Is anyone familiar with installing a turbo boost restriction fitting to improve mileage and increase horsepower?
I just had it done to my Cummins 250 diesel and when I first pulled out onto the hi-way and hit the accelerator, I could feel the difference immediately.
My coach has never accelerated like that before, so I'm sure about the horsepower increase. I won't know about the mileage improvement until I return from an upcoming trip on labor day week.
Back to the beginning:
I took my '94 Safari in to have the Pac brake worked on. It hasn't worked since I purchased the coach a year ago.
When I returned to pick it up from the service shop, the owner told me he had just had another RV with the same Cummins engine in his shop a few days earlier. He said he performed a service that the owner of that coach said improved his mileage about 2 mpg and he guessed about 50 horsepower.
I had been considering a Banks system, but had ruled it out after estimating I would have to drive the coach about 50,000 to 60,000 miles to recoup that investment. Now, here was someone offering me the same benefits for under $400. I figured it was worth the gamble to try it.
Here's what the invoice says was performed on the engine:
INSPECTED FUEL INJECTION PUMP. PUMP IS THE BOSCH P7100. PULLED FUEL PRESSURE PLATE AND RESET TO MAXIMUM FUEL SETTING. STARTED AND TESTED FOR PROPER FUEL AND TESTED FOR LEAKS. FOUND ALL OK.
CHECKED OUT TURBO GATE. REMOVED AND INSTALLED NEW RESTRICTION FITTING (90 DEGREE) AS NEEDED. COMPLETED INSTALLATION NOW AND TESTED BOOST PRESSURE. FOUND BOOST PRESSURE INCREASED BY 4-6 PSI. ROAD TESTED ALL OK.
The invoice shows 4.90 Hrs labor and $39.00 for the boost elbow.
I guess I should have researched this before hand, because now I'm wondering are there any negatives to this procedure.
Increasing fuel deliverey without increasing air flow (boost) is the surest way to toast your engine. By increasing the boost it leans out the mixture (good in a diesel). Sounds like a good mod if the fuel mileage increases.
Our ISC is an electronic controlled one so no fuel plate to change and the Banks SYSTEM works very well on ours.
Do you have a EGT (Exhaust Gas Temp) gauge? If not you should install one NOW and be sure it never shows much over 1,200°. If it does you risk melting a piston or two. With the ISC Banks system it's all automatic but so far I've never had it happen.
Deen - Vancouver, WA
'02 Dutch Star 4090 (41+', triple slide)
435/1200 ISC Cummins/Banks PowerPak
'08 Honda Civic/dolly
'05 Honda Odyssey/dolly
NRA Benefactor Life Member
FMCA f47302s, Life Member: Good Sam, Newmar DP Owners Group
51st yr of RV'ing
These are two very common mods for mechanical diesels.
Increasing fuel = more power.
Restriction fitting is a small tube fitting that restricts the pressure signal to the wastegate on your turbo. This makes the wastegate think your manifold pressure is lower than it really is. This pushes more air through the engine and improves efficiency and power (as long as you don't boost it too much, and a few other variables.
Now, the real weird thing here is that you will be about even. If he hadn't modified the injection pump settings you would have gotten better mileage with the old power levels. If they had instead advanced the injection pump (re-timed it) you would have gotten more power with the same mileage.
So if mileage was your main concern, he should not have increased fuel flow. maybe advanced it a bit.
I will assume you have an 8.3 Cummins. I made these same modifications to the 250hp engine I had in a 92 Dynasty some 12 years ago.
I definitely agree with Dean about installing an EGT gauge. Increasing fuel and boost WILL definitely result in higher exhaust temperatures, and those temperatures will be most critical in 5th gear at 2400 rpm plus. This is because that is the gear you are most likely to remain in for longer periods of time pulling grades, and therefore where the EGT readings will become most critical as they crawl up. In lower gears, you will find the shift-up occurs before these critical temperatures are reached, which instantly drops the EGT readings and starts the climb over again. Fifth was the only gear in which I was ever forced to back off on the throttle due to EGT temps getting to close for comfort.
Dean suggested 1200 degrees max. I agree, but it is important to understand that this is for a pre-turbo placed EGT probe. For probes placed after the turbo, the max temperature is 950 degrees. You will like the probe installed pre-turbo better because the gauge is far more responsive than post-turbo, which is very sluggish due to the turbo itself filtering the gas temps. Some people will argue that a pre-turbo prob could take out the turbo if the probe breaks, but I have never actually heard of that happening. I have heard worry-warts claiming so, but never any warts that could substantiate it. So for the more responsive gauge I recommend a pre-turbo probe installation.
And if you do see smoke on full accelleration, you need to back off that fuel plate (have the shop do it). When I first did mine, I was doing my very first 0 - 60 test, which had been 30 seconds previously. I hit 60 in 22 seconds and was thrilled. Then I happened to look in my rearview mirror and there was nothing there.........except a hugh cloud of black smoke. I played with that plate 10+ times after that until I got it just right. Final 0 - 60 was 24 seconds.
And just a comment on that change of restriction in the wastegate vacuum contol line. You could actually just plug off the line and throw away that wastegate, which is what I did. The most air you will ever pump is 30" psi, and then only at sea level. In other installations, like 500+hp Cummins marine engines using this same 8.3 block, they run turbos that exceed 40" without problem, and they do so because they have raw water cooling available to control temperatures. I have twin turbos on each of my twin Detroit 6V-53's (4 turbos in all)in my boat, and there are certainly no wastegates. These are 318 cubic inch engines, half the size of your Cummins, and they each put out 400hp, so uping the horsepower is not the issue with husky diesel blocks. It's all about controlling the heat, and a puny 30" turbo output on an 8.3 Cummins installed in a motorhome is actually ultra conservative (IF THE EGT'S ARE UNDER CONTROL).
I probably told you more than you ever wanted to know about this subject, so just enjoy your new found power ............. and get an EGT gauge!
StuartT wrote: I will assume you have an 8.3 Cummins. I made these same modifications to the 250hp engine I had in a 92 Dynasty some 12 years ago.
I definitely agree with Dean about installing an EGT gauge. Increasing fuel and boost WILL definitely result in higher exhaust temperatures, and those temperatures will be most critical in 5th gear at 2400 rpm plus. This is because that is the gear you are most likely to remain in for longer periods of time pulling grades, and therefore where the EGT readings will become most critical as they crawl up. In lower gears, you will find the shift-up occurs before these critical temperatures are reached, which instantly drops the EGT readings and starts the climb over again. Fifth was the only gear in which I was ever forced to back off on the throttle due to EGT temps getting to close for comfort.
Dean suggested 1200 degrees max. I agree, but it is important to understand that this is for a pre-turbo placed EGT probe. For probes placed after the turbo, the max temperature is 950 degrees. You will like the probe installed pre-turbo better because the gauge is far more responsive than post-turbo, which is very sluggish due to the turbo itself filtering the gas temps. Some people will argue that a pre-turbo prob could take out the turbo if the probe breaks, but I have never actually heard of that happening. I have heard worry-warts claiming so, but never any warts that could substantiate it. So for the more responsive gauge I recommend a pre-turbo probe installation.
And if you do see smoke on full accelleration, you need to back off that fuel plate (have the shop do it). When I first did mine, I was doing my very first 0 - 60 test, which had been 30 seconds previously. I hit 60 in 22 seconds and was thrilled. Then I happened to look in my rearview mirror and there was nothing there.........except a hugh cloud of black smoke. I played with that plate 10+ times after that until I got it just right. Final 0 - 60 was 24 seconds.
And just a comment on that change of restriction in the wastegate vacuum contol line. You could actually just plug off the line and throw away that wastegate, which is what I did. The most air you will ever pump is 30" psi, and then only at sea level. In other installations, like 500+hp Cummins marine engines using this same 8.3 block, they run turbos that exceed 40" without problem, and they do so because they have raw water cooling available to control temperatures. I have twin turbos on each of my twin Detroit 6V-53's (4 turbos in all)in my boat, and there are certainly no wastegates. These are 318 cubic inch engines, half the size of your Cummins, and they each put out 400hp, so uping the horsepower is not the issue with husky diesel blocks. It's all about controlling the heat, and a puny 30" turbo output on an 8.3 Cummins installed in a motorhome is actually ultra conservative (IF THE EGT'S ARE UNDER CONTROL).
I probably told you more than you ever wanted to know about this subject, so just enjoy your new found power ............. and get an EGT gauge!
You mentioned 2400 RPM and up. The 8.3, I believe is governed at 2200, at least the ISC. So, when the Banks install is done, do they turn that up from to 2200 to something higher?
You mentioned 2400 RPM and up. The 8.3, I believe is governed at 2200, at least the ISC. So, when the Banks install is done, do they turn that up from to 2200 to something higher?
Lug, not too sure that is correct. We had an 8.3 in our Ambassador and I think the cut-off was higher than that (but can't remember for sure). No doubt someone with an ISC will check and let us know. I seem to recall it was more like 2400 or 2500 rpm.
Don, Bev & Phil
07 Jayco 32SS on Kodiak May 07 Yahoo Kodiak Group
06 HR Amb 40PLQ ISC 330/950 9/05-5/07
04 Winnie Jrny 39W CAT C7 7/04-9/05)
00 Triple E Commander 5/03-5/04
Toad - 07 Tahoe LTZ 12/06 -
04 Colorado Z71 04- 06
Larry has a pre-ISC in that 94 Safari. It has Bosch mechanical fuel injection and the governed number is around 2800.
The ISC engine, on the other hand, developes it's maximum hp and torque at a lower rpm and is governed lower as well, 2400 or so. Funny, I have an ISC in my current moho and I can't remember the exact number. Someone else know???
* This post was
edited 08/13/08 08:19am by StuartT *
I did a similar mod on a '95 B5.9. In my case we replaced the fuel plate and boosted the turbo pressure. HP increase from 230 to an estimated 300hp. All I know it was very noticeable. I put many miles on this RV without any problems. I didn't notice any improvement in mpg.
Hey Stuart. 6V-53s are not that common is boats, I have a friend with them in a 50' Knight and Carver, very quiet running boat. What kind of boat have you got 6V-53s in.
You mentioned 2400 RPM and up. The 8.3, I believe is governed at 2200, at least the ISC. So, when the Banks install is done, do they turn that up from to 2200 to something higher?
Lug, not too sure that is correct. We had an 8.3 in our Ambassador and I think the cut-off was higher than that (but can't remember for sure). No doubt someone with an ISC will check and let us know. I seem to recall it was more like 2400 or 2500 rpm.
Don, I had an ISC 350 in '02, it was governed at 2200. The only time it would exceed that was during Pac Brake applications on steep grades. My question really is, does Banks Power Pack, or Stinger, increase this RPM speed. If so, I would think there is more cost involved in the long term than the intitial out lay.
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