2manyhobyz

iTrader: (4)

So if you could have a custom cams made for a 99-00 head specifically for a turbo application, what would you tell the guy for specifications? Would you look at what's been done with similar turbo motors? Evo, Supra, Nissan-GTR, Audi/VW/Porsche come to mind. Has anybody really nailed it on what they are using and why they like it. I'm still trying to understand more about this and thought there would be some of you would have a way better handle on this.
Thanks for the help.

18psi

iTrader: (76)

What are your goals?
Where do you want your power and how much of it do you need?
etc etc.

There is no "best" cam IMO, there are just ones "best for your needs"

viperormiata

iTrader: (24)

Find out what cam Eliminator was using.

18psi

iTrader: (76)

Wasn't that a custom 1-off?
Also he was using a non bp4w head

samwu8k

iTrader: (3)

from what i read most turbo motors do well with low overlap cams to avoid exhaust gas being sucked back in during the intake stroke. so i guess you would want to increase lift, and perhaps get a intake manifold with shorter runners to help it breathe better in higher rpms.

viperormiata

iTrader: (24)

No idea, just know his torque was unreal and his cam specs were surprisingly mild; OP stated "if you can have custom cams", in that case I want Eliminator's setup.

Yo, OP. Give us some details on your setup.

jtothawhat

iTrader: (7)

Kelford 272s are awesome, 10.5MM of lift...awesome sound awesome power.

viperormiata

iTrader: (24)

Does it sound like this?

2manyhobyz

iTrader: (4)

The build is an extra 99-00 motor I picked up off Craig's list. The usual stuff, forged rods, piston's, somewhere in the 8.6 to 9:1 range. Boundary's oil pump. I'm gonna try my hand at building my own intake and for now leave the FMII cast exhaust manifold lower on the priority list. Thought I heard the high end of the happy side of the 2560 is 14-16psi?
If I understand correctly, turbo motors like higher lift with not a lot of duration and try to keep the overlap as little as possible. That being said, I was looking at some that were about 288 IN/EX and lift 10.8. I know this is a na application what I don't know how is much overlap you can dial out with cam pulleys and not hit pistons.

sixshooter

iTrader: (12)

You might want to investigate lobe to lifter bore clearances with that much lift. Some light clearancing and machining may prove necessary. Troy (miata2fast) would know off the top of his head because he has a 99 head and bigger cams and has messed with the clearance issue already. He is N/A so he needs big *** cams, a ported head, and lotsa revs to make power.

2manyhobyz

iTrader: (4)

That's kinda an extreme example. I'm trying to spend some time seeing what's out there for turbo cams.


Comparison to other engines:

4v Modular Ford

See these cams that they sell for the 4-valve modular Ford which is almost a copy of the 928 S4 engine with a bit longer stroke and bit smaller bore:

http://www.compcams.com/Cam_Specs/Ca...?csid=962&sb=2

The _mildest_ turbo cam sold for 4-valve modular Fords by Comp Cams is 106260 / XE258BH-116. It has intake duration of 222 and exhaust duration of 224 degrees @0.05". The lifts are 0.475" and 0.450" for intake and exhaust. It has notes "DOHC-Street performance with excellent torque. Works well in Supercharged or Nitrous engines."

They have two real turbo performance cams too, which have more duration: 230 in / 232 ex for "serious street effort for Supercharged or Nitrous engines." 238 in / 240 ex for "max strip and street cams for Supercharged or Nitrous engines."

Even the biggest set above is milder than the mildest aftermarket 4v mod Ford turbo cam set offered!

Subaru EJ25

Here's another engine that is very similar to the turbocharged 928 S4: Subaru EJ25. The bore and stroke are identical to that of 928 S4. The stock valves are 36mm intake and 32mm exhaust. The Cosworth performance head for the engine has 37mm intake and 33mm exhaust valves -- the same as S4 stock. Of course, the engine is turbocharged.

What kind of cams do they use? The stock cams in the US and Japanese versions are

Cams, Adv. Dur., Dur @ .050, Lift (in), Lift (mm)
USDM EJ257 (’05-up STi) stock, 256°/256°, 204°/208°, .378"/.385", 9.60/9.78
JDM EJ254 stock, 256°/256°, 211°/209°, .374"/.371", 9.50/9.42

Notice the split seat timing for both cams. The two models have different AVCS (variable valve timing) operating ranges, so the cams shape is different.

Now, what aftermarket performance cams are available for this engine? These are more relevant because they are basically designed to be run with the AVCS off. Crower offers two cam sets, the milder one first:

http://www.bryancrower.com/makes/subaru/ej257.shtml

Street/Strip Specification. Plug and play application. Short duration for nice street manners, slight lope at idle. Excellent all purpose spec. OEM spring OK.
Adv. Dur., Dur @ .050, Lift (in), Lift (mm)
272°/272°, 222°/222°, .400"/.400", 10.16/10.16

Race Specification. Longer duration profile, added rpm potential. Intended for fully built engine. Tuning and ECU mods recommended. Requires spring kit BC0600.
Adv. Dur., Dur @ .050, Lift (in), Lift (mm)
280°/280°, 234°/234°, .425"/.425", 10.80/10.80

Again the turbo cam sets listed above are milder than the mildest aftermarket Subaru EJ25 turbo cam. Especially the exhaust timing is much, much shorter.

More reading here:
http://www.amsperformance.com/camtest.php

http://www.turbomagazine.com/tech/tu...8/viewall.html

Please feel free to contribute links/info to understanding the differences between a turbo specific and an NA cam

bobbiemartin

iTrader: (2)

You might want to read "How to Build Horsepower" by David Vizard.
While basically for V-8's he does cover twin cam 4 valve 4 cyl engines as well. There is a specific section on turbo cams. He says that back pressure (really pressure differential between intake & exhaust) should be the main criteria for turbo cam selection. He also goes into general cam selection and says overlap and lobe center angle (LCA) are the most important things to consider in cam selection, not duration. Its a very good read if you are considering modifications to any engine.

NiklasFalk

iTrader: (1)

Looking at my VVT head the stock intake cam don't have much clearance to the lifter bore "outside" edge, there might be .5mm or so. So maybe 9mm lift at stock base circle (27mm radii) would go free. 10.5 would need 1.5mm smaller base radii (33mm base diameter as with the Maruha cams) if you are not milling away a bit on the lifter bore edges.
My plan is to reduce the radii 1mm and take whatever I need from the lifter bore edges (10-10.3 max lift when I stop procrastinating and get the cams designed).
The cam lobe should not hit too close to the edge of the lifter (so there is a reason for making the radii smaller from that perspective too) I've been told.

Who said this was easy and free from voodoo

As for design parameters for Turbo, read up on all the theories and make your own approximation. Getting a custom cam is not that expensive compared to a general OTS one that is not designed for your purpose.
The BP is nothing special, it's a 80's 4banger with ports that flow decently, so general principles actually work on these too

1vicissitude

Kelford 272s have 10.00mm lift, the 280s have 10.50mm. They also don't have any cams listed for bp4w or bp05 either. For the 1.6 Toda has 264 with 10.30mm which should be good for a turbo.

If I were going for a turbo cam, I would find the lowest duration with the highest lift your head can handle. That way you don't move the power band too high in the rpm range.

2manyhobyz

iTrader: (4)

Yes, research seems to be pointing in the direction of low duration/high lift.
Also ordered Vizard's book.

1vicissitude

What are your thoughts on staggered cam lifts and durations? How would a higher lift and/or longer duration intake cam with smaller lift and/or duration exhaust cam effect output and spool? I have read a more aggressive intake cam can increase power, but I am not sure of any results in real world practice with our engines.

Currently in my 1.6 I have 252* .340" (8.63mm) intake / 250* .335" (8.5mm) exhaust, but I am curious if I swapped in the kelford 272* 10.00mm intake cam it could be of benefit? Perhaps, maybe even the toda 264* 10.30mm just on the intake and leave my current exhaust cam in.

jtothawhat

iTrader: (7)

The Kelfords are 'turbo' cam if that makes a difference, Toda I don't think is designed for FI applications.

TravisR

iTrader: (9)

The list so says me, if that counts:

1. On turbo engines the only important number is intake duration and lift.
   
2. Exhaust flow is completely constrained by turbine backpressure except for extreme race engines where intake pressure exceeds turbine pressure. Therefore exhaust lift and duration is not important.
   
3. Overlap should be limited to the maximum in order to limit reversion into the chamber and charge contamination. Exhaust duration should be sacrificed in-order to prolong intake duration length.
   
4. Over-sized exhaust valves should not be utilized as again exhaust flow is limited by turbine backpressure, and not physical geometry.
   
5. Where possible long turbo runner lengths should be used in order limit pressure wave generation in the turbine section. This can keep resonances from back filling the chamber during "inversely tuned frequencies"
   

/end

Travis

1vicissitude

Travis- Do you feel there is a point when too much intake lift can be a negative thing. Like would it be too extreme to just drop in the Kelford 272* 10.00mm lift intake cam, and leave the exhaust cam stock on the 1.6? Is there such a thing as too much stagger? If intake valve size is the only thing increased, we could probably go larger than the typical 1mm+ because the exhaust valve isnt fighting for the same space with the exhaust valve at stock dimensions, right?

I wonder if anyone has ever done any of this with any success?

TravisR

iTrader: (9)

** I don't know on that combination what would work. I haven't done any simulations of cams near that so. Who knows!?


So there was a man named Billy Glidden who worked on pro drag vehicles some years ago.

http://www.jegs.com/i/Edelbrock/350/...oductId=750172

He evidently got eaten by Edelbrock, but the most important thing that came from it is that maximum power comes mostly from intake efficiency and not from complete exhaust or exhaust stroke efficiency.

Calculating the integral over the perimeter of the intake and exhaust valves at .5in of lift, our ideal intake valve size would be 38mm following his ratios(absolutely impossible for us). This goes to show you though that increased exhaust valve size is not necessary.

Maximum intake valve duration is limited by reversion into the intake tract as the intake velocity loses out to pressure building from the piston moving up the sleeve, and charge contamination by the exhaust back pressure on the other side of the stroke. So optimal camshaft design would vary wildly by turbo sizing, intended operating range, operating pressures, and whether VVT was available.

There are many significant factors in the creation of viable camshafts, which is why people get such different results using off the shelf cams in even slightly different power adder combinations.