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First off, a big Thank you to whoever has been fixing my photo links. I should have fixed them but didn't realise till recently I can edit old posts.
Been a good summer so far and I have worked a number of issues out.
1. Been having on and off electrical problems, which turned out to be the 37 pin connector on my Megasquirt being a little wonky (worn out).
I shortened the wire harness to put less stress on the connector, which I will replace in the fall.
2. supercharger somehow ran low on oil. I noticed it was getting louder. After an oil refill it seems to work ok, except it's kinda loud. (ok, stinking loud) I will swap it out at some point.
3. I rewired the boost control solenoid, so it was not actually receiving power unless ETB2 was activated. This stops the boost control from working unless the supercharger is bypassed.
This works pretty good.
4. Waste gate fell off exhaust manifold after some extended track lapping (SC disconnected and running low boost). Used backing nuts which will help. This set up will not survive lapping for extended periods.
5. Turbo kept leaking oil into turbo inlet, so I changed the 10AN drain to a 3/4" drain. That has fixed it.
6. 90D oil inlet from 4AN line to turbo keeps failing (3x now). Finally modified the original heat shield to mount to frame rails, so hopefully that will solve that.
I gotta smile at the ton of attention and questions this car attracts at local events. It's proving to be competitive too, which is nice considering my driving has a way to go.
Here is a video from the weekend. Notice the last section where the car is taped by a spectator. The car sounds like a toy slot car or electric RC car.
Not exactly pleasing but certainly attention getting.
It hardly seems like an upgrade, when you replace a 10AN stainless braided hose that has nice anodized aluminum ends
with an EBAY rubber hose and hose clamps.Unfortunately, those nice aluminum ends had an ID of ~.375” and the hose was not much better. The rubber hose has a nice .75” inner diameter, and the elbows as supplied had an ID of ~.47”. I drilled them out to .55”, so have a pretty good flowing drain now.
I ended up remaking the stainless turbo shield.The turbo oil hose runs quite a bit cooler.
I found a few boost leaks, between the supercharger and turbo. I ended up siliconing the oval pipe as I couldn't get a clamp to do much.
I am planning on hitting the dyno late this coming week.It will be interesting to see how much top end power this thing actually puts down, considering the parasitic power drain the supercharger is taking. I estimate the supercharger is consuming about 25hp, assuming the below graph is somewhere close to reality. I am presuming there is a 1-2 psi drop in the piping, leading from the supercharger to the turbo. Yes, I am spinning the supercharger pretty hard and it’s probably not happy.I do think the supercharger will last, because above 5000 engine rpm,
the supercharger is seeing very little backpressure and moving a lot of air.Hopefully this will keep it cool.Time will tell. Not sure what is going on with boost control.I thought I had something that was working, but in reviewing my datalogs I see that it was not.Back to the drawing board..
Well, the dyno run has stalled. Old place I used to go to has gone out of business, and it seems no one else that I have contacted is really that interested in doing anything. I have made a few appointments, but they have all fallen through, when I call the day before to confirm. I did pop over to the drags(65miles away), but as luck would have it, we had rain (with nothing in the forecast).
I have managed to dial in the boost control. I ended up slowing down the control interval to 100mS, and limited the control duty to a limited range of 80-100%, with 100% being maximum boost. This is giving me a fairly steady boost control (+-3kpa or so).
Below is a redrawn EATON volumetric efficiency plot (sorry for the poor spelling), with some points plotted representing my install. I have never been able to correlate the EATON data to real world numbers. One thing that is nice with the twincharged setup, is that by adjusting the wastegate settings on the turbo, I can vary the amount of back pressure the supercharger is seeing (to some extent). This allows me to plot various rpm points at different backpressures(PR), without changing the drive pulleys.
I needed a starting point, which is the black dot. The EATON VE map, suggests that at 11,900SC rpm, .2psi boost, the SC should be moving 420CFM(typo, or 31.5lb/min. Looking at the Turbocharger map, at 22.8psi and the same engine RPM, I see 25.5lb/min. Quite a difference here, so I'm guessing my MP62 is not really at 99% VE at this point. But for this example, let's assume it is.
So to calculate these points, I have taken the manifold boost achieved at these various supercharger RPM's and backpressure points and divided it by the conditions taken at the black dot(22.8+14.7psi manifold pressure). I am assuming that the VE of the engine is relatively constant.
So here are the results. At low pressure ratios and high supercharger RPM's, the charger performs pretty close to the graph (yellow, pink and blue dots). At higher pressure ratios (brown=1.6PR) and lower RPM's the supercharger comes up way short of specifications. Now the flow at the inlet of this supercharger is horrible. There is quite a step between the throttle body and the SC, and at 2 points the SC inlet is quite a bit wider than the inlet pipe, and no effort was made to smooth this out.
So right now I have the SC out of the car, and am fixing this. I have taken the supercharger apart, and the rotors
case look good, but the SC oil is quite dirty.
We shall see if this mod makes any measurable difference in boost.
Seems like a lot of parts to remove, just to put in a stinking new clutch.
Old clutch was slipping, so I ordered a FM2 and a lighter flywheel. Should be here tomorrow.
Well, I got everything back together by the 21st, but then realized the clutch had to be broken in. FM's exact words are "drive like a granny for 2 tank fulls"
Since the clutch was extremely grabby I decided to follow that advise. (well almost)
6 days later, I was ready for taking a crack at improving my 1/4 trap/speed, but the weather did not co-operate.
Drags are now closed until spring. Did manage to datalog a couple of 5 gear allofit runs at 25psi. Here is the result in Virtual Dyno. Not exactly sure what the car weight was with just the turbo, but my earlier estimate was low.
The twincharged weight is correct which means the car is definitely heavy. Things look good, except above 6000 rpm, where it looks like I am down a bit on power.
What I believe is happening, is that the supercharger is seeing a few psi of backpressure at these rpm's, due to the restrictive piping I have between the SC and the turbo.
So one of the things I want to do, is throttle the supercharger back a bit at high RPM, where it’s really not doing anything, to see if that reduces it’s parasitic losses. I was told not to do this, because the supercharger will apparently overheat, however I don’t wish to entirely close the throttle body, and can do this progressively to not hurt anything.
Here is a plot of a 4th gear pull, and you can see the output temperature of the supercharger increase, and then drop, and then increase again. The full throttle pull itself is not affecting the temp much, however coasting down from 5000 rpm after the pull, increased the output temperature 45F in just 9 seconds.
The temperature did not get close to anything to be worried about though.Here is a plot of a 5th gear pull, where I put the clutch in after the run.
Temperatures during the pull were a little higher, but again, nothing to worry about. So I think the fact that I am running the supercharger without much backpressure at the higher rpm’s, is keeping the supercharger pretty happy.
Here is a much longer time sample, where I am doing some spirited driving at lower engine rpm’s, and the supercharger is doing a fair amount of work.
Over a period of time the supercharger output temp did get fairly high (and I doubt the accuracy at these high temps is very good with the GM sensor I am using).
So originally I was quite concerned about the outlet temps of the supercharger, considering how fast I am spinning it.
I am less concerned now, and plan on restricting the inlet slightly, to see if I experience better power.
This will require a trip to the dyno. If this helps, I plan on putting water injection on pre-super, which will be controlled by the Megasquirt.
Who knows, I may even be able to leave the SC connected when I track it.
Oh, and I am not liking the clutch much, but have a plan for that.
And this is a bit odd.
I was data logging launch control at a few RPM's and noticed something odd when I reviewed things.
In the graph below, note how at 2000 rpm both the manifold and supercharger output boost are in phase with each other, but the peak boost does not occur at the peak RPM
While at 3000 rpm, the manifold and supercharger output boost do not peak at exactly the same time, but this occurs closer to peak RPM.
and at 4000 rpm, the manifold boost reaches peak boost, just when the supercharger hits minimum boost. This occurs at peak RPM.
So I am wondering if MS2 is not capturing the timing of these signals correctly (I have noticed that boost control seems to be working counter intuitively at times) or
if this is just a function of resonance in the various pipes. Anyone else noticed this?
Been spending the last while improving throttle response, dialing in cold start and getting Accel enrichment where it needs to be.
I finally got around to running a test, to see what happens, when you spool the turbo with the supercharger, and then bypass the supercharger.
You would expect that the turbo would slow down, and boost to return to the normal amount of boost the turbo would be capable of, at that particular RPM.
That is what happened, but it took way longer than I was expecting.
I first tested the turbo with the supercharger bypass (ETB2) open and at 2900rpm, my turbo alone can produce 4.6PSI (after about 8 seconds of full throttle)
I then spooled the Turbo/super combination and then bypassed the supercharger again, so the turbo was running on it's own.
When I first bypassed the supercharger, the turbo was making 12.4psi (center of graph)
After 3 full seconds, it was down to 5.2psi. (too bad it doesn't stay spooled but this is what you would expect) Also, I got around to measuring the backpressure the supercharger is seeing from the small piping between the supercharger and the turbo.
I had to really neck down the effective pipe diameter, to clear the supercharger belt, and had calculated earlier that there would be ~2-3psi backpressure at 7000rpm.
I am actually measuring 4.6psi. Since the supercharger is not doing any useful work at this rpm, and this back pressure is taking power,
I tried reducing the throttle body opening to about 1/3 of full throttle. Since that reduced the air flow through the supercharger it reduced the back pressure to 0psi,
and did not seem to be making the supercharger any hotter which is good.
I need to figure out how to implement this, because if the supercharger is not bypassed, I want the supercharger throttle to be fully open,
otherwise I want the throttle partially closed above 5500rpm.
So after months of watching out for another supercharger, I got a low mileage unit for a good price.
I was thinking I would just swap over the rotor pack, but when I saw how good it looked, I decided to use the housing as well.
This meant making the same modifications as on the original unit. At least this way, I would have a complete spare unit.
New unit was very clean and looks to be very low miles The usual modifications were done I added an extra bolt with o-ring to the top of the snout assembly, so I could easily measure the oil level. No more running low on oil for me. (I hope) Here are the 2 supercharger rotor packs, with the recent acquisition on the left.The black magic marker line on the LHS gear, indicates the oil level that was in this most recently purchased supercharger.
This is the amount of oil that GM feels is good. Some suggest to use less oil, to reduce windage which should reduce oil temps.
I think I am going to start out safe and just use the GM amount.
Note the difference in the gears. Maybe GM was trying to lighten the assembly?I measured the gear lash between these 2 chargers, and found I couldn’t really measure anything on the new unit, while the old unit had about .015” of play, measured at the pulley outer edge.Just ordered a bunch of suspension parts.
Can’t think of any further modifications under the hood that make sense right now.
Oh, and Supermiata showed great customer service.
One item didn’t ship with the rest, and without a call from me, they aired it, so everything arrived at the same time. Nice.
Throttle Response
One other item I have not been particularly pleased with, is throttle response.
One would expect with a supercharger, that you would get nearly instant no to full boost response.
Well, not so much.
Here is what a typical response looks like, with about .4 seconds needed for supercharger boost to rise to maximum (less as RPM increases).
The .078 seconds, is the time it is taking for the electronic throttle to open, and the .312 seconds is the time for the boost to ramp up.
After a bit of analysis, (see attached excel file) I have come to realize that my intercooler and intake plumbing are much to blame for this.
My earlier setup, had a MP90 which was running high boost, so I needed a huge intercooler. I did measure the internal volume of it, and it is 7L.
I estimate the rest of the intake at 5L.
Regardless what I do, it’s going to take some time to pump up all this volume, considering my supercharger is just 1L per revolution (well, 1L per revolution under perfect conditions –less really).
Now I understand why most OEM’s use water/air intercoolers, and some members here, were such fans of un-throttled supercharger setups.
I think for autocross, I will use aggressive throttled settings.
The MS1 controlling the supercharger inlet throttle body, has a second map (normally for NOS setups) which I can control with a switch.
This means the setup will sound even more ridiculous during autocross.
08-28-2017, 11:08 PM
More teething issues
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