Does anybody know if there is any difference's in the 71 LS/5 & LS/6 blocks? How about any internal engine markings to differ one 454 motor from another?

 

LS5 are 2 bolt main caps, LS6 are 4 bolt main caps... you can go further and check the heads.. LS5 heads are round port intakes.. great for low end torque... LS6 heads are rectangular Port intakes. will give you higher flow at higher RPM. the oil boss taps right above the oil filter are bigger in the 4 bolt blocks also... Of course a 2 bolt block can be machined to be exactly like a 4 bolt block... so really not much difference..

 

Once the stamp pad has been decked they're all the same..........

 

Now, Mike....

 

I read, to tell if the casting numbers on a block have been altered is to look inside the engine. The same reference number is stamped in the block behind the cam journal. Any body familiar with this?

 

no one can really alter a casting number.. maybe grind it down and build up epoxy or something like that.. kind if easy to tell if one is looking out for it... then one would look at the date code...

 

Are you the same guy that asked this question on the NCRS board the other day? If so, the answer still stands.

The LS5 and LS6 used the same casting number block, a 512.

 

Its possible I am the same guy. I posted it on quite a few sights and got quite a varitey of answers. Now Mike you need to take a chill pill, because your much nicer than that, and I will be a little more carefull with the things I am asking, and I will try to ask questions that I already have the answers for.

 

I'm as chilled as they come. Seems to me that you're not really looking for the true answer, you're looking for someone to give you the answer you want. I hope I'm wrong. Either that- or you've misread the intent of the article regarding the inner identification marking on blocks. Perhaps if you were more forthcoming with your inquiry further help would be offered.

Please go back to the NCRS site and re-read the answer that Terry M gave you. You can take ignore my comments but take his to the bank.

There is no difference (at the casting stage) between an LS5 or LS6 block. There is nothing on a given block aside from an untouched stamp pad that would confirm that it was from an LS6 car, hence my comment above.

If you've been sold an LS6 car and are now finding out that it's bogus you wouldn't be the first. Again, I hope I'm wrong.

 

which of the big blocks are more desirable??? the ls6 or ls5 just curious!

 

Here is a quick version, but there is a lot to it. I bought a car from a guy that was retireing a few years back, its a 71 454/425 all original except for paint and an engine rebuild. The numbers match except the block was decked when he had the engine rebuilt 25 years ago. He claims its all the original block trans, everything down to the glass. All Markings are correct. The car had 72,000 miles when he purchased it 25 or so years ago. Well when the engine was rebuilt the blocked was decked. I hired a professional investagater (one who specializes is corvettes) to research for me. Aparently the car sat for 20 some odd years and when I purchased the car it had 76000 miles on it. This old guy didn't drive it at all. He said 25 years ago the car had alittle more value than your LS5 but restamping engine block's for deception wasn't much heard of but it did happen. Well any way I now have the car, the priveous owner swears he did not change the block # which does match the number stamped onto the frame, and when he bought the car it was very tired, had a couple of owners and buy the time he got it there was no paper work. The machine shop closed long ago and by the way the block was restamped you can almost see the original broach marks on the left side of the pad under the letters. So I have requests out to almost every DMV and with privacy laws its tough. My P.I. said he has some connections. All this is comeing from my P.I. I dont care if its original or not. It would be nice, but I like the car any way. So anyway I have been fishing every were for any info I can, trying to help crack the case . The only way tell if the info on the net is any good is to ask the same question different ways and evalueate your self its worth. I personally also feel the car is original and the ex-owner was a humble guy that did sell everything he had and retired. You knopw the LS6 corvette a few years back, you could buy one for 40 to 50 grand. It was the most overlooked muscle car out there. Just a couple of years ago they started to really shoot in value. Thats the short verson. There is much more to it since I have been lucky enough to have this P.I. working on it he has uncovered much. Thats why I was curious for any internal markings that would match the engine external

 

So you're looking for proof that this is a genuine LS6 car and still has the original engine in it. What evidence, other than what the previous owner told you, do you have that it is an LS6 car?

Sounds like you're relying on hearsay rather than fact. Real LS6 cars are worth well over 100K these days. If it were mine I'd be putting real effort into proving it's origins.

 

Exactly...

 

Thats what I have been working on. I have been working with NCRS and a investagater to try to locate a fellow named Scott in Virginia.(a hunch lead) The car is Migilia red with manuel breaks and a m21 trans convertable. I believe the car originated in Tenn. or Virginia. If I am not mistaken there were only a few with M21 and manuel break vert's made. As far as indications, the car looks like a real deal. I am not overinflated about makeing this something it isnt so I havent been running this hunt on dreams and wants. My self and My Investigater hace been peacing this together as calm as can be. we will just have to wait and see. If anyone would like to offer me advise I would much abliged. I have nothing to hide unless I am instructed not to by my guys (or my wife ha ha ha) Thanks

 

Well, you could start by answering the question I asked above.

"What evidence, other than what the previous owner told you, do you have that it is an LS6 car?

The combination of an M21 with manual brakes in a convertible is probably not 'more rare' than any other three option combination, nor is indicative of an LS6.

 

How would I know if it is an LS6 car? It has the 6500 rpm tach, all the date codes are correct the engine is the correct aluminum head. Could you be more specific please? What would you look for to confurm its LS6 originality? All the build dates engine dates head dates trans # rearend numbers, tell me what I am missing. I have collected cars for a long time, but never american muscle, mostly German and Italian and British and English. So I am new. I will tell you one thing the Ferrari's, Lambo's, Porsches, Jag's, R.R'ses and Austin's are great to look at, but American you can work on and have alot more interaction. I think I will start cleaning out my less favorites and jump on more of these brute's.

 

Thanks-that's all I was asking. Seems like you got a good start.

 

Have you looked for the build sheet?

 

Man, I guess I was wrong again. I always thought the LS-6 had iron heads.

 

Never had the gas tank off although I have a fiber optic camera and looked on the top of the tank through the rubber neck at the gas cap without any visual. Possibly its stuffed up under the dash somewere? I have read of some crazy places.