Perhaps I dont understand fully, what exactly would be the purpose? You have a set boost with a Supercharged motor, only changed by pulley size... Doesn't change like a turbo gauge does... Only purpose would be to know what PSI you are running at with that pulley? I was thinking about putting one in until someone pointed that out to me
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09:16 PM
freshfiero Member
Posts: 1150 From: jackson, Mi USA Registered: Nov 2003
to be very honest I just happen to ride in a lady from works 93 ssei and I noticed it had a boost gauge, and when she would get on it a little the gauge would spring! -gary-
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09:29 PM
The Fieromaster Member
Posts: 4124 From: Painesville, Ohio USA Registered: Jun 2001
The rotors on the supercharger are less efficient at low RPM. So they wont build much boost... in theory a Positive Displacement Pump or PD pump (what a charger is) should build the SAME pressure across its RPM band as it surpasses the CFM requirements of a motor by a certain percentage. So you should see boost at idle!! Although low rpm air escapes past the rotors and STOCK 3800 engines have a boost bypass valve so that the charger is only being used when needed!! This increases life and quiets down the blower.
------------------ "Raced That, Wrecked Better"~In Memory Of Jesse Cesek~ 1980-2000 US Armored Cavalry - Fox 2/81 - Death By 120 - 1 Shot 1 Kill 3800 SuperCharged Series II Swap, ZZP Intercooler, Fastback Swap
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09:33 PM
AaronZ34 Member
Posts: 2322 From: Colorado Springs, CO Registered: Oct 2004
The rotors on the supercharger are less efficient at low RPM. So they wont build much boost...
This isn't because the rotors/blower is innefficient, this is because at low RPM, low throttle the throttle plate is so close to closed that there is not enough air for the blower to compress. Basically the engine is taking in all the air it gets through the throttle body, and there isn't enough for the blower to compress. The main reason in addition to the first is that at low RPM, the blower isn't spinning very fast. This all leads to basically vacuum, and theoretically should make less power than a L36 as the blower is a restriction and compression is low. If the blower made boost all the time, your gas mileage would never be above 5mpg.
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in theory a Positive Displacement Pump or PD pump (what a charger is) should build the SAME pressure across its RPM band as it surpasses the CFM requirements of a motor by a certain percentage.
In theory yes, but this rarely ever happens. Superchargers lag as well, it is just not very much and it builds boost VERY quickly. But by definition they do lag, and they do "spool up" as RPM increase. Here is a boost chart off of a Ford SVT Cobra Mustang, 4.6l DOHC V8 M112 supercharged. The other compressors are a Kenne Bell 2.2l, a Vortech centrifugal compressor, and a turbocharger. All were properly sized and tuned for the application. The boost is pretty linear, but I wouldn't say the same. As you can see it goes from 12psi at 2500rpm, to a max of 14psi from 3800-5200rpm, then falls off to 11.5psi at 6500. So not much variance, but enough to make it worth mentioning.
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So you should see boost at idle!! Although low rpm air escapes past the rotors and STOCK 3800 engines have a boost bypass valve so that the charger is only being used when needed!! This increases life and quiets down the blower.
This is wrong, you should never see boost at idle on any roots, turbo, or centrifugal setup (Besides a diesel...lol). Low RPM air doesn't escape past the rotors at all. Even at low RPM, when you punch it, the blower moves more air than the engine can injest and it will make boost. In addition, I'm almost positive the L67 DOES NOT have a bypass valve. Bypass valves are all but useless on a roots supercharger, as the M90 is. The reasoning is that the Eaton superchargers are air pumps, not internal compressing units. Thus if there isn't a lot of air and the blades aren't spinning fast, it will just move the air without pressurizing it. This is in contrary to a Lysholm twin screw, where the air is physically pressurized inside the case. It doesn't matter how much air, or how little is pulled through, it is always pressurizing it. Thus a Whipple or Kenne Bell supercharger is the only compressor that makes boost all the time, any RPM, any throttle percentage. At idle some of these will make boost, but most will not as even though they will compress the air, there simply isn't enough to make noticable boost levels because the rotors do of course "leak." However I have seen twin screw blowers exceed atmospheric pressure levels at idle.
Therefore the compressor is being used all the time, in ALL SETUPS. Even bypassed setups still use the blower, it just spins and doesn't do much but compress minute amounts of air and make a very sweet noise. However on a roots system, the charger is being used all the time. Now used for physically boosting the engine it is on, it probably only does this 25-30% of the time the motor is running, but it is always moving air and giving the motor a much needed airflow increase at low RPMs and throttle inputs (less vacuum, but not yet boost).
------------------ "all pushrod motor are better than the dohc because it has less rotational mass" -rick17, MyMonte member, owner of a 3100 Monte Carlo LS
Boost can change by other mods to make the engine more efficient, the pulley will change the amount of air moved, but its not the only thing that determines boost, which is essentially the backing up of air.
THe L67 has a version of a bypass valve built in.
I have an A-pillar mount for a boost gauge. Others, as mentioned, have used the sunbird tach with mod for V6 for boost guage.
However, fact remains it does very little for an Eaton supercharger, as you proved. In fact, depending on how it operates, it could even even hirt part throttle torque. If you are at part throttle, and it is still open, you will not be making as much power as if it was closed. But having it open would give better gas mileage. This is a good strategory for a factory car where mileage is of so much importance and performance comes second, but when you need the performance it is there. On a Whipple, without a bypass valve you get the loud blower all the time (Which sounds REALLY MEAN, but annoying after time I bet), you also get decreased supercharger life, decreased mileage, etc. It is a critical piece on a Lysholm supercharger IMHO.
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02:08 AM
RCR Member
Posts: 4416 From: Shelby Twp Mi Registered: Sep 2002
This is the one I mentioned above... If you want to keep a more stock look. Some people have just blacked out the TURBO and made calibrations for it to work with the supercharger...
Here is one of these in Skitime's car...
[This message has been edited by Songman (edited 01-26-2006).]
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12:48 PM
PFF
System Bot
Silicoan86 Member
Posts: 1614 From: Savage, MN, USA Registered: May 2004
Perhaps I dont understand fully, what exactly would be the purpose? You have a set boost with a Supercharged motor, only changed by pulley size... Doesn't change like a turbo gauge does... Only purpose would be to know what PSI you are running at with that pulley? I was thinking about putting one in until someone pointed that out to me
Test drive a factory 3800/SC with a boost gauge in the dash. It moves - lets you know how much extra gas you're wasting by getting on the throttle too much
[This message has been edited by FieroGT42 (edited 01-26-2006).]
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08:51 PM
Deabionni Member
Posts: 4088 From: Kalkaska, MI Registered: Mar 2004
Test drive a factory 3800/SC with a boost gauge in the dash. It moves - lets you know how much extra gas you're wasting by getting on the throttle too much
I've never driven one... I didnt realize they moved, just going by what I heard in the fiero chat one night... but a factory 3800SC also has a boost bypass valve, mine doesnt
[This message has been edited by Nebiros88 (edited 01-26-2006).]
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10:18 PM
FastFieros Member
Posts: 2698 From: Dallas Texas USA Registered: Nov 2000
I've never driven one... I didnt realize they moved, just going by what I heard in the fiero chat one night... but a factory 3800SC also has a boost bypass valve, mine doesnt
Boost meters move all over the place.
I have the AutoMeter -30 HG to +30 PSI... in my GTP. The GTP also has the DIC with the digital version boost meter.
0 at idle for the most part..tiny bit minus.. Gentle throttle, DIC shows one bar, and AutoMeter about 4 PSI. Then 50% throttle is about 50% on DIC, and 8PSI. WOT is full bars on DIC, 12PSI. Chop the throttle all at once and about -10hg.. I am only running a 3.4 pulley. I do have a NIC cam, 72mm throttle body, and TOG headers. Runs good for a 3700 pound car. Wish it was all in a Fiero, but, I have 2 kids to haul around.
The boost dump delete works if you remove it on 90% of L67's. I have read some GTP guys have problems. I just dont see the problems they do for some reason on my GTP, nor the Fieros I remove the boost dumper from. Eaton had the article I placed on my website, and it works for me. The supercharger sings a nice whine all the time. I love it. When I get a LS1 installed to a Fiero, you can be assured it will have a supercharger sitting on top of it as soon as I can afford one. Right now , I have 3 LS1 engines, and no SC's
Loyde, you ever consider putting 2 LS1's into a Fiero? One in the front like boomtastic's car and one in the back? 700 hp AWD Fiero!
Also, you're going to give me the third LS1 for giving you that idea! Right? ....Right?
I remember someone was going to put 2 engines in the back of the Fiero and have one drive one wheel, and the other drive the other wheel. Maybe I can try that. Then I will have 16 cylinders. I can be W-FastFieros ... Do you get it? Two V V sitting side by side making the W... Ok, I better stick to working on engines and not joke making..
Anyway, that 3rd one? Humm, I bet I have a customer paying on a LS1 with a EcoTec 5 speed GETRAG with LSD to be installed to a nice 88 GT. Hopefully he will have the funds completed by March 1, and I can start that project.
