schip43

I'snt that nylon block in the middle of the cams the issue? I have only seen one S2 ever it was my friends car.

And is the 2 by 4 cut out only needed if you change the cam gears? cause me saws and sheet metal are not a good combo and it would look like hell anyway.

Chris appreciate the offer and the input but it's only a virtual motor at the moment!

Paulyy

yeah the nylon block wears. sometimes just the chain breaks and sometimes it's not a pretty sight.

JohnKoaWood

But you could always ditch the chain and tensioner, throw in a second exhaust cam and nose drive pulley, and belt it!

schip43

I thought I saw that, the conversion to two cam gears? So the OEM must be one gear and a slave to turn the other cam, is that what that chain in the middle is about? Is the conversion where the 2 by 4 cutout in the hood comes from?

jlturpin

Well, this thread is very interesting. I happen to have a 16V 2.5L and have been wondering about this for some time. It is also just another one of my many "plans to complete" and may never go further than reading this thread.

I have compared the intake and exhaust cams for the dual pulley setup and there is not a bunch of difference, I read the specs at some point in the past, but can't recall them now. Is there any information available about the front pulley setup and part numbers for pulley and TB?

Chris, what did the dyno results look like compared to a similarly built 8v?

schip43

Wow they are real, that makes at least three by my count (running or not) could you post some photos of the head.?

That video Chris posted sounds wicked!

JohnKoaWood

What it comes down to is, it CAN be done, HAS been done, and WILL be done again, however right now it isn't cheap, nor is it easy, nor is it a weekend swap.. it takes time to assemble all the constituent parts.. and as Chris already said, the cost difference isn't great between the 2.5 16V turbo and a decent 3L build, with differences being low end torque!

And yes, remove the intake cam, put an exhaust cam in its place, ditch the tensioner, and chain, put different pulleys on the front, different belt, and dial in each cam drive gear for timing..

As for why to use custom pistons, valves and springs.. well I can let Chris explain, or we can just sit and ponder this for a bit...
BUT has anyone among us experienced valve float from boost pressure, or valves hitting the piston without the timing belt breaking? I will save you the search... the answer is YES it can, and does happen! not to mention the differences going from 2 valves to 4 per piston... chamber size and volume.. valve overlap, TDC overlap.. etc..etc..etc.. you could write a book about it.. but it would be relegated to a shelf full of other books about it...

schip43

Man it takes me more than a weekend to change spark plugs! Not a daily driver so no issue there. Not cheap yeah I'm getting that, not practical or necessary for a 400 hp goal got that. Maybe delicate and unreliable, well unreliable... I got that now!

But... did you hear the video Chris posted! Man the sound, scare children and old people!

Worth the entry price, for the sound alone

67King

You'd be surprised. There are valve reliefs in pistons for a reason. Almost all modern engines have valve reliefs to account for valve/piston interference. It may not apply here, but it may, I don't know for certain. Plus the turbo pistons give you an ugly quench. And you don't know what CR you'd end up with.

There are three reasons you might want new valves. One, more heat. Two, higher spring pressures (I'll get to that). Three, in the event you need to regrind the cams to give more LSA to make them more turbo friendly, you'll need more length to account for a smaller base circle. Right now, the S has an LSA of approximately* 111 degrees. 114 degrees would be better.

Springs. The valves are 37mm, or about 1.45" in diameter. The factory springs are designed to close the valve without the added force from the air. When you add 18PSI of boost, that ads 30 pounds of pressure.

Ceteris paribus (i.e. same bore, stroke, rod ratio, intake pressures, and MBT), a pent roof, central plug chamber (4V) will give you about 0.7 points more compression than a 2V chamber. Sure you could bolt on a head, but that doesn't mean you'll get good results. I'd try to keep it between 8.5-9.0:1, rather than whatever the resultant is.

* from manual:
EVO 36CS BBDC
EVC 4CS BTDC
IVO 4CS ATDC
IVC 40CS ABDC
I assumed the lobes are symmetrical, giving peak lift for exhaust at 110 BTDC, and the intake at 112 ATDC. I do not know if that is correct.

schip43

Stock springs a no go, where would you get custom valve springs? Stock cams won't work? I thought most turbo motors did pretty good with NA cams?

67King

All depends on the grinds. My old car (2.3 turbo Ford) had a cam with a 111 LSA and it was horrible on the street. Took FOREVER to spool. The NA cam may have a friendlier grind, I don't know off hand.

schip43

2.3 Turbo Ford are you the Merkur guy?

JohnKoaWood

And I have seen a few of the "projects" in work in his shop too... when I dropped my motor off to him..

I agree with you on the sound, and actually chose to step back from the 2.5 16V due to extending the cost on an already extended build, including the changes that would be needed to an already expensive intake and exhaust setup...

But thats the stuff for a different thread...

67King

Is that what y'all call me when I"m not around Yeah, that's me.

schip43

Aww dude you were there! Well I am an audiophile also so I gotta go with the Noise! Street car would be my goal would this have a streetable power band, 3000 and up or would it be a 4000 rpm up motor?

Cause my current steed is already pretty pissy about 55 mph in 4th gear let alone 5th! Wouldn't want it to be any worse!

And yes I think I get it do the liter and the lower end sucks up dollars, do the 16 valve head and the top end sucks up dollars!