ATS_Scott

The test car is a 91 Turbo with an ATS TD06, running 1.0bar, STOCK CAMS. Run #23 is with cams set to true zero. Run #25 is with the exhaust cam retarded 6 deg. Run 24 actually showed an increase of 21+ HP but it was done after the cams were adjusted and the car had approx. 30 min. to cool off. No additional changes to the tune or boost control were made as evidenced by the slightly leaner A/F.



BTW, we currently have cam gears in stock.

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Scott
http://www.atsracing.net/
88 4runner
300rwhp daily driver 394rwhp on race gas Autronic ATS 2.2 MR2
03 YZ250F

Two Fun

Ooooo...

what other mods does this car have??


Scott

manning

how much does one tooth =?

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-manning
91t Viggen Blue
Fast street car.

the2ndr

So, retarding the exhaust cam gear makes the exhaust valves stay open longer or close earlier???

BraveUlysses

I think there are 36 teeth so one tooth should equal 10*

JekylandHyde

Nice results Scott ... I'm happy I have a set of those gears sitting here at my desk (they just arrived today) Thanks.

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manning

yah i was 99 precent sure it was 10..


so eh scott... wanna do some testing at 10degrees

the2ndr

1 tooth = 10* retard?
On a honda B series, 1 notch on the cam gear equals 2* at the crank. What is 1 tooth your referring to Manning?

Is there a picture of the ats cam gears somewhere? Are there notches to show how much adjustment you've made?

Stock settings on a cam gear should be at a Zero setting or the notches in the middle.

Can someone explain the way adj cam gears work on a dohc motor?

manning

yah not notch, (as in adj gears) but a tooth, would be 10, hence no need for adj gear, just time the belt one tooth off... cheap. but not sure if it would be worth any power, but even if it was 5 or so HP thats 5 free HP that you can get when you do the T belt.

and while im at it, dont 3s gears have 3 alignment holes in them? what about using another hole, and setting the belt up so it's a tooth or so off to try to achieve 5-7 degrees?

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-manning
91t Viggen Blue
Fast street car.

ATSAaron

Yes, there are degree marks. this is an old photo. The new gears are painted black and the centers have an "R" and an "A" engraved on them for Advance and Retard.



Manning - you tightwad. First off the "zero" on the stock cam gears is probably NOT "true zero." We test true zero by aligning the notch on the stock cam with the notches on the #1 cam caps. These are visible with the valve cover off.

A 10 degree change is usually too much.

Other mods on test car:
2.1 short block
ChrisK valve job
ATS TB inlet
ATS TD06
Greddy IC
Greddy PEvo exhaust
Greddy Profec B Spec 1
K&N style intake
ATS Cam Gears
ATS FPR
ATS fuel rail
Apexi AFC

See ya,

Aaron

ndisgii

Some more pics:

3sgt

Just a stupid question, but is your cam advance/retard data in degree camshaft or in degree crankshaft ?
And what overall adjustments did you make for run 24 ?

Normally camshaft spec data is provided in degree crankshaft and if you retard the cam gear 10 degrees this is 20 degrees crankshaft. This means exhaust valve closes 20 degrees earlier and opens 20 degrees earlier. And for top end power its good to stay the exhaust valve closed as long as possible, because when the exhaust valve opens the pressure from the piston is removed and the power stroke is over.

twoina2

Welcome to the Board.

Not a stupid question at all. Did I maybe detect a little sarcasm? Jumping a cam gear tooth would give way too much retard just as you describe. ATS Scott was undoubtedly talking about 6 deg crank.

Our stock cam gears have a series of holes and pins that allow for much finer adjustment than jumping a tooth, but you pretty much have to disassemble everything to adjust them. ATS sells modified cam gears that allow much easier adjustment - at the dyno for instance.

Mike R

3sgt

Thanks for welcoming me.

There was no intend of sarcasm in my words. I only wanted to say that there is a difference between degree camshaft and degree crankshaft.

It is really great when people spent money and time to find out coherences and then provide this information on the board. And perhaps ATS_Scott tells us the adjustments for the 21HP gain from the stock cams.

the2ndr

Thanks for replying. Is this generally the idea of what happens when you retard the exhaust cam. What happens if you advance it?

3sgt

Some simple thoughts about adjusting exhaust cams.

Exhaust valve opening
a) Late opening keeps pressure on the piston, good for power.
b) Early opening makes early high lift when the piston strokes up. Good to get rid of the burned gas.

Exhaust valve closing
a) Late closing flows remaining exhaust gas out, but generates bigger overlap with the opening of the intake valve. This makes exhaust gas flow back through the intake valve (internal exhaust gas recirculation) and the intake of exhaust gas without much oxygen is not good for power.
b) Early closing can reduce overlap, but maybe keeps some remaining exhaust gas in the cylinder.

All effects are no constants, they depend on piston velocity, exhaust backpressure, boost pressure, head design, number of valves, diameter, lift and duration. We can look at the points isolated, but in the end we must find out the best compromise and therefore we have to look at the intake cam as well, especially for overlap.

twoina2

Overlap is not your friend with most street turbos because the the exhaust back pressure is higher than the boost pressure.

The stock cams are mild enough that timing can be altered w/o much concern about overlap.

If you have a bigger turbo and/or low restriction exhaust, it is likely your car will make more power with retarded exhaust cam timing.

Advancing the exhaust cam will improve spool.

Mike R

ramicio

6 degrees crank would be 3 degrees at the cam. i really think he altered in by 6 degrees at the cam.

which one is it scott?

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timramich@gmail.com
AIM: GrimsterMcNasty

flupstar

one tooth is around 7.5 degrees at the CAM... 15.0 degrees at the crank. (48 teeth if I remember correctly, definately not 36..)

when degreeing, its usually measured at the crank... as that is where the degree wheel is attached. and 15.0 degrees is way off. Tried it once just for kicks actually.. it was revolting The most common gear to slip a tooth through fault is the exhaust cam.. and when it slips, its retarding. And anyone out there that has experienced a slipped exhaust gear by 1 tooth will tell you how much it destroys power.

As for using the pin holes to adjust.. it can be done, its a bit more messy and difficult... but it works just as well if you put the time into doing it

-Tristan

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ramicio

then what about the marks on the gears? they are actually relevant to degrees, and if say the 10 degrees mark was measured on a protractor from the zero mark, it would be 10 degrees. that just perplexes me.

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AIM: GrimsterMcNasty

flupstar

I wouldnt mind seeing someone with more experience than me answer this one..

cabe

i have a gen3 motor outside of my car atm which gives me the perfect opportunity to degree the cams, however i don't know what i should degree them to. a 17hp 15tq increase from JUST retarding the exhaust cam 6 degrees is DAMN IMPRESSIVE!

how should i go about deciding what advance or retard i should run on the intake/exhaust cams?

also, just out of curiosity.. what boost was that turbo running? and would higher boost see more benifiet from retarding the exhaust cam since there would be less reversion?

[edit]
it seems that advancing timing accomplishes the same thing as retarding the exhaust cam. if that car was equipped with an ems, would it have been better to advance timing rather than retard the exhaust cam?

flupstar

Advancing ignition timing has nothing to do with retarding the cam. Ignition timing refers to the spark time relative to crank position. retarding the cam refers to valve opening and closing time relative to crank position

Its true that changing the INTAKE cam position also changes timing .. as thats where our distributor picks up its signal for crank position. But that aside, the ignition timing and cam timing are totally unrelated.

They may give similar results (eg advancing timing and retarding cam CAN both result in a similar power increase).. but they dont both do it in the same way.. and the ignition timing advance is argueably more dangerous. In any case, the ignition timing should always be at its optimal safe point anyway if you have an aftermarket EMS.. and advancing it further isnt a good idea.

As for the gen III... they typically come with NON adjustable cams and gears. Pick yourself up some gen II cam gears if you have the non adjustable gen III gears... That will give you a limited degree of adjustment. Not as good as gen II.. but good enough

-Tristan

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cabe

i know, i was just saying that both advancing ign timing and retarding the exhaust cam will increase the ammount of time between when the fuel is ignited and when the exhaust valves open.

how would gen2 gears allow less adjustment on a gen3 than they would on a gen2? how adjustable are the stock gears, anyways?

also, any suggestions for determining what i should adjust the cam timing to?

retarding exhaust seems good as that would both increase the duration of the power stroke and increase overlap to help with evacuating exhaust gass from cylinder with low restriction exhaust and high boost. advancing the intake cam would increase the compression which may not be such a good idea at high boost on a stock motor, but retarding it would reduce valve overlap so maybe the intake cam should just stay where it is?

i understand the concepts of what's happening, i just don't know what benifiets weigh the heaviest (advancing intake cam to increase CR or leaving it alone to maintain valve overlap for example)

tia for reading all this

flupstar

got ya

The gen II gears have 3 holes.. for 3 levels of adjustment.. and the gen II CAMS also have 3 holes... allowing for 9 positions/combinations of adjustment per cam gear tooth... if you take advantage of all holes

however, the gen III cams and gears have one hole each

If you couple gen II gears with gen III cams, you end up with 3 holes.. enough for a rough degree job... but without the 3 holes in the cam too, you're limited

Of course you could throw a gen II exhaust cam in.. seeing as though the gen II and gen III exhast cam are identical!

In my experience.. on my gen III, retarding the exhaust cam can indeed give some good torque increases without hurting the top end power much, if at all.

Ive also heard floating around that gains from adjusting the stock intake cam on average setups are extremely minimal.. and not worth the effort. But take that as hearsay only

-Tristan

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kirkosaurus

Actually the 3SG cam gears have 46 teeth. The 4AG cam gears have 36 teeth.

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flupstar

hehe thats the one. I always remember its one away from 47.. just keep forgetting which way

ramicio

it looks as though he got a torque increase from 4k and up from the retarding, so that hurts top end? i have horrible top end, but then again, my belt slipped somewhere along the line and i am a tooth off. my distributor isn't anywhere near center, rather to the extreme to get 10* btdc. getting to 90 isn't hard. 100 isn't too bad, but beyond that it's a struggle to accelerate. i would like to try retarding the exhaust cam if i knew for sure if i could keep some top end, as i will be doing a timing belt very soon. only thing stopping me for this degreeing is the whole daily driver thing. i don't really have time to experiment with something like this these days.

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AIM: GrimsterMcNasty

flupstar

you'll notice that the power increased at the point the TD06 hit full boost.. or near it. Either there were no gains to be had below that point.. or more likely, not much effort was put into tuning it below full boost. In any case.. I consider 3000-5000rpm to be the low end.. or midrange. And 5000+ to be top end.. on a stockish motor.

remember.. these tests are only as good as the tuning.. and while the tuning done does demonstrate the point (that cam adjustment made an improvement), i dont think its extremely accurate. So focus on the point being made, not the exact power differences at exact RPM points. Too many tuning factors once you go into detail...

eg.. look at this. The lower power graph is also running richer. And the one point where the AFRs were almost the same is also the point where the two power graphs came very close to each other.

I put down a theory.. that if those AFRs were identical.. the power gains from tuning the exhaust cam would have been significantly smaller. Half that what is claimed actually, if that little bump in the red graph is any indication.

look closely.. you'll see what I mean.. the gap between the AFRs almost perfectly resembles the gap between the power graphs.

ATS- dont stab me for attacking your results.. just pointing out the obvious discrepancies. And Im not discounting your results entirely either.. I still agree that adjusting the cam makes a good difference in favour of your results.

-Tristan

And god.. fix your cam timing!

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