Dragonz818

Heres my problem...I had a boost gauge installed and noticed I was spiking to 14-15 psi with just downpipe and catback. I was told by many people that that couldnt be true. Also when they installed it they used the whole tube that came with it. So the sender is like a foot away from the nipple.
I then saved up for my PFC+commander. I wanted a boost controller and I knew I would need this soon anyway. The pfc says that I am running at about 7.5-8.3 somewhere around their. Much Much lower than 15 pounds.
Now being that the nights are getting colder and boost spike will get worse I really want to know exactly what boost I am making.
Which one should I be paying attention too. Should I be nervous? Can anyone give advise as to how do find out what the boost is really?? HELP ME OUT!!
I dont want to blow it...

FD Racer

Wow thats a big differential. I also have defi gauges and a PFC....the commander usually reads a bit lower, but not that much. Elevation could be playing a role, but in NJ? Doubt it. One foot away from the nipple is okay for the sender, mines at that much if not more. How does it feel? You should be able to tell the difference between ~8psi and ~14psi with the infamous Butt Dyno.

Dragonz818

I messed up the post. I ment to put .75bar and .83 bar I am still getting used to this psi and bar thing

Dragonz818

Defi boost gauge reads-15 pounds
Apexi PFC is reading- .75-.83 bar

GoRacer

iTrader: (2)

Metric conversion website

.75bar = 10.875lbs
.83bar = 12.035lbs
1.0bar = 14.500lbs

FD Racer

.83 is like 12 psi.
Thats a little better. I'm leaning towards believing the Defi. Keep in mind that the defi gauges are so damm sensitive that they record peaks that normal analog gauges would'nt even register. Do you know anyone with an analog boost gauge that you could borrow with a vacumm line going out the hood around threw the window for a quick test around the block?

Dragonz818

I can get it close, but anyway 15 pounds on defi compared to an average of maybe 11 pounds or lower on PFC???

What should I listen to/

Dragonz818

Nobody I know has one...

FD Racer

Actually bro, its kg/cm2 not BAR


Check it:

FD Racer

****...too bad your not in Cali, artguy (Jason) is still running around with my extra gauge all bouncing around in the passenger seat

FD Racer

record a run on the defi. How long does it spike for?

Dragonz818

What should I do if it is spiking to 15 pounds??

jspecracer7

Been there and done that. I have the exact same setup, and had the exact same problem. Defi boost gauge reads HIGHER than what is true. Not THAT much higher, but still higher.

According to my Defi boost gauge, I am boost 1.1 kg/cm2. My PFC reads .9 kg/cm2. Appx. 3 psi difference. I took a mechanical greddy and mounted it inside....reads the SAME as my PFC....leading me to believe that either my PFC AND the GREDDY mechanical boost gauge are wrong....OR MY DEFI BOOST GAUGE READS HIGH!

Dragonz818

Hey van whats up... What should I listen to?? On a hot day my car will spike 14 and fall to about 12 now being that its cold its spikeing to 14 and not falling. The PFC says no more than .83 bar....

What if the Defi guge is right?

GoRacer

iTrader: (2)

Hmm, ok but then why do people say "bar" and 14.7lbs?

.75kg/cm=10.665psi
.83kg/cm=11.803psi
1.0kg/cm=14.22psi

jspecracer7

To be honest, I would go with the Defi....simply because if your UNDER boosting, you won't blow your engine....but OVER boost will lead you down the blown engine road.

Try to find someone with a mech boost gauge. That may help you trouble shoot...but from MY EXPERIENCE, I found the Defi to read higher.

Also, are you reading PEAK...because even in non-sequential, it will sometimes peak out at 1.1 and then drop down...

jspecracer7

Just like ps and hp...VERY similar, but slightly off. The Metric system is what most gauges uses here in Japan....kg/cm2

FD Racer

Nice Avatar btw jspecracer7.

jspecracer7

Why thank you!...Tila Nguyen...So HOT...

Dragonz818

Ok heres the verdict

I just took it on the road I was watching the boost gauge. Coming from a dead stop out of a toll. First gear the gauge read 10 psi at wot. Second gear went to about 11 psi at wot. Third gear it spiked to 13.5 and dropped to about 12. Fifth gear at wot went straight to 15 pounds sat their for a second then dropped to 12.5 and 13.5 some where in thier

Also while driving at 80mph when the pfc says 0.00 boost the defi gauge reads 2.5. Basically the defi gauge is constantly reading between 2 and 3 pounds higher at all times.

Hope this helps you help me....

Dragonz818

Also the spiking doesnt show up as badly as it does the defi.. The apexi is more gradual

Dragonz818

I am still running with the sequentials never changed them. Its when the second turbo kicks on that I get a real massive spike.

GoodfellaFD3S

iTrader: (213)

I like my avatar better

Ok, back to the matter at hand. My boost gauge (greddy 60mm EL peak/hold) reads ~2psi higher than my PFC Commander. The autometer before it was the same way. I believe the commander--it's reading right off the stock MAP sensor and doesn't have a vacuum hose to introduce error into the equation. Dave at KD Rotary agreed with this, so that's what I'm stickin' to

Dragonz818

I didnt think my car was runnning 15 pounds maybe 12 but no way 15.

Also the fact that the boost gauge shows a spike to 15 and the pfc none makes me very unsure.

To get 1 bar on the pfc is impossibe right now. The gauge as soon as I hit the gas boom 15 psi.

Dont understand it. Should I buy a seperate boost controller?

I think I am going to have it dynoed. What should I look for? In the car and the reading. Big hp increase and decreases???

FD Racer

Hard to say....the chick on the left needs more top end and the chick on the right....her top end runs a bit low, if you know what I mean...