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Old 04-04-2014, 10:42 PM   #76
mod maniac
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Originally Posted by bswilmington View Post
Would have been nice to see a baseline with cam timing set at 0 then changed couple degrees so you/we could see the changes it made. Im sure its PIA but its going to be the only true way of knowing if changes are actually working.
This is true but I didn't have the time or money to do it twice.
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Old 04-05-2014, 09:10 AM   #77
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Can I just confirm that advancing the exhaust cams can bring on spool earlier but lose a bit at the top end as im sure I read earlier in the thread someone has said the opposite?
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Old 04-05-2014, 10:35 AM   #78
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Originally Posted by mod maniac View Post
Fuel is 91 and the turbo is a tomei 7760. The car is a fxt auto that is my wifes dd and auto cross car. The goal was to get a early spool and a smooth curve so as not to scare her. The hp came in a little lower than desired but the cams to allow us to make power down low and spool early.
I don't know much about this turbo so before I responded I went digging around. Apparently Tomei does not disclose cfm #'s and only rates their turbos according to whp. Anyway, from what I gather, this flows about like a 20g, 42-44cfm, but spools like a 16g? Although I heard conflicting info in this area that it flows more...

So, you what you have is a quick spooling turbo, but with cams that shift the torque whp curve to the right. Then, to shift it back you advanced the exhaust cams. (I know this is redundant but I like talking things through)... I wonder how much you were able to shift it back to the left? I think the numbers look a tad low but again, you are on 91 octane and really... screw numbers, it's all in how it drives. The flatness of the torque curve is where it looks really fun. This thread has been informative.
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Old 04-05-2014, 03:18 PM   #79
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Originally Posted by Jdc Typer View Post
Can I just confirm that advancing the exhaust cams can bring on spool earlier but lose a bit at the top end as im sure I read earlier in the thread someone has said the opposite?
Yes advancing the exhaust cams help spool the turbo a little earlier But this is a early spooling turbo so were helping it some. Yes you lose power on top but we only turn 7300 in this one so we probably lost nothing.
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Old 04-05-2014, 03:23 PM   #80
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Originally Posted by Type2 View Post
I don't know much about this turbo so before I responded I went digging around. Apparently Tomei does not disclose cfm #'s and only rates their turbos according to whp. Anyway, from what I gather, this flows about like a 20g, 42-44cfm, but spools like a 16g? Although I heard conflicting info in this area that it flows more...

So, you what you have is a quick spooling turbo, but with cams that shift the torque whp curve to the right. Then, to shift it back you advanced the exhaust cams. (I know this is redundant but I like talking things through)... I wonder how much you were able to shift it back to the left? I think the numbers look a tad low but again, you are on 91 octane and really... screw numbers, it's all in how it drives. The flatness of the torque curve is where it looks really fun. This thread has been informative.


Yes the turbo has a 20g wheel but runs a small td05 hot side so this turbo spools early but doesn't move a lot of air up top because of the small exhaust side.
We did get it to work well but the numbers do look low and I think that is because of the auto trans.
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Old 04-05-2014, 03:48 PM   #81
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Im running an SC54 ( which I think is the equivalent to the blouch dom 4.0 xtr ) on a 2.1. (Blobeye)
Would I benefit from advancing the exhaust cams on such a large turbo to improve spool as it is quite laggy?
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Old 04-06-2014, 12:27 PM   #82
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Originally Posted by Jdc Typer View Post
Im running an SC54 ( which I think is the equivalent to the blouch dom 4.0 xtr ) on a 2.1. (Blobeye)
Would I benefit from advancing the exhaust cams on such a large turbo to improve spool as it is quite laggy?
I don't know if you can gain much (try it) that is a huge turbo on a 2.1. It will never spool early.
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Old 04-06-2014, 01:47 PM   #83
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Tell me about it

I thought about rotating it and going EWG but I'm not sure that it will make much difference?
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Old 04-06-2014, 11:02 PM   #84
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I think if it spools between 4200 and 4500 that's about right on a 2.1.
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Old 04-08-2014, 04:02 AM   #85
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Advancing the ex cam decreases overlap = more top end.

For better spool you want to retard the ex cam or advance the intake cam. (Or both)
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Old 04-08-2014, 07:16 AM   #86
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I have just found this, post 2
http://www.celicasupra.com/forums/sh...and-advantages

Am I reading it right as you seem to be saying the opposite?
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Old 04-08-2014, 03:59 PM   #87
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That's one way of looking at it and it probably applies to a lot of cars.

But from experience it isn't an apples to apples comparison in a Subaru.

Our cars generally have very high exhaust back pressure and overlap causes reversion, which kills power.

Look at some of the more popular STi cams on the market:

GSC S2: -14* of overlap, LSA of 122.5*
GSC S3: -5* of overlap, LSA of 122.0*
Kelford 199-D: -7* of overlap, LSA of 122.5*

Compare that to something like a Supra cam:

24* of overlap, LSA of 116*

Now I'm not saying that's the only way to skin a cat, the cams on our car atm have 66* of overlap :P
But because racecar.

If you want to dial it in, rent a dyno and do it in two crank angle increments till you're happy with the powerband.
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Old 04-08-2014, 10:31 PM   #88
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Quote:
Originally Posted by Jdc Typer View Post
I have just found this, post 2 http://www.celicasupra.com/forums/sh...and-advantages Am I reading it right as you seem to be saying the opposite?
Read my post, exactly my findiings
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Old 04-08-2014, 11:55 PM   #89
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Quote:
Originally Posted by Jdc Typer View Post
I have just found this, post 2
http://www.celicasupra.com/forums/sh...and-advantages

Am I reading it right as you seem to be saying the opposite?
If you read that it says if you advanve the cams it makes more low end power and less top end. It also says if you lower the overlap (advancing exhaust does that) you will have more low end power and less top. So I agree with that post.
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Old 04-09-2014, 12:57 AM   #90
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Quote:
Originally Posted by DisoDisp View Post
Advancing the ex cam decreases overlap = more top end.

For better spool you want to retard the ex cam or advance the intake cam. (Or both)
totally agree ^^

Quote:
Originally Posted by mod maniac View Post
If you read that it says if you advanve the cams it makes more low end power and less top end. It also says if you lower the overlap (advancing exhaust does that) you will have more low end power and less top. So I agree with that post.
Mod Maniac, the article states moving both cams, but DOHC engines have the advantage of moving each separately, scavenging effect is good for spool up, but after boost is reached you wanna keep as much of that fresh air inside the cil as possible. cold air pushes hot (burnt) air out, if there is too much overlap on high rpms cold air and hot gases would go out reducing power and dropping tq. i believe that is the reason your turbo is holding that awesome tq line. since you advanced the exhaust and kept fresh air in. On a small turbo car you could even find advantage using avcs on the intake to advance the cam to aid the small turbo at higher rpms, however on a bigger turbo you need to fully retard the intake to take full advantage of your set up, it also depends on how good your heads breath, your exhaust design as well as BP.

if i am wrong please feel free to explain so that i could learn.

regards.
Roy
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Old 04-09-2014, 02:58 AM   #91
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Originally Posted by Psychoreo View Post
Count number of teeth on pulley.

Divide into 360.
There is 720 crank degrees in a full engine cycle and the cams rotate at half crank speed.
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Old 04-10-2014, 12:50 AM   #92
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Quote:
Originally Posted by majunche66 View Post
totally agree ^^



Mod Maniac, the article states moving both cams, but DOHC engines have the advantage of moving each separately, scavenging effect is good for spool up, but after boost is reached you wanna keep as much of that fresh air inside the cil as possible. cold air pushes hot (burnt) air out, if there is too much overlap on high rpms cold air and hot gases would go out reducing power and dropping tq. i believe that is the reason your turbo is holding that awesome tq line. since you advanced the exhaust and kept fresh air in. On a small turbo car you could even find advantage using avcs on the intake to advance the cam to aid the small turbo at higher rpms, however on a bigger turbo you need to fully retard the intake to take full advantage of your set up, it also depends on how good your heads breath, your exhaust design as well as BP.

if i am wrong please feel free to explain so that i could learn.

regards.
Roy
By moving just the exhaust you are removing the overlap and losing the scavenging effect but with forced induction its not needed because you are forcing the air in. There is always trade offs we lose a little on top which we weren't going to use anyway on this build to gain a little on the bottom.
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Old 04-10-2014, 02:01 AM   #93
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You're not wrong, but instead of the cold charge blowing straight through, it would seem that on most subarus there is so much Ex Backprrssure that you get reversion at the top end.

We've measured pressure on our single scroll "big turbo" setups up-pipe and the back pressure is significantly higher than boost pressure.
On one 600bhp car with a single scroll custom turbo and 3.5" exhaust we were seeing about a 2:1 ratio of backpressure. (4bar in the uppipe, vs 2bar boost)

Adjusting the cams so that you have 0 overlap nets massive gains.

Twin scroll dual EWG setups on large ex housings have much less BP. And as a result we run a lot of overlap on our current setup and custom cams.

Last edited by DisoDisp; 04-10-2014 at 04:16 AM.
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Old 04-15-2014, 01:28 AM   #94
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Reversion does happen up on top but this build was made for early spool and power down low. This build was never about up high power. For early spool and a nice flat torque curve it seems to work.
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