Big Cubic inch Cummins

Big Swole said:
I know a well known drag racer that went to a big bore motor...tested..and then went back to stock.....Bigger didn't gain him anything....

Ended up running his best yet with a 5.9 ...

Last I heard anyway....
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I know this person...he was running a 7.3 liter 5.9 block
 
"There are some secrets in that engine most people would be baffled by if they figured it out."


never seen a "secret" in a motor yet, that wasnt so not secret, as in has been done many times before - just elsewhere in another motorsport, usually on a gas motor, and especially never seen one that would baffle anyone who "knows" performance motor stuff

The only thing bafflin to me about diesels is why so many think there is some kinda witchcraft involved, or things need to be different in a diesel as compared to any other motor in order to get performance.

Its just a motor, that runs on air n fuel, and anything one can dream up has already been done many many times - and usually about a hundred years ago.

All we have done over the years, is refine those things and secrets.

Interstingly enough "ALL" curent diesel technology on the winning trucks, appears to be direct copies of the successful gasser motor technology thats been around for years. It is not in the too far distant future that the only difference between a performance gas motor and a performance diesel will be the fuel used.


High rpm motors of a diesel nature might very much like the short stroke large piston setup, as in "over square" as we used to call it in carting, because the heads we are using are marginal at best, and an oversquare setup would make the best use of the available airflow.

As stated previously - bigger isnt always better unless you have the airflow to work with

Time will tell - racing performance in a diesel is still relatively "new" to many
 
Smokem said:
I'm confused, I thought this was leaning toward the Sled Pulling side of things. But I hear "we are shorting the stroke", look past the grammar and you will see that is a good idea, now just add spark plugs and a throttle body and put it in a 6800lb Light Super. If you still pull in a Diesel Class, you might want to look into what others whom took the "antiquated sled pulling technology" to the tacky pavement and are doing just fine.
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I was under the same impression. I thought this thread was more on pulling motors seeing as the guy who started the thread does pull.
 
These mysterious big cube engines do not exist.

You boys have lost your minds LOL
 
Comp was right...


In a class where inducer size dictates the biggest hurdle, you do not necessarily want to increase engine displacement.

When a compressor moves more air it wants to see more pressure. This is why a compressor map will always lean to the right.

Well, for any given flow rate, the smaller displacement engine will require more pressure. This is precisely why a 5.9 will make more power on any given charger than a 7.3 will injection systems being equal.

The big cube engine needs bigger chargers for the same efficiency at any given flow.

When classes are limited based on inducer diameter, it makes little sense to purposefully handicap yourself.
 
In an unlimited inducer class bigger cubes would win, using Charles' definition.

I think alot could be learned from the Audi F1 engine...
 
So back to the subject at hand. Lets here some examples of how it has been done and how it worked, not just this my buddies cousin did it once stuff.
 
wouldnt be the first time a block skirt was generously releived in order to accommodate an offset ground crank, especially if there is a girdle to help strengthen things

Cam location may be a bigger issue, depending on how much one tries to offset grind
 
would a small base circle cam alleviate that?

Of course lookin at the head - icould see how easy it would be to make an overhead cam - man does that open up some possibilities for flow n such - completely redesigned head architecture -lose the lifters n pushrods...... ;o)


whats the bore spacing on a cummins - there may be a few overhead cam motors might be adapted lol
 
seeker1056 said:
would a small base circle cam alleviate that?

Of course lookin at the head - icould see how easy it would be to make an overhead cam - man does that open up some possibilities for flow n such - completely redesigned head architecture -lose the lifters n pushrods...... ;o)


whats the bore spacing on a cummins - there may be a few overhead cam motors might be adapted lol
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do this with a billet block and you could just about measure the stroke in feet, no water jackets or anything like that...
 
Well you guys are all wrong it is possible we did do 444 cubes but i agree with comp to some degree the cubes didn't net a lot of HP due to the head we couldn't flow the air required to benefit from the cubes. We decided to thump the stock motor harder and it was somewhat better for drag racing. I believe that the longer stroke would benefit the sled puller more than the drag racer but the bigger bore would help the drag racer. We did both but as they say hind sight is 20/20 I Believe the big bore and stock stroke or less stroke is better for Rev gain or engine acceleration.
 
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JerrodGlover said:
So back to the subject at hand. Lets here some examples of how it has been done and how it worked, not just this my buddies cousin did it once stuff.
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I love that, lol.

The thought that people cautioning against doing what you're asking about because you'd be running in the opposite direction in a sport where the classes are regulated by airflow isn't pertinent to the subject at hand is hilarious.


Lets start a thread about the best way to slit our wrists next. And by God, we don't want to hear anything about how that might not be the best idea, just tell us the best way to do it.

:hehe:


I hope your checkbook is sight bigger than your ability to reason.

;)
 
they been doin small base circle cams with a lot higher spring pressures than we run, for 50 years

I would be very interested in the parts/combo for that 444 and how it was achieved
 
So you’re willing the trade air flow, as in small base circle cams for cubic inches you can't feed now.

Besides the base circle on the cam is not the place the rod hits, it’s the root of the cam between lobes. this would be a very weak cam

Airflow is the most important improvement venue in any performance program. If you make the engine bigger, all you will do in lower the rpm where the engine will make peak torque, and peak cylinder pressure. This low rpm peak cylinder pressure is where you lose cylinder combustion containment. No amount of head studs, o rings, fire rings, wielding the head on will help.


In sled pulling its hp that pulls the load, tire speed is important, and if you pull the engine back down thru peak torque, this is the point where most people tear they parts up.


Bore is important, the bigger the better, this allows airflow in two ways. First bigger valves, we are using .150 bigger valves in the CR head, this equates to huge flow gains, if the head is ported.
Second the bigger bore unshrouds the valves and allows more radial flow on the bore side of the port.

Stroke is great if you have a cylinder head that flows numbers twice what a current Cummins head is capable of .

One other thought, is rod to stroke ratio, in a Cummins is not that good with the 4.72 5.9 crank with the 4.88 its going downhill, and with anything bigger it just keeps getting worse.
In a 2.6 engine the air is already limited so I would shorten it even further, to say 4.5 , add that to a 4.250 bore , and you have a great engine . Now in drag racing I would go even further to around 4.250. This is to help with acceleration, which is need in drag racing, but not in pulling
 
One advantage is that a big CID engine should spool turbos better which can help in both drag racing and pulling even if it doesn't make much more power.
 
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