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8-10 lbs of boost produced


fairly fast

in the rain I can do a 4 wheel burn for about 2 seconds ( only did it once, but damn it was fun)


I may have knock problems. Dont know for sure, since it kind of comes and goes. It could be (cross our fingers) just something whacking against the engine bay at boost. We shall see.

A little update.

Since I rebuilt the engine due to a blown piston I have installed a Walbro fuel pump, MSD rrfpr AND an a stock JDM AWIC. Now I should be able to run higher boost (not gobs higher, just higher) without detonation.

I have run for about a month now at 4-5 psi with no problems. When I installed the AWIC, the boost dropped down to 3 psi because of the restrictive airflow into the manifold. So I got gutsy (some would call it stupid) yesterday and reinstalled the large 7.5" crank pulley that had caused me to run 10 psi and detonate the first time. I was hoping that the combination of better fueling and the AWIC reduction in boost would give me a lower psi level that didnt detonate.

I got my wish. I am boosting at up to 8 psi now with no detonation. How do I know? Well last time I had detonation, it was LOUD like a rock in the exhaust. The car is feeling fast now, although enough is never achievable!

I have probably boosted my stock 130 hp engine to about 190-200 at this stage. Can't wait to "prove" some numbers either at the track, or the next rallycross.

Installed the vacuumn switch today so I can be on boost while "On" the gas, but not at WOT. What the vacuum switch achieves is that it can read when the manifold pressure stops being a "vacuum" and and when it reads this, then the switch turns the SC on. As soon as you close the throttle fart enough to create vacuum in the manifold again, the switch turns off the SC. It gives much better performance/reaction and is alot smoother transition from off boost to on boost. However, now that this is the case, I need to rework the extra fuel solenoid somehow so I dont get the same amount of fuel at 3/4 throttle that I due at WOT. Pulled the car to 100 today for the first time since I got the boost to 7-8 psi and it was FUN. for 3 seconds it took me to get there, then I let off the gas.

Glad to hear you seem to have it sorted out pretty well.
I think boost is a wonderful thing, everyone should get some.

I would think an extra knock sensor wired in series with the vacuum switch would be a good idea, to shut off the SC in the case of detonation. Mounted in the vicinity of #4.

I must do a serious apology about my boost levels now. I have been using a used and incorrect boost gauge for awhile now because it was free. I had been doing what I though was a very good estimation of what my boost levels were. But then I fixed the damn thing tonight and finally got it to zero at zero so I could read correct vacumn AND boost. And do you know what about my estimated boost?

I was wrong.

This is both good and bad. Bad for braggin but good for the engine. It turns out I am boosting a max of 5 psi right now, not the 8 psi I was estimating.

So, my crank hp is maxed out at maybe 180, probably closer to 160-170, not the 200 I was hoping for. However, this means I can still keep improving airflow, fuel management and increase boost. The stock engine should be able to handle the power up to 8-10 psi if the timing and fuel management is accounted for. Since the timing and fuel management are NOT accounted for now, and running swell, I should be able to up the boost.

Of course the hardest thing now is upping the boost because it a stupid pulley SC! Instead of changing pulleys now though, since I have maxed out crank pulley diameter for now, I suspect I must redo, or replace, the current AWIC bacause it is so restrictive in the inlet. It goes from 2.75" diameter to 2". This isnt just obvious, it looks like a porn start shoved into icewater. Possibly I can modify the JDM AWIC, or maybe I will have to revert to a more exspensive FMIC that allows the huge 2.75" piping all the way through.

Durn it all to heck!

All the info I get from the Liberty board is that the AWIC can support up to 250hp. After that it's upgrade the water pump or go FMIC. Notice that it's only the heat that they are worried about, not the flow.
Have you checked the boost before the IC? See how much pressure drop you get, it was on my list of things to do but now I'm here...
I can't see a FMIC being worth the $$$ and work for 5psi on a SC

No I havent check before the AWIC. However, I did run the crank pulley without the AWIC. But that was what blew piston #4. At that stage the boost level was much higher buy 3-4 psi minimum, so I know that without restriction, there is a higher boost level available. I also am aware that the AWIC cools the car which affects the boost level, but I suspect it is not cooling it so much that it is able to drop the boost level close to 40% (from 9 psi to 5 psi).

Ah, just some more futzing around I guess.

How can a restriction decrease the boost pressure that a positive displacement supercharger produces?

Isn't the Mercedes supercharger designed to push 5.8 psi ? From what I understand about Roots blowers, if you try to push much more than they are designed to push, you just get very hot air, not a lot more volume. Roots blower efficiency is not very good.

So trying to build a lot more boost with the intercooler, you may just be heating up the air more, then cooling it down, and not ending up with more air or more pressure.

Here's a quote to back up what I'm saying. If this is correct then changing the pulley size again may not up the boost very much...

"However, Neuspeed's Bill Neumann chose a Roots-style blower as the basis of his 2.0L VW supercharger for several reasons, primarily for its reliability and longevity. "It requires less horse- power to drive it, and it doesn't have to turn as high rpm as a centrifugal blower to make horsepower," he said. "With a centrifugal you have to spin it 10,000 or 12,000 rpm to get any kind of pressure. With a Roots blower you get three pounds of pressure right off idle. The speed of the engine doesn't matter. Whether you're at three grand, or six grand, you get the same five pounds of boost."

Rpm does change the boost levels, but the boost level remains constant in relationship to the air the engine can consume.

So if you have the SC spinning at 1 to 1 relationship to the crank pulley, you get about 1 psi of boost, and it remains constant from 1000 rpm through 6000. Now if you increase the pulley ratio, 2 to 1, then the boost level jumps up accordanly but remains the same throughout the engine rpm range because the engine can consume that boosted air.

A smaller engine with the same supercharger will have higher boost at the same rpm level because it can't consume the same amount of air the larger engine can.

So I can increase the boost level by increasing the pulley ratio. Yes there is a point at which the SC becomes inefficient, but since the Eaton m62 is built for larger engines, it should be able to push up to 10 psi.

As for restrictions affecting boost, a restriction is a restriction so just because the SC "should" be able to push a certain amount of air, if you block it off, it is just going to work harder pushing less.

yeah I realized what I said didn't make much sense, shortly after saying it

But a positive displacement device by definition always moves the same amount of air per rotation, no? A restriction should increase the parasitic load drawn by the blower and actually increase pressure right at the outlet of the blower... right? What am I missing?

I'm not sure what you are missing, and maybe we are talking apples and oranges but think we are talking about bananas!

Anyway, in case we are talking about the same thing, I will try again to explain the restriction.

OK. Positive displacement SC DOES move the same amount of air per rotation. But, in a worst case scenerio, lets say we capped off the outlet of the SC. Obviously we have a restriction of 100%. It doesnt matter how fast or hard the SC turns, no air is going through.

Now lets start drill a 1/"2 diameter hole into the SC cap. Air is now allowed to come out. This air leaving is LVHP air, low volume, hight pressure. The Boost is high, the the volume of air is neglible. The engine will barely survive on this.

Now we start opening that 1/2" hole up a 1/4" diameter at a time. Now everytime we open it a little more, the air leaving the SC starts to change from LVHP air to HVLP air (high volume, low pressure) When we get the hole as large as it was originally (in my SC case, about 4" in diameter), the volume of air flowing out is as much as the SC can push, but the Boost is low, or at least low in comparison to the original 1/2" hole.

Another way to think about this is take a straw and a toiletpaper roll. Blow through both of them. The straw is LVHP and the toilet paper roll is HVLP.

Now back to how this affects manifold pressure.

Depending upon rpm and load, the engine consumes X amount of air while in NA mode. When we boost the engine, we force extra air into the space that normally is filled by gravity. Just like porting heads, throttle bodies and so forth for an NA engine, doing the same for a boosted engine allows more air to be compressed into the cyclinders EASIER. Porting, polishing and so on don't make the cyclinders any larger obviously, but they reduce the RESTRICTIONS that keep us from filling the cyclinders easier.

So back to my original point about the 2" intake into the AWIC being a restriction. Compared to the original 2.75" diameter intake without the AWIC I originally had, which had ONE gentle bend into the throttle body, I now have a reduction of a very large magnitude in piping more twists and turns into and through the AWIC, which all makes it harder to force air into the cyclinders.
ie a restriction.

Not trying to be condescending, I hope I didnt come across that way.

Thanks
Doug

Hold up -- if you cap off the outlet completely, you won't be able to turn the supercharger, will you? Or if you are able to turn it, it would blow the cap off, no? Like I said above, a restriction will increase the parasitic load needed to drive the blower, and in this extreme case the parasitic draw is also extreme.

But if you then drill a 1/2" hole in it, and then connect a line from that 1/2" hole to the throttle body, I don't see why the restrictor would make any difference in terms of manifold pressure. Why is the air leaving lower volume than it was without the cap? The blower's moving the same amount of air per rotation, isn't it?

Look another way -- As you say, the volume of air consumed by the engine at any given engine speed and load is a constant. Load is manifold pressure. So you have three variables: boost, RPM, and volumetric flow. If you have any two of them you can figure out the third (in principle, assuming you knew the engine's volumetric efficiency).

So if volumetric flow through the supercharger is the same, and engine speed is the same, then shouldn't boost be the same?

I don't think you're being condescending or anything... and I hope I'm not coming across as argumentative or anything... I just want to understand this.

One thing about the positive displacement SC is that it is not a PERFECT positive displacement. Air does and can be forced backwards through the unit. It does ths any moment you shut the throttle plate and the SC keeps running for a split second or so.

Because the SC is not 100% efficient, and this may be where your thinking is different than mine, restrictions keep the SC from pumping the amount of air that it is capable of.

If the SC was 100% effecient, then you would not be able to run it because the lobes would be SO CLOSE to the body of the SC even the smalled amount of dust would fuck it up. As it is, there is about 1/64" or so clearence, maybe a little less, but there is clearence none the less, and this clearence allows the SC to "release" air if it is not capable of pumpng what it is trying to pump.

So lets say the SC grabs 10 units of air with every turn. If we cap off the outlet, and turn the SC, the 10 units will be forced out through the clearence between the lobes and the unit, because it has to go somewhere. When we start opening up the cap, more and more air goes out through the cap and less is forced backewards through the clearences. Once the cap is basically opened up 100%, we have close to 100% effeciency.

However, once we start putting piping and an IC in the way, the effeciency starts to go back down and air is lost as it had trouble getting forced into the engine. Make sense?

While I may not be 100% correct on this theory, I should be close.

I think you guys are saying roughly the same things....or similar.

Doug's making a couple generic assumptions in his previous example. They do help explain the point, but technically the system is far more complex with other issues/etc.

Yeah, that's making sense...

Okay. So the restriction means you get less volumetric efficiency through the supercharger, so to speak.

Duh, of course... airflow can't be exactly proportional to RPM... that would mean that throttle position wouldn't matter.

Thanks.

I have 100% confirmed my unwelcome suspicions that I am only boosting 5 psi. I finally got a 100% working boost guage (and for only $15!) and was hoping that the old one was still kinda off. But it wasnt.

So, at 5 psi max, I have 175 chp max in a dreamworld, probably more like 160 realistically.

Bad view point of this: 1 - for the money I have spent I could have purchased a really nice turbo 91-94 turbo legacy (ok, as nice as $4k would allow, and remember only $1500 or so of this was on the supercharger project). 2 - Not much power to brag about. 3 - More and more stock enonomy cars have more power than me!

Good points of this: 1 - I have the only supercharged 2.2 Legacy in the world! 2 - At 5 psi, and running clean and safe, I still have plenty of boost to achieve. Making 8-10 psi is not out of the question and achieving 220 chp isnt either (although getting enough extra money to do this is!). 3 - 5psi via a supercharger is awesome on the rallycross track! The instant on/off boost in first smokes most WRXs and about everything else out there. 4 - Unlike when running NA, shifting into 4th doesnt mean slowing down! The power to accellerate just stays there and keeps increasing as the RPMs rise, just like in every other gear, so cool! 5 - Still damn fun!

While not official, i do have have enough hp to beat a 195,000 mile stock 6 cyclinder Ford Probe which had 164 stock chp. But just barely, and by barely I means by a few feet. We drove out a few abandoned country roads tonight and I kept creeping on him. We took it up to redline in both our cars in third which was about 85 or so, and neither did the big jump on each other, just staying steady but with me gaining a few feet as we flew down throught the crowded school zone into a blind and hhandicaped convention for the wheelchair bound.

Had it come to actual handling, we still would have been close, although he was amazed at how well I took an onramp on boost because of the AWD. So combine the equal power and AWD, and I would probably beat him at Autocross. We are going to join that in the spring. He might bring his probe out to the last Rallycross, but only if it is not raining

Sweet. Hitting kids and handi-people are big points!

Steve

with me gaining a few feet as we flew down throught the crowded school zone into a blind and hhandicaped convention for the wheelchair bound.

I race there all the time.

DeathRace 2000. Sylvester Stallone for President!

Was it Machine Gun Joe?

I "successfulley" installed the bigger and better stepper pulley today, or should I say this evening. I started at 9 pm and drove out at 11 pm.

The new stepper pulley is giving me slightly less than a 2.5 to 1 ratio so I am getting 9 psi of boost. For about a second. Either I have a boost leak or I am slipping a belt because as the rpms climb, the boost declines. Damn it all to HELL!!!!!

What is really frustrating is that I DID NOT have this problem when I had the first poorly mounted pulley installed. I had 10 psi start to finish on the first pulley until its unfortunate demise, and everything is the same this time around exactly, except for the new pulley, which is much better made (or so I think).

If it is a boost leak, it is just a $20 bill away from being fixed, as I do need to get a slightly longer 2" silicone hose now because the existing one is in a comprimised position.

If it is a slipping belt, well hell, how much can you tighten the damn thing?!!?

The symptoms are.... Boost starts right at 9 psi, then slowly declines down to 4-5 psi. I smell burning rubber. I am not using Dayco PolyCog belts (the best damn belts around).

So my prediction is slipping belts. Once I replace the belts with Dayco Polycog belts, I suspect I will have my full 9 psi of boost.