The definitive ST170 VVT Information....

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Matt@ME
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The definitive ST170 VVT Information....

Postby Matt@ME » Tue Feb 25, 2014 9:00 pm

After reading countless (mostly incorrect) posts on countless forums about how the secretive VVT on the Ford ST170 works, and how different methods of control with systems that can't really control it properly effect the power, we took it upon ourselves to create a standalone, mappable VVT controller specifically for the ST170 Zetec engine...

First lets first get some recorded, proven facts out there, all research carried out by us, on the dyno:

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1. The solenoid is driven by 12v (switched via PWM to ground).
2. The cam swings approximately 45 degrees, and rests 'fully retarded'.
3. It is controlled by the Ford ECU.
4. Simply driving it with a PWM freq. will not work as oil pressure/temp/wear etc will effect the VVT valves flow, and hence cam position.
5. The Ford ECU monitors the cam position in relation to the crank position and then uses a PID control loop to Adjust the PWM duty to reach the desired cam angle, looked up in a map that is defined AT LEAST by RPMxLOAD.
6. VVT actuation does not begin until at least 1300 RPM.

With this in mind, we devised our controller, and the hardware and cam/crank decoding algorithms so we could track the position of the cams relative to each other. Then we did a few runs on the dyno, and the graphs can be seen below:

The following shows CAM ANGLE in relation to CRANK (240* is resting, fully advanced is approx 180*) as RPM increases from 1500 to 7000... very interesting...

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What is worth noting is that control strategies such as 'turning the VVT solenoid fully on at 1500rpm' or other such bodges are NOT going to give the results that are needed. The cam is clearly shown to fully advance and then begin to taper back as RPM increases, with some other points we have decided for now to keep to ourselves ;)

With this in mind it is clear to see that our system delivers higher torque at ALL points in the rev range as we can precisely position the cam (and map it to other modifications such as exhaust and intake etc) and get THE best from the engine, and not compromise with a simple 'RPM switch point'.

Stay tuned for some more info!

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Part 2: On the Dyno Again....

So now we return to the rollers, this time we are going to do some definitive testing showing what is what. We are using for this our basic OEM St170 Focus bought for this project, so lets start with a base run in OEM configuration, note the horsepower... no people your ST170 is not and never was 170bhp...

For all graphs, OEM is in GREEN and the changed/test run is in RED. The dotted line relates to the right axis (torque) and the other line relates to flywheel horsepower (left axis)


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Fig 1: OEM VVT Control vs VVT OFF (Fully Retarted/resting position)

As can be seen in Fig 1, there is massive lack of power across the rev range with some losses of torque in the region of 50 lbs/ft... so that's obviously a NO GO method of setting up your VVT.

The next, and very common method is to use a programmable output on your ECU and turn the VVT on fully at a defined RPM, in this case we are going to go for the 'forum accepted' RPM of 2250:

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Fig 2: Turning the VVT solenoid fully on at 2250rpm.

This going to cost a little over £5 for a relay and of course an ECU that can do it as well as a bit of wiring, but ok, so this time we get something a little better... sort of...

We lack torque at the get go, and generally we see a lack of power getting proportionately worse as RPM increases... so we get rubbish peak power, and an almost OEM bottom end torque... not the best compromise, but the most chosen one when tuning ST170s...

So what else can we do without a mappable VVT Controller? Well, we can choose to lock the cams mechanically at a set point, some say 22* advance, some say 33*, some quote a number that is not even attainable, so its probably a good idea, using our controller to 'set' a locked cam potision, not taking into account any mapping, just hold at X degress of advance for the whole power run. Here are the sequence of graphs at 10 degree intervals of cam advance...

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Fig 3: 10 degrees fixed advance (OEM in green)

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Fig 4: 20 degrees fixed advance (OEM in green)


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Fig 5: 30 degrees fixed advance (OEM in green)


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Fig 6: 40 degress fixed advance (OEM in green)


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Fig 7: 50 degrees (maximum) fixed advance (OEM in green)

Okay so looking at this we can see that if you are going to lock your cam into a position, aim for approx 40* advance (fig 6). That's the 'average' best, and I say best if you are willing to live with a lot less lower bottom end torque, poor idle/emissions, and a fluffy top end/peak power. Note that in Figure 3 (30* advanced) we actually IMPROVE on the OEM power output at the RPM range 5500 onwards...

Of course this is going to cost something like £100+ to get the VVT lockout hardware, then the time to fit the hardware, change the belt, DTI the cam angle (and the tools and know how to do so).... the list goes on...

What we really need to do is change the cam angle based on in this case RPM alone to give us the best of 'all' worlds. Luckily, here's a graph we made earlier of all runs overlaid...

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Fig 8: VVT locked positions against OEM VVT (RED)

Now lets go along the highest torque line and pick the curve that best represents the most torque at that point/range and punch those numbers into our VVT controller....

We need to run (RPM -> CAM ADVANCE (degress))
0-1000 -> 0*
1000-2000 -> 50*
2000-3000 -> 40*
3000-4000 -> 50*
4000-5000 -> 30*
5000-5500 -> 20*
6000+ _> 10*

FURTHER DEVELOPMENTS: Mapping Software and PID Tuning...

Following on, we now have a nice mapping environment for tuning and developing our VVT system:

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As you can see we have loaded in our OEM values, and using the datalogging features of the software we have recorded the Actual_advance and Required_Advance so we can start to tune our PID algorithm. After a few tweaks, we have currently got to this point....

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Good tracking with a max error when rapid angle changes are requested of around 7 degrees, that settles almost instantly... certainly as good as OEM response of the cam!


Final graph coming soon....

Remember that all of these results are based on a factory ST170 Focus running OEM management, we have simply disconnected the VVT solenoid, tapped in our system to the cam and crank sensors and plugged into the VVT solenoid with our controller. God knows what the factory ecu is doing fuelling and ignition wise whilst it loses control of the cam, but we can all agree this is the WORST CASE improvements to be had over the current methods of VVT RPM switch on and VVT Lockout using our mappable VVT controller...

Our controller is also 3D, so we can actually map it via throttle also, giving even more gains..... more data to follow on a nice Mk1 Escort fitted with a NODIZ Powered St170 on Bike Carbs... stay tuned...

The cost? £240inc. And time to fit? Well if you go with a system from Chester Sports Cars you get a fully click-n-go loom, so maybe 30 minutes to fit, and its already basemapped, so that's immediate, safe gains with no intrusion into the engines timing belt area...
Last edited by Matt@ME on Sun Mar 09, 2014 1:13 pm, edited 12 times in total.
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Re: The definitive ST170 VVT Information....

Postby Stoxs » Tue Feb 25, 2014 10:23 pm

wow.

Whos a cleaver boy then!

this looks the dogs danglies Matt

With a mappable ignition timing and this mappable on the inlet cam any future changes to engine spec should easly be able to tweak to max performance.

I thnk i might need to go find another st170 engine before they are all gone!

keep us posted cheers

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Re: The definitive ST170 VVT Information....

Postby Alex@ME » Tue Feb 25, 2014 11:07 pm

Matt@ME wrote:What is worth noting is that control strategies such as 'turning the VVT solenoid fully on at 1500rpm' or other such bodges are NOT going to give the results that are needed. The cam is clearly shown to fully advance and then begin to taper back as RPM increases, with some other points we have decided for now to keep to ourselves ;)


It's worth noting that even the more advanced systems only do a PWM-duty map based on load and RPM, something which is impossible to get working properly since the cam movement would be "all over the place".
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Re: The definitive ST170 VVT Information....

Postby Matt@ME » Thu Feb 27, 2014 4:37 pm

More information added to first post :)
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Stoxs
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Re: The definitive ST170 VVT Information....

Postby Stoxs » Thu Feb 27, 2014 11:04 pm

well that has put everything anyone has said about VVT control into one pot!

that is superb really interesting read.
thanks Matt

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Re: The definitive ST170 VVT Information....

Postby Matt@ME » Sun Mar 09, 2014 8:05 pm

Top post updated :)
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Re: The definitive ST170 VVT Information....

Postby Matt@ME » Tue Mar 11, 2014 12:33 pm

The results are in...

We carried out the testing on this Mk1, fitted with 6R carbs and a NODIZ for ignition management...

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The below are the AMAZING RESULTS. The RED is the normal switch on at 1500rpm Method, the BLUE line is running the VVTPro with a factory VVT advance curve. We never did any mapping, just plugged it in..

10ft/lbs gain for the mjaority of the graoh, with even more gains at the end, and 21bhp overall power gain...

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Stoxs
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Re: The definitive ST170 VVT Information....

Postby Stoxs » Tue Mar 11, 2014 9:05 pm

oooooooooooo
sounds like music to my ears!!!

This is really looking excellent matt.
cant wait to test the difference . Mine is currentlly fully advanced with a dash mounted switch!!! :oops:

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Re: The definitive ST170 VVT Information....

Postby Lukozade » Sun Apr 27, 2014 10:14 am

I've just bought vvt pro from you and it turned up the other day. Looks great, its a nice and compact unit too. I will be installing it in a few weeks when my engine goes in, very much looking forward to getting it up and running :geek:

Just curious (and for my own benefit), do you know a more detailed spec of the st170 engine in the mk2 escort? I'll be running bike carbs and megajolt on mine with a few other modifications and upgrades and am interested to know how much difference there is in the specs of mine and the one you used for testing.

I know its common on these engines to run a vernier exhaust cam pulley and retard it to 10 degrees, were either of the engines you tested your vvt management on running this?


Great work in developing this guys, it really is a game changer I think.
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- ST170 powered Mk2 Fiesta Popular Plus project & show car

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Re: The definitive ST170 VVT Information....

Postby Stoxs » Sun Apr 27, 2014 11:34 am

Hi Matt

How long before i can get my oilly mits on the VVT controller?

It is looking fantastic and cant wait to see the difference.

cheers Colin


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