Subscribed. Only thing I have done is after 5k rpm change the exhaust cam down to 11* because I have headers and no cats, so there is less exhaust restriction but definitely looking for info on how to squeeze more power out of the 15's with vct.
Subscribed. Only thing I have done is after 5k rpm change the exhaust cam down to 11* because I have headers and no cats, so there is less exhaust restriction but definitely looking for info on how to squeeze more power out of the 15's with vct.
How does the car perform with doing that? Did you see an increase in power? The only thing that would concern me with doing that is your moving in the opposite direction of overlap with advancing the exhaust, leaving the intake vct stock. So your having the exhaust valve closed before the intake valve is opening after TDC. All sorts of voodoo is happening inside the combustion chamber of the 2015 gt lol. I actually saw an increase in power by advancing the intake cam and creating a small amount of overlap over stock from 5000-7000. I saw about a 10whp increase from doing so, and I just have an intake and x pipe. Just food for thought.
Haven't had it to a dyno yet. Care to share exactly what you did?
Let me finish my vct tuning and then I'll share a little information.
Unfortunately I was not able to achieve any positive results with VCT tuning on my setup. Currently I have an intake and catback, I was not expecting huge results but wanted to see if there were any. Once I install long tubes I will retry and keep the thread posted on the results. I will also be tuning the VCT on a boss manifold once I get one as well.
I didn't figure much of a gain without headers/catless. Only thing I can see being a gain is messing with the exhaust cams. With less exhaust restriction I can see advancing the exhaust cam less, for less overlap if that makes sense.
The only issue I have with advancing the exhaust cam without advancing the intake cam is that the intake cam stock is retard to 14 degrees at peak power, the exhaust cam is also at 14 degrees. We have 0 overlap 14 degrees after TDC on stock configuration on both cams. If you advance the exhaust cam you will create a dead period to where the exhaust is closed before the intake cam starts to open when the piston is moving down to draw in more air. I am not sure what this will do for performance or operation. I have seen though on past engines, with the increase in exhaust flow with adding catless race headers, intake cam advance was possible and resulted in huge gains in power with a lot more valve overlap.
I'll post some tables I did Thursday. Gains weren't huge but flattened out the curve. You can also use maf readings but it's less precise. You set your intake cam first as intake valve closing is the most important factor. Then set exhaust closing point.
Thank you greg, what mods are done to the car and what kind of gains were there?
Lots of stock engines came with negative overlap (LS1's come to mind - I think they had -35*). Keep in mind that at the start and end of the piston's travel, it's not moving that fast. It's either accelerating or decelerating as the fastest point in the piston's travel is 90* and 270* after TDC. That being said, there's probably some wiggle room to play with the timing on less restrictive exhaust setups...the real concern is over piston-to-valve and valve-to-valve clearance.Originally Posted by kris5597
More info - http://www.svtperformance.com/forums...tock-Cam-Specs
Last edited by SSpdDmon; 09-20-2015 at 07:51 PM.
2013 Mustang GT
I don't think a cam can produce negative overlap, there will always be valve overlap on every cam especially a single cam engine like an LS1, but I could be wrong.
I can see on the link you have posted that the intake cam is more retard than the exhaust cam but only at idle. When air movement builds velocity, this would be a bad thing for power.
Last edited by kris5597; 09-21-2015 at 03:45 PM.
Also, I was not able to get anymore advance out of the intake cam over 20* of advance. Can anyone confirm this is max?
Intake:
0
0
-11
-13
-14
-24
-24
-2
6
8
9 (rescaled to 8,000 RPM)
Exhaust:
7
7
7
11
18
16
16
16
16
16
15
We were seeing maybe 2 horsepower changes max (within error of the dyno) on any changes, but there were some broadening of the torque curve with these adjustments.
Oh yea, there's some overlap. That's what I like to see. What are mods?
Mufflers. Lol. It received a procharger the next day.
Very nice. Good to see you had luck with valve overlap on a practically stock car. I will keep working at overlap on my personal vehicle to see if I can see similar results. I appreciate the info. Good to see someone headed in the right direction. I bet with long tubes, we could definitely see some nice adjustments to overlap. A new intake manifold would be very beneficial.
This is an elementary question, but I want to make sure I am seeing the process correctly in my head. Since we can only change IVO and EVC, that's what I'm discussing.
Is the IVO event happening before TDC and the EVC happening after TDC? Imagine the crank rotation is clockwise and IVO at 11 o'clock would be -30*, EVC would be at 30* and at 1 o'clock. This would represent 60* of overlap, correct?
If I changed IVO to -60*(10 O'clock) and changed EVC to 90*(3 O'clock), I would now have 150* of overlap?
If we know the amount of duration on the cams, we can determine IVC and EVO, correct?
Using Greg's example above, his IVO @ 8000 rpm is 9* AFTER TDC and EVC is 15* AFTER TDC, which give 6* of overlap?
Yes, VCT has always been IVO and EVC. IVO and EVC cam values are all relative to crank position. On the coyote intake and exhaust cams, a negative value represents BTDC and a positive value is ATDC. You are correct in all of your numbers. If you know duration of your cams, just add the duration, plus the IVO or EVC and and you can determine IVC and EVO. What I see on the 11-14 Coyote, Road Runner, and the CJ, is that they all like overlap. The Boss maps go up to -50* intake and 15* exhaust, that's quite a bit of overlap, even when it trickles down to peak power,-15* intake and 10* exhaust, still a decent amount of overlap, the 11-14 GT operates in a similar manner. Even comparing to the cobra jet, loves overlap. That's what leaves me to believe that the 2015 needs to breathe to increase overlap and benefit from it.
In Greg's example, he is showing what a 2015 likes. What confuses me on the 2015, is why the IVO moves from BTDC to ATDC throughout the rpm band. Stock 2015 calibration does this, but creates 1* of negative overlap at peak power. I am still a firm believer that the 2015 heads, valves, and cams are way more aggressive than people realize for the stock manifold.
Last edited by kris5597; 09-22-2015 at 07:34 AM.
Thanks Kris! I don't see how a negative overlap can be efficient at higher rpms. Since the 15s have IMRCs, I wonder if this is contributing to the weird VCT values?
Last edited by txcharlie; 09-22-2015 at 11:33 AM.
All this cam talk, I wish I was smart enough to figure out my comp cams and tune my car lol.
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