I have a 2013 GT with On 3 Performance twin kit. This is my First turbo car, and Im trying to tune the variable Cam timing. I tried to tune it like a centrifugal super charger but I lose 50 hp every time I put that cam timing in. How do you tune for a turbo using a SCT?
Turbo Cam Tuning Question
- Thread starter JDL0812
- Start date
I'm no expert, but you don't want any overlap. If you adjust the cams to ramp up and have overlap you will lose boost.
Sorry, really no help. If you find anything, please report back as I'm interested to hear.
:beer:
this is complicated shit so maybe you should tell us what your vct settings are so those with knowledge can look for issues. Not sure any pro tuner is going to give the info away.
Here is a piece from a tuning software suite for Honda's. Keep that in mind when reading the text when referring to redlines and when they mention that only the intake cam can be phased.
But it seems like with turbos, manifold design is the factor when altering cam timing. The bottom paragraph is the most relevant I think to you.
Tuning Guidelines
In short, the better the breathing of the engine; intake, cams and exhaust, the greater the cam advance needed. There is no situation in which best overall performance is achieved by fixing the cam angle to just one setting or using manual cam adjustment wheels for the intake cam. There may be benefits to fitting and adjusting the exhaust camshaft angle, which is not under computer control.
But it seems like with turbos, manifold design is the factor when altering cam timing. The bottom paragraph is the most relevant I think to you.
Tuning Guidelines
In short, the better the breathing of the engine; intake, cams and exhaust, the greater the cam advance needed. There is no situation in which best overall performance is achieved by fixing the cam angle to just one setting or using manual cam adjustment wheels for the intake cam. There may be benefits to fitting and adjusting the exhaust camshaft angle, which is not under computer control.
· With a naturally aspirated engine the cam advance should be set to maximum just after VTEC engagement until about 6500-7000 rpm. From 7000 rpm (where the cam advance should be near 50 degrees) to redline the cam is retarded back around 25 degrees. This procedure is correct for all commercially available after market cams at the date of release of this software, but camshafts which are substantially different from a Honda camshaft may require different settings.
· With a supercharged engine the cam advance needs to be set to maximum (50 degrees) throughout the rev range, with only a 10 degrees or so retard above 7000 rpm.
· With a turbocharged engine the cam advance generally needs to be less than stock. This is because a turbocharger generates much more exhaust back pressure than a naturally aspirated or supercharged configuration. The higher the back pressure the more cam retard is needed. With small turbos and stock catalytic converters you may need to retard the cam fully to 0 degrees at 8000 rpm. A log style turbo manifold results in a high VTEC point and low VTC angles - a manifold with longer, equal length, runners requires a lower VTEC point and higher VTC angles - closer to that which a naturally aspirate engine would require.
increasing intake cam advance in the spool region increases dynamic compression and will aid "pickup." Once the turbo is spooled however, you quickly want to ramp out any advance of the intake cam.
Basically the logic we would use on the turbo 4's I used to tune was we would retard the timing a hair in the spool region. This moves the flame front closer to the exhaust valve opening and gives us more heat energy (retarded timing leads to higher EGT's).
After retarding the ignition advance we would then increase the intake cam advance. Since doing so increases dynamic compression, we are essentially gaining back that natural torque we lost from retarding the timing and moving the engine along, as well as aiding spool.
Running the car a little rich on spool up will also aid spool, as well as prevent "spool up knock," as its often referred to, although I doubt that's much of a problem on this platform.
on my mazdaspeed3 with a gtx3576, if I floored it at 3500 rpms, id have 20 psi at 4000 (I kept it mild for street use). I left the Wastegate duty cycle the same and increased my intake cam 3* and was then hitting 31 psi at 4000 rpms. I did not bother retarding the timing in that case because I was on E85 and was not worried about excessive cylinder pressures.
As mentioned above, you want zero overlap. The pressure in the exhaust manifolds is often 2:1 in some cases, and overlap will cause pressure to push back into the cylinders and lose power. Just use small increments, when you're in the sweet spot, a little will go a long way.
Basically the logic we would use on the turbo 4's I used to tune was we would retard the timing a hair in the spool region. This moves the flame front closer to the exhaust valve opening and gives us more heat energy (retarded timing leads to higher EGT's).
After retarding the ignition advance we would then increase the intake cam advance. Since doing so increases dynamic compression, we are essentially gaining back that natural torque we lost from retarding the timing and moving the engine along, as well as aiding spool.
Running the car a little rich on spool up will also aid spool, as well as prevent "spool up knock," as its often referred to, although I doubt that's much of a problem on this platform.
on my mazdaspeed3 with a gtx3576, if I floored it at 3500 rpms, id have 20 psi at 4000 (I kept it mild for street use). I left the Wastegate duty cycle the same and increased my intake cam 3* and was then hitting 31 psi at 4000 rpms. I did not bother retarding the timing in that case because I was on E85 and was not worried about excessive cylinder pressures.
As mentioned above, you want zero overlap. The pressure in the exhaust manifolds is often 2:1 in some cases, and overlap will cause pressure to push back into the cylinders and lose power. Just use small increments, when you're in the sweet spot, a little will go a long way.
some good info here if you highlight the text you can read it over all the #'s http://www.forcedinductions.com/help.htm
A Turbo coyote guy on YB posted up that he had to keep the exhaust cam parked (fully advanced.. you might want to PM him. I do not know how the **** to tune these cams. Shaun is doing my cam tune on April 3rd.
Thanks for the info guys I think this will take some learning on the full needs of a turbo on my part so I will be leaving the stock cam settings as they seem to work well. Apprieciate the help I am sure I will be asking a lot of questions in the future. This is my first turbo car and I only know the basics about them.
Stock turbo settings have overlap because thats what N/A cars like to make power, and remember, turbos don't. Understand how N/A cams make power, how supercharged cams make power AND how turbo cams make power. An understanding of what is happening in each situation in relation to where the pressures are will paint a much more complete picture.
Heres a few links.
Heres 1: The platform is a DSM, but the principle is the same.
http://www.dsmtuners.com/forums/art...ing-dummies-understanding-what-happening.html
Heres another very good link with a very basic write up that i will excerpt below:
http://www.supraforums.com/forum/showthread.php?411951-Cam-tuning-Turbo-and-N-A-*Sticky-please-*
Last link:
http://www.enginebasics.com/Advanced Engine Tuning/Cam Gear Tuning.html
Said excerpt:
Simple cam tuning rules for BOOSTED engines:
Advance intake and exhaust => more low-RPM power, less high-RPM power
Retard intake and exhaust => more high-RPM power, less low-RPM power
Less overlap => lower EGTs, faster turbo spool, less fuel
More overlap => higher EGTs, slower turbo spool, more fuel
^^ i don't know that i agree with less overlap leading to faster spool, because as i mentioned earlier advancing the intake cam in the spool region will aid spool but... You're just gonna have to soak all this in and tinker for yourself. Its a very well written and informative posts / articles nonetheless. Keep in mind however, that most articles you will find are in relation to fixed cams with adjustable cam gears, not the type of sophistication that we have. Again however, the principles can be applied.
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