Please educate me on diffs between 12/24 valve engines: no holy wars intended

[TomGolden]

Howdy all,

I have been quite curious for a while now to post this question. I'm certainly no mechanic, though I have a decent basic understanding of engines/cars/etc. . I would like to ask you all if you could kindly educate me on the pros and cons of 12 and 24 valve engines (meaning 2 or 4 valves per cylinder).

The one [obvious??] thing I can think of would be quicker air flow intake and exhaust, but I'm certain there must be other benefits and likely drawbacks to having 4 valves per cylinder.

I certainly don't want to start any flame or religious wars over this, as I know for some it is a heated topic. I am merely trying to understand the differences in these engine technologies.

Many thanks,
Tom


------------------
Get outta the way: The Cummins is Cummin'!

Tom Golden
Godzilla: Patriot Blue 2001 2500 SLT QC 4X4 LWB ETH/DEE, Tow & Camper packages, 3. 54 Ltd. Slip, 4 wheel disc ABS, Isspro EGT/boost gauges, black SmittyBilt nerf bars
2001 Zinc Yellow SVT Mustang Cobra on order
NRA Life/CRPA/El Dorado #26 F. &A. M. of California

 

[Jeff Clark]

I know that 4 valves per cylinder allows the injector to sit in the middle rather than off to the side in 12v. This allows for a more complete combustion for less smoke and better economy. This is how Cummins was able to meet EPA standards without a converter on the 24v.

 

[tmacc]

I don't know about the "better economy" part. My '93 got 18. 5 mpg, my '01 gets 14. 5 mpg. Yes, the '01 has a auto trans, and 4. 10 vs 3. 55, I'm still a little disappointed. (I still love this truck though. ) All other factors are basically the same.

------------------
'01 2500 4x4 4. 10 White/Driftwood QC plain SLT auto trans snow prep camper package tow package bed liner mopar mud flaps Reading Ind. 33" tall contractors cap. Toys: 3 mountain bikes, a cyclo-cross bike, and a road bike, plus a couple of whitewater kayaks. Yeah, I know their human powered, but the bikes are fun to modify too. Like spending $$$ to make trucks more powerful, It takes $$ to make bikes lighter. Titanium isn't cheap.

 

[HC]

When Cummins says the 24 valve has "better economy" that is only relative to what a 12 valve would get IF it was held to the newer, tougher emissions standards. In real-world numbers, the 12 valve guys get better mpg.

I think we (24V'ers) do have an advantage on the maintenance end - I know I don't have a scheduled valve adjustment until sometime past 100k; for 12 valves it might be every 15k (somebody please speak up if I'm reporting unfairly on the 12V).

12 valve engines don't have the lift pump problems.

24 valve engines are easy to BOMB with a plug-in box.

12 valve engines might have a 5 speed with a 5th gear nut problem, or a 6 speed with a smaller input shaft. The latest (probably mid-2000 and up) 24 valves are paired to the latest versions of the 5 and 6 speed transmissions, which should have slightly improved designs.

Pros and cons to both motors, as you can see. I'd be happy owning either. I say drive the wheels off whatever you own! #ad


------------------
2001 ETH, QC, LWB, 4WD, 3. 54, SPA Pyro & Boost, K&N RE-880 w/foam pre-cleaner, ARE Z-series Cab-high shell, Rear ARB locker, and all kinds of synthetic fluids...

[This message has been edited by HC (edited 01-09-2001). ]

 

[Mad Max]

Both 5. 9L, 360cid of Cummins I6 directed injected diesel power.

2nd gen through 1998. 5
The 12v were mechanical beasts, the mechanically timed injector pump ran the show.

1998. 5-Current
The 24v are electronic, and an ECM plays a part in controlling the pump and making "cleaner/greener" power. The electronics allow for much more finite tweaking of fueling... and that likely keeps the EPA/CARB and the rest of the Eco-nazi's at bay.

Two very loyal camps, but with the 12v out of production as far as the Ram's concerned, its a mute point unless your looking into the used truck market.

Max