dug

iTrader: (10)

I thought off idle torque is a non issue with screw superchargers. 25lbs is probably too much but lower compression is always gonna be safer.

GMC_DUDE

Can't say about twin screws, but for roots type blowers off idle torque on smaller engines is very much an issue. There is a phenomena called "leak back" which creates a minimum rpm necessary to create boost. I ran into this issue on my 4.8 w/ Radix. To keep max boost under the legal 7 psi, the blower came with a 3.7" pulley. This caused the blower to turn so slowly that boost wouldn't start until about 2000-2500 rpm (true much better than a centrifugal's 4000 rpm but it still sucked). Putting on a 3.25" pulley moved boost onset to a more realistic value but raised the max boost to 10 psi, a bit higher than I liked. If you are going for a max boost of 25 psi (good luck holding the motor together) then you may be getting boost at idle, in which case you might not have a problem with low SCR (sort of a Miller Cycle engine). BTW, don't forget dynamic compression ratio either. I put in a GT2-3 cam which dropped my non-boost DCR from 7.7 to 7.4 and it made the truck a real dog.

dug

iTrader: (10)

thats my point, the more boost you run, the quicker it comes on. Also, you can get a higher stalled torque converter that allows higher rpms outta of the hole. Dont Ford Lightenings and cobras have 8.5 to 1 compression?

Stoichiometric

iTrader: (10)

Lower compression *can* have a benefit if you are in boost more often than not, i.e. race car/truck. There is a tradeoff with low compression of non-boost response that can make a street vehicle less fun to drive. It is a give and take, just like camshaft selection.

ajt86

iTrader: (1)

ive run up to 30psi on pump gas and meth in a buick v6, meth works wonders on forced induction

Slowhawk

iTrader: (11)

You never know how bad a low compression 4.8 is till you have one Our built up 8.5-1 comp. 4.8 made a whopping 200rwhp NA and 630hp with a Turbo. Off boost it sucked ,bad.

dug

iTrader: (10)

yeah, but still made 630rwhp

kbracing96

iTrader: (26)

Ya, but I bet it sucked to drive it around, you have to get it in to boost to go anywhere which KILLS mileage, lol. 4.8 have no NA power as it is. I wouldn't want a low compressions 4.8, my stock compression one is bad enough

dug

iTrader: (10)

Ive been warned.

The 2 things that frustrate me with boost are: too much scr which limits boost or not enough fuel supply.

I wanna be able to max out the boost!

dug

iTrader: (10)

maybe the longer stroke helps the fords.