Barry's70LT1

A few details.
The engine itself is stock. All GM LT-1.
Here are the exceptions: Double pump 750 Holley, and Headers.
The 13.02 time was run with open headers, choke butterfly removed, air cleaner base only installed and no alternator belt.
Tires were NOT sticky at all. First gear was mostly at half throttle, until you could feel the tires start to hook up, then full throttle to the end.

With open headers only, air cleaner on, belt on, I could run consistant 13.1x
all day long.

If I had sticky tires, I feel I could have been in the 12's easy. OR have left the rearend on the track.
I did manage to break the diff carrier while racing.

My understanding of the reason that the pistons were different was indeed the piston to wall clearance requirements.
GM produced engine blocks that had a pre configured bore size.
Since the LT-1 was a high perf/rev engine, then the wall clearance needed to be more than the L46.
Rather than rely on an assembly line technician to hone to the proper clearance, you simply install the correct piston to give the desired clearance.

This could start some controversy...
On the street, I've had a few stock/non stock 427/454's (No L88's) try their luck against the LT-1. None have managed to get by.
Most were quite embarrased.

The LT-1 (1970), has an excellent combination of components that produce lots of HP and still be very streetable, and not too bad on fuel.
Barry



[Modified by Barry's70LT1, 4:07 PM 9/5/2002]

Rowdy Rat

Joe,

You are correct... The LT-1 front exhaust pipes were swaged to reduce the pipe diameter from 2½" to 2" where it met the exhaust manifold. The forward pipes were made from doublewall tubing and had no compression "wrinkles" in the pipes (they were probably mandrel bent) like most other Corvette exhaust pipes at that time. The part numbers were also stamped into these pipes at the end farthest from the exhaust manifolds.

The LT-1 rear pipes were identical to the 454 (four speed) pipes of the 1970-72 era and carried the same part number. They had compression "wrinkles" where the pipe was bent and were delivered to St. Louis already welded to the muffler as an assembly. The muffler had a 2½" inlet and a 2" outlet; a locating tab was welded to the outlet to provide positive location for the exhaust tip. A "W" appeared on the body of each muffler (one facing up, the other down when the pipes were installed) identifying the OEM exhaust system supplier, Walker.

The LT-1 pipes were definitely worth a few horsepower over the standard 2" small block pipes... Even with the initial 2" diameter at the exhaust manifold.

Yes, the LT-1s do like a lot of gear. The standard gear ratio was a 3.55 with the M-20 and a 3.70 with the M-21... A "performance" gear set was available for each; a 3.70 with the wide ratio M-20 and a 4.11 with the close ratio M-21 (a 4.56 was available with the ZR-1) and were probably suited better to the character of the engine. My personal opinion is that the M-20/3.70 combination would be the quickest of the bunch...

I agree Joe, Pete's LT-1 Nova is an impressive performer! High 12s out of that combination on stock tires is amazing. I would think that a well set up LT-1 Corvette with a similar weight to the COPO 9010 Nova and better weight distribution should turn equal, if not better times. The Corvette LT-1 has a better ignition system (for 6000 rpm operation anyway), exhaust, and air cleaner than the Z-28/Nova version of the LT-1 which should also help in the drag racing arena.

Regards,

Robert N

Now comes the interesting part. Mine sat for 24 yrs, needs many parts to even come close to NCRS considering the original block is gone (ouch). As such, the thought was to rebuild to 1970 LT-1 specs and make some minor changes to see where HP gains can be had (headers, etc). Esentially a LT-1 tweaked with modern technology.

I was thinking headers, larger carb jetting, diferent distributer (TI gone too), ??

Suggestions anyone?




[Modified by Robert N, 2:19 PM 9/5/2002]

Solidlifters

Somebody posted that there is a dome difference between an L46 and LT1 and there was also a comment about piston clearance. The L46 runs a flat top cast piston, while the LT1's are forged with a dome. That's where the 11:1 compression comes from in the LT1. Forged pistons always require more clearance than cast ones because of the different expansion co efficient of the two pistons. The LT1 has the domed pistons, larger valves in the heads, the aforementioned intake and carb to name the important differences from a horsepower standpoint. The LT1 is solid lifters while the L46 is hydraulic. (I'm not sure if this was already pointed out) I think that these internal components made much more difference than the intake/carb itself. One thing that supports this theory is the fact that the 350/350, which was available in 69 and 70 was basically an LT1 with a hydraulic cam and cast iron intake. It had the 11:1 pistons and big heads and a hydraulic cam that was fairly similar to the old L79 camshaft. It was a great performer and would give an LT1 a run for it's money if the LT1 wasn't tuned to perfection.

Edit: In each case above where I said "L46" I was attempting to describe the base engine. This mental error also cause me to misread the prior engine comparisons, in which I thought the writer was alledging the base engine had the same pistons/heads as the LT1. Sorry for the confusion. It's sad when your mind starts to go.


[Modified by Solidlifters, 12:35 AM 9/6/2002]

Rowdy Rat

I was the one who had posted about the differences in domes between the LT-1 and L-46 pistons...

Both the L-46 and LT-1 used a forged piston with a small dome (although there was a slight difference as noted previously)... They were very, very similar; they had to be as both engines had the same reciprocating assembly, same compression ratio (11.00 to 1 advertised), same cylinder head casting ("186" with 2.02/1.60 valves), and even the same steel shim head gasket.

I agree with your comments regarding piston to wall clearance requirements of cast and forged pistons. Forged pistons DO require more clearance as opposed to cast for the reasons that you stated. The big question is why is there a different clearance requirement between the base ZQ3 (cast), L-46 (forged), and LT-1 (forged)? Each has a different clearance spec... You would think the two forged pistons would be the same, but they aren't. Barry's comments on the topic are the most logical that I've heard to this point; mill all the blocks the same and account for any clearance differences with the pistons... Quick and cheap, just the way GM likes to do things.

I think that I had also mentioned that the 1970 LT-1 piston was probably not offered as a service part for very long (if at all). At any rate, the part number for the L-46 piston is listed as the service replacement for both the 1970 LT-1 and 1969-70 L-46 engines by the early 1980s.

Is it possible that you are confusing the L-46 (350/350) with the base ZQ3 engine (350/300, often referenced as the L-48)? The base engine used the flat top, cast piston that you mention...

Regards,

Solidlifters

Stan, you're exactly right, I was in my mind using the L46 designation as the base engine and that's what my comments were based on............the comparison between a base engine and an LT1. I actually bought a totalled 69 Corvette with the L46 years ago and used the engine in another car and that's why I'm familiar with it performance wise. I just always refered to it as the "350/350" and never knew it as the L46. I think my post above would make more sense if "base engine" was injected everywhere I wrote L46.

Now you're throwing me something that is new information. I've always thought that the LT1 and L46 (350/350) were exactly the same shortblock, except for camshaft and used the exact same heads. I can't account for your statement that the pistons are different between the two, althought the advertised compression ratio is the same. I wonder if there wasn't some production change to correct a problem, possibly clearance related, and the domes were the same.

Raydon 3000

Guys,

You have given me so much useful info on the LT1 and the L46. Now I'm thinking, maybe a few mods on the engine wouldn't hurt, except the pocket book. Please keep this discussion going, I'm learning a lot.

Chuck Harmon

Solidlifter,

The reason for the extra piston clearance was because of the higher expected rpms this engine would use. Its configuration almost demanded to be run to 6500-7000 rpm 50 times a day! It was just too much fun and so eager to indulge the driver with this kind of enthusiastic driving.

Chuck

joe58

The engine likes more piston/cyl clearance for high RPM operation but the drawback is piston knock when engine is cold. Maybe Chevy figured the 350 hp owner would complain about the piston slap noise but the LT1 owner would not since they had solid lifter noise anyway. On a side note, Chevy has a big problem with customer complaints of cold startup knock on Chevy trucks 1990-95. They did a temporary fix with a PROM change, which retarded the timing on cold startup.

BobJ

Man, what a wealth of information!!!

My L46 has been "cloned" so only the very knowledgable know it's not a real LT-1. I bought it this was knowing it was cloned (and the original owner didn't try to tell me it was an LT-1). It has the correct L46 block, M-21 and 370's. Mods are Performer Manifold with 1" rise, Performer carb, K&N open air element, headers, and 2.5" exhaust. Outside it has the LT-1 hood with decals (no stripes), LT-1 info plate, and 370 hp '70 LT-1 air cleaner decal.

All I need is a tach!!!! :D

Did the '70 L-46 and LT-1 come from the factory with the same valve covers?

Bob

Robert N

Yes.

Fevre

The LT-1 came with full floating pistons, did the L-46?

Barry's70LT1

The L46 in 1970 came with TRW 11:1 forged pistons with press pins on "pink" rods.

Rowdy Rat

The 1970-72 LT-1s and 1969-70 L-46s all used pressed pins... Almost certainly a better choice for street engines that would see limited rebuilds.

Regards,

Fevre

Must have been only the 69 Camaro LT-1 or the info I am getting from 'How to Hot Rod a Small Block Chevy' (Fisher and Waar) is incorrect. It does state that later in 70 the LT1 was switched to a pressed in pin.

Solidlifters

"Must have been only the 69 Camaro LT-1 "

Say what????????

corvgreg

What are the specs on the LT1 camshaft, and where is the best place to get one? I want to put the 72 back to stock, it has a radical hydraulic in it now.

Greg

Fevre

Of course no camaro was every badged LT-1 but they had the LT-1 in them.

Solidlifters

"Must have been only the 69 Camaro LT-1 "

--------------------------------------------------------------------------------

"Of course no camaro was every badged LT-1 but they had the LT-1 in them."

Not in 69 they didn't. 69 Z 28's were 302's still.

Robert N

Could it have been the 70 Camaro with the LT-1? And for that matter, what was different in the camaro that had the engine rated with 10 less hp at 360?