Single Turbo RX-7's Questions about all aspects of single turbo setups.

Some Really Stupid Questions.

Old 12-01-16, 01:40 AM
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Some Really Stupid Questions.

Ok, not really rotary specific, but choosing a turbo for a different vehicle atm, I'm realizing what i don't know would fill a phone book. So, some dumb questions for those with more of an engineering mindset.

1) Compressor efficiency; Generally a map goes from inefficient to efficient to inefficient. Is it measured in heat loss? Does that mean at the less efficient zone at the start of the map is making heat? or is that something else - pumping loss? And if so, what are the effects?

2) Compressor Trim. As far as i understand, a smaller trim means a bigger difference between inducer and exducer.
I have also read that a smaller trim (on smaller turbos) will spool faster than a bigger trim - something to do with needing less shaft speed to make boost.

So does that mean that say, a compressor with a 43mm inducer and 60mm exducer will spool quicker than a turbo with a 43mm inducer and a 53mm exducer?
And which one will flow more all else being equal?

3) Turbine trim. What difference would be expected from a large or small trim?

4) Turbine size. Will a smaller turbine make more shaft power than a big one? And back to trim again, what is the more significant dimension - exducer, or inducer?

5) Lastly, BB vs JB, and low inertia efr. Will there be much difference between the two bearing types at this size - will one actually spool at a lower rpm than the other? Or is it just transient response? Same with the efr - the smallest efr is (i feel) one size too big for the application, will the low inertia wheel actually make more boost with less turbine flow and pressure? Which would lead into Q6 about the ins and outs of turbine maps, but i feel I'm already pushing my luck, lol.

Thanks in advance!
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Old 12-01-16, 01:59 PM
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Anyone? All input more than welcome.
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Old 12-01-16, 10:31 PM
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those are great questions!

1. i've always thought of efficiency as a heat gain, compressing air adds heat, and there is some amount that is normal, and then they derive the percentage from that. i'd think pumping losses would factor in, but they would effect the shape of the map.

2. i forget which is which, and one does spool faster, vs the other.

3. the turbine side should work similarly, although it seems less picky.

4. lmao, i read an SAE paper about the design of the turbo that is on the 6.7L powerstroke, and i literally have no idea. i think i'm going to say smaller, the paper made it sound like they needed more gas flow so they used a smaller turbine. or i think read the paper and know less than i did then when i started.

5. the SAE was really clear about the BB vs journal, the BB helps everywhere, but it helps more at low shaft speeds. it was 5% at high flow, but like 15% better at low flows. they further mention that there are three components to "lag" one is the weight of the rotating assembly. the second is the bearings, and the third was something weird like ideal tip speed or something, i had never heard of it before today. so the 6.7L power stroke, got a little better at the ideal tip speed, because they made a compressor that let them run a more ideal turbine. wheel weight stayed the same, and bearings got way better, for a total net improvement that is quite big.

the 6.7L engine is a challenge because up to 40% of the flow through the engine is EGR, to meet emissions. the turbo sees this flow, and it raises the pressure ratio. they ended up with a double sided compressor, and this let them run a more ideal turbine (the EGR has to go through the turbo, but since its inert, it doesn't help drive the turbo)
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Old 12-02-16, 01:43 PM
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Thanks j9.
Anyway, here are two turbos (ingnore the fact they are china chargers) Can anyone predict which one will make more boost down low?

Ball Bearing Turbo GT2554R .42 Hsg For Nissan Y60 Patrol RD28T

MAMBA GTX Billet Turbocharger 2.2" TD04L-15T w/ 5cm T25 Hsg

and a garrett; Turbochargers Garrett GT Series : Garrett GT2259 Turbocharger | GCG Turbochargers
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Old 12-02-16, 02:59 PM
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Originally Posted by WANKfactor View Post
Thanks j9.
Anyway, here are two turbos (ingnore the fact they are china chargers) Can anyone predict which one will make more boost down low?

Ball Bearing Turbo GT2554R .42 Hsg For Nissan Y60 Patrol RD28T

MAMBA GTX Billet Turbocharger 2.2" TD04L-15T w/ 5cm T25 Hsg

and a garrett; Turbochargers Garrett GT Series : Garrett GT2259 Turbocharger | GCG Turbochargers
nobody runs those size turbso, you would have to test and tell us..

neither of those turbos will break 300 on a rotary.

this one should do about 350 max.. and spool around 2.5k or better.

6+6 Ball Bearing Turbo 4" GTX3076R GT3076R w/ A/R .64 T3 V-Band
is would on a par with the efr 7163 i think, but the 7163 giving better spool for more price.

the garrett line you should start at a gt30, and move up... some say a gt30 is too small, you asked about a gt25.

for the MHI td05 13g.. i think is the smallest people run from the mistubishi turos

Last edited by lastphaseofthis; 12-02-16 at 03:08 PM.
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Old 12-02-16, 03:07 PM
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Sorry, I should have mentioned - Its actually for a 3l diesel.
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Old 12-02-16, 11:03 PM
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Originally Posted by WANKfactor View Post
Thanks j9.
Anyway, here are two turbos (ingnore the fact they are china chargers) Can anyone predict which one will make more boost down low?

Ball Bearing Turbo GT2554R .42 Hsg For Nissan Y60 Patrol RD28T

MAMBA GTX Billet Turbocharger 2.2" TD04L-15T w/ 5cm T25 Hsg

and a garrett; Turbochargers Garrett GT Series : Garrett GT2259 Turbocharger | GCG Turbochargers
they should be pretty similar, you may want to see if the garrett turbine AR is equivalent to the mitsubishi
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Old 12-03-16, 03:44 PM
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So in theory, the smaller turbine/smaller A/R combo will spool with less exhaust energy, yeah?

Id be interested to know how the A/Rs of the different manufacturers compare too. I read somewhere that the area measurement, eg 5cm/3 is more reliable than A/R as A/R doesn't account for width, only height or some such.

The reason I am looking at these Taiwan Chargers is they are available with smaller (claimed) A/R housings than genuine. Also Genuine manufacturers dont seem to make anything this small with "extended tip" compressors.

Will confess I've been running the GT2554r linked above daily for most of the year - its a good turbo. Big improvement on the stock unit (some tiny, tiny hitachi thing) but a little bit lazier spooling up - in fact although it makes boost off idle - it doesnt get the full 18-20psi ive set it to until after 3000rpm, and i dont like revving it past 3000rpm too much in normal driving.
Avoiding going VNT because of the electronics involved.

Apologies for posting this here too. There is a forum for these vehicles , but they are pretty much all bogans (rednecks) who are no help at all with anything that is even slightly outside the norm.

Mods feel free to delete thread or remove non rotary content.
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Old 12-03-16, 04:16 PM
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So is this a 3l diesel car?
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Old 12-03-16, 04:57 PM
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Yes, a 4x4 pick up

Last edited by WANKfactor; 12-03-16 at 05:07 PM.
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