Herr-Kuhn

Agreed...I just wanted to see if anybody on here has experimented with changing camshafts.

special tool

If that is all you want to know - then yes, I have changed camshafts about 1,000 times.
Is there anything else you are asking, because you said you don't need a lesson in camshafts.

TurboTommy

With camshafts, it's not an issue of just using a more aggressive cam and thinking it will up your performance.
Camshafts have to be matched to the flow characteristics of the head and more importantly to the boost pressure vs turbine inlet pressure relationship.
It's actually good to have some valve overlap if your turbine inlet pressure is close to or even a bit less than your boost pressure. During this overlap period the higher boost pressure will totally scavenge the cylinder, which would otherwise never be possible. Throwing boost away is never an issue, but too much overlap combined with a very positive boost/exhaust ratio causes excess unburnt fuel in the exhaust (this will probably never happen with our cars unless you want to put up with a very laggy situation).

Blindly changing cams without knowing your exhaust back pressure (between exhaust port and turbo) can cause less than ideal results.

Herr-Kuhn

Why is it everybody on here is such a smart ***? My question about running different cams pertained to the 944 turbo and specifically with the K26-6. These are the chargers I intend to run on the twin turbo 928, so it is the basis for the comparison.

I know the cams I am investigating using are worth 30 HP normally aspirated on a 928 and are a bit more agressive than a stock 944 turbo cam, but not as agressive as the 273 grind on the Webcam cam that is reported to work well on the 944 and 944 turbo. That cam has a 112 LCA and a .480" lift.

This is not a blind change. I've studied the grinds on the stock cams, Euro 928 cams and 944/ turbo cams. All I was looking for was some real world feedback on more agressive cams in the 944 turbo which uses the same turbo I plan to run on the 928. Granted, there will be more back pressure in my system because of my manifold design, however I only intend to run 12 psig on this engine.

So, is there anybody who has done this? Again, I ask the question directly with the hopes of not getting the smart *** comments back.

Dark Lightning

Everyone has an opinion and is ready to spew heresay...

Crazy Eddie

They say,
"Opinions are like ********
Everybody has one"

DanG

I have an NA cam already installed in my new car. The engine must be rebuilt right away (bought it in non-running condition), so I'm trying to decide if I should pull the NA cam in favor of a stock turbo cam or drop $$$ and get an upgrade.

The stock cam specs show these are the only differences between the turbo/early NA cam (944.105.155.05) and the late NA cam (944.105.155.09)...

The turbo cam has:
1) 8 degrees less duration on the exhaust lobe, with the same center.
2) 1 mm less lift on exhaust

Does anyone have any dyno numbers comparing these two stock cams back to back? What are your thoughts?

For comparison, JME's cam specs show his stage 1 cam has equal lift to the stock turbo cam, while his stage 2 cam is equal lift to the stock NA cam. So it can be reasoned that Milledge's "mild" cams work only on duration and timing, lift isn't much of a factor.

http://www.jmengines.com/camshafts.htm

DanG

Anyone have any thoughts on the NA cam in the turbo engine? Should I pull it, or is it fine. Zero performance advantage is fine with me, I just don't want to be taking any big hits.

Pauerman

Dan, check this out: members.rennlist.com/951_racerx/CamProfiles.pdf

For what it's worth - former head wrench at Powerhaus Chris Carroll told me that the N/A cam is the way to go. According to Chris, in the 10 years he was there he used this cam for many 951 applications and claimed the dyno results showed the power gains were equal if not superior to a comparable Milleage cam.

HTH
Vic

Magown

So Vic, the Carroll guy is saying to use the 944.105.155.09 cam in a 951?

DanG

Vic, that .pdf started me off on tracking down the cam data.

Hearing that about the NA cam sounds good to me, but I'd still like to back it up with some supporting cam theory.

I guess I just need to find some books or something to read up on why/if an extra 4 degrees of exhaust duration before and after the center, plus another 1mm of lift is the right thing on a turbo engine. And if it was, why did Porsche switch AWAY from that cam? Doesn't make much sense to me.

Crazy Eddie

And if it was, why did Porsche switch AWAY from that cam? Doesn't make much sense to me.
I am by no means a cam guy but the reason Porsche may have gone with a diff cam could be distilled down to a # of factors
Fuel consumption - EPA
Drive ability ( everyday ) Idle smoothness.... driving in traffic etc.
Typically there is a give an take with using diff cams ....
There are usually trade off ..
regards
Ed

Eyal 951

anyone have some technical insight, or dyno numbers?
~Eyal

TurboTommy

Measure your turbine inlet pressure and then make up your mind from there.

DanG

Good points, although it still seems odd that the NA cam could have any kind of significant benefits, and still be kindof a well kept secret.

I'd think everyone on this board would have an NA cam if they really offered significant gains.