theory vs reality - 4AG(Z)Es

[nick.parker]

Howdy,

The exhaust port on my 4AGZE is 30mm, and the exhaust valves are 25mm.
The area of 2 x 25mm valves is equivalent to 35mm circle but is this relevant?
The actual open area, converted to an equivalent diameter would be SQRT( 25dia x 8mm lift) = equivalent to a 28mm hole, so two of these = 39.6mm hole. Now obviously this is completely ignorant of any fluid dynamics but are there calculations useful?

Does this mean my exhaust port is the limitting factor? (assuming my engine had enough air going through it in the first place)

The reason I ask is I was thinking about getting some bigger valves for my 4AGZE, as a couple of people in the US have anecdotal evidence that this made a worthwhile difference to the higher rpm performance, and I want to squeeze the most I can out of my SC14 GZE setup, just for fun / learning basically. At the end of the day it wont cost me the earth to get some +2mm OS valves, but is it a complete waste of time?

Regards, Nick

[Joshstix]

The valves don't cost a heap but you will have to get new valve seats put into the head to accept 2mm OS valves. You could probably get away with recutting the stock seats for +1mm though.

Exhaust side porting is something I am not familiar with though I'm afraid. Most of the info around is aimed at getting intake flow.

[The Witzl]

Nick,

when it comes to anecdotal evidence, the one place you dont listen to as a trusted source is the USofA.

Time and time and time again, real world evidence has proven that USA-bred anecdotal evidence is complete garbage - take for example the following (now disproved) "facts" born of US origin:

• 2JZ W58 gearbox has dual row synchros on 1st & 2nd
• 4A-GZE pistons are not forged
• 18R-G 88250 heads have 37mm exhaust valves

... there are sooo many more to add to that list.

I would talk to a few knowledgeable folks who have a lot of experience with the 4A-G* engines, and see what they have to say about your thoughts and ideas.

In my opinion, there aint much to be improved on the smallport 4ag head..... but that's just my opinion, and im no expert!!

[nick.parker]

Hi,

When I enquired about the valves, it was going to be the case that oversize seats would be installed too.

To add to my first post is I have some nicely crafted headers for my ZE, the flange hole is 35mm (the inside pipe is probably 37mm) and the stock flange (cast ZE manifold) is 33mm, does this mean I could bore out the exhaust port a couple of mm, to take advantage of the increase the effect of bigger valves. Is there a rule of thumb for this so called 'anti reversion' step in diameters.

To some this whole thread probably sounds a little silly, but down the track I am thinking about a lot more power via a turbo or a compound SC/Turbo setup. In the mean while I'd like to find out if any breathing mods will work at the lower power I get running 1 bar on my SC14 setup.

Regards, Nick

[Joshstix]

Honestly unless you have the head off already I'd be looking at cams rather than valves. A nice set of billets from Wade are going to be cheaper than the parts for 2mm oversize valves.

If you want more power down the road then opening the engine up would be a good plan. At this stage you'd most likely want to freshen up the bottom end as well as putting in the oversize valves and getting the head ported.

The amount of work involved in pulling the head off a working engine just to change valves seems like a waste to me.

On the other hand when I built my 3S I went for oversize valves along with big cams and this allows it to make good power at really low boost. I don't know specifically about oversize valves but for the 3S the 1mm oversize gives a significant improvement.

[nick.parker]

Hi,
Witzl, you dont trust those North Americans do you :-).
Josh, I have already installed a set of Wade 267 cams, which I feel are slightly too big for supercharged motor, as I lost the amazing bottom end torque the car used to have, though it does drive very nicely at the moment and mid range is good, the car really takes off at or above 3500 now, and it used to be 2000! I was thinking about putting say bigger inlet valves and a smaller duration inlet (bigport 240deg,7.56mm) inlet camshaft in. I have simulated to death on some budget software and it _seems_ to do what I want.

Regards, Nick.

[Joshstix]

Fair enough then. If you think it's the way to go I'm keen to hear what results you get.

Have you played with the timing of the cams? Reducing the overlap may be of use to you in getting back some of the bottom end. I also don't know what management you're running but I have to assume it's some fully programmable setup otherwise a serious loss of low rev power would be what I expect to see.

[nick.parker]

Hi Josh,

The engine management is custom (I made it, not megasquirt or anything like it, but totally custom -see my home page in profile), and I have done all tuning via wideband sensor which I frequently calibrate. etc.
As for the cams, they have adjustable wheels on them, and have played with the timing a bit. Its a fair amount of work as every time I change them I need to do some light driving followed by Volumetric Efficiency map tweaking followed by more driving, hehe if only I have a chassis dyno at home!

Cheers, Nick.

[Joshstix]

The thing is that fuel tuning really isn't going to do anything for you in the lower end where you've seen the power loss. Big cams are very dependant on accurate ignition timing. There is really no efficient way of tuning ignition timing other than a brake type dyno. I think if you could get the thing onto a dyno and adjust the ignition timing for maximum torque then you'd see a really nice improvement.

[nick.parker]

Hi,
Yes this could be the problem, I am currently in the process of building a 'knock' monitor so I can tune the ignition better. I run about 22 degrees at 1 bar from about 2500 rpm upwards, and I suppose don't have a great feel for ignition timing. My engine with the stock cams seem very sensitive to ignition timing, like add a few more degrees and holy cow there was a big torque difference, now the car seem less senstive, but I am too worried I wont hear detonation at the higher revs untils its too late, low revs = easy to hear - sounds kind of like somebody throwing stones at the block, but high rpm not sure if I'd hear it! Maybe I need to try adding 2 or 4 extra degrees.....

Cheers, Nick

[camrygt?]

As Joshstix was saying. You tune ignition timing on a dyno for maxium torque or limit before knock begins as measured while you are tuning. But maximum torque does not neccessarily occur just before the engine knocks so tuning timing by ear or knock sensor alone may not result in maxium torque over entire rev range.
Its very hard to do on the road as you can only set the timing by feel/sound but if you have a lot of spare time you might get it fairly close

[nick.parker]

I agree that I may not find maximum torque, but in experimentation to find the maximum SOTP torque ;-) I definitely want to avoid blowing up the motor.