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Discussion Starter #1
I've been trying to decide what would be better and easier to install on a carbureted 460. I hadn't considered a Vortech or Paxton until recently, when I saw that Vortech has a kit for carb'd sbc's. After that I've been weighing things like cost, ease of install, driveability, etc. of installing either an 8-71 blower or Vortech. What I'm aiming for is a torque-monster, 600+ lb/ft of torque at 2500rpm, probably around 450hp with an RV cam and stock heats (probably buy Edelbrock heads someday). According to some reasearch I've done and playing around with Desktop Dyno 2000, both the roots and Vortech should be able to deliver that kind of power with around 8psi of boost. Here's what I've come up with so far:

The 8-71 install would cost around $3000. Installation would require hood modifications (which looks cool, but requires work), but other than that would basically be like installing a new intake and a different crank pulley. I think I would need a vacuum pump for the power brakes and accessories (correct me if I'm wrong). This would definitely make good boost at low RPMs, and ultimately would produce the power results I'm looking for.

Cost of installing the Paxton would probably be around $2000. Installing it would require fabrication of brackets (not a big deal). I would probably run a cogged belt, but getting a crank pulley for a big-block ford might be a problem. Hood clearance would not be an issue, meaning it would be somewhat of a sleeper, which is cool. Again, I would need a vacuum motor for my power brakes and such. Since the entire carburetor is pressurized, I don't know what would have to be done about fuel feed. I believe I would need to get an electric fuel pump to supply the carb with greater pressure than there is boost, meaning at least 10psi of fuel pressure. I'm not sure how well it would feed a big-block, but since I'm looking at a redline around 5000-5000rpm, I should be able to run slightly smaller pullies than normal to get better boost out of it. According to Dyno2000, it would produce just as much power as the 8-71, even though it's actually not making as much boost. This is probably because of the theory that roots superchargers heat the air more than centrifugal superchargers, but I'm not sure how true that holds in the real world.

Sorry for the HUGE post, but this has been something I've been thinking a lot on recently, and I figured that at least a few of you guys might have some input on this topic.
 

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Hmmm, you've done some interesting research so far. I'd love to hear that the guys here think. I'd love to go to a paxton ot vortec durring my next fit of insanity
. (assuming of cours it coensides with that rare instance of actually having 2K$ sitting arround.
 

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A centrifugal supercharger makes more boost as RPM rises and really doesn't make any at low 2500RPMs like you want but a good 6-71 will give boost RIGHT NOW! Powerdyne belt drive makes very good low speed boost though.
 

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You'll need one seriously HUGE centrifugal blower give a 460 much boost. Most of those Paxtons/Vortechs are sized for 302's. They DO offer racing units, which will be about the right size for you engine, but the cost goes right up to what you're paying for the 6-71... if not more. If you went with a cogged belt on a centrifugal blower, you'd need a blowoff valve in the piping. Cogged belts are really hard on those blowers.

Regardless of which blower you go with, Detonation is a REAL problem. You'll want a boost retard. These ignitions plug a sensor in the manifold that hooks up to the ignition box to retard the timing as boost increases. They use a cockpit mounted dial that adjusts the amount the amount of timing that is retarded for each pound of boost. It's a really slick setup, and pretty much mandatory for any street driven blower car. MSD sells one based on their MSD6A. It's called the MSD 6BTM. (Boost Timing Master) They might have one based on their Digital 6 box by now as well...

Carburetors can be specially built for blower applications. I'm not sure of all the details, but there are modifications that need to be looked into if you want to really do it right. I would think it would be easier to set up a carb as a "draw through" unit (6-71 setup) than a "blow through" (centrifugal).

Do your research.


Good Luck!

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<font size=-1>[ This Message was edited by: n2omike on 1/6/02 9:01pm ]</font>
 

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Discussion Starter #5
I thought the same thing about Vortechs not making any power at less than 3000rpm, but Dyno2000 seems to think otherwise, so that's what I'd ultimately like to find out. Also, the centrifugal superchargers I'm looking at (the V2-S trim for instance) say they are capable of making over 18psi of boost and flowing over 1000cfm (granted, not at the same time, lol). A 460 turning 5000rpm with 100% volumetric efficiency will only consume 665cfm, and most likely with only 6-8psi of boost I'd never see 100% VE.

Both you guys mentioned 6-71 blowers, do you think they would better fit my application than an 8-71? From what I've seen the 6-71s are a little cheaper and easier to get ahold of, but I thought they were better suited for small block applications.

I'd thought about the timing retard boxes, but I didn't know if they were really a necessity? I guess when you install a Vortech on a newer stang or something, the computer probably retards the timing on it's own, but I thought I'd just need to recurve the distributor and get rid of the vacuum advance. One thing I was wondering about, on a roots blower, you still have vacuum at the base of the carburetor, but is there too much vacuum to run your brakes and accessories off of?

Thanks for the input guys


edit: typos
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<font size=-1>[ This Message was edited by: Motorhead on 1/7/02 2:04am ]</font>
 

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I hava Procharger D3R planning on fitting to a mildly built 460, any tips or tricks that you have found before I start spending money in places that I don't need to? Any advise you have will be greatfully appreciated.
thx anthony
 

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(the V2-S trim for instance) say they are capable of making over 18psi of boost and flowing over 1000cfm (granted, not at the same time, lol).


You would have to spin the hell out of a s-trim to see any boost, again there great for 302's but not for a 460.

If they have a bolt on kit like a 8-71 it will be far cheaper and less headaches than trying to mount a centri and making it all work
 

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I can't contribute to the answer but I am curious about you why you would need separate source for vacuum when you hit the brakes.
 

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Brake booster needs vacuum. With a blower the manifold has positive pressure, not vacuum.

The only centrifgal blown big block I've seen had two carbs and a supercharger on each one.

Where can you get a Paxton setup for $2000?
 

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have you thought about a turbo or two?
 

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youd be alot happier with the 8-71 setup, compared to a 6-71 you dont have to spin the bigger blower as fast to make the same boost which creates less heat, i'm for the roots setup, not only do they give instant throttle response and boost but they look damn cool too, i am too looking at doing a roots setup on my 460 in the future but the thing i hate about doing one on a ford is the damn thing sits up so high because of the distributor that looks kinda odd
 

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Brake booster needs vacuum. With a blower the manifold has positive pressure, not vacuum.

You mean so you can do burnouts, where you stand on the accelerator and the brake pedal at the same time?
 

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Random thoughts and replies: Benefits to Roots types on 460 are ease of installation, cool looks if you want that, nearly instant boost, and minor carb mods. CS (centrifugal superchargers) benefit from higher efficiency on-boost, easy charge cooling, reduced low-RPM torque (great for driving with street tires), moderate carb mods, and better stealth. Turbochargers benefit from lower cost, flexible installation (but custom), high boost efficiency, easy charge cooling, and a choice of normal spool-up (helps with traction control) or instant boost off the line with anti-lag systems, and moderate carb mods. None of the types are free horsepower.

Retard beyond a couple degrees is not necessary unless using a fuel insufficient for the boost you are planning to run, and pump gas usually falls into that category. If using better fuel (race fuel, methanol, or ethanol/E-fuels), you're good to go to the knock limit of those fuels. If you have vacuum advance - keep it. It will improve idle and cruise efficiency and is not affected by boost. A mapped electronic ignition would be optimal for easy configuration the the engine and fuel requirements. CDI is not necessary and won't be any better than II (inductive ignition) at these boost levels. Distributorless ignition can be done to allow less clutter and tighter packaging.

Vacuum pumps are not necessary in any boosted installation unless you plan to run boost and brakes simultaneously. 1-way valves with bleeds are handy for certain vacuum operated devices. It is good to note that boosted engines of any type (except 2-strokes and most diesels) do not operate with manifold pressure unless you are asking more power from the engine than it can supply NA. That means on a street car that you will only see boost when you're pushing it hard. The rest of the time you'll see normal vacuum like any other NA engine.

Charge cooling (intercooling) is a benefit above 5-6 psig in the typical system. Below that, the air isn't cooled enough to make gains, as the compressor must make more boost (hotter) to overcome losses. Above that, it is very beneficial to reduce charge temperatures (both power and knock resistance) and especially with sensitive or crappy fuels like pump gas.

Better heads and quench mean more flow and reduced knock tendency. If you're running calculations, stock heads will give high 60s to low 70s volumetric efficiency at your target RPMs. Good aftermarket heads will give high 70s to mid 80s, and better and faster charge burning requiring less advance for the same power with less det tendency.

Carb mods are simple for draw-through, and nearly as simple for blow-through with gasolines. Meth and Eth carbs require much more work just like NA engines. Boxed carbs are a pain and are generally not worth the cost and complexity. EFI is the hot ticket for any of them, but may have to be top-mount on wet-case Roots blowers to lube and cool the rotors and case to prevent damage. If the blower is dry-case, then the injectors can go underneath. There are several sites that describe carb mods so you can get an idea what it's about.

Camshaft - make all your decisions about the build before deciding this one. There are too many factors to just 'pick one' before that, and it's an important choice.

Compression ratio should be selected based on the fuel and boost you plan to run. With det-limited fuel, your static compression ratio should be lower to allow more boost (good stuff) into the cylinder without exceeding the knock limit of the fuel. Don't be afraid of lowering compression if it's a street engine. Even dropping below 8:1 will not make it "a dog" like some say, and will allow much better performance under pressure. As you can see, most of your decisions will be based at least in some part, on your fuel. Hope that helps.

David
 

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Roots-instant boost at most any RPM (no lag and no wating for RPM to build) but you can't hide a big 8-71 on top of a BBF.

Centrifugal-more boost with more RPM. Low speed-no (or little) boost. Basically the more you rev it, the more the engine comes to life. Pretty quiet operation if set up right and fits under a stock hood (sometimes)

turbos-if sized correctly, boost at ANY rpm but just not "instant" (lag). VERY quiet operation (silent), can easily fit under stock hood unless a carb hat is too tall.

Centrifugals and turbos use similarly designed carburetors-expensive either way you look at it. Yeah you can modify your own BUT having done it myself, I'd rather just pay someone to set one up for my needs. It takes a LOT of time to get one remotely close to being right-and sometimes mistakes are made, which can (and in my case, WILL) cause engine damage during the tuning process.

Roots carbs are basically bolt 'em on & go type thing. Not much science to making a carb work on a roots. Boost referencing maybe but again that's pretty simple.

Having had/driven/tuned all three types I prefer the "no lag" of the roots but I also love the power and "hit" of the turbos. Not a fan of centrifugals as basically they're nothing more than the compressor of a turbo with more parts to go wrong (belt, gears, brackets, etc). Turbos are, IMO, simpler than centrifugal superchargers. Just a bit more plumbing.

I love the driveability of my LIghtning but at times it's boring. Just about like a more powerful NA F150 that makes weird noise when making boost. Boost comes on when I open up beyond about 1/2 throttle maybe a little less depending on RPM. Makes 6 psi at 1500 if I floor it. 8 psi max, and that depends on altitude, air density. Higher altitude it only makes 2-4 psi. Cold dry air in winter it'll make 10-11 and traction is nonexistent in first or second. All of my turbo cars were SUPER fun to drive, relatively easy to tune, got great fuel mileage for the most part, and easy to mod. Then again none of them were BBF's either. 302 in a Maverick, and several 2.3's. They were all less prone to changes in air density-they make X amount of boost reguardless of how dense the inlet air is due to wastegates. Maverick-I never seemed to leave it along long enough to know what boost "stayed" at...started at 6, went to 10-12-14-18 20 was about max but it would make max boost at 2400 RPM. Could have gone to smaller turbine to bring it down to 1800-2000 but 2400rpm 18psi max boost is PLENTY in a light car. No traction in any gear, any speed when the turbo "hit".
 
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