Hi,

Anyone know what effective "profile" the STi7 has when its VVT, ie when the VVT kicks in higher up the rev range, the cam profile changes to?

 

Not sure I understand your question, but the AVCS just advances or retards the timing, I believe it has a range of upto 35 deg.

 

Oh, I thought the VVT system was like variable valve timing, in that it changes the cam profile to a higher lift cam? This gives you a lower lift, better mpg/emissions cam lower down and a more aggressive cam, lower mpg etc higher up.

 

No that is not how the AVCS works, The cam profile is constant.
Basically oil pressure is used and controlled by a solenoid to rotate the camshaft backward and forward (Advancing or retarding Ignition timing).

By doing this will determine how efficient the engine is.

 

Interesting...so is there a variable valve timing setup that say Honda works with, which alters cam profile?

Just wondering really as I once almost bid on STi7 heads with VVT on ebay and thought that's what was on offer.

 

Not as far as i Know. From what you have put above I think you have been led to beleive that on VVT cars the valves open longer and harder at high rpm's, Have heard people saying this myself but it quite simply is not true.

It is all in the Ignition timing.

 

Hmm, interesting...If say my car without VVT has a "map" for ignition advance, 3d based, what's the difference the VVT would make? Just trying to remove the "cam profile change" brain cells and absorb this timing thing.

 

Vtec changes the effective profile, but the AVCS doesn't. What is it you actually want to do?

 

These namings are getting a little crazy. I think Vtec was VVT and that "changed" cam profiles as such - I take it no sti's run with this function, even the latest ones?

I was thinking of head changes as my profile as present is 285 and its great up top but not low down (below 2500) and with VVT or Vtec you get best of both. I wanted to know what the effective profile would be on an sti if it was running at the higher lift "profile" - hope that makes sense

 

VTEC is different to ACVS,

Ignition advance on a non VVT car, is not the same as changing the timing of the Inlet cam In relation to the exhaust Cam (which is what the AVCS does).

I think I understand, you want to know what profile AVCS cams you would need give you the same result as your 285 non avcs cams? (but with a bit more low down)

 

Spot on chap...my real issue is that my wild cams are lumpy low down...2500 and they clean up but I'd prefer it a little lower, say 2000 but at the same time dont want to lose the higher up grunt.

 

Not sure of your current setup, but think will cost you a fortune to change to AVCS heads, Your ECU needs to be able to control AVCS and you will need the loom to go with it.

I must admit I thought 285 duration cams would only be used on the Strip not on a road car!!

Maybe you can use a less duration cam that has a greater lift?

 

Already looking at after market ecu which should be able to control that..but yes, agree cost might go sky high . Totally undecided at present as not even sure I want to change the oe ecu - only because she starts to stagger during running (due to ecu chasing the correct mix but seeing misfires since the cams have massive over lap at lower revs) did I even look at another ecu. Not sure costs are worth the gains....

I know you also get option like anti lag etc but I think that requires extra plumbing etc to work? So, doubt I'd use that either.

 

Have you considered your cam timing on your existing set up ? I use cams with more duration than that and it runs sweet at low rpm, pulls smooth from 1000rpm and thats with 1100cc injectors.

What cams are you using ? Sti 3/4/5/6/7/8/9 profile will run to over 500bhp so no need to go wilder than that unless you are really chasing big bhp.

Andy

 

If he used adjustable pulleys to reduce the overlap at low rpm's, how much of an effect (reduction in power) would it have at the top end of the rev range?

 

Depends on the cams, compression, porting etc but if I can get a smooth idle and decent vacuum on my car then he shouldn't have any top end power worries.
Its not just the overlap, its cam timing. Turbo cars don't need much overlap but the position of full lift can have a big impact.

 

Hi Andy,

They're piper cams with 285 profile, no idea lift or other spec of them though..I'll have to have words with bob about this as I know nothing of cam timing. 500 bhp is going to be my limit with my existing setup and turbo, etc, etc...I bought those cams without really understanding the full spec and implications of what they were like, you live and learn!

Cheers

Swiss

 

So basically you want to improve the low down running of the engine, the idle quality and the transition away from idle.

In my experience the OE ECU can struggle with wild cams, and you can run into problems with the closed loop running. Sometime you can get around them but not always, and I seem to remember that Bob improved things over the original setup when he first started to get involved with the mapping.

It's worth pointing out that the Piper "285" profile is less than 285º, so should be able to be set up to provide a sensible idle at around 1000-1100 rpm. even on cars running a reasonable amount of overlap I've had no problems with running just off idle at say 1500rpm, but not on a newage OE ecu.

If you have variable cam pulleys then I would say that an adjustment to the timing is what you want, otherwise investing in some adjustable pulleys, or modifying the original pulleys to allow a slight change in timing, is probably a the way forward.

pual

 

Hi Paul,

Well, my idle isn't bad really, even with custom flywheel, pulleys, 800 injectors etc Bob's got her running at approx 850 revs and doesn't stall (unlike before) but my "issue" is that with the oe ecu she just doesn't run "clean" until 2500 when she then takes off like a complete animal. I'm sure the turbo (Garrett hybrid) could spool a little lower if she'd run a little cleaner/pull better....I dont like the sooty running.

I've also got an issue with ecu not handling the mixture below 2500 as she then drops to idle and then does a "wave" of slight rev changes from about 1000 to 1500 to 1000 until you blip the throttle again - something Bob is aware of and can fix with aftermarket ecu (nothing is set in stone regarding this though).

So if I get adjustable cam pulleys, do you need the engine out to fit/setup these babies?

Cheers

 

Andy F/Paul - would I be able to fit cam adjustables, have it setup and still run under the OE ecu? Or would after market job be the best? Just trying to keep the cost down a little. I will be talking to Bob about all of this asap.

Cheers for your help guys

 

Cam Pulleys just bolt on the front end, setting these up should help considerably. A possibly cheaper option to consider than a replacement ECU would be relocating the maf to a blow through position. This also eliminates any part throttle issues you may or may not have.

Andy

 

Thanks Andy...Bob's come up with the same idea of "blow through" MAF move as he said the vernier cams option can be expensive and needs proper setting up with engine out. I fancy this maf move idea as already looked at price of ecu replacement...

On another note, what's the chances of just an ecu change fixing the low running issues if maf etc stays in same location?

 

If Changing the ECU would probably be better to throw the Maf in the bin

 

Sorry chap, my question should of stated "what's the chances of ecu change with IC pipework as is and no maf to fix the low down running issues?" Is ecu enough with cam timing as is (ie oe pulley set and piper 285's)

Oh, document from Piper says profile is 285 deg...not that it matters.

 

I'm sure Bob has explained it but yes, if you change to a speed density ECU such as Autronic/Motec (no maf) then the existing problem of measuring the airflow at low rpm is removed.
Adjustable cam pulleys may well increase power and torque and you CAN do it with the engine in place although it is a bit time consuming and slightly awkward !

 

Andy, how in heavens name do you get a DTI on the top of the bucket with the engine in Situ, or are you using a verdict (finger type) DTI?

I presume you are setting cam timing using traditonal IMOP and EMOP, or are you doing it with some other method?

Also, how are you finding an accurate TDC with the engine in situ? Surely there is no room to get a DTI and extension down the plug hole? Or are you using a modified spark plug or similiar as a 'dead stop' either side of TDC.

I am very interested to know how you set it up in such an enclosed space!

 

Thinking about it, not having inner wings on your car might help with access?

 

When the cam covers are off there is enough room to get a conventional DTI on the buckets and onto a rod through the plughole onto the piston crown. I have changed the cams and dialed them in a number of times on my race car this year. My front pulley has a permanent attachment of vercro for the timing disc
I still have inner wings/chassis rails although I do have the luxury of no ABS (or anything at all really) cluttering up the space

 

Thanks for the info guys...I'm now at a cross roads and need to decide which is the best path. I've got the cheaper "move maf option" which "should" fix the running but means moving of the water injection setup and IC pipe amendments. I've then got ECU change/no maf, but then I still want secs monitor usage with warning lights etc, so cost runs to approx 2K or I've got the vernier cam pulley setup which I'm not sure I can talk my local garage into going for as it sounds very fiddley and unknown cost running with oe ecu and maf...I really need to think on this.

Also, the ecu change gives me options of launch control, anit lag, VVt etc all of which I'll never use.

Cheers

Swiss

 

How about just putting the std cams back in, job done.