High boost pressures at interstate speeds

[brandongarnold02]

I bought a K3500 about a year ago. Had some major electrical issues so ended up converting it to a DB2 pump and manual wastegate. I turn the pump up some before installing it and found it smoke a bit to much so turned it back down some. It seemed to smoke some off the line and under acceleration. After owning it a yeah I have not had it on the interstate much but the few times I have the boost has been about 7-8 psi at about 65mph which seems to me a bit high. This truck has 4.10 gears also so it is turning pretty high rpm. Would turning the pump down some more lower my boost pressure at cruise speed or does this have no affect on boost at a steady speed?

[sctrailrider]

Doubt it ..... the stock GM turbo is small and at around 65-70 is at it's worst... these were designed for slower speeds, so the faster you go the more cruse boost you will have.

A larger / different turbo would let it breath better through out the rpm range and give lower cruse boost.

How are you working the wastgate....

[brandongarnold02]

I have a homemade manual wastegate set around 10 psi

I thought a larger turbo may be my answer. I figured the boost I am running on the highway now may be harder on the engine than if it dropped to about 3 at cruise speeds. I don't drive the truck much and it's mostly around town but when I get in the interstate it kind of make me wonder if this is safe.

[DennisG01]

Since you have a manually controlled wastegate, see what the MAX boost is at a few different RPM's and MPH's. If I remember correctly, the max you want to see on a non-modded 6.5 is somewhere around 12psi? Someone correct me if I'm wrong, there. I would start by finding your MAX, and then go from there.

[DennisG01]

Looks like we were posting at the same time...

It's been a while since I used a manual wastegate, but if you're max is 10psi, then what you're running on the highway seems too high for the speeds you're going. Do you have a really heavy load or are you towing a good sized trailer? I wonder if something else isn't causing you to have to be heavy on the throttle?

[brandongarnold02]

I am talking about unloaded on flat interstate. One thing I forgot to mention was I have the NV4500 and I turn about 2500 RPM at 65mph. It will produce well over 10 psi of boost when the wastegate is cranked down. just have it backed off to 10.

[DennisG01]

You're turning about 400 RPM's (maybe a bit more) higher than I do at that speed with my auto and 3.73. Maybe that higher RPM explains it all? How does it drive? Does the engine seem happy and very little smoke (once it's warmed up)?

[sctrailrider]

My 93 CCLB is the same as yours, same rpm, mine cruising at 70 is 5-7 on flat ground... sounds normal to me...

[brandongarnold02]

Well I may just not worry about it much then. I thought it might be a little high.

[a5150nut]

I am talking about unloaded on flat interstate. One thing I forgot to mention was I have the NV4500 and I turn about 2500 RPM at 65mph. It will produce well over 10 psi of boost when the wastegate is cranked down. just have it backed off to 10.

My 94 K2500 with 5 speed with boost fooler would run 2 1/2 to 3 1/2 lbs at 70/75 on flat ground.

When you start getting above 10 lbs the added boost is lost to heat gains.

[brandongarnold02]

What gear ratio did you have?

[a5150nut]

410 with 285/85/16 tires so effective gear ratio was 3.73