banshee

Don,

Actually, Scott just mentioned:

.

He just asked about the general application to CTDs. Noting that, I'll answer back without the attitude.

As far as the pullers... I don't know of everything about them all, but I do know a fair amount about one. Not saying anything beyond that. I will say this: Why spend thousands on stroker crank with matching rods and pistons when the stock stuff is adequate for strength when you can get an equal power increase with more fuel & boost that's practially free. Until you see guys max out the engines with turbos, cams, pump and injectors why spend much more on hard parts? I'd say that is the exact reason the guy who spend $7k on bearing hammers didn't go longer... you'd have to get a new crank or pistons with higher wrist pins... or both.

I didn't say you had to look up the rod length... good for you that you know it. You say yourself that no one has contracted for a different rod... I guess the stockers are pretty stout.

How you get from discussing extra stroke to designing a whole new engine with the stock head I'll never know.

John

HOHN

I'll throw my nickel in here. Instead of arguing about what to argue about, let's talk the pros and cons of rod:stroke ratio.

In gasoline engines, 1.75 is considered "ideal" for most applications. As you get closer to 2.0, you get a very peaky, high rpm powerband with little torque (anyone remember the small block Chevy 302 used in the original z/28s?)
Conversely, as you LOWER tha r/s ratio, you favor lower RPM ranges. There is a reason that 454 chevies have such a low ratio (4" stroke, 6.135" rod)-- they were conceived as a low-rpm truck engine. Contrast that with a Mopar 383 (6.358" rod, 3.38" stroke). Yes, a mopar 383 big block is WAY different than a chevy 383 stroker! The Chev will have bottom end, while the Mopar is a screamer.
The reason Don is correct has mostly to do with cylinder wall loading. Your piston rings are the SINGLE largest source of friction in the engine. So guess what happens when you decrease r/s ratio, and INCREASE the load on those cylinder walls??
The HUGE increases in friction at higher rpm easily offset any marginal gains allowed by longer piston dwell time near TDC. Since a turbocharged diesel does not depend on the "overlap" period breathing like a gasser does, any benefit to longer period near TDC is VERY slight, maybe unnoticeable. At lower rpm, this longer dwell near TDC might help with burn efficiency ( more time under pressure), BUT at higher rpm, this benefit goes away. Also, as RPM increases, your pistons start to run away from TDC so quickly (with the short rod ratios) that you can't extract much work from the combustion event. Moreover, shorter rods have much less leverage on the crankshaft.
Smokey Yunick and Larry Widmer always get in this rod ratio debate. Larry says 1.75 is ideal. Smokey says the highest possible is the best way to go. Notice that NEITHER of them believes in lower rod ratios. They are of the mind the 1.75 is the SHORTEST you should go for even a torque type of engine!

It's no accident that most NASCAR engines use ratios around 1.8, or even higher. F1 is an even more extreme example because of the excessive RPM involved.

Wanna guess what they use for rod ratios in Pro Stock cars that turn 10K rpm? Surprise! They are always at least 1.75, sometimes higher.

IF the CTD had a MUCH higher rod ratio to begin with, then there's a chance that stroking the engine would yield useful benefits at higher RPM. Even then, they would surely be very slight improvements.

But, the fact is the the CTD has a VERY short rod ratio, and VERY VERY heavy internals. The only reason it can handle 3200 rpm+ is brute strength-- it CERTAINLY was NOT designed for high rpm at all.

So, for the most part, Don is 110% correct. (do I get free Mach 3s for sucking up?)

But banshee is onto something when he talks about offset grinding only .020" When compared to a 4.72" stroke, a mere 20 thou is neglible.

So we can say then that it would be a negligible step in the WRONG direction..

BTW-- if the bores are stable, boring out a CTD can do nothing but help performance in every way.


Justin

MCummings

Scott,

So, You what you are saying is, you want to "Stroke This" ?

:P

Merrick Cummings Jr

RCW

I may as well toss in my two cents. A few years ago a couple of us decided to try to stroke a B 5.9, for use in a sled pulling tractor. It cost us three blocks, and untold hours of machine work and dyno testing, before we gave up and went back to fueling and airflow enhancements as the only economical solutions to more power.

The biggest issue with a diesel engine is the movement of the cylinder wall during the compression and firing strokes. They buzz like a bee, and will crack the block if the deflection gets too high. Increasing the stroke in the baby Cummins increases the deflection of the cylinder walls (unless you seriously drop the compression ratio by milling part of the piston crown down), and this deflection degrades the available rpm in which the piston rings will still seal and run effectively.

blackjack

Wow Scott what a can of worms you have opened. to directly answer your question as written is simple. does bore and stroke increase H.P. the answer is yes. This is fairly simple to understand boring or stroking adds cubic inches and cubic inches adds horsepower. Any internal combustion engine operates as an air pump increase the volume of air you pump and you increase the horsepower. light the fire and displace the air. increase the r.p.m and increase the horsepower. all are true statements. however add old man torque to the equation and you have added the element that makes horsepower usefull. the equation is simple and undebateable
h.p.= torque*r.p.m
___________
5252
foot lbs of torque accellerate equally at different r.p.ms
example: 400 ft lbs @ 2500
= same acceleration
400 ft lbs @ 3500
the magic of horsepower is in taking advantage of gearing at torque peak

Now the real question is what would you like to do with your horsepower or where would you like to use it in the power
band. are you going to pull with it or accelerate with it It makes a huge difference
you see it is impossible to do all things at once with the same build. pull the hardest ,go the fastest, have the best 1/4 mile times.

I recently built my Harley to do what I wanted it to do. the heads, cam, exaust and gearing were combined to make torque peak in the low to medium r.p.m. range I can now ride 2 up with loads of power taking advantage of the gearing so I am not constantly downshifting on grades and in traffic. I know a Harley and a CTD are miles apart but the principal remains the same. What are you going to do with it. to say that stroking an engine causes a H.P. loss is false to say that stroking an engine causes the torque peak a a different R.P.M. is a fact. Remembering that you cannot feel horse power and that torque can nail your butt to the seat. So with that said as you read the replies ,most have well thought out answers as they apply their logic to what they believe you want

just another .002

Missouri_Mule

I was just sitting around with nothing to do so i ran some of these strokes through a calculator to find out what kinda piston speed the cummins would have at several different strokes. Lets assume a 4000 fpm piston speed as a limit to rpm. Stock stroke of 4.72 can reach 5100 rpm and has a rod/stroke ratio of 1.62. Stroked to 4.92 the maximum rpm drops to 4900 rpm( how many people spin this high anyway ). Destroked to 4.52 the maximum rpm goes up to 5250 rpm and the rod/stroke ratio goes up to 1.69, getter closer to what could be considered the best ratio. At what could be the best rod/stroke ratio of 1.75 the engine would have a stroke of 4.37 and would be able obtain 5500 rpm without having too great a piston speed. This would be good for those dyno horsepower queens out there becuase everybody knows horsepower is great than torque after 5,252 rpm. However must people out there don't rev their cummins as high as any of the above examples so this small changes in stroke will probably have little effect on their horsepower and torque curves. I do have a question to end what is probably a somewhat meaningless post. How much can a cummins be overbored?

dsljunkie

Id say opening a can of worms is the understatement of the year .
To all that contributed (especially Don and Banshee): You all obviously know your stuff and Ive learned more in this thread than Ive learned this whole semester in College . I appreciate the VERY informative replies and hope to see more of them comming.
BTW: the truck that I mentioned in the begining will be designed to be a sleeper more than anything, meaning: interlocking silencer cans quietening turbo (or turbos), quad mufflers, etc. etc., you get the picture. A clean, harmless looking truck pulling up to the stop light, the sled, the light tree, the exact use is still up in the air, but the result is the same .+500 ponies in a truck tippin the scales @ 2500lbs ;D. The rpm range wont be anything outrageous (under 4k) I cringe thinking of that 150 lb crank turnin 5 grand :-X.
Were exploring all possible aspects before the actuall build and strokin' and borin' is one of them, because of the success with the pullin tractors.
Thanks again for all the excellent responses/
Scott
Nice touch

MCummings

[quote author=RCW link=board=7;threadid=22049;start=15#msg206686 date=1068162633]
It cost us three blocks, and untold hours of machine work and dyno testing, before we gave up and went back to fueling and airflow enhancements...
[/quote]

No matter how bad I want to, and still want to have a 6.0 Cummins,, THAT ^ is why I won't do it.

Merrick Cummings Jr

HOHN

[quote author=eieio link=board=7;threadid=22049;start=15#msg206825 date=1068176051]
Wow Scott what a can of worms you have opened. to directly answer your question as written is simple. does bore and stroke increase H.P. the answer is yes. This is fairly simple to understand boring or stroking adds cubic inches and cubic inches adds horsepower. Any internal combustion engine operates as an air pump increase the volume of air you pump and you increase the horsepower. light the fire and displace the air. increase the r.p.m and increase the horsepower. all are true statements. however add old man torque to the equation and you have added the element that makes horsepower usefull. the equation is simple and undebateable
h.p.= torque*r.p.m
___________
5252
foot lbs of torque accellerate equally at different r.p.ms
example: 400 ft lbs @ 2500
= same acceleration
400 ft lbs @ 3500
the magic of horsepower is in taking advantage of gearing at torque peak

Now the real question is what would you like to do with your horsepower or where would you like to use it in the power
band. are you going to pull with it or accelerate with it It makes a huge difference
you see it is impossible to do all things at once with the same build. pull the hardest ,go the fastest, have the best 1/4 mile times.

I recently built my Harley to do what I wanted it to do. the heads, cam, exaust and gearing were combined to make torque peak in the low to medium r.p.m. range I can now ride 2 up with loads of power taking advantage of the gearing so I am not constantly downshifting on grades and in traffic. I know a Harley and a CTD are miles apart but the principal remains the same. What are you going to do with it. to say that stroking an engine causes a H.P. loss is false to say that stroking an engine causes the torque peak a a different R.P.M. is a fact. Remembering that you cannot feel horse power and that torque can nail your butt to the seat. So with that said as you read the replies ,most have well thought out answers as they apply their logic to what they believe you want

just another .002
[/quote]

EIEIO:
I felt that I needed to comment on your post. While the analogy of an engine as an air pump is as old as the hills, it isn't really a good analogy.

The QUALITY of flow is FAR more important than the QUANTITY of flow. So we can easily say that if we increased the displacement of the 5.9 to 6.0, but we destroyed the quality of the flow, we would have taken a step backwards.

Furthermore, your statement that increased bore and stroke always equals more hp is simply not true. While the hp equation may not be debatable. The utility of the inputs into that equation, and the relative merit of each is CERTAINLY debatable.

Since hp=tq*rpm/5252, what happens if we increase torque in such a way that we decrease rpm even more than we increased torque?? VOILA-- LOWER HP, even though we increased displacement. An example would be if you had an excessively low rod ratio. You might increase torque a little bit, but you will decrease rpm by a LOT bit. Thus, you would have lower peak HP.

Example, say you take a stock ETH, rates 245 hp@2700 rpm and stroke it by a half inch or so. What if we created geometry so bad the engine will only rev to 2300rpm? Let's say that this stroking netted us 50lb-ft of torque. We assume flat torque curves here.

Stock: 245hp@2700rpm, the engine is making 477 lb ft here.
Stroked, we add 50lb ft and compute the HP at the lower rpm:

477+50=527lb-ft

527lb-ft*2300rpm/5252= 230 HP!!

Guess what, our increase in torque made us LOSE 15 HP!!!

So to summarize: increased displacement does NOT always mean more HP. Efficiency plays a key role.

Besides if you've been driving a 5.9 and eating up 6.6dmaxes and 7.3PSDs, you should ALREADY know that there IS a substitute for displacement (like maybe a turbo?)

Justin

blackjack

Justin I understand all you have said and in fact you are saying nothing more just in a different way. all factors being the same bore and stroke creats horsepower. Its mathmatical do not change rpm do not consider air flow do not consider gearing and H.P. increases. AS I was trying to state the peak torque band will change with any given change I happen to believe that stroking the CTD is the wrong thing to do but my desired result may be different than Scotts. The question as Scott asked it has many answers. As far as an engine being an air pump simply stated it is no more than just that, However you are 100% right when you say that air flows and efficiencies play a key role they are everything to making a better pump. Turbos pump air and help to make a better air pump,
your own example confirms that changes to displacement causes changes to where the peak torque output comes in. making horesepower is easy putting it on the pavement is entirely a different story. The end result is everything compared to just making H.P. Old guys like myself that grew up in the 60s new that boring and stroking made H.P. later we had to learn that air flow had more to do with it than we ever imagined. it wasn't that long ago when we could not even imagine holding the tolerences that would allow a motor to stay together long enough to spin at todays rpms. well just starting to ramble here besides torque is king and horsepower allows you to take advantage of gearing options, You are also right in stating that 5.9s eat maxes and psds because of the turbo (air pump) good bantering with you Justin. We are really on the same page just making many of the same points in a different way. Scott if you can apply only a part of all the info from the replies ypu have recieved I have a feeling you will be winning alot of pulls.

AlpineRAM

I'll throw in my 2c here:

I think thatthe main disadvantage of boring and stroking the ISB would be that even though the block is rather massive with the high hp-high torque that comes along with the fueling mods we are getting close to the block capacity. Stroking will lead to longer levers on the crank and therefore introduce new problems, especially with the differeent angle of the rod and the bigger moments acting on a weaker block.

AlpineRAM

Don M

Hi Alpine!!

Don~

Hammer

Strokin Or Destrokin.....
Hmm seems like quite the battle on this.
Guess I'll add my .02 and see where we go..

With the dimensions of the little 5.9 internals to stroke it would not make the best choice.To make use of doing this properly you would need to re design a piston that will allow you to move the the pin up into the piston further to keep the geometry and not add more side stress to cylinder walls.Sometimes what we try to gain by stroking a motor will bring on other bigger problems than most care to deal with.In our small block Chevy's we run on dirt stroke did increase HP but at what cost?.Turning our motors nightly on the big ends of the chutes to near 9800rpm with the stroke to make 410.2ci has cost us alot of bent,broken,stretched and all we netted when we did it was about 50hp.Was it worth it,maybe not at some tracks less than 1/2 mile,but on the big tracks where HP determines the outcome,if you want to play you have to pay.Our 383ci motors fair better on the 3/8 and smaller tracks as they wind up faster and will stay there longer with alot less stress or breakage.


Far more would be gained in the 5.9's to destroke them as it would allow rpm's to be attained quicker and them to be held longer,especially for pulling sleds where HP is better suited than torque to pull a sled.Sow what is the best answer here,it depends on what you sport is with the truck.Street driving wars,drag racing and dyno spins would be better suited for destroking where all out HP wars would be better stroked.Depends on what you wallet can stand and if you have the cash to have the speciality parts built to stroke one big.

I will now go and take some stress tabs and asprin due to having to agree with Don,that hurts alot,,LOL ......Andy

P.S.-The resident Mountain Motor man in our area,Charlie Garrett,will tell you this statement and its one ALL of the street racers in my area live by.......

"There is NO replacement for displacement"

Don M

I will now go and take some stress tabs and asprin due to having to agree with Don,that hurts alot,,LOL ......Andy


LOL!!! Me too, I just puked my liver up

Don~

AlpineRAM

Hi Don ! ;D

To keep this on topic:
I don't know the costs for boring and stroking/destroking a Cummins, but wouldn't it be feasible to replace some of the heavy parts of the body with light plastic parts and net much better ET than the little that could be gained by the engine mods? I'm thinking about the hood, doors and complete bed.

AlpineRAM