Factory experimental

[Jim Bailey]

Bill: this would probably be better addressed in a "new" Thread. Or if you want to PM me. Valve Springs are more of an issue with Alky than they are with Fuel Cars. And the mere Size/Mass of a Screw Blower,(Case and Rotors both), Filled with Almighty Nitro - BANG - You can't have that much energy flying around in specator seating. In an effort to Slow these Cars, NHRA has to really keep a handle on New Proto Type Parts. Today's Fuel Motors are more of a SPEC motor than any in drag racing. Including stock elim.
But, with that said, and the popularity of this thread....Give NHRA Tech just a little more credit, watch and see what happens, I don't look for the New Fords to be way outta line within current rules. It'll be when the Racers begin to "tweek" the combo (and rules), especially the supercharger, that we'll see an unfair advantage.

[Greg Hill]

If any of you have outlaw street cars at your local track take a look sometime. A lot of them run a procharger blower and absolutely fly. These are generally small block chevys and fords and routinely run low 7 seconds with 10.5" tires. The tech department has no clue how to monitor these cars. You talk about opening a can of worms.

Greg

[Tim Kish]

Based on the rotor profile and port geometry of a screw compressor there are areas within the supercharger where the air is compressed, this does not occur in a roots style supercharger which is purely a positive dispacement device with no internal compression. Introduce nitromethane to a screw compressor and you are trying to compress a volatile fuel - Kaboom

[Tim Kish]

Originally Posted by Jared Jordan

One aspect that hasn't been discussed in this thread is the effect the supercharger will have on those cars at an altitude track. Those of you in the Eastern U.S. don't have nearly as many of those as we do out West. If you're getting blown off at sea level by one of these cars how much further behind are you going to be in thin-air against a forced-induction vehicle?

Main difference being that if drive ratio is controlled then you are still pumping the same volume displacement of air at sea level or at altitude. And that air volume is less dense at the same ratio as the NA cars have to deal with. Where you can benefit from a boost device (supercharger or turbo) is if you pump more air volume at higher altitude to keep the charge density at the same power level you can achieve at sea level. The only way to do that with a crank driven supercharger is to change the drive ratio - the pro guys can and do this at the altitude tracks. In stock this will not be allowed.

The boost level achieved by a roots blower is a function of its physical displacement, drive ratio, blower efficiency (mechanical and thermal) and inlet air conditions. If only the inlet air condition varies you get the following results:

A setup to run 10psig boost at sea level with an atmospheric pressure of 14.696psia (29.92 baro) as measured at the supercharger inlet is said to be operating at a 1.68 pressure ratio.

As the pressure ratio performance of this setup is fixed (fixed drive ratio, blower displacement, etc), as inlet pressure changes, the measured gauge pressure in the outlet (Boost) will change as well.

At 2500ft above sea level atmospheric pressure drops to 13.41 psia (27.32 baro), the resultant measured boost level will be 9.12 psig

Likewise for those so fortunate to run at 1000ft below sea level (and not drowned), boost level would be 10.35psig.

So help me understand how a tell tale boost gauge will work, unless of course it has an altitude correction factor which we all know are so accurate.

Another huge factor in intake manfold pressure changes is cam timing. Ex: Less overlap = more boost at fixed drive ratio. So again within the legal mods for stock, how do you maintain some "stock" boost level.

Not trying to be critical of anyones concerns or ideas, just trying to help educate on how supercharged engines function.

[bill dedman]

Tom,

Good points all, I think. Thanks for the technical insights!

In regards to a telltale boost gauge, I think it could work like this:

It would be plumbed, of course, to intake manifold pressure.... period. If the factory boost figure were say, 10 psi, measured in the intake manifold during dyno testing to determine flywheel horsepower output, that 10 psi figure would be the determining factor in the engine's eligibility at any given time. But, not quite...

Increases (or, decreases, which we are not concerned with) in ambient barometric pressure would change this pressure incrementally, as per your demonstration in the previous post, but the changes in boost, upward (say, at a reading of 2,500 feet BELOW sea level,) could be dealt with by giving the participants who run forced-induction, a boost "window" that would forgive, if you will, levels of boost that would be influenced by anomalous weather conditions; a "grace" amount of an indeterminate amount, at this point. That could be discussed by NHRA's "experts" so that a car that is legal, operating in sea-level barometric pressure, wouldn't become "illegal" when the boost goes up due to favorable weather conditions.

Those weather conditions would sometimes happen, of course, but I don't think the amount of this "leeway" would have to be very much.... not to the point that it would be something that could be taken advantage of by an unscrupulous competitior. It could be a matter of percentages; say, two percent of the maximum boost figure??? That is just a wild guess....

I have NO IDEA if that is even close to what an engine's manifold conditions might experience under high barometric pressure, but you might have a formula that could get us in the ballpark for the increase.

The agreed-upon "window" would have to include boost increases (percentage-wise) for the worst-case scenario regarding records having to do with barometric pressure "experience". Location wouldn't matter; this would be a blanket figure that would, ideally, cover any possible eventuality with regards to barometric pressure increases below "sea-level" accepted standards.

It would be implemented so that the Tech who reads the gauge is oblivious to its existence; it would just be say, for instance, a one-pound of boost value, tacked onto the original boost limit figure (obtained from the OEM source.

As a PERCENTAGE, agreed upon by NHRA Tech, it would be easy to apply to any and all forced-induction engines, and would be in evidence on the boost spec sheet as a part of the total boost allowed. It would always be a part of the acceptable boost level figure, so no one would even be aware that it was being implemented.

Is there a reason why that couldn't/wouldn't work?

f so, what am I missing, here?

Thanks again for your excellent technical advice and information. I am (obviously) not educated in this area; I just deal in generalities, so my thinking may well be flawed.

As regards your comment, "Another huge factor in intake manfold pressure changes is cam timing. Ex: Less overlap = more boost at fixed drive ratio. So again within the legal mods for stock, how do you maintain some "stock" boost level?"
I will leave that one for someone else, as I am not sure what would be fair, or even workable on that score. Sorry; my resources are limited...

Bill

[bill dedman]

Jim Bailey... you're right about my hijacking of this thread, and for that, I apologize. But there are two questions that you responded to with answers that I think would be more beneficial if they were explained by you, on here (rather than in a PM.) Indulge me just these two issues, please, and I won't write on here, about this, again.

1. You said that valve springs are more an issue with alcohol cars than Fuelers. which is undoubtely true, but still has no answer for why they are banned by NHRA. They could save those racers TONS of money... like I said, they only have to be bought ONCE. What's the downside of that (unless you make your living selling steel springs...) I realize that YOU don't make the rules, but having "been there" in Professional racing, you have info and insights that we "outsiders" are not privy to, and I just thought you might have heard why this "no compressed air valve springs on ANY vehicle in competition" was enacted.

2. Is it not possible to use port (fuel) injection and keep nitro out of the supercharger on a T/F car? I agree that a nitro-fueled BOMB sitting on top of an engine that can have an intake valve hang open at any time is NOT a good idea... so, why don't they keep the nitro below the blower/compressor, so that the only thing in the supercharger at any time, is AIR? That would seem to relieve the potential for a monumental explosion by a significant amount. Of course, there could still be an explosion of the mixture trapped in the manifold, but the volume is significantly smaller, isn't it? It's such a simple idea, I'm sure multitudes of people have thought of this, before, so why don't they do it? I'm obviously missing something here; what is it?

Thanks for your time and the information you've posted here. I still wonder if your A/SA car is a Stage III motor.. I guess, if it's a '64, it would have to be...

Bill

[Jim Bailey]

Bill: in answer to your first question, I don't know? Cost Maybe? On Jim Head's Nitro F/C we use a Manley Triple Spring installed at around 650# Seat pressure. I Cryo all of them when they're new, and we use 'em all year. They're not really a high cost item in the overall scheme of things. Don't forget we have around 10 to 15 set's of heads assembled and ready to go most of the time. What would the initial cost out lay be for Air Springs?( That's about 240 springs without spares) Question #2 has pretty well been answered by Tim. Along with his technical expertise, I can only add, that we use the fuel to COOL the Blower. Our clearances, Rotor to Rotor, and End to End are so tight that with out some liquid to help cool the parts, they won't live. We left a fuel line off (to the Injector) on top of the blower once, and the blower galled up about 50 seconds into the warm up. It ruined it. And as he said, the last thing you want to do is compress the nitro in a screw blower. Heck, we've blown the side out off a block putting studs in with an impac, just with a little nitro in the bottom of the threads....Hey,MAYBE, we'll see our FIRST Stocker Blower explosion this year!! Are they required to have a bag and restrants? LOL.

[Bruce Noland]

Evan,
Since starting this thread, I have heard from four different people who say the motor in the new Mustang has made 800 Horsepower on the dyno. Is this true? To be clear, I'm asking about the motor in the new CJ that is coming out of the Roush building at the Ford plant.

Also have you heard about any nhra technical issues with these cars? And have you heard about one of these new CJ's rolling thru the traps at 142+MPH? I hear all these stories and I know you know the full story and it would be good to hear the straight story from you.

Thanks

[bill dedman]

Thanks, Jim, for an interesting and informative post.

Bill

[Mike Gray]

Anyone want to buy their own Cobra Jet?
http://cgi.ebay.com/ebaymotors/FORD-...QQcmdZViewItem