dsljunkie

Curious... I know with pullin tractors and other high hp motors, it is very benificial to put a little stroke on the crank as well as boring up to about .050.
Has anyone tried or heard of putting say, a half inch of stroke on a CTD? I would imagine with a half inch of stroke and a .030 bore you could see increases of about 150-200 horses and about 4-600 ft. lbs of torque, those are just based on other motors Ive seen stroked so I imagine I am not entirely correct, but I am curious if anyone has done this. This may come in handy on my next project. +500 ponies in a 46' 1/2 ton 4x4 ;D 8).
All replies welcome 8),
Scott

Don M

Nope the HP will drop with more stroke. More stroke adds TQ not HP. Piston speed goes outta sight too. Gassers have little bity strokes. 3.5 inches or so. We have 4.72

Don~

Superduty12v

Hey now... my gasser has a 4.25" stroke :P (496)

Shovelhead

My gasser has a 4 1/2" stroke.
Harley Shovelhead

banshee

Don,

How can you say it will add more TQ but not add HP? They're related. (HP=TQ*RPM/5252)

IMO any increase in displacement is always going to make more power. There's simply more area and/or leverage for the cylinder pressure to do its work. I will agree that a bore increase will be more adaptable to high rpm HP since it has numerous advantages over stroking, but adding stroke will still add HP.

High piston speed isn't an issue with diesels at all. Even at 3500 RPMs the piston is travelling a lowly 2753 fpm. Most engine builders don't even raise an eye until that figure climbs over 4000 fpm.

Adding additional bore (standard is .030) will help by A) adding cubes and probably more importantly B) unshrouding the valves.


John

dsljunkie

As I understand, which may not be correct :-, the strokin alone will not add much hp, and as Don said may decrease hp . however, does the strokin not make extra fueling mods more effective? Also, the effect of strokin a crank is mainly more torque with minimal hp. The effect of boring is more hp with minimal gains in tq ... as I understand :P.
Don, Im curious as to why you say it will decrease hp? Im not doubting you, because you obviously know what your talking about and Ive been told you are very thourough in your testing. Have you tried to put some stroke on a crank? If so, how much? And did you do any boring at the same time? How about fueling?
Banshee, the math seems to make sense. Have you seen or tried strokin a CTD? Im just tryin to get everyones opinion here so are all still welcome 8),
Scott

Don M

Its hard to make any generalized statements anymore :'(

Yes, you are correct....John you can gain HP with increased stroke, but if the goal is higher rpm as stated in Scotts posts I personally would not stoke an engine that already has a rod to stroke ratio the Cummins has to gain HP at high rpm. If anything I would destroke the engine to crank the rpms up.

Most of the big 427 small blocks that use either the Callies or Crower cranks to get the big cubes are known for great TQ but lack the higher rpm HP of even the smaller 383's. I know this cuz I built more than a handful of rats.

I gotta say the increased piston speed being a trouble spot. I have weighed the components of the rotating assembly and the weight alone is the enough to get me nervous. Rod stretch is already a problem at 3500 rpm. Yes I have data to that effect.

Can a guy get all the parts made special to take more abuse? Yep, you can spend all the cash you want and build anything you like, but the end result of a stroked B series is not going to be a cheap date and the normal stroke can, IMO work better for high rpm use.

I do agree that an overbore is going to help shrouding....this is why I feel that the vendors who are currently installing larger valves in cylinder heads for standard bore engines are ripping folks off. Selling them stuff they DO NOT need or that has shown to lower flow at low lift ( the area most camshafts for Cummins spend a long time at)

On piston speed...I agree that most builders are good with a piston speed of 4000 plus FPM, but we are talking about components that weigh a lot less than what the Cummins uses. The forces involded to sling around that kind of weight are very high.

All this leads us back to what you think you are going to gain from a stroking an engine that is just 360 cubes and already has a stroke wildly higher than most engines in that cube range.

Many small blocks at 350 cubes use a 3.5 inch stroke. Piston speed is doable with their lighter components, and short strokes @ say 8000 rpm

Look at your piston speed and the forces of heavy weight pistons, pins, and rods with the stock stroke of 4.72 inches and tell me this is a good thing @ 8000 rpm.

Now look at the same engine and tell me if a shorter stroke will help more in durability and HP in the higher rpm bands.

A quick look at the high rpm engines in all racing classes reveals some clues...none of them use a long stroke.

An indicator is F-1 cars using the new BMW engine that turns 18,000 rpm and makes 900 HP normally aspirated! Albeit an extreme example...the stroke on this engine is reported to be less than 1.5 inches!!!!!!!!!! trying to tell the guys @ BMW that they should increase the stroke using your TQ/HP formula alone is going to raise some eyebrows.

Don~

Don M

[quote author=dsljunkie link=board=7;threadid=22049;start=0#msg206480 date=1068133903]
As I understand, which may not be correct :-, the strokin alone will not add much hp, and as Don said may decrease hp . however, does the strokin not make extra fueling mods more effective? Also, the effect of strokin a crank is mainly more torque with minimal hp. The effect of boring is more hp with minimal gains in tq ... as I understand :P.
Don, Im curious as to why you say it will decrease hp? Im not doubting you, because you obviously know what your talking about and Ive been told you are very thourough in your testing. Have you tried to put some stroke on a crank? If so, how much? And did you do any boring at the same time? How about fueling?
Banshee, the math seems to make sense. Have you seen or tried strokin a CTD? Im just tryin to get everyones opinion here so are all still welcome 8),
Scott

[/quote]

Scott,

There is more to the "whole picture" than just putting in more stroke and giving the pressure more time to act on the piston top. Trade offs begin to eat away at gains. Airflow in and out of the engine is one place to look. Factoring in the reliability portion is another one.

Offset grinding of cranks is old news in gassers to gain some stroke or the Callies and Crowers I mentioned earlier that are custom strokers. This is not to gain HP, but rather to gain off the line low rpm TQ to move heavy street stock cars or just plain old street racer stuff faster in the short times. These are used in engines that already have a short stroke when compared to the Cummins anyway. 35% shorter in many cases.

Johns math is solid, but you cant look at a single formula when designing an engine for a task. All the strokes in all the engines would be super long if this were the case. The trade off begin to hurt more than help in the end.

Don~

banshee

Don,

I see the point that you're trying to make, but you're mixing gasoline race engines with diesels. No matter how hard you try you're not going to spin a diesel 8,000 rpms much less 18,000. Ferrari and BMW F1 engines are a far cry from the CTD. We have a limit to how high we can rev, and our limits are quite a bit below the line where undersqare or oversquare begins to matter.

Contrary to what you mentioned in your post, the big engine builders of today (Lingenfelter is Decatur, IN, MTI in Houston, ARE in Canada, Cartek in NJ, MMS in Cali) see impressive gains when going from 383 cid to 422-427 cid in GM LS1/LS6 motors. The average 383 motor will make ~460 rwhp while the 422/427 motors are around 525-550 rwhp. The hp curve for the big "superstroker" is sick compared to the "small" 383. All things being equal, more displacement (no matter how it is acheived) is going to make more power. I have 2 race bikes - 1 with a standard displacement (349cc) and one that is stroked 6mm and bored 2mm to 403cc. The stroked bike will walk to dog on the stock displacement bike, and the engines peak at ~12,000 rpms. Yes, they're both still oversquare, but adding stroke even at that rpm makes an impressive difference.

I agree that loads on the CTD would be bad at gasser RPM levels, but, on the other hand, the crank, rods, and bearings are built to support it. Hold a CTD rod in one hand a crower or oliver for a SBC in the other!!

Spinning a CTD to the moon will take lighter parts... I agree. You can't take stock parts from a SBC and go 8k rpms with it, either. Winston Cup motors are lightened to the extreme to make the revs they do (8500-9000), and they yet they often don't even make 500 miles.

For a guy who is doing a rebuild anyway the extra stroke from offset grinding the crank and boring the cyliders .030 is NOT going to sap power. Adding more cubes will ALWAYS make more power. I agree that more bore is better for High rpm motors as it allows bigger valves, unshrouding valves, better combustion chamber shapes, and an overall lighter rotating mass, but for our diesels it isn't the only way. I think you missed the point of my first post. I'm not saying that stroking is better than boring or vice versa... they both have their advantages and disadvantages. I'm just saying that displacement has the unique advantage of always adding more power.

John

banshee

dsljunkie,

No, I have never stroked a CTD myself, but I have seen and done plenty of other motors myself. The result is always the same... adding displacement adds power. The cylinder pressure in a diesel is far higher than on a gasser, so it only makes sense that adding displacement will net even bigger gains than on a gas engine. I don't think it's done very often because the stock cranks are already so strong, so spending the money is silly. I know of guys that have bored their motors (CTDs), but I don't know how it affected power due to just those changes.

John

Don M

John,

Yepper a larger SB will make more HP, but these guys are not limited by cylinder head design and the most important, port flow like we are. They are years ahead of us in the number of options they can go for more flow.

John Lingenfelter actually writes in his book:

quote" I complemented the stroker cranks with a 5.85 inch rod that results in a rod to stroke ratio of 1.51 to 1 that is not ideal, but then this engine is usually intended as a TQ monster rather than a high rpm horsepower engine." unquote.

Further he states: quote" Typically, the larger displacement small blocks ( this is the stroker engines we are speaking about here ) generate great TQ, but sometimes suffer in horsepower per cubic inch because the longer strokes create additional piston speed that can eat horsepower ar higher engine speeds" unquote.

This is one of the trade offs I was writting about. The airflow issue is much larger with the cylinder heads we have now and nothing is available to fix it yet.

As he states the rod to stroke ratio is getting out of hand at 1.5 to 1. Any guesses as to what the Cummins B has now and would have with say an additional .250 -.500 stroke added on top of that?

Sit back and think about how easy it is to push air into our engines with turbos...and now go figure out how you are going to get that air out the back side with a turbine in the way. Add more cubes to the equation and even more CFM of air and tell me how you are gonna get the stock sized exhaust port ( which we are stuck with right now ) to flow enough air. This is a large pumping loss that nonne even thinks about. This is only a small part of the airflow limitation we now have.

You are incorrect that the rotating parts can take the stress we would put on them at high rpm. In stock form they cannot take it. I have enough data here to tell me the stresses are higher than sound engineering is willing to accept.

The Cummins is contructed and designed to make good BSFC at low rpm. High rpm use requires less stroke, not more, to move the power band upwards in rpm band. Look at the shorter stroke Powerstrokes, both models of it and the Duramax.

Don~

banshee

Don,

I'll say it again, I'm not saying that stroking is better than boring, especially for high RPM power. You stated in your first post, however, that stroking along will sap hp... wrong!

As for right now, the LS1/LS6 guys are limited by intake manifold design. With wide open sheetmetal intakes the superstrokers make massive numbers, but streetability suffers. Just like with anything there is a tradeoff between top power numbers are usable, streetable power.

John Lingenfelter makes those quotes, and he's right, but the RPM limit he speaks of is lower than most street engines will see and is waaaay lower than what an CTD will see. Even pulling trucks are staying around the 5,000 rpm window, and guess what, they're doing it with stock cranks and rods... they can take it! I must be somewhat right.

I'm not sure about the rod length of the CTD, but I'll bet it's more than 1.5:1. Offset grinding .020 is not going to detrimentally affect the R/S ratio.

I also agree that head ports, valve size, and intake and exhaust manifolds are highly restrictive at high rpms, but they're not designed for that. The 24V head flows roughly 65% of what a LS6 head flows while having to feed more cylinder volume. Like you said, they're made for good VE at lower RPMs.

John

Don M

So we are back to the beginning of the first post...Scott asked about high rpm and adding stroke to gain power.

I still say that stroking is a step backwards for increased RPM.

The reasons in part I can see the dyno graph fall off at anything past 3800 rpm on my engine is the internal friction from the long stroke beginning to take its toll on HP, diesel fuels inability to mix and burn as effectivly at the higher rpm range, and the airflow I mentioned. Timing, etc do help, but not enough to change.

A sled pull is a short duration event. Rod stress and eventual breakage are almost always induced by long term stress. Short duration is cake. So they live. I did hear that Scheid broke the crank in three pieces though..Rumor or fact? I dont know...

Acceleration is the killer. Longer rods add to this.

Our rod length is 7.65 inches center to center. Im surprised you dont have this number.

If Scott had asked the question and left the "high rpm" part out, the answer may have been different.

I have already worked out most of the calcs in the past on increased stroke and it keeps coming back to avoid the practice. Actually I would avoid it in either situation. Low or high RPM.

Don~

banshee

Don,

Your dyno graph drops off for more reasons that the long stroke in the engine. Airflow Inefficiencies and combution duration come to mind first. At 3800 your piston is running away faster than pressure is rising, and air can't get in there anyway. Stroking will increase the piston dwell, or time the piston spends near TDC. For example, for a 4.72 stroke vs a 5.00 stroke, the piston with spend more crank degrees at +/- .050 of TDC with the longer stroke. This means, as the pressure rises the piston will stay at the top of the stroke longer (keeping voulme smaller) to take advantage of the pressure rise longer... more torque is built from this as well as from the longer lever... thus, more HP.

Remember, you don't run at 3800 all day everyday. Stroking is the streetable displacement increase because it increases usable power better. In no way is it going to cause power to drop. As an example, you can get two types of 383 kits for an GM LS1... an "All-Bore" or a stroker kit. they both cost about the same when all is said and done, and they both make about the same peak power. The difference is the area under the curve... the part that really matters.

I don't have all the numbers for the B in front of me, and I didn't take the time to look it up.... 7.5 would have been my best guess off the top of my head. BTW, that puts the ration at 1.62:1... still some room for stroking until 1.51:1.

You're right that sled pulling is short, but it's also very violent. All it takes is the stress to exceed the ultimate once and it'll break... it happens all the time with driveshafts, u-joints, yokes, and hubs, but not with the crank. It's plenty strong!! Scheid has broken the cam before, but not the crank as far as I know.

I agree that adding stroke isn't the only way, but for our engines it's a darn good way. A combination of the two can only help.

John

Don M

John, The question was increased stroke at higher rpm. Not increased stroke for power under the curve.

So, I still say its a losing prop to stroke the engine for higher rpm power. He even made mention of the sled pulling stuff.
They use higher rpm more than any of us.

BTW, you said they use the stock rods...so the engines are not stroked...is this coincidence that they know it will hurt high rpm power or a budget thing?

I did not need to look up the rod length. I have several different designs on the table now. That number tumbles around in my head all the time. Call the head rod builder at Crower and ask him who submitted the CAD drawings on a custom set of Cummins B series rods 20 months ago, complete with stress analysis and the CAM files for the machining centers they use. NO I did not have it done. I did it. As of last month not a single guy had contracted for a custom rod from Crower with design change. One other guy had some stock length titanium rods made at a cost of 7000 bucks. Wonder why if he had that kinda cash laying around he did not increase the stroke and take the perceived advantage?

I know the exact time the piston spends at any crank degree with any stroke at any rpm. I have the data here and have had it. Heck I even have a fast calcing spread sheet to enter the data with a corresponding graph to help me visualize it. Further I still use COSMOSWorks to tell me the stresses involved. IMO, a longer stroke is not good after looking at it from all angles. Without emotion.

If you can design a stroked B series engine that will make more usable power in the higher rpm bands using a stock cylinder head...knock yourself out.

Don~