Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 08, 2025 ...

Turbo Boost Pressure

May 21, 2025, 12:23:28 pm

Driving up hills I watch the turbo boost pressure and at 100% load I see 23 PSI max. on my VMSPC. Just wondering if that is what you all see from your ISL 400 engines....

Thanks, Tyson

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Re: Turbo Boost Pressure

Reply #1 – May 21, 2025, 04:10:20 pm

Boost Pressure for ISL 400 with CAPS

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Re: Turbo Boost Pressure

Reply #2 – May 21, 2025, 05:19:37 pm

Driving up hills at 100% load, @ 1200 torque and 400 hp. I see a max of 24.5 to 25 PSI max. on my VMSPC it does seem to vary a little when on long grades making pulls. Never duplicates the max boost pressure on the same grade pull, I imagine it's do to ambient air temperature and the air density, condition of air filter ect..

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Re: Turbo Boost Pressure

Reply #3 – May 23, 2025, 11:41:31 am

Tyson, When I bought my coach in 2019 on my way home I kept thinking it just didn't feel like it ran like it should. I stopped at the first Napa store I came to and checked the air filter, it was plugged. They had one in stock, made a big difference but still felt lacking. When I installed the Blufire I was only seeing 17 lbs boost. I got to poking around looking at the waste gate and just happened to notice the 4" boost hose right next to the turbo had a hole burnt in it the size of 4 fingers to pass through. replaced that and heat wrapped and saw around 22-23. The CAC had been repaired in a few places so I set up plugs to pressurize, I still had some large leaks. Replaced the CAC and now have seen a quick jump to 27 with normal from 25-26 Psi. Jim.   

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Re: Turbo Boost Pressure

Reply #4 – May 23, 2025, 04:08:37 pm

Thanks Jim I'll give it a real good inspection and tighten the clamps when I get home.  I do see around 1100 torque and right at the edge of 400hp shown so I'm not losing much. I'm surprised at the difference between the CAP and Rail fuel system in terms of boost pressure and don't understand the relationship.

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