How much horsepower and mpg could I possibly get out of these?

http://www.summitracing.com/parts/sc...-size/4-3l-262

 

Increases would depend on what you were installing them onto.

The 4.3's after 2001 or so already have a roller trunnion rocker with teh standard slide tip.
The only GM enegine to have ever gotten PEM roller tipped AND trunnion rocker arms was the GEN 2 KT4 engine that came in all 3 versions of teh 1996 Vette(Grand Sport, COllectors Edition and "regular" Vette) you could only get the LT4 if teh Y-Body was equipped with a manual trans. No auto LT4's. Also there was teh balanced and blueprinted LT4 engines in the 33 1997 Firebird Firehawk LT4 and in the 104 1997 LT4 SS Camaro.

Crane built these rockers for the LT4, they are the exact same as the Crane Gold aluminum extruded roller rockers, except that the LT4 units used the 7/16" rocker stud. The LT4 cars had 2 recall notices for the rocker arms alone. 1996 LT4 owners were told not to drive the car as severe engine damage could result. The rockers were coming apart and sending needle bearings into the engine. Once they got the 2 issues resolved, they were proven durable engines. With GEN 3 LS1 power in theolder GEN 2 package. Rev limited to 6412 rpm, the LT4 required roller rockers as Chev engineers revealed serious rocker galling at rpm exceeding 6000rpm.

Going from a typical stamped steel 1.5:1 rocker to a 1.6:1 roller rocker will result in 8-13 hp at the crank on a V8 engine, divide by 1.25 the V6 gives you a power gain range of 8hp-10.4hp.

You woudl certainly get more power and mileage from a decent PCM tune.

peace
Hog

 

they would be installed into a 2013 4.3L. that is alot of really good information btw. would it be worth the time and money? im not really trying to make the 4.3L fast cause that would take alot of unnecessary money and time and headache, but i would like it to have a little more pep. im thinking to change to these rockers, a 2600 stall and 3.73 gears. what do you think?

 

look for 1.6 rockers. the ones you have are more or less stock ratio