DOHC Cam timing Discussion

[BadAssPerformance]

I'm a 16V n00b so thought I'd start a thread discussing tips and pointers on cam timing.

I have a 2.4L, but this discussion should be good for those, plus T-III, Masi, etc DOHC applications so lets try to compile everyones experiences and knowledge in one thread

So, in general, for each the Intake and Exhaust cam, what are the perforance effects from Advanceing or Retarding each?

[inmyshadow]

The neon performance book I have recommends the following for dohc.

Retard the exhaust cam until power is stabilized. Then advance the intake cam until power is stabilized.

They really don't go over how the powerband will be affected. They constantly state "it depends on your motor". Nor do they offer any idea on how much horsepower can be made. They just talk about moving the powerband around with a preference to top end the 2. DOHC motors.

later

[CSXRT4]

SRT-Forums.com has some pretty good info on this

Cam Talk Definitions & Cam Gear Talk Understanding

By: Pit Viper - "Why you NEED to dyno-tune your cams"

I see way to many people setting their cams based on what someone else has, or recommends. I can't count how many times I've seen someone set their cams to -2, +2 as a good "starting point".
There really is no replacement for going to the dyno and tuning in your car for what works the best for YOU.
In some cases, guessing can really hurt your output. Here's a brief example. I recently took my car to tune in a new set of Crane 14's. We installed them, set at 0,0, and started there.
First, we retarded the exhaust cam to -3 and dyno'd, then advanced it to +3. The red line is advanced, the blue line is retarded. Obviously retarding the exhaust cam was the way we wanted to go.



Next, we put the exhaust cam back to 0, and then retarded the intake cam to -3 and dyno'd, followed by setting the intake cam to +3 and dynoing. The green line is with the intake retarded, the other one is advanced.



So, while a base setting with the exhaust retarded would have been good, advancing the intake cam hurt my power big time. At the end of the day, we had the exhaust cam retarded -12, and the intake cam retarded -9 for the best power output.

[turbovanman²]

I have that thread somewhere from the SRT forums with all the info, if Frank would sticky sh*t, it would be easily found.

[Turbo3Iroc]

I bet his belt is off a tooth at the crank.

[Speedeuphoria]

Retarding both moves power to top end
Advancing both moves power to lower end
Moving independently changes overlap and LSA(this is the part that will vary from setup to setup, so dyno or track time is best judge)

[BadAssPerformance]

Good advice guys, keep it coming!

After I get the car tuned at the next boost level, I will start tuning the cams.

[Frank]

I have that thread somewhere from the SRT forums with all the info, if Frank would sticky sh*t, it would be easily found.

Which thread? I am willing to sticky a thread here and there, you just need to request it. What I don't do is sticky five million threads like you want everywhere because... well we won't go there and beat another dead horse.

[Speedeuphoria]

well that sticky on srtforums was removed, then they reposted it in a thread but it was never stickied again, also it had the adjustments and what they do backwards on some.
heres the copy over here
http://www.turbo-mopar.com/forums/sh...ad.php?t=21837

[GLHNSLHT2]

cause the forums would be full of Simon's sticky mess?

[WickedShelby88]

cause the forums would be full of Simon's sticky mess?

Yeah just ask the green men in Franks avatar. They know all about that.

[contraption22]

Yeah just ask the green men in Franks avatar. They know all about that.

SHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

[zin]

I've always looked at it like I've got a single cam that I can move the intake and exhaust lobes on the shaft relative to the sprocket (and each other). So, I can advance or retard each side (intake or exhaust),and in the process I can change the Lobe Separation Angle, and opening and closing events, but not the duration or profile. Its pretty cool, but it does open up a pretty big can of worms. Kinda like a 4 Link in a RWD car, there are 400 combos, but only 10 that "work".

Mike

[86Shelby]

From what I have gathered looking at dyno plots and reading notes from people who have been tuning with DOHC engine this seems to be a general rule of thumb:

1. Exhaust timing will move the powerband vertically.

2. Intake timing will move it horizontally.

3. Go spend some time on a dyno to see what exact timing works well for your setup.