cfr865

I hope this isn't a dumb question but here goes. Most people agree that anything over 450 rwhp you are getting into dangerous territory with the stock internals. However if you arrive at 450 rwhp with the addition of the s/c only, what happens if you were to add headers, delete plates, electric water pump, udp, which would add another 40 or 50 rwhp. Does the danger of blowing up come from the total rwhp or from the boost of the s/c only.

tmf

It comes from the cylinder pressure. The powdered rods can only take about 10,000-11,000 psi before they break up in a spectacular display of carnage down the track. Ask me how I know... Ok, I ran an ATI ProCharger at 14psi on a stock 03 32v bottom end and three rods finally exploded when I had it dialed in to the tune of 476 rwhp. In that particular motor, the procharger generated enough boost that it exceeded the pressure the rods would withstand.

So, do headers affect this? Everything affects the cylinder pressure in some way or another. I would tune for low 400's and be happy knowing your motor will last longer than 450 or 475...

My new motor? Totally forged and ready for the 6-71 blower bolted to it!

John

TMSBrad

I've been pushing 461 rwhp on my daily tune for 11 months with no problems. I have JBA shorty headers and Magnaflow catback exhaust. The key is in the tune. Give Doug at BamaChips.com a call.

tmf

See, that's a common misconception. You can have the best tune in the world but the rods will only withstand so much PSI before they fail. If you boost it too far, the cylinder pressure exceeds the rod strength and KA-POW!

I'm not saying there is a magic number, just that you know when you exceed it.

John

Rebel73

Ok,

just to add to this discussion...

let's say, theoretically, that you have a SC Mustang with 450rwhp at 9si, but drive it like an old granny (I know, humor me) 100% of the time, never exceeding 3000rpm. Would the motor life be comparable to a N/A stang?

tmf

Absolutely. Don't get into boost and they have the same probable longevity.

John

S197 GT

I'd like to add that RPM's are also bad for these powdered rods. I now know about 15-20 people who have blown their motors in these cars, and most have definitely blown by pushing the limits...(i.e. 550+ rwhp). I am starting to see a trend with the guys who are sustaining high RPM's as well.

Push 550+ and you'll likely put a window in your block pretty quickly, but plenty of people have also blown with just over 400. It's all depending on how you drive, your tune, and your set up...

TMSBrad

I didn't mean it was "all" in the tune. Like S197 GT said, you can blow an S/C'ed engine at 400 hp with a bad tune, and clearly the stock block has a hp ceiling that even the best tune can't break. I just don't think that ceiling would prevent you from reaching some outstanding horsepower numbers on a daily driver.

tmf

Absolutely! A crappy tune that goes lean under boost and the results are just as scary. I also corrected your comment in the text above as I'm sure you meant it to read that way. So yes, shoot for a good low to mid 400 RWHP number and the engine should stay together.

I would also caution anyone trying for the 450-500 RWHP number to make sure the tune is done with 91 octane. Anyone that fools themselves into thinking that just because it says "93" on the pump they are safe, usually end up with damaged engines. Always carry a tuner with a "crappy gas" tune loaded and make sure you resist the urge to "mat it" if the gas is unknown.

Happy holidays!

John

Hatchman

The term "it's all in the tune" just means that a good safe tune is better than a crappy one. If car puts down 450hp on the dyno, but is running lean with a ton of timing, chances are it will start detonating/raise the chance of engine failure much sooner than another guy who is putting down 450hp on the dyno with a flat, conserrvative A/F curve and nice conservative timing map running good octane fuel with a fuel system that supplies the proper fuel pressure at all times and a set of HTO spark plugs that run a range colder than stock with a smaller gap than stock so there is a less chance of spark blow out and thus detonation. So of course it's not all in the tune, but it helps.

I'm happy with my 440 at the wheel, which I feel is safe. but anything can happen.

But to answer your question:
Headers for the money don't really make that much of a difference, but you're getting more air in, so might as well let more air flow out, but they don't give a lot of HP per dollar spent (IMO). If you're going for a particular sound (ie long tubes and off road h pipe, etc), then go for it. The stock manifods actually flow pretty well, but look like rusty crap. Don't want to get into a huge "Are headers a good mod" discussion, I just feel the money could be better spent saving for a built block.
Delete plates: I think most of the twin screws get rid of these anyway, so not really an issue
electric water pump is good for 10 or so, and I consider it more a mod for track guys so they can cool down quicker between runs, just watch the battery
udp will only decrease your belt driven S/C output, since the crank pulley is smaller, thus lowering your boost

But to sum it up, once you've got around 450, the money is better spent saving up for a built block, since the very easy and cheaper way to raise the hp is by going up another couple psi in boost. Either way, 500hp is 500hp, and after that you're living on borrowed time. Some have lived long and prospered over 500, but most have not.

My recipe for safety:
Always run highest octane available (sure they could've pumped 87 in that tank for all I know)
Fuel Pressure guage (should get a wideband)
Minimize the high speed runs
keep the rpms below 6000
change the fuel filter every 10K miles (there only 10 bucks)
Keep it below below 450RWHP SAE
Colder HTO's with .032 gap
Custom dyno with conservative A/F and timing curves

But who knows, could have a rod take a peak on the way home with only 440.

06GTwJUICE

tune or no tune, parts have their limits.

Rods will only take so much pressure on them before they snap in half and pistons will take only so much heat before they melt.....

If you exceed the physical capabilities of a part, it will break.

bottom line...

No matter what you do or how much HP you plan on putting down, always have a little extra in the hidden fund to build her back up if she blows 2 seconds after you leave the driveway. - jake

tom281

You guys are right about the mechanical limits, but the tune is VERY important in order to help eliminate the chance of detonation. Detonation causes the extreme abuse on the parts which in-turn makes them exceed their mechanical limits instantly- at that point, KA BOOM.

Its pretty commonly accepted that if you stay at or below 450 rwhp on the stock internals and have a conservative tune (both air/fuel and timing) to help eliminate detonation, these engines can live healthy lives for a considerable time. Just don't go winding them out to 6000+ rpm every day.