amascio

So what are you saying: that you have 6.5 pounds of boost or 6.5 inches of vacuum at idle? I ask this because a while back a member who had a boost gauge installed said that although you can hear the turbos at cold start, there was no boost. Just curious.

This may become an interesting thread! For the record both my EB trucks have roughly 17.6 mpg on a long time trip B. Despite different gearing (3:73 vs 3:55 ) they are very close to each other.

goodburbon

by checking more than one vehicle with solid data, I can eliminate the fuel as the cause.

Good suggestions engineermike, Ill see if i can't get some data along those lines as well. Just for the sake of consistiency, anyone doing a deceleration test should check the time it takes to coast from 70 to 55. Please do so safely with a 3rd party managing the stopwatch. Also note your altitude in your post and only perform this test on level ground.

sllydderrr

One additional consideration: wind. It may be difficult to measure wind speed and direction so will 'calm' be sufficient?

Al Kohalic

Goodbourbon, I hope you know what kind of daunting task you are getting yourself into. I do not underestimate your ability to collect data and find out that one engine is less efficient, but finding out the exact cause of the inefficiency without a complete tear down will be damn near impossible. You may be able to narrow it down to excessive drag on the crank vs the other engine or a some kind temperature difference, but finding out what is causing that issue will be the hard part. Making it even worse would be that you may have two engines with excessive drag on the crank, but there may be two totally different causes for it on each engine like a pitted bearing or some other piston issue.

By the way, I know you understand this but some others may not. Even though two engines may come out of the same engine plant, the same line with the same parts, and the same employees/computers assembling them does not mean their specs are "exactly" the same. There might be a spec for 365hp but the engine plant might have a bell curve of +/-5hp or so allowing a 360hp enging being given the green light just as a 370hp will. Of course a +/- of 5hp is rare and it is usually around the line of +/- 3hp since something as small as the way your spark plugs are positioned can give you a 1 or 2hp bump in power.Just like when I worked at Cummins and a feloow co-worker of mine(both of us were FNG's) took upon ourselves to narrow out why two ISB engines would have have a difference of 4 hp. Of course all of the older guys laughed at us with a "Damn noobs, you don't think that has been done before" comment. In short, even though we had all the data telling us that the two engines had different numbers, we could not norrow out why in short of tearing down both engines and Cummins was not going to allow that on two perfectly fine production ready engines. And what is to say that just because we found the issue in one that it was the same in another so we gave up and just accepted it like those who came before us did. Then when the new FNG's came and tried the same thing, we gave them the laugh and the "Damn noobs, you don't think that has been done before" comment. I hope you atleast find the cause in your too trucks though so you can fix it.

engineermike

I know this is getting off-topic, kinda, but Al - I am very surprised to hear that the variation was only 4 hp. My Mom had two different LS1 trans-ams, with basically identical build-sheets. One of them ran 14.0@ 99 mph, while the other ran 13.0@ 106 mph. That's a heck of a lot more than 4 hp, yet most considered either time to be fairly normal for the car. I think we eventually chalked it up to false-knock causing retarded timing.

Al Kohalic

I am just going by memory as this was over 10 years ago and the torque was a bigger difference but I cannot remember how much. I think it was almost 15 ft-lb difference but not sure exactly. I know that due to Cummins spec regulation, me seeing anything more the that was rare since they would have either been redone or for QC testing before they got to me. This was also Cummins own regulations. We usually saw engine roughly +/-2 or 3hp out of the 235hp spec at the time. This one just happen to be the first one we saw that was about 4hp bellow the 235hp spec. The furthest I saw was 240hp which was +5hp out of spec so imagine if you compaired the -4hp out of spec engine with the +5hp out of spec engine. That is a 9hp differnce between the two not to mention a lot more torque difference. I don't know what other manufacturers put on their own engines as it could be more of an acceptable +/- range on their bell curve. This was just a little side project that aco-worker and I had to find out why since we were curious. If our head boss at the time found out we spent the amount of time we did on it then our ***** would have been in trouble.

Back to the topic. Goodbourbon, have you done any of the cruising 75mph numbers yet? I am curious to see what the difference is doing 75mph on both engines.

engineermike

I have heard, though haven't seen it in writing, that the outboard engine hp ratings are required by some government entity to be within 10% of actual. This gives them as much as +/-35 hp (!). Of course, the manufacturers are capable of much tighter tolerances, so you'll generally see engines under-rated in a competitive market segment (a 150 making 165 hp) or over-rated if they had difficulty reaching the target power level (a 300 making 270 hp).

MXD

...

EBinMT

Huh? +/- 10% on a 350hp motor would allow +/-35hp.

goodburbon

glaring differences so far

175-200 psi fuel at idle on the good MPG truck. 275-300 psi on the bad MPG truck.

86°ambient temp on the good MPG truck, 59° ambient temp on the bad MPG truck.

intake temps were the same though.


all manifold pressure measurements are in psia

yes I know that no 2 trucks will be exactly the same, but its literally like one is running a tune compared to the other one when they both have the same stock tune loaded.

yes of course calm winds should also be the norm when doing the deceleration test. I will also suggest that it be done 5 times, throw out the high and low, average the other 3. I got 2 in today and they were 14.15 and 15.67. my wife wasn't cooperative enough to get it all done today. I had the cruise set on 70 and the speed was stable. starting the stopwatch when pressing the cancel button.

I hope to get out tomorrow and gather some more info, and I've got a friend nearby with another good MPG truck so I may be able to gather data from a third truck, but I can't control the fuel he buys.