Playing with cam timing

[Joe_Van_Duno]

So looking for some opinions here. I had a huge story written out, but I'm just going to cut to the chase....

When advancing cam timing you gain bottom end power and loose top end power, but how does this affect A/F ratio? I advanced cam timing 3 degrees and all of a sudden I was really rich I'm hoping this is related....

If thats correct, then could I retard cam timing, get more top end power (which the wonderful 2.5 lacks) and lean out the A/F ratio? I know this would slow down how fast I build boost, which is all ready a major concern of mine, but if I can make my max power closer to the 5000 mark I think it would help me out at the track. I'll spray enough juice to make up for any bottom end power loss.

[cordes]

There was just a great discussion about this, but I forget which thread it was. Some of the dyno graphs were amazing and highlighted the advantages of retarding the cam on our motors. It doesn't look like there's much to lose IMO.

[tryingbe]

Only way you can really play with the cam timing is on the dyno.

[cordes]

Only way you can really play with the cam timing is on the dyno.

You can't do that at the track?

[glhs875]

Only way you can really play with the cam timing is on the dyno.

Disagree!

[tryingbe]

You can't do that at the track?

What track gives you a print out of the engine torque curve, HP curve, boost curve, and A/F curve?

[glhs875]

There was just a great discussion about this, but I forget which thread it was. Some of the dyno graphs were amazing and highlighted the advantages of retarding the cam on our motors. It doesn't look like there's much to lose IMO.

How much hp is a slightly ported 1pc intake good for is the thread

[cordes]

What track gives you a print out of the engine torque curve, HP curve, boost curve, and A/F curve?

You need all of those to play with cam timing?

[Vigo]

Trap speed is king. If you change cam timing and gain trap speed, it worked. You may still have to 'tune it in' but that's a 100% valid way to verify gains.

I talked about changing cam timing in my TBI van project thread. You may not be able to get away with as much as i did because you're auto and large turbo. Unless you have enough converter stall to make up for it or are willing to do anti-lag or nitrous to spool etc. Sounds like you might be.....

In any event you want to be making power high enough that when you upshift you never fall below the 'full spool' rpm of the turbo. You can experiment with cam retard to see if you gain more top end than you lose in spool, you may or may not end up with net gains that way.

But, it should make peak power at 5000rpm anyway with stock cam timing.

[Joe_Van_Duno]

Thanks for the input guys. Il check out that "1pc hp" thread later tonight.
I'll also see if I can find the thread Cordes was taking about, that sound like an interesting read also.

But overall it sounds like I have nothing to lose with retarding my cam timing a little bit. Guess that's something you'll be playing with at SDAC 26

[glhs875]

Thanks for the input guys. Il check out that "1pc hp" thread later tonight.
I'll also see if I can find the thread Cordes was taking about, that sound like an interesting read also.

But overall it sounds like I have nothing to lose with retarding my cam timing a little bit. Guess that's something you'll be playing with at SDAC 26

The "1pc hp" thread is the one Cordes was talking about!

[wheming]

I need to re-read that thread also. I was thinking similarly Joe, specifically how does changing the cam timing affect AFR. What can i expect for an AFR change as i retard cam timing (if/when i choose to test).

[contraption22]

If I am not mistaken, changing the cam timing will shift where peak power is made a bit, but it of course will not change the physical limitations of the engine. The valve events are not the limiting factor in making the 2.5 happy at high RPM.

[Joe_Van_Duno]

The "1pc hp" thread is the one Cordes was talking about!

I misunderstood I thought we were saying there was two different threads I need to read

[glhs875]

If I am not mistaken, changing the cam timing will shift where peak power is made a bit, but it of course will not change the physical limitations of the engine. The valve events are not the limiting factor in making the 2.5 happy at high RPM.

Not disagreeing with you but changing cam timing can help a 2.5!

[Vigo]

I misunderstood I thought we were saying there was two different threads I need to read

The gist of what i posted in my van thread was that i was limited to ~230hp by the tiny inducer on the stock mitsu turbo, and i retarded the cam 6 degrees and still was able to make 230hp. The only reason i did it was to limit midrange torque (typically the highest cylinder pressures it would see) because i was trying to tiptoe around my tbi pistons at first. In the end the cam retard slowed my spool up, but my turbo is so small it still spools early, full boost by ~2400. On the top end i was able to move my powerband enough that i go to the 6200 limiter on a completely stock top end whereas before i NEVER EVER hit the rev limiter in a 2.5 because it didn't feel like it made any power up there. It was a pretty dramatic change according to the seat of the pants. I didn't make any more power (limited by the turbo) but it changed the way it drove and where i shifted it.

[OmniLuvr]

On the top end i was able to move my powerband enough that i go to the 6200 limiter on a completely stock top end whereas before i NEVER EVER hit the rev limiter in a 2.5 because it didn't feel like it made any power up there. It was a pretty dramatic change according to the seat of the pants. I didn't make any more power (limited by the turbo) but it changed the way it drove and where i shifted it.

this almost makes me want to put a 2.5 in my omni... hmmmm

[tryingbe]

You can't do that at the track?

Way to many variables on the track, plus, I am lucky to run two runs on the entire night where as on Dyno, I can change settings, run it, get a graph every time to see if it improved or not.

Silly not to do it on the dyno.

[GLHS60]

You need all of those to play with cam timing?

I was going to suggest "work on Engine, play with self...
Better not

Thanks
Randy

PS: This from Gary, gold as usual:

"I discovered the wonders of cam centerlining and the effects of rolling the timing from as low as 106 to 114. One would give me buckets of torque that would blow the tires away.. and the other end of the range would make the car soggy down low but have a hell of a top end charge. The trick is to find that sweet spot with just enough torque to keep the tires from getting blown away on the bottom end of the track while having enough juice for the top end charge."

[Joe_Van_Duno]

I will definitely be playing with my cam timing this weekend unfortunately weren't here to get on the dyno for tuning is way to expensive. Sometimes you can get $75 for three pulls but there's no tuning in between it's just three pulls and you're done. I'll just take the van up to the country and do some testing.