better mileage with higher octane?

Dan, You seemed to know what you're talking about. Me too I have seen what you described, however there is a way to control the Detonation into a controllable burn. And the trick is, I can't share until I get paid for my research. The saving is huge.

Venus

wrote in message news: snipped-for-privacy@v33g2000cwv.googlegroups.com...

Solar Flare wrote:

Mustn't confuse detonation with normal combustion. The fuel/air mixture should burn across the chamber at about 100 feet per second. Detonation is a different process and flame fronts can reach 5000 fps or more. The enormous pressure spikes and abrupt release of heat does plenty of damage. Detonation happens when the complex fuel molecules, under the rising pressure ahead of the flame front of normal combustion, begin to break down into simpler structures that can autoignite; they don't wait for the flame front to set them off in a normal chain reaction. The whole works might go off at once just becuse they're being squeezed and their temp is rising. Detonation requires time for those molecules to break down, so low RPM is a problem, large combustion chambers (which require more flame-travel time) are a problem, lean mixtures (which burn more slowly due to the distance between molcules) are a problem. Normal combustion is not an explosion; it's a controlled burn. Detonation is an explosion, totally uncontrolled, and higher octane fuels were designed to increase the capability of handling the higher pressures and temps without breaking down into autoignitable components. In aircraft we're still using leaded fuels because the engine technology is stuck in the 1950s. Some avgas grades have large amounts of lead in them, and sparkplug fouling is a big problem, even in the heat of an aircooled engine. Those amounts of TEL are necessary for the big cylinders found on aircraft engines, their low operating RPM, and the higher operating temps (cylinder head temps to 550°F, depending on the engine). We've been promised unleaded avgas for some time now but haven't seen it yet.

Dan

Factory CR on '69 Olds 350 rocket is 9.0 Up to 10.0:1 on the high output version. 13.8 is VERY high. The 429 Cobra Jet Super Cobra Jet, or Boss 429 ran 11.3:1 That's the highest stock north american CR I've seen in the sixties.

The Olds Diesel was 22.1:1 Diesels can run from 15:1 up.

Just as another data point, I have a '63 Studebaker Avanti engine that is spec'd at 10.25:1 CR but it's currently got composition head gaskets so it's likely more like 9.75ish. I think the "R4" version (304ci, hand-assembled by Paxton Products, dual quads) was 12:1. Yes, I would very much like to try one of those, but I'm not sure how I would feed it :)

nate

clare at snyder.> >

My 1970 Rover 2000TC was about 10:1 IIRC and had a prominent label under the bonnet / hood insisting that *5 star* petrol be used - 99 or 100 RON IIRC.

To my amazement you can still even get something similar for classic cars.

Graham

Everything you have post up to this last statement have been on the money. But.....

One has to distinguish between fuel economy and performance as the engine is operating in different regimes. For performance one is invariably at high-load and moderate to high speeds. In this region of the engine speed/load map octane requirements are highest. And "if" the engine is unable to run at optimal ignition timing on low octane fuel, then going to a higher grade of fuel can increase performance if the ignition timing is adjusted.

For fuel economy though, most of the time the engine is at lighter loads/lower speeds. At light-load the engine just doesn't need high octane fuel. Most modern engines are calibrated to run very close to optimal ignition timing at part-load. Here, increasing the octane rating of the fuel is wasted as there is no need to change ignition timing. The only iffy part is if the driver spends a lot of time at high-load during accels.

Gee Mr. Venus, where should I send my money? Do you have a paypal account or should I send cash? I'll bet you have that perpetual motion thing figured out too.

Seem to recall Dodge had a 413 wedge with 13:1 around 1963. It may have been a special order from the factory thing. The 1964 hemi had about 12:1. My '68 340 Barracuda has 10.5:1 stock. When I put a turbo kit on my Kawasaki 1000 I put in a set of 7:1 blower pistons so that I could crank the boost up to 18 psi. Makes a lot more power that way than running higher compression with less boost.

Bruce

Rover called the vernier adjustment on the distributor the 'octane selector'. When I had it of course it had to be retarded to run on 4 star which was the best you could get then.

It was a very nice car for its day. Probably the 'best' in some respects I've had until the Saab I drive now.

Graham

Can you see that sort of thing successful these days, in an era where most car owners wouldn't even know where to find the oil dipstick? Some might not even be able to open the hood. Electronics have allowed us to abrogate our responsibility to know at least something about the automobile, so much so that the slightest malfunction means a tow truck for most folks, and leaves them at the mercy of the mechanic. I dread the day when the manufacturer welds the hood onto the car after everything's installed. It's bad enough now trying to get at some stuff.

Dan

UPDATED MAINTENANCE SCHEDULE: 1. Replace vehicle at 50,000 mile intervals.

--scott

May as well weld it shut on a 24 valve Mondeo/contour/mystique for all you can reach without dissassembly -

A friend of mine had a V6 Vauxhall/Opel Vectra. For the life of me I couldn't see how you could get to anything under there.

Graham

OK, did some more research in my fairly extensive library.

1961-65 413 was only 10:1 on the high compression version - 9:1 on the RC1 and VC1. The early 426 was 10.25:1 (1966-67) The NASCAR version was 12.5:1 in 1964, down to 12.0:1 in '65. The "Street Hemi" was an 11:1 engine Dodge only got the 413in 1965 in Canada - was a Chrysler only engine from '61 up. In the US the D500 got the 413 in '61 with 10.0:1, even on the 375 horse version. In the US for 1962/63 there WAS a very limited edition "RamCharger Max Wedge"413 at 13.5:1, but this was a COMPETITION engine. The "Street" max wedge was 11:1

Yabbut, "stock" gets hard to define ;-)

The Max Wedge 426 engines were "available" as "stock" items (along with 'body in white' bare chassis with no interiors) for various drag classes, and they were somewhere around 13:1. But for something you could buy down at the dealer and drive home under its own power, yeah

11:1 or 12:1 was about the max.

Non-turbo prechamber diesels like the Olds are the ones with astronomical compression ratios. Direct-injection diesels with turbos are at the low end, I think some are down in the 13:1 range.

Its called a knock sensor with feedback electronic engine management, and virtually every car now has a system like that... ;-)

in an

Very true. And sad. I find it ironic that the enviro crowd wails and moans about exhaust emissions, but doesn't do anything to prevent the huge waste of good automobiles (and all the energy and pollution required to produce each one) that are destroyed by owner negligence every year. At least nothing more than a token "tune your car and inflate your tires to save the planet!" type ad now and then.

Some car company- I think it was T*yota, I'd expect it from them- had an ad based on welding the hood of one of their cars shut. Of course it was tongue-in-cheek, but its amazing how many fools think that way about cars.

But a 13:1 CD diesel will NOT start without preheat.The old listers were 19:1/15:1 and 22:1/19:1 start and run.These were "variable compression" and used the high compression to start. They were prechamber engines similar to a Ricarro or Comet.

Back in the 50's and into the early 60's NASCAR required engines to be "stock" in that everything in them had factory part numbers that anyone could order. If you knew the codes you could get most things made to order from the factory. There were also dealer installed options. There were no EPA restrictions at the time, so you could run any engine they sold you on the street.

The 426 Hemi was intended as a race engine from the beginning. When it became obvious that Ford would no longer have a snowball's chance in hell (and GM was officially out of racing) NASCAR broke from the "gotta be stock" rules. The Hemi was restricted to a single 4 barrel carb even though it came stock with two fours. The 427 Ford was allowed to run two fours, even though it only came with a single four as stock.

About '76 I had a '67 Barracuda with after market 13:1 pistons in it, among other things :) It ate starters for breakfast and barely got by on Sunoco 260. When it came time to choose between it and the '68 340 Barracuda that I also had, I kept the 340. Still have it :) It is a much better balanced car.

Bruce

That's OK, the Olds usually didn't start *with* preheat ;) Nor do many other prechamber diesels once the glow plugs start going south. Intake air heaters are usually plenty to get DI diesels going, no need for troublesome glow plugs.

Listers were just nifty, no question about it.