i had 12lbs of boost on a stock 5.3 with full timing w/ a procharger and a 2 core intercooler.

 

the radix can spin to 16k rpms
my buddie has a radix on a 6.0 and he dosent hit boost till 3k the compressor is to small for the motor.

 

TByrne has a 4 different size pulleys available for the Radix.

I was under the impression that the Radix came standard with a 3.4" for all 4.8-6.0L since the '00-'03 4.8-6.0L all use the same Magnuson part numbers, 01-12-60-001 for silver & 01-12-60-002 for polished finish. I purchased 01-12-60-001 for my 4.8L but after spending many nights with you guys in the forums decided that a supercharger & headers just wasn't going to cut it! Based on the 9:1 Ross pistons and 6L '317' heads I'm having installed in the 5.7, I intended to get a 3" pulley to put it at approx. 9-9.5#. The pistons are 9:1 with 64cc chambers...with the 71cc chambers of the 317s, it should be down close to 8:1, which would be plenty safe for 9#.

This has me thinking. A supercharger is an air pump...it pushes air into the engine at a higher rate than it normally "draws" in by the reciprocating intake stroke. So in terms of supercharging, is the boost value [psi] A) the maximum psi developed in the cylinder by the compressor at a given compressor rpm and time interval, or B) the maximum psi of constant pressure developed at a given compressor rpm irrespective of time and cylinder volume? In "A", cylinder volume would have a determining factor upon the psi, but in "B" there is no dependency on volume...the psi is a factor of the compressor volumetric output (i.e., the supercharger will produce xx lbs of pressure at xx rpm, whether flowing into an engine cylinder or into the atmosphere which is a constant 14.7 psi). Confusing...

 

Boost is dependent on more than just supercharger speed or output.A Ford Lightning will show higher boost levels with a 5.4 displacement and a unported M112 than a Radix ported M112 on a 5.3 Vortec motor.The main reason Lighnings produce higher boost numbers is that have more restricted airflow at the head.A 5.3 Vortec motor makes more power than the Lightning at lower boost levels.Why?How can that be?It's because the Vortec has less restriction is the head design.A 5.3 will lose about a 1/2lb. of boost running longtube headers and gain horsepower while doing it.You've got to look at more than just boost numbers to get the most out of the combination.Ported heads will cost you boost but you'll probably gain horepower.If you can make big horsepower at lower boost levels you are probably better off.What I'm trying to say is that you have to look at the entire combination,not just pulleying up to increase boost.

 

Oh boy...so, back pressure (factored by the flow rate, or restriction of flow if you will) does affect psi value? Hmmm. Okay, just to compare apples to apples, we take a Radix and place it on a stock LS1 with stock LS1 heads and we get x.x lbs., then replace the LS1 heads with stock LS6 heads (same chamber volume & valve sizing but better flowing intake tract design) and we see a lower psi value than the LS1 because of higher flowing head?

I suppose that the pulley sizing could be calculated out, but I'll be darned if that is a formula that I can conjure up. So, when this engine of mine is assembled and running, would I want to take a compression reading to determine what size pulley to jump to next, or do people just keep buying & trying progressively smaller pulleys then back up to one size when their timing keeps retarding due to knock? Seems like an expensive way to do it...

 

If you look at boltons for a Ford Lightning,you'll see oversized crank pullys as well as smaller supercharger pulleys,you'll see some of those guys spinning 19,000 rpm with a M112 to increase boost more.This has 2 negative side effects,it uses more horsepower to spin up the supercharger that high and creates more heat in the intake charge.That's why the came out with the Kenny Bell supercharger upgrades and why they made such a big difference.Some of the Lightning setups are running 19 to 21 lb. of boost and creating huge thermal loads on the motors.

 

Thanks, this has been a real informative thread. Whitt, give me some advice... should I go smaller pulley or look into ported heads or long tubes? I'd rather have quality and an engine that's gonna last. The engine's pretty much stock with radix. and flowmaster I have a K&N but I heard it really doesn't increase performance. I'm just looking for a mid 13's if possible (only when necessary) but keep it domisticated enough for a daily driver.

 

A 6.0 should be safe with the stock Radix tune and a 2.75"pulley,just use a wideband to monitor fuel mixtures and check for KR as you add spark advance.Longtubes and ported heads are a great idea and when you select a cam go with higher lift,longer duration,a 115 lobe separation and low or no overlap.

 

Will I need to go with a smaller belt if I go with a 2.75 ?

 

whitt1, then a custom tune would be a safer way to put a 2.75" pulley on a 6.0?