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Old 04-18-2015, 04:47 PM   #1
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Default JRSC High IATs and High Boost

Hi All,
I just started tuning my new DIYPNP and two things immediately jumped out at me in the logs:
-hitting 8psi by 4k rpms
-IATs are getting up to around 240F

Notes: Intake is pulled from under a gutted headlight (i.e. not from right above the header as in a normal JRSC install). GM IAT sensor calibrated per DIYAUTOTUNE's numbers here. No crank pulley overlay or downsized blower pulley (standard 72.5mm 1.6L pulley).

Sample screenshot of log attached. The car runs quite well. I was expecting maybe 6psi of boost and maybe 175F IATs, so needless to say I'm concerned. Anyone have a theory to explain one/both observations? Maybe a plugged cat? Any other guesses?
Attached Thumbnails
JRSC High IATs and High Boost-screen-shot-2015-04-18-10.47.27-am.png  
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Old 04-18-2015, 05:09 PM   #2
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The m45 will do that, have a few burn scars on my arm from touching the charge pipe before the IC
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Old 04-19-2015, 08:48 PM   #3
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That may be, but there seems to be very little evidence of people experiencing IATs this high and almost no evidence of people making that much more boost than "stock" for a JRSC. I'm inclined to figure out why my car is different, hopefully without just throwing $$ parts at it (new cat) or just masking a problem (e.g. intercooler).

It seems probable that the heat and the extra boost are related. The two explanations I can think of are:
-Substantial exhaust backpressure (e.g. clogged cat): Extra pressure->extra heat. An inlet/outlet temp test seems to be the only test that's viable for me to perform (short of buying a new cat on theory).
-Out-of-spec rotor clearances (e.g. rotors scraping against each other or s/c housing): Extra heat->extra pressure. Could open 'er up for a visual.
-Bad sensor readings: I'll continue logging and confirm previous findings. A bad ECU ground seems like the only explanation for the MAP readings being off.

I'd have expected to first notice either of those first two through drivability or sound symptoms, but maybe I just don't have a good baseline (this is the only Miata I've ever driven).

If anyone has other theories, or other ways to test/things to look for to identify the problem, I'm all ears!

Thanks!
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Old 04-20-2015, 07:33 AM   #4
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Perhaps a timing belt w a tooth off ?
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Old 04-20-2015, 08:02 AM   #5
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Quote:
Originally Posted by HHammerly View Post
Perhaps a timing belt w a tooth off ?
^That could do it.

Tiny stock exhaust could do it. Clogged cat could do it.

Is the exhaust mani shielded from the blower body? It should be. Excess heat can cause distortion of the blower case which can destroy the guts of it.

Are you using an intercooler? You should. Roots style blowers typically make much more heat than turbos at the same pressure.
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Old 04-20-2015, 09:35 AM   #6
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Are intake temps gradually climbing in boost or are they pretty constantly that high (even when the car is cool)? I had a loose connection on my IAT sensor and it would read something around that. Intercooler seems like it'd fix both your problems, even though I know it's not exactly the answer you were looking for.
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Old 04-21-2015, 01:15 AM   #7
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Appreciate everybody's input!

Quote:
Perhaps a timing belt w a tooth off ?
Timing belt is an interesting theory, never would've come up with that one. PITA to check, but good idea.

Quote:
Is the exhaust mani shielded from the blower body? It should be. Excess heat can cause distortion of the blower case which can destroy the guts of it.
There is no blanket/wrap on the header, and no OEM header heat shield (if it had one at some point).

Quote:
Are intake temps gradually climbing in boost or are they pretty constantly that high (even when the car is cool)?
It looks like in this case it took about 20 minutes for the IAT baseline temp to stabilize. On this particular (60-70F) day, that baseline temp was ~140F when just cruising out of boost. IATs rose sharply from there, whenever boost was present. Attached are a couple more screenshots of the log at a couple different timescales (boost & IAT).

Quote:
Are you using an intercooler? You should.
I'm not opposed to installing an intercooler (or, more likely, water injection for throttle response reasons). But if there's a problem that should be addressed I want to find it before I mask the symptoms.

I'm thinking I'll start by:
-cracking open the supercharger for a visual
-testing temps before and after the cat, maybe yank it for a look if the hardware holds up
Attached Thumbnails
JRSC High IATs and High Boost-screen-shot-2015-04-20-4.47.01-pm.png   JRSC High IATs and High Boost-screen-shot-2015-04-20-4.47.56-pm.png  
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Old 04-21-2015, 12:58 PM   #8
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Sheet aluminum heat shield would be where I would start.
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Old 04-22-2015, 01:12 AM   #9
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Doesn't sound too far off on the temps to me. My MP62 was hitting something around 240F on hot summer days and long pulls on the highway until I installed an intercooler.

An intercooler may make your idle a little trickier to tune/stabilize, but it's doable. Else, pick up a water/meth injection kit instead of an intercooler.

I tried both options together and independently, and personally preferred just the water/meth injection since I don't daily drive or track my car.
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Old 04-29-2015, 01:22 AM   #10
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Thanks for the input, you might be right. Pulled the cat today (breaking most of the studs in the process, of course), looked pretty good.
Current plan from here:
-pull supercharger outlet and look for abnormal wear
-TDR header blanket
-give up, call it normal, and install water injection (despite daily)

Still open to input/suggestions/theories, though!
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Old 04-29-2015, 01:35 AM   #11
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I just finished tuning a buddy's car (JRSC, 8psi with different pulley, MSPNP2). We were seeing about 110F over ambient at redline for a 3rd gear pull (about 120f at idle and 170-180F at peak under load). Something is up with you car, I can't say what. I have his car running quite conservatively at 14 degrees of timing at redline and an AFR of 11:1. I will note that his car has more or less a completely rebuilt and refreshed JRSC, and he is using a TDR blanket.
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Old 04-29-2015, 01:46 AM   #12
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Quote:
Originally Posted by thehellodonkey View Post

Still open to input/suggestions/theories, though!
go turbo
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Old 04-29-2015, 10:33 AM   #13
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Where is your a it sensor located?
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Old 04-29-2015, 09:05 PM   #14
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Quote:
Originally Posted by albumleaf View Post
I just finished tuning a buddy's car (JRSC, 8psi with different pulley, MSPNP2). We were seeing about 110F over ambient at redline for a 3rd gear pull (about 120f at idle and 170-180F at peak under load). Something is up with you car, I can't say what. I have his car running quite conservatively at 14 degrees of timing at redline and an AFR of 11:1. I will note that his car has more or less a completely rebuilt and refreshed JRSC, and he is using a TDR blanket.
That doesn't seem too off to be honest. I tuned a NA8 with a old JRSC @ 4psi and saw nearly 150F doing third gear pulls with similar timing and the same AFR target. Once he got a small intercooler I was seeing around 120-130F and it made a solid 155WHP on a dynojet at 4psi. These old blowers run REALLY hot, I'd see a major difference in power output between two back to back pulls on the dyno.
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Old 04-30-2015, 09:38 AM   #15
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Roots type positive displacement blowers have always required a great deal of energy to operate and much of the energy is converted to waste heat. It is inherent in their design.

But your setup has other issues. The shielding should help some.

What timing are you running in boost?
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Old 06-23-2015, 10:37 AM   #16
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Sorry for the late response, I must've missed the memo.

Quote:
Where is your a it sensor located?
It's threaded into the dummy throttle body, so I was concerned about heat soak. The quick IAT dropoff transitioning out of boost makes me think that it's not an issue, though.

Quote:
What timing are you running in boost?
Using timing map from the DIYAutoTune 90-93 basemap. Screenshot attached.

Yanked the supercharger outlet cover; things looked great in there. The TDR blanket has arrived and will go on in the coming days. We'll see how much it helps...
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Old 06-23-2015, 12:33 PM   #17
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The 240 F does not surprise me. With the observed boost (assuming amb. pressure of 14.7 PSI absolute, temp of 90F) and a thermal eff. of 55% for the Gen 3 roots, my calcs say you will have an IAT of ~290F. I am drawing from memory here, so I could be off a bit.

I noodled on this a touch, and at first wasn't in the reversion camp, but now I think that is a great place to start. You already have the CAT off, so I would suggest you take it for a drive (away from people if possible) and see if that drops your manifold pressure. As a point of reference, the magniflow hi-flow cat on my setup reduces the observed manifold pressure by as much as 1 psi over the stock CAT.

Remember that the SC flow is based on a fixed swept volume. It is almost impossible for the SC to deliver more air than expected. Furthermore, SC efficiency is inversely proportional to the outlet pressure. This being the case I think the best place to start is on the engine side. Specifically look into elements that will effectively reduce the engine volumetric efficiency, and in-turn reduce the air ingested for a given RPM. The exhaust is the easiest place to start. The next "phase" would be getting into the valve-train and valve timing, which is going a bit deeper.

You should actually already have a measurement of the engine VE with your autotune. While the autotune VE number is not usually very accurate due to other interacting factors, it could provide insight into an issue from a relative standpoint. Feel free to post the VEs if you would like us to consider them.
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Old 06-23-2015, 03:09 PM   #18
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You are seriously just chasing a ghost looking for a cause to the high temps. What you are seeing isn't anything abnormal for that type of setup, it's just that most people with the same setup just set it and forget it and never worry unless something breaks. That's why you don't see too many people with superchargers posting about their high temps...they could care less if it's at 100F or 300F, so long as it runs.
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Old 06-23-2015, 03:38 PM   #19
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To be clear, it is the 8psi out of a stock JRSC setup that has me interested. The 240F is expected.
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Old 06-23-2015, 04:28 PM   #20
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The 8psig is because the air temp is 240F. If the air temp was cold like when JR tested it in their factory, you'd pull the same lower pressures.
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