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.

 

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.

 

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?

 

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.

 

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

 

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.

 

yeah, but still made 630rwhp

 

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

 

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!

 

maybe the longer stroke helps the fords.