Twins with Twins, Anyone?

[DAVe3283]

Does that mean the issue was cross talk on your harness? Might be interesting to track that down, if it didn't require load to mess with it.

So those turbos only good for ~625 HP, if I'm seeing it right? (Graph is fuzzy on my phone) What do you have in mind to replace them?

What was the limiting factor? Drive pressure ratio? Shaft RPM? Started coming apart under high boost? Having killed a couple S371s due to excessive RPM nuking the bearings, I'm curious if this is a similar problem.

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[kidturbo]

No positive conclusions on misfire cause yet. Gotta review some more data, and check runout on first engine reluctor ring. We only moved the bail connectors further away from injectors, and removed those scroll block off plates. Then this engine was also logging multiple cylinder misfires at idle, but pulled fine to 4200. Making less torque at same rpm however. So few things left to hash out yet.

On turbos, just to dang big on exhaust side for this type of setup. We was thinking they might finally light off around 3800r and spin up to make 45-50psi up at 5000r. After a couple tuning adjustments, was obvious that wasn't gonna happen. Engine ran outa camshaft by 4100 and they were only making like 30psi.

With single scroll blocked off, they would likely made 40psi and mid 700hp tops. Nowhere close to where we need to be. So going to toss a big single on there and see where it lands. Other option would be stick a small blower on top of em like Banks did it. But that opens up whole new set of known issues.

Besides that, both engines performed well as expected in all other aspects. Ran cool and clean at part throttle, and should live happily at 700hp 1100ft-lb all day long. But customer wants to see what they can actually do..




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[kidturbo]

Here is nice little WOT pull that told the tale on those twins. Open scrolls, peaking out at 30psi and 730hp corrected. She sure is a happy camper there.

https://youtu.be/MLXG2bSWb9s

To warm this one up, we ran about 3 minutes loaded at 50% throttle to emulate normal cruising speed in the boat. Was only making 4-8psi, where I would like to see about 12-17psi. Besides that, all the other data looked really good. FTEMP is actually Oil Temp in this pic.

 

[JoshH]

What is the next step for the turbo setup? I know it’s twins with twins, but have you considered going to a proven single turbo setup?

 

[kidturbo]

Might have to change topic to just Twins...

Gonna toss a S475 on it to get some data, then decide which way to go. We need more boost to bring the power curve up and keep it clean. Finding that range map in symmetrical twins isn't looking very promising at the moment.

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[PureHybrid]

What's the minimum rpm that these will likely see while under load? Or guess I should ask, what rpm will they rev to before the props really start pushing water? Obviously you could change that, but didn't know what the goal was. Sorry, kinda boat dumb here

 

[kidturbo]

Below is our engine RPM to boat speed chart. Current drive gearing and prop selection is setup in the blue section. It's pretty straight fwd 1:1 trans gear ratio, like driving a stick stuck in 4th gear. We do have a 2spd trans, with 1.50:1 first gear that can be used to help get boat on on plane. But beyond about 40mph, she's locked in high gear.

The rpm to speed scale is based on a prop slipping factor of 15%. That's typically good as ya get on big pitch props. The scale is pretty accurate above 3000rpm. Below that rpm, the slip % will be higher, like in 20-30% range. That said, chart shows 1700RPM at around 40mph. Probably the slowest boat will stay on plane, and hard bottom of normal operating range. Need to start making some boost at part throttle around there.

Second, graph shows speed by gear position and RPM. The green block is expected shifting speed range.

 

[JoshH]

What is the peak horsepower goal?

 

[kidturbo]

850 -950

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[JoshH]

I really liked the single 472 I ran at that power level. It was fairly responsive and made good power.

 

[kidturbo]

Yeah Mark broke out a stack data logs, maps, and a calculator. Everything points in that general direction. Trick is finding best etup now that runs clean and doesn't have a bunch of drive pressure and EGT.

Nelson is willing to work with me to develop a smaller custom symmetrical turbine housing, somewhere between what we have now and the next best thing we found, GTX3071R GEN II Turbocharger..

That 3071 comes in a left / right config, but looking at the maps, we just don't see em hitting the 50psi mark paired up.

By Friday we should have good numbers on the singles, then can decide on a course of action.

 

[gmduramax]

You could just make it a triple setup

 

[JoshH]

If needed, I would be happy to ship my 472 for you to use for testing. It’s a cast wheel that is supposed to be some special high flow cast wheel from Borg with an 87mm turbine and a 1.0 T4 housing.

 

[kidturbo]

Thanks Josh.
I'll let ya know after we test the options we have on the schedule for Thursday.

 

[THEFERMANATOR]

I know spool-up is a concern in marine use. Is that your reasoning for running twins? Do you think a big single with a spool valve would provide enough boost down low to get you on plane? I'll admit turbos is not my forte, just trying to better understand your goal.

 

[kidturbo]

Yeah spool and EGT are two concerns in a boat.

The twin setup is supposedly more responsive down low [better curve] than big single on a gasser, so was following that plan. Just thought we could pick up where Banks left off on this design. But soon realized why he added the blower atop, to move into the 800's.

 

[kidturbo]

She's Single...

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[Dozerboy]

I just can’t believe you can’t spool a 61mm turbo in a parallel set up. What about adding a crossover in the up piping to get a a steady flow? Wonder if you could do it if it was a VVT? I imagine just like compound set ups drive pressure could be through the roof.


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[Chevy1925]

I just can’t believe you can’t spool a 61mm turbo in a parallel set up. What about adding a crossover in the up piping to get a a steady flow? Wonder if you could do it if it was a VVT? I imagine just like compound set ups drive pressure could be through the roof.


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techincally only 3.3 liters to spool each one and a low RPM range to do so. if the exhaust housing is as loose as hes saying, i very well can see the issue. higher flow heads, different cam might change all that but still comes back to only 3.3 liters driving each one.

throwing the crossover in wont really change much, wont increase drive pressure to the turbos or anything to help.

 

[kidturbo]

Got one good 4200r pull in today before it chucked the belt and tried to eat the cam sensor. But results are as we expected.

At basically same pw and timing as the best runs on other engine with twins and a scroll blocked, she picked up 10psi boost. Peaked at 45psi, 1:1 drive press, and 1050egt. Made 1190ft-lb and 708hp uncorrected at 3200r. Stayed flat at that hp up to 4200. See run comparison below.

Temps were good and exhaust was much cleaner. We added some fuel, and was mapping it part throttle loaded when our acme belt tensioner cut loose. By the time we resolved that, it was 7pm.

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