Question about cruise control and turbocharged cars

"Nibbles" (nibbles) 11/01/2013 at 08:41 • Filed to: COTD QOTH, turbo, boostlopnik

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Last eve's COTD article got me thinking. Do today's turbocharged cars allow for any decent boost while on cruise control? My '87 Saab has a feature that, when cruise is activated, limits boost to base levels (less than 5 PSI if not modified). It works great for keeping the fuel economy up while cruising and keeps surges to a minimum. Do new FI cars provide this functionality, or is full boost available while in cruise?

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 08:49

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Interesting thought!

I need to get a bluetooth dongle for my obd port so I can test this on the SHO. I really don't know how boost behaves in cruise!

Ford would've been stupid not to put the feature in! Because that would indeed save quite a bit of fuel. Especially on hilly roads.

I wish cruise controls were smart like that, when they sense a hill, let the car drop 2 or 3 mph, it would save so much money.

I would love to be able to set my cruise to + or - 3mph.

Jayhawk Jake > Nibbles 11/01/2013 at 08:50

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Well, mine doesn't have a boost gauge so I don't know how much boost is going on cruise, but it's definitely boosting a little bit. It sounds the same as when cruise control is off, but that's not exactly a scientific measurement.

deekster_caddy > Nibbles 11/01/2013 at 08:53

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I'd have to install a boost gauge of some kind to answer confidently. Our '08 VW Passat Wagon 2.0T 6spd has no problem holding high speeds going uphill with CC on. I can't say exactly how high, but let's just say comfortably above the limit...

Nibbles > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 08:55

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In theory, this wouldn't be a hard thing to implement especially on vehicles with onboard GPS. Attach an accelerometer to the system as well. Use the GPS's elevation data in correlation with map geographical data, and use the accelerometer to calculate the throttle position change before / during / after the hill.

Tom McParland > Nibbles 11/01/2013 at 08:56

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Excellent question, I am curious to follow this thread and see what others say. Having had both a supercharged car ('04 Cooper S) and a turbocharged car (05' Legacy GT) I didn't notice much in terms of boost difference in cruise. Of course the LGT had a lot of torque (about 250) so the power was always ready.

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 08:59

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That would be awesome, I bet so many people would pick up MPG's! I think the problem with it is, are cars without this system would get really annoyed by the constantly changing speeds of these cars. So perhaps they also need adaptive cruise control to become part of the equation, so that the system doesn't kick in during heavy traffic situations.

ColoradoTaco > Nibbles 11/01/2013 at 09:00

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I have a boost gauge (all turbo cars should) and I will see boost in cruise, usually when the load increases and the car wants to maintain its speed. I'd imagine I'd never see full boost unless on a very steep hill, but then the mountain roads don't lend themselves to much cc usage. Full boost on my S4 is 18psi, stock is 9-10 :)

Meatcoma > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 09:01

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You can monitor this with torque app(free) and a cheap odbII connector with bluetooth. As long as it works with your car. You can monitor the boost continuously.

DocWalt > ColoradoTaco 11/01/2013 at 09:03

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Yup, I've also seen boost in cruise control.

Nibbles > Meatcoma 11/01/2013 at 09:04

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You can also monitor boost continually by installing a vacuum-actuated boost gauge ;)

Yowen - not necessarily not spaghetti and meatballs > Meatcoma 11/01/2013 at 09:05

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this is why I mentioned I should get a bluetooth dongle for my obd port, lol.

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 09:05

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haha yes, indeed, but I've not yet seen an install on an SHO where I say to myself "I would do that to my car".

Nibbles > deekster_caddy 11/01/2013 at 09:05

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Boost gauges are seriously the best things. I don't understand how so many people are saying their new car didn't come with any way to monitor pressure. This should really be a factory default for FI cars. It means so much to have that information readily available.

Nibbles > ColoradoTaco 11/01/2013 at 09:08

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You should test out my question for science .

I just want to know if your car can get over base boost while in cruise control. Even if you set cruise then manually accelerate, it (in theory) should not kick cc out so you would be restricted to any cc-related boost policies, if they exist.

Nibbles > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 09:10

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Just looked at SHO interior pics. Your interior doesn't really have much usable space for modifications, does it

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 09:13

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Haha, not really. But you just got me thinking.... It has 4 cup holders in the center console, 2 sets of 2, each hidden by one of those click panels that rotate out of the way to reveal your cup holder. I could sacrifice one for a boost gauge, lol. This way I'd also score better on the Jalop meter! Because I eliminated a cup holder, lololol.

Nibbles > DocWalt 11/01/2013 at 09:13

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But have you seen full boost?

Nibbles > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 09:16

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Idea

Install boost gauge in one of the cup holders, on some sort of extendable platform. That way when you open the cup holder panel, the gauge silently, smoothly raises out of the cup holder and into your periphery

Patent pending

DocWalt > Nibbles 11/01/2013 at 09:17

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Nope, but considering the Evo X was known for blowing up at high loads in 5th, I was not too interested in finding out if it would ever hit full boost.

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 09:20

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That would be awesome! Haha.
Imagine it laying flat in the cup hold, but while it raises up, it also rotates for easier viewing, making it even sweeter! I just need two motorized antennas at slightly different lengths, lol.

Nibbles > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 09:31

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Don't even need motors. Just cams in the shafts, or a pin and groove. It could all be driven smoothly be resistance in the spring loaded mechanism (like those fancy fold-out cupholders in newer Saabs)

Or, it could be motorized. Push a button on the dash, the cupholder opens and the gauge slides up. Push it again, and the gauge silently returns to resting position and the panel automatically closes

PATENTPENDINGPATENTPENDINGPATENTPENDING

KusabiSensei - Captain of the Toronto Maple Leafs > Nibbles 11/01/2013 at 09:38

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I would need a gauge on my E300 Turbodiesel to know for sure.

However, I do notice a bit of boost which comes online to deal with hills and such. The computer generally locks up the transmission a tad more (The late 90s 722.6 5AT torque converter doesn't completely lock up by design) to keep the revs constant.

But I tend not to use the cruise, since I get better mileage without it.

Yowen - not necessarily not spaghetti and meatballs > Nibbles 11/01/2013 at 09:40

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That would be awesome too, that way, if well-built, it would be completely silent.

Don't boost gauges also tend to bring a little bit of turbo woosh into the cabin?

WOOOSHWOOOSHWOOOSHWOOOOSH

Nibbles > Yowen - not necessarily not spaghetti and meatballs 11/01/2013 at 09:43

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Hmm

Can't say I've ever noticed that, but that could also be because the turbo is loud enough from the outside as it is lol

May have to include an "induction ambiance generator" at extra cost

ryjacobs > Nibbles 11/01/2013 at 09:57

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The other day I had cruise on somewhere between 65-70 mph in 6th gear ('11 STi). Going up a hill for some reason boost hit about 11psi so I turned off cruise. A few psi on hills in high gear doesn't bother me, but that one was a little high.

Nibbles > ryjacobs 11/01/2013 at 09:58

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Good info, thanks!

Do you know what max PSI is in your car, as a reference point? Being an STi, I would imagine it's more than 11, but I don't really know.

ryjacobs > Nibbles 11/01/2013 at 10:08

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The car is currently tuned, so target boost is usually somewhere in the range of 19-20.25 psi in 3rd or 4th gear. I may be mistaken, but I believe the stock tune target boost is around 14.7 psi.

Nibbles > ryjacobs 11/01/2013 at 10:15

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Cool, thanks

When you cut the cruise, was it peaking at 11 PSI, or do you think it would have continued to climb?

Sorry for the questions, but I'm actually going to present data if I get enough to quantify

ryjacobs > Nibbles 11/01/2013 at 10:43

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I can't confirm at this point, but I'm sure if more throttle was given, it would have gone up more. If I were to go WOT in 6th gear, I'm sure target boost is lower than in other gears, but maybe not.

From what I understand, at least in my car, it isn't the best idea to be hitting higher boost levels in "cruising" gears. I didn't check the AFRs to see if it was leaning out or anything either - it was more of a "hey, you don't need that much power to make it up this hill!", so I took over and didn't think much of it otherwise.

Normally, on inclines with cruise on, I'll see 4-5psi at the most. I can't recall what it did when the car was all OEM parts/tune.