DOHC Adjustable Cam Gears
 

When adjusting the cam gears on an engine its said you you shift the torque band higher or lower in respect to RPM. I often hear about advancing the exhaust, but what about the intake?

Does anyone have experience with dual cam gears? Id like to shift my torque lower down in RPM where I do the majority of driving, but would like to know how it turned out for others, is there a rule of thumb when advancing and retarding cams (advance one, retard the other), did you have positive results?

Are there any other factors that need to be watched for (reduce timing ect)?

If anyone has some experience Id love to read about it.

Thanks very much

don't have any specific experience with your engine but this might help .

Think of valve timing events(intake open/closing , exhaust open/closing) as if it was a SOHC (1 cam) , then split it up to what you want on each cam of DOHC .

Generally advancing SOHC (intake + exhaust) tends to optimize in lower rpm ranges .
when it comes to each cam more valve overlap at TDC =better high rpm and less overlap at TDC better at lower rpm ranges .

from my experiences the affects of say 4 deg advance are small affect but this depends on engine for sure .

Be careful with some interference engines on how much you change timing with adjustable gear (make sure you don't make valve to piston clearance to small ). Probably not a issue with small changes .

Ive tried out driving with +4 and +4 and did seem to notice a little bit mroe torque down low, nothing very substantial. As I advanced the intake cam, that controls engine timing I will need to recalibrate my ignition timing aswell.

Ive been reading differnt threads on here and opnions seem devided over advancing or retarding cams to get best results. On a stock car with Variable Valve Timing I believe they advance the exhaust cam in low rpm and retard it in high rpm?

Ignoring the intake cam, would and advance solely in the exhaust cam result in more torque and theoretically more MPG in the 1500-2200 rpm range of an engine with a redline of 7000. Later variation of my engine had vvt on the exhaust cam.

Thank :D

here info from Honda K24 doc on VTC operation .
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Driving Condition , VTC Control, Description

Light-load = Base Position, For stable combustion the cam angle is retarded, and reduces the entry of exhaust gas into the cylinder.

Medium/high-load = Advance Control, Cam phase angle is controlled to optimize valve timing, improving fuel efficiency and reducing emissions.

High speed = Advance-Base Position, To reduce pumping loss, the intake valve is closed quickly. This gives the air/fuel mixture a charging effect that helps to maximize engine power.

VTC System
The VTC system makes continuous intake valve timing changes based on operating conditions.
Intake valve timing is optimized to allow the engine to produce maximum power.
Cam angle is advanced to obtain the EGR effect and reduce pumping loss. The intake valve is closed quickly to reduce the entry of the air/fuel mixture into the intake
port and improve the charging effect.
The system reduces the cam advance at idle, stabilizes combustion, and reduces engine speed.
If a malfunction occurs, the VTC system control is disabled and the valve timing is fixed at the fully retarded position.
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when you say you advanced +4, +4 , you mean both cams 4 deg .
I think it depends on the cam timing as to what can be improved when altering just 1 cam .

You would be looking to advance the intake and retard the exhaust. Running both at +4 would negate the gains of the one with the losses of the other. When we were doing some work on a motorcycle engine for another application, we pulled a significant amount of overlap out of the engine. Stock was 110 degrees crank. I believe we removed 24 degrees total. Take your +4 on the exhaust and go -4 and tell us how it goes.

here some info Google search . This is for DOHC

Cam Gear Tuning | Adjustable Gear Tuning | Cam Wheels

here some info on checking and single cam timing affects.

http://www.enginebasics.com/Engine%2...%20Timing.html

Looking at this picture would indicate that exhaust would need to be advanced and intake retarded to reduced the overlap. is this the goal to low end power gains?

http://www.enginebasics.com/Advanced...Camtiming2.jpg

overlap increases higher rpm hp, bottom rpm tq not so much.

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?

There is definitely a possibility that in my mind, my visual aid was screwed up. Yes, remove overlap. Keep in mind that if you are doing 4 degrees camshaft timing, that would be 8 on the crank.

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 ) .

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 .

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

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.

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 .

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

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!

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.

ok, well good you notice a difference with just 4deg changes .
So lets see so far . I assume you started with Ex=0, In=0 .

you tried Ex 4+ , In 4+ and this felt sluggish down low ?

The you tried Ex 4+ , and In 0 and this seemed improvement down low , did you notice any lose in upper rpm band ?

I am afraid its going to be just trail an error to find sweet spot .

hum I always thought it was exhaust cam that was varried but you totally correct, all th engines are playing with intake settings. Ill try t track down the settings for a stock VVT, and copy the settings that are used for my target crusing rpm.

Thanks guys!

Most VVT vary the intake by like 25deg depending on throttle/load and rpm . Like what I posted on the honda K20/24 info .
recap, idle they run it retarded , mid rpm-high loads advanced then it backs off as rpm goes up .At part throttle- light load they advance it for EGR affect .
From my understanding its very dynamic for most manufactures .

I was running 0 / 0 and then +4 +4, it didnt feel bad, its really hard to tell honestly, but I felt +4 exhaust gave more grunt past 1500, but didnt feel the best below, as i changed my a/f ratio leaner it would very well be the cause. I did find today ive never driven with such low injection time at 40-50 mph, probably a combination of the two changes. I upped my ignition and hope to have even better results tomorrow.

I hope to find stock intake cam vvt settings I can imitate

right the 4+ , 4+ is not changing cam spec in relationship to each other just related to crank so that would be harder to notice IMO . Just the Ex 4+ is changing overlap so that should see change . If you did something similar on intake side should be more noticeable . Does Toyota Have a VVT version of that engine , If memory is right there 3.0 straight six did (used in turbo supra's .
You might be able to hunt down some info online or from there repair manual .

Mmmm, 1JZ, very nice, and very nice mileage figures. I still have the Nissan straight six from my hodrodding days, hybrid turbo and intercooler, 12.89@110. I can get 30 mpg on the highway, but I don't drive it much except for the track.

heres something I found relating to toyota ttv-i, on the intake cam

http://img.photobucket.com/albums/v4...Data/vvt-i.jpg

Now it seems as though intake advancing the intake and increasing overlap produce an improvement in MPG in low to medium cruising, the opposite as what many have been thinking. Ill look for more information to back this up

Heres more info relating to intake timing, an advance in intake timing would help to raise compression ratio and efficiency in lower rpm.

"Dynamic CR
At low rpm, there is little-to-no ramming of the cylinder from intake charge velocity. As the piston starts to move up the bore on the compression stroke prior to the intake closing, some of the induced air is pushed back into the intake manifold. This means the volumetric efficiency (breathing efficiency) and thus the effective displacement of the cylinder is well below 100 percent."

So maybe adding +2 intake degrees to my current +4 exhaust would help to shift the power band lower in rpm (+2,+2), raise Dynamic compression raito (advancing intake valves to close sooner) and reducing overlap (+4 exhaust - 2 intake = +2 exhaust net)

Reset my timing, and see how it drives

Thats basiclly same as honda , only honda has 2 cam lobs for low speeds and high loads over like 5k rpm .

They raise intake timing to increase overlap and EGR affect to help with lower temps (they probably raise ignition timing and lean out too) at part throttle low-mid loads .

The problem you will run into is this is only good at one area , it would be bad to do it across the board and why OEM don't use it unless they have VVT .
I still say slightly lower overlap like you did on exhaust is best compromise with turbo , your only really tweaking the timing, any more will hurt in other parts of powerband .

Like trying to advance intake a lot for good low rpm/part throttle would give bad idle, very rough sluggish off the line .

Sure you can try it, but its going to be hard to see change as its only 2deg shift, but maybe you can tell from adjusting ECU specs, if you know what certain specs (ignition advance, A/F ) could do before without side affects .

Results

Hey guys,

Ive been testing different combinations of settings and Ive come to a conclusion for my car.

I found that +4 exhaust and 0 intake resulted in more torque down low

+6 exhaust and +3 Intake resulted in more torque than just +4

What Ive chosen to run : 0 , 0 (stock)

What I experienced

the increase in torque was a noticeable one, the issue is that I would only feel this torque increase with load on the engine, -18" to +12 psi. below this load, at -18" to -22" the engine seemed to produce significantly less. Where i was once cruse at 1.5 injection time in town, jumped to 1.6-1.7 be because i need to give it more throttle.

I think for many eco cars out there, this mod would very well help, because when your driving your engine is loaded to say -10" to -16" normally, my Datsun will cruse at -20" on flat ground, due to the light weigh body and engine swap. I only noticed a bonus to MPG's at much higher speeds than i usually drive, where the engine is turning a higher RPM and was under more load. I changed my cams back to stock part way though a drive and noticed a significant reduction in fuel injector times when cruising at very light loads (as i most often do)


So to conclude, I did produce more torque, but not in my required engine load area. Someone with a small engine would probably have benefited from his change where it only hindered me

Thanks for the input everyone. I may get ambitions and do some more testing but for now I think Ill take a quick break from it

If you can run with that much vacuum maybe you can crank up ignition timing in a small window ( low load /1500-2500 rpm ) .

In my load load-lower rpm range I'm running around 36-43*, I think i can still push it but I want to build a knock sensing circuit first. With my new slightly more aggressive ignition map and lowering my a/f to 15.87:1 I just returned 35.5MPG, new record :)

43 deg sounds pretty good but that depends on what your able to run , say max TQ mid range at 0 vac " and max boost .

Is it like,around 36@0 vac and 28-30@ boost (this will depend on how much but rough valve).

Generally could might be able to stand 8-10deg of part throttle advance , so in above it be like 45 deg max .

You could maybe make a electronic stethoscope , I have seen a few DIY on it from old electronic parts .

in my 1500 RPM catigory, it is -38* at about 20" and by 0" it is about 26 i think, at 2000 RPM its about -42* at 20" and 30 at 0 or something close to that. I know theres a few DIY knock kits ouit there I might try one

that sounds good to me, your not running retarded for sure .
what rpm range do you cruise at on Highway ?

i dont know why I put a negative in -38*, but I meant 38* advanced, at 60 id be at 2200 ish