capacity thing has never been about free fuel but instead fuel for points. Not free; something has to be given up to get fuel. A fundamental difference in perception there. P.S. When did it become necessary to make sure an SC300 was the fastest car?
  3. Yes, he's doing heel and toe but only gets half the blip needed before letting out the clutch and dragging the engine up past the 6300 rpm fuel cut-out. He was very proud of his downshifting and felt that I was wrong to criticize his heel and toe technique - but I was the car and engine builder so I won. It's a Fiero so not your average RWD, and I find that our Civic is much more forgiving of a miscue/over/underrev.
  4. Sounds much like my method, Drew. I learned early on to make my downshifts as gentle and unobtrusive as possible. I try to use only as much revs as needed to engage the lower gear and also the least amount of throttle (fuel) and as late as possible to reduce the revs needed for the gear. My goal is to have the trans in the right gear with the clutch out and ready for throttle as late as possible. I don't use engine braking as an active part of decel but I also don't push in the clutch early to avoid it. I'm pretty good on the brakes, and I noticed almost right away in my racing "career" that the traditional blip for heel and toe made it hard to maintain even brake pressure. I didn't have many racing habits back then so rather than using the Jim Russell instructor's suggestion, I applied shoe leather pressure to the throttle as I was braking to bring the revs up to around 4000 rpm (Formula Ford) while dipping the clutch and engaging each gear on the way down. Later I started skipping gears when possible, again to reduce possible disruptions to the brake pressure. No rocking of my foot to hit the gas so my braking pressure stays very constant. I haven't been able to convince many people to even try my method. I didn't have brake pressure available back then ('80s) but my G.Analyst showed smooth high rate decel with no ripples, so I'm pretty sure my method works well. I'd like to get some DAQ on my recent cars to see how true that is. My other main driver was very much into the early downshift and using engine braking. I think it was the sound as much as anything that he liked, he couldn't brake into the corners as well with the Fiero because it upset the balance. This video is the one that brought my notice to his technique, which then led to a discussion of that little yellow light just inside the steering wheel in the video that was coming on during his downshifts (shift light set at 5500 rpm; tach readings were usually 1000 rpm higher during his downshifts). The big yellow light that comes on during cornering is the surge tank level light. Go to 19:12 or 21:00 or 22:48 I don't have a youtube video of me driving that corner but you have to listen very hard to hear that I downshifted there. He shifts at the flag stand, I shift at the cones. I'd like to hear from anyone who's willing to try my method out. Comes in very handy when diving into a corner under braking, shorter braking zone and less tendency to upset the car with shifts.
  5. mender

    Statistically Speaking, Fuel Capacity

    Or so we thought before all the free stuff showed up. The high VPi cars got a lot of things that used to cost points and that took away the advantage that the low VPi cars had but without giving the low capacity cars an avenue to make up the deficit.
  6. mender

    Anyone have Aero questions?

    I can answer that one: venting the air through the hood (I assume that you mean from the rad from the hot air reference) adds downforce by changing the position and speed of the air coming into the radiator. Changing the location and speed requires force, and the car provides that force. For every action there is an equal and opposite reaction, so the car gets forced down as the air gets forced up.
  7. Almost looks like the green TPS went off line; perchance a (4 second) re-alignment to synchronize the traces? Do you have speed traces of this segment as well?
  8. mender

    Teach me about leak down tests

    That would be fun! I know a couple more guys that I'd want on the team.
  9. mender

    Teach me about leak down tests

    I broke three top rings in my 1/2 mile oval enduro car when we had a red flag at about half-way. Leak-down was in the 35% range for worst one and 20-25% for the other two. I ran one more 3 hour race with it like that and lapped that field 11 times. It was down on power but not on handling.
  10. mender

    Teach me about leak down tests

    For the purposes of examining the amount of blowby, the duration of the event (0 rpm vs redline) doesn't really matter as much because the leakage could be consider a function of the amount of time spent at high pressure. In other words, a cylinder has X amount of time under combustion pressure. At 3000 rpm that event is twice as long as at 6000 rpm but only half as often, so the result is (should be) about the same amount of blowby for a given leak-down rate past the rings regardless of the rpm. The more power the engine is requested to make, the higher the amount of blowby because of the higher cylinder pressure, so in theory it's more related to throttle opening than rpm. The reality is that the rings at 6000 rpm have more difficulty sealing the cylinder than they do at 3000 rpm. This has two effects: 1. Obviously combustion pressure is lost as more air goes by the rings but 2. The intake stroke isn't as effective because of the loss of pressure differential So you have a two-fold effect that reduces both the air coming in and the amount of air left to generate the pressure against the piston to push it down. And just to make things worse, you now have crankcase pressure also resisting the downward motion of the piston. Oh yes, the other pistons are going up but the air in the crankcase doesn't move quickly enough to zero out that effect. Read up on the crankcase "windows" in LS engines. So now your top ring is allowing air past and is getting trapped by the second ring during compression/power, which drops the top to bottom pressure across the top ring which generates a lot of the sealing of the top ring (see gas porting of pistons). This is a positive feedback loop with only the tension of the rings keeping things from being a runaway. Current practice is to increase the ring gap on the second ring to help bleed off any air that gets past the top ring. Vacuum in the crankcase also helps keep the top ring seated to reduce the two-fold ill effects that I mentioned, and that shows on the dyno with up to 20 more hp on bigger engines. Different places on the bore: the most important part of the bore is of course at the top, and wear in this area is what we're mostly checking for in a leakdown. However, it's not a bad idea to loosen the valves and check leakdown at the bottom of the bore, especially if the engine has been overheated. This is the best way to check for cracked cylinder walls without tearing down the engine for a visual or magnaflux inspection. Valve leakage will be relatively constant over the rpm range but if it's an exhaust valve, the valve can change shape slightly because of the lack of heat transfer to the valve seat, warping the valve and again starting a positive feedback loop which can end badly. Valve float or more correctly bounce will be seen as a ripple in the power curve first before it becomes chronic. This can be due to harmonics in the valve train and surprisingly can be over a narrow range of rpm with usable rpm well above that point. Hope that addressed your questions!
  11. mender

    Teach me about leak down tests

    Doesn't quite equate to that amount of blowby for only 10% leakage.
  12. mender

    Statistically Speaking, Fuel Capacity

    Very few people who are advocating revisiting the accidental Fuel Rule would say otherwise. However, this type of argument and that of unintended consequences pops up frequently but without explanation or expansion; would anyone care to elaborate on either scenario so it can be looked at more closely? I'm convinced with facts and numbers and plausible explanations much more easily than by vague repeated statements.
  13. mender

    Teach me about leak down tests

    Most drivers including professional level would be hard pressed to detect a drop in power purely by the seat of the pants. Those same drivers are quite good at claiming that the reason that their lap times are off is because the engine is going soft. A leak-down tester tells the crew chief things that a driver can't, like how much leakage there is and where. Done regularly, that can be used to track the engine wear and much more accurately determine when intervention is advised. Also, the type of work is indicated during the test; oil usage only tells the extent of the problem, not what is causing it. Same for a compression test. In engine terms, it's like the difference between using chalk on the sidewall of a tire to see how much it's rolling over vs using a tire pyrometer to set alignment and tire pressures.
  14. Keep it clean. We were watching Judge Judy last night and a woman apparently had enough of her musician roommate and started beating him with his guitar collection. The judge asked, "First offender?" and she said, "No, first a Gibson then a Fender."
  15. mender

    Statistically Speaking, Fuel Capacity

    Just like everybody else.
  16. mender

    Statistically Speaking, Fuel Capacity

    So much easier for me to swap to a larger fuel cell rather than investing $10,000 to convert to diesel. Besides, I can already go slow enough to never lift and I'm pretty sure it'll go at least four hours like that. And astronomically better chance of getting hit from behind than to win a race.
  17. mender

    Statistically Speaking, Fuel Capacity

    https://www.motortrend.com/news/topgearcom-america-does-it-builds-84mpg-81-vw-rabbit-for-under-7000-4300/
  18. mender

    Statistically Speaking, Fuel Capacity

    Wait, what??? You want to have the same fuel as us? Speed creep 'n unintended consequences 'n doom and gloom because we don't want anyone else to have what we have! Who cares if The Fuel Rule became sacred only after we found out that we had it and they didn't! Who cares about open discussion and logic, we want to keep winning! There, I think that added as little to the topic as your post did.
  19. mender

    Statistically Speaking, Fuel Capacity

    Done poorly, I agree. Done properly with the possible issues in mind, I disagree.
  20. mender

    Statistically Speaking, Fuel Capacity

    Personal observation with one of the lowest capacity cars out there: no. Friday: we ran at the front of the field when running the car hard and not conserving fuel. Other things happened that dropped us to 10th by the end but the pace that we were running would have been good enough for a podium. We weren't fast enough to lap the field three times so not stupid fast. 1:40 minute stints average. 7 hour race so the best case scenario. Saturday: changed strategy to see how we would do when going 2 hours. Our pace was so far off the same cars we had been running with the evening before that we quickly abandoned that plan but it was already too late, even with an extended yellow flag then red flag period. 6 hour race so the worst case scenario. Quite a difference just because of the affect of low fuel capacity.
  21. mender

    Statistically Speaking, Fuel Capacity

    With fuel for points, they would have the choice of reducing their speed by using their points for fuel instead of power. What most people here don't seem to understand is that the law of diminishing returns definitely applies to reduced lap times. For example, it is much cheaper in both investment and running costs to have a slightly slower lap time in exchange for not having to make extra pit stops.
  22. mender

    Statistically Speaking, Fuel Capacity

    I've previously offer a means of doing that.
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