What are the physical differences with these engines? Are they of the same design just ones bigger? are they setup,the same? ignition, intake , fuel delivery, etc to make up the differences?

They are totally different designs. The 8.1 is a next-gen 7.4 (454) and hence shares key dimensions with the GM big-block family. The 6.0 is the largest-displacement Gen IV smallblock, sharing bore centers and other key dimensions with the 4.8/5.3/5.7. The 8.1 does benefit from several of the same technologies as the 6.0 such as sequential fuel injection.

Nothing is the same in these motors, the RAT is the mighty Rat and the small block is just that! On the serious side, nothing is interchangeable, other than the oil filter or something like that. Rat heads are huge, valves, piston, crank, just about everything is bigger. They breath better, they are just starting ta come on when the small block is done. The Rat is about the best all around motor ever designed. They have dominated Pro. Stock for over 20 yrs. They are the best RV. motor ever made. cept maybe for the duramax, and there is so much potential from this thing it should be around for a long time. I have owned one for 20 yrs. including one of the Keith Black replicas and it was a runnin mothea. So I am partial to the Rat. If you want detailed info. pick up the Hot Rod Mags. tons of it there.

The biggest and most noticeable characteristic between the 6.0 and 8.1 is the very big grin on the face of the 8.1 driver and the reduced number of points left on his license....those things just fly!! The 6.0 is a good engine but I really love my 8.1!

Mike Mac Quote Rat heads are huge, valves, piston, crank, just about everything is bigger. They breath better, they are just starting ta come on when the small block is done. End Quote When the small block is done with what?? smokin the big heavy big block off the line! LOL SZ

Zman,

Not to argue, if you've never had a big block, you just don't know.
Nuf said.

I'm not going to argue either!I have had both!! They Both Rock!! and have their intended purposes! SZ PS were neighbors!!!

Zman , you in Phx.? I'm at 19th ave and Thomas.

Thats close!! I'm in Chandler!! But my work is 10 st Bethany home rd !! Now you know why I did not want to argue!! lol Scott

Hay Man,

Ya, thats close. When I was young, I had a small block in my truck, and I asked a buddy what to do with a rat my dad gave me. He said lets build it to the specs. of the Keith Black 454 being built at the time. So we did and WOW! what a differance! So from then on small blocks were absolete to me. Know I was looking for a new truck and was looking forward to the new 496 with the new ally. and saw the 520#of torque on the diesel and thought I should probally try one out, and ended up with one. Now, I will NEVER say the venerable RAT is dead because I believe it's the best gas motor out there, but this diesel stuff is hard to beat. So now, thats where I am,coming from! If you ever need help with something, GM wise I know a little bit.
Take care, drive safe, You never stated what your driving. LOL Mike

Hi Mike!! I have a 2005 6.0 ext cab! It does what I need just fine!! I also have an 81 Full size Jimmy with a 383 built by me that can toast the 454 Loper's built motor in my 3/4 ton!! With Chevy's torque management system I really think the faster winding lighter small block has an advantage! and the big block torque will out pull the SBC My opinion! But we can always got to firebird and check out our theory lol SZ

both get about same gas mileage. Small block has to work harder to move same load.
JMHO
Actually I drove both before I bought BB. SB(6.0) with 4.10 gears and mine with BB and 3.73 gears, both CCLB, personal opinion? 6.0 felt like it was struggling just to move truck while 8.1 plants you in your seat, so I bought 8.1
3 friends have 6.0 engines, one standard cab LB other 2 CCSB, all get no more than 12-13 mpg, dad's 04 ECSB gets same, mine gets 11-13, 9-10 with loaded trailer on it, and I have 35's on it. All 2500hd's, 3chevy 1 gmc

Hi Mike!! I have a 2005 6.0 ext cab! It does what I need just fine!! I also have an 81 Full size Jimmy with a 383 built by me that can toast the 454 Loper's built motor in my 3/4 ton!! With Chevy's torque management system I really think the faster winding lighter small block has an advantage! and the big block torque will out pull the SBC My opinion! But we can always got to firebird and check out our theory lol SZ
Huh?..The torque management in the small block is what KILLS its performance. I know it's not a big block, but if you invest in a performance tuned PCM that gets rid of the torque manangement, you'll feel a difference. I sure did and I wish I've done it sooner....

JRKRACE I hear you!! But its so new I'm a little nervous!! and honestly it's plenty enough for my 30 foot boat and really hauls ass with no load!!! maybe I'm getting to old! lol Scott