Raydon 3000

What are the differences between a 1970, LT1 and L46. The blocks seem to be pretty much the same. LT1 has solid lifters, L46 hydraulic. I think the LT1 had a Holley, L46 Q-jet, I don't know the cfm of either. The exhaust on the LT1 was 2 1/2", L46 2". Was the intake the same? What about the heads?


[Modified by Raydon 3000, 10:48 PM 9/4/2002]

1970 Dave

bout 20 horses :lol:

SEMPER FI--1970 Dave

Robert N

LT-1 had aluminum high rise dual plane intake, Holley 780 cfm, single fuel line (no return), solid lifter, steel forged crank, hardened "pink" rods and guideplates, hopped cam, 6500 redline. There are a few more differences, but theses are the main ones.

Blocks are the same.

While the horses are only listed as a difference of 20, it should be greater than that.


[Modified by Robert N, 4:09 PM 9/4/2002]

sb69coupe

The L-46 had the same crank, rods. pistons, heads as the LT-1. The differences were the carb, intake, cam, lifters as mentioned.

BobJ

$10k :D

Bob

Barry's70LT1

The information already posted is accurate.
Just a clarification on the heads. The L46 & LT-1 both had 2.02 heads,
however the L46 did not have the pushrod guide plates.

Chuck Harmon

In addition to the above, the LT1 had slightly more piston clearance in the bores. The 69 L46's had pressed in rocker studs while the 1970 and later L46's and LT1's got the better screw in variety.

A cam, intake and carb change bring an L46 to LT-1 specs is very rewarding. Been there, done that! Absolutely loved the results!

Unfortunately, you will probably need to change to the LT-1 hood though as there is not quite enough room under the stock SB hood.

Chuck

Raydon 3000

I know that there was a 20hp difference!!! But I've also heard it is a lot more. GM is said to have under rated the LT1. Anyone have any ideas on that?


[Modified by Raydon 3000, 4:51 AM 9/5/2002]

Chuck Harmon

To put it in modern perspective, I think the 370hp LT-1 was about on par with a standard C5. About 400 gross hp, and 345 net hp.

Chuck

Raydon 3000

Any LT1 owners out there had their stock, 1970, LT1's checked for net HP?

SuperFast80

I am going to have to support Chuck's notion of 400 gross hp. I have seen stock LT-1s with trap speeds of 105 mph.

Barry's70LT1

My stock LT-1 trap speed 110.30.

SuperFast80

What if anything did you do to that car to get so low down in the 13s?

Chuck Harmon

My guess is sticky tires, and a very talented driver! I should also add that the LT-1 has a long duration cam that like the L88 cam responds very well to a free flowing exhaust system. It was really the only modification other than tires needed to produce excellent track times for the strip and/or road courses in its day. It can still make very respectable times even today in the hands of a good driver.

Chuck

Rowdy Rat

Chevrolet first started using screw in rocker arm studs about half way through the 1969 calendar year on big valve (2.02/1.60) heads... I've seen very original 1969 Z-28s with May/June 1969 build dates that have had screw in studs. Z-28s at this time used the "186" heads just like the L-46 and later, the LT-1 Corvettes. I would guess that L-46 Corvettes built later in the 1969 calendar year would have screw in studs as well, but I've never been motivated enough to start surveying this feature on original cars... Perhaps now would be a good time to start.

One of the reasons that the piston to wall clearance on the LT-1 engine is greater is due to the fact that the pistons are different than the L-46 pistons. This is really odd considering that both engines used the same heads, reciprocating assemblies, and had the same advertised compression ratio. Both pistons were supplied by TRW, were forged, and used pressed pins, but the LT-1 piston is heavier (about two thenths of an ounce - almost insignificant really) and has a slightly different dome shape (again, the difference is minimal, but you can see it if you know what you are looking at). As you would expect, the part numbers for the two pistons are different as well and are stamped into the top of each. I don't know how long (if at all) the LT-1 piston was listed as a service part, but by the early 1980s, the L-46 piston was listed for both applications.

Chuck,

I'd be willing to bet that the intake was responsible for most of the improvement... The LT-1 camshaft performs better at higher rpm, but I don't think that you'd be able to take full advantage of it without the intake. The Holley carb is neat too, but nothing a well set up Quadrajet can't match.

The LT-1 engine was supposed to debut in 1969, but a shortage of intake manifolds (which was used by the Z-28) kept it out of production. GM seriously underestimated the demand for 1969 Z-28s and didn't want to ruin a good thing by limiting parts needed for a car/engine with a proven sales record.

This intake is probably the most copied in automotive history. It remains an effective high performance dual plane manifold and is still available from GM and in similar form by aftermarket suppliers.

Regards,

Robert N

Chuck, thanks for the comparison to a modern day C5, as it gives me a good perspective on mine.

Raydon, Superfast, Barry - I have not had mine checked, but based on the the trap speeds and times mentioned, the gross HP at 400 and rwhp at about 316 when figuring a 20% drivetrain loss is close based on sites like smokeemup.com.

Chuck, is it safe to assume that the LT-1 is a small block equivalent to the L88? Given what this feels like to drive, I would love to take a ride with you!

Superfast, I have not run mine at the track, but the car does move when you hit the gas. I have driven a few fast cars and this one, for a SB, impresses me. Chuck is right that a good driver and sticky tires could hit low 13s times. Kinda makes you tghink about the BB vs SB issue.

joe58

Didn't the LT1 also have the 454 exhaust system except for the manifold ends were made to fit the small block? If so the 454 exhaust system had to add a few HP. I would image like the 302 Z/28 an LT1 would like a 4:11 or higher gear to perform well at the drag strip. Great motor - there is a guy with a COPO LT1 Nova that runs high 12s in the pure stock class with full stock exhaust and stock size polyglass tires.

l2vette

Please help me out here with a stupid question. Was the RPO for the stock 1972, 350 CI motor the L46??
:confused:

Chuck Harmon

The LT-1 is more civilized than the L88 as the cam is not quite as big. I am speaking more about duration than lift since the actual cam timing makes more difference regarding the engines personality than simply higher lift.

The 20% power loss conversion you mentioned is probably about right since the LT1 doesn't have a functional cowl induction and the exhaust system is pretty restrictive. Based on Jay's factory L88 dyno's on the bench and at the wheels, headers and cowl induction reduce the lose to less than 13%.

As Rowdy Rat so greatly noted above, the cam would not be much good without the intake. I agree whole heartedly. But I firmly believe that the whole package must be together. The intake without the cam is probably worth only 10hp at best. An L82 is basically a low compression L46. If you were to put the cam and intake on an L82, it would have a little better performance, but the 11:0 compression (real compression was 10.5 as they anticipated normal carbon buildup would make 11:1) was needed to keep the "bite" of the engine with the cam overlap. To me, the '72 LT-1's had lost their vibrancy. This was why the L82 was the better engine to replace it.

Rowdy Rat is also right that the QJet can be made to make about the same power. My problems with the QJet were that it would float out on hard cornering while the center pivot bowls of the 780 Holley kept the fuel level over the jets. Now I am really spoiled with the "right now" throttle response of the double pumper Holley's. My L88 throttle is just as responsive as my ZO6, unless I am at a low rpm.

The BB vs. SB will never be resolved. The small block in my Z is nearly equal to almost all of the factory BB's with iron exhaust manifolds. Even concerning torque, the Z's roller cam makes it pull like most factory BB's. Until the new LS6 engine came along, there was not a small block I liked better than a factory LT1 with headers. For less than $1,000 you can install a roller cam in an LT1 and have the same thing. Reasonable idle, 340 pounds of torque at the real wheels over a huge rpm range, a screaming 7000rpm redline, and perhaps 360rwhp. This is as good or better as any normal factory BB. But BB's can be tweaked too!

Chuck

sb69coupe

No, the L-46 is the 350hp option from '69 and '70.


[Modified by sb69coupe, 2:28 PM 9/5/2002]