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Do I use the 93 turbo heads, or the 91 NA heads?

Posted: Tue Aug 09, 2005 1:25 am
by douglas vincent
Obviously I don't have a turbo, so I don't need the turbo aspects of the turbo heads (oil and water line connections).

But are the cams better or worse, ie has anyone gotten any updated flow rates for these heads?

I have three sets of NA heads, and 1 turbo set. As it is, I am taking an NA set in tomorrow morning to have rebuilt.

Thanks

Posted: Tue Aug 09, 2005 2:53 am
by Legacy777
I would think the heads are going to flow similarly.

The word is that the n/a heads have bigger valves. I can't confirm this, however since you have heads sitting there, you can.

Also the n/a cam is going to have a little more valve overlap for cylinder scavenging.

If you plan to run without the supercharger at times, I'd definitely go for the n/a heads.

I'd still probably run the n/a cams....

Posted: Tue Aug 09, 2005 5:58 am
by scottzg
Legacy777 wrote:
I'd still probably run the n/a cams....
Why?

I'm curious.

Posted: Tue Aug 09, 2005 6:25 am
by entirelyturbo
Aggressive cams are of little use in forced-induction cars. You can actually be forcing air from the intake valve right out the exhaust valve if there is enough boost and enough valve overlap.

Posted: Tue Aug 09, 2005 6:59 am
by douglas vincent
So your vote is which direction?

Posted: Tue Aug 09, 2005 2:25 pm
by professor
>>You can actually be forcing air from the intake valve right out the >>exhaust valve if there is enough boost and enough valve >>overlap.

yep. which is why cam re-grinds basically don't do much for turbos, you have to be real conservative on overlap, and the valve timing tends to be different than N/A to prevent detonation

if you are going to boost it, use the turbo heads, the original engineers couldn't have been stupid. valve size is not going to be crucial at under 10 psi

plus you can subsequenty put a big-assed turbo on it if you want

Posted: Tue Aug 09, 2005 3:21 pm
by BAC5.2
If cams don't make a difference on Turbo cars, then why are such huge gains seen from different cams?

There are EVO's running hot cams making 20whp more than before the cams.

TurboXS themselves couldn't break 400whp with the stock cams and stock EJ205 heads. They dropped in a set of JUN Prototype cams, retuned for them, and made 498whp.

Posted: Tue Aug 09, 2005 3:38 pm
by legacy92ej22t
I agree. Ever heard an open class rally car? They have some wicked ass cams. They sound hot.

Posted: Tue Aug 09, 2005 3:40 pm
by legacy92ej22t
I probably shouldn't generalize like that, a lot of open class rally cars have hot cams, but probably not all.

Posted: Tue Aug 09, 2005 4:00 pm
by Matt Monson
Well,
As you go to a larger turbo, and more boost, you can afford more overlap, but more importantly you more duration. The simple explanation of what happens is that as a bigger turbo has more lag, it kicks in at later rpms, just like the cams with more duration do. But the difference in the Ej22 stock cams from turbo to NA is only a couple of degrees in overlap and a slight change in where they open. I've got the specs at home and will try to remember to bring them in and post them up.

Personally, I would use the NA heads because of the larger exhaust valve (1/8" larger). If you are worried about the cam profile, just put the turbo cams into the NA heads. But I think that a little more duration (and overlap) will give you better performance.

I often make example of Xephyr, because he is a friend of mine, and I have witnessed his experiments first hand over the last 5 years. He runs the DOHC EJ25 heads on an STi block these days. He played with cams a lot. He ran the stock cams. Then he put in some WRX cams with virtually no change in total power. There is that little difference in stock turbo vs na cams. Then he put in some HKS v3 STi cams which have 272 degrees of duration. What he found was that while he gained about 15hp above 5000rpm, he lost a lot down low. His power under the curve was less than on the RS cams. He almost immediately went back to the stock NA RS cams since those were the ones he made the most total power with...

A mild aftermarket NA cam has duration in the 220-230 degree range. This is only 15-20 degrees more than a stock turbo cam. It is not enough to worry about the blowby issues on a smaller turbo or SC, and will gain you power...

Posted: Tue Aug 09, 2005 4:59 pm
by professor
you guys are all talking about totally custom rigs with stand-alone engine management tuned by experts over several hours or days of dedicated dyno time, all to get timing fuel maps, etc exactly right to prevent the dreaded engine-destroying detonation, and not only that but screw general drivability and idle quality, etc which tends to suffer with over-hot cams turbo or not

that has little to do with well under 10 psi of boost on a street car on at best piggyback management or none at all, plus if he goes with the NA heads the very convenient fittings are missing if you want to change to turbo. maybe that doesn't matter if you like to change heads regularly

if the NA heads are best why the hell did they bother making turbo heads ?

Posted: Tue Aug 09, 2005 5:29 pm
by Matt Monson
Well,
The question I would pose in response to your question is why would a smaller exhaust valve be a performance adder?

I don't think it would. I think that likely the factory's thinking behind the smaller valve was port velocity and torque out of a stock engine. But start playing with upping the boost levels, and it becomes a liability and not an asset.

Aside from that, the EJ22E and EJ22T heads are the exact same castings. The oil and coolant returns are drilled in after the fact. As is the exhaust valve seat on the NA heads widened to accept the slightly larger valve.

Same thing with the DOHC EJ25 heads I spoke of before. They are the same castings as v3 and v4 '97-98 WRX heads, and have bigger port size than the new EJ205 heads.

The point of this is that Subaru shares a lot of parts across the model ranges, and slightly modifies them for the intended application.

Personally, if I were in Vincent's shoes, I would use the NA heads. They are going to flow better when he turns up the boost. And from what I have seen, he will not abandon the SC, and go turbo anytime soon, and so the whole oil/coolant return issue means he's got to cap them until he turbo's the car, which will likely never happen...

Posted: Tue Aug 09, 2005 6:19 pm
by Legacy777
scottzg wrote:
Legacy777 wrote:
I'd still probably run the n/a cams....
Why?

I'm curious.
For pretty much all the reasons Matt talked about....

For what Doug is wanting to do, and what he's running, I think they'd be the best setup.