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Discussion Starter · #1 ·
On this engine, how much boost do you think the stock pistons, rods, and crank can safely handle on a regular basis before it becomes a problem?

Forget about the block for now; i'm just concerned about the stock pistons, rods and crank.

pistons = hypereutectic

nodular iron crank, which i assume is not forged?

 

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your question is vague at best. So many variables that can scatter your engine,,, too much spark and boost wont go high before it scatters, ring end gap too tight, cooling issues, rpm, rpm where you use boost,,,lower rpm with big boost is slightly more dangerous than higher rpm, a/f too lean and bang,,,list goes on
 

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Hates: Liver. Loves: Diesel
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Assuming a proper tune can be found and you don't get any of the destructive forces that Moosecountry mentioned, you'll be limited first by the pistons and the block. Look to HP levels, not boost levels. You're using forced induction to increase BMEP and IMEP... basically the overall pressure seen on the piston and therefore the crank. The first thing to go will be the pistons deforming somewhere around the cylinder pressures required to make about 400 hp followed shortly by the crank ripping the mains out of the block. Again, assuming a perfect tune, which in your case should include aftermarket heads. Trying to stuff more air through tiny ports is not part of this complete breakfast.
 

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Too start with the LO5 has Swirl Port heads, they don’t breath for crap even if you huff and puff into them. Plus they have an oddball intake angle on the center plenum bolts that do not fasten to the typical 55 through 86 intake. To the eye they look like the standard 6 bolt preside pattern which bolt to bolt they are, but the plenum bolts are at 72 degrees to the intake face of the head instead of 90 degrees, so there are damn few intakes that bolt up.

The bottom end of cast modular iron crank, powder forged rods and hypereutectic pistons is reasonably robust for 400 plus hp of normal aspiration. But feeding laughing gas or supercharge of some sort brings high risks of detonation and a lot of top end heat. Typically these pistons give first with the ring lands melting out or busting from the rings running out of end gap. Actually if you pull 400 NA ponies out of this bottom end for long enough the pistons fail the same way. Hypers run hot and are set up tight as they are quite thermally stable but for any kind of power the rings and the tight skirts will lead to land and crown breakage and skirt seizures.

So basically the LO5 heads aren’t going to bolt to a blower manifold and do to damn few simple carb manifolds usually ProComp and Professional Products market an intake with a flipper gadget that will bolt to pre 1987 intakes when the gadget is in one position and for 87 through 95 heads in the other position. But as I said these heads will not breath.

It’s important to remember that a 10 second power pull on a dyno is not the same as pulling power on the track or street where a 10 second burst is only the beginning of a run.

Bogie
 

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Discussion Starter · #8 ·
i'm very sorry; i should have been specific: (why do i do this?)

1) i posted the LO5 350 because the (i ASSume?) pistons/rods and crank(not exactly the crank but i ASSume they are both cast) are exactly the same as a 4.3 v-6 and the specs for the LO5 are more easy to post:

But the actual engine i propose to use is:
LB4 4.3 v-6 i can't find the specs online, it may be similar to:

Anyways, the LB4 is an "earlier TBI" engine, i THINK similar to the LO5 except the 4.3 has a roller cam. But i THINK they would both have similar if not identical pistons/rods. The crank on the 4.3 is probably actually weaker than the 350 due to the split disk design of the 4.3? But i ASSume they are both cast?

i want to use a vortech centrifugal supercharger.

i should have phrased the question as : Would the boost required to have the engine put out approx 300 hp be harmful/stressful to the pistons/rods and crank on a regular basis?

a) The goal is run in the 11.7-11.80 range and the car is going to be fairly light---chevette or monza and under 2200 lbs, so i feel 300 hp should do it?

b) i think the block can take 300 because Chevrolet even said so in the chevy power manual, and the syclone was 280 hp with this engine block and you know the factory was being conservative.

c) Why not just do it the easy way and plop in a 383HT? It's cheaper, more fun this way; i already have a running 4.3.
However, 383 is still on the table.

Sorry for the confusion, i will try to be more direct next time.
 
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