Low RPM + High boost = Bent rods?

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 4:59 pm

Ahh ok, the reg on this motor is beside the injector so I should be all good with fuel pressure.

Thanks for the info on the pre-igntion too. I think this will ultimately be what kills this motor, if/when it does fail. I can imagine unusually high exhaust backpressure as this turbo comes on boost which won't fully evacuate the cylinder in the previous exhaust stroke giving the next intake charge a pretty hard time on the compression stroke. I can limit how restrictive the nozzle is, it'll introduce lag but might make the motor a little happier for a little longer?

Interesting what you write about Rod angle force vs RPM. The lower the RPM, more of the combustion process will complete with less crank rotation giving higher peak force on the rod? This would explain High torque at low rpm = bent rods.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Fri Apr 09, 2021 9:04 am

I'm interested to know how far you are willing to go with your project with this set-up.
For argument's sake, if you blew a head gasket, would you break out the spanners or just move to the 1.8l w/ stick trans.
What would be the cut-off point.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Fri Apr 09, 2021 10:18 am

I've had the head off a few times, someone said you can bolt the 1.8 head to the 1.6 block so I tried that. You can, kind of... The 1.8 head is 1mm lower than the 1.6 so the cam timing is off plus the valves just kiss the block due to the smaller bore. If you used the 1.8 gasket (maybe two of them) with the 1.8 head it would absolutely fit and you'd get the better breathing head, lower compression again and multi point. Or grinding into the block to give valve relief would do it too. Going much below 8:1 is a little counterproductive I think.

Now I'm wondering if my block would fit in my mill...

I can do a headgasket on these in about 15min now so no huge problem if it does blow. I'll call it a day at a cracked ring landing or worse. If the motor has to come out, the 1.8 will go in.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Fri Apr 09, 2021 10:26 am

Could you adjust the cam timing with the 1.8l head so you wouldn't have the interference problems and make up for the difference in height.
Gasket stacks are a bad idea.
I've seen block relieving done 'in-situ' with a die grinder. As long as the gasket ring is large enough to clear the valve.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Fri Apr 09, 2021 11:49 am

I'm not to sure how much meat is there before I punch through the water jacket. Likely enough for the valve clearance but then it would probably be asking for other combustion issues. See how we go with the 1.6 head. The ports are bigger than on the 1.8L anyway, just smaller valves

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Re: Low RPM + High boost = Bent rods?

Postby vlad01 » Fri Apr 09, 2021 12:02 pm

Valve size doesn't matter too much with boost, you can always brute force the problem anyway.

I agree, stick with the setup you got and work from there.
I'm the director of VSH (Vlad's Spec Holden), because HSV were doing it ass about.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Fri Apr 09, 2021 3:10 pm

I'm not trying to push you one way or the other (no really), but the difference between TBI and MPI is a chasm when you consider the much better fuel delivery and distribution can make the difference between a cooked engine through a lean-out, and one that is a happy runner.
Then there is the added bonus of less 'stuff' in the way of the intake charge.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Fri Apr 09, 2021 3:36 pm

100% agree on all the benefits of MPI, but back to reason #3 for this build, will TBI injection offer enough charge cooling to negate the need for an intercooler. That's something I wanted to test myself

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Re: Low RPM + High boost = Bent rods?

Postby In-Tech » Sat Apr 10, 2021 2:16 am

There isn't enough gasoline in the mix to really affect IAT although it does a little bit, e85 or meth will help due to its' mass and evaporation qualities.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Sat Apr 10, 2021 8:32 am

I've heard that, and i've also heard that carbs will give a higher peak HP due to charge cooling all other things being equal.

There's also a video on youtube where a guy installed an IAT before and after his throttle body (TBI) and was seeing 10-20deg difference depending on manifold vac and rpm. I'll see if i can find that link

As for quantity of fuel, a TBI on the 1.6L is like a shower head at WOT. A significant amount of fuel being atomised

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