Exhaust Flow

[comdiver]

Here's a question for the engineers out there. Does anyone know what the exhaust flow for the LDT 465 1 D is? It would be a CFM rating. The flow through the air filter should be the same, I think.

 

[Jones]

Not sure exactly what CFMs for exhaust should be. I'd guess higher than for the air filter because of the expansion of heated gases from combustion. Might get into a Machinery's Handbook and see what pipe/tubing of a given I.D. flows and go from there. Remember that bends slow down flow due to friction. Lots of variables in play.

 

[acetomatoco]

reason for question? Muffler? Figure that 700 CFM might suffice..and work using that value... ACE

 

[comdiver]

Your right, muffler "system". I have talked with an engineer that knows engines and mufflers and is willing to make some educated suggestions, but he needs the cfm first. So I thought OK, 465cu in/ revolution x 2600rpm convert that to cu ft and I'm there at 100%. 700cfm Well I forgot the boost if it was 14.7 (easy number) we would now cram twice as much in there, 1400cfm. I think we are getting closer, but if anyone has the engine spec's or knows where to find them that would be better. Jones is right too, hot gas! Anyway as we well know if it is too restrictive performance will suffer but if it is too open the noise won't be muffled.

 

[jasonjc]

There is a post here some where about a NAPA muffle that works great. Its a flow thought. takes out the noize and still runs good.

 

[comdiver]

I will most likely use that muffler, but if one of the many very well read experts in SS has the information we could end up with a better breathing and quieter design. I have already measured the cab noise. Stock is 93db@55mph on blacktop. Let's see what we can do.

 

[Jones]

I use a straight-through truck muffler on my Cummins with passable results but then I have a stock length exhaust system. Deuces are a little shorter. What is helpful with any set-up is a way to cool the gases and thereby get them to shrink back in volume/pressure. Sound is, after all, nothing more than any pressure over atmospheric. Unfortunately, most of the efficient mufflers are that way because they're BIG with lots of baffles and surface area. For pure stealth, a spiral insert is going to give the exhaust further to travel before it gets out. Or noise cancelling baffles like Flowmasters use but then we're back to a "can" type muffler again. Might consider this; take a 12" - 16" (?) wide strip of coarse hardware cloth (maybe 1/4" openings) rolled around a piece of 1 1/2" or so pipe 'til you get a screen cylinder close to the I.D. of your exhaust pipe. Wire the end down so it doesn't unroll, pull out your pipe former and stuff the screen cylinder into the stack. The screen will give you a lot of surface to act as baffles and heat sink while the opening through the center can be dialed in for restriction. Several could be made and inserted to fine tune the exhaust note and when they get dirty/fouled, they could be pulled out and cleaned by soaking in solvent or carb cleaner. If hardware cloth layers up too dense then maybe fine mesh expanded metal ("once rolled", not the smooth stuff) is an alternative.

 

[houdel]

Re: RE: Exhaust Flow

Your right, muffler "system". I have talked with an engineer that knows engines and mufflers and is willing to make some educated suggestions, but he needs the cfm first. So I thought OK, 465cu in/ revolution x 2600rpm convert that to cu ft and I'm there at 100%. 700cfm Well I forgot the boost if it was 14.7 (easy number) we would now cram twice as much in there, 1400cfm.

Don't know if your idea is sound or not, but your math is wrong. The LDx 465 engine is 478 cubic inches, but it is a four stroke cycle, so you only exhaust each cylinder every other revolution. Therefore it should be (478 cu in/2 rev x 2600 rev/min)/1728 cu in/cu ft = 359.6 CFM (theoretical). I say theoretical because of various pumping and friction losses you will never completely fill the cylinder with air. Even with a turbo running at typical Deuce pressures, the intake valves are too small and are not open long enough to get a full cylinder fill, and the fill ratio gets worse at higher rpms. That, and you are drawing all that air though an air filter element which is rated at 390 cfm.

If you wanted a real number you could insert a pitot tube and thermocouple into your exhaust stack, measure the exhaust gas speed and temperature, do a bunch of calculations and come up with a good "hard" number. Probably not worth the effort though unless you are going into the business of manufacturing mufflers or exhaust systems. I'd just pick a number between 300 and 400 cfm and go with that.

For what it is worth, I looked up some specs on the Fleetguard/Nelson exhaust products guide. Following are typical maximum exhaust flow rates for some of their more efficient mufflers. The flow rates are measured at 2"Hg (approximately 1 psi) backpressure.

3" inlet - 883 CFM
3.5" inlet - 1204 CFM
4" inlet - 1571 CFM
5" inlet - 2451 CFM

You might be able to find a suitable muffler there. I am interested in their 201563N muffler. It has an 8.4" round body, 3" inlet and outlet, both in the same end, like the old N/A multifuel mufflers (except they had either a 2-1/2" or 2-3/4" outlet), and is rated 883 CFM at 2"Hg backpressure. It should fit nicely behind the battery box like the N/A muffler did.

http://www.fleetguard.com/pdfs/product_lit/americas_brochures/LT32002C.pdf

 

[comdiver]

RE: Re: RE: Exhaust Flow

Can't find fault with your math, I must admit I didn't think 2 stroke - 4 stroke. I still think the 300 -400 cfm range may be low, just a gut feeling. During my few moments with the engineer (couldn't find a listing for a Ldt 465) I asked if he could find the specs. for an 6-71. I know it is a 2 stroke, it is the first one that came to mind. Anyway, 270hp@2100- 1500cfm. 6x71x2100/1728=517.7. I don't really know what that means, but...... I'm not sure what the boost on the 6-71 is but I think this may be part of the answer. Thank you all for the brainstorm education. I think we are getting close.

 

[jimk]

RE: Re: RE: Exhaust Flow

air flow in lb/min at 5/10psi. Sorry don't have time to find the formula for converting to CFM.

http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&p=111182&highlight=#111182

The naturally aspirated engine might have peak volumetric efficiency (VE) around 85%(a guess). I was hoping for bit more than 100% with the new (added) turbo. My filter is stamped 410CFM. I used the NAPA #xxxx (will add later) the 3-3/4OD stack seen here. Gasses cool and volume decrease as it get farther away from chamber. A restrictive muffler can effect turbine speed

VE generally matches the torque curve and as Lee points out drops off as speed increases, but manifold pressure is big player as higher boost increases VE and adding fuel increases boost. Torque curve graph for the LDS ( higher HP/torque) is avail in LDS-465-1Trouble Shooting manual in TM section page viii. Interestingly peak torque (440 at 1800rpm) occurs at lowest BSFC(fuel consumption) Induction airflow for LDS is 550 cfm (at rated power - 2600rpm) (page 11). JimK

p.s While related, torque is more important(useful) than peak HP

 

[JasonS]

Not to be too argumentative... but horsepower is really all that matters. Torque can be multiplied and equalized via gearing; horsepower can't.

 

[jimk]

I would argue they both "matter". I just put 'HP torque formula' in goggle to make sure I don't butch the equation for a reply. The top hit looks like it should answer this faster than I can type something .While it's context is cars this issue matters even more with trucks (I need to wrench on the stolly).JimK

http://vettenet.org/torquehp.html

 

[JasonS]

I am an electrical engineer, so I like to use electrical analogies. One horsepower equals 746 watts. Voltage and current can be compared to rpm and torque. When someone says that torque is more important it is equivalent to saying amps (or volts) is more important. One correction to your link is that horsepower can be measured directly. You use a generator and load bank to measure watts (horsepower).

 

[ironhorsethegeneral]

We put a blowthrough on both of our trucks. Our newset truck has a NAPA muffler. It really helps with the noice inside the cab.

 

[houdel]

Re: RE: Re: RE: Exhaust Flow

I asked if he could find the specs. for an 6-71. I know it is a 2 stroke, it is the first one that came to mind. Anyway, 270hp@2100- 1500cfm. 6x71x2100/1728=517.7. I don't really know what that means, but...... I'm not sure what the boost on the 6-71 is but I think this may be part of the answer. Thank you all for the brainstorm education. I think we are getting close.

As I recall, all Detroit two strokes were supercharged and most were turbo'd, so they probably had a VE well above 100% which would explain the high air flow, but even then 1500 CFM sounds a bit high.

You are correct on the 410 CFM Deuce air cleaner, I just entered the wrong number trying to work from memory. But think that filter is rated for an LDS465 at 2900 RPM and with a bigger turbo.

Jimk - Thanks for bringing up the turbo nomograph, that should answer comdiver's question. However, if you note, the graph assumes a VE of 85% for a turbo engine, so 85% for a NA engine is pretty high.

Using the graph, a 478 CI engine at 2500 RPM and 10 PSI boost flows about 22.5 lbs of air/min, a cubic foot of air at 70F weighs about .07492 pounds, so 22.5 lb/min divided by .07492 lb/cf = 300.32 CFM.

COMDIVER - The hard numbers are in. Use 300-400 CFM, as I suggested in the first place.

Jimk - It is not too surprising that peak torque and lowest specific fuel consumption occur at the same RPM, that is where the engine is operating most efficiently.

JasonS - Both torque and horsepower are important, torque more so in trucks than cars. Somewhat crudely stated, torque is the force available to move your vehicle at a constant speed, and horsepower (which is the rate of change of torque) is the power available to accelerate your vehicle. Thus you need enough horsepower to accelerate your vehicle to a desired speed in an acceptable period of time, and enough torque to be able to maintain that speed up hills and in head winds, etc.

Pure torque alone will NOT accelerate a vehicle, because acceleration is speed variant. More horsepower will accelerate a vehicle faster, but more torque will have no effect on acceleration because by definition, torque is speed constant. On the other hand, horsepower alone is not enough to maintain a constant speed. If you had a heavy truck with a high horsepower/low torque engine you could accelerate it to a desired cruising speed but would have a hard time maintaining a constant speed. The truck would slow down going up hills and in headwinds so you would have to frequently downshift to accelerate the truck back up to speed.

A somewhat crude and simple explanation, but I hope you can understand the point.

 

[JasonS]

Lee, you are mostly correct. However, horsepower (and therefore torque combined with rpm) is required for any work. Accelerating or maintaining speed both require horsepower.

 

[jimk]

When someone says that torque is more important it is equivalent to saying amps (or volts) is more important.

Well voltage is more important to a spark plug. Amps rule when stick welding (both are arcs).

As for trucks, at risk of crossing over to the realm of junk science, I can offer this.I drive a little rig tractor trailer. I say 'little' because we use 'city' tractors for road work., 99% it's a Mack These are not the 500HP monsters you often see crossing the continent. I've made the Reading Pa turn at least 1500times. This means going over ~20 big hills (each way) so I get a good feel for the power curve. I'll spew some data from memory(bad) and from a few years back(when I cared) and the co. does turn them down (then expects me to rush?)).

The EM7-250 Torque-1040 at 1200/HP250 at 1700.(these would be peak values)

The observation is this- climbing hills, without shifting, it -always- falls off rated power(~1700).It is strongest, albeit slower, at 1200. It still pulls strong down to 1000. There is not much diff between 1000 and 1400. Climbing hills with downshift- I usually lose 5mph.While this puts the engine at the peak HP it still drops away.If you are thinking wind there are times w/ heavy loads when see the same thing in even lower gears . And there is 70 odd traffic lights on the Rt61 leg that ,for some reason I yet can't explain, the traffic engineers have figured how to turn the light red so that I can stop at the base of some big hill to watch -no- traffic cross. I see the same thing at 20mph.These engines run at 1700 but when the going gets tough they move towards the torque peak.

However, if you note, the graph assumes a VE of 85% for a turbo engine, so 85% for a NA engine is pretty high.

Lee,
I'd guess they needed (graph) a single value and used some average. VE does vary a lot(w/ RPM,between engines,w/compressor efficiency...).When I look to exceed 100% that is compared to NA (my LD465), quite easy to do with any supercharger(and a few wild NA cams).When I think NA I use my hot rodding idea where 90 is concidered low.I don't know much about he LD eff. After you note about valve size I guess a pocket port job is due next time I have my head off.I'm sure we can all agree that you can't have to much HORSEPOWER.JimK

 

[jimk]

Just to point out the obvious- extra air filter capacity- because they get dirty.JimK

 

[houdel]

However, if you note, the graph assumes a VE of 85% for a turbo engine, so 85% for a NA engine is pretty high.

Lee,
I'd guess they needed (graph) a single value and used some average. VE does vary a lot(w/ RPM,between engines,w/compressor efficiency...).When I look to exceed 100% that is compared to NA (my LD465), quite easy to do with any supercharger(and a few wild NA cams).When I think NA I use my hot rodding idea where 90 is considered low.I don't know much about he LD eff. After you note about valve size I guess a pocket port job is due next time I have my head off.I'm sure we can all agree that you can't have to much HORSEPOWER.JimK

I agree you can't have too much horsepower OR torque. But the multifuel is not designed to be particularly efficient. Small, compact squared-off intake and exhaust manifolds, small internal passages, all 90 degree bends, unequal length passages, all of which contribute to inefficiency. Not at all like a hot rodded engine with a multi plane intake manifold with individual large, polished equal length passages and exhaust manifolds with large diameter, rounded, equal length collector tubes. The biggest detriment to good airflow (and correspondingly high VE) are small diameter, rough air/exhaust passages and sharp bends which pretty much defines the multifuel intake and exhaust. So I wouldn't expect high VE numbers for a multifuel unless you crank in a whole lot of boost.

 

[jimk]

The fact that it uses ~50% more fuel AND puts out less than half the power of my new Mack says a lot about effiency. One advantage it has over a hot rod [in VE] is the low rpm keeps CFM down. Usually the worst intake tracts respond the best to some grinding. JimK