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Discussion Starter · #1 ·
I'm in the final stage of tuning my compounds and am at the point where drive PSI and the temperature of the first stage charge are getting into conflict I "think".
It seems to be happiest with the Wh1c carrying the load beyond 2,000 rpm so 25 psi in the 1st stage with 42-48 at the manifold, my issue is I'm at around 330* F for the air feeding the HX30. Now this is really only pulling a grade at WOT above 70mph so not a constant condition.
Does anyone have data on what temp is getting risky for factory Holset compressor wheels.
I have the option for the 30 to carry more of the WOT load but my drive PSI seems less than desirable when doing so where things stand now I'm pretty close to 1-1 except while building boost and less than that on level ground under cruising conditions at 1,800 +/- 100 rpm.
All in all it's running well but using more fuel than I would like, I've been seeing 15MPG's over the last 2,000 miles of mixed driving and would like to see 18 if I can get it without giving up any power........
 

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So I see it as a tradeoff of turbo health vs power.
You'll get the most power (through lowest total drive pressure) when the small turbo is running almost in bypass and the big turbo is doing all the boosting. But this puts a lot of heat into the little turbo.
You'll be the safest running lower boost on the big turbo and using the little one for most of the boost. I don't have any hard numbers for safe inlet temps. But a general rule of thumb is metals start to creep when they're above half their absolute melting point. I don't know the alloy that compressor wheels are made from.

Holset HTi edition 7 has some info: http://caboturbo.nl/wp/wp-content/uploads/2012/03/HTi_07.pdf
Al-Si-Cu-Mg aluminium casting alloy
This article discusses the solidification of it: A Review on the Heat Treatment of Al-Si-Cu/Mg Casting Alloys
If we took a conservative 600C for melting point then in absolute that's 873K.
Half that would be 436.5K or 199.5C (390F).

That's an absolute max. You're still going to lose strength below that.

This article: Turbochargers: How They Work, and Current Turbo Technology, by EPI Inc.
Says a common compressor wheel metal is 354-T651 aluminium alloy.
Matweb says it has a melting range of 538-596C: http://www.matweb.com/search/datasheet.aspx?matguid=33d79dc22a0b48a4822fd83019ec3022&ckck=1

That would give you a max temp of only 132C. But this seems low and it could be other factors push temp limits higher.

Cruising economy is going to be made or lost with the most efficient boost. The HX30 is likely a more efficient turbo than the WH1C. Swapping the WH1C for a HX35 would get you better efficiency but I can appreciate that's a fair bit of modification.
I've gained/lost 10% economy just with turbo change. But you're looking for 20%.
 

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Discussion Starter · #3 ·
Thanks Dougal,
that gives me something to work with at this point I'm still lowering total boost without adding any fuel to see just where I end up while still running clean and below 1,250* on my EGT's.
My last change has still left me with more boost than I need but at this point it takes longer between changes for me to decide where to go next as one small mod effects EVERYTHING, it's running well so I might be just nitpicking but I have the time and know it can run better overall.
18mpg might be unrealistic for where, what and how I drive it, a gearing change is really needed I'm thinking 3.3x or 3.2x would be ideal with my 3.55's 70mph is 2,000 and 75 is 2,150 with a D-60 in the rear I'm limited in that range so not sure where to go with gearing. I could slow down... but doubt I will and I'm still getting 75% better mileage than with the gasser I replaced.
 
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Steve, wonder if there is anything like an intercooler between the turbos to lower the air temp? Don't remember ever seeing one but doesn't mean it couldn't be done. Might need to be a water to air unit for size but could be an interesting test project. Don't remember anyone having measured the air temp coming off the primary turbo.
 

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Discussion Starter · #5 ·
I have been thinking about that option however I just do not think I have the room that side of my engine compartment has become a bit crowded.
I know I can lower the total boost for the 1st stage more it's just getting real complex at this point, I never truly appreciated just how dynamic and interconnected everything was with compounding until I was so close to "ideal".
My last change was to increase the total travel for the 2nd stage waste gate by ~ .060" without changing the gates setting this did not affect the 2nd stage boost but did wake up the 1st stage considerably above 2,000 and it dropped the drive psi by 15 lb, hence my latest issue 1st stage charge air temps higher than I'm comfortable with.
I'm pretty sure that I have more total boost than I need so getting it lowered to the minimum needed for my current fueling is my goal while at the same time keeping 1st, 2nd and drive PSI in balance, next step is gonna be opening the 1st stage waste gate earlier with a little luck that might just do the trick. reaching the waste gate is gonna take 2/3 hours as it is below and behind everything... Nothing worthwhile is ever easy so I'll just take it one step at a time, I'm in no rush really as it runs strong and everything is safe now as it's cold here now so intake air is closer to 30* now and the 330* was with it closer to 100*, I'll have it worked out before summer temps hit.
 

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Steve, wonder if there is anything like an intercooler between the turbos to lower the air temp? Don't remember ever seeing one but doesn't mean it couldn't be done. Might need to be a water to air unit for size but could be an interesting test project. Don't remember anyone having measured the air temp coming off the primary turbo.
Intercooling between stages is the perfect theoretical answer. It makes everything better. But fitting it in can be almost impossible.
 

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Discussion Starter · #8 ·
Yes Charles it would and I have not discarded it as an option but it will be a last resort, I truly believe I can get it where I want given enough attention.
The closer you get to "ideal" the more time consuming it becomes, as I stated earlier everything is interconnected in an extremely dynamic environment where a small change has widespread effects across all the other components and settings.
 
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