Miata Mailing List: September 1997, Message #2595
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From: "shiv pathak" <shiv_p@hotmail.com> Subject: Frankenstein's boost vs. rpm vs. tps vs. intake temp vs. timing Date: Wed, 17 Sep 1997 13:57:21 +0000
Warning: Long Post and a shameless plug Hello boost mongers! Shiv here in Dallas. Did some data logging last night. Plugged in a laptop into my TEC II and recorded several parameters realtime. Saved it on to the HD, imported them to an Excel spreadsheet. Relevent hp related car mods (once again): 1.8 liter 94R Black/Tan Electromotive TEC-II programmable ECU with: Programmable knock sensor (GM microphone) Map sensor (no stock air flow meter) Manifold temp sensor 550cc low res. peak and hold injectors (not saturated inj.) Crank mounted trigger wheel and sensor (no crank angle sensor) TPS sensor Idle control motor Bosch 4 wire heated O2 sensor General Purpose Output for purge control Etc,… Warner IHI RBH5 based turbo system with: Custom K&N intake (no panel filter) BEGI "Sport" larger intercooler 2.5" downpipe to cat 2.5" FM cat FM dual tip exhausts Centerforce DF clutch (#3) Situation: 85 degree F Dallas night. Flat empty road. Coasting in 5th gear at 1200 rpm (25mph or so). Stompped on the throttle. Results (I hope the format is retained. If not, sorry for the eyesore…: Note: Closed throttle = 0.51 volts Wide Open throttle = 3.51 volts Partial throttle = anything in between Engine Timing Manifold Manifold Throttle RPM Advance Pressure Temp. Position (degrees) (psi) (degrees C) (Volts) 1,201 23 (6.94) 50 0.51 1,146 23 0.23 49 0.88 1,195 23 1.50 49 0.96 1,233 23 2.32 49 1.31 1,296 23 2.77 48 2.80 1,359 23 3.35 48 3.39 1,424 23 3.70 47 3.39 1,488 23 4.04 47 3.43 1,557 26 4.28 47 3.51 1,629 27 4.51 46 3.51 1,699 28 4.62 46 3.51 1,778 29 4.75 46 3.51 1,849 30 4.98 46 3.51 1,925 30 5.20 46 3.51 1,995 31 5.44 46 3.51 2,073 31 5.67 45 3.51 2,139 32 5.89 45 3.53 2,229 32 6.36 45 3.55 2,307 32 6.71 45 3.55 2,391 31 7.41 45 3.53 2,477 29 8.10 45 3.55 2,561 28 8.79 46 3.55 2,665 30 9.37 46 3.55 2,760 29 10.18 46 3.55 2,873 28 11.22 46 3.55 2,993 27 12.16 47 3.55 3,101 27 12.61 47 3.55 3,220 28 12.61 48 3.55 3,324 27 12.61 48 3.55 3,429 28 12.85 49 3.55 3,527 27 12.74 50 3.55 3,653 26 12.61 50 3.55 3,750 25 12.85 51 3.55 3,863 22 12.96 52 3.55 3,986 19 12.74 52 3.55 4,081 19 12.96 53 3.55 4,189 17 13.30 54 3.55 4,296 17 14.01 55 3.55 4,414 16 14.23 55 3.55 4,501 17 14.12 56 3.53 Not exactly "stereotypical" of a turbo. No turbo "lag." Immediate boost. Instant boost was achieved as fast as my foot can press the throttle. As much at 4psi of boost under 1500rpm. An instantaneous 2.77psi of boost before my foot can even push the pedal fully to the floor (see TPS voltages). Full 12psi by 2900rpm. Initially, the boost curve has practically a vertical line. I presume this is because the 1.8 flows enough exhaust to keep it somewhat "pre-spooled" under vacuum cruise conditions. This is why the turbo achieves up to 3psi of boost immediately (regardless of rpms) on the 1.8. The RBH5 turbo on my brother's ECU'd 1.6 did not produce such immediate boost. Instead, the boost needle jumped to 2-3" of vacuum, and then rose quickly. This is also the exact SAME 7 year old turbocharger unit that my brother used (he mailed it to me). A larger compressor wheel and turbo rebuild should even help boost performance further. After the initial nearly vertical rise, the boost curve assumes a nearly perfectly linear curve up to 2900rpm (12psi of boost). The boost "curve" flattens out horizontally until 4000rpm when it ramps up until 4400rpm (14.23psi of boost). This phenomenon is boost creep. The wastegate begins to open prematurely due to its inability to remain closed from all the air flow. This can be solved with an electronic wastegate controller (from Greddy, HKS, or Electromotive). This would bleed off the signal line going to the wastegate, fooling it to remain fully closed. When desired boost pressure is reached at the intake manifold, the bleeder (which I think is a solenoid) closes completely, causing dramatically increased signal to the wastegate, forcing it open. These units basically keep the wastegate totally open or totally closed. Nothing in the middle which can result in a less aggressive boost rise. Extrapolating the effects of proper wastegate control would suggest full 14.23psi of boost by 3500-3600rpm! Now that would be something to feel. Another point of interest is intake temps. Notice that intake charge actually declined from 1200-2500rpm under wide open throttle. This is probably caused by the increased air flow over the intercooler as speeds increased from 25mph to around 45mph. Notice also how the intake temps remained in the 45-46 degree C range up to 11-12psi. This suggest that the RHB5 turbo is operating within it's efficiency range. Above 12psi, temps begin to increase. Also note that this entire run from 1200rpm to 4500rpm took exactly a whopping 28.7 seconds at wide open throttle! Much more brutal than normal driving. In normal driving, it would be impossible to stay at full throttle for more than several seconds (especially if it only takes 12 seconds to reach 100mph from a stop :) Low intake temps, coupled with high intensity ignition coils, colder plugs, wide gaps, and a knock sensor also allows a surprisingly advanced ignition curve (see above). The 46 degrees if timing advance at cruise with a 15.5:1 air/fuel ratio also results in a surprisingly good 26-28mpg on highway (even with typically aggressive turbo driving J) The computer should pay for itself in about 10 years :) I hope to be attending the Miata Mania dyno day at Hennessey Motorsports on October 11th. If Corky Bell and Bill Cardell make it, I'll definitely be there. I've never seen the two of them together in person… hmmm… I wonder if… nah. Shameless Plug time: For Sale: FM dual tip exhausts Great condition Looks and sound very nice Dual big 89mm resonated tips 100% Stainless Steel Less than a year old. New: $610 delivered Sell for $410 + shipping (needless to say, Texas locals would be preferred for convenience reasons) I really don't have an email account I can check yet regularly. Try this email address. Or better yet, call me at "work" at 972-986-5118 ext. 26 if you have any comments, questions, concerns, or are interested in the FM dual tip exhaust. Yet another shameless request: Living, temporarily, in an apartment in Irving, TX has its benefits. Only 2 miles from "work" Next door to Wendy's. It also has it's problems, mainly NO GARAGE to satisfy my vampire-like taste for Miata tinkering. So…if you are in the Dallas/FW/ Irving area, have a garage, and don't mind company from the likes of myself, give me a call. I could even bring Jack, my 2 ton jack, along! I would be more than happy to pay you back in the form of unintelligent conversation, miata stories, food or beer. Thanks. Better yet, perhaps you have a garage AND are interested in the FM exhaust. Now wouldn't that work out nice? Only in TX do you look forward to winter. Shiv ______________________________________________________ Get Your Private, Free Email at http://www.hotmail.com