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Discussion Starter · #1 ·
I am considering a supercharger for my stock 302.
I am trying to dedcide between 5lb or 8- 10 lb unit. I don't know too much about them yet. Is the boost set by the pulleys or is changed other ways? Also what is a- trim and what does s trim mean?
 

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For a stock motor, your best to stay below 7 lbs of boost.

Yes you can control the boost with pulley size.

Anything ove 6lbs of boost on a stock motor will seriously compromise your reliability.

The Stim has a more efficient design and will allow you to produce more boost. However, I do not recommend the kit on a totally stock motor unless you drop the boost to 6psi.

A trim is a good starter kit, especially for the money. They are virtually bullet proof.

David
 

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Just Glad to be here - back to working on the car
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Dave,

Can you use a variable waste gate on automobile superchargers like we do on aircraft. I would like to have a boost range of say 3 to 7 pounds on a "built" 347 stroker using something like the Paxton "carb in a box" setup. I have worked on similar unit for Allison and RR Merlin engines. I have very little experience on other than pretty stock sixties stuff when it comes to cars.
 

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On a supercharger the compressor is run by pulleys off the front of the motor. Therefore boost is linear, according to the rpm of the engine. If you look at a graph of boost pressure vs rpm, that line theoretically will be perfectly straight.

Maximum boost can be changed by changing the size of the pulleys. But that just moves the boost line up or down in the rpm range. The basic line of boost will still be the same, it will just match a different rpm range. (Sounds confusing the way I write it.) Limiting top end boost by slowing down the compressor will also limit bottom end boost, and vice versa. Also, because it is run off a pulley, you will always have the same amount of boost at a given rpm, whether you need it or not.

If you want rapid onset of boost, with a fairly consistant pressure, you need a turbo. A turbo is run off of the exhaust gas flow, not a pulley. And there is a wastegate to dump pressure when it gets to the set limit. Bost is determined by need. When you crack the throttle, you get boost. At steady cruise, you don't.

My Harley Wide Glide has a turbo. I generally run 2-3 pounds of boost in a steady cruise; 0 psi when coasting down hill. When I bang the throttle open, it will jump to 12 psi. Turbo lag isn't enough to matter, but I can feel it.
 

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Just Glad to be here - back to working on the car
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Bob,

I understand the operation of the blower system, but what I'm asking is can we use a waste gate on a car like we use on airplanes.

The problem on planes is that as you go up you loose air density and the blower system is designed for maximum output at altitude. The waste gate serves to bleed off excess pressure so that at lower flight levels and on the ground you don't over boost the engine. The system is adjustable based on true air density to maintain a constant XX inches of manifold pressure at any altitude up to the service ceiling of the supercharger.

What I would like to do is set up the pully system to deliver 7 PSI and then adjust down from there with a waste gate so that I have the option of not always operating at max boost. This would in effect give me a variable horsepower range of say 350 to 500 on a properly built 347 stroker. I figure with the "carb in a box" setup this should be fairly easy as the carb must normally compensate for the build-up of boost as the engine revs to speed.

The turbo system might work the same but I have no practical experience with turbos. So that would be a whole new ballgame for me.

[ November 16, 2002, 05:41 PM: Message edited by: Rocket Scientist ]
 

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You could use a waste gate type of setup with the carbuerator box. I don't know why you would..but you could.

It wouldn't be practical on an EFI setup. You could do it, but you would have to use a blow through MAF and vent prior to the MAF. You could probably do it with DFI, but now we're way above and beyond the scope of stock anything.
 

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Just Glad to be here - back to working on the car
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I just figure that the more time I spend running at low boost the longer the engine will last, and I have the option of higher boost when I need it.

The idea of "dial some horsepower" just facinates me.
 

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Seems like you could over drive the blower so you would have good boost down low, then bleed it off when the rpms come up with an adjustable waste gate or blowoff valve. I would look into the aviation set up for design ideas. Has to be a very stout design to pass FAA standards.
 

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Stout and pricey, The only systems I know of are for large displacement engines like the RR Merlin from the P-51 and the Allisons from the P-38. Blower rates ran from 85 to 130 inches of manifold pressure across a 5.75" distribution duct. Many many CFM.
 

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Discussion Starter · #11 ·
The kit from Vortech offers a V-1A for about $1700. It says you can use stock fuel pump, injectors, and ignition. If you jump to the next kit at around $3100. You get ignition t-rex pump. If you have to upgrade these items and spend the extra money, then you might as well go for the extra kit??? Any opinions to this are appreicated.
 

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Bill, I have never seen a waste gated supercharger system. But I don't see why it would not work. Especially with a carb set up. The wastegate on a turbo is mounted in the feed line between the turbo and the engine inlet. I don't see why you could not buy a turbo wastegate and mount it in your feed line. They are usually adjustable, so that should not be a problem, either. Then you could use a bigger pulley, which would bring your boost up faster, and then maintain it at the set pressure. You'de also have plenty of boost left over for track days.

I don't see why it wouldn't work with EFI, either. I wonder why nobody else has done that? Like Paxton?
 

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Nobody's done it 'cause it's not necessary. It's a benefit vs. price thing. A guy on corral did it on an EFI setup with a blow through MAF. His whole reason for doing it was that he wanted the "Whoosh" that the blow off valves make.


The whole principle kind of wastes the whole idea of using a stock engine. You're already going to be into it for all the engineering and extra parts and odd stuff for a potential tuning nightmare.

All superchargers come with a variable boost controller - the gas pedal.

You'll find with a centerfugal supercharger that unless you mash the loud pedal it won't build any significant boost.

If you just wanta 'cause you hafta, then do it - but you're going to spend big bux trying to be Mad Max. Rent the video. $5.00 ;)

[ November 16, 2002, 06:56 PM: Message edited by: Ozona ]
 

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I've been running a Greddy "R" blowoff valve. It's adjustable and will "pop" if boost rises above a specific level (I've got mine set at around 12-14#s) The biggest problem with it, is that when it pops, boost drops like a rock until the spring pressure is able to close the valve.
I did it this was so I could spin my S-trim harder down low for added torque then bleed off the pressure at 6000rpm if I ever got stupid (sig below was with my S-Trim).
Now with the T-trim it's another ball game. I've pullied waaaay down until I learn the car and can afford a low impedence injector driver so 96# injectors can go in.
Thats the only option I've been able to find, outside some wildly expensive adjustable wastegates...
 

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Rocket Scientist,

The easiest way to control boost is with the pulleys, if you want to do the daily drive thing, put on your 5/6 lb pulley, when it is time to race throw on the 8/9 lb pulley, it only takes ten minutes to do a swap.

No one had mentioned Powerdyne, this is a great mid range blower, I have been running it for six years and it makes nice horsepower, powerdyne has 6,9,11,13lb pulleys, and it doesn't require an oil tap and they are pretty cheap.

They have double shielded ceramic ballbearings that are rated around 45-50 thousand rpms, although these are the guys that will go and if they do they are about $145 each and you will need two.

The throttle body plate allows the air to come in, so you don't get much boost until it is open, most recomendations are that you don't need a by-pass valve until you make over 9lbs of boost.

Centrifugal superchargers are very linear in their rate of boost, based on rpms, but roots style superchargers make upwards of 85-90% of their boost at low rpms and don't make much more after that, it could be still considered linear but not as noticeable as a centrifugal blower.
 

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The Traveler
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I have a lot of miles on my Powerdyne supercharger 9# boost. BUT I listened to David and Gordon about how to be sure my engine held together. Upgrade the fuel system as others above have noted if you are going over 6# boost. Upgrade the ignition system Crane or MSD with a timing retard. ARP bolts throughout also are a good idea.

When you have the supercharger working right it's an awesome feeling. Doing 60mph, just step down on the throttle and feel the car leap forward. It's as though you are sitting in a rocket, at any moment you could just nudge the throttle, lower the wings, and you are off! I got the chance to safely enjoy the urge on my trip to and from Calif. a couple of weeks ago. Feeling the car step out lively as the posted speed was 75 in in someplaces no one seemed to care. At about 2500 rpms it just felt like the car was loafing along at 110. Of course the fuel gauge now was more like a speed-o going in reverse!! No vibrations, car was very stable, just me and the exhaust sound "idling" through NM. and AZ.

I have ordered the extra pulleys from Powerdyne so I can raise the boost even more. This I expect will be my final undoing! The need for more power!!
 

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For most of us 99%+ of the time we are driving the engine is not working very hard at all. I think for most cars at 50-60 MPH it takes between 15 and 20 HP to keep things rolling. Under these conditions, the engine doesn't "know" it's supercharged or not. All it has to do is make"X" hp which is controlled by your foot. The percent of available power you use will be different, but I don't think the loads on the working parts are any different. When you ask for all the power is when the additional loads occur. So, you could do a waste gate on a supercharger, but to the point made by someone else, it isn't really necessary. IMHO
 

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Traveler, what pulley are you currently running?
I switched to a 9LB pulley about 4 years ago, and it gave a gob more torque. If you are going to this it is very fun. I have a stock bottom end with 30lb injectors, crane boost retard and 190 pump, with no problems.

Are you using the stock fmu. If so it will run very rich, and even slow the car down with the 9lb pulley, I got a fish tank bleeder valve $5.00 and it adjusts the fuel pressure perfectly, and it is a lot cheaper than the vortech adjustable fmu
 

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The Traveler
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I have a 255lpm in tank fuel pump, 30 # injectors, large diameter fuel lines, and as of right now a 9# boost pulley.

When I when to the supercharger I also went with a Crane cam that was designed for crank driven superchargers.

I also have a chip burnt for the car.

As Ed notes most of the time - 99% of it, the car just idles along. But when you want to pass some one hang on! You are GOING to pass them like they just dropped a boat anchor! And that's even at highway speeds of 60+.

The most fun was doing it on a uphill, in the mountains between NC and Tenn. on I40! I'm sorry I just couldn't resist doing it to a 4 cylinder rice burner with a BIG exhaust out the back and a wing hunging on the top of his trunk... lowered so that the sides of the car scraped the ground on turns! At 65+ going up over the Smokie Mountains, I close in on him and he steps down on the throttle. I could tell cause the engine sounds went way up... but he didn't really move much faster. I looked over at him, a little over the top of my sunglasses, and as I'm still looking at him, stepped down on the throttle, the brief look I had of him as I rocketed UP the mountain was his eyes opening WIDER! My hands never left the steering wheel, my car just took off. And I wasn't even pushing it hard!
 
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