[rhauf]

Okay, the answer to this seems like a simple one.. but i can't seem to figure it out, and i can't find the answer anywhere.

i know there are other minor factors involved (head material, combustion chamber design, etc) but what is the major factor in determining boost level? i've always heard it was compression ration, but it is the static comp ratio, or the dynamic comp ratio? it seems if i have a cam with the intake valve closing way, way late that i could therefore run more boost because the cylinder couldn't reach as much pressure.. right?

then there's the other question, of how the intake and heads flow capability's impact boost.. it seems that if you have restrictive heads and/or intake, you could just run more boost pressure to compensate and the cylinder would see the same result.... if so, whats the point of upgrading heads/intake etc if you could just run more boost instead?

[Trick Tuners]

Not simple at all. All of these play a major role in max safe boost.
Block strength
piston material
piston shape
compression ratio
heads
cams
rods
crankshaft
fuel system
tune
maf capacity
fuel octane
etc.
Compression is key to power, either from boost, cams, piston type, deck height, etc. If you use cams with tons of overlap you will just waste blower energy and make less power.


If you upgrade the heads and cams you can make more power with less boost. This puts less strain on the engine because there are less losses from turning the blower so hard. Blowers can take a ton of hp to turn. Top fuel dragsters can use 900hp just to spin the blower!! blowers on the mod engines can take between about 50 and 150+ hp to spin depending on blower type and boost levels. That is why turbos always make way more power at the same boost.

[rhauf]

Well, the two engines i had in mind were my '96 3.8 v6 (bone stock with a vortech v1 on it) but i've already gathered that it'll take about 12psi before it self-destructs (the only question here is how much i'd gain from split port heads/intake, and perhaps a cam swap)... although it sounds like the mild stock cam is probably the way to go.

the other engine i had in mind is an old international 345 in a scout.. i rebuilt it a coupel years ago, and i over-cammed it a little (so there will be a cam swap soon). the block is gigantic, high nickel, fully skirted, tons of cooling and strong as hell. pistons are hypereutectic flat-tops. comp ratio is 8.7:1, heads are stock cast iron w/ ported exhaust and hardened valve seats. crank is stock (Forged), it's carb'd. i only plan on running pump gas, but i'm willing to run premium. if i boost it, i'd probably do it with a couple small draw-through turbos... (i know it sounds like a bunch of bad ideas here but i think it'd be cool). i'm only thinking maybe 7 or 8 psi.

there is very, very little after-market available for this engine (no heads, no pistons other than stock-replacements, etc). so it's sort of a fun challenge to try to milk a bit of performance out of it.