Wnts2Go10O

iTrader: (12)

a motor will make the most power right before it blows.

now i know almost all of us here have heard it but, have any of us sat and thought about how or why? im kind of comming up empty. basically the only thing i can think of as a possiblity would be a clearance issue. so any ideas?

The Butcher

I would kind of disagree with this theory though becuase there are plenty of engines who's HP peaks while the engine has plenty of rpms safely left. Like when you look at a dyno graph, the hp falls off in the end, but in order to see that, the engine is still turning higher and higher RPMs. Think about a truck engine. They're usually tuned for low end torque, so all they've got peaks low, while the engines harmonics would allow it to turn maybe hunreds, if not thousands of RPM more. Just my $.02

Ferocity02

iTrader: (60)

Pretty much all engines make their most power before redline, and then "blow up" after redline, so there ya go.

The Butcher

/\ I guess it all depends on how close to redline we're talking then

2002_Z28_Six_Speed

iTrader: (19)

As far as a consumer gasoline engine goes, I would have to completely disarge. You aren't going to have the head design to get the high RPM power. Almost all consumer motors modified or not are going to loose power before the redline. Most people messing up new motors probably do so from too high of RPM and not kicking a rod before max rpm...unless something was built wrong.

If you were talking about Top Fuel I could see a bottom end failure before the valvetrain caused a failure.

Wnts2Go10O

iTrader: (12)

i think you guys misinterpreted a little. i meant more time wise. i mean yea i can see the rpm limit be an issue in certain motors but im more interested in the time the motors been ran.

machinistone

I know exactly what you are talking about, and although I have never personally experienced this, I cant count how many people have told me this story - " the car was running great, felt much better coming out of the turns...then boom" Same thing with street cars, high mileage and all of a sudden it feels like new again, then the next week it is dead...

Uthinkso

Yes I agree I've heard this same thing. It gets strong again and feels "responsive and snappy" those the are the words I've heard. It really put ya back inthe seat like it used to.

Considering break-in, an engine will make the most power once it has some break-in and heat cycles through it.That will seat the rings to the bores and break the bearings in as well as everything else in the engine. So in the begining and the end of its life would be where its the weakest. No the "seat of pants" dyno may say something different, but thats just people being people.

dlc1609

iTrader: (20)

i have experienced this first hand many times in dirt track racing. i would say i've blown at least 10-12 sbc's and at least 6-7 of them felt very noticably faster the lap or two before they blew. the reasons i figure they get faster is for i would guess the clearance issue like you said (motor getting hotter, thinner oil and lower oil pressure sometimes which drags crank and cam journals down less). but like i said, i have experienced this many times first hand.

hammertime

iTrader: (1)

"when you shift the gear and that little needle on the tach goes into the red and reads 9000 RPMs, that's BAD. " - Harry Hogge

Mighty Whitey

I totally agree with you guys on this! whether it be fourwheeler's, dirtbikes or cars, I've seen/experienced this quite a bit (okay, so a lot of my pals around here have some REAL **** rides, but still...)

my old 300ex ran like a scalded dog the day before it blew apart, I have no logical reason as to WHY, same way with 2 stroke stuff...

I don't know about ultra-high performance, or diesel- applications where cylinder pressure is everything- but in a low-performance car or just about any bike, I would assume the lack or ring tension in the bore overcomes the loss of cylinder pressure, and/or the bearing clearances are loose enough to not let the rod journal, or main journal "dig" in to one section of the bearing, but rather act like a loose wheel bearing... one that spins forever with a minimal amount of thrust (your hand spinning a loose hub as opposed to a tight hub).

if the added benefit to a roller cam and roller valvtrain is in the reduction of friction, maybe there is something to this myth?

I sure believe there is, but it could just be the back-woods eastern kentucky thought process we all have around here, who knows?

RednGold86Z

They probably blow up because you held the pedal down longer and didn't shift, and realized there's still some power up top at or above redline, and you're passing all your friends and having fun, then whammo.

Or, something begins to go right (like the distributor advanced some on its own), then you start to have fun with it too much, and you brake your toy.

Or, that durn distributor kept on going and took out your pistons.

Or, when it loses all power, your body/brain remembers only the last few laps as being fast, even if they all were the same.

Or maybe all that carbon fell off the valves from the high revs, and gave your old engine some new power, and you use that power to break the old parts of the old engine.

Or, maybe some carbon actually built up on the piston (from oil getting in there somehow, all bad) and gave you more compression. Then no more oil, or too much fun again.

Or, maybe you get an exhaust leak, and it just 'sounds' more powerful before you blow it up.

This could go on and on, but it's probably half (or more) mental.

DRIVER456

Have you ever used a chain saw and right before it runs out of gas it revs up and then stalls,Probably cause it leans out.So what I'm thinking is some motors seem to run better then blow is maybe they are leaning out.I could be wrong,But Just a thought to your theory...............Paul

XxGarbSxX

The leaning out theory makes sense, since engines make the most power at stoich. Unfortunately, the limit to how close to stoich you can get before detonation is usually pretty far away from stoich, usually in the mid 13's n/a, and lower for f/i.

The oil thinning and the loss of oil pressure theory doesn't really make much sense to me. If you're racing a car, especially one with an old engine, you want to make sure you have enough oil, and that it's the right weight and viscosity for the application and conditions. This happening would lead me to believe that it wasn't the motors fault that it blew.

5550racing

Well it goes lean and stalls. Doesn't kick a rod out the side. And the chainsaw being a two stroke is different. I've also heard this from a couple asphalt late model drivers. That right before the motor went south It felt as stong as It ever did. Never really thought about It though.

DRIVER456

A chain saw motor does not have much weight to it,But an 8 cyl. spinning around 6,7,or 8 thousand rpm and leans out an seizes a piston in the cylinder wall,Those rods gotta go some where,Which equals ..............................Paul

1320FEVER

iTrader: (9)

Density altitude could have something to so with it. If your motor is already on edge and the density altitude changes to optimal conditions allowing the motor to make more power than it normally would. That could possibly be one explanation. (I'm assuming a non-EFI car here)

280Z28

iTrader: (1)

False due to generality of the statement:

Proof:
Take an 8 cylinder motor with hyper eutectic 10.5:1 pistons, and force a lean-burn heavily advanced preignition every 10th turn on cylinder 7 when the RPM exceeds 3000 rpm.

Motor won't be making the most power, yet piston 7 will crack in short order.

Alternative proof:
Run a motor without oil and set the timing to 5*.

mzoomora

iTrader: (36)

I think that sums it up. The clearances are looser so the motor is more free. A lot of motor builder will set up a motor with more clearance than stock simply from the fact it makes more power.
I have also experienced this before, and it does happen, to the point that I have remarked on it before the motor blew.

dynocar

Having witnessed many engine "blowups" on dynos, a little more scientific, for the past 20 yrs, I have never seen one "make the most power right before it blows", unless someone tweeked it for more power that caused it. Then we get into a similar question, "why does the furnace usually fail the coldest day ot the winter"? Usually an engine makes less power then due to increased friction from a bearing, piston or ring starting to sieze, often giving plenty of advanced notice which was ignored.