Michael, Can you comment on why the variocam was disabled? I'm planning on using and aftermarket ECU, and I should be able to fine tune the variocam on/off. Is it even worth chasing variocam? And finally, do you know where I could find an ignition map that would be a good starting point for stock compression?

Thanks

 

Hi Justin,

The 968 Variocam advances the intake cam between 1500 and 5500 RPM. This is a fine street arrangement, but a big race cam won't react favorably to the (rather dramatic) valve timing change. If you're just warming over the cam, keep the Vario. Otherwise, disable it. What cams are you running/planning?

I did a head and cams for a guy that got 240+rwhp in an S2. That sounds like what you'd like to see in yours. Be sure to get a good header; all the cheap stuff out there is junque (that's the Canadian spelling, eh?).

Why the aftermarket ECU? There are a few guys that can properly tune the Motronic. I can refer you if you like. It would keep things simple. The ignition map would be pretty basic. I can provide you one if you like.

Cheers,
MM

 

Thanks for the response Michael. The engine is being nikasil coated as we speak and getting new matched pistons for the coating. The car already has a stahl long tube header and millege cams, carillo rods, baffling etc. The head has had some work, but I'm not sure how much. I have a motronic box with RSbarn chip that should be matched pretty well, but I'm a tinkerer and I like to have access to the internal workings of the ECU. I also have a megasquirt setup I used on my previous n/a 944 sitting in a box waiting for a new project.

If you have a base map for timing, that would be very helpful. If you are wanting to keep it private, PM would work, but I know there are some other members out there who would find it very useful.

I may run the motronic to see if it's good, but I feel like there is room to improve with fine tuning on the dyno.

 

this head and cam setup you speak of... the 240+ hp... is it very streetable? ive basicaly got the stahl headers and the RSBarn stage 2 chip with the intake hole mod. what would need to be done $ wise to get there from where i am? you can pm if you like... sorry for the barrage of questions but i assume you might've expected that

 

Michael, would you also disable Variocam with a turbocharged version?

 

The 968 variocam is a long way from BMW Vanos so they cannot be compared. Plus the fact that Michael here talks about very aggressive cams.

For stock cams the Variocam should never be removed. I tuned my 968 16v turbo engine on the dyno working and found best result to use the Variocam, but with other parameteres than stock.

 

So what is considered an aggressive cam for the 968?

As I understand it (someone please correct me if I am wrong) the 968 cams have an intake duration of 224.5 degrees and the variocam advances the intake cam 15 degrees between 1500 and 5500 to increase mid-range torque, (instead of the intake valve opening at 7.5 degrees ATDC, it now opens at 7.5 degrees BTDC)

If you have a more aggressive cam, for example my cams have an intake duration of 274 degrees, at what point is this mid-range variocam advance no longer an advantage?

Admittedly my engine spends 90% of its time above 5500 anyway, but I still have variocam connected and have not been able to see any improvement from tuning with it disconnected, or from altering the solenoid opening and closing points? Then again, maybe my tuner was crap....

Would love to have some more definitive thought on how useful the variocam really is with non-standard cams, different activation points etc.

 

You are referencing a turbo engine which right off the bat shows the extreme case of your arguement (of course turbo engines will show the most gains). Also you are not taking into account the fact that a turbo engine will not have nearly the cam a high compression NA engine will have.

I can tell you from personal experience a race S54 engine will gain close to 40 ft.lbs of torque if you keep dual VANOS - but, this is all below 4500 rpm - on the track, if you are below 4500 ever with that engine, you made a mistake somewhere or you are using a 5 spd.

In the end, the customer makes the decisions, has a budget, and is paying the bill.

I don't think anyone disagrees having variable camshaft timing will give you a broader torque curve. On a turbo engine more low end torque means more energy to spin the turbine, of course.

Have you done the testing with this cam to see if it idled and also made power to 7500? Why do you think race engines do not idle at 900?

 

As a starting point you should do one dyno run with it deactivated and then another run with it activated throughout the full rpm range so you can overlay the curves and pick your activation/deactivation points.

 

Oh this has me thinking.

I may need to get in contact with you in the fall.

 

wow. big words from a guy who knows nothing about the OP or members in this thread that know a thing or two about these engines... VVT is not the same as our very primitive 15 degree advance variocam... I'll take michael's word on this for now. hes the one building monster (and streetable if needed) turbo and NA engines...

 

all due respect, i think you could possibly be right, but, he's running a fairly narrow power band (nothing like a street engine).... my knowledge is very general. the engine is a good design, but notice how neither the 968 Turbo S nor Turbo RS ran Variocam.. not sure about F1 teams keen on running it either.... with a limited racing budget, i'm sure it's a lot easier simply to run the desired cam for a fairly narrow band at the top of the usable range, rather than all the R&D that goes into running a milder cam with the variable valve timing.... it ain't like there's 5 or 6 different cams for the 968 floating around out there.... or maybe both (methods) would work fine. in the end, sometimes it's just better to let things slide and just enjoy what the man is doing with his car, especially since he was nice enough to share his ideas about his project with us....

just my 0.02.

 

i got the solution for the street. but you all know what that is.

 

he said this was a race engine, that would also be streetable. i imagine the racing this engine is intended for is 5000RPM+ most of the time...just about where torque/HP cross on a SAE dyno graph, so if its making power then thats all that really matters...also he mentioned that the race cam wouldn't do so well with that kind of cam timing change (i imagine high lift and different duration, and changing that 15* might screw things up)

this is the same guy that built the 330HP+ 968 motor and is currently working on a 400HP NA 968 motor...i think he knows what hes doing, no disrespect to you.

 

guys have a blast in 944 n/a's.... w/ the power he's got, and the 968 tearing it up in the corners....

a few extra ponies is always nice, but with a capable driver.....