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8.1L dyno test today.

What does the injector duty ratio look like in the lean areas? If the pressure is OK, maybe the injectors are maxed out or the ECM places a max duty restriction. It sounds like you're lean in the engine's best volumetric efficiency area, so it just needs more fuel.
 
Im thinking the injectors are not the problem. So my master plan is to get a 2003 8.1L pump, which has a return line, and cutting up the factory line and installing a Corvette fuel filter which has a return line boss. As the 04 has the filter in tank with the pump. So that should solve that, then using a 03 FP regulator (which is vac referenced), I just will cap the vac line to it, and it should peg the pump at 70ish PSI, then I will adjust it back down to around 65 or so. Then take it back and test it from there. I havent had much luck with injectors for it, I may end up shoehorning LS1 injectors into it and machining the manifold if I have to which is no big deal. O ye lust for Horsepower has no limits.
 
I have an 07 LBZ duramax that was rate at 365hp from GM at the flywheel. They would dyno around 290/295 at the rear wheels. The Allison is your limiting point in one of these trucks. The 5 speeds are good for about 350 rwhp and the 6 speeds are good for around 375 rwhp stock. After that point you can put them in limp mode pretty easy at hard acceleration in high gear. That is when you need shift kit, pump kit, a better torque convertor and clutches to hold the power. There is not much tuning you can do the allison to make it better. It is always learning how you drive, if you let someone drive it that drives different then you for a while, it can shift weird for you when you get it back for a while

I had an 05 with an edge tuner that I limped several times. The 07 has EFILive and a built allison with between 425 and 450 RWHP and so far no issues.

So if you limp the allison in stock form you will know you are over 350/375 RWHP.
 
Very valid points on all teck. Although I'm guessing a gasser will be able to roll a bit more hp before limping an Allison without all the massive torque the duramax smacks down.

Hijack - If you have a built trans why not more power? No lift pumps?
 
I didn't go full build, just upgraded the easy stuff when it was new. Wasn't looking for crazy HP. I pull a 30' travel trailer and the upgrades were for pulling it more then abusing the truck.
 
Most likely the Allison will be next. Plus a locker in the rear end. Its eventually going to end up with a 60 in the front and some mud tars on it Im sure.

Strangely, most companies dont offer gasser Allison converters as the Allison was behind the 8.1 for only a few years so its not a popular setup. I havnt seen to many of these trucks. I found a few guys that would make one for it, but at 1000$ it can wait as its not been a problem so far. But, I am considering it as a future thing as it cant last forever. Took it out last night and put the whooping to a few trucks in drag races. Runs excellent cant complain thats for sure.
 
454Sub said:
Strangely, most companies dont offer gasser Allison converters as the Allison was behind the 8.1 for only a few years so its not a popular setup. I havnt seen to many of these trucks.
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A few years? The Allison is still used behind an 8.1L today. Most people think the L18 died in 2006 but it is still in production today. Workhorse Custom Chassis used the L18 mated to Allison 1000’s and 2000’s from 2001 to 2011 and PSI purchased the production rights of the 8.1L platform from GM about 18 months ago and are building it for several OEM RV chassis and commercial truck manufacturers even still today. In fact, PSI has hogged the 8.1L out to an 8.8L. The big block is not dead….it is just not built by GM anymore. The Allison behind a Dirtymax is just more known by the masses. Surely some automatic hot rodder has a beefy torque converter for a big gas. I work for Workhorse (Navistar). We consumed more L18's than GM used in the Silverado/Sierra. Everybody thinks the L18 as just an 2001-2006 GMT800 truck engine....not so.
 
I meant from a average consumer truck platform. Its used for alot of other uses outside that.

I found a few guys that would make the converter for me. Its just not as popular as say a Duramax and a 6.0. So its something ya have to call and ask about. But like I said, I have fueling system stuff that needs attention first, then I shall go on to the other stuff.
 
A $1000 would be cheap for an Allison convertor. I think I paid around $1600 for my Suncoast back in 07.
 
Yea, they probably have came down since its not "brand new" anymore. But, thats tomorrows problem. Tonights problem is much simpler.
 
Working on buying a 02 8.1 2500hd. It will be stock but dyno tuned with mpg and tq in mind. I already have HP tuners so it will be used.
 
Larry said:
A few years? The Allison is still used behind an 8.1L today. Most people think the L18 died in 2006 but it is still in production today. Workhorse Custom Chassis used the L18 mated to Allison 1000’s and 2000’s from 2001 to 2011 and PSI purchased the production rights of the 8.1L platform from GM about 18 months ago and are building it for several OEM RV chassis and commercial truck manufacturers even still today. In fact, PSI has hogged the 8.1L out to an 8.8L. The big block is not dead….it is just not built by GM anymore. The Allison behind a Dirtymax is just more known by the masses. Surely some automatic hot rodder has a beefy torque converter for a big gas. I work for Workhorse (Navistar). We consumed more L18's than GM used in the Silverado/Sierra. Everybody thinks the L18 as just an 2001-2006 GMT800 truck engine....not so.
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Not to mention the 8.1 is still serving duty in marine applications (Mercury Marine 8.1L Horizon), although without a TC of course...
 
Once its dyno tuned you wont need a hand held tuner anymore. And if you do, try not to turn it up all the way. That's what happened to this 8.1. Detonated so hard is muffin topped the bearings out of the rods. He keeps the tuner for tire sizes and code reading
 
Mine is a laptop based. Timing will be conservative. I know 8.1s are detonation prone. It will be getting a 180 thermostat to help a little.
 
That's the plan for this one as well. 180 thermostat and a new fuel system to get the most out of it. But just tuning alone will surprise you with that motor. GM really choked them out with conservative everything. The one I did averages 15 mpg with the hotter cam and such. Not to had considering it only averaged about 9 or so before.
 
Did he mess with the lean cruising? Not sure if that is what is called. I may try it on mine after I learn more.
 
Well, we couldnt do all that with it yet, as the fuel system isnt up to snuff so its running lean as it is. So, after the pump, regulator and such is replaced and the thermostat is as well I have to take it back and redo it all over again. There is a huge amount of programs and info in the 8.1. Torque management and all that nanny crap. But, you will be happy with just having it tuned. I would recommend headers, I know they are expensive and all that. But, the factory manifolds are crap, plain and simple. GM had to recall the trucks and put heat shields on the motor mounts because so much heat was backing up in there it was melting the rubber and the motor would vibrate it apart. The 8.1 mounts are completely different than a regular old BB/SB mount, and its not near as mechanically attached as the old mounts, the 8.1 I did would jump up and down inches. Plus, the manifolds suck and you will get MOAR POWER. Not to mention the motor mounts are a GM only thing and cost 110$ a piece.
 
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