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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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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