legacycentral bbs

Hi,
I know for some of you this will seem like a dumb question but humour me.
What is the reason for going with a quad cam engine, you can fit the same amount of cams on 2 camshafts, do the cams on each shaft differ slightly meaning that each valve opens and closes at different points, maybe 1 set for lower rpm 1 for higher???? I realy have no idea here, just guessing, would be interesed to find out why.
Cheers

hmm? Do you mean why do you have 4 camshafts? You've got one for the intake valves on the driver side, one for the exhaust valves on the driver side, one for the intake valves on the pass side, and one for the exhaust valves on the pass side.

I think he's asking why it's better to have 2 cams vs one.

hi,
yea sorry should have cleared that up, why have 2 as its not necessary, 1 camshaft will do both intake and exhaust, whats the reason for having 1 shaft for intake and 1 for exhaust, other subaru
engines dont use this configuration, i.e. the wrx which is a DOHC.
Is there any advantage to having a quad cam???

Less rotating mass per cam, therefore they can spin faster and get up to speed faster.

This extra room for play allows better control of both the intake and the exhaust valves (i.e. infinitely independently adjustable) and therefore creates a better breathing engine up top.

Quad-Cam = Dual Overhead Cam. The WRX motor is a quad cam. Your EJ20T is a DOHC. Our EJ22T's are SOHC, dual cam motors.

More cams are better for up-top breathability.

Thanks for that, feel like a bit of a twit now lol.
cheers

This pretty much hold true for any car. The more cams and valves you have, the better your high-end breathability is going to be. The fewer cams and valves you have, the more punchy and torquey your engine will be at lower rpm's.

Here is a good article to understanding cams.

http://auto.howstuffworks.com/camshaft.htm

You have better control over your valves when each cam is responsible for one job. SOHC has to work both I and E valves. Sometimes running SOHC can limit your cam profiles do to the size and duration of the cam lobes.

Also another thing to be considered is valve angle, the wide angle of early quad cammed EJ's wouldnt be possible with a one cam per head set up

After the BC/BF, Subaru stopped calling the boxer setup quad cam.

Just so you know, the USDM EJ22T is a SOHC engine.

I want, in the worst way, to buy a used WRX engine and do a top-end swap to convert my EJ22T to DOHC.

I had several people offer me 1998 JDM WRX heads for about $750AUD which is like $580usd if im not mistaken when I posted about it on the MRT forums. They bolt right up, same coolant passages and whatnot. You can also drop in most STi cams if you're looking for a more aggressive cam angle and higher lift valve operation.

Since then I've decided to just go with the phase I 2.5RS heads on the personal advice of mark ramirez.

I'd like to buy a COMPLETE WRX engine, do a longblock swap and hook it back up instead of peicing everything together.

It's unfortunate though, since the whole engine would be apart, It would be smart to re-do EVERYTHING at once. Plus, I doubt the stock ECU would be able to control the beast, so I'd need to go with some good engine management. And all of that would put me about 10k in the hole, and my tranny would still need lovin.

Oh you mean just drop the ej20 into your legacy?

That's a WHOLE different project!

Really though, the legacy shortblock is much better, it just needs a little polish to make it run like a shiny new wrx engine!

ej22 + dohc heads > wrx ej20

stonger block, better pistons, more displacement...add a nice turbo and you're ready to spin tires.

I'm going with the new heads once I decide it's time for a rebuild, as the engine will be out of the car anyways. The amount of oil coming out of my PCV system is sending me a strong signal that I need a nice motor refresh!

Phil, did you mean a short block EJ22 swap with a WRX? Redoing everything like seals and such is a very easy job and would be baqrely any time extra to swapping short blocks unless you were doing bottom end components.

Steve

I'm not sure anyone has really hit this question on the head. Basically, you want more valves per cylinder in order to improve head breathing. In order to maintain proper valve angle and cylinder dome, the valve stems go off the top of the engine at an angle away from each other. In order to articulate those stems, you have to make a mechanical connection to the camshaft. If there's one cam, you have to put a lot of lever between the cam and those valve stems to bridge that angle between the stems. THAT'S where the extra reciprocating weight comes from. More cams means less lever weight. More cams doesn't mean less cam weight. This weight is significant - this is the area that really limits your redline. When you over-rev the engine the common failure is valve float, which is thanks to too much weight in this system.

It's true that DOHC allows independent intake and exhaust variable valve timing, although I don't think that's the main reason we see it.

Another reason that manufacturers like DOHC for four (or five or more) valve engines is that the lobes on a SOHC have to be very narrow to articulate four valves per cylinder, increasing manufacturing costs and leading to possible failures.

More cams always better, unless you drive Mazdas.

ACP

Isn't valve float the overpowering of the valve springs by revving to high?

I didn't think it had anything to do with cam weight.

The problem is that the spring doesn't return the valve to a closed position quickly enough. Although the cam lobe pulls itself out of the way in time, the rocker stays in contact with the valve stem even while the cam lifts off the rocker at the other end. If the rocker is longer, it's heavier, and THAT'S what the spring is fighting against.

CAM weight is not the problem: valvegear weight is the problem. More cams means lighter valvegear.

A

musketeerracing wrote:The problem is that the spring doesn't return the valve to a closed position quickly enough. Although the cam lobe pulls itself out of the way in time, the rocker stays in contact with the valve stem even while the cam lifts off the rocker at the other end. If the rocker is longer, it's heavier, and THAT'S what the spring is fighting against.

CAM weight is not the problem: valvegear weight is the problem. More cams means lighter valvegear.

A

Wow, that's a great explanation, thanks!