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2903 Views 11 Replies 8 Participants Last post by Ronnie Pendergrass, Jul 6, 2005

Ronnie Pendergrass

Discussion Starter · Jul 4, 2005

After reading an article on the RL forums of a guy(clownhair) who swapped his pulley to a 3.25 and is making 14 psi steady after doing something called the "clowns vaccum mod". I have a few questions: What is "clown vaccum mod"?
If i get the 2.8 pulley, (FPH advertises 6lb increase over stock), would the SC be able to make 6 more lbs safely? I know the SC would make a lot mre heat, so could i use an injection kit to overcome this heat? If i did this "clown mod" would the SC be able to hold around 18psi steady? (i know that boost is relative to rpms, so max boost would be around 5k)

If the 2.8 wont work, what is the smallest pulley that I could/should be used?

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MY GTP 8 U

· #2 · Jul 4, 2005

NO NO NO NO NO. DO NOT GO THAT SMALL!!!! I would say the smallest you could go safely with alky injection is probably 3.0"

If you want to go to a 2.8, you're just asking for trouble by upping the boost that much. A 2.8 will require extensive PCM tuning and depending on how well the IC really does work, it might need alky injection as well. A header and full exhaust work will probably be mandatory to keep the exhaust from backing up and causing "boost stacking" which will give you serious knock retard. But do NOT go that small until its been proven what mods are needed to run such a small pulley safely. Let the pros at Modern or Gravana or any other shop be the ginuea pigs for that kinda stuff unless you got the money to buy another motor.

Just my $.02

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Ronnie Pendergrass

Discussion Starter · #3 · Jul 4, 2005

The guy on the RL forum used 3in i am ready to do something to the car, but no one really has anything yet, gravana has short shifters to preorder, tog is thinking of a group purchase on headers, no kn intake, no AEM, the onlything so far is water injection kits and filters. I was just wondering about the pulley sizes, do you know about the boost mod they are talking about?
I am definetly going header and exhaust intake as soon as some reputable names come out and see which onees performt he best.

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Raven322

· #4 · Jul 4, 2005

do not due the boost mod. not recommended. you might through a code. the smallest on stock ECM is 3.25" which is good for 2psi

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clownhair

· #5 · Jul 4, 2005

Boost mod will throw a code, sometimes it will shut your car off. It dosn't make more boost it just makes it longer. 3.25" is as small as you can go with no ECM upgrades. Want any more info just ask.

BTW I am in the process of just running the SC belt directly on the SC shaft, figure its onlt about 1" and should get 35 psi of boost

yeah I am joking, did you really need to scroll down here to figure it out?

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hitthecones

· #6 · Jul 4, 2005

You know guys, at some point you will achieve an operating frequency (from air in/out) that could correspond to a mode in the supercharger itself. This could blow it apart, and honestly, you could be getting close with a pulley that small. I really have no idea what the design natural frequency for the supercharger is, but I would be nervous as the first one to try this.

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Blue04RedLine

· #7 · Jul 4, 2005

hitthecones said:
You know guys, at some point you will achieve an operating frequency (from air in/out) that could correspond to a mode in the supercharger itself. This could blow it apart, and honestly, you could be getting close with a pulley that small. I really have no idea what the design natural frequency for the supercharger is, but I would be nervous as the first one to try this.

Listen to him, he's a pro.

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WopOnTour

· #8 · Jul 5, 2005

hitthecones said:
You know guys, at some point you will achieve an operating frequency (from air in/out) that could correspond to a mode in the supercharger itself. This could blow it apart, and honestly, you could be getting close with a pulley that small. I really have no idea what the design natural frequency for the supercharger is, but I would be nervous as the first one to try this.

HTC
Shouldnt the M62 supercharger be good to the Eaton published maximum RPM of 16000 RPM? Sure there might be a resonant frequency issue, but we may have already passed right through it at a lower RPM correct? (Since we dont really know what it is) Now I realize there is a HUGE issue getting the engine managment system to accept the additional boost produced by a pully induced RPM increase. (that would certainly need to be solved first- and as you know it's currently being worked on from a number of directions)

But the smallest pully SFPH offers for the M62 is currently a 2.8". With a crank pully diameter of 6.375" that would equate to 14,799 supercharger RPM at 6500 engine RPM. This represents 7.5% LESS than the maximum M62 speed which IMO leaves acceptable overhead for error. Wouldnt you agree?
Are you guys running the stock pully on your A-Xer??

Regards
WopOnTour

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hitthecones

· #9 · Jul 5, 2005

Yeah the pulley is stock on ours. It has to be to make the car legal for our race class. We did consider making the car an S Mod car, which would make the modification list nearly limitless. Then again, we would end up with a 350 hp front wheel drive car. That would be a little silly for autocrossing.

The reason I even brought this up is that I was speaking with another engineer regarding the LC3. He made a good point that there is a design frequency and if that operating frequency were to correspond to a resonant frequency then it could result in a less than pleasant effect. At GM, we like to call that "non-conforming."

That said, I've never seen the full specs on the LSJ blower. The operating RPM should indicate the maximum amount of air that can pass through, but it does not tell you if there are a bunch of modes before you hit that max RPM. I honestly have no idea what the modes are, and this is why I will let someone else mess with their engine first.

OK, so basically I'm giving no advice as to what to do with your engine. It's your stuff and your warranty and I want to part of that. But, it is always interesting to see what these companies come up with. I'll keep watching this stuff, but I really want no part in this. I'm sure you guys understand.

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Raven322

· #10 · Jul 6, 2005

my buddy out a smaller pulley on his GTP and from then on, he had nothing but problems, including the nose dive leaking

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SS4ME

· #11 · Jul 6, 2005

The people that want to mod should start small, always. Start with a good intake and maybe a nicely designed exhaust system, when available. These cars are pretty new with little support at the time. Give it 4 to 5 years and maybe GM or some other well known aftermarket supporter will have figured some so called safer modifacations that have been tried and tested.

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Ronnie Pendergrass

Discussion Starter · #12 · Jul 6, 2005

SS4ME said:
The people that want to mod should start small, always. Start with a good intake and maybe a nicely designed exhaust system, when available. These cars are pretty new with little support at the time. Give it 4 to 5 years and maybe GM or some other well known aftermarket supporter will have figured some so called safer modifacations that have been tried and tested.

4-5 years-----thats too long to wait. By that time one will have to mod there car just to keep up with the new models coming out. i.e. I have a 2001 Camaro SS (325 hp stock 305-320whp) I have spent nearly 10k on motor, trans, and rearend work (417 rwhp 11.86 @116 mph on DR), one can go and buy an 04 Cobra and not loose to me by much at all!!! soon i will have to spend another 10k just to keep my car up to par. Hopefully it doesnt take that long to come up with substantial mods for the car.

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