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L18 8.1L swap resource thread
- Thread starter Larry
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I pm'd you
y5mgisi
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Do you have any stock gm 8.1 dyno charts, Larry?
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Nope, they used to be on GM Powertrain’s website but I didn’t grab them in time before they purged all the old stuff.
I found this one on another site.
y5mgisi
1 ton status
Looks about right eh?
y5mgisi
1 ton status
I don't know why but for some reason it popped into my head to wonder how the chart would compare to the latest 6.2l. Here is that chart. Not trying to see if one is better than the other. Just curious how close or different they would be.
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Those do not appear to be not level playing field charts though. Plus the HP and Torque columns are swapped on those two charts making it more confusing. The 6.2L is on a J1349 SAE scale whereas the older L18 chart looks to be more J1995 or something else. Heavy duty truck engines often ran a different SAE scale than cars and light trucks. Liars figure and figures lie….Hard to say, but my ass dyno does not confirm the 6.2L has more twist than a 8.1L after driving a few new Silverados. HP, yes…for sure but you must beat on them at much higher RPMs. Torque is what gets the job done, not HP. It would be fun to compare the two in the real world. It would seem if the 6.2L was such a hoss GM would approve it for the upcoming medium duty trucks and allow marine to use it. Neither are in the stars that I know of.
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This L18 GM Powertrain Application Manual engineering document indicates 355 lb. ft. of torque at 800 RPM (tad above idle), which is quite a bit higher torque at a lower RPM than a 6.2L. I wish this book said what SAE scale they were using for certification back then.
At the bottome of the test condition table it shows J1349 for truck applications. So these are apples to apples comparisons. The 6.2l is a little slower to build torque than the 8.1l but the 6.2l is still quite impressive considering it's down over 100 cubic inches. I've often wondered how the 8.1l would do if it received the same technology as the later LS engines have. Just applying the same power density the 6.2l has to the 8.1l calculates to 595 ft lbs and 540 hp. I'd take that over a diesel any day.This L18 GM Powertrain Application Manual engineering document indicates 355 lb. ft. of torque at 800 RPM (tad above idle), which is quite a bit higher torque at a lower RPM than a 6.2L. I wish this book said what SAE scale they were using for certification back then.
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OY! Oh, YEAH! I am blind! It does say J1349, although if you research SAE documents J1349 was updated around 2005ish so this may not be apples the apple. I agree, the 6.2L is indeed impressive (I love the direct injection) and it would sure be fun to do a true apples to apples dyno to see which puts out what to the WHEELS. I could see the 6.2L doing well in HP but not in low speed torque, which is where a big block shines. I also don’t see the 6.2L being built to handle the rigors of sever duty as the 8.1L was designed. Power coming on at high RPMs is the exact reason Ford cannot mate an Allison to their V10 in the new F650/750. The engine spins too high for the severe duty trans where the torque converter would balloon. The 6.2L would be in the same boat. Great engine for a hot rod truck but don't see it being a tow machine in the big truck world.
Speaking of what “if” the 8.1L was updated to current technology that has already happened. The PSI 8.8L running on propane for School Bus applications is laying down 565 lb. ft. at 1,800 RPM but with the cam profile the propane engine currently runs it is only rated at 270 HP. Research their site…. Neat stuff! Actually, I got to tear a few 8.8L’s apart a few weeks ago in Chicago and they are impressive. The gasoline version has not been finalized for on-road duty and is still going through validation and EPA Certs. Initially the gasoline version will be port injected but DI is coming in a few years as well so they claim. PSI has already begun advertising the 8.8L in the RV Business Magazine at 500 HP but give no RPM or torque range. That is just the port injected engine for now. It will be fun to see where that goes. I’m excited to see how the 8.8L does once we get more of these into service in our new school buses (I’m a field service engineer for International Truck). I'm so anxious to see the diesel issues stop once customers start moving back to gasoline power in medium duty trucks. Not every vocation needs a damn POS diesel.
Not every consumer needs it either!! That is exactly why I want to stay away from diesel's. They are so freaking expensive just to maintain and/or fix and replace parts on. For the average dude like myself who wants a 3/4 ton or 1 ton pickup around to tow some stuff around on the weekends, a big block gas motor is all you need. I understand why GM stopped production on the 8.1's when they did as gas prices were through the roof and diesel was cheaper, but I am hopeful they will recognize there is a market in the consumer world for the 8.1 (or this new 8.8) and bring it back as a alternative to the duramax in the consumer towing world....here is to hoping, haha
Larry - is there an 8.8 in your future? 
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I hope so! It’s going to be hard to get one for a long time as they will be on containment for the first couple years where any engines with internal failures will be exchanged and go back for analysis. It will be hard to buy any cores for a few years at least. You don’t want to know what they cost new and I can’t say but they are big money!
y5mgisi
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I wasn't trying to say one was better than the other. I mostly just wondered how close their newest technology compared to the "old" stuff. I too would love to have seen the 8.1 evolve along with the ls motors. There is no doubt in my mind that if there was a 2015 8.1 it would probably have numbers around 525ft.lb and 425hp or there abouts and I bet the dyno chart would mimic the old one almost exactly.
y5mgisi
1 ton status
In other words, no body has to try and defend the 8.1. It can do that on its own!
I'm on eBay and Craigslist watching for them pretty much all the time.
I'm on eBay and Craigslist watching for them pretty much all the time.
Call that guy in Idaho - he seems to always have them. Got mine for $900 delivered - here is his website: http://www.silveradoautosales.com/index.html
Here is a roller for $600 http://spokane.craigslist.org/pts/5306701268.html
Wait, are you saying that auto sales place pulled an 8.1, crated it up, and sold/shipped it to you?
That guy has a parts/salvage business as well as an auto sales yard. Pretty sure the parts business came before the sales yard. I believe he also does Duramax conversions in Suburbans. I saw a low mile '06 8.1 on Craigslist this weekend - but it's gone now. I think he wanted $1700 for it.
I got my 8.1 from him about 4-5 years ago. It is an '01 motor with 90K or so - delivered to Portland, OR area for $900 (his buddy was coming this way) I think he was a bit hard up for cash at the time - he started at $1500 - and I was emailing him off and on over two weeks - then he called me out of the blue and threw that deal at me.
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Well, WTF did you expect?
First, you ask for a stock 8.1L dyno chart then you drop the 6.2L in. How do you not expect a comparison and conversation? 
Funny thing is we constantly see this same thing happen on the FB page from people that don’t understand the difference between Torque and HP let alone the difference between a high RPM engine and a low RPM engine. Each have their own places where each work well.
Some places will do that. I have a buddy here in Pueblo that is building a 8.1L CUCV K5 where he got engine from LKQ out of Texas. Yanked, crated and shipped. Not cheap but there was nothing around here at the time. The engine took a beating in shipping but nothing major.
