LT-1 Cylinder Heads

[Richard Reif]

I am looking to find the correct heads for a 1972 Air/LT-1. The judging manual lists casting numbers as follows:

1970: 3927186
1971: 3973487
1972: 3973487(x), 3998916, 3998993

The questions I have are: What is the difference between the various castings,(chamber vol., intake size, exhaust size, etc.)? On 1972 models, can it be predicted which casting would appear on a given engine based on the assembly date? Also I have seen pictures of 993 heads with "Made in Mexico" (couldn't see a date code). Is this possible for heads cast in '71 or '72?

Thanks in advance, Rich

[Jeremy D.]

Re: LT-1 Cylinder Heads

According to my just-acquired "Chevrolet By The Numbers" book, the LT-1/Z28 1970 186 heads have 2.02 intake/1.60 exhaust, while the 350 hp. 'Vettes and other cars have 1.94/1.50 valves. The 186's had a 63.305 cc combustion chamber. It says that the 2.02 heads used screw-in studs and guide plates.

In 1971 and 72, 487 heads for the LT-1 Vettes and Camaros had 2.02/1.60 valves as well, but with 75.47 cc chambers, hence the lower compression and horsepower rating than the '70. It says here the heads featured swirl polished valves and chrome valvestems, as well as screw in studs and pushrod guideplates.The lower-horsepower cars with these heads didn't have swirled valves.

The book says that 993's were introduced in cars built after January 4, 1972 and replaced the 487X head, which was the same as the 487 but used late in the '72 model year as well...book says the reason for the overlap with the 993 is unclear.

SOOOOOOOOO...I guess that if your car was built after Jan 4, 1972, you should either have 993's or 487X's. If built before, I guess 487's were the heads you need. The book lists usage of the 916's as "unverified." Could Chevy possibly make this more confusing, I think NOT!

[Jeremy D.]

Re: LT-1 Cylinder Heads

According to my just-acquired "Chevrolet By The Numbers" book, the LT-1/Z28 1970 186 heads have 2.02 intake/1.60 exhaust, while the 350 hp. 'Vettes and other cars have 1.94/1.50 valves. The 186's had a 63.305 cc combustion chamber. It says that the 2.02 heads used screw-in studs and guide plates.

In 1971 and 72, 487 heads for the LT-1 Vettes and Camaros had 2.02/1.60 valves as well, but with 75.47 cc chambers, hence the lower compression and horsepower rating than the '70. It says here the heads featured swirl polished valves and chrome valvestems, as well as screw in studs and pushrod guideplates.The lower-horsepower cars with these heads didn't have swirled valves.

The book says that 993's were introduced in cars built after January 4, 1972 and replaced the 487X head, which was the same as the 487 but used late in the '72 model year as well...book says the reason for the overlap with the 993 is unclear.

SOOOOOOOOO...I guess that if your car was built after Jan 4, 1972, you should either have 993's or 487X's. If built before, I guess 487's were the heads you need. The book lists usage of the 916's as "unverified." Could Chevy possibly make this more confusing, I think NOT!

[Duke W.]

Re: LT-1 Cylinder Heads

The L-46 heads used 2.02/1.6 valves, but I'm not sure if they had threaded studes.

Duke

[Duke W.]

Re: LT-1 Cylinder Heads

The L-46 heads used 2.02/1.6 valves, but I'm not sure if they had threaded studes.

Duke

[Joe L.]

Re: LT-1 Cylinder Heads

Duke, Jeremy, and Richard-----

Yes, 1969-70 L-46 both used 2.02/1.60 valve size with '041' or '186' castings. However, L-46 used pressed-in studs. 70-72 LT-1 heads, regardless of casting, used screw-in studs.

1969-70 small block cylinder heads, regardless of casting, used 64cc, nominal, combustion chamber volume. 1971-72, regardless of casting, used 75cc, nominal, combustion chamber volume. Different compression ratios among engines were accomodated by piston head configuration.

NO '993' cylinder heads originally used on Corvettes were EVER cast in Mexico. However, the tooling and production equipment for the 993 head, which was used in SERVICE for many years and even up to the present time, was transferred to GM's Toluca, Mexico engine plant in the 80s. SERVICE cylinder heads for many Corvette small block applications were/are produced in Mexico.

Also, for those who may be interested, NO 1953-96 or 97-02 Corvette engine, or, with one exception, major casting thereof, was/is produced in Mexico. Many GM SERVICE engine assemblies, and major castings thereof, were/are produced in Mexico. At the present time, ALL 96 and older small block SERVICE engine assemblies, and major castings thereof, which are still available from GM are produced at the Toluca, Mexico engine plant.

The "exception" that I mentioned above? All '01 and '02 LS1/LS6 cylinder heads are cast in Mexico.

[Joe L.]

Re: LT-1 Cylinder Heads

Duke, Jeremy, and Richard-----

Yes, 1969-70 L-46 both used 2.02/1.60 valve size with '041' or '186' castings. However, L-46 used pressed-in studs. 70-72 LT-1 heads, regardless of casting, used screw-in studs.

1969-70 small block cylinder heads, regardless of casting, used 64cc, nominal, combustion chamber volume. 1971-72, regardless of casting, used 75cc, nominal, combustion chamber volume. Different compression ratios among engines were accomodated by piston head configuration.

NO '993' cylinder heads originally used on Corvettes were EVER cast in Mexico. However, the tooling and production equipment for the 993 head, which was used in SERVICE for many years and even up to the present time, was transferred to GM's Toluca, Mexico engine plant in the 80s. SERVICE cylinder heads for many Corvette small block applications were/are produced in Mexico.

Also, for those who may be interested, NO 1953-96 or 97-02 Corvette engine, or, with one exception, major casting thereof, was/is produced in Mexico. Many GM SERVICE engine assemblies, and major castings thereof, were/are produced in Mexico. At the present time, ALL 96 and older small block SERVICE engine assemblies, and major castings thereof, which are still available from GM are produced at the Toluca, Mexico engine plant.

The "exception" that I mentioned above? All '01 and '02 LS1/LS6 cylinder heads are cast in Mexico.

[Richard Reif]

Re: LT-1 Cylinder Heads

Thanx Guys,

In further surfing, I also found that the 993 casting is currently being produced in Mexico for Goodwrench crate motors.

Rich

[Richard Reif]

Re: LT-1 Cylinder Heads

Thanx Guys,

In further surfing, I also found that the 993 casting is currently being produced in Mexico for Goodwrench crate motors.

Rich