Whats the biggest cams for the 4AG?

[Mulisha]

Hey all,
What is the biggest set of cams you can get for the 16v 4AG without changing the ECU?

[Knudsen]

Ill guess theres "no limits" but if you really want to get full profit on the cams, you´ll have to raise the limiter...

[auxoura]

I think would be the HKS 288' with 8.3mm lift...any higher i dun think its safe. Might cause your valve to float and there goes your engine. But I heard with OEM ecu, the best cams are the TRD 272' 7.5mm. I just got a pair of em for £240

[Mulisha]

yeah I don't plan on changing the ECU. That would be 272 with 7.5mm lift on I and E right?

[Ivan141]

I read somewhere that 260 is the max for the stock ecu. Wilder cams seem to work also, but their vacuum around idle is very low. This could sometimes cause idleproblems (who cares, just blip that throttle at stoplights) and, more seriously, lean conditions in the first moments of off idle acceleration. This could cause short bursts of detonation.

Also remember that camflow is not only determined by duration and lift. The lobeprofile is what's really important aka the area under the duration vs lift curve. This differs significantly between brands and is the reason why on cam can work better then another even though they seem to have exactly the same specs.

[robokill]

I had a talk with Bill from Billzilla he sayd he once bought a stock engine with 292 cams and 8.5 lift without any upgrades.

The engine ran good but the stationair rpm was fucked up. 272 is good to do take somthing with 8.1 lift

[NoHachi]

Go and ask Bill whether he would do the same thing to an engine himself. I think that engine is one for the "weird an wonderfull" category, not for the "see whats possible with a stock engine" category.

How do I explain this to you guys.
The stock ecu works on a MAP system, yes? So the ECu figures out how much air is coming in (based on vacuum) and injects accordingly.
Ok, so the stock engine runs in a fixed interval, meaning RPM fluctuates between X and X and so does the manifold pressure.
When you add a wild cam things start going a bit crazy. Sure, the engine still runs within its normal parameters during most times, that means ordinary rpm values with corresponding vacuum (MAP) values, that the engine knows.
These values are present in the computer to be able to handle all sorts off load situations (eg driving up a hill etc). So with the new cam the engine measures a situation thats similar to running downhill ordinarily (only now you are actually driving full throttle on a level road). That doesn't matter, the engine is familiar with this load/RPM combination and will inject the correct amount off fuel.
So when do things start to go wrong? Well those who could understand what I wrote above (don't worry if you don't...lets just say that I make a crappy lectioner) already know that there are two possibilities:
1. The ECU encounters RPM/MAP combinations that it has never seen before.
2. The ecu encounters MAP or RPM values that are outside the programmed bounderies.

Situation 1 is not that big of a problem. The ECU uses a fixed points RPMvsLOAD (vacuum) map. Of course the engine does not run in fixed points, so there's a nifty interpolation algorithm that calculates suitable values for all inbetween points. It keeps on doing that when it sees these unknown combinations, just guess whats appropriate from the known values.Usually thats good enough.

Situation 2 is more problematic. basically there is no programming available for these situations. As far as the ECU knows these values simply do not exist. What it then does is hold the fuel and timing steady at the last familiar point it encounters (and start throwing CEL codes).
In practice this leads to the following: when you remove the revlimmiter it just holds the fuel that it knows from the last familiar point. So you are still getting the fueling from 8000rpm, even though you are at 9000. Not a problem when the engine doesn't increase in power much in those 1000rpm. BAD when it does...
Same thing happens at idle. Vacuum drops of off the map so it just does what it did the last time it saw something it recognised...Not a real problem mind you, unless you start accelerating from that RPM point. You go to full load from the incorrect fueling situation. The ecu needs a little time to recognise the new needs and in the mean time you are running lean. This allows for short bursts of detonnation that almost undetectably starts chewing away at your pistons

[Mulisha]

wow, I didn't realize that was actually going on. I thought the ECU went into almost a "limp" mode when it didn't recognize what was going on. Good stuff. If I knew who bill was then I would ask him about the cams,... but I don't. I looked on Club 4AG, but I don't like their server and the people who run that place are not friendly. Anyways, they just talked about lift and duration, but didn't really specify what is good for the 16v 4AG

[NoHachi]

Check out Bill pretty legendary 4age site here: http://www.billzilla.org/4agmods.htm
Chances are you have already seen this site, very usefull!

On his site Bill mentions 256 cams as the practical upper limit for the cam duration, thats seems about ok..

[JonT]

Bill seems to be saying that 264 is the max on the standard ecu, which is also what i have heard from other 4AGE sources. That's also why i have a set waiting.