What did Chevy do to the LT1 to make it into the LT4? I know the cam is hotter, but what else? Is the intake plenum different? Heads ported? What are all the things they did, because they both look alike except for the red paint on the intake manifold of the LT4's and the ID plate.

 

LT4 heads come with .100 raised intake ports, also 2.00 int valves compared to 1.94 on the LT1..The LT4 Manifold is also has raised ports to accommdate the taller ports..The LT1 and LT4 cams are very similar except the LT4 comes with 1.6 roller rockers that gives it an additional .30 valve lift plus a little less valve train friction. The LT4 came with 10:8:1 compression as to 10:5:1 for the LT1, this was acvheived by having only 2 valve relives on the pistons as to 4 on the LT1. Also the LT4 came with larger #28 injectors.the LT1 came with #24 injectors.These were the major diffrences between the two for the performance diffrence..There were other improvements as well.


[Modified by JB'S LT4, 12:50 AM 7/6/2002]

 

from: http://www.automotiverebuilder.com/ar/ar99928.htm

THE LT4 CHEVY
There is one more version of the LT1 out there that could cause some confusion if you get a core and don’t know what it is. The LT4 was the high performance version of the LT1 that was standard in the 1996 Corvette "Grand Sport" and optional for any 1996 Corvette with a manual transmission. There were also 100 1997 SS Camaros built by SLP that came with the LT4. Chances are most rebuilders will never see one, but just in case you do, the following are a few things that make the LT4 special.

BLOCK - Should be the same LT1 casting with the four bolt mains.

CRANK - The LT4 has a special nodular iron crank with undercut and rolled fillets for added strength.

RODS - Powdered metal rods are used with a "cracked cap" instead of a machined parting line.

CAM - The LT4 cam was similar to the ones used in the high performance LT1, but it has had considerably more lift at the valve because it had 1.6 to 1 rockers.

HEADS - The heads had smaller 54cc chambers that gave the LT4 a 10.8 to 1 compression ratio. The intake ports were raised 0.100", too. The LT4 used larger intake and exhaust valves (2.00" x 1.55" ). The intake stems were hollow to reduce weight and the exhaust stem was sodium-filled to improve heat transfer. The valve springs were made of oval wire to prevent coil bind with the higher valve lift and fitted with lightweight retainers to help the engine rev to its 6,300 rpm redline.

All of these changes enabled the LT4 to make 330 hp at 5,800 rpm instead of 300 hp at 5,000 rpm.

Eric

 

Everything you want to know about the LT4 can be found at http://www.lt4.net website.

The comparison between the LT1 and LT4 is thoroughly documented at http://home.tir.com/~steveher/lt4.html

 

Wish mine was an LT4. :yesnod:

 

"The heads had smaller 54cc chambers that gave the LT4 10:8 to 1 compression ratio" ...................................... The LT1 heads also have 54cc chambers, the compression was raised to 10:8:1 by using a 2 valve relief piston, the LT1 had 4

 

Go here for everything you need to know about LT1 v. LT4. (Go with an LT4, there's a big difference!)
http://corvetteactioncenter.com/specs/1996/lt1lt4.html

 

The Lt4 actually has 4 valve reliefs as well. I have 5 in my shop right now. This is so they can use the same casting on both sides of the motor and still have the thrust side correct for the pin offset.

 

That's what I thought. I've heard the LT1 chambers are ~56-58 cc, but I can't find any documentation to confirm.

Eric

 

I'm looking at a few 96's. I want an LT4 but I have a bum clutch knee, so I'll probably go with an auto since it's going to be a daily driver. Also I won't feel so bad putting miles on one that's not a collector car. Oh well. Even if it's only an LT1 :rolleyes: , it's still the American Legend. :flag

 

Don't worry though, an LT1 is still pretty strong and can be brought up to LT4 power levels with reasonable $$ put into the right mods, and beyond LT4 levels if you want-- all depends on how much time and $$ one wants to put into it :yesnod:

 

I just bought an LT4 and can tell you the clutch is pretty stiff! Guy