Is AVCS worth the effort?

[ReubenH]

I'm just looking into options for a future build, and i've long wanted AVCS. The idea was to drop a Ver. 8 engine in, use a 2.2 block and do some headwork. but if you're going to do work on the heads anyway, is AVCS really needed? Do you stick with the old 98 3-plug loom and heads, and play around with those... or will bothering with AVCS unlock allot of power or help the low end or what.

Essentially what i'm asking is, what are the benifits to AVCS, will it help the daily drivability of the car, will it help add top end power, or will it help the bottom end, or both? Or will it just double the expense of everything for not much benifit at all...

And no fucking flaming, i'm just trying to learn more about engines here...

[nt_a_foz]

From what iv seen and experianced the AVCS are good for big numbers..

As in they are mint heads from factory..

Case being a gt35 2.5L Motor setup in a v8 sti with factory heads making 350kw...Factory heads from what i was told...

Id imagine that they help both low end and top end.

IMO buying a set of AVCS heads and fitting (if your running a link or something) would be cheaper than working heads by the time you buy cams, valve springs nad cam gears etc

[funkytown]

totally not a stupid question Rheubs..

*subscribed*

Can we extend discussion to working non AVCS heads as well and what the net effects are by doing so?

[Shale]

Subscribed.

Thinking of a very, very similar build myself.

IIRC, the LinkPLUS ECUs have no issues with AVCS - doesn't the newest, range-topping unit do AVLS also?

Keen to learn more about all of this ;D

[Guest]

AVCS improves spool time and general daily driver friendlyness.

In short it allows you to run a hotter cam and / or bigger turbo with less downside to a non avcs intake cam.

With std avcs cams then the advantage is better spool which is only an advantage if you runnng a non vf turbo as they are pretty close to the surge line anyways.

Going to more capacity also achives this but better. I prefer the simpler solution lol

Headwork will help spool / midrange power and top end - turbo dependant - Done properly you will make more power on less boost. Done incorrectly you will lose power and bottom end.

But the cost of doing proper headwork is quite expensive. Something to only do if your racing on the track. imo

By all accounts the latest variable intake / exhaust cam head is very hard to port due to water jacket issues.

[Joker]

shamelessly stolen from another forum

[ReubenH]

 Qwerty said:

Headwork will help spool / midrange power and top end - turbo dependant - Done properly you will make more power on less boost. Done incorrectly you will lose power and bottom end.

But the cost of doing proper headwork is quite expensive. Something to only do if your racing on the track. imo

By all accounts the latest variable intake / exhaust cam head is very hard to port due to water jacket issues.

Well just how expensive are we talking?

Can you get aftermarket cams for AVCS easily? And the latest heads being hard to port, does this include V.8 heads? I like to stick with the older stuff, i'm thinking 8 since to my knowledge was the first with intake and exhaust AVCS. V.7 i heard only had it on the intake.

[Guest]

Some prices for good work.

"$3k for fully assembled heads with clearances set, new seals etc - ready to bolt on.

That does not include parts.

For fully assembled heads with Ferrea 6000 series valves, Kelford AVCS cams & Kelford springs they'd be around $5300-5400 - dpending on the exchange rate at the time & the parts cost variations that go with it.

"

Yes Kelford do cams for AVCS - about $1000 for the cams alone. You would also want new springs etc to go with.

Ver 7,8,9 AVCS is intake only - only the latest Sti has dual avcs.

Only the dual avcs is hard to port.

Std Sti 4 heads and cams are good for 500hp with the right turbo. Its much more cost effective to up the capaicty

[ReubenH]

I see i see, well, i suppose they'll be fine then, i'd prefer to stay away from the new stuff. V7/8/9 will all be much the same won't they? You can pick up whole engines and looms for a good price, i should think it'll actually be quite affordable to get a whole engine/loom/gearbox setup in a year or two.

And i do plan to up the capacity, but only to a 2.2 block, be it from the states (closed deck) or a sleeved 2.0. I don't want a 2.5 for various reasons.

When it comes down to it, would you prefer a ported V3/4 head, with cams, or a stock AVCS head? I suppose that's what i have to decide...

[funkytown]

 ReubenH said:

I see i see, well, i suppose they'll be fine then, i'd prefer to stay away from the new stuff. V7/8/9 will all be much the same won't they? You can pick up whole engines and looms for a good price, i should think it'll actually be quite affordable to get a whole engine/loom/gearbox setup in a year or two.

And i do plan to up the capacity, but only to a 2.2 block, be it from the states (closed deck) or a sleeved 2.0. I don't want a 2.5 for various reasons.

When it comes down to it, would you prefer a ported V3/4 head, with cams, or a stock AVCS head? I suppose that's what i have to decide...

i suppose you mean with associated cams, valves etc as well as porting? or just porting... ??? i have the same question essentially

[Guest]

A ported + cam'd v3/4 head would have more power potential than a std avcs head.

If i didn't have to pay for it i'd take the v3/4 head.

But if you did all that to the avcs head - it would be better.

In the end you have to decide how far you want to go and for what purpose.

I would think the fastest car on CS around a circuit is Tony's version 4 RA and thats std heads AFAIK.

[funkytown]

 Qwerty said:

A ported + cam'd v3/4 head would have more power potential than a std avcs head.

If i didn't have to pay for it i'd take the v3/4 head.

But if you did all that to the avcs head - it would be better.

In the end you have to decide how far you want to go and for what purpose.

I would think the fastest car on CS around a circuit is Tony's version 4 RA and thats std heads AFAIK.

his is around 230-240kw right.. I do agree with your statement but there are several things to point out in your statement.

Tony in my car would be faster than me in my own car - the guy is a top driver

Fast car round the track doesnt require the biggest amount of KW

That said it comes down to a bunch of other things to go fast round a track.

Totally agree its about stuff fit for purpose - and a good discussion otherwise.

so the two things to consider are cost and performace

cost

v3/4 heads

v8 AVCS heads

V3/4 heads worked and ported

V8 heads worked and ported

performance

as above...

Would this be correct?

[Guest itsgotgo]

Quote "By all accounts the latest variable intake / exhaust cam head is very hard to port due to water jacket issues."

So in effect the late model heads have either less material to port or an unusual water jacket arragement?

The late model stuff always costs dollars because you are paying for someone elses R and D?

Thats on the premise that very few have been done

[Guest boostin]

MY04-on Legacy GT has dual AVCS. Plenty of those in wreckers yards now.

[Guest]

 itsgotgo said:

Quote "By all accounts the latest variable intake / exhaust cam head is very hard to port due to water jacket issues."

So in effect the late model heads have either less material to port or an unusual water jacket arragement?

The late model stuff always costs dollars because you are paying for someone elses R and D?

Thats on the premise that very few have been done

The castings are significantly different in the water jackets, including a steam hole between exhaust bowls.

This makes it difficult to go oversized on the exhaust valve - u can still do a port on them but your not going to get the same flow as the earlier heads.

[Guest]

An AVCS head is a better starting point - more for the variable intake cam which helps broaden the potenial power band esp spool with a bigger turbo. I haven't seen any evidence it will make more peak power tho.

There is nothing wrong with ver5/6 Sti heads they seem to make similar power to 3/4.

I mention Tony's car as i have seen alot of big build expensive engine never get properly used.

No money left in the budget to go racing or to rebuild if it turns to custard. Car then sold for half the cost of making it.

For a street car its all overkill - sure its all cool stuff but you can't use the performance in full.

If you just using it to chase times on the track where do you stop ? And what does it achieve ?

You spend x dollars and do a 1.10 lap time. Do you then spend xx dollars to do 1.09 ?

[ReubenH]

 Qwerty said:

For a street car its all overkill - sure its all cool stuff but you can't use the performance in full.

I see you've got a good point here. This build i'm thinking of in the distant future would not be for a track car, it would be for a gran tourer. The track car will be an impreza, which will likely get the PBMS block that i'm using in the GTB now. The plan has always been GTB daily car, Impreza track car.

The idea was to get that AVCS for quick spool on the turbo, to compliment the 2.2L. What about just getting some mild aftermarket cams, would they be wasted if i don't get the heads ported? Hmm, now i really should go off and read up on cams...

[Tony]

 Qwerty said:

I mention Tony's car as i have seen alot of big build expensive engine never get properly used.

No money left in the budget to go racing or to rebuild if it turns to custard. Car then sold for half the cost of making it.

For a street car its all overkill - sure its all cool stuff but you can't use the performance in full.

If you just using it to chase times on the track where do you stop ? And what does it achieve ?

You spend x dollars and do a 1.10 lap time. Do you then spend xx dollars to do 1.09 ?

EXACTLY. You seem to share the exact same thinking as me Qwerty (pretty much what I was going to post!)

You have to decide what you want, and how much you want to spend - then work out how much cash you ACTUALLY have to spend, taking into account all the other things along the way (repairs, servicing, etc etc). Everything adds up.

I know having worked heads can make good power, and it is definately a needed thing when you want to run larger turbos etc. I have a few friends that have gone right down this path as well. It costs a good amount of money, which is why I didnt go that way. I couldnt afford it. My build is very budget - for those that have seen my car, it may not look like it, but it is built on a fairly tight budget (and I have a lot of friends/supporters to thank for that).

For me, reliability was the number 1 priority - as Qwerty said above - I cant afford to rebuild an engine all the time. Unfortunately its a Subaru, and I dont care what anyone says, if you regularly race a high HP Subaru, it WILL break, seen it all before, and then there is the issue of all the other things wearing out/breaking quicker - again, I didnt want that stress cos I wouldnt be able to afford to keep going... at the end of the day, what good is a race car if you cant race it?

So basically do what your cashflow will allow, and what you are happy with. If you can find some AVCS heads for a good price, grab them. 200-240kw seems to be a good all-round amount of power without running into too many issues - and the main thing is, the car will still be very DRIVABLE. Past that, I reckon is "open your wallet" territory!

And Funky - I am by no means a top driver, just done a fair few laps, and the car is far better than I am, so thats where the credit can go

[funkytown]

haha all good dude.. let me rephrase then.. your driving > my driving regardless of the car we'd be put in.. You've done a fair few more laps than I. My aim is to be getting a dam sight few more though..

My build like yours is built for reliability.. and i think i have a long block built for it. And im not making right in that power band you talk about. Given my car is still street - but realistically its pretty much not for much longer..

Agree its budget for fit purpose and reliability every day of the week

[Shale]

Minor thread jack (sorry babe)...

As AVCS seems to essentially make more use of the power band when talking bigger than stock figures, this could also be good with a non-turbo build (you saw it coming, my apologies), by dealing to anotherwise dead and undrivable low end, yes? None of the other silly N/A builds overseas seem to have made use of AVCS as no one's had the ability to run it. (Could be outdated info though - can't recall, hasn't there been a 12:1 build with new vs old heads vs block somewhere?)

...and back to the turbos.

[nt_a_foz]

Keltik was tellling me the other day he reckons in they UK they have a 1.5R impreza which is obvioulsy a 1.5L boxer and it had AVCS heads factory and some crazy revlimit....

Weather this is 100percent true or not i dunno ....

We all know what keltiks like ay lol

[Shale]

Hahahaha. Just wait til he sees that...

The little engines could be good for even Subaru experimenting with crazy rev limits. But with a 1.5L, they kinda need it!

[Guest]

 Shale said:

Minor thread jack (sorry babe)...

As AVCS seems to essentially make more use of the power band when talking bigger than stock figures, this could also be good with a non-turbo build (you saw it coming, my apologies), by dealing to anotherwise dead and undrivable low end, yes? None of the other silly N/A builds overseas seem to have made use of AVCS as no one's had the ability to run it. (Could be outdated info though - can't recall, hasn't there been a 12:1 build with new vs old heads vs block somewhere?)

...and back to the turbos.

You would need to replace the cams as they would not be aggressive enough even for a std na engine.

Forced induction air flows differently so the heads may or may not flow well enough for na.

[Shale]

I'll be getting built cams regardless of what heads go on so yeah, goo opportunity to mate the correct stuff with the build.

Guess it would be good to properly compare DOHC N/A heads vs DOHC STi heads and see where to go from there. After all there are modern N/A heads that tick all the boxes aside from STi that could work.

[ReubenH]

On reliability, i'm not kind to my engines. Yes i look after then, don't drive them hard till they are warm, change oil every 5000k with 10w-60 etc. But i use WOT bloody all the time, and frequently rape it.. When i blew the big end on the 20R (not a hard thing to do) i didn't want it to happen again, so i got a PBMS built bottom end, with ARP headstuds and such. Been 25,000K's now, and it's still going strong, and i hope to see that engine to 100,000k's (dunno if it'll make it )

At present though, my cashflow will allow; researching... Just trying to figure the options.

I really am liking the idea of AVCS, to get usable power through the rev range... but then again, the lag i have at the moment, i really do not mind... Could be a means to offset the lag of a FMIC setup and bigger turbo?