hey, just wondering about a couple specs on the 4.3's. it's on a '95 blazer. curious about the lifter specs, spring weight, and max lift the stock heads can take. also wondering how much horsepower... and boost... the bottom end of a stock 4.3 can handle before needing to be built. our plan is to take an M90 from a Grand Prix and put it on top of a 4.3. just wondering how the internals of the engine would handle 5lbs of boost, and how much lift you can put onto the stock heads to get more air in/out.
TIA
Corey

 

If you are going to go through all of the trouble to put an Eaton M90 on, make sure it is off an '04 or '05 GTP. The '04-'05 GTPs came with the Gen5 M90 which is much more efficient (a gen5 with a 3.8" pulley == a gen3 with a 3.4" pulley). How are you going to mate up the m90 to your lower intake? What fuel system are you going to run (the CPI won't work with the blower)?

Inorder to truely find out how much lift the heads and stock pistons can deal with, you should clay it and measure the thickness. Pull the heads, drop a ball of clay onto the piston top, put the heads back on with headgaskets and torque them down, then run the engine atleast twice over. Measure the thickness of the clay with a scale (precision metal ruler) and you'll get a gross estimate of what you can safely run without going to custom valve reliefed pistons.

As far as how much boost the bottom end of the 4.3L can take, I believe that they didn't change much when the Cyclone (or Typhoon... can't remember) came out (turbo 4.3s) and they were damn quick out of the box. Run a google search on them to find out more on them.

Good luck with the retro fit. It's going to be a pain to get the fuel system worked out let alone get the S/C on there straight and a belt to run it!

 

hey, im friends with Corey (the guy doin this) as well as the one that actually posted this for him. the whole thing got rolling when we got a Gen III M90 for a pretty good price. though they're not as efficient, a ported Gen III is about equivilant to a stock Gen IV. so we're going to port and polish the Gen III we've got. (actually the one we got is going onto my GTP, and the one that's on there now is going on the blazer).
Plans for the mating right now stand at obtaining a Carberated intake manifold for the 4.3, then modifying it. either an adapter plate, or by actually reshaping the manifold. probably an adapter, though.
we're not sure about fuel systems, yet. i want a good variable sequential port injection system. being boosted, it will have to be high volume, and incredibly variable. still looking into that, though.
We're also worried about spark, as a distributor isnt the best setup for a blown application, especialy when you cant mess with the timing at all. so we're looking for a self contained MSD system for it.
so what's the stock ratio of the lifters on these engines? and no one knows how far you can take the lift? one thing im worried about is that it's not a stock cam, and i dont know the specs on the cam yet. (im looking, though). but we need to get this thing to breath better if it's gonna get blown!

sorry for the long posts, but it's a lot of stuff we've got to get straight.

 

Actually, everything that I have read says that even though a ported gen3 will get close to the same as a gen5, it still isn't going to match it's efficiency. The gen5 gets its efficiency from a coating on the rotors that actually wears away to form a perfect seal. The gen3 does not seal perfectly between the rotors. The rotors are coated on a gen3 but they are far from the same. You will still generate more heat even with a ported gen3 trying to match the performance of a gen5. And heat is the enemy in boosted applications. If you are going through all of this trouble, you probably want to put on an intercooler as well.

 

part of the reason we are puting a gen3 on is as my friend andy said we got a good deal on the gen3 and initally i was going to put a centrifical s/c on it but we decided that a roots blower would be alot cooler so we started looking around and found the gen3 and even with all the other modifications it will take it is going to be cheeper to go roots and cooler to go roots just harde and more time consuming

 

so not a soul on this forum knows specifics of the valvetrains of their vehicles? not even the ratio of the rockers? i mean, cam specs i can understand, but no one having any idea of the max lift the heads can take, or the valvetrain can take before piston interfearence?

 

Welcome to the world of CUSTOM engine building. No one here has done what you are doing. And I highly doubt that anyone has ever tried to push the envelope on the max lift without actually pulling down the engine and doing a complete spec out with a degree wheel, clay, and a dial indicator. I've done it on a few sb350s and one s2 3800, but never on a 4.3L vortec.

 

yeah, i guess it is a little different than the world of 3800's. im use to a community where everyone builts up the engines they have, lots of blazer guys (absolutly no offence meant by this) either dont mofidy their engines, or drop an entirely new engine in and dont use the 4.3. and he knows this hasnt been tried much, which is why it's going to kick so much a$$!!!

edit: not my project, im just helping. wanted to make that a little more apperant with the he's and such.

 

and the stock rocker ratio is 1.5. so if anyone asks again, it's 1.5

 

IIRC, the 4.3L is about the same, valvetrain wise, as the Gen2 350's of its day. Its an outdated engine to be sure.

Also, you have to remember that because many Blazers are 4wd, many, many owners use them as winter vehicles (me included). So when it comes down to it... I've got 2 other toys in my garage... Do I need the Blazer to be fast? Not really, I just need it to be reliable.

I am very interested in how things turn out for you. The information will come, it'll probably just trickle in though... Good Luck!