Might be a dumb question but can you run a lot more boost with diesel vs pump gas? I'm hearing of Cummings Ram turbo trucks running 55 lbs of boost with stock internals.

 

it way more complicated than differences in fuel

 

Please educate me

 

Well first off a diesels compression ratio is typically way over 20:1 to start with. And the fuel pressure can be in the thousands.

 

i always run diesel. its a dirty little secret

 

55psi? is it broke? most people run about 60-120psi. deisel is ignited by combustion heat, gas ignites by spark. apples to chickens.

 

How do you think skinnies is running 8's on a stock shortblock? The answer is easy, he runs diesel.

 

The difference is diesels only inject fuel milliseconds before the combustion event happens as the piston is traveling on it's way back up from the intake stroke. Unlike a gas engine a diesel is only ingesting air on the intake stroke and not air/fuel. Because of this they can run incredibly high cylinder pressure(16-17:1 compression and 50+psi of boost) and not detonate because the combustion event is much more controlled by only injecting fuel right at the precise moment it's needed on the compression stroke to create combustion.

On top of that they use a fuel that burns much slower than gasoline and doesn't have the tendency to auto-ignite.

There is more to it than this, but this is the short version. This is also very similar to how direct injection works and is the reason fuel mileage can be increased in vehicles utilizing it along with added horsepower. Compression ratios and boost levels can be increased without the tendency to detonate or pre-ignite.

Now I'm not a diesel or direct injection expert, so I may have some things backwards, but I'm pretty sure what I've posted is correct.

 

wow, looks like we need some deisel lessons... lets start with 17-24:1 compression. the internals are way stronger, more aluminum in the top half (above the wrist pin) a diesel piston than intire gas piston. diesel has more BTUs. lower volatility rate, will not ignite on spark. and its not kinda like direct injection, it is direction. common rail system are high pressure electricaly controlled. (pressures as high as 26,000 psi). someone else can keep going on this... lets get back to real fuel and forget this lamp oil.

 

I think most factory diesel engines are more like 15:1-16:1. That's not to say that the sled pulling and drag guys aren't running much higher CR's than that.

 

Thanks guys. I've never owned or worked or obviously even looked into diesel. Closest was accidentally putting it in my bike one time....boy did that run like ****

 

Guys, you're talking about two different engines. 60-120 psi is a stretch by far. 15-50lbs is more like it. Diesels are built for one reason...to tow and work. I'm not saying that there isn't a place for them in the race world, but you're going to be dealing with two totally different animals altogether. (obviously) The compression is about on par with the numbers around 17:1 to 20:1 They are built with the intent for longevity and harsh working environments. The rotating assemblies are built very heavy and don't really have much regard for light weight, high revving perks engineered into their design. I realize that the engines that I'm talking about might be quite a bit different than a duramax, cummins or power stroke, but they are built with the same use in mind. Our deck engines on our workover rigs are rated at 600 hp but they'll do 1950+ftlbs of torque at 1200 rpm. They endurance test these things at full load for a 24 hr period! They are meant to be ran for several tens of thousand of hours which include revving up and down all day long and running several different accessories such as hydraulics along with the drawworks and the drive train to move the rig all on the same allison trans. I had a buddy with one of the biggest engine that caterpillar makes (3612). He used it to frac wells here in wyoming. It made 3500 hp and did it at around 1000 rpm. It would consume 4-6 gpm a minute on full tilt! They are brick shithouses. I could go on and on about all of this right down to the assembly procedures to achieve the clamping forces on the caps which is mind blowing. (involves hydraulic presses along with a **** ton of torque) The amazing thing is these things can be rebuilt in the field! It's not uncommon for a mechanic to "roll a new set of bearings in" right where the engine sits. lol Sometimes its not economical to take the engine to the shop since the size of them might be a hinderance. 55,000 lbs for the 3612 I believe. On the flipside look up "mustang with three turbos" on youtube. All you tree huggers out there will ****. lol Oh and one other thing diesel in gasoline engine = catastrophic failure and gasoline in a diesel engine = the same thing. You probably hurt that engine if you got a big slug of diesel into it. Just my humble input.

 

^pretty much...diesels will range from 14ish to 25ish compression ratio but typicaly in the 17s to 21 is most common, but i wont argue with you about boost, depends on wich hill billy's you hang out with, down here these jokers throw so much fuel at em 60lbs of boost aint that big of a deal and water or meth injection on just head studs. you put gasoline in deisel detonation broke pistons, diesel wont burn in gas. it seeps past the rings (saying it was mixed enough to run) and will thin out your oil and well you know the rest. been an industrial equipment tech for 5 years. (use to work on cars).

 

How does a triple turbo work? Do 2 spool up a third hitch then feeds the engine?

 

ya 2 feeding into the inlet of a single, google pics of that ****, holy pipes batman

 

A diesel engine will survive a fuel mixup. The worse that will happen is the injectors cups will dry out. they used to be some drivers who would mix half a tank of diesel and half filtered burnt grease like from McDonald s. Cummins make some pretty tough engines. On the N14 the engine can survive with just 8psi of oil pressure.

 

On my bike I t was easy, drain the tanks and bowl on the carb, change plugs and good to go.

 

In the diesel world, they are compression ignition motors. They will not run until the compression literally ignites the fuel.

The duramax, Scorpion 6.7 (ford) and 6.7 cummins, the compression ranges from 16.8-17.3. Ive never read of any diesel over 20:1 compression.

They are direct injection, with pilot injection, to calm down the diesel clatter and make them quieter. Fuel rail pressures vary from 10k-29k. Yes, 29,000 psi of fuel pressure


Sled pullers and race diesels actually LOWER the compression, but it makes them harder to start in cold scenarios.

As for boost, my stock 6.7 cummins made 30, with a smarty it made 34. My duramax only makes 20-22 stock. The programmer is in the box Most twin turbo setups make 50-80, rarely do street driven trucks make more than 80-90 psi. Most single turbo stuff is in the 50-70 range. The 6.7 cummins stuff, most guys are in the 50s. Drive pressure is very important in the diesel world. Its what makes those things so efficient. pressure ratios are rarely more than 2:1.


they only turn 3000-3500 in most stock apps, and race engines turn 4000-5000 rpm tops. Diesel fuel begins to lose a LOT of efficiency in the burn process over 5000 rpm because it takes so long to burn, hence why most diesels are in tow vehicles, but thats changing quickly because they are getting extremely efficient in small displacement applications. Its just hard to fight the notion that they are smelly and smokey.

You can run a diesel at most any airfuel, up to 50:1 AFR. Most are tuned off smoke and EGT. Make more power? Give it more fuel. EGTs get too high, add nitrous or a bigger turbo, then change where the fuel comes in

the only way to really hurt one is to over fuel it ( Too much fuel, not enough air, EGTs skyrocket.)



Diesels are cool. Its a small undergound world of gearheads. totally different animal.

As far as multiple turbos, yes. Its called compounding. The primary is fed by the secondary. Primary is the small one, secondary is the large one.


Ive owned several diesels over the last 10 years, and only recently started modding them the last 2 years

Louis

 

Good short overview^

I think most would call the large turbo the primary and the small one the secondary, as that is the staging of the compressors

 

The primary is the small one from my experience and a quick google search.