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JMortensen

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Everything posted by JMortensen

  1. JMortensen
    General rules: Front engined cars usually have lower roll center in front and rear RC is slightly higher than front. For performance, low front roll center is best. If it's too high what it does is force the wheels to move outwards in order for the suspension to compress. This can really make it hard for the outside suspension to work under load. Conversely, an underground RC will want to compress the suspension more than it would otherwise with cornering forces. Higher roll centers can be used to allow softer spring rates. If you spring the car stiff enough, you can run low roll centers and not have excessive roll and reduce the jacking forces. As a kind of rule of thumb, 80% of the turn happens in the first 1/10th of the turn. This is why the minutia is important. If the car won't turn in the instant you turn the wheel, then you're not getting around the turn very well, regardless of what it will do once it changes direction and is in a steady state corner. Again, as a general rule, the end of the car with the lower RC will tend to grip better, so RC is a way to change handling balance. This is why you have a lower RC in front. Solid axle cars have a hard time with high rear RCs and they use different solutions to lower the rear RC to improve handling. Not really germane to this convo, but here is a link to a discussion of a Mumford link, which is a modified Watts link that can lower rear RC: http://www.locostusa.com/forums/viewtopic.php?t=77
  2. JMortensen
    I've started my own thread on the dual ball joint setup, going to see how feasible it is because I have serious issues with scrub with 15x14 wheels.
  3. JMortensen
    Inner control arm pivot height: 5.5" Ball Joint height: 6" Control arm length: 11.5" Clearance to xmember: 2 3/4"
  4. JMortensen
    If that's all it takes it sounds pretty easy to do, but I feel like there have got to be some complications we're not factoring in. Looking at that Pontiac video looks like the end links will have to be reworked and made as long as possible. Cary has some software that figures it out too. He's asked me for a few dimensions, but he's gone until next week, so I haven't gotten around to measuring yet. Thread should pick up next week.
  5. JMortensen
    That's similar to how the Autopower bars attach. They used to be SCCA legal. Not sure if they are anymore. I do think it's a LOT better for seat clearance, but it's very hard to connect door bars to. I haven't seen one of their bolt in cages in a really long time, but I seem to recall they had one door bar that clamped to the roll bar then bent down in front of the door and went forward to the A pillar. I don't think the door bar bent into the door area and I think it was only a single door bar.
  6. JMortensen
    Looking at your cad drawing I have a couple suggestions. First is the strut tower to dash bar. Hitting the middle of the dash bar is not ideal because there is no load path. The BSR car had the tube from the middle of the dash to the main hoop. Also not the best, but a lot better than just ending in the middle of the dash bar. Built the way you drew it, it will probably be an improvement over no strut reinforcements, or reinforcements to the (weak) firewall, but a better idea is to do an X from the strut tower to the dash hoop, and then hit the dash hoop on the other side with the upper door bars. I don't know how much interior you're going to have but it's tight in that area. Also will probably have to have a plate on the inside of the firewall and then bolt in the part in the engine compartment so that you can take the engine out. I actually have the bars as you have them and I had to tweak the windshield wiper linkage to clear where they went through the cowl. Another issue is the shoulder bar is bent back for seat clearance (necessary if you're over about 5'7" or so. The problem is that your diagonal looks as thought it is bent back to the bent shoulder bar. That's illegal per SCCA, NASA, etc. You could put the diagonal in the main hoop and then put a short tube in to connect the diagonal to the shoulder bar, or you could do a straight bar across the pass side and then bend around the back of the driver's seat. I was also able to take bars from the bottom of the A pillar to the strut tower. It managed to squeak in without interfering with the clutch pedal. Not hard to do and the stronger the strut tower reinforcements are, the better.
  7. JMortensen
    280Z stubs are 27 spline vs 240 at 25 spline. 280Z stub axles are far from unbreakable. Even the 37 spline ones can be broken, especially with drag strip launches. Rather have mtnickels's weld on adapters than adapters bolted to the stock stub which bolts to the CV, so move that one up a spot from "the rest" and it falls behind MM's billet Z31 adapters, which have a thicker, more nicely radiused flange than the stock companion flange.
  8. JMortensen
    The longnose R200 loads the strap mounting holes vertically, the way they are deisgned to take a load. The shortnose does not. It adds what acts like a lever to the mounting holes, then pushes up on that. This is why there have been a few cases of high hp guys tearing up the unibody right there with shortnose diffs. If it has happened with a longnose and RT mount, I haven't seen it.
  9. JMortensen
    Eliminating the stub axle is a good idea. The TTT upright looks like a dumbbell weight to me. I'm not a big fan of shortnose R200 swaps either because of the way they usually attach to the strap bracket in the chassis. Some good, some bad there IMO.
  10. JMortensen
    No, it doesn't, but the angle of the TC rod doesn't change any of the geometry of the control arm though, having the arm in line with the ball joint just loads the TC rod straight instead of at an angle. You can look at a BMW or Porsche lower control arm and they are shaped kind of like a boomerang. More room for the tire, but the geometry is controlled by the pivot points, not the shape of the arm.
  11. JMortensen
    Typical race car "10 lbs of shit in a 5 lb bag" stuff. Looked again, due to tie rod to rim, steering rack to alternator, and other space constraints I'm going to have to stick to this wheel offset to make everything work, or do a whole bunch of other work to make it all fit.
  12. JMortensen
    I can swap rear wheels to the front and the drop center on the wheels is different and won't need the spacers. I'd have to check but I believe those wheels are 5" back space, so that would lessen the scrub to closer to 5". Might have issues in the rear with hitting fenders, and possibly front wheels hitting splitter.
  13. JMortensen
    OK, figured out one problem. Measure to the CENTER of the tread, so that is 6.75" and that gets scrub radius of closer to 6".
  14. JMortensen
    I want to believe I'm doing something seriously wrong here. Please tell me I am. Cary asked for measurements including scrub radius. I looked up how to measure it. Looks like imaginary line through upper strut mount and lower ball joint, and then wherever that meets the tire contact patch. These are 15 x 14 wheels with 13.75" slicks. If I'm doing this right, and I think I am, I'm looking at about 13" of scrub radius. These wheels have 4.5" backspacing and 1/2" wheel spacer. So this means that a typical 15 x 8 with 0 offset and a 23" ish diameter tire is going to have about 7.5" scrub or so. If I have this correct, I will wait to see if Cary can figure out where the mounts would need to be to fix, but I suspect that it's not workable in any event, and the solution will be SLA suspension instead.
  15. JMortensen
    Best? www.modern-motorsports.com 930 setup. It doesn't have adapters that bolt to the stock diff output stub and companion flange. It has a proper chromoly stub that plugs into the diff, and chromoly companion that attaches to the stub axle at the wheel. Couple with their 37 spline upgraded stub axles, and that IMO is as strong as you're going to get for the R200. Next best? www.modern-motorsports.com Z31T setup with shorter CV shafts. The Z31T shafts can be tough to find but they're pretty strong and with the shorter shafts they fit well. Same thing on the stubs, m-m sells chromoly stub axles and adapters to connect to the CV instead of an adapter that bolts to the stock companion flange and diff output flange. After that: everything else. DSS, Wolf Creek, Ermish, whatever other vendor you want to pick. These have adapters that bolt to the stock companion flange and diff output flanges and usually use 930 CVs. 930 CVs are strong, no doubt, but attaching to the stock flanges is going to be where the weakness is in terms of ultimate strength. Also 930 CVs are very popular with off road and racing crowd, so there is a wide variety of quality out there. Cheap ones have slack in them and will cause clunking. The other issue is the adapters: they bolt to the stock pieces and the bolts come loose. Seems to be the norm with this setup, bolts continuously coming loose. Heard of this happening to 510 and Z guys, most recently Mark Haag's car as he had issues with vibrations on the dyno, traced it back to the CVs.
  16. JMortensen
    Here is an oversimplified, crappy drawing of what I have in mind.
  17. JMortensen
    No, I'm talking about the front. Here is that video again:
  18. JMortensen
    Cary (tube80z) has been mentioning this idea of the dual ball joint front end off and on for the last couple years. I hadn't really given it too much thought until I autoxed my car and was really lifting the inside rear tire, and Dan (74_5.0L_Z) suggested that the problem might be scrub radius and caster related. I guess the idea is that the outside wheelbase increases significantly enough due to scrub that the car leans over in that direction and the inside rear comes off the ground. Recently this thread popped up talking about swapping front suspensions and it quickly devolved into a pissing match for reasons beyond my comprehension, but it did get me thinking more seriously about the dual ball joint idea. Cary seems to think it's doable with the ball joints in the same plane, and had thought of a modified bumpsteer spacer as a possible way to do it. That got me thinking that it might be easier to just make a square tube knuckle and bumpsteer spacer combo, so that's where I'm at right now. Thinking square tube with simple clevises welded to it for the ball joints, and then taper the front end and have it open and then use shims above and below the tie rod to adjust bumpsteer. I have absolutely no idea how to figure out the spacing on the clevises to minimize scrub and that sort of thing but I'm very interested to see if I can make it work, and to see if it would be as easy as I think it should be.
  19. JMortensen
    I have no idea why you took that turn Leon, I was simply trying to continue the discussion by pointing out that strut suspensions have evolved since 1970, not starting a pissing match. If you're happy with your static camber setting, more power to you. Have a nice day.
  20. JMortensen
  21. JMortensen
    Many newer strut suspensions use dual ball joints. I know BMW uses them on some of their vehicles, new Mustangs, etc. Not sure about Porsche. You still have to take into account that the Z was designed for a 175mm tire and when you put wide enough rubber on it to compete with today's cars they have issues with scrub radius and the more modern cars aren't running the same caster, ackerman, camber gain, etc that you'd find on a 1970 Datsun. Grafting on a SLA setup that has better geometry should actually produce gains in performance. Not sure why you would argue to the contrary.
  22. JMortensen
    Agree with Ben. Struts can be fast, but it's harder to get them there. The other issue with struts is the dearth of racing quality struts. Race quality shocks are readily available and much cheaper if you compare like for like to struts. I wouldn't do a Miata front end. The suspension geometry is great, but they have weak bearings and racers have to replace them a lot. Maybe a RX8 or something bigger. Mazda really does build awesome handling and painfully underpowered cars... If you're going to fab it up, I'd suggest looking at circle track parts. They have everything you need from prebuilt control arms, hubs, uprights, all the way down to weld on bosses for shock mounts. The problem is that the angles of the arms and length of the tie rods and all the particulars have an effect, and just because it's SLA suspension doesn't mean it's done right with camber gain and bumpsteer that is better than what you started with. Takes more math and geometry skill than I have to figure all that out, which is why I'm still on struts. I'd avoid the Mustang II prebuilt subframes that you see on drag racer sites. My understanding is that they usually have terrible geometry.
  23. JMortensen
    Fair enough, I can see how just a peak flow wouldn't be sufficient. I think something that is fairly instructive though is zredbaron's first stroker build which IIRC has had a small cam and no porting and made something pitiful like 160 whp vs his current one with the ported head and very particular cam profile that puts out 270 whp. He's a details guy, might PM him and see if he still has the rest of the specs you need on those flow numbers.
  24. JMortensen
    From: i just got my e31 head from sunbelt, am putting it on tomorrow. the printout i received showed the following data: stock (head before any work) port flow: .......................intake.................exhaust .425" lift...........158.9 cfm...........110.2 cfm .525" lift...........163.5 cfm...........118.4 cfm (.525" lift never reached with the cam i had in it) final port flow: .......................intake.................exhaust .425" lift...........180.6 cfm...........129.3 cfm .525" lift...........201.6 cfm...........145.1 cfm according to sunbelt, 200cfm by their flowbench (flow pro) is 225cfm by anybody else's (super flow). the cam jim set me up with has a lift of .520, and powers from 3500 - 7200. i think the duration is around 280. this is the max lift (valve-piston clearance) you can put in a 3.1 stroker without cutting valve reliefs into the pistons (using a 2mm gasket). the stroker kit produces a positive deck height of .025". hopefully i can dyno the car this week and let you know what this puts to the ground with a 3.1 LD28. i have pics, but won't post until i have guidelines since i remember john coffey saying something about sunbelt not liking that. john coffey, my 3,4 exhaust ports do look "funny" (but why do that only to cyl 3 and 4?)and i have single springs. all in all, i'd say ~225cfm per cyl is pretty damn good for an e31...i cant wait to hear and feel it!
  25. JMortensen
    What are these graphs supposed to show? HP and torque with the .480 vs .540 cams on stock and ported heads? If that's what it's supposed to be, I have to say I don't think they're very accurate at all. My takeaway from these graphs would be that porting is a waste of money, but my personal experience and the experience of a lot of the people on this and other forums is that the L heads benefit A LOT from porting. Put in a couple grand on porting and looks like you're estimating 7 hp and 7 lb ft return. Same on the camshaft itself. If going with .060" more lift nets you 7 hp, I think the larger cam profile is leaving something to be desired. As to the original question of which cam to use, I think .480 is right in that zone where you have to do the work anyway (needs different valve springs and retainers and stem seals to prevent coil bind and prevent the retainer hitting the seal). If you're going that far, I'd spring for the bigger cam. And if those cams only have 5 hp peak difference between them, find a better larger cam.
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