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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine> 8.1L 496 vortec big block chevy, what is it?
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Topic Review (Newest First)
11-03-2014 11:11 AM
Hogg Correction, I had a buddy take a pic for me.

Here is a GEN 7 L18 8.1l exhaust manifold. You will have to drill out the 8.1 manifolds to fit the correct diameter GEN 6 bolt size.

And his quote to go along with the pic
"Both manifolds have one cylinder that the holes are the correct size for the retention bolts. since 8mm bolts hold the manifold on. So if you wanted to use them on an older bbc you would have to fix the hole size on both manifolds on one cylinder. You then could use factory exhaust off of a newer truck."

EDIT AND another

11-03-2014 08:49 AM
Hogg The 2001+ 8.1 is a GEN 7 BBC, it is Coil Near Plug CNP. Rated at 340hp and 450lb/ft torque. The GEN 6 Vortec 454 7.4 rpo L29 it replaced was rated at 290hp/410lb/ft torque.
the GEN 7 L18 8.1 uses the different firing order of 1-8-7-2-6-5-4-3, just like the GEN 3 SBC like LS1's and such.

The 8.1 is comaptible with and transmission just like any other Chev engine. The 8.1 came stock with teh 4l80e/85e and the 6 speed manual as well as teh Allison transmissions.

IIRC the exhaust manifolds are compatible.

Back in 2003 GM was using the 8.1 in a marine application for APBA racing. The engine was a truck L18 with ported stock iron heads. It was rated at 525hp and 560 lb/ft torque. It was a standard truck engine with factorry iron ported heads, higher pressure FPR, HP3 specced camshaft by Crane cams, and heavier valvesprings.
The HP3 engine was listed as COMING soon in the GMPP Performance PArst calatogue back in 2003, but the engine was cancelled after much testing as Mercury was choked that GM had a "truck" engine that was beating its high dollar race engines. Mercury was GM's largest BBC buyer so GM dropped teh HP3 program.

HP3 8.1

And the boat it is in

11-02-2014 08:58 AM
hotrod-z28 You or someone might know this, is the 8.1L balanced the same as the 7.4 or does it have it's own balance. The reason I'm asking is I'm going to install one were a 7.4L was and the 8.1L had an auto. behind it and the 7.4L has a manual. Another thing is the exhaust the same or is it different
05-02-2013 08:22 PM
matt167 The crankshaft and rods can be used in the earlier big blocks and is somewhat common as the cranks are nodular iron, not much else for performance tho.
05-02-2013 04:34 AM See other post.

Back in 004 I had my first 8.1L and was going to make a street motor out of it. I found no reasonably priced stuff for the engine. Mostly marine stuff. So I sold it.

Since then I have had several customers with the same ideas and experiences. Too costly for parts.. Even the stock stuff is $$$$$$
05-02-2013 02:32 AM
laughlin81 So I found a 2002 Chevy vortec 8.1L with trans and I want to throw it in my 57 Bel aire. I want to completely rework the engine and make some serious power with it. Think it's a good idea? I want fuel injection and I'll probably supercharge or turbo the thing as well. Any clue on where to buy performance parts for these things? Any way to get rid of the auto trans and put a beefed up 6 speed behind it? Any help would be much appreciated.

08-26-2006 03:19 PM
Duke of Cruel
Originally Posted by 406 ss monte
i found a 496 bbc. i've never heard of it before. is it the same as the 454's & any other big block chevy? do the bolt up like the older ones? do they use the same heads, intake, & other bolt on's? are they a good choice for a build up? like i said, i've never heard of them. i know about the 454 stroker 496, but this is a factory short block. thanks for your help.

its an vortec big block , same as the truck engines and in family with ls1/ls6 etc.
08-08-2004 02:02 PM
deuce_454 4.5x4, id say that getting the 496 shortblock and installing the rotating assembly in a bored 502 block with some aftermarket gen 6 heads, pro topline 320 or dart 360 allong with a rollercam is your best ticket.. a healthy mechanical-rollercammed well breathing 555 bigblock should be good for 750 Hp on pump gas with mufflers
08-08-2004 11:24 AM
GoneNova/406 if you would jump over to,i think you can look at their bore and stroke list for big block chev's and find out that a 496 is a stroked 454=4.250x4......496=4.250x4.37....i'd almost rather have one of these than a 502which is 4.66x4
08-08-2004 11:01 AM
68c10owner there is a post at about performance heads and a intake for the 8.1 motor. the parts were expencive but they were aluminum and would make alot of power.
08-07-2004 06:02 PM
Super Streeter There is limited swapability between the 8100 and most other bigblocks.The shortblock is a gen 6 type lowdeck with a 4.25" bore and 4.375" crank and stock length heavy duty rods.The crank is nodular iron with winged counterweights and is a good performance piece.I assembled a 555 using the crank from a 8100 vortec in a later 502 block{.030" over} and with lightweight pistons and steel 4.385" rods it lives fine making 850 hp at 7000rpm.We had some of the prototype stuff when it first came out and GM's intentions were to build a 496 inch shortblock that used standard bigblock valve angles and valvetrain components but had symetrical port prostock style heads ib it.The early version that I worked on had a 10 bolt head pattern like a ford motor but it used massive 5/8" studs.The intake used 4 bolt per side composite plastic intake.The heads flow very well and with a little bowl blending and some 2.25" intake valves they will outflow even the best aftermarket standard bigblock heads,and the cross section is small enough to make it all very streetable.Like I saud,the heads are very prostock like.I never worked with an entire production engine,but I know that the production piece uses a standard bigblock head bolt pattern and gen 6 water passages,and will use at leas regular mark 4 rocker arms if the studs are correct.It would be a great performance piece,and when I first got it I was working on building a combination to run my rae car in a class that requires production part number car or truck casting engine blocks and heads,with displacemnt limited to whatever you could stuf in a stock block,and since the original prototype was a siamsed wall casting,I was looking into it as the ultimate loophole combination once the engine went into production.The rulemakers required carbs and a regular distributor and sheet metal intakes or distributorless coversions were illegal,so the engine lost it's potential.All in all,if you dont mind working with the efi,the longblock has lots of potential for a drag race or stret rod buildup.Good luck.
08-02-2004 12:35 PM
deuce_454 the best way to check engine type is to look up your castingnumber. im betting yours is a 12556110. its a 01 up 4-bolt, Gen.VII 8.1L, "Vortec 8100", Truck engine

im not sure if you can get performance heads for a gen 7. but mercruicer just came out with a performance big block based on that engine that put out about 425 Hp with gen 7 heads, 9:1 comp and a 5000 rpm marine cam, so dont dispare
08-02-2004 11:00 AM
406 ss monte all there is is the short block, so if the older "good" heads wont work, i can't use it. i'm sure the heads & they use anen't worth a dime for 600 horse power like i'm wanting.

how can you tell the differance from all the blocks to know what it is? like the differance in a mark 4 & a mark 5 block?
08-02-2004 08:01 AM Correct. The water passages are different and the oiling is different. They do use a coil pak but the block is still for a distrib. The intake is impressive looking with the black and aluminum theme carried over from the cast valve covers.
08-02-2004 02:50 AM
aren't the 502, & 396,427,454 heads all the same as fare as the bolt pattern on the deck surface? if they are, why wouldn't the older heads, intakes, & distributors work?
actually they are not the same.. the waterpassages are diferent, if you try and bolt a mark 5 head to a mark 4 block the water will pour into the oil.. and if the new vortech 8.1 is reverse cooling nothing will work.. it would be like bolting a set of camelhumps on an lt4. it might bolt up, but cooling would be non existent...

but with some tall reared gears i think it would be a killer engine, and if you can have it cheap.. have at it..
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