Bullitt995

Is it actual rwhp #'s or PSI? I know in the end it's technically detonation but if an 05 GT made 550rwhp on 8 psi would it be in any more danger than the same car making 450rwhp on 8 psi?

G.T

an 05GT making 550rwhp on 8PSI is running much more advanced timing than the one pushing 450rwhp at the same boost level..
This in effect leaves much less room for error tolerance and detonation under such timing becomes more likely (unless you're using much higher octane fuel/race fuel).

in my opinion you're likely to throw a rod if you detonate and/or rev your engine past the limit it's meant to reach (~6250RPM) or hit the rev limiter frequently.

70MACH1OWNER

It's dentonation that kills these motors first. It will pound these hyperpathetic pistons to death. Second weak link is the powdered metal rods. There is a great debate about how much power they will take but 450 rwhp seems to be the more widely accepted upper safe limit. Of course without a great tune 300 rwhp and a little detonation could bring an early end.
Scott

traffic142

I am no motor mechanic or short block builder, but all components are designed to handle a certain amount of stress. That is why there are cast pistons and rods and forged pistons and rods. Why there are 4 bolt mains on the caps or just 2 bolt.

I believe that the lower psi is better for the same HP numbers. A friend of mine, thinks that for the average driver a NOS kit is the way to go. You are not stressing your motor on the daily drive.

As for the SC idea, my reading of the situation is all the big dogs so to speak are using roots style, sit on top of the motor, low psi boost. (FRPP, Saleen, Foose, Unique, Roush, etc). Not one of them are using a centrifugal blower (sans the shelby CS 6). That may have some bearing on the use of low psi blower.

tmcolegr

Biggest motor killer is a poor quality tune

SteelTownStang

F R I C T I O N

bob

PSI isn't really a good indicator, take your engine, and port the heads, improve the intake tract, and give it full exhaust and it will show a lower boost level, yet make more power, cylinder pressure is a better indicator.

Boost is relative to the amount of restriction the motor imposes on the super-charger, ultimately cylinder-pressure x RPM = operating limits.

IMO, while super-chargers provied a constant level of stress, nitrous produces more instantaneous stress on the motor by virtue of being an on/off power adder.

tom281

"Hyperpathetic"....... I agree with everything you said Scott!

kevinb120

Yup, too lean a condition with any supercharger is probably #1, too much boost is #2.

Bullitt995

Is there a way to messure cylinder pressure? This seems to be the key to it all.

kevinb120

Well as far as boost goes, 5-6 psi with a good tune non-intercooled is fairly safe, 8-10 intercooled with a very safe tune at 10 seems to be ok. Funny enough, the older 2v motor was about the same psi formulas for staying out of trouble.

Bullitt995

I know about boost levels but neither boost nor hp levels are what actually destroy a motor.

kevinb120

Well run 25lbs on the stock engine good tune or not and see what happens. The rods return to their original powdered state.

281GT

These engines have too much compression for any significant amount of boost. Combine this with the stock short duration camshafts and pistons that have the top ring land located closer than normal to the top of the piston makes for an engine that simply isn't desgined to be supercharged.
With all due respect there is nothing wrong with hyperutectic pistons. There are many aftermarket manufacturers that offer some very strong hyperutectic pistons. What makes these PARTICULAR hyperutectic pistons weak is the afore mentioned ring land issue.
As for the rods, Ford never intended these motors to be boosted. They are more than strong enough for any N/A application.
In regards to the original poster's question. The simple answer is the crazy high cylinder pressures caused by too much compression too much boost and short duration camshafts. With the cylinder pressures in these engines that would occur as a result of running too much boost you'd have to retard the spark timing so much that you wouldn't get the full benifit anyway.
With all that said you can run FI on these engines but any more than 5 - 6 lbs of boost and you're asking for trouble.

70MACH1OWNER

[quote=281GT;931030]These engines have too much compression for any significant amount of boost. Combine this with the stock short duration camshafts and pistons that have the top ring land loacted closer than normal to the top of the piston makes for an engine that simply isn't desgined to be supercharged.
With all due respect there is nothing wrong with hyperutectic pistons. There are many aftermarket manufacturers that offer some very strong hyperutectic pistons. What makes these PARTICULAR hyperutectic pistons weak is the afore mentioned ring land issue.
As for the rods, Ford never intended these motors to be boosted. They are more than strong enough for any N/A application.
In regards to the original poster's question. The simple answer is the crazy high cylinder pressures caused by too much compression too much boost and short duration camshafts. With the cylinder pressures in these engines that would occur as a result of running too much boost you'd have to retard the spark timing so much that you wouldn't get the full benifit anyway.
With all that said you can run FI on these engines but any more than 5 - 6 lbs of boost and you're asking for trouble.[/quote

Your correct on every single count. But they are all existing conditions for the guys that want to supercharge their cars and they all have to deal with it. It will cost some of them big $ if they get greedy and some of them will skate by. But you are correct on all counts.
Scott]

Bullitt995

So technically a car running 8 lbs of boost with less spark could be just as safe as a car running 6 lbs with more spark? Could you actually kill a N/A motor in the same way a boosted motor by giving it way too much timing? Or is that different?

281GT

Detonation caused by too much spark timing for whatever fuel you are running could defintley kill an N/A motor as well. Detonation litteraly hammers your rods and pistions to death regardless of induction method.
In my experience of messing with cars for some 25 years I have seen a number of types of damage ranging from broken spark plugs, cracked pistons, bent cranks, bent or broken rods, and cracked heads because of detonation. Some of these damaged motors were running FI and some were not. Detonation = VERY VERY BAD!
Avoid it at ALL costs!!
Detonation is also the reason many dealers, regardless of make will deny warranty of they know an aftermarket tune has been used because they have no way of knowing how much extra spark timing or leaner A/F ratio the aftermarket tune introduced. The two things that they are concerned with are detonation and running too lean, both of which can result in catstrophic damage in a very short time depending on the severity.
In regards to your question about the 8 lbs boost vs 6. It would be safer if you were going to to run 8 lbs boost with less spark timing yes but I'd still be very carefull with spark timing and A/F ratio. There are some who have had success with this by being careful with spark timing and running only 93 octane or better but more than 6 lbs is not something I would gamble on one of these motors.

bob

Hypereutectic pistons and high ringlands are all a consequence of emmisons control. Hypereutetic pistons dont exapand as much, allowing the factory to run tighter clearences and the high ring position minimizes dead space for unburnt fuel to hide. As for powdered forged metal rods, IIRC, the process produces (as weird as this may sound) a better rod due to the manufacturer being able to blend the various alloying agents more precisely (as well as thouroghly). I also suspect that the process minimizes the amount of machine work needed to produce a workable rod. The weakness inherent to the factory rod maybe a consequnece of running a minimalist design (both for cost control and light weight???) as I have seen powered metal rods designed for heavy duty use in a few magazines (Circle Track Magazine comes to mind with powered metal rods designed for 500 to 600 HP applications)

Ultimately this all comes back to detonation which is an uncontrolled burn in the cylinder which produces pressure spikes that shock the engine. Forged componets are better able to absorb this shock typically by being both stronger and less brittle than thier cast counter parts. However these shock loads just dont end with the pistons, rods, and bearings. They can rattle rod caps and main bearing caps loose as well.

Seems to me that somebody somewhere also mentioned that the 3v heads were more detonation prone than the old 2v heads (and 4v heads) which seems to be true, In my own experience when I run 87 octane on a hot day depending it seems on throttle position and load I can induce a little knock, with 89 or better octane (or strangley adding some Lucas Upper Cylinder Lubricant) to my fill reduces or eleminates the problem.

Then again when I think about it, the 3v design might also run hot??? Ford uses a nice inconel exhaust valve, prety pricey stuff for you average everday run of the mill engine.

don_w

My 2 cents... I prefer to keep the timing low and up the boost, especially when running pump gas. In other words, I'd rather make 450rwhp on 12psi with 17* of timing, than 450rwhp on 10psi with 23* of timing. Of course, if you are running race gas, then you can increase timing because higher octane fuel is basically a deterrent to detonation. And as mentioned before, detonation is the devil (along with catalytic converter failures ).

Bullitt995

Haha I was waiting for you to chime in with catalytic converter failure. But no worries! I'm running an O/R pipe!