333pg333

Koren, I thought you were from the UK. You from NZ?

JDS968

Variocam, unlike VTEC, for example, does not switch between two cam profiles. Rather than being "variable cam timing [duration] and lift", it's just cam "phasing"...that is, you have one intake camshaft profile, but Variocam advances or retards the entire intake camshaft based on whether the solenoid is activated or deactivated. It does this by flooding a piston with pressurized oil, which pushes on the chain tensioner running from the exhaust camshaft (run by the timing belt) to the intake camshaft (run by the chain).

Now in theory, this means that Variocam engines COULD be converted from 2-position cam phasing to continuously variable cam phasing, if only we could equip that piston with an adjustable oil pressure regulator. I just have no idea how to do that, is all. Oh, and it's probably only relevant to naturally aspirated setups - with a turbocharged Variocam motor, you probably just want it fully advanced at all times when you're off boost, and fully retarded at all times when you're on boost.

Wormhole

Hey duke, what did you do for cam timing? Looks like you are using the stock s2 chain setup. Did you shim it at all to advance the timing? Your dyno chart is interesting the hp and tq numbers are reverse from what I saw from my 16v initially. It took a lot of cam adjustments to get the torque up.

fortysixandtwo

In-case anyone is interested. Here is the difference in cam timing with vario-cam

Basic valve timing:
Intake opens 7.5 deg. after TDC
Intake closes 52 deg. after BDC
Exhaust opens 31 deg. before BDC
Exhaust closes 1 deg. after TDC
Torque valve timing:
Intake opens 7.5 deg. before TDC
Intake closes 37 deg. after BDC
Exhaust opens 31 deg. before BDC
Exhaust closes 1 deg. after TDC

below 1500RPM: Basic timing (solenoid on)
1500-5500: Torque timing (solenoid off)
Above 5500: Basic timing

Korenwolf

Yup I'm a Kiwi, but I've been in the UK/EU for almost a decade now.

I'd like go back, just can't justify it financially, I'd have been lucky to earn anough back home to buy and do the mods I plan to a 944, let alone owning an Ultima GTR for a couple of years - which ended up costing me 15UKover the time I owned it in depreciation, insurance and running costs, but it was worth every penny, nothing like the kick you get when you have a 1 ton car, and >500 bhp of Chevy less than a foot behind your back !

Chris White

I played around with the stand alone controlled Variocam quite a bit…..and decided the benefits are way too small. The intake cam position change is pretty drastic. The basic reason that the system was included in the 968 was idle emissions restrictions. The added power based on Porsche’s testing was pretty small (5hp). I have owned S2 and 968 cabs and I always liked the midrange response of the S2 better.

The one idea that I heard (I think it was one of the Aussies!) was to shim the hydraulic cam control to limit the cam change to a more reasonable degree and then retime the cams for optimal on/off performance. That’s a lot of work!

The easiest (!) way to have a continuously variable cam system is a plusewidth controlled hydraulic regulator, it can even be done in a closed loop system with the right linear sensor for tensioner movement. I still don’t see the end benefit being worth the effort.

The ‘twin cam’ adjustable cam system works nicely for track cars and street cars. On some cars you do have to work out the gear to hood interference (there are a number of ways to fix that).

John – I think the big difference in Duke’s response is the displacement. The 3.1 liter testing I have done looks a lot like Dukes chart. Your 2.5 in not as much of a torque beast and I think your turbo is set up for more RPM than Dukes. BTW – it was interesting the difference between dyno test and real world running for your engine, ‘seat of the pants’ cam adjustment in the field made a difference! And that’s why I like the easily adjustable cam gears!

Duke

"Benefits way too small"?? Please define
With a 968 head and a good standalone you can set it up with perhaps 30 min of work and $5!
I did not gain any peak hp but I did gain pretty much in my midrange - probably the single best thing on my engine when it comes to cost/benefit. It doesn't seem that any of the "naysayers" have actually tried to control Variocam on the dyno and done back to back testing. I did it and the increase was significant in the upper midrange and it should net the same results on a similar engine.

What does the the twin cam system you sell cost? Now that is something I would question the cost/benefit ratio of. I'm sure it could be setup well and be beneficial but it's a lot of stuff involved and much more time consuming to setup on a dyno. So I would assume the total cost to be very high, plus the fact you might not be able to close the hood

I think it would be easier and net better results with custom cams instead of stock exhaust cams and twin drive. Perhaps the same cost too.

Duke

Here's a caption of HP from a dyno run when Variocam was tuned in.
Look at the big dip in power, that was the effect on the whole midrange without handling the VarioCam.
Pretty good benefits for a coffee break's worth of time

333pg333

...and if you've read "The Girl with the Dragon Tatoo" series, the Swedes like their coffee!

JDS968

I understand why it's 30 minutes of work, but once you already have a Variocam motor and an EMS, where does the additional $5 come from?

V2Rocket

beer, the most important tool of all

JDS968

Beer will change the world...or at least my valve timing.

Duke

I always drink beer on coffee breaks!
The 5 bucks is for a relay, 2 pin minitimer connector and a little wiring

Chris White

Ok, maybe I was being a little harsh on the variocam. If you have one then it makes sense to wire it up and use it.

But then you got off a little tangent about the twin cam system…..
I think you might be missing something in your post. Remember that the 16v cams (S,S2 or 968) are all designed as normally aspirated cams. They are designed with a degree of NA style cylinder scavenging in mind (that’s the short period where the intake and exhaust valves are open and the rapidly escaping exhaust gases help to draw in the intake charge). NA style scavenging does not work so well with turbo engines due to the exhaust back pressure. Luckily the 16v cams do not have a tremendous amount of overlap so they are ‘OK’ for turbo use…..but who wants to build a 16v motor based on ‘OK’?

To answer the question directly - the twin cam set up goes for $750 – that’s for two cam gears, the crank gear and the belt. How much does a new variocam tensioner go for (or are you happy with a 20 year old used part?) Have you seen the results of a chain tensioner failure? Its not pretty…..and it s not uncommon .

Set up cost of the twin cam? its the same as degreeing in a stock cam other than the fact that you need to procure a second exhaust cam. You can set it up in the stock alignment and then do your own A/B tests. It takes less than a minute to adjust the cam timing – so you can do it in the car and at the track where you can measure the difference in the ‘real world’. When we tested Wormholes set up on the dyno he later found a better ‘real world’ setting by trial and error out on the track. How much time does it take to change the exhaust cam timing on the stock set up? Nothing I would want to do at the track.

Duke is right about custom cams – it would be easier to go with custom cams….but how are you going to know what cam timing you want? Rely on what is being sold as 16v turbo cams? Custom cams are pretty expensive (they make the twin cam drive seem cheap!) and trying out a couple of different grinds will really add up quickly in parts and labor. Webcam charges $1035 to hardweld a new profile on your core cam…..RS Barn is $1595 plus core….

BTW – I have done several variocam engines using a standalone to activate the variocam – it makes a difference – but I believe that being able to select the right lobe separation and intake / exhaust timing will do a better job. If you go to the trouble of doing all the R&D to design a turbo based camshaft for the 968 then I will change my opinion!

Obviously the NA 16v cams actually work fairly well. I have two different circumstances where a 16v turbo engine was set up at stock cam timing and both responded better when the timing was changed. In other words – they worked well in stock position but they worked better when that was changed. That’s enough proof of concept for me. Duke - maybe there is another 5% power left on the table in your engine….if varying the cam timing of your intake by the fixed amount allowed by the variocam gave you that kind of increase then doesn’t it make you wonder if there is more available?

Duke

I don't think I got of tangent about the twin cam system. I said that I'm sure it could be beneficial but not very beneficial for the price and time involved.
On the other hand I think you get a little of track now with the "just OK" comment. I would be the first to say that using stock cams is a budget choice and NOT the all in, best you can get, type of solution. But as you know, with a budget there must be a line drawn somehere. And for me the stock cams are for the moment "good enough". And obviously they work very well. I have my dyno chart, I have my numbers, and most importantly I know how smooth and nice my engine delivers power. Maybe that is just "OK" for you, but for me that is pretty good!
And in perspective you compare this with a solution using 2 stock exhaust cams, now how can that be better than "just OK"..

Why would I buy a new tensioner? New pads and chain is basic maintenance. Now you're talking like a marketing guy

So the twin cam setup is $750 and then you need another exhaust cam so in total it's over $1000 for benefits not backed up by any dyno or real life data.
I have no negative things to say about your twin cam setup, but compared to stock 968 cams with controlled VarioCam I fail to see what I would gain for $1000+ extra.

Well the selling point was that you're able to adjust the cams individually (which is great!) but that is way more than degreeing a factory cam and you need time to set it up. And IMHO it should be on the dyno because power curve and +/- 10hp is very hard for most people to evaluate on the track.


Yes it's more expensive. As with all things you just need to draw a line where to stop. This would IMHO be the best approach and not the "just OK" solution with stock cams we're using.


This is an easy target I am extremely confident there is a lot to gain for my setup so I'm totally with you. BUT, the effect I got from VarioCam can not be replaced directly with a static cam setup. I gained a lot in the midrange, while in another part of the curve (top end max HP) there was no difference with or without Variocam activated. So with a static setup I would have a compromise: more top end - less midrange, more midrange - less top end.

There's a lot more than 5% left on the table in my engine. I wonder how many % is left in your engine that would come forward with a real cam setup. I still haven't seen any proof of a better solution than stock 968 cams with VarioCam. You have a great dyno sheet, but you have 4-1 headers, dry sump and race gas along with your cam setup. So in that comparison it would seem that the stock 968 cam setup with Variocam works at least as well considering my results on stock headers (!), stock oiling and pump gas.