6.0 Vs 8.1 - GMC Truck Forum

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#1 · Apr 25, 2011 Which one is mo' betta? :big_banana_Dance: Background - It will be going in my '83 CCLB that probably wont see much street time and will weigh 7000 or more most likely. I'll be running rockwell axles and 40"+ tires. - I'm not concerned with going fast. - I don't want a "high dollar" engine build. i.e no forced induction. - Reliability is my primary concern, making at least 400 HP is my second. Advantages/Disadvantages - The 8.1 can make 425HP & 505 ft/lbs with just a tune. - The 8.1 is used in boats, so there are existing MEFI systems for it. - The 8.1 doesn't have to rev quite as high as the 6.0 to make it's powaah. - The 8.1 seems to like oil. Is this a concern, or fairly harmless as long as you don't let it drink itself dry? - I found a 155k mile 8.1 for $600. - The 6.0 owns the 8.1 in terms of aftermarket support and interchangeability with other LSx motors. - I would have to throw money at it to get the same power as the 8.1 - Motors aren't really my "specialty" so I'm ignorant to the relationship between swapping in aftermarket internals and reliabilty. I had originally planned on throwing in a stock LQ9 and then building it once I had the rig finished for a while, but it seems like with the 8.1 I could just throw it in and forget about it, but like I said, I'm pretty ignorant when it comes to motors. So what say ye, oh GMFS? See less See more Sort by Oldest first Oldest first Newest first Most reactions #2 · Apr 25, 2011 Also, I found a thread by Willyswanter asking pretty much this same question, but he was asking in regards to a 4500 lbs vehicle and the votes were split about 50/50. #3 · Apr 25, 2011 6.0 i like my 8.1/allison a lot but there is very little aftermarket support and the engines aren't really built for high levels of power IMO. i'm not sure who tuned for 425hp, but i would definately like to know. except for crockett/dart finally releasing a few parts, raylar has the market and the guy is a DOUCHE BAG. talked to me like a child when i called to order a cam.... not the best approach for how much money he wants for parts. it shares a few parts with the previous gen. big blocks however a lot of crap is metric. the 6.0's aftermarket support, availability, and reliability with mods is a clear winner for me. if you REALLY want a big block.... do a 454 or other variant on that block. #4 · Apr 26, 2011 There's a guy on several different forums (DirtyLarry or Larry) with an 8.1 in a '78 K10 who was running it on MEFI and now switched to a regular PCM, tuned by Howell EFI who claims those numbers, although he has no dyno sheet to prove it. I know the HO boat versions put out more than that, but don't they have a different cam? For the 8.1 I would need, - The engine (no harness or computer) = $600 - Howell harness (manual transmission, no DBW throttle, no EGR) = $600 - Cable throttle body from one of the LSx motors = cheap - P59 PCM = fairly cheap - The 8.1 can bolt up to my SM465 with its stock flywheel and the 465's stock clutch set up, the 6.0 you have to dick with the 0.4" crank spacer unless I find one of the earlier ones with the longer crank and then mismatch all of the other components to get it to work. Or buy the $700 kit from AA. I may be wrong, but it seems like it will be about the same cost to actually get the engines running and mate them up to my transmission, but then the 6.0 would need to have some work done on it to make the power levels I want/need. Maybe subconsciously I just wants a big ass motor to go along with the big ass truck. :crazy: #5 · Apr 26, 2011 Yeah, the 8.1 is kind of a bastard child of the GM engines. It is fairly beastly for a stock engine but IMO it leaves a lot on the table that's never been capitalized on, and like Lindsay said Raylar has pretty much cornered that market and his shit is $$$$. On another note I did read somewhere that the 8.1 has lsx and standard big block Chevy mounts so it'd be easy to throw in. The 6.0 on the other hand can be done fairly cheap, will get better mileage, and its potential is only limited by your wallet. I've thought about a LsX swap in an older vehicle and there are a ton of ways to do it. The simplest would be a carb intake with a 4 barrel and then a MSD ignition to fire the stock coils. GM Performance does make a distributor for the LS engines but it isn't worth the hassle IMO. A buddy of mine has a carb'ed 370 and it is a beast, its easy to tune and was done fairly reasonably. His setup isn't the same as you're going for since its in a 3rd gen Camaro and runs mid 10's but its a good example. #6 · Apr 26, 2011 The 8.1 does have both sets of mounting bosses on it, just in metric threads. I think I'm going to have to scoot the motor back/ move the axle forward, so the Rockwell 3rd member doesn't bash the oil pan in since it sticks up ~11" from axle centerline. The smaller size of the 6.0 would definitely help in that area. What kind of coin would I be looking at to get 400 hp/torque out of the 6.0? I've read about the 496's grenading pistons since the skirt was shortened to keep it out of the crank with the longer stroke compared to the 454. Anyone got any clue as to how common this is? Gas mileage isn't too terribly big of a concern since it won't be a DD, and I don't think 7000 lbs and gas mileage can happily coexist (without a diesel).:rofljest: #7 · Apr 26, 2011 Between those two engines I would go with a 6L.. Like they have said aftermarket support for the 8.1 pretty much sucks and the 6L you can get anything you want. The only thing I don't really like about the ls engines esp in big huge heavy trucks (like mine) is no matter what you do to them they still won't make hardly any power under 3k unless you have a roots style supercharger strapped on. The iron headed 8.1 big block isn't gunna help your wieght situation at all either.. Atleast most ls engines after 00 have aluminum heads and aren't really heavy engines compared to that 8.1 That being said I would build a 454+ ci big block.. Something that will make so toque to get that big tank moving... Keep it carb'd and simple #8 · Apr 26, 2011 You can get 400hp out of either 6L fairly easy both should do it with a set of 243/799 casting heads and alittle more cam.. Basically have a iron ls2 (405hp). This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread. Insert Quotes Post Reply

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