I read the Gas Mileage discussion and wondered about a different approach to spending less on gas.  Having a way to vary the octane requirement, so for daily driving you'd use lower cost 87 and for the strip, 92.  With a blower and a way to adjust the boost from inside the car, you could cut back to a few pounds of boost for the street and low octane, then fill it up with 92 and kick the boost up for the drags.  Maybe a small block could be built for about 300 h.p. on regular with low boost, that could also put out 450 h.p. or more with maybe 10 pounds of boost on 92 octane?  What do you think?  

That's more or less what I do with my Grand Prix. No blower though.

I'm running about 11:1 with an iron headed SBC and in proper tune it needs 92. But I live in a small town and the only thing at our station is 87 or 89 blend. It's a 30 minute drive to get descent gas, so if I'm just going to be puttering around town I do a few carb tweeks and knock the timing way back to get it to run on the 87. I'd estimate a drop about 75 horse doing this.  It's not the most desirable method, but it's cheaper and probably keeps me out of trouble at times!

The best way to do it is with an auxillary fuel system that pumps in high octane fuel (Race gas, toluene, alcohol or blends of these) on demand.  

Some speed shop in Detroit or Chicago (can't remember which one) already builds these sorts of systems for high-end EFI applications.  But an auxillary octane enrichment system could also work with cheaper, backyard-style set ups (auxillary injector systems, auxillary carbs/high octane fueled secondaries, etc.)

The biggest problem (other than cost, complexity, weight and some legality/fuel tax issues) is figuring out how to lean out the primary fuel system so that the octane balance is correct and the engine is not overfueled.

However, the simplest way to run dual fuels is running two tanks and a tank switch along with an adjustable timing controller.  But, the fuel return lines will undoubtedly lead to cross contamination and tank switching takes some premeditation before "getting on it."  

Finally, turbocharging is the best way to "adjust the boost."   10 lbs of boost on a properly-built, good breathing small block ought to be worth a lot more than a mere 450 h.p.

That's kind of what I had in mind.  Something simple where you're not making a lot of changes to go from 87 octane to running on the good stuff when you want to hit the strip.  I'm wondering though, why do you have to tweak the carb at all?  Would think you'd just have to kick back the timing.  It's be nice if you could do that without having to get out the timing light and turn the distributor.  Seems like I've seen something advertised that allowed you to dial back the advance from inside the car.  It may have been part of an MSD ignition for use with nitrous.

  I was thinking the concept would work best with a supercharged motor though.  That way you could run a smaller engine with maybe 1 or 2 pounds of boost on 87 octane for daily driving.  That way you'd be saving by using regular gas and also by getting better mileage on the small motor.  Then you'd fill it up with 92 octane, kick up the boost, and head to the drags.

I remember reading about a dual fuel set up like that, either in Car Craft or Hot Rod.  A slick way to do it, but more complicated than I was picturing.

  I don't know much about supercharging, but the overall approach of running a smaller motor that can perform like a bigger motor sounds like it would work well if you could easily vary the boost depending on the octane level you're using.  A got a book that looks good, Supercharged by Corky Bell, but I haven't read it yet.  Am I right in assuming that you're saying it's easier to vary the boost on a turbo by controlling the speed of the turbine?  Is there any way that you know of to control boost from inside the car on other types of superchargers or is a turbocharger the way to go for that?

silly question but wouldnt a smaller engine have to work harder to produce the same hp as a bigger mill all else being equal?   and what about nitrous?    daily driving run the dog water 8_ octane,at the strip add the good gas and go. if you arent using a huge shoot you can set the timing up to use n2o and leave it their and have no problem

The most important variable* in how much "boost" a Supercharger makes is the rotational speed of the supercharger. 

And on all modern superchargers I'm familiar with, this is invariably and directly linked to engine speed.   Thus, boost is mostly set by the supercharger belt-drive ratio (the ratio between the crank pulley and the supercharger drive pulley). 

Absent a pulley change or a yet-to-be developed "supercharger CVT" system, there is no easy way to change supercharger boost on-the-fly.  (Of course changing pulleys can be a part of the weekend "track-prep" ritual)

Some smaller Eaton OEM Roots-style systems use an electric "On-Off" clutch (mainly Mercedes-Benz 2.3 and Volkswagen's European "twincharger" system), but this clutch doesn't allow variable boost--just absense of boost.  Some 1950s Paxton centrifugals used a prehistoric variable pulley arrangement for low-boost operation, but Paxton gave up on it in the early 1960s. None of the modern centrifugal superchargers I'm aware of have any sort of variable drive mechanism.

Other boost reduction schemes, such as intake throttling or post-compressor dump/"pop-off" valves add heat and cost too much efficiency for their marginal benefits.

The inherent lack of low-end boost in centrifugal superchargers is used by some to lessen octane requirements on the street. Simply by avoiding high rpm while on the cheap gas, they avoid the high octane portion of the power band.  That takes a lot of discipline and isn't much fun.  It also leaves no margin for error.

On the other hand, turbochargers easily accomodate  on-the- fly "boost" changes.  The most important variable* on turbo boost is exhaust flow volume and velocity through the turbine section.  Velocity is generally fixed by the turbine housing and other parts of the exhaust system.

 But exhaust flow volume is easily altered through an exhaust bypass valve called a wastegate.   A wastegate allows  bypassing "excess" exhaust volume around the turbo to control turbine speed and thereby limit maximum boost pressure from the the turbo's compressor section.  This permits builders to "size down" the turbine housing for a lower "boost threshold" and a wider torque curve or to use larger-than-normal compressors for increased midrange and top-end "boost" or even a combination of  both turbine housing and compressor sizing changes.

In other words, a turbo's boost can be easily varied by "turning the screw" (most commonly achieved in modern turbo systems by a manual or electronic wastegate controller)

*There are plenty of other variables in supercharger or turbocharger "boost," such as type of compressor (positive displacement or centrifugal (turbo-style)), compressor size, volumetric efficiency of the intake and exhaust tracts, cam timing, etc.  However, these other variables are generally not easily changed for octane variablity after the engine/power adder system is built (and certainly not on a daily or weekly basis).

has anyone read this book yet? its called "You must turbocharge everything" by GOD (aka. TurboTed) can be found at most retail stores or carcraft.com

I am categorically against all turbocharging of any 1971 Big Block Novas.  I also haven't found any turbos suitable for my Weedeater or lawn mower . . . .

But wasn't the ORIGINAL topic about adjustible boost?

("With a blower and a way to adjust the boost from inside the car, you could cut back to a few pounds of boost for the street and low octane, then fill it up with 92 and kick the boost up for the drags.") 

This would suggest a discussion of the relative adjustability of supercharging and any more flexible alternatives, wouldn't  it?  

BTW, I certainly wouldn't put TurboTed in the same league as the Supreme Being!  Maybe Saint Christopher . . . .

nah, novas are better procharged. for some reason it makes them the worlds fastest pump gas cars. On the other hand, a turbo lawn mower would be pretty kick ass.  

Yet a turbocharged SOHC four-cylinder Mustang came within hundredths of beating a centrifugally-superchaged 400+ cube Nova (packing the almost SAINTED LSx engine, no less) in power-adder small block at the 2006 HRM Drag Week (tm) (the REAL test for street cars).

BTW, those turbochargers sure seem to wake up the BBF . . . .

http://www.promodfullthrottle.com/News/2006/FFWFinals.htm

Ortiz finishes #2 in FFW Pro 5.0 points championship

"Horsepower & Heels Crew Chief, Dan Parker, was also recognized as the series' coveted Crew Chief of the Year recipient.   This honor came as a result of his hard work with Erica's PRO efforts, as well as his chassis tuning expertise on PRO 5.0 competitor John Gullett, as well as Outlaw 10.5 standouts Dan Millen and Dennis Lugo.   Parker was able to fully maximize the potential of the low-budgeted operation, making the most out of the limited funding and surprising many with the performances out of the early 80's Thunderbird.   The Al Moody built powerplant proved to be the most impressive piece, utilizing a stock Ford block filled and cast crank to propel the T-bird into the 6's. " 

http://www.briskusa.com/images/photogallery03/pages/Brisk%20Silver%20Racing%20D8S%20spark%20plug%20in%20Erica%20Ortiz%20Twin%20Turbo%20Thunderbird.html

coming close aint winning  

I probably just don't know enough about it, but I hesitate going with nitrous.  Instead I like the idea of somehow easily regulating the boost to control the power output of the motor and the octane needed.  It does sound like using nitrous would work the same way though.  

Thanks for the very thorough reply.  I didn't realize Paxton used a variable pulley system like that back in the 50s.  I remember a Studebaker Lark with a Paxton blower that would show up at NHRA points meets at OCIR and did real well in Stock.  Think it was a '62 or '63.  We always wondered if tech really knew what the specs were supposed to be on that car though.
  Hadn't heard of the clutch setup either.  I'd wondered if anyone had developed something like an air conditioning clutch to control a supercharger.  Actually an on/off like that would pretty much work out, but I'd rather be able to dial in as much boost as the low octane would handle.  It'd be good if someone did come up with in-car controllable CVT type pulley.  Also it seems like I read somewhere about a company that makes a quick change pulley.  I'll have to look into that.  Maybe it would just be simplier to go that route with a small pulley for the strip and a much bigger one for daily low octane driving.
  But from everything you've said, at this point a turbo definitely sounds like the way to go if I want to easily vary boost.  Guess I'll be buying another book about those.  
  Your mention of the lack of low-end boost in centrifugal superchargers did get me wondering about using a rev limiter to keep the boost low.  Guess that would work, but seems like it would really cut down on the power for around town driving.  At least with a few pounds boost on a turbo the car would still perform as well as a car with a good running normally aspirated motor.
  Thanks again for the education.  

http://www.vs57.com/history.htm  Here's a good link with the details of Paxton supercharger history, including the variable-ratio VR-57.

I think your doing well in working through the design questions and wish you the best on your project.