Ansat527

Heya, looking for some advice.

My engine will be ready for tuning in a few weeks, and I recently acquired the Skunk2 Cam Gears, and I was wondering, for our engine, what would work better in terms of timing? I'm a tad clueless in terms of timing, only what I read regarding that most cams for our engine would benefit some kind of timing adjustment. So what should I be aiming to? Clearances will obviously be checked, just want some help in pointing me the right way regarding the timing

Gernby

It depends on your goals. If you want to give up some peak power in exchange for a bunch of midrange torque, then cam adjustments would be an easy way to do that.

b.r.i.a.n.

With some bolt on modifications there are gains with cam timing adjustment. Get on a dyno, make adjustments to the cam gears and see what it does to the powerband.

K20iVTEC

this seems like a very long and tedious process having to remove the valve cover every time you need to make an adjustment. Its not like the 4g63 where you can keep the upper timing cover off and make adjustments and dyno again.... seems like a pain in the ass for the tuner lol

Ansat527

What about some kind of guideline, so as not to waste that much time? I don't think I'll need a lot of mid-range, since the car has lost quite a bit of weight, was stroked, and has ITBs, so a guideline as to what I should try would be thankful

Slowcrash_101

Think about it logically, advancing exhaust timing means the exhaust valves open sooner retarding exhaust timing means they open later. The same goes for the intake valves.

Let's say you advance intake timing, during the intake part of the combustion cycle, the valves will open sooner, allowing air to enter earlier during intake but they'll also close sooner before TDC on the compression stroke, this will help torque and throttle response in the low to mid rpm range up to a certain point, without affecting high rpm power. After this point you will start sacrificing high end power for low end power. Retarding intake by itself will create more overlap with the exhaust valves at higher engine speeds, but will sacrifice low engine speeds as the valves now have less time to operate while the piston moves to BDC during the intake phase, you will also sacrifice fuel efficiency, unless you can change injector timing as well. Retarding intake has a higher probability of causing damage to the engine due to burned valves if the cam is retarded sufficiently.

Combining with the exhaust timing becomes a bit more complicated, but is where all the power is, and where the greatest damage can be done. Again increasing valve overlap by intake retarding, and exhaust advance will move the power band up higher, to a point, and decreasing it will increase torque and mid-range power, to a point. The trick is to finding the sweet spot for your setup, and tuning your ignition and injector timing is critical for extracting the maximum benefit.

There's a reason i-Vtec only works on the intake cam. You can get 90% of the torque and throttle response gains, with a much wider safety window, without affecting top end power..

LostMotion

I have tested cam gears extensively, you can see some notes here:
https://www.s2ki.com/s2000/topic/509...-build-thread/

If you want to set it and forget it, I would put +4 intake and +1 exhaust. Those are "safe" numbers. Sometimes the gears you buy can be a little mis-aligned from what they say they are. Mine were misaligned by 3 degrees (a lot more than a "little"). The safe settings mostly account for that chance of being misaligned, although nothing is truly 100% safe unless you measure. That involves checking where the pistons are at various crank locations which takes some specialized equipment and knowledge.

If you know the gears are right, you can push the intake cam to +7 and have 4-5 degrees of separation ("overlap") on the exhaust. That would be +2 or +3 in this case.

In general, this car loves intake advancement, so the more the better. You just have to keep the exhaust cam close enough to the intake so it doesn't hit.

I figured this all out by claying the motor, running some engine math and playing on the dyno for several hours.

Ansat527

LostMotion, I'll read it all as soon as I get home.

One thing I didn't get was, you mention advancing the Intake, and Slowcrash mentions retarding. I got the part about the overlap, but from Slowcrash's explanation, advancing the intake makes me lose on the higher up, instead of making power.

My engine is basically for Time Attack/Road Course, so most of the time it will be between 5,000RPM and 9,500RPM. Wouldn't retarding the intake and advancing the exhaust lead to better numbers on that area?

If that's explained in your thread, sorry, and I'll go over it as soon as I get home (:

LostMotion

The guidelines he gave seem to be general and apply to motors generally (I have read the same thing). In practice each motor behaves differently to changes. The S2000 loves intake advancement, it benefits the entire curve.

If you are racing the car, take the time if you can to degree in the cam gears and/or clay the motor so you can push it as much as possible. If I had a stock head (meaning not decked), I would run +6-7 intake and +1-2 exhaust (but would double check my prior work by claying the motor with the exact setup I was going to run).

I currently run +1.5/-3.5 but only because +1.5 is the most I can run because I have a decked head which impacts clearance substantially. The tuner where I live pretty much always set these +4 / +1 on stock heads -- that is safe, but I calculated you could push it further and that was backed up by claying my motor. I currently have run 5 degrees of overlap for 40k miles, so I know that is safe.

LostMotion

Here's a picture from when I clayed the motor.