More boost via boost controller...
 

Hi gang,

I'm new to the bonneville gang and the 3.8 supercharged gang, too. I've been playing with turbo cars for quite some time...

Anyway, I was going over the mods that people around here discuss, and wanted to ask...

From what I've learned, the maximum boost is controlled via the "bypass valve", which poking around mine is actuated by both vacuum (for "in cruise vacuum" control) and by boost, on the other side of the diaphragm. It's identical to the turbo wastegate actuator setup on 84 Dodge/Chrysler Turbo 1 cars, and to the 89-90 Dodge VNT turbo 4 vane actuators.

Most people seem to increase their boost level via a smaller pulley on the supercharger, and nothing else. I think that means that the supercharger will spin fast enough to kind of saturate the bypass opening, and raising the boost.

Has anyone (or have I missed it?) used a simple bleed or ball and spring type valve on the pressure side of the bypass actuator to raise the boost?

I would *think* that keeping the bigger pulley on and raising the boost to, say, 11psi, would make more power than a small pulley pushing to 11psi for two reasons: #1 less load on the crank, #2 less heat (adiabatic efficiency type heat) at lower supercharger RPMs.

The flip side would be that with the larger pulley you will reach peak boost at a higher RPM than with a smaller pulley, but I know on mine even with the big pulley boost comes on plenty quick.

Is anyone doing this? Any comments?

Thanks, I'm trying to learn about my new toy :)

Dan Culkin
86 Daytona Turbo Z CS intercooled
89 Shelby CSX VNT intercooled
89 Omni 2.5L turbo intercooled
92 Spirit R/T 16V DOHC intercooled
95 Bonneville SSEi <========NEW TOY!
98 Grand Cherokee 5.9 Limited

Interesting concept.. always thought of just changing pulleys only. Sorry I don't enough to help u out with that.. but would be more than interested in the outcome.. a colder charge ( from stock pulley compared to smaller pulley ) would definitely be better, and I wouldn't mind keeping the stock look. Most people that run smaller pulley will usually run into a higher KR ( in mostly stock form ).. I wonder would this bypass that problem, and still allow you to run a higher boost.

Most people that run smaller pulley will usually run into a higher KR ( in mostly stock form ).. I wonder would this bypass that problem, and still allow you to run a higher boost.[/quote]

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KR? What is KR?

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This is something I'm going to try out, but was curious as to whether anyone is already doing it and could give me a heads up on any problems they ran into.

Thanks!

Dan

Oh, Knock Retard, sorry, I didn't catch the meaning until after I posted.

Yes, if it is a cooler charge, it should be an improvement in reducing/eliminating KR.

Good old 94 Octane will help there, too!

Dan

My understanding is the bypass valve is fully open at WOT. Is this true? WOT is where I want maximum boost, anyway. With a mofified intake, in cool or damp weather (or with water injection :wink: ) I'm hitting 9.5lbs of boost. Eaton sez these things are rated for 10.......yes we can get more, but it sounds to me like the bypass valve is working optimally. I'm open for suggestions, Dan, I'd like to see if and when that sucker opens up fully. I could be wrong, and it WOULD be the first time, but if I am, I'll deny it.

Play around with it, and if you figure something out, let us know!

]My understanding is the bypass valve is fully open at WOT. Is this true?
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From what I can tell, I think this is true at higher RPMs ... the boost shoots up to 7 at maybe 2500RPM, and stays there until maybe 4500 RPM, and then creeps up to about 9 or so. That would mean that the bypass is open partly by 2600RPM, and opening more and more until it's all the way open at 4500RPM. After 4500 RPM, it won't open any more, but the SC is continuing to want to flow more air, so it creeps up.

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WOT is where I want maximum boost, anyway. With a mofified intake, in cool or damp weather (or with water injection :wink: ) I'm hitting 9.5lbs of boost. Eaton sez these things are rated for 10.......
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Well, sure, Garrett also tells me that it's useless to run more than 15psi on a 2.5L motor, but my Omni sure likes 22psi an awful lot (it is intercooled...)!

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yes we can get more, but it sounds to me like the bypass valve is working optimally. I'm open for suggestions, Dan, I'd like to see if and when that sucker opens up fully.

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By the bypass being fully open, that would mean that that is the *minimum* boost the system is able to run, no?

If at (for example) 4000 RPM, if to run 7psi it's 15^ open ... if you altered the pressure to the high side of the diaphragm so that the bypass was only open maybe 8^, perhaps you'd be at 10psi.

I mean, if the bypass were fully open all the time, I would expect to see the boost be very low in low RPMs, and continue to creep up with RPM. In the case of my car, I'd guess it'd be something like 2psi at 2500RPM, 4psi at 3300RPM, 6psi at 4100RPM, 8psi at 4900RPM...

Does this make any sense?

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I could be wrong, and it WOULD be the first time, but if I am, I'll deny it.
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Oh Geez!!!! I'm wrong frequently, but occasionally get a light bulb that stays on for a little while :)

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Play around with it, and if you figure something out, let us know![/quote]

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Will do!

Just a side note, by using a smaller pulley, you'd expect the bypass to be completely open by a much lower RPM ...

Is it correct that the computer/LM/whatever controls one or two "vacuum" solenoids to the bypass actuator?

Thanks again!

Dan

Guys:

On the L67 engine, the boost bypass valve is designed to bypass boost backwards around the supercharger when no boost is wanted. The valve is open in Park, Neutral and during deceleration for example.

Our valves only have two positions - open and closed. Open means most or all the boost is being dumped backwards around the supercharger. Closed means all boost goes into your lower intake manifold.

Adjusting this valve will make no difference in performance whatsoever, unless it happened to be adjusted incorrectly from the factory. If you want more boost, you've got to go with a larger supercharger or a smaller supercharger pulley.

Hope this helps.

Scott

The man has spoken! Thanks for the info Scott, I was wondering about that. :D

On the L67 engine, the boost bypass valve is designed to bypass boost backwards around the supercharger when no boost is wanted. The valve is open in Park, Neutral and during deceleration for example.

Our valves only have two positions - open and closed. Open means most or all the boost is being dumped backwards around the supercharger. Closed means all boost goes into your lower intake manifold.

Adjusting this valve will make no difference in performance whatsoever, unless it happened to be adjusted incorrectly from the factory. If you want more boost, you've got to go with a larger supercharger or a smaller supercharger pulley.

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And this is almost *EXACTLY* what I found when I played with it this morning!

The top port on the actuator is the vacuum side, the bottom (with the real sharp triangle looking vacuum hose out of the solenoid) is the "pressure side".

This morning I unhooked the "pressure" side of it, and put a manual boost controller on it, and went for a ride. It produced a perfect and stable ... 4psi. Eh? Turned up the boost controller, and got a perfect and steady 6psi. Hmmm ... simply unplugged the high pressure side of the cannister, and good old 7psi!

Just to convince myself that the bypass wasn't being blown open, I routed the manifold pressure right into the *vacuum* side of the cannister, i.e. having it press the bypass closed. Same good old 7psi!

Thanks for the input! I guess what I've come up with is a perfect way to *lower* your boost, LOL! Could be good if you wanted to install a "high boost / low boost" switch ... in other words, use a vacuum solenoid connected to a toggle switch for inside the car. With your small pulley on the supercharger, if you switch the solenoid, it'll go between the "boost controller" for low boost, and the normal route for high boost.

So why is the pressure side of the bypass actuator there anyway? Is it for traction control, and/or limp in modes?

Thanks Scott!

Dan

Leave it to Mr. Blowzilla to humble us! Scott, you need to spend more time around here :D