New Jeep HEMI V8

[MITCHAY]

Has anyone seen the new Jeep ad? Its the new Cherokee with a HEMI V8 that produces 240kw. It also has a feature that deactivates 4 cylinders to save on fuel consumption when they arent needed.

I thought it was pretty cool. Maybe this sort of technology could be incorporated into cars. Definately could be a promising technology to develop into sedans.

Flog it like an 8 when you want to and cruise on 4cyls and save petrol.

[EDManual]

i dont know why they(all car companies) havent done that earlier?!! Great Idea!

How well does it work i wonder?

[merlin]

It's called DOD (Displacement on Demand) - I thought this was going to be a feature on the LS2?

I heard that it only save something like 5% fuel and its hardly worth the extra cost and more things that can break.

[LTDHO]

Wouldn't the 'DOD' be EFI controled therefore nothing extra to brake?

I don't see why all cars don't have it. 5% add's up over the year!

[merlin]

http://www.popularhotrodding.com/eng.../0405sc_gmdod/

The saving should be around 8%

[MITCHAY]

Jeep claim a 20% saving on fuel economy. Thats whats on their website.

[fordel]

The 300C does the same thing as well AFAIK from one of the Top Gear episodes.

Chris

[16wantsI6]

i saw that earlier on the year on howstuffworks.com except it could do 360 turns on the spot, because all the wheels turned, it also looked cooler i think it was a prototype but, it had that piston cutoff feature aswell

[grey_esp]

Its been available on Jags for a few years now. I dont know what figures they quote for efficiency tho.

[johnydep]

8% or 20% wonder which is closer to the truth?

There would be a lot of friction/drag to overcome; piston rings, bearings, camshafts.

Wonder if it would work on the Barra I6?

[smciner1]

Just wait till you see the S-RT 8 version, complete with 415 hp of 6.1 litre HEMI (tm)!

[parawolf]

Originally Posted by johnydep

8% or 20% wonder which is closer to the truth?

There would be a lot of friction/drag to overcome; piston rings, bearings, camshafts.

Wonder if it would work on the Barra I6?

What they make sure that they do is for a complete crank rotation (or is that double rotation for 4 stroke?) is that they fire differing cylinders on opposing rotations.

eg: rotation 1, fire cylinders 1-8-2-5: rotation 2, fire cylinders 3-7-4-6

What they would also have to do to maintain lubration is to feed a small amount of fuel (tiny bit) into the cylinder for lubrication on the shutdown cycle vs a full load on the firing cycle.

Someone has to have read something about this DoD to tell me if this is how they are doing it...

[OzJavelin]

Originally Posted by parawolf

What they make sure that they do is for a complete crank rotation (or is that double rotation for 4 stroke?) is that they fire differing cylinders on opposing rotations.

eg: rotation 1, fire cylinders 1-8-2-5: rotation 2, fire cylinders 3-7-4-6

What they would also have to do to maintain lubration is to feed a small amount of fuel (tiny bit) into the cylinder for lubrication on the shutdown cycle vs a full load on the firing cycle.

Someone has to have read something about this DoD to tell me if this is how they are doing it...

Being one of probably very few Mopar nuts on this Board I believe this is basically correct .. this is all computer controlled, it involves shutting down injectors, but not completely .. they cycle thru a firing every so often to keep things lubed. I *think* they also muck about with the hydralics to the lifters to either stop, or reduce valve lift??

Ahh .. 5.7L Hemi in my '70 Fury convertible .. sweet!!

[XB_fairmont]

I believe the lifters shut down deactivating the valves.
Nice motor, i'm not really keen on shutting down valves.

I don't think it's the smartest way to get power and economy.
why don't they just run turbo diesels?? Cummins 5.9T hauls ****. Power and economy

[EA2BA]

how do you shut down lifters ? <--- umm impossible trick if you ask me

stoping injectors would be a piece if cake, and no fuel in, means fuel saved.

[LTDHO]

by just shutting of injector would make it very lean and the oxygen wil still combust, unless the spark is switched off but there will still be compression.
The valves are controlable and I believe they are a left open a little during combustion stroke so the engine will bypass the cylinder, hence fuel efficiancy.

[EA2BA]

Originally Posted by LTDHO

by just shutting of injector would make it very lean and the oxygen wil still combust, unless the spark is switched off but there will still be compression.
The valves are controlable and I believe they are a left open a little during combustion stroke so the engine will bypass the cylinder, hence fuel efficiancy.

Well I am running 5 cylinders and my effeciency has not improved, still 12-13L per 100 to work and back in peak hour traffic on the Monash.

[LTDHO]

ha ha

You will find that #6 is still getting fuel!
Also when you accelerate the Hemi would engage all cylinders, your car probably isn't!

[EA2BA]

hehehehehe

its actually #2 and umm yeah its in permanent economy mode :

[XB_fairmont]

Nothing's impossible.

http://www.allpar.com/mopar/new-mopar-hemi.html

In V8 mode that's lot of power for a production car!

It must be a real power drain draging 4 cylinders!

[Bossxr8]

It has lifters that can be electronically shut down so the valves don't open.

[Steffo]

Originally Posted by Dellboy999

Well I am running 5 cylinders and my effeciency has not improved, still 12-13L per 100 to work and back in peak hour traffic on the Monash.

Different scenario. Our van had a burnt valve, so it was only running 3 cylinders. But #4 was still being fed fuel, even though it wasn't doing anything. The thing was really bad, used lots of fuel. Because it was feeding fuel to a functionless cylinder, plus the other 3 had to work harder to acheive the same result as before. The thing was a 2.0 4cyl getting worse then 20 litres/100km economy.. hehe.