Originally Posted by 77'Omega
Now a 4.3 i do know, i have mine in my s10 runing low 13's but not constantly on stock intake and heads with a jet programmer and kb 350 flat top pistons zero decked block milled stock heads. but if you want a good 4.3 engine it needs to be 96 and newer,the LF6, produced in 1996 with the introduction of Vortec cylinder heads and a balance shaft that helpt get rid of vibrations which can make it more efficient and reduce the risk of blowing it at higher rpms.but this particulare one was discontinued in 98.All Vortec 4.3s use a cast iron block and heads and 4 in bore and 3.48 in stroke, both of which are the same as a 350, which gives them a displacement of 262.39 cubic inches . Connecting rods still measure 5.7 in although the rod journal diameter is 2.25 in
The Vortec heads used on the balance shaft engines are the best to use but they present problems with the use of a TBI manifold. I certainly did not want to use a balance shaft engine. i could not even find a Cloyes roller timing set or a high lift camshaft for a balance shaft V6 engine.
My 1991 4.3L V6 TBI engine has Speed Pro L2256F-30 forged pistons. The un-cut 1991 V6 heads are the same as the ones used on the Syclone and Typhoon. My heads have 69 CC combustion chambers using Ferrea 2.02"/1.600" SS dish head, unshrouded valves. The compression ratio is 9.7:1 which only permits the use of 93 octane Texaco/Mobil with Techron to prevent detonation and keep the injectors clean. I tried 87 octane but the ESC would not permit it. The old low-tech SP power forged pistons have a compression height of 1.563" which is about .020" closer to the heads than OEM and cast rebulder pistons. The heads were perfectly flat corner to corner so it was unecesary to mill more than a 0.005" clean up. The block was perfect as well. The MSD Pro Billet distributor fit perfect. I replaced the MSD red cap with a NAPA black distributor cap so every thing appears to be OEM to the uneducated eye. The OEM distributor would have probably worked just as well.
Thanks to the Comp Cams 09-412-8 short duration roller cam with 0.500" valve lift and only 39 deg. valve overlap, the engine is still computer compliant and performs as planned using Comp Cams ovate valve springs. However, if I want to get a better ET than 15.00 seconds, I may seek some of your advice on choosing and installing a computer chip, especially if I choose to install those pricey Edelbrock headers and a 454 TBI. I don't know how free flowing exhaust system will effect the O2 and EGR. I have two spare OEM intake manifolds I am sending one to the machine shop next week to see if the throttle bores can be opened to 2.00". That will be necessary in order to acept the 454 TBI without using a funky adapter plate. I have been given some advice that if I install a 454 TBI on The Blazer with a 4L60 transmission, it may turn out to be a re-programming nightmare. I have not secured a good 454 TBI yet so I may not follow through with that idea. I may resist the temptation to follow "More's Law" .... "If some is good - MORE is better".