hammeron

great, thanks BruceH

Simon1

When my car was being tuned with the turbo, I had two tunes done. One for the street @ 10 psi (91 oct) and one at 12-13 psi with 100 octane. The difference between the two weren't all that dramtic if you looked at peak numbers. But the 100 oct tune had 150 more rwtq and about 75 more rwhp from 2500-4500 rpms. I asked the tuner about it and he said he played with the cam timing to get the jump in power. Now, the cam timing is also combined with more overall spark timing, but I think it applies to what we are talking about.

The difference in low end torque was just stupid. At any gear on the race tune from 1st thru 4th I could stomp on the gas and break the tires free. The street was more a 1st and 2nd gear burner, sometimes third.

I suspect alot of tuners, when they are an FI car, are hestiant to get really aggressive with the cam timing because of the possability of a VCT failure. It's a legit concern. Frankly, I'm considering putting some limiters in my VCT because of the power level I will shortly be at.

I'm okay with driving around at 500 rwhp at around 10 psi, but not comfortable being at 15-16 and 600 rwhp with the VCT in full speed.

Maybe I'm paranoid . . .

hammeron

now you got me curious how all that midrange
torque is produced.

i don't think you are paranoid, with all this talk
lately of blown motors it's only reasonable to
take as many precautions as possible.

i'm surprised you are not doing phaser lockouts.

GT Bob

You've hit the nail on the head right here. When I am dialing in a tune for WOT I disable the VCT function to keep a few other variables steady until I have everything else where I like it. The result it that the low end basically goes in the crapper, and driveability suffers something fierce too. As I bring back the VCT functions, you can really feel the lower end and even some of the mid range come alive. VCT does in fact play with mid range as well, as well as transient conditions (i.e. Cruising at 40 and then mash the gas).

As for how the cam timing can add mid-range power... take the same principle of adding timing and instead of firing the spark earlier (or rather, in addtion to) you delay the opening of the exhaust valve giving the fuel more time to burn, or delay the opening of the intake valve to create a slight bit more of a vaccum in the chamber. With the VCT on the 3 valve setup and all the timing options you have, every single degree of crankshaft rotation can have literally several million combo's of ignition timing and camshaft positioning.... and thats only with ONE camshaft per bank... imagine what will be possible with the Coyote Motors next year...

Back to the more power in the mid range, something I just noticed that was said... that extra power was also stepping up from 91 octaine to 100. Every degree of timing will add, on average, 3% more power... and jumping up 9 octaine will certainly allow you alot more timing, especially on an FI car, where those gains are added on top of those from the pressurized air.

Hammeron... you seems like your trying to dig for an answer without asking the question... or it could just be that I'm way too tired and missed the question... what exactly are you looking for? I know what you originally asked but it seems like your digging for more... and by the way, yes you 100% SHOULD care that the VCT is disabled. It's there for a reason, and any tuner who won't work with it, imo, isn't worth your time or money.

breathegood

In a custom tune, are both closed and open loop taken care of? I know that in open loop, the tuner basically has free reign (this is what we see on the dyno), but in closed loop, isn't the PCM just going to do everything it can to keep the AFR stoic and timing just high enough to keep from pinging? I realize that a tuner has to make some adjustments for things like cams and larger than stock intake tubes, but does he really have controll over the closed loop part of the tune?

hammeron

GT Bob, thanks very much for weighing in
on the subject. you bring up some interesting
points about the exhaust opening and intake
opening events. i had been focused on where
the intake valve closed and resulting cylinder
pressure. i figured there had to be a sweet
spot in the cam timing (how much retard) to
give the most efficient operation (possibly best
MPG also?).

i'm not really digging for anything more than
what i asked in the original post. i am extremely
pleased with my custom dyno tune and just
noticed that the VCT being left disabled in
the lower rpms, just seemed like unfinished
business. i realize that tuners only have so
much time to spend on a customers car and
that is totally understandable.

i have an unlimited supply of time to devote
to perfecting my tune and would love to restore
the VCT tables, but only if it is worth the
time and effort. you make a good case for it
being so.

you've already given much insight and if you
don't mind, could you give me a hint of how
you go about bringing back the VCT. you don't
need to go into great detail, but a general
brief overview would be appreciated.

hammeron

breathegood, great questions. answers below.

Simon1

I'm actually going to do phaser limiters, not lockouts. Haven't decided on which brand yet but I wll be doing them in March. My tuner is flying in from Florida in April to tune a whole bunch of cars. I will be driving around until then with the stock pulley that makes like 9-10 psi. Prior to him arriving I will put in the limiters and strap it to the dyno for a complete dyno tune with the street pulley and then 100 oct and the 15-16 psi pulley.

Simon1

[QUOTE=

Back to the more power in the mid range, something I just noticed that was said... that extra power was also stepping up from 91 octaine to 100. Every degree of timing will add, on average, 3% more power... and jumping up 9 octaine will certainly allow you alot more timing, especially on an FI car, where those gains are added on top of those from the pressurized air.

[/QUOTE]

I beleive it's combination of several things in my situation:

Overall timing, from 17 degrees to 25.
Dfifferent cam timing on the lower end.
More load at lower RPMs causing the turbo to spool faster.

A combination of all three yields the gigantic results.

At the big end, there was basically 60 more rwhp and twtq. Not seemingly that impressive for 2.5 psi more and 7-8 degrees more timing. At the low end, it was around 150 rwtq and I forget the rwhp difference.

Simon1

I found it.