VPC Guys

[DlandryTSI]

Ok for all you vpc guys here is a few experimentation results. If you recall my car was very happy with the following settings

22psi
VPC all 0's
safc
1k -22
2k -22
3k -22
4k -22
5k -22
6k -18
7k -18
8k -18

Now from what John was telling me yesterday through one of our conversations. The 660's are 47% larger than 440's. So in reality it would take -47% to run the stock boost level and still retain the correct fuel misture. So in theory I should just have to put ~8% more fuel back in. Wrong. At 27psi here is what happened. The vpc seems to dump in more fuel around 5500-7000 rpms. So to compensate I had to take the s-afc curve the opposite way. here is what I did.

27psi
vpc - all 0's
s-afc
1k -15
2k -15
3k -15
4k -15
5k -18
6k -20
7k -20
8k -20

This seemed to be enough to not only run 1500 degree egt's and get the power back at 27psi but it was also enough to run the 60 shot at 25psi and not go over 1550 degrees. There was no knock on any of my runs and my average timing was 21-22 degrees where it should be.

Granted yes the supras are a different beast but john was seeing the same symptoms as I was the closer you got to 27psi the more fuel the vpc started to dump in on the high end of the rpm band.

Well just thought I'd share what I found out....

--Dave

[hoffman]

sweet, good to see everything is coming together. so if your VPC is at 0's, whats the point of haveing it? or is this still initial tuning again?

[DlandryTSI]

Because then you can do all your tuning with the afc and not get confused.

--Dave

EDIT: Also the vpc has different maps when you adjust the gain. So that can play a big part in tuning.

[hoffman]

gotcha.

[Hal]

The 27 psi mark is CLOSE to the limit of the VPC's map sensor.

Perhaps that plays into it.

Hal

[DSMxTSi]

Originally posted by hoffmangsx
sweet, good to see everything is coming together. so if your VPC is at 0's, whats the point of haveing it? or is this still initial tuning again?

Another good reason to use a VPC is to get rid of the MAS. Granted you can go pretty far with a MAS, but you get much more air flow without it in the path. I have a VPC backed by a GCC and love it. If your goals are low 12s or better I'd recommend a VPC backed by either the S-AFC or GCC, but if you want just a fairly quick car then the S-AFC is just fine.

Cody

[john]

FWIW, one of the more EE-type supra guys recently did some VPC MAP sensor testing. It maxes out at 1.7 bar. Above that it will not add add'l fuel, as the 5v max output from the MAP sensor has been achieved already. Beyond 1.7 bar it's all adding fuel (well, removing airflow) with the AFC.

I'm sure you are still pig rich, Dave. Tuning for no knock is valiant, but not realistic. Sure, more timing is pretty much alwas better than more boost, but there comes a point where that isn't going to be the case. You say 21-22 degrees of timing - in which gear, and what was it across the entire WOT run in that gear?

I still stand by the statement that 27psi of flow from that big turbo is just too much for the stock head, even with cams. You really need to tune with a wideband, preferably an incar unit so you can tune for real life conditions vs stationary dyno tuning.

$0.02 worth from a guy who has probably forgotten most of what he learned about 4g63s... :) Luckily these are more or less turbo basics, and the 4g63 can be substituted for the 2jz-gte for these generalizations.

You've got a lot of airflow capabilty, that big honkin intake manifold, and a stock head. I'd take one of the spare heads you guys have lying around and have it WORKED. The race head I had from Darren @ FFWD was hogged out pretty well. And polished up nicely. And had oversized valves. It flowed a good amount or air.

Good luck with it. Most of the parts to run deep 11s seem to be in place - just get rid of the bottleneck. Another suggestion would be to have an EGT in each exhaust runner to REALLY see what is going on in there.

[ edit ]

Just FYI - here's what I've got my AFC set at. I'm using a 680cc chip in my VPC running 720cc injectors with around 1000 hp worth of fuel flowing thru the lines.

My VPC is at all Zeros.

20psi - 11.8:1 AFR as set by an FJO in-car wideband O2

Below 4500 rpm - all zeros
5000 -1%
5500 -2%
6000 -2%
6500 -2%
7000 -2%

25psi - 11.4:1 AFR per the FJO

4500 -3%
5000 -5%
5500 -5%
6000 -6%
6500 -6%
7000 -7%

11.4:1 is still REALLY rich, but it's miles better than the under 10.0:1 that the car did at Dyno Pro @ 26psi. Once I get the DIY wideband into the car (if it ever arrives) I'd probably tune it as lean as 12.5:1 on a combination of 104 & 110 octane at 28psi.

Also, the 11.9 @ 126 and 11.4 @ 123 were run with the car running as pig rich as it was on the dyno. I can only guess that it'll run faster, if not quicker, leaned out some.

[ /edit ]