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Old 10-01-2011, 08:52 PM   #1
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Question ISL 370 turbo boost

If any of you are ISL 370 owners, can you tell me what your max turbo boost is? Mine seems to be 24 psi, which seems low compared to what I see on an ISC. I can watch the boost on my Trip Tek monitor and it runs right up to 23.8, touches 24 or maybe even 24.2 and immediately cuts back to 23.6 again. Sure looks like t is being limited to that number.

I'm wondering if the factory limited the boost to keep the horsepower down to 370 rather than 400 in the other version of this same engine. I'm told the only difference between an ISL 370 and an ISL 400 is the ECM. Comments?


Please don't reply with your ISC turbo boost numbers. Different engine, different numbers, and not relevant here.
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Old 10-01-2011, 10:51 PM   #2
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There is a lot more difference between the ISC and the ISL other than the ECM.

I think you will find that 25 is a good number for boost. The way you get more HP is to dump in more fuel.
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Old 10-02-2011, 05:05 PM   #3
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I stated ISL 370 vs ISL 400 when I mentioned the ECM difference - not ISC. The ISC is an entirely different engine than the ISL - which I believe I also stated pretty clearly.

I've heard greater boost numbers for the ISL 400 and even the older ISL 350, e.g. 30-32 psi.. That's why I'm wondering what other ISL 370 owners are seeing (if they have a boost gauge or engine monitor).
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Old 10-03-2011, 02:02 PM   #4
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2004 ISL 370. Very seldom nudge 24psi of boost. Usually in the 23+ range for displayed boost, when in max power hill climbing mode.

The Cummins Cal Pacific Dyno test we paid for at purchase, indicated at the wheels 79% max power (going from memory, don't have paper work with me). The comment was that this was on the 'good side' of what we should expect to see at the wheels. 13K miles on the unit when this was done.

Interested in following this thread, to see what others are noting too...
Best,
Smitty
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Old 10-06-2011, 11:51 AM   #5
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Your results are the same as mine, Smitty. I'm pretty confident that the ECM is programmed that way. The ISL 370 also has a slightly different HP profile than the ISL 400. Both have the same 1200 lb-ft peak torque 1300 RPMs but the horsepower peak is at different RPMs. The 370 peaks at 1750 RPMS and levels off, while the 400 keeps on climbing to reach 400 hp @ 2100 RPM. That suggests to me that they apply more boost on the 400 so it can generate more power from the same block & pistons.
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Old 10-06-2011, 10:12 PM   #6
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I remember at a FMCA rally in Pomona years ago, Monaco was telling owners of the ISL 370 that they could have the ECM recalibrated to the new (at the time) 400 HP at no charge. Since I still had a ISC then, it didn't concern me. And, if they sold one of the 370 HP display coaches, they would have it recalibrated to 400 HP before delivery.

My current ISL 400 has reached 39.6 PSI of boost on the Aladdin. The picture below shows 38.4 boost. (It was hard to take a picture while driving and holding the camera still. So, it is a little blurry.)

Maybe a phone call to Cummins would let you know if you can uprate yours.

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Old 10-07-2011, 02:25 PM   #7
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Thanks Harry (Assume Harry!),

Most ISL 370 owners I've talked to, said very little seat of the pants difference by the re-flash.

The 08 vs 04, could be apples to oranges, due to all of the changes Cummins had to make for the new rules. Interesting that your boost reading is so high.

The 04 vintage ISL, seems to be an engine with little wiggle room for mild tweaking. For those that want just a bit more power (all that I'd like, is perhaps a 5-10% increase for hills and passing), the exhaust and intake air cleaners seem to be the only way to improve things. I ruled out the air cleaner shift, as my coach came with enough air cleaner air flow to feed the ISX - so no restriction on the intake end. May still do the Aero Turbine exhaust at a later date, as I see no down side to this, with the exception of a bit more noise.

I understand that larger injectors, propane injection, etc. - all will increase power. But I did not want to get into it that much, thinking that KISS is best. I'm still researching reprogramming (as that is what the bump to 400 is, a re-flash and change of parameters) of the ECU.

Not looking for a race up a hill! And I do understand that the Allison does not have as much torque handling as the 4000, and that anything I do - needs to be a balance between a bit more power, while still having a cool running, and non damaging situation for the engine. With the Silver Leaf, I can always back off, based upon real time readings.

Warranty is no longer a factor.

Best to all,
Smitty
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Old 10-07-2011, 07:57 PM   #8
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Anyway you know what the part # and serial # of your ECM is?
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Old 10-07-2011, 11:05 PM   #9
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Smitty,
I ordered my 2008 coach in March of 2007. At the time Monaco still had (3) 2006 ISL 400 in stock and I stipulated the 2006 pre DPF engine for the purchase. So, our apples and oranges are almost off the same tree. And they might be from the same tree if your Cummins is a CPL 1096.

I also installed a 50X50 Aeroturbine muffler, as I was able to buy one for $130. Not much performance improvement, but then I understood that going in. I checked the exhaust backpressure and had about 1.6 psi as I remember. Over 2 psi on a car is too much restriction. Too many variables to tell if the fuel mileage improved.
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Old 10-08-2011, 09:40 AM   #10
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Thanks Harry - Could stipulation on the ISL in your rig. That will make them much closer...

I suppose a call to Cummins would not hurt, and I can find what the max boost rate is suppose to be on our ISL.

I've assumed (yep, we know what that means) that when Cummins Cal Pacific did my pre purchase Dyno test, they would have let me know if we had a boost problem with the turbo. The at wheel power measurement, was reported to be very good, on the higher end of the scale. The tech said it was higher then he expected to see.

I'm not in a big rush on my search for a bit more power. I do check around from time to time, and keep coming up with results that not many products are available for this era ISL. I'm not real interested in propane injection, larger injectors, etc. May change on this in the future, especially for the propane injectors, as they've been around for along time. I like the ability to turn on the injector when needed, say when hill climbing. I'm quite content with the ISL370 in most driving situations. It was my choice to not keep looking for a big block Cat or Cummins, so no real regrets.

Variable Geometry Turbocharger (VG Turbo) by Holset, plus probably the lower number of RV's with this pre 2006 change ISL, are probably what keeps the aftermarket tweaking gang from investing the funds to develop products.

If anyone has had success finding a bit more power, safely, please share!

Best to all, have fun, be safe,
Smitty
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Old 10-08-2011, 10:32 AM   #11
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I cross posted this question on the Country Coach User Group on Yahoo. I copied a response from Mike, indicating the readings we are seeing are within range.
Best,
Smitty

Re: Question on ISL370 Turbo Boost readings

Smitty, I have an e-mail from John Wolf-Cummins Northwest - Coburg, OR,who for
years was the top liason for Cummins Engines with CC.

Quote from John based on my ISL 370 HP manufactured in mid 2002 installed in a
2003 Allure 1st Ave. "Boost should be 23-25PSI @ 100% throttle full load pulling
a hill, 1900-2000RPM. If you do not have a hill to test, put transmission in 4th
Gear, find a nice straight flat road, slowly accelerate until you have the
throttle pressed completely to the floor, verify nothing is limiting travel of
throttle pedal i.e. carpet, floor mat etc.

Now with 100% throttle applied, very softly apply service brake to pull the
engine rpm down to 1900rpm (peak horsepower). Record your boost pressure. Do not
brake for long as it will build heat in brakes.

If not to spec, have engine troubleshot for low power, Which would include
pressure testing intake system, inspecting turbo for damage, measuring intake
restriction etc."

Regards, Mike 03 Allure 1st Ave #30898 ISL370
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Old 10-08-2011, 02:38 PM   #12
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I guess that pretty well says that my 24 psi is normal for this engine (mine is a late 2003 engine in a 2004 chassis).

I inquired about an uprate back in 2007 and was told that the ECM would have to be replaced at a price somewhere around $2400 (I've forgotten the exact number - too much for the 30 hp gained). But that info did not come direct from Cummins, so don't consider it gospel.
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Old 10-08-2011, 03:57 PM   #13
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Your TripTek may NOT be displaying correctly.

For whatever reason, my TripTek (on an ISM) will only read a max of 30psi when the chassis gauge indicates sustained pressures up to 38psi. I am very sure they both pull from the same sensor (that is the engine ECM). I have no idea why the discrepancy, but I have always had it.

Hence, your TripTek displayed reading might actually be maxing out lower than the actual psi.

I'd get a second gauge opinion.
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Old 10-08-2011, 07:21 PM   #14
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36 to 38 on my ISM
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