Cam overlap on a boosted setup...

[Phantom GTZ]

Hey guys have a question:

If one were to be running W41 or 226 degree cams, what kind of advance/retard would be best for a turbocharged setup?

4 degree retard on the exhaust, and 4 degree advance on the intake?

or the other way around:

4 degree advance on the exhaust and 4 degree retard on the intake?

Maybe just advance the intake?  retard the exhaust?  vise versa?

I understand best results would have to be reached on a dyno, but I'm trying to understand the concept.

Thanks,

-Joel

[nocutt]

...most tuners/DIY have different ideology on cam theories coupled with turbochargers especially.
taking your post for face value, I will say retard the xhaust AND advance the intake...by how much is definately based on clearance first, then the turbo and finally the compromises you are willing to accept etc, etc...

BTW you can make power with 'bigger cams' and overlap...but I doubt a full fledged race car is part of your equation... :hammer
hths

[Asylum]

You need to retard the exhaust to compensate for the turbo, and advancing the intake, well you have to be very careful.
It is the tendency, but detonation becomes your new friend.
4 degrees both ways sounds pretty safe, but as "nocutt" states, there is ALOT more to be considered.
How much boost?

[Phantom GTZ]

15 lbs through a GT3255E.

I'm running the 226 degree/.410 lift cams right now with the stock cam sprockets.  The setup is still very much streetable, it does however require the 92 getrag swap.

The gear spacing from 2nd to 3rd with the higher powerband is like a kick to the teeth.  Even more so than stock.

I just get spooked easily as of late.  I'm not sure how much of an exact science playing with this variable is.

I'm very near completion and I'm trying to cover all the Quad 4 demons.  I just don't know if this is one I need to concentrate too hard on, or live with.

[wicked-irocz]

I would suggest running smaller overlap cams unless you are looking to run this thing like the honda owners do to 11000 rpm.  A turbo will not make low speed torque but will make more and more power to the redline.  You need less overlap to get off the line.  The turbo will take care of the hp.

[rweatherford]

I think the stock cams work pretty dang good and keep the revs from getting really high.  I sold my larger cams.

[Conscious]

(wicked-irocz @ Apr. 21 2006,21:30)Q
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EI would suggest running smaller overlap cams unless you are looking to run this thing like the honda owners do to 11000 rpm.  A turbo will not make low speed torque but will make more and more power to the redline.  You need less overlap to get off the line.  The turbo will take care of the hp.
I thought you could make more power with overlap? also I am sure a turbo can make low end torque I guess it will be how the system is hooked up to begin, right?

[rweatherford]

You probably can, if it is all done correctly.

Try looking around at V-8 cams just for a relative duration amount vs the application.  I think you will find split durations on SC and turbo engines and large duration cams for high HP NA applications (also with high RPM)

You can always call someone like Comp Cams and get their thoughts on the issue.  I am far from a cam expert.

As far as "low end TQ".  I'm not sure what he means.  It is all in how things are setup.  My car can hit full boost at less than 2000 RPM and I'm sure that will make more "low end TQ" than any Beretta designed V-6.  The Quad4 in a NA application makes as much or more TQ at 3000 RPM as a 2.8 V-6.

Depends on what "low end" is defined as.  If it is from idle to 2000 RPM, then NO the turbo car may not have more, but it will have as much as a NA version of that motor if set up correctly.  This is partially why my car can still get 34 MPG, yet a WRX will only get about 28 with a smaller engine.  Still hard to believe that those cars have so much lag with such a small turbo.

[IsaacHayes]

WRX engine probably doesn't make the same HP NA the q4 does NA. Probably less torque too.

[nocutt]

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E Originally posted by Rex:
Try looking around at V-8 cams just for a relative duration amount vs the application.  I think you will find split durations on SC and turbo engines and large duration cams for high HP NA applications (also with high RPM)

You can always call someone like Comp Cams and get their thoughts on the issue.

...cam theories with turbos are a headache to follow. I think as mentioned your application will ultimately define the way you will run 'em. I have seen different sides of the spectrum make plenty hp...those who swear by minimum cam specs, maximum, negative overlap cams, cams w/ plenty overlap etc,etc...
The good thing here is you have the ability to tune the cam independently to a certain degree.
Good luck

[wicked-irocz]

(rweatherford @ Apr. 22 2006,07:39)Q
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EAs far as "low end TQ".  I'm not sure what he means.  It is all in how things are setup.  My car can hit full boost at less than 2000 RPM and I'm sure that will make more "low end TQ" than any Beretta designed V-6.  The Quad4 in a NA application makes as much or more TQ at 3000 RPM as a 2.8 V-6.

Depends on what "low end" is defined as.  If it is from idle to 2000 RPM, then NO the turbo car may not have more, but it will have as much as a NA version of that motor if set up correctly.
Yes, I was talking about below 2000 rpm.  I really dont care to have an idle over 1000 rpm and have to slip the clutch at 2000rpm to get going.  But I just dont care for that kind of stuff when the car is going to get driven on the street.  What I was saying is below 7000rpm your not going to see much of a difference between the 226 cams and the HO cams other than below 2000 rpm.

[rweatherford]

Have you guys ever driven a Quad?  I slip the clutch out at idle and pull away without the gas pedal if necessary.  My idle is probably around 900 RPM.  That is on 8.5:1 compression...

Yes the 226ers are for BIG RPM.

The NA Impreza motor is a 2.5L 160 HP and 160 Ft-lbs.  I see that the new ones are 173 HP and 166 ft-lbs.

[Phantom GTZ]

http://www.drivingsports.com/a/template ... z=5&page=2

The suburu guys spool it at about 2900 RPM.  I'm hoping for 2500 rpm, but more lag will probably end up giving me more traction.

Rex, didn't your cams much more lift as well?  mine are 226 degree .410 lift (similar to stock).

You figure:  

HO (212 degree) = 6800 rpm redline,

W41 (219 degree) = 7200 redline,

soo.......  

226 degree cams = 7600 rpm redline.  I'm probably going to limit it to 7400 due to it being the max recommended for the stock valve train.  Besides, the peak horsepower of the quad is seen before the redline.

I probably will contact Comp Cams.  Do you possibly have a contact?

[rweatherford]

Just call the tech line or customer support.  We toured that facility at BFest in Memphis.  It is a nice place.

My cams had a .408 lift.  They may have actually been 224 degrees too, I can't remember exactly.  I'd have to look them up if I have any info on them.  Doesn't really matter now.  They are gone.

[Phantom GTZ]

Jus kinda curious,

How much power did they put down N/A once you tuned the car?