So, I'm starting my engine build... I'm aiming for a reliable 20psi boosted engine.
I recently picked up a .030" over 250 that has forged TRW(?) pistons and polished/shot peened rods. This engine was running a blower. The owner started a rebuild and got sidetracked into other projects.
The pistons have the large chamfered edge, which I'm not excited about. I recall reading here that these were not optimal pistons to run for boost. Could I safely mill or lathe the tops to reduce the chamfer? I honestly don't know.
At 20 psi, do I need to have billet 4 bolt mains and a stud girdle? Does anyone make a stud girdle?
I really would love to open the channels for guidance here!
Annnndddd, go!

polished/shot peened rods: were the bolts replaced, and with what?
What blower? what manifold?
Chamfered edge meaning around the bore edge? Leave it be, removing metal reduces quench.
Just my 2¢? The lower end is OK, 20 psi is only 250 hp.
Read Santucci's book:
http://victorylibrary.com/mopar/Mopar-books.htm#CI-LS2

I've not looked too hard at the rod bolts... but I will. I was planning on a set of forged H-beam rods, but wanted to know if these ones would be ok to use.
I would assume it had an eaton m90 on a custom intake... the guy had built another just like it.
Yes, I mean the edge of the pistons around the cyl wall.
I'm holding the book in my hand... 20 psi is 450-670hp ish. Depending on the level of build... I've also read the book he references... maximum boost by Corky Bell, though I do not recall this formula in the book. .052 x displacement x (boost + 14.7)
I'll have to look it up.

Hope this doesn't come across as abrasive... it certainly isn't meant to be!!!

20 psi is 450 hp if everything else in the engine has been grabbed by the neck and choked: ported head with lumps, big cam, high ratio rockers, big valves, tuned exhaust.
Power obtained from boost is never linear, the first 5 psi is far more valuable than going from 15 to 20, the results decay as boost goes up.
In round numbers (assuming the original engine to give the factory rated 155 hp, atmospheric pressure is 14.7, and the WOT vacuum is 1.5 psi), 20 psi with no other changes will make about 45% more than stock or 225 hp.
670 hp is a $10,000 engine.

The M90 produced 260 hp in the original 231" V6, so it's going to run out of capacity with a bigger engine and higher boost.

The easiest power is the low boost stuff. On the dyno 250 , in N/A form it made a easy 275 with a 4 BBL. With 5 PSI and a 2 BBL it made almost 350 HP.
That is 15 HP per LB of boost. Same happened with the TQ.
I bet my engine would have made a additional 10% power if intercooled at the same boost.
So 450Hp @ 20 PSI is low. That engine would be a corked up stock type engine. Probably 500-600 is more like it. Better build it strong.

Some engines of that era had chamfered top lands to reduce the crevice volume above the rings, which can account for up to 25% of the total hydrocarbon emissions. It did have a negative affect on other aspects of the burn quality though.

I probably should have noted that I am not running a supercharger... I've got a GT35 turbo on my stock 250 @ 7 psi now. It will be used on the new engine.
IIRC, someone on this forum stated their largest gains in head work was through dividing the ports... something I will be looking into. The head will be done, make no mistake.
The engine I picked up is a block, crank, Pistons and rods.
I will have a custom grind roller cam made. Roller rockers. 292 exhaust manifold (already in use). Worked over Offy intake. Holley 500. I will stud the bottom end (possibly, if really needed, make billet 4 bolt main caps) and the head. Also, meth injection will be used.
Originally, I wanted 30 psi... but that is an unrealistic target for a street car/driver! So, I look to 20. I've seen a mild 250 at 15 psi produce 385hp to the wheels in the dyno.... I'm hoping to improve on that a little.

Is it not true that 15 psi doubles the HP on the same na engine? I read that somewhere. That was not a rhetorical question, I'm really asking!

This is my first inline build and I'd like it to hold together. I've read snowman's thread, twice. There is too much there to filter it all down. That's the reason I started this thread... targeted guidance.

Thanks!

Is it not true that 15 psi doubles the HP on the same na engine

Very popular, appears on many sites, everyone says so.

Sorry, that was rude.
No, it's not true, it's where some "If I have 100 hp now, 30 psi of boost will make 300 hp" predictions come from.

I don't have any real world experience with turbos, so all I have to go by is what I read in books and what people with the experience tell me.
Anyway, I'm less concerned with the actual number than I am with the seat of the pants... I don't care if it's 200hp, if it makes me smile! And, as anyone boosted knows... it's addictive! I want more!
I do actually value the opinions and guidance offered on this site because the people here seem to have the best interest at heart and the experience to go with the intentions!

The "people with experience" are the ones who say that, like this compression ratio chart at Blower Drive Service:
https://www.blowerdriveservice.com/technical-charts.html.

A GT35 is pretty big, you probably need a tighter A/R to get the boost up. Do you know your compressor diameter in mm?

If I did everything on your $$$$ shopping list, and I got 200 hp, I would shoot a flare into the gas tank.

BTW: I have a fairly stout turbocharged L6, but it's a Toyota.

An engine with small restrictive ports will see high boost but less HP....There more to supercharged power than boost numbers.

Remember that the "experts" were the people who told Galileo that the sun rotated around the earth.

Whatt?? It doesn't? Martha, go get me the earth-dial.