want to build a 406

Hi all. I have a SBC 400 4v Lt4 but I want to make it a 406 wat do I have to change and. Wat parts do u guys recomend. Thanks for any helpl  

If I understand you correctly. You have a 400 SB. Want 406 out of it.

Well you have a 4.155" bore X stroke of 3.750"=400 gives you 400 Cubic Inches. If you bore the block .030 you should get 406 cubic inches with the same stroke. Is that what you mean.

I don't understand the LT4?

Bob  

The LT4 was a 350 smll block with reverse cooling. I think someone has not done enough research on what he has..or wants .  

The 350 LT4 was only made for a short time and I believe it was only put in the Vette.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

+1 Dave.,. the original poster has not logged in since his one and only post.
It seems like a dead horse might be getting whipped here.
So again, what have we got, a 350 LT-4 or a production 400.

LT4The LT4 was a special high-performance version of the new-generation LT1. With the addition of a slightly more aggressive camshaft profile, 1.6:1 roller aluminum rocker arms, high-flow cylinder heads, and an intake manifold (painted red) with extra material above the port available to allow port matching to the raised port LT4 cylinder heads, it was rated at 330 horsepower (250 kW) and 340 lb·ft (461 N·m). It was introduced in the 1996 model year, for the last year of the C4 Corvette, and came standard on all manual transmission (ZF 6-speed equipped) C4 Corvettes. The engine was passed down to special versions of the Camaro and Firebird the next model year.

The LT4 was available on the following vehicles:

1996 Chevrolet Corvette when equipped with 6-speed manual transmission (includes all Grand Sports) (Production: 6,359)
1997 Chevrolet Camaro SLP/LT4 SS 6-speed (Production: 100 for the U.S., 6 for Canada. There were 2 prototypes)
1997 Pontiac Firebird SLP/LT4 Firehawk 6-speed (Production: 29)
All 135 production engines for the Firehawks and Camaro SS were completely disassembled, balanced, blueprinted and honed with stress plates. One in 5 engines was tested on a Superflow engine dyno and every car was tested on a chassis dyno in addition to performing a short 6-mile (10 km) road test).

 
When The Flag Drops,,,



The Bull Chit Stops,,,


P. Engineer, Engine Builder

Thanks Tuff, I did not know it was put in the 97 Camaro's too.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

Let's iggy this thread until the original poster replies

 
When The Flag Drops,,,



The Bull Chit Stops,,,


P. Engineer, Engine Builder

+1 Tuff and +1 Dave

When a poster runs on with a sentence, it's hard to decifer whats what!
Thanks Guys
Bob  

Sorry been busy these past few days. Ok I have a 1975 Chevy laguna s3 with is original motor.  The motor is a lt4 400 small block. It has 175 HP and 300ft/lbs of torque. I want to make it a 406 , I know I have to bore it 0.30.  But I was told I should also change the crankshaft. So my questing is what parts should I change ?  

.. OK, stock SBC 400 is actually 4.125" bore by 3.75" stroke... (4 1/8" x 3 3/4") that gives 400.75 cubic inches displacement... since Buick already had a '401', guess they called it a 400 to reduce confusion... 0.030" overbore ( a size that gives best selection of replacement performance pistons nowadays) gives a 4.155" x 3.75" -> '406' (~406.75")... usually nobody wants a 406, that's just a size you end up with after overboring to clean up bore wear...  (standard replacement pistons are available for .020", .030", .040", .060". and .080" overbores, which gives 5 rebuilds/ 1,200,000 miles for taxicab/pickup truck use engines, etc.)...

.. Whether you replace the crank depends on whether the old one is any good and what performance level is your goal... how big your budget for this project is... for a strong performing street / street/strip engine with good drivability and good MPG (better than stock!) up to 500HP/500 lb.-ft. torque and 6000-6500 maxRPMs the stock rods and crank should be fine with new flat top pistons, mild cam (214/224 - 234/244) range, and 195cc - 220cc heads (stock 165cc heads max ~375HP)...

.. IF going for more power and RPMs and strip/street / race use, I'd go right to an internally balanced forged crank and 5.7" or 6" 4340 steel rods... forged pistons...  

If this is just for street use you may not need to overbore at all. Check the taper of the cylinder wall to see if there is enough wear to warrant the overbore and new pistons.
Just a rebuild, mild cam and headers with get you a moderate boost for street driving.
To get 400+hp out of it you are going to have to change just about everything except the block.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

The stock heads need to be the first thing to hit the trash can. Those mid 70's years were the worst with 75cc combustion chambers. With a rebuild, Newer Vortec heads (drilled for steam holes by your machine shop) will give you quite a boost in both compression and performance (and gas mileage). For street use they will be very good, and very reasonable price wise. Depending on your budget, you can do many things to improve your performance. Lots of experience on this site, listen to their advice and your project will get you where you want to go.  

1975Lagunas3:
Sorry been busy these past few days. Ok I have a 1975 Chevy laguna s3 with is original motor.  The motor is a lt4 400 small block. It has 175 HP and 300ft/lbs of torque. I want to make it a 406 , I know I have to bore it 0.30.  But I was told I should also change the crankshaft. So my questing is what parts should I change ?

I can't say for sure But I can't remember a 400 being available in the S3. May could have Ordered it but those days they came down the line in Groups of 50 or more and that is where a special order got there,Matter of fact the S3 was Out sourced and started as an SS I believe. The OP is still refering to it as an lt4/400, the tourqe looks to be a 400 though so ? Please get us a block number of the back of the block or count the Freeze plugs on the side of the block  

Yes those early smog heads were horrible. I think they are truly bottom of the barrel when it comes to performance.
It all depends on the cash available. Heads, intake, carb, headers, and and mild cam would top the list for replacement. I think Edlebrock makes a kit like that.  
[[SUPPORT AMERICAN CARS, STOMP A RICE CAR TODAY.]]

edelbrock does make a "Power Package Top end kit" has everything he needs to wake that 400 up. All matched to work together. They advertise 410 HP from a 350 for $1799 in Summit Racing. Trick Flow also has a similar kit (350 HP)for the same price. I think for the price and getting everything engineered to work together it's a good deal for a first timer.