Mechanical boost controller vs electronic and effect on fuel economy

[jeffreydmet]

I have been playing around with changing the boost on my truck (99 K3500 drw c/c). I put a gage on the vacuum line to the waste gate to see what the computer is trying to make it do. I have noticed when the truck is not pulling hard like cruising on level interstate the computer releases most of the vacuum on the waste gate. Under the same conditions if I bypass the solenoid it will cruise with nearly 10 psi boost.

I am thinking those of you with the Turbomaster or similar waste gate controller are running with higher boost under low loads than the electronic models. Am I right about this? My thoughts are that any time air is throttled such as on the waste gate energy is being wasted.

Does anyone know how the electronic control vs the turbomaster affects the fuel economy? I know some of you have replaced your electronic ones with mechanical.

[Cowracer]

I have a Turbomaster with the Heath chip, and while my fuel economy has not improved a whit, the performance gains were remarkable.

On electronic trucks like yours, you cannot simply increase boost alone. The computer will see an overboost condition and set a code. Heath programs his chips to allow extra boost with the turbomaster. Kennedy programs his chips to make more boost with the stock vacuum wastegate setup

Either is a good choice.

Tim

[turbovair]

Ronniejoe, are you there?

[rjschoolcraft]

Yes, I'm here. I had been gone for 4 days, though.

Jeffrey, you are correct in surmizing that the TurboMaster can give higher boost at low power cruise conditions than the electronic control in stock trim. However, a simple chip change (for the OBD1 trucks) or an electronic boost control will change all of that. For instance, with the stock program, my Suburban would run at zero psi boost when cruising at 75 mph solo. Now it runs at 6-7 psi depending on the conditions.

In stock trim, towing my trailer at 70 mph, I would see boost levels of about 6-7 psi and egt's of around 1350-1400F. It was a struggle to maintain that speed. Now, I see boost levels of 9-11 psi (depending on conditions) and can just cruise along at that speed with egt usually under 1000F.

So, the electronic system can work to give good performance. In fact, I think it gives me more flexibility. For instance (and Kennedy has commented on this before), ebp can spike due to transients...the TurboMaster will open the gate and dump pressure during these spikes (as long as they are of sufficient duration to allow the linkage and spring to react). The vacuum controlled gate will stay closed during these spikes which helps to spool the turbo up more quickly.

In fact, I would think that the vacuum controlled gate could actually close at times the mechanically controlled one couldn't to aid in such transients...if the program commanded it.

Furthermore, I still think the electronics give you more for altitude compensation. This is a complex set of circumstances and I haven't thought it all the way through yet, but it seems that the mechanical control can not give more boost at altitude while the electronics can. Again, I'm not completely certain of that statement... I do know that my truck will make more boost (gage pressure) at high elevation than at low... I've seen it.

My question for those with mechanical waste gate controls is: What happens with your boost level at high rpm? Say you're climbing a mountain, running in 3rd gear, foot to the floor and rpm climbs through 2500 and heads for 3400. What does your boost do under these conditions?

[Cowracer]

Ronniejoe-

I cant comment on the mountains, but on the hills here, my boost holds at 9psi and on a downshift it has just a quick spike to 10. For most instances, the boost stays resonably level.

I dont understand how an electronic setup can have any advantages over mechanical at high altitude. 9 psi is 9 psi whether you are in denver or death valley.

Tim

[rjschoolcraft]

True, if your talking about gage pressure...

Gage pressure is referenced to whatever ambient pressure is at that time and location. So, 9 psi in Denver is ~21.2 psi absolute, while 9 psi in Death Valley is ~23.8 psi absolute on a standard day.

With this in mind, 9 psi boost in Denver doesn't put as many air molecules in the cylinder as 9 psi boost in Death Valley... So there's less there for combustion.

The electronic trucks sense the atmospheric pressure (the BARO sensor) and adjust boost accordingly. What I think (but I'm not sure of yet) is that the electronic trucks will run with higher exhaust back pressure (gage) at high elevation than at sea level. The TurboMaster cannot do that.

[Jim P]

My homemade turbomaster will do that, all you have to do is jump out, open the hood and crank the adjustment nut down a little tighter ;)

My boost comes up to 15 psi at about 1500 rpm and stays steady up to 3400 as long as you don't let off the throttle.

Before making my boost controler I tried to get my vacuum system to work but I think the wastegate solenoid was bad. I tried hooking the vacuum line from the vacuum pump straight to the wastegate actuator but I could only get about 10 psi of boost. I don't know if wastegate actuator just is not strong enough or if the vacuum pump was weak. I do know that with the homemade turbomaster, that I can get the boost up to 20 psi if I crank down the adjuster a little tighter. I haven't tried it but I think I could crank the boost up to 25 psi if I wanted to.

[rjschoolcraft]

I'm sure you can. That's the nice thing about a TurboMaster... But then, you can do that with the electronic boost control as well.

When I towed my current trailer out west with my old 67 C10 Chevy pickup with home built 350 gasser, I stopped in Gallup, NM for the night. That evening, I pulled the front float bowl off the Holley 600, and put three sizes smaller jets in the primaries. This solved my rich mixture problem at elevation. On the way back, I stopped in Ogallala, NE and put the first jets back in.

That's the nice thing about this electronically controlled truck. It does all of those adjustments for me...automatically. ;)

[autocrosser]

I have both the electronic and mechanical boos controllers. The only difference is that when your vacuum system starts to go bad you have to fix it with the electronic one.

With the mechanical boost controller you can take the vac pump off and use a belt for a earlier model that didn't have the electronic pump.

Neither one seems to have any advantage over the other as far as the amount of boost that can be generated. I haven't seen any codes set with the mechanical one set for 13lbs. I do see one once in awhile set with the electronic one but they clear after a bit.

Go for the mechanical one it's a lot simpler.

[rjschoolcraft]

So are horse drawn carriages and dog sleds! smile.gif