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JMortensen last won the day on October 19 2018

JMortensen had the most liked content!

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About JMortensen

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    Seattle area, WA

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  1. JMortensen


    Agree with Leon. I have to wonder if there is a measurable difference in a 6-3-1 vs 6-2-1 design. I would think if you grouped the primaries so that you got an exhaust pulse every 120 degrees on the 6-2-1 you'd get roughly the same effect as the 6-3-1. The main thing is the primary lengths, and according to Vizard, even that is secondary to not having as many bends in the tubing on a V8. You see some people go to great lengths to get equal length primaries, and I think especially when they use a lot of really tight bends to make the rear cylinder primary as long as the front, they're probably losing overall.
  2. JMortensen

    Manual Pedal Assembly

    I believe there are differences in the pedal assemblies, although I can't tell you what they are. The pedal box is the same between stick and auto, just use different pedals, so if you could find a 280 brake and clutch pedal you should be good to go.
  3. JMortensen

    Protecting inside of frame rails

    I did. Haven't yet sprayed oil in there, but that's the plan. I am going to use Corrosion X when I eventually do it.
  4. JMortensen

    Protecting inside of frame rails

    I think you're right about creating a space for corrosion, but if you look, the whole chassis is built by layering sheet metal and spot welding it together. My 70 is pretty rust free... except for all of those areas. I just cut the pass seat mount out. Rust between the seat mount and the floor. No rust anywhere else on the floor, as I fixed it years ago. That's the story for the whole car. My take is that trying to get the rails perfectly sealed is a fool's errand. For frame rails and hollow cavities, I think the best thing to do is shoot oil inside of them after welding. This is what Krown rust prevention in Canada does: https://www.krown.com/en/ I suppose you could spray oil everywhere there are overlapping sheet metal panels too, but there are a lot of them inside the cabin, and you'd have to dig out the seam sealer to get access. It would be messy.
  5. I think it's a matter of running the right compound that still functions at high temps. Back in the day katman had a thread where he was talking about running 2 3" ducts to the front brakes to keep them cool. I looked for it and couldn't find it. Joe Demers was making a heat sink that fit between the piston and brake pad, might be a tight fit on a 14" wheel. Found it: http://www.coolshims.com/coolshims-technology.php. John Coffey talked about adjusting drums in between sessions. Heard from several people that ditching the AL rear drums and running the cast iron ones off of a 510 is an upgrade because they can take more heat. If brake recirculators are allowed that would be a biggee, as this would protect against boiling fluid: http://www.colemanracing.com/Brake-Recirculator-P3775.aspx
  6. Coilovers are a better solution, but no problems with cutting. I ran my first Z on cut springs for quite a while. My friend who cut mine also ran 240 springs and perches on 280ZX struts in his street 510s. He cut all of the springs, and again, never had any issues. There are a lot of rednecks that cut them with a torch, or just heat the spring up until it sags to the proper height. This takes the temper out of the spring, and can cause the spring to fail. If you cut them with a cutoff wheel the heat is very localized and doesn't cause a problem IME.
  7. JMortensen

    Is this site dead?

    Terry sold his Z and bought a Manta, which he did up to an even higher level than the Z. It's just awesome! http://www.fototime.com/ftweb/bin/ft.dll/pictures?userid={7DC317B0-8EDB-4B2E-A837-F708D07C9769}&AlbumId={B0B466A9-4204-4F78-BC4C-DEBD9966B5B9}&GroupId={E9BD2EDD-A388-43BD-B264-DFF5CB43B8E2}&nt=a I still see Pete posting from time to time. Katman was moving away to focus on engineering on more modern racecars, E36s at the time. I assume if he's still in it he's probably working on newer stuff than that. Mike Kelly sold his Z after several failed attempts to put an engine in it. No idea on Denny. I miss Coffey. We emailed or FB'd with each other on a weekly basis. As to miata.net, they allow for the newbie questions over and over. I haven't seen the antipathy that you describe towards those posts. Seems like there isn't a "protect the searchability" drive like we have here. I know when I got my 99 I searched and found so many threads on my particular issue that I posted again and immediately got an answer with no admonition to search. Turns out coils were dead, killed precat, killed cat. PO had replaced coils and left it like that and I had to go through the exhaust to fix.
  8. JMortensen

    Is this site dead?

    FB is great for sharing pictures. For sharing tech info, it sucks. I often respond to FB posts with links to posts here a lot just to save the hassle of typing it out or having to copy/paste. Not an attempt to boost numbers here, but if it works out that way so much the better. When I was an admin here we talked about what the purpose of the forum was, and the general idea was that it should be like a library or an wiki page where people could go to find the info they were looking for. Adding a million posts about the same issue makes searching harder, so that was strongly discouraged. I still think this is the right policy, and I'm sorry to see that it isn't as strictly enforced, and also happy to have had my hand in pruning the information tree in that way. There is a mix of "HybridZ is great" and "HybridZ screwed themselves by being too strict" on FB but seems to me most of the other forums have declining membership as well, and this one seems to have a fairly consistent level of tech postings that is higher than most of the others that I'm on (miata.net beats this forum out, but I think it's pretty safe to say there are a lot more Miata owners than Z owners at this point). I think the response to the funding issue a year or so ago showed what is really going on. Casual Z owners don't care enough to engage in a serious forum, they just want to post pics and have people like them. People who are more serious about modifying or racing are going to stick around, because this is (still) a repository of very good info.
  9. That's the second time I've been wrong in a very similar way in about a week's time: the other was trying to relate a traction vs slip angle curve to a tire that was broken loose. Ah well, thanks for the correction. What did you think about the videos I posted?
  10. Thought this through a little more. I think a better way to explain would be to say that a stalled wing doesn't create lift, but instead creates drag because of the big wake that is created by the flow separation. You wouldn't say that there is more pressure on the rear of the car inside the wake than on top of the car, and likewise there is more pressure on the top of a wing when it flow is attached than there is when it is stalled.
  11. First, let me say that I'm enjoying digging into this, so thank you. Second, I'll point out that I'm not an engineer and have no training whatsoever, but I have read a few books on aero. Third, I think you're missing something here. When you look at a plane wing that is not stalled, it makes aerodynamically EFFICIENT lift. A stalled wing still makes lift, but there is more drag than lift and that's what causes the plane to fall out of the sky. Just look at the yarn on the plane wing. When it isn't stalled, the yarn is pressed down on the wing surface. When it stalls, the yarn is no longer pressed down, and it flails all over the place. This is proof that there is more downforce with the flow attached to the surface than when it stalls. The yarn is literally pressed down on the wing surface. Back to cars: the thing that we're trying to prevent is the rear of the car from acting like a stalled wing, and the reason why we're trying to prevent it is to reduce the size of the wake behind the car and its drag. Also, if we have a spoiler or wing that would be in the region of separated flow, we can make it work. The purpose of the whale tail is to change the angle of the flow off of the back of the car. If the flow over the top of the car points down, you will get lift. If it points up, you will get downforce. You can intuit this if you watch F1 in the rain and see the rooster tails shooting up 20 feet behind the cars, but it's not something that I ever read in a book. There is a guy on youtube that runs Gray's Garage and he does water flow testing with model cars, and he talks about this at some length, in addition to showing the rolling separation vortices behind various models. Pretty interesting. Here's one that compares your whale tail 911 vs other fastbacks with CFD: Here's another where he does the water tunnel testing with an MR2, which is particularly relevant as it has a Pantera style rear deck:
  12. JMortensen

    240sx OBX lsd and s12 r200 LN 4.11 diff

    There is another thread about swapping out the belleville washers and making sure the gears are installed properly, but this one will help when it comes to installing it in the housing.
  13. If you look at a Z in profile, you can pretty easily imagine the leading edge of the wing being analogous to the windshield/roof junction. As to the VG's increasing lift, that's not what they're supposed to do. From the original Mitsubishi paper, lift and drag decrease with addition of VGs: https://www.researchgate.net/publication/316855385_Effect_of_Vortex_generators_on_Aerodynamics_of_a_Car_CFD_Analysis
  14. Agree with calZ. I'd like to see some better shots of the yarn on the stock hatch. I would bet that the separation is not that bad; that there is separation, and it is creating drag, but not in a huge way. If you look at the VG test from the windtunnel, it actually shows an INCREASE in rear lift. Unfortunately they also took the side skirts off when they did this test, so it's not really a good indication of what exactly the VGs did. All we can really say is that the net change of removing side skirts and adding VGs resulted in increased rear lift and increase in drag by .04. The VG thing bothers me for a more fundamental reason though. If you look at a low speed aircraft wing, they put the VGs close to the leading edge of the wing. Most everyone who runs VGs on cars is following the Mitsubishi example, but I don't think it's really all that relatable to the Z. The EVO has a relatively flat roof and a sharp rear window angle. The Z has a bubble roof that leads smoothly into the slope of the hatch. I really think that VGs on a Z should be mounted close to the top of the windshield, and getting rid of the hump from the weatherstripping around the rear window is probably as important. https://www.youtube.com/watch?v=SXwVyxorvno Here is a video from a guy on another forum. I know you can't really compare different cars, but the point was to show that it is possible to have some separation without huge roiling vortices coming off the back (which would have the yarn standing flipping all around, including straight up). My GUESS is that this is somewhat similar to what happens on a Z. We do have this shot, but there is a spoiler on the car. Even so, there isn't any yarn pointing backwards or standing straight up.
  15. JMortensen

    New source for CV axle conversions?

    I wonder where the came up with the torque limit. Breaking welds? Doesn't seem likely since guys are running Z31T CV adapters welded to stock companion flanges. Maybe they're using particularly weak CVs. Maybe they're just under-rating them. In a 510 the U-Joint angularity can be a really serious issue. Haven't heard anyone having problems with Zs in that respect. I think the issue is the semi-trailing arm rear suspension and the ride height that 510 people tend to want. Being that the stub axle is such a weak spot in the Z, I'm not inclined towards anything that doesn't address that issue. Still think the modern-motorsports.com chromoly stubs and companion flanges are a good answer, and I like the Z31T CVs. If that's not enough the full chromoly setup with 930 joints and stubs for the diff and wheel ends from modern-motorsports.com is as good as you're going to get for an R200. Still blowing that up? You're going to need bigger axles, that means F8.8 and some kluged together stub axle for the wheel end, at which point why not SLA and change the shocks and the brakes and then while you're at it...