saving Stock rods by keeping peak torque low ?
 

Id really like to end up somewhere close to 240-250whp with my setup. its a stock 95 engine with good compression (180psi), Exhintake mod, GT2560r and I will be running MSpnp

its my understanding that the big killer of rods is torque is this correct ? my plan is to set the timing to keep peak torque low (210-220wtq) Assuming a good tune this should make it less likely that I will bend a rod right ??

Yes torque, but also revs... and how much torque is being made at how high of revs... in other words, POWER.

A lot of bent rods are the result of detonation.

Basically. Keep boost and timing down (but not low enough to melt stuff) to keep torque down. Also keep stock redline.

Yes was planning to rev it to 7k with a limiter set at 7100. I want to beable to beat on it pretty hard on the street. If I take it to the track boost will be lowered to the 190-200whp range

A friend of mine runs 15psi on a large 16 with stock BP. Wastegate spring only, no boost controller. He absolutley rapes his car on the street every day, and its still just fine.

From my previous experiments, wastegate spring only is MUCH smoother onset from mbc. I think that's the difference between straight and gay rods.:giggle:

You know... i never really thought of that.

This is also why DISIs like to bend rods... it's the ridiculously fast spool up and sudden onset of torque that's the issue.

HRM.

That's also why they blow balls on fuel mileage.

What is DISI ?

my wastegate is a 7psi non adjustable unit. I guess when it comes time to up the boost maybe ill just get a new wastegate actuator

Mazda's Direct Injection technology.

Its cars like your friends that make me want to run 250whp but then I hear of people bending rods making only 230whp/wtq

I see plenty of 250whp stock engine dyno graphs on this site but havent seen much talk about how long people have ran at that kind of power and with what kind of abuse

^detonation

A street machine could probably make 300 without bending rods if there is absolutely zero detonation.

On the track youre building up so much heat, for such an extended period, that detonation can happen even with conservative boost and tuning. That why most well sorted setups are not even hitting 250 on a stock bottom end, and why shitty setups blow up way before that.

You never told us what you wanted to do with the car.

I like to beat on it pretty hard on the street and go out on curvy back roads and push it.

If I were to track it id lower the boost to get close to 200whp. I might even end up lowering the boost to that level when I go drive back roads since im pretty freakin hard on the car when I do that

Where is Paul when you need him...
All I can say is: stock block, gt2560, 18ish psi...319whp.

I made 280 whp with a holset hy35 on a stock BP until the oil pump blew. another guy on clubprotege made 300hp on a stock BP. he had an aem stinger with a good tune that motor lasted for two years and then the oil pump gears shattered. I could probably list a dozen who have been around 300whp with stock internals granted some of them didn't last that long. its all in the tune.

I could probably list 5 dozen people who claim they want 300whp, but have never ridden in a Miata with 240whp. 240whp is pretty damn fast.

I wasn't satisfied with 280whp it is never enough. I got used to it and it seemed slow. I wouldn't even worry about blowing it up with 250 lbs torque if you have a decent tune.

hasnt he been at that level for over a year ? dont know how much he drives or beats on the car though.

I take that car/setup/numbers with a grain of salt. I'm not doubting the numbers, or the fact that its held up at that power level for a long time, but find me a handful of others that did the same: you won't find any more than 1 maybe 2. Which makes me think that car is the exception, not the rule.

Remember when leatherface made well over 300 and ran something silly like 27psi on stock block? Yeah, same thing.

That car also made the smallest amount of power i've ever seen huffing that kind of boost.

Impressive that it held together... not impressive in the power it was (or wasn't) making.


There has been numerous Escort GT/Proteges in the past living for a relatively long period of time over 300whp on stock motors.


My Miata spent at least 50k miles over 250whp before i paid FM to tune it and they hamstrung it.

How did they F$%& things up ?

Just curious were you running a stock or lightened flywheel ?

Im planning to run a stock flywheel with a FM clutch. With all the vibrations that are going on at the crank with 250whp using a light weight flywheel seems like a bad idea

FWIW I've been running 17psi-18psi (MBC) with a GT2560 on my stock 97 engine daily for a couple years. I do have minor oil consumption (.5L in 1500-2000km).

I only operate the car this way because I have a vvt head sitting there and intend to build a bottom end anyways.

YMMV

The flywheel side of the crank is held in place by the rest of the drive-train, worry about the oil-pump end instead.
Or are you planning to use 250+hp while free revving (or slipping the clutch massively)?

Yes I was using a lightened flywheel. Shouldn't of been why it blew up though it was balanced and I had the stock harmonic balancer.

Fwiw I was using the fidanza FW with 244hp 218Tq and it felt fine and never gave me a problem

how many miles at 244whp and with what kind of abuse ?

I have an ACT 13lb flywheel and it's great except if you like high load, low rpm driving. If you do your transmission will rattle, otherwise it allows for faster, smoother shifting. I've only had it for ~5000km.

Again, YMMV.

Paul actually sold his car and put that money into a business or something a few years back if I heard correctly.

There have been a few GT2560's on stock bottom ends making around 300hp reliably throughout the years. Saint_Foo was also pushing right around that much on his setup, and I know he beat the shit out of it. One thing is that just about every gt2560 making that sort of power is on an absurdflow setup.

So when it comes time that I start tuning the spark am I correct in my thinking that the way to tell if my timing is too far retarded would be

1. get an EGT probe and watch for high temps (which I havent really planned to use on my setup)

2. Watch the AFRs and see if they start going richer

egt and afr won't tell you if you reached mbt.
well, egt might but still I wouldn't trust that at all.
only way to know is to get on a dyno and keep advancing til it stops making power or knocks. or you can do the whole butt dyno/virtual dyno thing but not as accurate.

Under 4k Im not really going for MBT. Id like to keep torque down a little lower than most people making 240-250whp in an effort to keep from bending rods. I should beable to keep the torque down by retarding the timing. But dont want to go too low and cause issues

so stay in the range most have it at and don't sweat it

I just see no reason to get an egt sensor/gauge unless you just want to

not running boost control going straight off the wastegate is the best way

Resurrection.

Conservative tune, stock engine, '99. Concern is rods, just like this thread.

Can I run 200- 210 Ft-Lbs torque safely as low as 3500 RPM, if the mini-turbo can make it? Right now I'm hitting it at about 4000, same as Karter74 did.

You can run 200 ft lb at any rpm you want, but not 250.

We have done dozens of reliable 260rwhp cars making 220ftlb this way.

Dann

I use boost control to ramp in boost slowly with rpm, 10psi at 4k and ramp to 15 by 5,500 rpm. Never on a Dyno but runs mid 12's @108 which is enough to be solidly in the mid 2xx's

I would theorize that the RPM doesn't matter, but the ignition timing matters a great deal. Lots of ignition timing = tons of peak cylinder pressure. In order to get big torque from a turbo before the cams are in their sweet spot, people typically pile in the timing, which bends rods. Keep the timing soft and you can probably make 220wtq at 3000rpm on a stock motor if you want to.

Honestly, I've heard a compelling argument that you can run even more torque in the top end because the force is applied for a smaller period of time when rpm is highest. But I still stick with 220ftlb and make certain the timing is very soft in the 3000-4500rpm range.

Dann

It's a combo of both, less air and fuel in the cylinder sparked closer to MBT will make the same power as more air/fuel sparked later in the cycle. I like to spark the mix earlier in the cycle with a rich mixture, helps to dampen that cylinder pressure spike and keep an even pressure on the piston through out the cycle.

To your point timing is very important but it gets to be a lot easier to control with less boost pressure.

There is no time component when it comes to a force applied to a body, though. The force is applied, and the body can withstand it, or the body can't.

It certainly takes a period of time for force to bend something, and the combustion period is an extremely short time at 7500rpm. So without further knowledge, its a compelling idea for me, but I am not sure whether it is true or if the effect is significant enough to be relevant.

Dann

Which engineering equation describing the yield strength of a structure includes time as a variable?

A better question might be, what assumptions are made in those equations, and are they only useful for static loads.

Dann

The best clause I have seen in this is from Savington... "if you want to".. in this statement: "Keep the timing soft and you can probably make 220wtq at 3000rpm on a stock motor if you want to."

Because as I have thought about it more, there are few times, if any, where torque at such a low RPM has value. Even at the drag strip, I would plan to launch at higher RPM; and on the street, I cannot hook that much torque in first gear, and all other gears are then above 4-5 K if running up through them.

And in first gear, there is not enough time or load to spool the turbo before the engine is well past 3K.

A thought experiment:

Take a 3 foot long steel roundbar, 1/2" in diameter.

You stand it on its end and apply increasing mass to the top of the steel rod until you find the force required to fold the rod onto itself.

If you watched the rod fold on high speed you would see that the rod is being initially bent through its elastic deformation stage and quite a few milliseconds would pass before the rod reaches its plastic deformation stage.

Therefor if the load is applied for a lesser period of time than it takes to reach plastic deformation the rod will not permanently deform.

Assuming 8,000 rpm in a 4 stroke, and 20 crankshaft degrees of peak cylinder pressure the load is applied for less than 1 millisecond.


What do you all think? I have run this past a mechanical engineering phd (a friend) and a physics phd (my auntie) who agree.

Dann

you might feel differently if you had low end torque :) Power everywhere, regardless of gear or rpm, is pretty nice on the street.

I ran 200-210 at 2500 on a stock 1.6 bottom end for 6 months without failure.

210tq at 2500 rpm? what turbo setup can achieve this on a 1.6L?

a gt2554r cant even do 210tq at 2500 rpm on a 1.8L vvt motor.

Gt2871 churbo + Autorotor OA2076 compound twin

impressive.

sup with the neg cats? am i expected to know each MT.net members wild setups??

chill out people, it was just a question.

Strain-rate dependent (i.e. time dependent) behavior is a pretty big research field in solid mechanics. I'd imagine the time scales you see in engine combustion are small enough to make this relevant, but I'm definitely not informed enough to say for certain,


https://cimg0.ibsrv.net/gimg/www.mia...4cf67f08e9.png

This is what I have been referring to, thankyou for sharing your knowledge and giving me some terms to google.

Dann

The most literal form of "breaking as a function of time at applied load" is creep.

Creep describes plastic deformation below yield stress as a function of time. So the more general question of "what stress will this part meaningfully deform at" can include time as a variable, even if it's not strictly called the yield stress. But I agree that this is not relevant to this discussion, since a con rod run at 3000rpm for 1 minute and a con rod run at 7000rpm for 1 minute spend the exact same amount of time in compression.

FWIW, I ran 240-ish rwhp (dynojet) for 50K+ miles on a totally stock 99 motor, and when I took it apart to build it (because I wanted to make more), the rods were straight as an arrow. That motor never ran boost with less than 95 octane though.

--Ian

But each time force is applied it's applied for less time the higher the revs are, and therein lies the root of the question.