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Thread: RX7 6L Wannabe Sports Sedan

  1. #151
    Registered User neil_se's Avatar
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    Thanks

  2. #152
    Registered User neil_se's Avatar
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    And with a flurry of activity to wrap up a dozen small jobs, I've made it to my first event. I'd planned to get to a practice day on Wednesday but it was cancelled late, I headed down yesterday but it was rained out except for a small window of time that I managed about 10 laps at 50% to bed in the brake pads.

    Today was Day 1 of the SCMSA short circuit & sprint series at Morgan Park. I missed the first run as the engine wouldn't rev over 1500rpm (possibly false positive engine protection?) and there was a few hours of down time with rain in the afternoon, but I still got in three 4-lap sprints at about 70% pace. It's a very raw driving experience and instantaneous power like I've ever experienced before. Fucking loud too.





    Back tomorrow for Day 2 and trying to build up a bit more pace.
    Last edited by neil_se; 10-03-18 at 08:04 PM.

  3. #153
    Registered User lukevl's Avatar
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    Nice work! Keep it in one piece at least for a week or two!

  4. #154
    Registered User neil_se's Avatar
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    It's been a few weeks and probably time I updated on the second day and some further notes.

    Day 2 didn't start so well. On the first run I had a rear lock-up which flung me off the track and did a bit of cosmetic damage to the front end. It also happened to be the only run I recorded all weekend so you can experience it here (jump to 2:40 if bored).


    The video looks so deceiving compared to the in-car experience (don't they always). The GoPro dampens the sound quite well but it does make it sound like I'm idling out of the corners and changing early.



    I was able to remove the lower radiator duct section and continue on the rest of the weekend. I didn't bother check timeslips until the end of the weekend but I ended up 4th out of 14 competitors in Sports Sedans and about 14th overall out of 70 odd, which i was pretty pleased with given that I was pretty much cruising around corners, braking early, and giving it some stick down the main straight.



    Some further notes and thoughts about the car's performance:

    - The engine protection issue turned out to be the fuel level trigger (sender isn't properly set up yet) so I switched that off

    - Water was pushing out the overflow on occasion, even though it wasn't overheating (I tried a few different caps). As you could see in my initial video there's a fair amount of upwards pressure from the electric water pump so I've since changed to a smaller restrictor and swapped the upper part of the housing to another I had in case it's a cap sealing issue.

    - I was pleasantly surprised not to hear any tyre rub on cornering, clearance was pretty darn tight when we were doing the alignment. I did end up changing to 17/14 rates and body roll seems well controlled (still has stock sway bars). A faster circuit layout will be more telling.



    - Steering effort was pretty manageable with the wide tyres and no power assist. The amount of feedback through the wheel will take some getting used to.

    - Throttle control was very difficult. My final pedal setup gives 82mm of travel which I thought was pretty reasonable. The issue is that at 2-3% TPS (3-4mm of travel) the engine is revving around 2000rpm and already has plenty of power on tap, so it's difficult to modulate just driving around the pits and to launch. I can adjust leverages at the bellcrank to give pedal travel of 105 or 120mm but that's pretty long and still only gives 5mm of travel to go from 1000-2000rpm. I either need to get used to it or change to DBW throttle so I can make the relationship non-linear. I'll see how the next event goes.



    - It's time I learn to heel-toe downshift. I never had a real need with any previous turbo car, but this will just lock the rears at any reasonable revs (as demonstrated in the video above). I guess it's just the amount of engine torque vs light driveline and overall weight. The throttle pedal was positioned too low but I've now altered the height to make it possible.

  5. #155
    Registered User neil_se's Avatar
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    Round 2 of the SCMSA sprint series was on this weekend at Carnell Raceway, Stanthorpe. I didn't have much free time to make changes to the car since the last event besides an oil change and throttle pedal position, but it ran well all weekend and I didn't need to turn a spanner. The brakes just aren't gripping as much as I'd expect so I need to look into that further, perhaps another change in master cylinders.

    It was a small field of around 40 cars but was pleased with my times overall. I finished 1st in Sport Sedans >2L and I think 4th outright behind 3 open wheelers (Dallara F396, Minetti SS-V1 & Steinard Mk1 Formula Libre). Still a lot of time to be lost though as I get more confident, improve the braking, put on some aero and sticky tyres.

    2 videos of my runs, though not my fastest.


  6. #156
    Registered User neil_se's Avatar
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  7. #157
    Registered User neil_se's Avatar
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    I did have another short trip off-track after braking in the marbles and the front bar is looking a bit worse for wear.


  8. #158
    Registered User lukevl's Avatar
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    lol truck box. My shifts look just like that. Iím running Dex 3- what oil have you got?

    Looks strong though!

  9. #159
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    How is the brake feel now you have changed master cylinders?

  10. #160
    Registered User neil_se's Avatar
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    I'm running the Penrite Pro Gear 70w75 Luke. It shifts pretty smoothly but I did manage to grab 5th on one run.

    The brakes just don't throw me forward like they should and I couldn't lock them even on this dusty track, pushing hard enough that I thought I'd bend the pedal box. That's with Ferodo DS3000 pads. I'm not quite sure where to look next.

  11. #161
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    Pedal going beyond vertical can make you feel like you're exerting a bunch of pressure but actually not that much...if there's an over-travel happening?

    Looking back to the previous page, I see you've listed the rear as a 1 piston caliper. I'm not familiar with how that program works - and no xls here, but most times for floating calipers, they're considered to be 2 piston for any brake calculations I've ever done.

  12. #162
    Registered User neil_se's Avatar
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    Just above that in the calculator it has caliper type where the '2' is floating so it does double the effective number of pistons.

    The pedal is almost vertical at rest so that might come into it. I need to have a look at the MC rod lengths and positions at rest. I might also try a larger cylinder on the front for more pressure.

  13. #163
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    Ah!

    If you're trying to increase line pressure, you've got to go down in master size.....and pedal travel will increase....which might make the situation worse, depending on all the geometries. Adjustment available in the box for pedal ratio might be another cheap way - if there's any.

  14. #164
    Registered User neil_se's Avatar
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    Oh yes of course, smaller. I keep pouring over the calculator though and I can't see a reason why the current combo shouldn't be working. I think I'll take a look at the rod positions, give it a bleed and get to a practice morning with a set of street pads to try too.

    Spreadsheet for reference, 4th sheet 'Design' for calcs
    https://docs.google.com/spreadsheets...it?usp=sharing
    Last edited by neil_se; 29-04-18 at 07:30 PM.

  15. #165
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    Looking back at the figure you have for the front caliper area, is that correct? Rear seems around right with a 34.9 piston floater, even the bigger typical AP 6 piston is way less...if that figure is per corner.

    Hated working in imperial as a kid, nowadays despise it, maybe try the lucky dip and see if this will give different answers!!!

    http://brakepower.com/index.htm

    The jz SS on the weekend only did a 39 at the creek, early days in the development yet, but similar times to a well driven twins powered 13b prodsports spec car.

  16. #166
    Opens Guido's Avatar
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    Quote Originally Posted by gxxr View Post
    The jz SS on the weekend only did a 39 at the creek, early days in the development yet, but similar times to a well driven twins powered 13b prodsports spec car.
    Track conditions looked pretty shit for most of the weekend though.
    Rust is lighter than carbon fibre.

    My Sports Sedan

  17. #167
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    ^^Believe it was mostly Sat morning that wasn't the best, looks like Mr Boost has missed his seat time too.

  18. #168
    Moderator Cal's Avatar
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    Holy shit, I thought Carnell had shut.
    The most dangerous risk of all - the risk of spending your life not doing what you want, on the bet you can buy yourself the freedom to do it later. - Randy Komisar.

  19. #169
    Non Compos Mentos Gammaboy's Avatar
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    Quote Originally Posted by Cal View Post
    Holy shit, I thought Carnell had shut.
    I believe it's more open than ever!
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  20. #170
    Moderator Cal's Avatar
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    Sounds awesome!
    The most dangerous risk of all - the risk of spending your life not doing what you want, on the bet you can buy yourself the freedom to do it later. - Randy Komisar.

  21. #171
    Registered User neil_se's Avatar
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    Carnell is allowed to operate for something like 14 days of the year with retarded hours of 10am-4pm. The surface is pretty dusty, course and hard on tyres but I can't imagine they'll ever have the money to resurface. I always enjoy driving there though.

    Quote Originally Posted by gxxr View Post
    Looking back at the figure you have for the front caliper area, is that correct? Rear seems around right with a 34.9 piston floater, even the bigger typical AP 6 piston is way less...if that figure is per corner.
    The fronts are 6 piston with diameters of 28, 32 and 36mm. There's a calculation over to the right and I think it all checks out ok.

    I'll have a go with that other calculator.
    Last edited by neil_se; 01-05-18 at 08:43 PM.

  22. #172
    Registered User neil_se's Avatar
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    I rechecked some figures and made a few small adjustments with pretty much the same result.




    Having a play with various figures and seeing their influence on the recommended sizes did identify a big hole in my assumptions though. I've been inputting the peak friction coefficient of the pads which I wouldn't be getting close to on on short sprints. With the current 0.7/0.625" cylinders and cold figure of 0.4μ it would require over 120lbs pedal pressure (75-100 recommended) for 1.2g braking. With 0.625/0.625" it'd still require just over 100lbs but as they warm up to 0.45μ it comes down to a heavy but reasonable force of 90lb. Next cylinder size down is 0.5" and I think that'd give too much pedal travel.

    Last edited by neil_se; 01-05-18 at 09:24 PM.

  23. #173
    Down with ma homies Greg Rust's Avatar
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    Iím running 0.625F 0.75R on a Tilton floor with 5.75 ratio. Pedal travel is fine if itís bled well. Mind you I do a lot of squats at the gym but still have to push bloody hard.
    xw Falcon 393 full race cam, NGK spark plugs.

  24. #174
    Registered User neil_se's Avatar
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    Cheers, that's what I'd always read as a more common combo. I'm going to swap in a 0.625 front and get to the next practice day to test it out.
    Last edited by neil_se; 02-05-18 at 10:08 PM.

  25. #175
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    Quote Originally Posted by neil_se
    The fronts are 6 piston with diameters of 28, 32 and 36mm. There's a calculation over to the right and I think it all checks out ok.
    Looks good. I might pull the cover plate off the pedal box and see what's happening below with pedal depressed, swapping the 5/8 master seems a good step.

  26. #176
    Registered User neil_se's Avatar
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    After the last track day I changed the oil and worryingly drained 0.5L from the catch can as well (was emptied before). The LS is known for breathing pretty heavily but that amount from about 1 hour of run time had me concerned. I had it compression and leakdown tested this week and they checked out fine.

    I took it down to Morgan Park practice today to test the 5/8" front brake master and I also ran some logs. In my first stint after about 10 minutes, the Haltech ecu cut power as the oil pressure had fallen below the min value. I immediately pulled over and shut it down for a short while before restarting, checking oil pressure and slowly driving back to the pits.

    The catch can had about 100ml in it (it also did a few dyno pulls yesterday) but there was also a lot around the can vent and the dipstick had been forced out. I added another 1L of oil and went back out a while later. He's some of the logs from that stint.



    The oil pressure gradually drops over the session until I back off and return to the pits. This curve would inversely follow the increase in oil temp (I don't have a sensor but the water temp increased in that manner) so perhaps the oil is too low viscosity (10W-40 Penrite).



    This snippet shows the oil pressure dropping quickly and dangerously low with braking/dropping rpm. I can't really determine whether it's just the oil pump being spun slower or if the oil is also moving away from the rear sump pickup (which is in a deep and baffled pan).

    Need to do some more thinking and consider what my options are.

  27. #177
    Registered User Staples's Avatar
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    I've got the same thing in terms of popping the dipstick. I have two an10 breathers one from either valve cover and I dont think its venting enough crankcase pressure. I want to add in another or enlarge the ones I have now.

    https://i.imgur.com/dNSvIPO.jpg

    However, I have not been catching oil in the catch can since I fitted them. Prior to this using 4 factory valve cover breathers (the small pipes) would catch about 500ml after a track day. After a few track sessions perhaps 10 mins each on the last track day less than 15ml oil in the can.

    Also oil temp skyrockets in my car. After 5 flying laps of about 70s lap I'm up to 120 degrees from a starting point of about 60 or 70. Obviously the pressure drops as it gets hotter but I dont log so if I'm getting those low spikes like you are I wouldnt know about it.

    I'd suggest a thicker oil and try again. Because of my high temps I usually use a fully synthetic.

  28. #178
    Non Compos Mentos Gammaboy's Avatar
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    cough*drysump*cough.
    "Where can we get hold of a Vincent Black Shadow?" "Whats that?" "A fantastic bike," I said. "The new model is something like two thousand cubic inches, developing two hundred brake-horsepower at four thousand revolutions per minute on a magnesium frame with two styrofoam seats and a total curb weight of exactly two hundred pounds."

  29. #179
    Down with ma homies Greg Rust's Avatar
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    Can you put a bigger oil cooler on there?
    xw Falcon 393 full race cam, NGK spark plugs.

  30. #180
    Opens Guido's Avatar
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    How much cool air is the oil cooler getting?

    Thicker oil, bigger oil cooler/betting ducting to it and then reassess.
    Rust is lighter than carbon fibre.

    My Sports Sedan

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