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Author Topic: Stock Mazdaspeed Miata Turbo Compressor Efficiency, VJ35  (Read 3808 times)
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TheBigChill
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« on: January 13, 2016, 03:40:12 PM »

So, I've always been wary of technical claims without quantitative data to back it up.  We've all talked about how much boost the stock turbo, engine, etc can take or produce, but not a lot of documentation exists on the Forum.

I was never able to find a Compressor Effciency Map for the stock turbo, so I contacted IHI directly and requested one.  Within 10 hours a Product Engineer had replied with a copy.

Note that while I know the stock turbo is a RHF5 VJ35, the map provided is noted as RHB5.  That letter merely dictates the Generation of the turbo, and I was assured that the compressor specs are identical.

You then need to calculate the data points on the X and Y axis.  Quick & boring lesson on how to calculate both:

The Y axis is Pressure Ratio.  PR=  Desired Boost + 1 Atmosphere (14.7) / 1 Atmosphere (14.7).  Example:  10psi + 14.7 / 14.7 = 1.68 PR  You'd find that on the Y axis and draw a horizontal line.

The X axis the Mass Flow Axis, and you first need to find the flow of our engine in Cubic Meters/Minute.  (% VE at full power) * 6500 RPM * 1.8L / (2 revolutions per engine cycle) * 60 minutes per hour * (a cubic meter per 1000 L) / 60 (min) =>  Below is what I've calculated for our 1.8 motor.

0.93 * 6500 * 1.8 / 2 * 60 / 1000 / 60 min => 5.43 cubic meters per minute.

Now find 5.4 on the X axis, and draw a line upward, and note where the lines now intersect.

The lines intersect in the center of the smallest center efficiency island, indicating that 10psi on our internally stock motor (no head porting or big valves) is almost perfectly efficient for the VJ35 compressor.  12psi is just barely outside of that, but still perfectly fine.  15psi (PR of 2.02) while not ideal, isn't dangerously inefficient either, though turbine speed is now approaching 140,000 RPM and producing more heat.


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Maduh
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« Reply #1 on: January 13, 2016, 04:39:00 PM »

Awesome! Thanks for providing concrete data on this!  thumup
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RIP #361 05' Black Mica Mazdaspeed mx-5, swap in progress to 1999 Miata Base. Follow my build thread here: http://tinyurl.com/pwtx3f9
barmato
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« Reply #2 on: January 13, 2016, 04:56:30 PM »

Thank you.  I never knew how to interpret those compressor maps.
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TheBigChill
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« Reply #3 on: January 13, 2016, 05:46:38 PM »

No problem.  I just got tired of not having the data, and having to guess based on _____?

We could actually keep that tiny turbo cooler and more efficient by increasing the Volumetric Efficiency of our motor.  This would shift us further right on the X axis, and would allow higher boost while maintaining good compressor efficiency.  Example:  6.5 Cubic Meters/Min flow and a PR of 1.9 (~14psi) is still in the smallest efficiency island, and as a result fairly efficient.  Though, increasing VE generally means doing head work.

As a general rule, you never want to be left of the Surge Line, nor right of the choke line (last shown line labeled 0.60).  Think of these as almost like topographical maps, and when compressor efficiency is what you want, you want to be "on the top of the mountain" in a sense.
« Last Edit: January 13, 2016, 05:55:39 PM by TheBigChill » Logged
'95MSM
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« Reply #4 on: January 14, 2016, 12:13:10 AM »

Does anyone know exactly what compressor Blouch used in their upgrade?? It would be cool to know what the numbers were on the original Big Enchilada from FM.
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'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
Chrisbee
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« Reply #5 on: January 14, 2016, 06:42:24 AM »

This is pretty cool!
Thank you for putting this together for us!  afro
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2004 TI #3021. Purchased Oct. 2014 with 56k miles.

Engine: FM 2 kit with Hydra 2.7, 700cc injectors, and full 3" exhaust.
FM Crossflow radiator w/stage 2 airflow kit.
Suspension: Fox Racing with FM sway bars.
Wheels: 15x8 Enkei PF01s running 215/50 BFG G-force Sports.
Misc: Custom Speedhut boost gauge in place of stock oil pressure gauge. Temp gauge mod. ScanGaugeII. Blue instrument panel lights. Eclipse dash vents.

Definitely a work in progress!
VolCrew
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« Reply #6 on: January 14, 2016, 12:40:59 PM »

What is the basis of the 93% VE?
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2004 Ti MSM GT  - my Red Barchetta
apalac01
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« Reply #7 on: January 14, 2016, 01:02:27 PM »

Want to say the compressor wheel was pressed on our stock turbo, the wheel was from a mitsubishi 16g turbo I think been a while and all my stuff is at home to be sure. I'm at work at the moment. The compressor housing was milled out so clearance issues were eliminated.
« Last Edit: January 14, 2016, 01:03:56 PM by apalac01 » Logged

05 Black MSM, OEM hard top, FMII conversion, Inconnel studs, Garrett GT2560R, FM crossflow, FM Stage 2 fans, MS3X, I.D. 1000cc  injectors, Hallman RX PRO MBC set at 10psi, Full FM exhaust, Ebay FMIC, Forge BOV, FAB 9 COP conversion, Walbro 255 LPH fuel pump, GTX PCV valve, Gates blue racing belts, EBC delete resistor mod, Racelands, FM frame brace, HDHCDD HT roll bar, HD harness bar, Schroth 4 point harness, Lotus Exige seats, TDR SS clutch line, Spec stage 3 clutch, Beatrush PPF bar, FM sway bars, Advanti Storm S1's 15x9's, 949's Adj. end links, Fog light grills, Buddy club cubby, LED map light, LED licence plate lights, Nautilus Stebel Air horn, Miata Roadster Short shifter, Innovate DL-32, MTX-D, LC-1, 2ea. XD-16's. for now.
TheBigChill
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« Reply #8 on: January 14, 2016, 02:16:27 PM »

What is the basis of the 93% VE?


It's based on how you calculate VE.  If you're unfamilair with how to do that, I can go through that too, though there are calculators available.  The exact # I got was 92.6%.
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TheBigChill
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« Reply #9 on: January 14, 2016, 03:44:35 PM »

As an addendum to my last post, the Mazda Miata Performance Handbook puts the 1.6l engine at 88% VE, and also says the 1.8 has a realistic flow of ~205cfm, which equates to 5.8 Cubic Meters/Min.  I would guess the MSM slightly lower flowing w/out VVT, and because of that I find my calculated 5.4CMM fairly accurate, VE aside.  Though, I did calculate 92.6%, which seems reasonable given the 1.8 vs 1.6 #'s.
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'95MSM
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Turbo clocked downward, new i/c plumbing


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« Reply #10 on: January 15, 2016, 12:44:26 AM »

Did the handbook specifically indicate it was an NB 1.8? If from an NA, there are many differences and even the MSM would be more efficient.
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'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
TheBigChill
Fifth Gear
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Posts: 555


« Reply #11 on: January 15, 2016, 01:05:42 AM »

Did the handbook specifically indicate it was an NB 1.8? If from an NA, there are many differences and even the MSM would be more efficient.

I believe the book was published in 1999, but that's a good question.  I'll have to dig up the exact quote again.  Either way, the factory changes between one 1.8 BP and another 1.8 BP won't likely have a huge effect on VE or maximum flow, but you're right; it's worth considering.  BUT, VVT on any motor is precisely an attempt to increase volumetric efficiency at certain RPM's.  With that, I feel that it's very safe to say that when you compare a 1.8 Miata w/ VVT to a 1.8 Miata w/out VVT, he who has it will have better VE.

Overall, the result is nearly the same as it applies to the VJ35 compressor and it's efficiency on this motor at various PSI.

« Last Edit: January 15, 2016, 01:07:41 AM by TheBigChill » Logged
'95MSM
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Turbo clocked downward, new i/c plumbing


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« Reply #12 on: January 15, 2016, 10:08:27 PM »

I agree about +VVT will inevitably be more efficient, but the cylinder head and cam changes between the NA version and 99/00/MSM non-VVT BP were significant.

If not updated since the '99 publishing, it certainly does not reflect the VVT BP.
« Last Edit: January 15, 2016, 10:10:10 PM by '95MSM » Logged

'05 running gear + '95 body
3.63 ring & pinion FM content: Blouch compressor mod, FM-Link, i/c & no-MAF intake.   BEGi: Stainless SGDP w/ metal core performance cat.   Custom stuff: Compressor clocked downward w/ new i/c pipe, big radius throttle elbow, 2.5" mid-pipe w/ Hushpower II, dual 2" axle-back w/ open Supertrapps, Toyota 4 pc cop ignition

245.2 whp on default FM-Link maps (with OEM midpipe)
VolCrew
Fifth Gear
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Posts: 1411



« Reply #13 on: January 15, 2016, 11:58:08 PM »

I ordered a copy yesterday.  Indeed, 1999.
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2004 Ti MSM GT  - my Red Barchetta
TheBigChill
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Posts: 555


« Reply #14 on: January 16, 2016, 08:50:58 PM »

I agree about +VVT will inevitably be more efficient, but the cylinder head and cam changes between the NA version and 99/00/MSM non-VVT BP were significant.

If not updated since the '99 publishing, it certainly does not reflect the VVT BP.

Of all the changes that exist from one 1.8 BP to another that could potentially affect Volumetric Efficiency, VVT is going to be the most significant.  To get back on track, what I'm saying is this:  When comparing two or more engines of the same displacement, with the same peak RPM, with the same estimated IAT, etc, you're going to find that what may seem like a significant rise in VE (say, 5%) doesn't equate to all that much of a change in the actual CFM or CMM of the motor.  I mention this, because the point of the thread is compressor efficiency, which is calculated roughly using Pressure Ratio and Corrected Air Flow. 

I'm not saying you're wrong; I'm saying ultimately, the changes aren't as significant as you may think, in the end.
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