please help!!!!!! why 24 valves???

[Cummins Cowboy]

ok while driving to work this morning i started thinking and this really bothered me cause i couldn't come up with an explaination. so here goes this may sound like it is heading in a wierd direction but bare with me. Ok in gasser motors first there was the carburator then later came electronic fuel injection. ok the electronics made it so that the computer could monitor all sorts of things, timing and i think most importantly fuel mixture and amount of fuel going into the enigne. It monitors this varies ways O2 senosors etc. the reason for this is to maintain as close to as possible a perfact stoiacoimetric(i know i mispelled that) fuel ratio of 14. 7 parts air to 1 part oxygen. if this was attained the engine would emit only carbon dioxide. thus would be completly efficient as possible.

Ok with that said i asked myself why did cummins switch to the ISB engine. The only reason that i have heard that makes since is something to due with emissions and meeting those standards. OK we all know the ISB does not get the kind of fuel mileage that our 12 valvers get. I think the difference in fuel mileage in the 2 engines is close to 20%. With all the electronics on the engine WHY is the ISB not as effiecient???? it is using more fuel to make roughly the same amount of power. So that led me to ask where in the hell is all the extra fuel going??? it can't be being burned or else the engine would make more power. I thought the reason for electonics was to make engines more effienct. ie less fuel for a given amount of power. seems to me like we are steping backward instead of forward. there is just no way that an engine that uses more fuel for the same amount of power can be doing better when it comes to emissions. what do all of ya'll think am i out of my mind.

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93 D250 5sp 3. 54 gears sans muffler, ISSPRO tach, K&N filter, needs to be bombed BAD
I would rather be cummin than stroken

 

[CDR]

I think I have a halfway decent explaination, which somebody may be able to elaborate upon. I read in the last (my first) issue of the paper TDR article discussing just this particuliar phenomenon. I don't have the magazine with me, but the article is about 3/4 of the way to the back. It compared stock to stock, 12 to 24 valver's. Newer 24 valver's are rated at higher horsepower. It measured the brake specific fuel consumption (BSFC). BSFC measures the rate of fuel consumption in terms of pounds of fuel PER horsepower PER hour... The 24 valve is more efficient in this way due to the fact that it has a higher horsepower rating. This does not correlate with miles per gallon. In summary, the article basically said that 12 valvers will yield better mileage, but the 24 valvers will allow you to tow faster (or less slow on hills).

Real world experience may vary, but that is one explaination. I too think of efficiency in MPG.

BTW 18. 8 MPG @ 75-80 w/ approx 50 miles of city on recent trip w/ 9500 miles on truck.

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Chris 01. 5 2500 ETH/DEE 3. 55 LSD 4x4 QC/LWB SLT Patriot/Silver Camper,Trailer,Snowplow prep...

 

[illflem]

Maybe all the extra fuel is going to turn the alternator to supply the juice for all that electronic crap. I'd rebuild my 12 valve and put it in a brand new truck before I'd have a 24 valve. Probably would be cheaper than replacing injection and lift pumps all the time.

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95' 25004X4,AT,Driftwood,Banks Stinger,Warn fender flairs and running boards(work truck)
95 3500,5 speed 3:54,BD E-brake,Driftwood,Banks&Psycotty,34,000 GCVW apple and tractor hauler(works harder truck)

 

[Gonzo 1066]

I have to say that the milage differnce between my 1995 2500 and my 2001 3500 is very slight. Now I am comparing loaded milage. I almost never use these trucks unless they are fully loaded (#20,000 gcvw). I do find that the 2001 is driven faster and pulls the mountian passes better than the BOMBED 1995. The 24 valve revs higher and has a much flater torque curve. Dont get me wrong I still love the P 7100 pump and I do bieleve that it will outlast the hamstrung electronic pump in the 24 valve. But I dont think I could agree in my experiance with the notion that the 24s get 20% less milage than the 12s.

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1995 2500 5 spd US Gear 2 speed,PackBrake, bombed,big turbo, injectors CUMMINS POWER!!. 2001 ETH 3500 PackBrake, gagues,otherwise stock. 1972 "1066" International Harvester 414 ci diesel pulling tractor, big pump,turbo and injectors. Alcohol injection,BINDER POWER!! .
GONZO

 

[HC]

I don't know, but like most who post on the internet I'm not going to let that stop me from having an opinion! #ad

The emmissions standards are not set up for total emmission per mile driven. Thus, higher mpg doesn't necessarily help you meet the standard. It should, but, it doesn't. If it did, a smokin' 2 seater at 60 mpg would require few controls, and it might be impossible to even build a truck that could be sold in the US. So they go by emmissions per Hp, or some other standard. Also, different emmissions get ranked as more important. So if you can get the % of unburned hydrocarbons real low, then maybe they don't care so much if you're burning twice as much fuel and putting out twice as much CO2. Like many rules and regulations, it is really hard to set a standard that has the desired effect and that all parties (rulemakers, lobbiests, industry) will agree to. Bottom line is that a 24 valve engine is meeting much more stringent standards than the 12 valve. Take away those standards, or build the right box or reprogram the ECM, and the 24 valvers could truly get a few % better mpg than the 12 valvers. But in the real world, the 12 valvers will probably continue to kick 24 valve butt for the foreseeable future, at least in the "light load" mpg department.

 

[Archive]

I would think the head was redesigned to center the injector spray pattern above the piston in the combustion chamber. (emissions) The increased volumetric efficiency of the head is mainly lost in the injection timing changes. (emissions again) I do like the "no maintenance" valve adjustment intervals. Thats hardly ever mentioned, but noteworthy if you do your own wrenching. There are 10 of the under-valved engines in service at my workplace, and they are incredibly durable. Well, 82 degrees, sun is shining, TT hooked up to Ram, fish are biting, pocketful of $$$,..... Gentlemen, have a GREAT weekend - I'm outta here !!!! #ad


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1999 White Quad Cab SLT Dually Auto 4:10 Posi. NOT BOMBED... ... ... ... (very much) 31,000 miles

 

[RonaldLarson]

Gentlemen, it's called volumetric efficiency and EPA. EPA said " clean 'em up". Good Cummins engineering said 4 valves breathes better and allows for closer control of emissions. Chrysler said "more power".
Can't get more power wihout more fuel and air. Can't clean up the emissions without electronic engine control. Can't have it all without a sacrifice in fuel mileage. By the way, what's wrong with my trucks 16/17 city, and 23 highway in summer anyway? Sure is easier to add horsepower to my 24 properly valved than any 12 valve!
Ron

 

[Power Wagon]

I think I've posted on this topic at least once before. The answer is technical in nature, and somewhat imprecise, as well. Milage, as we define it, is turning fuel in physical motion down the road. 1 gallon gets you so many miles, in our case.

In order for this to happen best, we have to enhance certain things. For instance, we need to inject the fuel as rapidly as possible, and as finely distributed as possible, at the precise moment that creates the combination of maximum torque on the crankshaft (caused by maximum pressure against the piston).

And, we have to lose as little energy as possible due to heat loss, friction, airflow, turbo restriction, and the list goes on. Some of these factors are minimal, some not.

Now, here's where the real world intrudes into our life: Producing maximum pressure means generating maximum heat, and heat above certain temperatures creates oxides of nitrogen. How are those controlled? By lowering temperatures... How's that done? Oh, we can inject the fuel a little late, dropping peak pressures and temps a bit. We can stuff a LOT of cool air in, which will absorb heat that would otherwise be used to expand the air and drive the piston down.

The ISB uses all these techniqes to limit pollution output. It meets emissions without a cat, meaning we had to make extremely clean burning the priority, not maximum efficiency.

Those 24 valves that bring in lots of air also mean that that all that air coming in is compressed (that takes energy), and those small compressor housings having that greater amount of air going through it means it takes more energy to push it out.

Further, if you've ever looked at the nozzle tips on an ISB compared to a 215HP engine, you'd see the holes are microscopic by comparison. The fuel flow through them just can't be very fast. While that fine flow is good for emissions, it's not that good for efficiency.

But, the airflow enhancements, the higher pressure fuel system, the tighter and dynamic timing control, the better chamber shape all means that the engine has the ABILITY to outperform the 12V engine, and get better economy doing it - especially under load.

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ICQ 3807791 Power Wagon
www.my2kcity.com/powerwagon
Mark Koskenmaki, General Diesel Moderator

 

[JohnE]

Powerwagon got most of it correct for the emissions versus efficiency debate. The single missing detail is adding cool and <em>de-oxygenated</em> air back into the combustion chamber meaning EGR or Exhaust Gas Recirculation. The detuned air interupts flame fronts and lowers maximum combustion temps which lowers maximum pressures. These maximums are what produce maximum NO^X (oxides of nitrogen) and maximum fuel efficiency. The little bit of lost fuel efficiency is mostly gained back with the electronic controls. The California units use EGR to meet very strict requirements. Electronic injection controls to delay optimum advance injections (and follow a tighter profile than the old cam plate) fits the others.

Cummins is doing a great job with the 24 valves and electronic controls in the B series and the C series I see.

Detroit had to go with electronic controls many years earlier to meet the emssions standards. We just got done building a batch of buses with Detroit 40 series power plants. I loved the Garret variable turbine. The EGR system was not as pretty. The exhaust gases had to be pulled pre-turbo in order to push it back into the intake system. Pre-turbo means hot as hell which is why they had a coolant powered heat exchanger to drop the air temps. (This may be the same as a California B series EGR system as I've never seen one. )

12 versus 24 valve each has the advantages. Has anyone of the Bombers tried using 24 valves with a conventional injection sytem?

BTW I run a '97 2WD. Last good road trip got me mid 20's with winterized fuel running 75-80 in the mountains and around 8k gross. I cannot complain about 12 valve technology!

Cheers;

JE


[This message has been edited by JohnE (edited 04-07-2001). ]

 

[Vaughn MacKenzie]

An observation of 12 vs 24 valves at the last dyno day I went to (April 2000) was the BOMBed 24 valvers made considerably less smoke than the 12-valves at comparable HP rates. I do like the improved breathing of the 24V & be able to make HP without clouds of smoke, although the injectors and electronics contribute to less smoke as much as extra valves do.

Vaughn

 

[Cummins Cowboy]

ok many thanks to those that have bothered to contribute to this discussion. I love it when things get kinda scientific. Kinda makes you have to think a little. Ok here is my next point. Oxides of nitrogen are just one thing that is measured when it comes to emissions. What about carbon monoxide and hydrocarbon levels. If i understood my talk with my mechanic friend correctly. Carbon monoxide is unburnt fuel and hydrocarbons are partially burnt fuel. Kinda sounds like the same thing until i thought of hydrocarbons is being like partially burnt wood and carbon monoxide a wood that hasn't been burnt. please correct me if i am wrong. so my point is i am trying to figure out where all the fuel is going if less of it is making power in the ISB as compared to the 12 valve. So is the oxides of nitrogen the critcal factor here and hc and carbon monoxides the less important factors. And also what makes the ISB more efficient under load

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93 D250 5sp 3. 54 gears sans muffler, ISSPRO tach, K&N filter, needs to be bombed BAD
I would rather be cummin than stroken

 

[Bad340fish]

Without getting scientific, Have you ever driven a 24V truck?? IMO(Gonna catch some crap for this) They are more pleasant to drive. Smoother throttle and a wider power band. TDR Member Hiperf360 just sold a 12v running 45PSI Bombed pretty good. His 2001 ETC 5-speed pulls a trailer a heck of alot better than the bombed 12V truck. How many of you guys have stress problems due to your constant concern in MPG? lol My truck wieghs 7000lbs its a 3/4ton and it gets over 12MPG I am happy lol


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Clark
1999 2500 QC SB 5spd Flowmaster 3 chamber, K&N Re-0880
1968 Barracuda Formula S Viper Blue 11. 98@112

NHRA member for life

[This message has been edited by Bad340fish (edited 04-07-2001). ]

 

[Cummins Cowboy]

Yeah i have noticed that a 24 valve is alot nicer to drive. actually my first gen doesn't really compare. My dad has a 2000 ISB with auto. 2 things i did notice is that my truck seemed to start better in cold weather situations. Maybe it is just because he hardly drives his truck and it sits for a week at a time without starting it. but mine almost always starts on the first turn no matter what. Second is that turbo in his truck spools like right now. That makes it a lot friendlier to drive with the boost coming on so soon.

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93 D250 5sp 3. 54 gears sans muffler, ISSPRO tach, K&N filter, needs to be bombed BAD
I would rather be cummin than stroken

 

[DocStressor]

CC, diesel fuel is predominantly a mixture of complex hydrocarbons that combine with oxygen during combustion (oxidation and burning are the same chemical process). Diesel fuel hydrocarbons are chains or rings of carbon atoms with attached hydrogens. Some also contain some nitrogen and sulfur. When hydrocarbons burn completely in the presence of the proper amount of oxygen , the combustion products are primarily water vapor (H2O), carbon dioxide (CO2), and nitrogen (N2). However, the combustion process in an engine is a complex process that is not really fully understood. Incomplete combustion produces partially burned hydrocarbon molecules known as volatile organic compounds (VOCs), carbon monoxide (CO), oxides of nitrogen (NOx), and “baked” fuel droplets known as particulate matter (PM). Because diesel engines have high compression and air to fuel ratios, they have very high combustion temperatures. As a result, most of the fuel is oxidized with high efficiency and diesels produce very little CO and VCOs relative to gasoline engines. But NOx formation increases as a function of temperature and nitrogen oxidation products are the limiting emission in diesels along with PM. That means that modern engines must be primarily engineered to keep NOx and particulate levels low. Particulates form at the cooler edges of combustion zones and one way to reduce them is to add more air and increase the combustion temperature. But that would result in more NOx. This is not an easy problem to solve.

The stock ISB ECM reduces Nox by retarding injection timing when under light load. This keeps combustion temperatures low enough to minimize NOx formation yet doesn’t let the PM emissions get over specs. A lot of this also has to do with the shape and physical properties of the combustion chamber, injector spray pattern, etc. According to Cummins, the original ISB was designed to be 2-4% more fuel efficient than the 12 valve. But the stock ECM program for DC prevents this advantage from being realized for emission control purposes. Some members have reported 1-2 mpg increases with the EZ box set to modify timing only. That would be consistent with a return to the original Cummins specs. This should result in some increase in NOx emissions, but I don’t know if this is the case or not. When operating under a load, the ISB can operate more efficiently than the 12 valve engine because the ECM can sense the load and adjust the air:fuel ratio to an optimum. Mechanical fuel injection cannot do this.

So while it seems that increasing combustion efficiency should result in more power and fuel efficiency as well as reduced emissions, that is not the case when NOx is the limiting pollutant.




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1999 Quad cab 2500, SB, SLT, 4X4, 5-speed, 3. 54, tow and camper package, Lance 820 camper, Lance cabover stabilizers, Rancho 9000s, Airlift airbags,Reese Titan V hitch, Mag-Hytec differential cover with Amsoil 2000 75W-90 lube, Amsoil air filter

 

[Cummins Cowboy]

nice reply LEE

Thanks

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93 D250 5sp 3. 54 gears sans muffler, ISSPRO tach, K&N filter, needs to be bombed BAD
I would rather be cummin than stroken

 

[jwgary]

CC, you had it backwards. Carbon Monoxide (CO) is formed when you don't have enough oxygen to completely burn the fuel and for CO2. Hydrocarbons are just unburnt fuel. Since diesels are lean burn engines, it is really hard to form CO. Usually the only time you have a problem with unburnt hydrocarbons is when the engine is cold and there is not enough heat in the combustion chamber for complete combustion (blue smoke). I could go into more detail, but it's getting late.

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B I G O R A N G E AMBER-FIRE (BURNT ORANGE) / BRITE SILVER 2001(. 5), 2500, SLT, Q-CAB 4x4, SWB, AUTO, 3. 55, LSD, TOWING PACKAGE
ADD-ON'S: LINE-X, 1/4" STEEL LONGHORN HITCH COVER, WESTIN NERF BARS, YELLOW-TOP OPTIMAS