MacGyverGTP

I hear there is a HP limit before things break, is there also a boost limit?

Here's what I mean... Mustang w/KB 8# makes x hp
Same Mustang with Long tubes & Offroad X-pipe will make more horsepower on less boost.
I think an 8# pulley will only really be pushing closer to 7# with a few breathing mods.

Does that mean I can change the pulley to get that boost back safely or not? What kills the rods boost or HP?

Would love to do the entire rotating assembly & may do that soon, any idea what kind of boost you can run after that's done? I'd love to get up to 15psi so I can hear that thing whine!

I don't want to blow my $ on the long tubes & x-pipe if there's not a significant reason...

MacGyverGTP

Not too many KB folks around? I suppose this question isn't really specific to Kenne Bell blowers.

jaiasmit

You're right, this isn't really a KB specific question. It's a good question by the way.

My thought would be that higher boost is not what's going to cause something to break. It's simply a matter of the higher boost creating higher horsepower which is what causes things to break.

I've heard that our cars will handle between 450 and 500 RWHP without breaking. Most would say 450 RWHP max.

I think a lot has to do with the tune of the engine also. It would be as easy to break something at 400 RWHP with a crappy tune as it would to keep things running smoothly at 500 RWHP with an outstanding tune.

Another thing to consider is the intake charge temp in relation to your boost level. So, if you're running 8+ psi of boost on our cars, you're probably going to want to get an intercooler to help prevent detonation (which is a major cause of damage). You'll probably also want to step your plugs down to a lower heat range (HT0) to help prevent detonation as well.

If you're running less than 6 psi of boost, you're probably safe without the cooler unless you're running in extremely hot conditions.

All in all, I don't think engine damage in our cars is caused just by the boost level. It has more to do with the horsepower (which is where the stress is) created by the extra boost, and the quality of your tune and supporting components.

If you have a crappy tune, no cooler, and HT1 plugs on 12 psi, you could only be running 400 RWHP and still blow the engine. But, you could probably just as easily be running a safe 480+ RWHP with a good tune, HT0 plugs, intercooler and 12 psi.

Those are just my thoughts, and I am by no means an SC expert. Hope that helps.

carmanwelder

I can only give you what the speed shop I go to recommends. He has run his 05 and had it featured in MMFF mag. 500 is the magic # to the wheels thats the supposed # the mechanics somewhat agree on. After that the bottom end rebuild is required, which is a few bucks(5,000). As I have posted before the speed shop did a KB install everything else stock on an 05 GT, dynoed on a dynojet 460 to the wheels, dailey driver even sometimes to FL from NY. The guy has not had a problem with it.

CaptRestless

If you have a good tune and don't hammer the gas pedal every time you drive you should be ok. After reading all the stuff on the KB site, it seems that a bad tune and high rpms or over-revving are what kill the motor. Our stock internals are not meant to be revved to 7500-8000.

AmericanMuscle4.6GT

what kills the engine is detonation. see, with 350 RWHP, you can have detonation and not blow your motor, but with 450RWHP, at the slightest hint of detonation, your toast. hence, it's all about the tune.

GT Bob

Long version:
To get really technical... the answer is that neither does. Its the cylinder pressure created by the compression and ignition of the fuel charge combined with the inertial forces that are put on rods by moving down, coming to a stop, moving back up, and repeating a few thousand times a minute.More boost is going tostuff more oxygen into the cylinder. More oxygen, the computer will add more fuel to burn... more fuel creates a larger burn and more pressure on the pistons (and the rods by their connection to the piston). Both of those stresses together are what cause rod failures.

Actually, detonation will kill motors with 125 hp as easily as it will kill motors with 500 hp. ANY time the fuel charge explodes instead of burns, its a VERY bad thing, regardless of HP levels. The reason for that is, with detonation, your getting all of the heat that the fuel charge will produce at once, and since motors typically fire and start the burn of the fuel charge BEFORE the piston reaches the top of it's travel and begins moving downwards, all the force of that cylinder is trying to push down on the piston, while the crank and the other 7 cylinders (or 5 or 4 or 3 depending on engine size) are trying to push up... Granted, that with more power engines, the forces involved are greater, but generally, less powerful motors are going to be built less strongly, so the failure rate will be similar.

MacGyverGTP

For a slow start, these are some great answers, thank you very much for clarifying things.
Anyone know what the magic horsepower number is for a forged rotating assembly, not that it will add power, but what can it support?
Thanks again!