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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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Subscribed. Hope to have some comparison data for you on this soon :)
 

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Discussion Starter · #10 ·
A quick update I now have the wh1c gated to 20 psi but still have a bit more boost at the manifold then I want/need next I'm gonna give it a little more injection advance to see what that does, I do not think I have near the injection timing I was running with the old pump. For now I'm much more comfortable with 20psi from the first stage however I think I can still keep the power I have with it closer to 15/18 psi a little more timing might bring it there, with luck I'll make the change this weekend.
 
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Discussion Starter · #11 ·
OK on Thursday I advanced my pump, it was initially where the marks on pump and housing were lined up but as i do not know the CPL of my new replacement pump I can't know for sure exactly what the starting point was but I'd guess "stock" for 4BT of a later year than my '88 it's now the "normal" 1/8" beyond stock.
It is happier here compared to where it was and sounds pretty good and now 1st stage boost stays at 15-17 unless I wind it beyond 2,200 at WOT on my 6% test grade that starts at 5,500' and ends at 7,000' , I did lose a bit of torque but EGT's would not go beyond 950* so today I added a half a turn on the fuel screw and around town it seems better but I still need to take a bit out on the bottom with the AFC as I get a little smoke on takeoff and shifting 1st through 3rd.
Boost on the 1st stage at cruise is under 15 now and my drive to intake manifold pressure is closer than ever before +/- 10% unless I'm adding fuel or at WOT where drive is ~20% over intake I just filled the tank so in 800-900 miles I'll get a mileage figure and decide what my next move will be IF I think I need one.
I believe I'm where things will be safe where the charge air temps feeding the 2nd stage are concerned so time and miles will tell the tale, but it's getting close for sure.
 
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Discussion Starter · #12 ·
Took it up the test grade this morning to test the WOT EGT's and on a 5 mile pull I'm seeing 1,100* so the half turn on the fuel screw helped, the mid range power is also better however it does not recover speed as well as I would like after letting off on the grade pretty much 70mph was all I could get out of it.
Thinking another 1/4 to 1/2 turn on the fuel screw will fix that and bring EGT's up to my 1,200* target but when there I'm guessing that I'll need to open the wh1c's waste gate another turn to keep max pressure at 20.........
So progress again and closer to where I would like it to be.
 
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Sounds pretty good to me. You said your running 20 psi on the wh1c, what is your manifold psi?
I did find timing is a fine balance of fuel economy and higher rpm power with low rpm power.
I've got my hx30 opening around 25 psi and I disabled the hx35s gate and used fuel screw to limit max manifold psi to 40 psi.
 

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Discussion Starter · #14 ·
I'm seeing 45 at the manifold now but think I can get away with 42, my goal is 42 at the manifold and 17-18 from the wh1c with my fueling where I see 1,200* EGT's with extended WOT up the 6% grade. Since I gated the wh1c at ~20psi which decreased drive pressure by10% across the board and a bit more at WOT I got a 1.25 mpg increase, I'm hoping the timing bump will give me another 1 or 2 MPG. It is running real nice now but I'll wager I can improve it some as it sits now it hits a wall at 2,340RPM at 83mph on basically level ground so might not be much more power to gain at this point but smoothing out things across the board is still worth a little time, all in all 83mph at 5,000' from a 8,000# brick is quite respectable for a 3.8l turbo diesel 😊
 
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Lol, yes not bad at all. 4bts are amazing little engines, that's for sure.
I've definitely got a similar situation as my truck is heavy too, 7200 lbs. But I've never run a stock cam(I'm running a colt stage 3) and it's been years since I've had a stock pump. I know mine keeps pulling and pulling up top, but I'm curious as to what I've sacrificed down low.
Can't get nothing for free, but when u get thes engines dialed, they sure run and pull great
 

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Discussion Starter · #16 ·
Lol, yes not bad at all. 4bts are amazing little engines, that's for sure.
I've definitely got a similar situation as my truck is heavy too, 7200 lbs. But I've never run a stock cam(I'm running a colt stage 3) and it's been years since I've had a stock pump. I know mine keeps pulling and pulling up top, but I'm curious as to what I've sacrificed down low.
Can't get nothing for free, but when u get thes engines dialed, they sure run and pull great
When I was picking components for my long block I thought about camshafts a lot but decided that I really wanted to keep the power band where Cummins designed it so i chose a OEM shaft and looking back i happy that I did.
 

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Discussion Starter · #17 ·
I took it for another run up my test grade after adding another 1/4 turn on the fuel screw and it's now where I wanted it, I can now drop back to 60mph and easily recover back to 75mph in OD EGT's are still below 1,150* but boost climbed up to 50psi. I think when i lower boost for 1st and 2nd stages to my goal of 18 and 42 my EGT's will still be in the safe range so SUCCESS!!
The AFC will need to be addressed as there is more smoke than I like on takeoff but only when I get on it real hard, I'm really happy with the bottom and midrange torque it's better than it ever has been and all numbers are solidly in the green so gonna just drive it for a while now as all this work has really aggravated my preexisting tendonitis so need some downtime before diving back to reach the wh1c's wastegate, I should have a mileage number in a couple of weeks as i have put near 300 miles on it during this round of adjustments.
 
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Steve, have you thought about adding a back pressure gauge to your setup That gauge setup can be useful especially in twins. You can used a regular boost gauge for the reading and install the plumbing in the exhaust manifold It is wise to add a small particle filter in the line since soot deposits may clog the gauge. Must also be sure all your connections are good as you're introducing a carbon monoxide source into the cab. You make a coil of copper turbine coming off the exhaust manifold to help dissipate the heat, then the filter, etc. There are electronic versions of these gauges but they are a bit pricey.
 

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Discussion Starter · #19 ·
I have one and on basically level ground between 1,700-2,000 RPM intake to exhaust manifold pressures are +/- 10% of each other and when adding fuel and at WOT exhaust manifold pressure tends to be ~ 20% over intake pressure. I'm thinking that is well within the except able range for my fairly archaic turbos but I expect to see things improve when I adjust the wh1c's gate seeing as I saw a substantial improvement when I did it the last time, with my fueling the wh1c's 12 cm exhaust is a bit tight above 2,100 RPM and with my numbers I need to have both waste gates open earlier so I'm hoping for better numbers once that has been done. I'm to the point now where it's truly Baby Steps with each change and each change seems to require one somewhere else as everything is so interconnected.
 
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It's interesting that you are dumping off your high pressure turbo so soon. I have found( on both sets of compounds I've ran over 8 years, hx35 over h2e and now hx30 over hx35) that if I hold the smaller turbo on longer more power is made. I'm no engineer, but I feel as though you end up doing more compounding and less sequential turbo action when the high pressure gate opens sooner.
Having said that, I know that u have put limit stops on your wastegates so this might achieve the same thing?
Definitely it's a balancing act, the longer the high pressure gate is closed, higher egt and I bet(never measured) higher drive pressure.
Just me thinking out loud....
 
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