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    Thread: Building the Ultimate 1983 Rabbit GTI (vw mk1)?

    1. 05-09-2017 11:41 AM #576
      I sourced Hoosier 225/50-15 DR2 slicks and mounted them on Enkei 15x8 RP1 racing rims and used 10mm spacers to clearance the struts - if I hadn't lowered the car so much they would have fit perfectly but in my case I have also sourced 1" rubber spring spacers to lift up the front end and provide more of a fender gap.

      I also sourced a solid rear transmission mount which is something a lot of VW mk1 drag racers have recommended - it keeps the engine from rocking back and forth, improving traction on the track.

      I have sourced the required components to get a brake cooling/ducting system put together - something I will get done before heading out for a road course track day ...

      On the electronics side of things I have put together a full video recording system using the 'Harry's Lap timer' App on my iPhone, plus a high frequency bluetooth GPS, a bluetooth OBD/Canbus transmitter, and a Hero4 GoPro - mounted to the middle of my new rollbar - this will allow me to record HD racing videos complete with embedded track location/performance data.

      I got my shifter extension built and love it ...

      My rollbar was powder painted and installed, and I also mounted one of the Sparco EVO seats to my new seat frames and installed the harnesses - it all looks so 'trick' now with the other seats removed.

      I fabricated an aluminum 'X' brace for the rear of the car which holds everything in position for road racing and also works nicely as an angled mount for the nitrous and air bottles - it still needs to be painted though.

      This Friday is the local Mission RaceWay 'test and tune' day but the weather does not look promising. Possibly later in the day the track might dry out but I am not sure it will be worth the cost and effort to go out and sit there watching the rain come down, waiting, waiting for the track to dry out (something I have done many times) - It may be May 26th for the next T&T day

      Finally, I cleaned out the intake fuel filter again and found some more of the black gunk in it - I still believe it is the remaining crap from the silicon sealant I had previously used to seal up the fuel sender - I will check the filter again in another month. I also purchased a combustable fuel vapour sniffer and used it to confirm that my stainless fuel lines are releasing vapours - and this has been confirmed by the manufacturers of stainless/rubber lines - they don't fully keep the fuel sealed up and cause a slight odor. Strange as I think that is a bad design/material spec. I will likely rip out all of the fuel lines and replace with stainless/teflon lines at some point down the road as I don't like my GTI smelling like gasoline when I go into the garage.

      New photos here: http://www.derekspratt.com/html/auto...rformance.html

      New video here: https://youtu.be/kwf63fa6mOk

    2. 05-20-2017 03:26 AM #577
      I spent a few hours at Blitzkrieg Automotive in Vancouver today with the GTI axle-bolted to their Dynapack dyno today and it was really a fun and worthwhile experience. The traditional roller-type chassis dynos have some potential variables with rolling friction that can vary depending on how tightly the car is held down onto the rollers while the Dynapack unit not only removes this variable (and any tire slip) but also securely holds the car in place without risks. The units are super expensive ($150,000) but their accuracy and repeatability are 1st rate. I was able to look for 1 and 2hp improvements over a range of parameters and slowly find missing power. We did about a dozen pulls covering fuel/air ratios, timing, injector end angle (the point in time when the injectors stop firing relative to the compression stroke), removal of the air box and filter and replacing the long intake trumpets with shorter trumpets. We were also going to test the nitrous system but the nitrous ECU enable line wasn't triggering the system properly so I will have to do this at the track and on the road next week (I found the problem later - Holley has a naming convention bug with the nitrous enable input that I had to work around by creating a touch-screen 'master nitrous enable' and then a ''stage 1 enable' using my dash mounted switch - I am pretty sure it will work now). Here are the test results:

      191 hp @ 7200 rpm, 150 ft-lbs @ 6100 rpm - 13.0:1 A/F ratio, 26 degrees of total timing

      192 hp / 151 ft-lbs - 13.2:1 A/F

      194 hp / 151 ft-lbs - 13.4:1 A/F (13.6 saw a drop in power so this is the ideal A/F)

      196 hp / 150 ft-lbs - 28 degrees of timing

      197 hp / 150 ft-lbs - 30 degrees of timing

      198hp / 150 ft-lbs - 32 degrees of timing (I did not attempt to advance the timing any further)

      198hp @ 7200 rpm, / 162 ft-lbs @ 5400 rpm - no air box or filter

      204 hp @ 7200 rpm / 164 ft-lbs @ 5400rpm - shorter intake runners/trumpets

      Leaving the injector end angle at 0 degrees (start of compression stroke) was the default ECU setting and made the most power.

      The big story was the removal of the air box and air filter - it increased the engine torque dramatically over a wide area from 5000-7000rpm and moved the torque peak down 1000 rpm - this will improve the overall acceleration 'area under the curve'. On the street it isn't practical to run unfiltered air into the engine (it will ruin it over the long haul) plus the noise from the ITBs is massive - you can hear the engine accelerating 10 blocks away with the air box removed - it is much louder than the exhaust system.

      Dynapack dynos are reliable and conservative power measuring devices - to calculate crankshaft power add back the estimated 15% loss which brings this engine to 240hp which agrees exactly with my accelerometer testing last month so I will simply use my accelerometer testing for the nitrous system benchmarking next week. FYI, my 2L GTI engine produced the most power these guys have ever measured on this dyno of this size and type of motor - no other 2L 16V NA engine has exceeded 200hp before so they told me I have a 'sick' motor ...

      Here is a link to full-size plots of our #2 and final dyno pulls showing the net improvement achieved thru ECU tuning: http://derekspratt.com/Images/Automo...ull%20size.JPG

      New photos here: http://derekspratt.com/HTML/Automoti...rformance.html

      New video here: https://youtu.be/AGIJ3cUHXhc

    3. Member rabbitnothopper's Avatar
      Join Date
      Oct 19th, 2009
      D-Town REPRESENT : Texas
      RIP81. 78 VW Rabbit 1.5L EH 4speed 020 GC->GP, 82 Rabbit Pickup 1.6D
      05-20-2017 08:30 AM #578
      great numbers

      i wouldnt run without an air filter either.

    4. Member
      Join Date
      Dec 27th, 2005
      Burr Ridge, IL
      81 S, 84 GTI, 86 16V, 92 Cabby
      05-20-2017 11:05 AM #579
      Three things I loved about the video:

      1) 200hp without boost

      2) Tweaking parameters just is super easy and quick when everything's electronic

      3) The dyno guys are drinking beer at work
      Work: it works, ibtches.

    5. 05-20-2017 09:37 PM #580
      Very Nice setup. Thanks for sharing the tuning - what worked and what didn't work. I wonder if there is some air box tuning that can be done to gain the power with it installed. I remember that during the Formula Super Vee days, VW 1.6 motors making 190+ HP(@ the flywheel) @8500 rpms. ITBs were allowed but an air box was not. Now if something wasn't allowed then that means it makes more power (and wouldn't be fair for the carb based engines) Little of info here on the FSV motors. http://scientificrabbit.com/node/5

      Last edited by ny_fam; 05-20-2017 at 10:00 PM.

    6. 05-21-2017 03:43 AM #581
      I made a custom radiator specifically to allow me to mount the largest air box possible to my ITBs in the hopes of not killing power - I think the air box needs to be taller and deeper to avoid impacting the power #s. Mine is just too small I think ... and I agree that if optimized it might add power - or at least mid-range power.

      Those ITBs are seriously loud on the street - even on the track I might get flagged for exceeding 100dB noise levels ... so I may end up racing with the air box. But not drag racing though ...

    7. 05-21-2017 01:02 PM #582
      Could a twin plenum manifold/box help restore tq?

    8. Senior Member dubdaze68's Avatar
      Join Date
      Oct 29th, 2001
      '81 Sportruck, '82 Jetta Diesel
      05-22-2017 09:44 AM #583
      Those numbers are impressive.

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