DOHC Adjustable Cam Gears

[EdKiefer]

Originally Posted by Meph

sorry i think i edited my post as you posted this one, reducing the overlap is the theory behind increasing torque by making better use of the combustion pressures at lower rpm's resulting in greater efficiency/mpg?

meaning Id need to advance exhaust and retard intake?

yes, that will lower overlap , lower lobe separation angles. altering both cams 4deg kept overlap the same but advanced timing in relationship to TDC which also has affect of advance = better low end and retard = better top end . with DOHC being able to do both I would start with intake then move to exhaust as generally intake is more important .(thats why most VCT is done on intake side ) .

[Meph]

cam gears are in crank degrees, so im good.

the cams are advertised as "Set the exhaust cam gear to +1.5 marks on the cam gear (+3 actual degrees) and the intake to -0.5 mark (-1 degrees). On average this setup yields 5-7rwhp." ...... oh god, this would remove overlap as per the example and make no sense with everything else we discussed! nothing make sense! It should reduce power not create more! oh god! *resets everyting to 0 and hides under the bed*

[EdKiefer]

Originally Posted by Meph

cam gears are in crank degrees, so im good.

the cams are advertised as "Set the exhaust cam gear to +1.5 marks on the cam gear (+3 actual degrees) and the intake to -0.5 mark (-1 degrees). On average this setup yields 5-7rwhp." ...... oh god, this would remove overlap as per the example and make no sense with everything else we discussed! nothing make sense! It should reduce power not create more! oh god! *resets everyting to 0 and hides under the bed*

It really depends on cam specs and were you want peak power .
Are these cam's stock or aftermarket ?

read second link I posted above first , then the first one. That should help you understand relationship of timing events some .

Note : that pic of cam rotates CC , which I bet yours turns clockwise , that confusing if yours rotates different direction .

[autoteach]

check those gears and make sure that the cam gears are not marked opposite. I have seen crazier things.

[autoteach]

and, it could potentially add hp, where they are talking about adding hp is totally independent. You could put a part on the car that adds 5 hp, to the total max or to the midrange? That is the important question.

[Meph]

Yep i rotate CW, my cam gears are correctly labeled too, I checked this as I was worried as well.

Ill take another read though the posting too.

What if I were to do it in two steps, shifting the cam events +4 degrees advanced (Intake +4 and Exhaust +4) then took the next step of lowering overlap (Intake +4 - 1 = 3 Exhaust +4 + 3= 7)

Would this theory work (+3 intake, +7 Exhaust) or would the ideal be more like intake -1 and exhaust +7



After all this messing around I assume resetting the base timing is a good idea, its triggered by the intake cam so Id have to adjust my ecu (standalone). Would any of the cam timing changes warrant advancing or retarding the ignition?


I'm starting to lean towards running +4 exhaust and leaving the intake at 0 so i wont have to redo my timing, and seeing if I can notice a differnece, or maybe try +6 ex and +2 intake giving me a +3 shift and a +3 ex / -1 intake

Sorry for all this mindless thought, Im slightly thinking out loud , hopefully it makes a little sense

[EdKiefer]

Originally Posted by Meph

Yep i rotate CW, my cam gears are correctly labeled too, I checked this as I was worried as well.

Ill take another read though the posting too.

What if I were to do it in two steps, shifting the cam events +4 degrees advanced (Intake +4 and Exhaust +4) then took the next step of lowering overlap (Intake +4 - 1 = 3 Exhaust +4 + 3= 7)

Would this theory work (+3 intake, +7 Exhaust) or would the ideal be more like intake -1 and exhaust +7



After all this messing around I assume resetting the base timing is a good idea, its triggered by the intake cam so Id have to adjust my ecu (standalone). Would any of the cam timing changes warrant advancing or retarding the ignition?


I'm starting to lean towards running +4 exhaust and leaving the intake at 0 so i wont have to redo my timing, and seeing if I can notice a differnece, or maybe try +6 ex and +2 intake giving me a +3 shift and a +3 ex / -1 intake

Sorry for all this mindless thought, Im slightly thinking out loud , hopefully it makes a little sense

Hard to say, but me I would try 4+ 4+ and note any gains (if you got any type of datalogger be great to test performance) . The I would try lowering the overlap way, but starting with stock 0, 0 as baseline . After noting that you can combine any improvements noted in each test .

The thing its going to be hard to tell improvements unless you do it on dyno for power in X rpm band or test mpg over time in each mode. There so many variables with 2 adjustable cam gears , IMO its hard to recommend a setting .

One thing to note, since your on turbo car you don't need a lot of overlap or long duration openings, especially on exhaust side as you don't want to blow intake charge right out exhaust on boost (not that this be problem on stock or mild cam) . I would not go more than 4deg on either cam without some good way to test .

Does this engine have ignition pickup on intake cam end ?
can't you just adjust it with timing light the few deg you move cam or is it not adjustable .
If thats the case yes you could just try advance on exhaust side first as test run .
Try 4+ on exhaust and see out come as thats easy .I would not combine both methods as your altering deg a lot then .(meaning I would try Ex -4+ , In 0 and then Ex4+ , In-4+ but not Ex 8+, In -4+ , max I would go would be Ex 6+ , In 2+ combined . Again I would focus on doing each separate to even notice which gives some improvement then if both did try combining , again this is tough call .

[UFO]

Meph, what engine is in your 240Z? All the Zs came with factory SOHC, none DOHC.

[Meph]

Hey UFO, I have a Toyota 1JZ-GTE in the car, 2.5L single turbo conversion.

I took my intake cam back to 0 and my exhaust +4, with my intake at +4 is felt a little limp down low, with the exhaust at +4 I could feel a a noticeable amount of grunt 1500-2000 range, it didn't seem to really help below there.

I also pulled my a/f ratio back from 15.6:1 to 15.87. My injection times crusing at 40-50 miles an hour seemed to drop around 0.1 ms (from say 1.2 to 1.1). Im going to add another degree or two of ignition take more advantage of the lower a/f too.

My trip today was 32.5 mpg, not as good as my 34.5 mpg tank last time, but it was only 40 miles of driving, on some extreme hills (drove up and past a ski resort) I really feel with cam and a/f I stand to gain a decent improvement.

as cams rotate in the order exhaust->intake advancing the exhaust would remove overlap. I hope to have better results soon!

[Daox]

In the world of progressing VVT technology, most mfgs went to varying the intake cam first. They're now varying both with newer engines. I'd imagine tweaking the intake would have more of an effect than the exhaust.