My brother bought himself a beautiful '81 caddy fleetwood about a month ago. This car is in pristine condition, inside and out. What can I say, I'm a sucker for a nice caddy.

Nonetheless, this car is equipped with a system to disengage 2 or 4 of the 8 cylinders depending on the demand for power. Seems like an amazing feature for a 1981. Looks quite simple, from what I can see under the hood. The valve covers have lumps, that likely house solenoids to lift valves, and make 2 or 4 cyls run free.

Inside the car, there is a info panel that shows current gas milage, your cyl mode and how many litres of gas are left (quite a vague estimate I would say).

Anyways, its a cool feature that until he bought this car, I never knew existed on a vehicle this old! Anyone else know much about this?

Heh, neat, I've definitely heard of it. Although I heard it doesn't exactly too well...

Hi 88delta88, hello everyone,


It was called "V8/6/4" and is an example of a good theory that didn't work well in actual practice.

Traditional Luxury Car buyers could well afford the gas, and were not interested in an economy car that would lead people to think they couldn't. For that reason, more sales were lost than gained, as many moved to the manufacturers that sold Luxury Cars with bigger gas tanks.

No matter, that the net mileage improvement was minimal and the transitions between cylinder combos was much less than smooth.

Definitely, one of the bigger steps in the erosion of Cadillac's reputation as "Standard of the World".

Regards, Norm

still, it was daring step in the world of producing big luxury cars that were able to get a better mileage..

How does that compare to the "displacement on demand" used in some newer GM engines? It seems to be the same in principal, but I don't know much about the inner workings of either system.

The goal is only thing common to both. Execution was/is entirely different.

V8/6/4, kept the intake valves closed in the cylinders that wouldn't be used. Since the reciprocating mass (and it's friction) was still there, the gain was far less than expected. My guess is, the project only went forward for marketing reasons.



I don't remember enough to discuss either in any depth. Might have something to do with my lack of interest in gaining fuel economy at the expense of performance.

Earlier (possibly '82) Corvettes used a manifold with two runners to each intake port. One was used for normal driving, both for max power. It was a variation of an early '50s street/strip design by Offenhauser. They achieved a significant improvement with the use of the computer.

Late designs vary the actual valve timing events for power or economy/driveability. Equivalent of instant cam changes on demand. Needed changes in manifold behavior would be an important factor, but I don't know how they are being handled.

Hopefully, someone can chime in, and fill some of the holes.

Regards, Norm

i know Saab had a concept (that was never produced, only one prototype motor) that changed the compression. easy ridin had 1:7 or so and when u floored it it becam 1:11 or so...

Static compression ratio? How did it work?

Norm

I beleive Crossfire (misfire injection as it was affectionately known)injection is what is being referred too. Had 2 TBI units on a cross ram style intake. I beleive prodution for the Y-body was 80-84 (replaced by the TPI in 85), also found in F-bodies (Camaro/Firebird) of simular vintage. Not one of GM's better ideas (like the Doug Nash 4+3). However I believe both TBIs functioned at all times, LH TBI fueled RH cylinders and vice versa. I found the following on a tech site for the Crossfire Injection.
Olds aren't my only passion .... I just can't afford a Vette

"The Model 400 Electronic Fuel Injection (EFI) system is a computer controlled system that uses a pair of Throttle Body Injection (TBI) units, which are mounted on a single manifold cover on the 5.0L (VIN 7) engine. Since each TBI feeds the cylinders on the opposite side of the engine, the system has acquired the name of Crossfire Injection.

Fuel is supplied, by an electric fuel pump located in the fuel tank, to the front TBI fuel accumulator. From the accumulator, it is carried to the rear TBI fuel pressure regulator by a connecting tube. Unused fuel is sent to the fuel tank through a separate return line.

Fuel is supplied to the engine through electronically pulsed injector valves located in the throttle body"

as for the Saab, that had to be some sort of varible forced air induction (read super or turbo charger), I dunno how static compression could be changed ... but I'd love to find out, if I am wrong

found the link for the Saab engine on Popular Mechanics and yes there is a supercharger

http://www.popularmechanics.com/automot ... 66656.html


ohh btw the Caddy 8-6-4....never did work right and was plagued with problems. The currenty displacement on demand is a far more advanced system .... hopefully less problematic as its using the ECM to kill off the air/fuel flow to cylinder. Here is a quote I found on a page discussing the DOD vs V8-6-4

"Readers who remember the 1980s will recall this isn't GM's first rodeo with cylinder deactivation. That first happened at Cadillac with the 8-6-4 engine, which was roundly criticized for its service record and its poor vibration (NVH) characteristics. The old adage of once bitten, twice shy applies here not only to potential LH6 customers, but also to the folks at GM working to make Gen IV the best engine architecture yet. GM's Meagher quickly points out the lessons learned: "I worked on the V-8-6-4 earlier in my career and [the LH6 is] the same idea. The key difference is the control system configuration. The key part of it that makes the transition imperceptible is electronic throttle control. Once the computer determines operating conditions are met to enable DOD, it uses engine vacuum as an indicator of customer power demand. When the computer decides to disable four cylinders, it calculates where the throttle needs to go such that the torque will be equal when you end up with four cylinders."

With the different modes of cylinder deactivation in the Cadillac 8-6-4, there was a dramatic change in NVH, and a corresponding difference in throttle response and exhaust tone. All of these were deemed unacceptable in a luxury car, and at the end of the day, the improved vehicle economy wasn't capable of offsetting the loss of comfort and power. In one sense, the failure of the Cadillac was a windfall to DOD engineers because the design obstacles had been clearly defined years ago."

I know BWM has been doing something similar, but using variable valve timing instead. Thought Id add my 1 cent

Crossfire has nothing to do with variable displacement. Like TPI, it tunes the "ram effect" of the intake manifold to a specific powerband. Difference is, carbs or throttle bodies are placed at the intake end, while injectors are at the combustion chamber in the TPI system.


I wasn't aware "Crossfire" had problems? Please explain.


The "Turbopac" was designed for, and intended, to improve throttle response in Diesel applications. Leads me to think they had a different view of hybrid design.

http://www.popularmechanics.com/automot ... 66656.html

Don't know about anyone else, but it leaves me with more questions than answers.


Please post the link.


Along with everyone else, except US mfrs, that builds performance cars. First that comes to mind is V-TEC.

Regards, Norm

"DrRansom442 wrote:
........ misfire injection as it was affectionately known ........

I wasn't aware "Crossfire" had problems? Please explain. "

I also have heard this and if I remember right when the guy nextdoor was looking for Corvettes he avoided those with crossfire injection models.

my appologies there, I thought I copied your prior post regarding



The Crossfire Manifold design was the major issue. Gas would "puddle" at the bottom during normal driving. When coming to a stop, this gas splashes over the restrictions (cast edges in the bottom) and causing a flooding, stumbling or dying situation. Engine backfires when taking from a light or engine is sluggish during accelerating, were also common place. Most Vette enthuisists avoid crossfires like the black plague. The TPI was lightyears ahead in design. I believe electrical problems were also prevelent and lets face it the system was overly complex especially for the "state of the art" ECMs of the early 80s. They were slow and crude and the Crossfire controlled not one but two TBIs, when one would act up it would mess with one entire bank of cylinders

I don't believe this is the same article I originally found but the same quote appears here

http://superchevy.com/technical/engines ... 5sc_gmdod/