well i have searched , but i still don't understand why not many specs. on lo3 cylinder heads ? i am just curious , i am not going to change anything . i'm a cruiser not a racer , and a hwy. traveler ( 27-29 m.p.g. ) . so i like the m.p.g. . did g.m. just throw heads out there , and say here you are ?? oh yes , 89rs , van nuys , 305 t.b.i. , t-5 , 3.08 . anyway just general info. , thanks in advance .

 

They're nothing to write home about. ~58cc chambers, 1.84/1.50 valves, 87-up intake bolt pattern. The main thing to know about them is that they are "swirl port" heads where the intake port is very odd looking- about half of it is blocked off and the area under the intake valve is one big swirly "ski jump" in an early attempt to induce swirl to the mixture. As you can imagine, this was not so great for intake flow (power), although it helped emissions and economy. Various members have flowed these heads and typical numbers are 165 intake, 140 exhaust.

 

Then you've got the perfect heads.

 

GM designed the engine for police cars, heavy sedans, pickup trucks and work vans. It has decent torque and gets good fuel mileage with the stock gearing.