Low RPM + High boost = Bent rods?

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 11:08 am


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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Thu Apr 08, 2021 11:22 am

Interesting design concept.
Reminds me of a torque converter developed by Jim Bell of Kenne-Bell. He used a ' pitch switch' on the vanes where the angle was changed to give either low or hi stall from the flick of a switch.
Don't know what became of that.
I guess you can try with the Delco and see what results are achievable.
Did you buy the 'charger for the VNT feature.
If not, you can likely lock those vanes in a preferred spot to take the hassle out of tuning. :twisted:
Last edited by 'quipt4it on Thu Apr 08, 2021 12:05 pm, edited 1 time in total.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 12:05 pm

Yeah i wanted to test VNT. I've never seen another petrol VNT build in any forum or group (using an off the shelf turbo anyway - there was that Garret VNT developed for porche that i've seen used in a civic). They're usually used on diesels as they can control their EGT to keep the vanes and ring happy. I doubt I'd ever push this little motor hard enough to melt it down and if I do, I'll know better for the next build.

This was a test to see if:

1) I can boost the 1.6LF - It's never been done according to the pulsar forums+groups and I'm stupid for trying
2) VNT's can be used in a petrol application without failing and they can offer something over an equivalent wastegate turbo
3) The TBI can offer enough charage cooling to negate the need for an intercooler. Ideally on premium but I'll go e85 if the injector allows it and there's any additional cooling

Locking the vanes would remove any boost control and any benefits from using the VNT and I'd need to fork out another $150 in an external wastegate... I'd rather drop a GT28 or K03 in there for the same price.

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Re: Low RPM + High boost = Bent rods?

Postby 'quipt4it » Thu Apr 08, 2021 12:10 pm

The downside is tuning...

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 12:22 pm

Maybe I'm over thinking it, it might not be that bad :-)

I figure Vane position would be linear with RPM once we're at boost so WOT should be easy enough to tune. It would be the transients of high RPM/low load and going WOT which would drop VE a whole lot as the exhaust chokes up. At least it'll go filthy rich over lean. The other option is to maintain a fixed boost, or fixed vane position (using a lookup table) to keep the turbo always in boost, or pushing a high CFM out of the blow-off. Going part throttle to WOT in this condition would reduce VE transients and give instant response at the expense of turbo life/heat/fuel/backpressure...

Or drive-by-wire throttle to manage boost/VNT...

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Re: Low RPM + High boost = Bent rods?

Postby In-Tech » Thu Apr 08, 2021 12:40 pm

Just a quick note in case I missed it. It appears the TBI will be blow through. Make sure to boost compensate the fuel regulator.

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 12:43 pm

The reg is in the throttle body, the diaphram and its reference should all be under boost too. I opened it up to double check, seems simple enough, membrane, spring, pintle. I guess we'll see!

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Re: Low RPM + High boost = Bent rods?

Postby In-Tech » Thu Apr 08, 2021 3:03 pm

Hiya, the tbi trucks here in the states will not see a reference to the regulator hat, of course I am not sure on yours. In the trucks I would have to get a referenced hat or weld/drill/tap. If not referenced you will have lean out due to the boost pushing against the 12psi fuel pressure. At least with a boost ref it stays 1:1
I'm sure you know all of this but thought I would mention it as it's an easy thing to overlook thinking all is well and then blammo :wall:

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Re: Low RPM + High boost = Bent rods?

Postby BennVenn » Thu Apr 08, 2021 3:19 pm

Thanks In-Tech, I'll definitely go over it again tonight to be sure.

Where's the reg on your TBI setup?

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Re: Low RPM + High boost = Bent rods?

Postby In-Tech » Thu Apr 08, 2021 4:31 pm

Hi,
It's on the underside of the TB where the inlet and outlet of the fuel is. I'll see if I can grab a pic of one this week but I think if you look at yours you will see if the diaphram can see anything but atmosphere.

I hope you don't mind if I butt in a bit about cylinder pressure. I'm sure you know the high cylinder pressure diesels have at very low rpm. They don't detonate, they preignite if the fuel is introduce too soon. Preignition and detonation are NOT the same thing. Some of the combustion process can be controlled with ignition timing, the rest has to be controlled with many other things. In any lower octane fuel, diesel is one of the lowest, it can be controlled with timing of the fuel. Of course this is dependent on temperature. Some of my statements in my life have been, heat is energy, energy is horsepower...but you have to control the heat.

When we talk cylinder pressure I hope we are talking about cylinder pressure AFTER combustion. This is the key and of what crank angle and piston position after TDC completely(well,not but for this example) controls combustion efficency.

We can EXPLODE a very efficient "pro stock" type super efficient 4 valve engine at almost any rpm you want. The better the parts involved allows a leniency. The goal is to make the combustion process better to accomplish.

Bottom line to this question is, do not go into preignition. It is a silent killer within a few heartbeats/cycles. Check rod angle force vs rpm and it's all time based. More rpm = less time per event.

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