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8.1L dyno test today.

Alright, and yes, the drivetrain (mostly Allison and probably that massive AAM 11.5in rear end) and the 33in BFG M/Ts sucked up quite a bit. But it came in at a grand total of 312 hp and 422 ft lbs. (Which is actually fairly close to what they put out factory at the crank). And yes, that is at the wheels for anyone who didnt see that in the earlier post. We are assuming anywhere from 100 hp/tq and up on the losses, but its just a guess at best. No honest idea on what it does at the crank. He rarely does 4wd stuff there, and it was his first Allison. So its anybodies guess on the real loses. Im going to guess and say somewhere as of now in the lower to mid 400s for HP, and the mid to high 600s for torque.

He ended up drawing another 60hp alone out of getting it semi close to right after the cam and blah blah install. The tuning is done via labtop, and basically he hacks into the PCM and re does what GM couldnt do. As their program couldnt handle the amount of air going in or exhaust coming out. Its tuned for 91 octane for anyone curious.

Now for the problems, its got a real bad lean condition. From about 2500 to 4500 its running around 15-1 AFR. Strangely after 4500 we could get it to 13-1 AFR easy. So we are going back and start going through the injectors/regulator/pump and finding the cause of our low fuel flow. Most likely, its going to need injectors, a big Walbro, and a regulator of some sort. But, when I drove it there, it was reading up in the 17-1 AFR category :eek1:. But, its running decent enough that it can tool around town as long as its not pulling anything heavy and its ok.

In all, I went by myself and drove it there and back. On the way there, it ran pretty good (to my mind), would easily of raped a stock 8.1 all day even missing OD, but now, its a rocket. Sets you back in the seat like a car and pulls like a train. Plus, picked up 2mpg and now it averages 13.4 on the interstate. Best part is it sounds dead stock except for the mufflers, and you cant tell anything by looking at it. Raced a Hemi 2wd whatever that thing is called with the RumbleBee stripe on the back and dusted it like it wasnt even there.

Now for the cool, there was not ONE, but TWO original 67 Shelby Cobras there (you know them ugly little 2 seater gocart things). And I mean ORIGINAL. (Owned by the SAME GUY) One was a 4 speed 427 with just a hair over 1 million in worth, and the other a 289 4 speed coming in at 800k. A 70 Chevelle with an 8-71 on a 502 aluminum BB, and the nastiest sounding small block 71 Nova I have ever heard. Didnt take any pics because I will be going back soon enough with the truck and can probably get them then anyways. (And I was more awestruck than anything)

And lastly, I aint got no membership, but I do have a sweet video of it raising up on the dyno and stretching the straps when it starts winding up.

And btw, that crank is crazy heavy. I still didnt want to pick it up after it was lightened.
 
Photobucket is your friend for pics and video. ;)
 
photobucket sucks ass, find another host.

Nice numbers BTW!
 
He using efilive to tune or hp tuners? Just curious? Regardless what he is doing it in it's just a software that let's you alter the factory tables. If he is using efilive u can download thier software free(the hardware costs the $) and he could give u the stock file and his tune and you could look at them both and see what he did.

I'm guessing the 8.1 has some stupid amounts of torque limiting(detunes itself) that can be manipulated to make it run harder. May be the Allison tcm/tables comanding the gheyness? Not familiar with 8.1/Allison programing at all.

Non load cell dyno?

4th gear is 1 to 1 so most dyno in that. Not sure on 8.1 Allison but guess you could command that gear with a tech2 and or efi live? That way you could get a fuller sweep without it wanting to start downshifting? also most run in tow haul mode although I'm guessing the converter locks at wot in the 8.1 Allison so not sure if it really matters?

I would actually guess around 50hp lost with that drivetrain. Based on what I remember seeing in duramax land
 
Stomis said:
I bet you're making more at the crank than you think. probably a 35-45% total loss through the allison, tcase, and tires.
Click to expand...

Yep. My engine setup has produced 490 at the wheels on my brothers grand American Modified, and we're speculating it will be about 290 through my K5 drivetrain. Our trucks gobble up a ton of HP.
 
Correct, GM uses whats called Torque Management (basically a program keeping consumers from tearing stuff up) and its been since deleted. That alone makes a large difference, as he can just do that as well.

I have a huge printout of timing and fuel tables (pages and pages and pages) stock vs his and its different from 500 rpm till it hits the rod tossing speed of 5800. Obviously his fueling percentages are higher, some as much as 18 to 20% more, and the timing ramps up faster overall, and is also higher at the get go anyways (also duh obvious). But yes, basically he just went in and manipulated the fuel/spark tables to compensate for the new cam and more air/exhaust flow.

Not sure of his programming tools, I left the papers in the truck and really didnt read all that into the fine print. And yes it was on tow/haul to keep in holding its gear for the WOT tests and such, and the high speed cutoff had to be/and was left removed.

The Allison couldnt be messed with this time around, and since it has to go back, I didnt feel like running it around and testing shift firmness and points. It was always pretty decent anyways, and from the factory the converter always felt loose and sloppy, but now its alot tighter and alot better to drive. We shall see how it tows once we configure the fueling problem and get it finished up, then we will dive into the Allison and firm it up and change the points if need be.

And I am hoping its burning more than 50 of either through the drivetrain, as if its only using 50 from the crank to the wheels, 2000$ was just spent to get it to what GM rated them at to begin with. So I would be a less than happy camper. If I remember correctly, from the factory GM had them at 340hp 450ftlbs at the crank. So its eating quite a bit more I would pray, because from our baseline to our final sorta done tune we picked up 60hp. Thats how far outa wack that cam and headers had that pig.

And I know Im only 26, but Im not computer literate worth anything, so all them photo things dont mean much, lol. I had a huge toy when I was growing up, and it was called outside, and I had better be playing with it on the daily, or I would have been helping mama clean out the cabinets and rearrange the soup cans.
 
Really I wish I knew what a stock unmolested 8.1L Allison with the 11.5in axle had on the dyno. Then comparison would be easy. I mean the seat of pants dyno was like going from a super sweet Honda Civic to a LS1 Camaro.

Really, I would expect this motor to react to the cam (even though this isnt a HUGE cam by any means) basically the same as a run of the mill 454. The intake ports is different, but I would bet it would outflow a peanut port 454 no problem, and probably keep up with a rough casted oval port factory head or be within reason of one. I mean I didnt get all CAD/CNC on the head's intake ports, but did what could be done and shined them up, and smoothed the bowls as best I could, but they are a factory almost cathedral port style much like you would find on the big LS motors sorta.
 
454Sub said:
Really I wish I knew what a stock unmolested 8.1L Allison with the 11.5in axle had on the dyno. Then comparison would be easy. I mean the seat of pants dyno was like going from a super sweet Honda Civic to a LS1 Camaro.

Really, I would expect this motor to react to the cam (even though this isnt a HUGE cam by any means) basically the same as a run of the mill 454. The intake ports is different, but I would bet it would outflow a peanut port 454 no problem, and probably keep up with a rough casted oval port factory head or be within reason of one. I mean I didnt get all CAD/CNC on the head's intake ports, but did what could be done and shined them up, and smoothed the bowls as best I could, but they are a factory almost cathedral port style much like you would find on the big LS motors sorta.
Click to expand...

Your motor has cathedral ports on it like the GEN III LS motors. They were a good design. They are almost as good as the redesigned GEN IV LS motors and way way better than any oval port ever, not just peanut ports.
 
I would def not screw with anything other than ****points, converter lock up, etc if you want. Jmo but don't try to change the firmness via tunning or monkey with the tcm much.

Might have him put it in fast learn/clear the taps if he can. It will speed up the Allison "learning". He may have did this already.

Also jmo but I really don't see a 40% loss through the drive train based on all the duramax's I've seen on the dyno.

Dyno is a running tool. Different dyno, operator, day etc can all lead to some WILD fluctuations. Just get people all excited on the net for nothing. A good operator can make it pretty repeatable day to day on his dyno. If you dynoed it stock there that would of given you a good baseline. Dosnt really matter though. If it reads 90 hp it dosnt matter, just keep dynoing and tuning it till you get 93hp. And then do some driving and smoothing as needed of the low throttle and tip in drivability type stuff. I know you want a big number to lay down but IMO it's not necessary and you know what you got :) the most fun is finding some "control subjects" and whoop their asses. In the name of science of course :whistle:
 
Yea, he did do that for the Allison, it seemed to pick it up within the first few miles, it shifts beautifully. No complaints out of it at all from me.

But, be it 5hp or 500 more, it runs like a scalded cat. No complaints either way whatsoever. I will find out what they push stock on a dyno, and give it a roundabout guesstimate. I am very happy with how it turned out. Just need to go back in and add some fuel with probably a pump and some other wildly expensive parts and see what the deal is then. The tip in throttle response was the biggest problem originally after the cam, very sluggish and had a large fall on its face flat spot until it picked up some rpm, and it has been smoothed over to seamless. Pulls solid and hard from idle till 5800 RPM. Then I had the RPM held to 5600 as there is no reason to be up that high anymore anyways. But in all the guy really knows his stuff it seems. To me anyway.

All in all, these motors can make some serious numbers, and are not the laughing stock some old school 454 guys make them out to be. I am now in the market for one and going to ditch my 2000 454 in favor of one, probably with the same cam and such.
 
Want to sell me that old turd BBC of yours cheap then? :D

Is it maintaining fuel pressure?

Can't imagine that the stock fuel pump is that close to maxing out in stock form? Maybe on it's last leg? wonder what guys run that are pushing these 8.1s hard? Double stockers? Another gm pump outa something else? If it's just boarder line maybe just a boostapump :dunno:

Glad you are happy. That's what counts not a dyno sheet. This thing is suppose to be fun to drive and not just a dyno queen right? :waytogo:
 
Well thats what Im researching now. And it seems taking one this far isnt as common as a 6.0 and such. Probably have to find an Aeromotive or Walbro pump for it, and cut and splice fuel lines for a after market Aeromotive adjustable regulator. The injectors are rare for it as well, I may try and machine the intake to accept LS1 injectors. The stock 8.1 ones are 36 or 38lbs or so. I know LS ones are made bigger than that. Im sure I can finagle something on it.

Surprisingly its got the pump just about maxed as far as we can take it. And yea, that was our first hope was dropping psi at WOT, but no dice.

Im going to use the 454 in my 58 Impala 2 door when I get around to messing with that pile. :whistle:
 
If you arnt dropping pressure at the rail then it's not a supply issue. Although running a higher pressure can make up for smaller injectors and the like obviously.

Can you command a higher pressure and will it hold? Know nothing about the 8.1

Boost voltage to the pump may be easiest and cheapest alternative?
 
We considered the boost voltage upgrade, which is a nifty thing. But the pump is factory and at 100k, not worth the risk. So, its probably going to get replaced with an aftermarket pump anyways just to be safe.

Im hoping that just the pump and a regulator letting maybe 8 or 10 psi more through will help, but if not, I can work the good ol Summit or GM website pretty well.

The 8.1 is a returnless, constant set pressure EFI setup. Not exactly what I had hoped to find. But, its what GM delt me, so I shall fix it for them and see what this thing is actually capable of.
 
L18 8.1’s definitely become animals just with some ECM tuning and bumping the fuel pressure. I have a bone stock 2001 2500HD ECSB 4x4 with an L18 and ZF 6 speed manual that I bought new. As it sits in the garage tonight it only has 56,000 miles on it. It runs well but the 2002 L18 that I swapped into my 1978 K10 a few years ago runs like an entirely different animal just by running an ECM with torque management removed, EGR delete, Electronic throttle delete along with a performance tune. L18’s also love higher than stock fuel pressure. My K10 seems to run best with the fuel pressure adjusted to 67 psi at idle.

2001 through 2003 L18’s had a return type fuel system with an adjustable regulator on the fuel rail. 2004-2010 they were returnless with the regulator built into the fuel module in the tank, which makes adjusting the fuel pressure a hassle. Changing your pump to an aftermarket pump won’t do you any good as the stock pump has more than enough capability to deliver the pressure and volume needed even for a modded 8.1L but changing your fuel rail, and fuel system to the return type would definitely make it easier to adjust the fuel pressure. Like I say, 67-68 psi seems to be the sweet spot as far as L18 fuel pressure. The PSI will actually move upto around 70-71 psi when you snap the throttle to WOT. I am using a stock EP381 pump originally used in 1996 L29 7.4L trucks. The EP381 is a small pump like the old TBI pumps, not like the large fuel module used in the GMT800 trucks.

I am surprised to see the drivetrain eat up over 100 HP and that much torque but Allison's are known to be a hog like that. Howell Engine Development did my ECM tuning for my K10 and claim the tune was dyno'd at 425 HP/555 lb ft of torque on a bone stock engine through stock manifolds. I would love to get it on a dyno to see how much is actually getting to the ground though but I don’t think the truck will fit on a dyno. It is amazing the difference between the two L18’s I have. The L18 in the K10 will run circles around the L18 in the Silverado but the engine in the K10 has also eaten up two sets of Napa engine mounts, 1 rear trans mount and barber poled a rear drive shaft on asphalt while ratting on it going around a corner (big torque, Detroit locker, and heavy truck = driveshaft go boom). Good testament as to why GM used Torque Management in the first place :haha:

I actually have two more L18’s (2005 and 2008) laying around which one will be going into my Suburban sometime soon. I plan to use a 2001-2003 fuel rail on the next L18 project as well just for the sole purpose of having an adjustable regulator right on the rail. L18's don't need big cams, headers, big injectors, blah, blah blah to get big power out of them. A decent tune and bump in fuel pressure will surprise you, any other hot rod parts thrown on top is just icing on the cake.
 
That's exactly what I needed to know. Thank you Larry. I drove it again last night and it runs like a dream. Still getting used to being careful with the throttle on loose gravel, but lol, sometimes a little extra throttle never hurt anyone except the wheel wells.
 
Do you have part number list of parts you used?

Curious about your moly rings as well as push rods and valve springs

- I know folks have had issues with the rod / valve spring fitups on these...

Do you have a engine build post?
 
The rings are from Hastings. Everything else is from Comp Cams. The cam was a XR270HR. If you click on that on their website, it will give you the part number of the recommended extra parts like springs, retainers and so on.
 
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