Originally Posted by Strongjeff
I forgot to mention this was back in 03 on a liberty. It had the old 42rle transmission (complete crap) and 32 inch tires so the numbers are lower then normal. Factoring in the 42's 30% driveline loss and bigger tires it put down 159 rwhp. I forget the torque figure. On the s/c with tune and bigger injectors it put down 302rwhp on 5psi. It blew on the last pull at 302. This was on its 6th pass.
Saw this on a older post of your's.
This is what happened on the 4.7L back then. 4-5psi was fine and then there were guys that wanted more power and put smaller pulleys on the SC and 7-8 psi and they blew. The SC manufactures didn't want the liability of blown engines when owners upped the boost. This is bad for business. The other problem is when using a centrifugal SC like Vortech and Powerdyne, they put out very little boost until higher rpm. So to have a reasonable gain in power at lower rpm you have to turn up the pulley ratio and spin the SC faster but it will aslo spin faster at higher rpm and especially over 5000rpm it would be making 7psi. A better solution is to use a roots variant pr a stin screw SC which builds boost at lower rpm os you don't have to spin them as fast and limit the boost over 5000rpm.
Here it doesn't make any sense-
5psi adds 5/16 more power, about 30%, which is 207rwhp (302 must be calculated crank power)
The fact that they used bigger injectors tells me that there was no intercooler and no attempt to lower the charge IATs.
This is the exact same story with the 4.7L and it's short top ring land. They kept cranking up the boost and when it blew, they called it a fail.
CORRECTION Found this on another forum-
210 bhp @ motor 235 ft.lbs @ motor
166 rwhp 193 rwtq
296 bhp @ motor ---------- +86 343 ft.lbs. @ motor -------- +108
235 rwhp ------------------ +69 275 rwtq. ------------------ +82
So it's 210 to 296 @motor which requires 7psi
and 166 to 235 rwhp which requires 7psi
We have a M90 SC on a 4. 7L GC with 'Low Boost' 4-5psi and it runs like a raped ape. Over 1 year now and no problems. Tuning is important as is lower Intake Air Temps. We use a 9th injector to add the fuel needed under boost and to cool the charge IATs to a safe level and a controller that retards timing with boost. It might not be the fastest or a dyno queen highest HP but with 'only' 4-5 pounds of boost, it really wakes up the sleeping giant in the 4.7L.
Many will argue that for Low Boost 'only 4-5psi' why bother, it's not enough. Well adding 30% more rwhp and tq is very noticeable. All the 'bolt-ons' will only add 10% as you have found out, but that 10% is very noticeable.