Low RPM + High boost = Bent rods?

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Low RPM + High boost = Bent rods?

Postby BennVenn » Wed Apr 07, 2021 9:48 am

I've read over and over High boost at low RPM (peak torque) will bend (stock) rods. I've also read all kinds of theories for this - tensile and compressive loads, longer duration of loading at lower RPM, heatsoaking the piston/cylinder, engines just like to detonate at lower RPMs...

Then there's the guys in the supercharged groups who don't mention this at all. Full boost from Idle and no bent rods.

Some say its all in the tune, torque limited tuning <3000rpm.

Is there truth to the myth? Does it only apply to higher boost?

I'm about to start tuning a stock 1.6 N13 motor, turbo sized for full boost by 1800rpm. Should I limit boost/torque/timing until 3000rpm? planning 6psi, 8:1 compression, intercooled and charge cooled (TBI)

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Re: Low RPM + High boost = Bent rods?

Postby The1 » Wed Apr 07, 2021 10:44 am

maybe depends on how your loading it to, manual or auto, if auto what stall? Then advance or retard and fueling. There would be so many factors id imagine.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Wed Apr 07, 2021 11:31 am

Can you get your hands on a 1.8?

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Wed Apr 07, 2021 11:33 am

It's currently in an Auto, will be moving to manual if the engine survives. So there is a known condition you can put the motor in to bend rods?

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Wed Apr 07, 2021 12:08 pm

yes, I've got a 1.8 manual on a pallet ready to go in, wanted to test the 1.6 first and see how effective the TBI is at charge cooling. I've got the IAT sensor at the port on #4

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Re: Low RPM + High boost = Bent rods?

Postby The1 » Wed Apr 07, 2021 12:20 pm

BennVenn wrote:It's currently in an Auto, will be moving to manual if the engine survives. So there is a known condition you can put the motor in to bend rods?


Yeh knock lol.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Wed Apr 07, 2021 12:22 pm

Something that can't be tuned out? - I've bolted a wideband knock sensor to the block as hight as possible and run it through a pre-amp so I *should* be able to hear it fairly easily. Is there something special at that kind of RPM that will cause knock - that timing can't control?

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Wed Apr 07, 2021 12:24 pm

BennVenn wrote:yes, I've got a 1.8 manual on a pallet ready to go in, wanted to test the 1.6 first and see how effective the TBI is at charge cooling. I've got the IAT sensor at the port on #4

Perfect, best of both worlds.
Don't do the job twice. Go for gold. :lol:

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Wed Apr 07, 2021 12:52 pm

Unfortunately this turbo will choke up on the 1.8 and I've already made the manifold, dump pipe and oil drain for this little VNT turbo. I'll be starting over for the 1.8 with a larger turbo hidden behind the engine for a more discrete install. But first things first! Will 6psi at 2000rpm be the end of the 1.6? I guess we'll see!

Also on the lookout for a 2.4L rodeo motor, supposedly will bolt right up to the stock mounts, just need to drill one or two dowel holes for the box to marry up.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Wed Apr 07, 2021 12:56 pm

Would like to see a build thread.
Keep us posted.

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