View Full Version : why only 15 psi????
Finally got my boost gauge and did some tests earlier today. At 2700, I got 15 psi in 3rd, 4th, and 5th. I got 15 psi in 2nd as well but it came at like 3600.This was done with 93 octane fuel. Is the factory overboost switch set at 15 psi? I have a tweaked box and I have messed with the wastgate. Should I turn the wastegate down to get more boost, or should I disable or bypass the overboost switch? Thanks.
Disabling or adjusting the fuel cutout won't increase your boost at all. It will mean however that if/when you do end up running more boost, your head/bonce won't hit the windscreen when you go over somewhere near 1 bar (approx 14.7 psi) and the fuel is shutoff.
If you are running an APC, the wastegate sets the base boost. Turning in the actuator rod may trick the APC and give you a sudden surge of boost but once the APC realises what's going on, it's gonna come straight back down. Not really a good state of tune, and definately bad for an already fragile gearbox.
What APC mods have been done? Removing R23 is a good mod, it removes the annoying boost taper which occurs mechanically anyhow.
IMO the best source there is regarding APC's and modding them is on the "Turbo Team Europe" site. That's where I learnt the majority of what I know on APC's. Theres a lot of literature about them there.
Turbo Team Europe - APC Literature (http://web.inter.nl.net/users/turbo-team-europe/apc.htm)
Also running 93 RON fuel isn't really a great idea if you are considering going much higher with regards to boost, you will end up having the APC backing off all the time due to pre-ignition/pinging/pinking etc.
You are also running into the dreaded "lean out" area +15psi, so maybe if you haven't done so, investing in some uprated fueling equipment may be a good idea if your planning to go any higher, that is of course unless you've already done so. :smile:
Hope that's of some use. :smile:
_________________
Saab 900 T16
http://homepage.ntlworld.com/stnuts/900/nuts_900.jpg
Some Mods...
<font size=-1>[ This Message was edited by: Nuts on Mar 13, 2002 5:50pm ]</font>
Ok, I just spent the better part of an hour trying to sort out all the info. mentioned on the webpage mentioned in the previous post.
Towards the end there are different views as to tweaking the APC, and it is mentioned that
"And the other Tweaker's "tweak": "I personally prefer settings as follows:
R42 - bypassed, R138 - 31Kohm, P-23Kohm , F-360ohm. Fast, quite stabile
boost up to 5800 rpm. (peaks @1,15bar, slightly comes down to 1,0bar)"."
What exactly does "bypass" mean? Is it removed totally? Any info would be appreciated as I'd like to try this particular mod.
Remove the resistor and replace it with a piece of wire = bypassed
conradFL
13-03-02, 08:58 PM
Nuts, he isn't running 93ron
the octane numbers in the US are
(RON+MON)/2 = AON which is
Research Octane Number + Motor octane number divided by two = your US octane rating :smile:
it is the average of the research and motor octane figures.
The research and motor octane figures are obtained from testing the gasoline with the engine turning at different speeds.
I am assuming that the cause of much confusion in posts is the apparent fact that the US takes an average of two numbers, and the UK only uses the RON number, or else I am real confused?
AON is also known as Pump Octane Number (PON) or AKI (Anti Knock Index).
RON effectively shows the knock resistance at part throttle in the mid range, while MON reflects knock resistance at wide open throttle at higher rpm.
More info at
http://www.osbornauto.com/octane.htm
Its an amazingly old test though that dates back to '50s!
Right sorry for the confusion...I wasn't really aware that the U.S used a different rating to the one used here in the UK.
So what is the RON of U.S 93 octane fuel?
If it's still under 95 I don't think it would be adequate for running higher than standard levels of boost i.e. over +15 psi. Unless of course, you are gettng very cold charge.
_________________
Saab 900 T16
http://homepage.ntlworld.com/stnuts/900/nuts_900.jpg
Some Mods...
<font size=-1>[ This Message was edited by: Nuts on Mar 13, 2002 9:28pm ]</font>
conradFL
13-03-02, 09:45 PM
yeh, my friends nissan manual calls the octane rating the AKI
the research number is higher, 93 octane (premium fuel in the US) will be say, 96ron and 90mon.....giving 93 aon.
not sure on the numbers now but I can look the next time I fill up
American 93 is roughly equivalent to 98 RON. Most of the info seems to suggest pumps fuels have a difference of 10 between MON and RON.
Nuts,
I have invested so much money in this car, including a new gearbox. I too have read extensively on all the apc novels on the net and through other owners. I have never heard of removing R23 though. If mine is still factory spec, should I bypass it or remove it altogether?
This car is not leaning out. I run 94 sunoco octane and also add 2 gallons with each fillup of $4.25/gallon 100 octane race fuel so I highly doubt it is leaning out. Adjust those numbers for the system you guys use overseas.
You never did tell me if the symptoms that I have are the result of me slamming the overboost switch under the dash. I get 15 psi and that is it. This car cannot be leaning out with all of the high octane race gas that I run through it. The time that I tested it was the only time I actually put in anything less than 94 octane. If I am hitting the overboost, how do I get rid of it? Thanks.
I think R23 is where the rpm signal comes into the APC, Tweakers site has changed so I can't double check this without pulling my APC to bits. If so removing it means the APC box will always think the engine is doing less than 3.1krpm, so it will stay on the default duty cycle which is way too long for high boost at high rpm. So boost taper will be worse than staying on the active cycle, so I found anyway.
Keith
Janne Selinummi
14-03-02, 11:00 AM
Viktor, have you not upgraded your fuel system? If you run high boost, the mixture will lean up in the hight boost area, and this you can't help by using high-grade fuel, as it's a question of injecting enough of the fuel to the combustion chambers. A rising rate fuel pressure regulator along with a fuel chip to the management system should me enough for your application.
Keith:
I think you are wrong on your interpretation of what R23 does, ad how it effects the duty cycle.
By removing R23 all you are doing is disabling the control of the boost via engine RPM. Therefore it is only controlled via boost pressure & knock sensor. The APC will only enter the duty cycle once the set pressure has been reached or if you get any knock.
FYI if what you said was correct I would be getting base boost all the time.....and I am not.
This link’s some another of my favourite resources on the APC. It describes what does what, and what can be done etc.
(Mostly) Ripped off APC info (http://www.badbricks.com/main_files/faqs/apc.htm)
Viktor:
I think you are misunderstanding what "lean" mixture is.
Basically what I meant is that with the standard fuelling equipment (and the way the fuelling ecu is set up)and running higher levels of boost will mean that simply you can't supply enough fuel for the charge that's going in, therefore your mixture becomes lean i.e. more air than fuel.
If you are getting a lean mixture, and you continue to run without enrichening it at all, it is possible to burn holes in the tops of your pistons & destroy your valves. This is much more expensive than a RRFPR, bigger injectors, a fifth injector or even a reprogrammed fuelling ECU!
Hope that helps and sorry to be so disagreeable, just on this one occasion, I believe myself to be right :smile:
_________________
Saab 900 T16
http://homepage.ntlworld.com/stnuts/900/nuts_900.jpg
Some Mods...
<font size=-1>[ This Message was edited by: Keith on Mar 15, 2002 5:37pm ]</font>
Marko A
15-03-02, 04:58 PM
Hey Keith, are you following this discussion?
Did you check the APC link? Know what I mean ;o)
Anyways, Keith is right with R23. RPM signal comes through it and if you remove it, no more RPM signal -> defaut duty cycly all the time unless it knocks. Not really good for highboost/high rpm.
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Marko Alatalo
SAAB 900 TurboS
./uploads/boost.jpg
<font size=-1>[ This Message was edited by: Marko A on Mar 15, 2002 5:04pm ]</font>
I have now, unbelievable. :sad:
I think we oculd argue all day about what does what in the APC, that's why so many resources and opinions are conflicting.
The proof of the pudding however, is in real life examples, here is mine:
Example: Saab 900 T16
Trent Saab APC
Water injection & lots of other irrelevent mods that I won't bother to mention.
With R23 in place: Boost rises to 17Psi then tapers down to 13.5Psi @ around 5200 Rpm [APC controlled boost taper].
Without R23 in place:Boost rises to 17psi then tapers down to 15 Psi @ around 5500 Rpm {mechanical taper].
I really recommend trying it to your own APC, if you don't notice an improvement then put R23 back in!
I noticed a substantial improvement, otherwise I would have put mine back in!
Marko A
15-03-02, 06:06 PM
How did you get the idea of getting R23 off?
Marko
NUTS
I have tried it, and it was no good ON MY CAR. It struggled to get over 10psi past 5krpm. If it works for you fine, go for it.
I get much better high rpm boost with the APC working actively.
I am just pointing out that pulling R23 off may not work for everyone. There are so many variables.....
Marko,
Can I just ask why you have trimmed down your excellent site to the barest minimum?
Alanb
Marko A
15-03-02, 06:42 PM
AlanB,
I´m sorry if I disappoint you.
The reason why I deleted the APC site..
Well, lately I´ve had some bad input (I´ve had it all the time, but not so much that I cared) people blaming me if their mods won´t work etc. etc.
I got badly frustrated since I´ve answered several (hundreds) email and trying to sort out all the problems that people had with their mods. What I got for it? I was happy if people were happy, but if someone is saying that I´m lying and I don´t know s**t about APC. I didn´t mind it at first, but enough is enough.
Maybe I´ll do new (better) site some day.
Time will tell... At least I seem to have some friends who cares.
For now, the site still says all you have to do with your APC to get good results.
Cheers
_________________
Marko Alatalo
SAAB 900 TurboS
./uploads/blackbox2.jpg
<font size=-1>[ This Message was edited by: Marko A on Mar 15, 2002 6:47pm ]</font>
I for one am gutted the site had to go, though I completely understand why :sad:
Thanks for all the time and effort you put in to it. I know my car would not be anywhere near us much fun as it is now without it.
Cheers Marko,
Keith
Marko,
How about putting a copy of your pages (less your e-mail addy) onto our technical help section!! This way your friends on here will have access to your excellant information!!
OK Keith point taken, I just wanted to reiterate that I have seen gains with this particular mod on two seperate APC's.
But if you've tried it as well and found it was detrimental to performance, then fair enough, I am not trying to dictate what anyone should do, just my own experiences with my own APC's. :smile:
I think it's a shame about your APC info page Marko, I think possibly John-w has the right idea with an email-less page. :smile:
P.S: Should I expect my messages to be edited by others or should I find it a suprise? Just wondered as it's the first time it's happened.
I'd just like to add to the support for Marko and his site. I suppose those of us who appreciated it should have spoken up earlier rather than remaining the silent majority. I for one owe him at least 35bhp!
Cheers,
Alanb
I did some more tests today.
I filled my tank with 100 octane and subjected my beloved spg to lengthy high rpm use. Here is what I got....
3rd, 4th and 5th gears all had very consistent MAXIMUM boost between 15 and 18 psi(it spiked to 18 only a few times though). At around 4500 rpm to 5500, it tapered to 12 or 13.
I do have a 3 bar fpr and I have heard that this will effectively and safely(knock not driveline I should add...) support boost pressures up to 16 psi. My question to Nuts and Marko is, should I take off R23 to get a consistent 14-16 psi up to redline? I never spend any time above say 4000 in 3rd through 5th (damn speed limits) I just want the capability. I just want to know if the removal of R23 is safe.
Marko,
I wont get pissed and send you an email if your theory does not work. I am perfectly happy with 11-12 psi. If you hold that to redline, these cars are plenty fast for the road. Mine will never see the track and I dont race losers in rice roasters so I worry more about drivetrain reliability now that I have spent tons to keep my 900 alive. Thanks all.
My advice after hearing from marko & keith would be to try removing R23, and see whether you get a gain, if however you get no benefit put it back on. Its a 10 minute job so there's no harm in trying.
But let us know how it goes :smile:.
Do I need a soldering tool for that? I have not messed with my apc at all, I have only read up on it. There seems to be too many conflicting reports on the net as far as the 'theory' behind that box. Forget <15psi in a 14 year old money pit, Im through with messing with my boost.
Does anyone know how much boost a 3 bar fpr will safely support? I have heard 14 but I am not sure.