C3 Lt1 Engine History

[Vincent F.]

Re: C3 Lt1 Engine History

Dan, how did you get your hands on a ZR1, what was there like 25 made.

[Steven G.]

Re: C3 Lt1 Engine History

Dan, great technical pointers, I had L-46 top end oil smoke issue during a really hard run, using aftermarket cam and hyd. lifters, no collapsing lifter problems, floating rings ?? maybe?, slowed down, smoke disappeared all is well. Steve

[Dan P.]

Re: C3 Lt1 Engine History

Dan, how did you get your hands on a ZR1, what was there like 25 made.

Vince - here's the story. Just fortunate I guess.... Enjoy the read.

http://www.corvettes.com/articles/?p=18

[Paul C.]

Re: C3 Lt1 Engine History

The LT-1 had solid lifters, a high performance cam, aluminum intake, and probably other things I can't remember. The L-46 didn't have these. There are other differences but I am speaking just of the engine.

[John G.]

Re: C3 Lt1 Engine History

Thanks to all , I have also received article from Roy I had heard there was some one from the UK involved in the LT1engine but nothing has been raised about this so guess just another rumour, don't see many Corvette articles in the old mags at swap meets here.
john

[Alan T.]

Re: C3 Lt1 Engine History

Warren, I think that it is a common misconception that the LT-1 ran in SCCA B Production. I used to think that, too, simply because I thought all small blocks ran in B/P and big blocks in A/P. But a few years ago I started vintage racing, and since we have to conform to the SCCA period rules (1972 or earlier), I was told that if I ran a Holley in my small block '69, it had to be grouped in A/P. I thought, no, the LT-1 had a Holley and it was a small block, and since it was a small block, it could run in B/P. Well, I was shown the 1972 SCCA General Competition Rulebook and, sure enough, it clearly states all Holleys must run in A/P. Now, I'm not saying that at the local level that no Holley smallblock was ever allowed to run in B/P, I'm sure it happened if the tech guy looked the other way, but at the more strict national races the LT-1 had to be in A/P. So, in strict interpretation of the SCCA rules at the time, an LT-1 had to run in A/P with the big blocks. Funny, huh?

Alan

[Michael W.]

Re: C3 Lt1 Engine History

I WONDER how much H.P. loss occures due to the emission pump, I was told 5-8 H.P. loss, i

It's less than 1 HP. GM's own figures.

[Duke W.]

Re: C3 Lt1 Engine History

together with a smog cam.

The LT-1 cam is not a "smog cam".

Duke

[Steven G.]

Re: C3 Lt1 Engine History

The LT-1 was also equiped with a Holley carburator. The non emissions cam using an AIR pump ??? I have been told that emissions requirements was the reason an AIR pump was used even though all engines produced during this period had not been originally designed for AIR pumps, but done so to conform CA. and federal standards. State safety inspections require 1975 and later vehicles to have cat. converter installed except for base 1-BBL 140 vega. Steve

[Michael W.]

Re: C3 Lt1 Engine History

State safety inspections require 1973 and later vehicles to have pump + cat. converter installed, and not for 1972 and older vehicles that never had factory cat. converters. Steve

No Corvette prior to 1975 had a converter and many Corvettes new than '73 did not have smog pumps.

Many Corvettes prior to '73 had a smog pump or oher means of complying with regulations.

I suspect your source of information is incorrect.

[Patrick H.]

Re: C3 Lt1 Engine History

No Corvette prior to 1976 had a converter and many Corvettes new than '73 did not have smog pumps.

Many Corvettes prior to '73 had a smog pump or oher means of complying with regulations.

I suspect your source of information is incorrect.

Mikey,

Catalytic converters started in 1975, not 1976.

[Duke W.]

Re: C3 Lt1 Engine History

There is no such thing as a "smog pump", but that's what bubba calls it.

The system is known as Air Injection Reactor, or AIR, and the pump is called the AIR pump.

Early exhaust emission-controlled engines evolved from their non-emission controlled antecedents.

The basic strategy for meeting tailpipe standards of the era was carburetor and spark advance map calibrations and the AIR system when necessary.

Actual internal changes, such as camshafts specifically designed to aid in exhaust emission contol did not go into production until about the 1973 time frame. In particular, some camshafts were designed with more overlap to control NOx by leaving a larger exhaust gas residual. In the case of the LT-1 cam, since it had considerable overlap it was low on NOx, but required the AIR system to meet HC and CO limits.

The first NOx standards went into effect in CA in 1971 and 1973 for the reamaining 49 states.

The LT-1 was originally schduled to be released in the 1969 model year, but certification problems delayed it until the 1970 model year.

Development and emission certification was an expensive proposition and the OEs had to deal with both CA and federal standards. This is likely why the LT-1 was replaced by the L-82, which was basically a low compression version of the '70 L-46. This reduced the number of engine options to two above base - the L-82 SB and one big block, which was essentially a low compression version of the L-36 with a Q-jet instead of a Holley. It used the same camshaft as the L-36.

The camshaft changed in '73 and the LS5 became the LS4. I've never been able to locate accurate engineering data for the LS4 camshaft, but my hunch is that it was designed with more overlap to control NOx.

The first use of catalytic converters in the auto industry was 1975, and virtually all GM engines had them. One exception was the base 1-bbl. Vega 140 engine.

Field emission testing managed by states includes a "visual inspection" for all originally installed emission control devices such at AIR pumps and catalytic converters. The techs have reference books that tell them what each engine should have, and even if the car passes the tailpipe test, if any required emission control device is missing the car should be failed.

Of course, there are hundreds of configurations going back 40 years, and some cars are older than the techs who test them, so missing equipment can often skate as long as the measured emissions are within the limits for the year group.

Duke

[Michael W.]

Re: C3 Lt1 Engine History

Mikey,

Catalytic converters started in 1975, not 1976.

You're right, I corrected my post.

[Thomas A.]

Re: C3 Lt1 Engine History

Actually it is not all that unusual -- there are a fair number of M20 LT1s on the survey in all three years. They have the best of both worlds. With a 3:36 ratio and the "low" first gear one gets dig off the line, and the 3:36 gives one relatively low (for the time) cruising RPM.

Terry,

Thank you for your wealth of information. I started reading yesterday for the first time and can't stop. My 1970 LT1 has the 3:36 gears. I think it was called LT1 economy. My 1972 LT1 had 4:11's the 1970 is a much better driver.

[Vincent F.]

Re: C3 Lt1 Engine History

I think a main piont here is that if you have a M21 or M22 it had to be an LT1 or big block car. To my knowledge these were not offered in the base engine package. its another way to prove the authenticy of a car.