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Discussion Starter · #1 ·
Hi all,

Some time ago I remember a few people asking and/or debating about the benefits (if any) of having an Evo cylinder head ported, polished, gas-flowed, etc... (here in the Philippines, and I believe maybe in America, also referred to as getting headworks ). I know for instance, that there's a pretty popular school of thought that says you don't really need headworks with a forced induction engine, and therefore getting an Evo head ported/polished with bigger valves, etc will yield marginal improvements in power.

Anyway, I'm glad to say that I've just enjoyed a very measurable and fairly significant improvement in power, from fitting a pretty heavily modified head onto my car (Evo 5). The head has been gas flowed, has bigger valves, titanium retainers... but am currently still running stock cams and valvesprings.

Here's a bit of my car's tuning history so far, which I THINK demonstrates the improvements that may be derived from a properly done head.

- car dyno'd at about 210-212HP @ the wheels
- this is to be expected and about right, as stock Evo's do just that on the Dynojet RR where I get my tuning done);

- car dyno'd at 232HP @ the wheels
- boost set to peak at 1.1 bar with the AVC-R
- S-AFC used to fine tune fuelling

- car dyno'd at 253HP @ the wheels
- boosting between 1.1 to 1.2 bar (spike), holding at about 0.9 to 1.0 bar
- (as mentioned,) head has been gasflowed, with bigger valves, titanium retainers
- stock cams, but with HKS adjustable camgears
- stock valvesprings

note that with this set-up, I was unable to maximize the potential of the improved flow, because with the limited adjustments allowed by the S-AFC, I would experience intermittent fuel cuts. A programmable ECU was needed, and not having the resources to purchase a Motec, I went with the Apex'i Power FC.

and finally, just today:

- car dyno'd at 273HP @ the wheels
- as above, still getting boost spikes to 1.2 bar, but settling down at between 0.9 bar to 1.0 bar
- Power FC used to eliminate fuel cuts by remapping ignition timing and fuelling

The upshot: of the sixty HP I've gained over stock from mods and tuning, IT SEEMS I'VE GAINED ABOUT FORTY (40) HP LARGELY FROM THE MODIFIED CYLINDER HEAD. Of course, I wouldn't have been able to maximize the head without the new ECU, but it seems a fair bet to say that just fitting a new ECU w/o changing anything else on the car, would NOT yield any significant benefits.

By this time, some of you are probably thinking: big deal, you could have saved yourself the time and effort to get that additional power, by simply turning up the wick on the boost! . I suppose I could just up my boost to say, 1.3 bar or more, but I'm afraid of my engine going bang (I still run the stock turbine and internals,) and wanted to see how else I could make power WITHOUT resorting to silly boost.

I have yet one more incremental mod to try, and that's fitting 272/272 cams. My tuner feels that doing this would squeeze out even more power from the head, as he says that the high flow characteristics of the head are wasted with the very conservative profile of the stock cams. Anyone have any ideas how much I'll gain? I suppose if I can get to 290HP @ the wheels with the addition of the cams, I'll be chuffed!

Anyway, I just thought I'd share this information here, for anyone who's interested. Am curious to hear what people think!


Discussion Starter · #2 ·
Nice write up :)
Very interesting, I also saw the two schools of thought previously over porting/gas flowing and forced induction. I am of the opinion if you reduce any restriction in flow then obviously you can get more air and fuel in there for the same boost level. Keep the restrictions and turn up the boost and you get the same result, the difference is you have to wait for the turbo to boost up to the higher level and intake air temperatures will also rise. The fact you have bigger valves is also an advantage, more so that the porting/gas flowing but every little bit helps. In my opinion you have done it the 'proper' way, now you can turn up the boost if you want and get even more power!
Definitely go for the cams, might as well take full advantage of those bigger valves. You have the ECU so go for it!

Discussion Starter · #3 ·
Yep, go for it! I've been holding 1.45 bars for 5.000 kms without problems, peaking at 1.6 bars.

Discussion Starter · #5 ·
Many thanks for the positive comments, guys.

I actually already have the cams, and am just waiting for my valve springs to arrive.

What I WILL probably need to do is uprate my injectors. The stock injectors already max out duty cycle when pressing on, and I've been told that for safety's sake, you don't want to keep pushing them beyond 80% (what think of this?). So maybe go for 800's or something, as my tuner said 1000's are too much right now.

I also have a fuel pressure regulator and an uprated fuel pump-- both of which haven't fitted yet. My tuner says with the cams, these may well be required.

As you can see, I am trying to hold off getting a bigger turbine for now!

The dyno's printer is not working, so I haven't yet gotten print outs of my RR plots. As soon as the printer is fixed, I'll post my plots @ each stage of tune.


Discussion Starter · #6 ·
Great info. Hesperus!

Do you know any flow figures for your head? How much bigger are the valves that were fitted? Are only the inlet valves larger?

I'm going to be going the same route as you shortly but I'm tossing up whether to increase valve size as I have heard that the increase in flow is very marginal compared to the cost.

Discussion Starter · #7 ·
Excellent report and very interesting. One thing that came to mind (not that it's very relevant), how's the fuel consumption now? I've had the Apexi gear fitted with cams, induction and exhaust etc, running 1.6 peak and holding 1.4bar. One thing I've noticed is that the fuel consumption is now worse than before!!! Apart from track days that is.

I know it's not really the point, but I found that remarkable from the extra power just because the fuelling is now a lot more accurate rather than running rich as standard!


Discussion Starter · #8 ·
did you match, or miss-match the inlet manifold to the head ?
and roughly by what ammount did they open the exhaust ports at the manifold end of the port ?

Discussion Starter · #9 ·
Aussie / Just Custard:

Unfortunately, I know very little about the specs of this head-- believe it or not, I bought it USED off a friend's Evo! His car was up to 380HP @ the wheels with the head, but running an HKS 2835 turbine, big injectors and a Motec. Car was good for low 11's in the quarter mile (it was drag raced a lot). When he finally sold the car recently, he took off most of the aftermarket bits, and I was the lucky beneficiary of the head.

So as mentioned, I couldn't start to tell you the precise specs. All I know for sure is that it is pretty severely modified, and I think both inlet and outlet valves are larger than standard.

As for fuel consumption... I've only had it sorted with the new ECU since yesterday... but I have a funny feeling my fuel economy has dropped precipitously! May have something to do with a much heavier right foot now (enjoying the newfound power!)


2,295 Posts

regarding the cam you probably ought to try to find out who did the head work for your mate and check with them. As always you need to select components that are well matched. In this case a cam that is best matched to the head in terms of valve lift and duration. Otherwise you dont know what you are going to get. Chances are you should get a decent increase in power ~15hp.
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