turbo camshaft

[Froggx]

What would be good specs to regrind the stock 3400 camshaft to for a turbo running between 7-10 psi intercooled.

[bszopi]

Problem with trying to do a regrind for a turbo is the stock LSA isn't the best for a turbo application, and you can't change the LSA with a regrind... :S

[bszopi]

Hmm... I could be wrong.

http://www.60degreev6.com/index.php?name=PNphpBB2&file=viewtopic&t=2926&highlight=turbo+cam+specs

Compare it to the stock 3x00 cam specs:

http://www.60degreev6.com/modules.php?op=modload&name=Pushrod&file=index&req=viewarticle&artid=29&page=1

[Froggx]

Problem with trying to do a regrind for a turbo is the stock LSA isn't the best for a turbo application, and you can't change the LSA with a regrind... :S

It could be better but it could be worse, but either way a regrind will beat the stock setup.

Also I should add I am converting to LS6 springs so higher rpms and lift to around .500" are available to me. Also, I'm reprogramming my own ecm, so computer issues are not a problem.

[Froggx]

I decided to use the same cam profile as the crane H-260 for my regrind. This is 204*int/216*exh @ .05" and a lift of .455" int/.484" exh with 1.6 rockers. I feel this will give me optimal characteristics while not being too big. It is recommended for "mild turbocharging" anyway. I'm not actually going to call in until tommorrow after school though as I get the impression that they won't be open today. Any comments or suggestions on whether you feel I am correct in my choice of grind will be more than welcome.

[skalor]

Well, the problem with trying to get a perfect turbo cam is that it will be different according to what size turbine housing you are running. The idea of a turbo cam has to a lot with reducing exhaust gas reversion. Reversion results because usually factory turbo cars run around a 2:1 pressure differential between the exhaust and intake pressures. So, if you're running 7 psi of boost then you pressure in the exhaust manifold will be around 14 psi. So, when there is valve overlap the exhaust gases actually back up into the intake manifold and not the other way around like most people think. This is all relative to the setup your running so the 2:1 ratio is just an example. Anways, if your running a restrictive housing(like TGP...damn T25) then you'll have less valve overlap to keep reversion to a minimum. Thus the opposite is true if you run a very large turbine housing, then you're cam is going to look very similar to an N/A cam since reversion will be virtually non-existent.

So, when you say whay would be the best cam for a 3400 with 7-10 psi of boost...that not's enough info. We need to know what size A/Rs on what housing you are running. However, if your just looking for a little more lift with stock lobe seperation then H260 spec will be OK.

[Froggx]

I the a/r is .82 in a t3 housing.

[TurboGTU]

Overlap..thats your number one enemy on turbocharging. Not so much on LSA. LSA (lobe seperation angle) is not constant with ovelap. If both cams have the same duration..LSA would be a good determination of a good turbo cam.
Lets say we have two cams with 114 lobe seperation. Ones is a 190 duration cam and the other is a 230 duration cam. The overlap on the 190 would be about 30degrees..while the 230 is 60degrees of overlap. Why? Because the lobes of the cam become more of a square when the duration increases. You would need way more lobe seperation on a high duration cam. Any corrections..please feel free to add. Im still learning as I go.

[Froggx]

If lift varied proportionally to duration, wouldn't this squaring effect be negated? Also, wouldn't the angles the cam can ramp up to only become so aggresive before bad things happened, so if the approach and departure angles remained the same wouldn't the duration in vary simply by the number of degrees?

Of course, consider these events in a theoretical world, as we know the real world skews results.

[Guest]

Lift does not change with duration, at least not maximum lift, duration is just simply how long the valve will be open, actually usually it is measured at .050" lift, since most engine builders agree that any lift below this point is pointless to count, as there is very little flow.

Duration will effect lower lift flow rates.

Basically it boils down to, the area under the curve.

In most performance cases, you want as much area under the curve as possible, but other factors such as induction, head flow rates, exhaust, sanctioning rules, etc, to determine just the right grind, and even still, you'll probably get it wrong the first time. LOL

[Froggx]

you'll probably get it wrong the first time. LOL

If this weren't true, cars wouldn't be such great money pits