smkn951

hello everyone, been thinking. i have a mbc, i got after market guage that reads at 15 then drops off to bout 11-12 psi and the only way i can keep the boost up is keep on accelerating.
the question is... since my wg is shimmed can i turn the mbc all the way up? will the waste gate (stock) hold till 15 psi and relieve any excess pressure?
is there any way that i can run 15 psi till redline while maintaining the desired speed and rpm?
tia

turbo944

If you are hitting 15psi now as you accelerate and you have a K26/6 turbo (doesn't mention your cars year in your profile), then it seems like most often you will find some boost dropoff toward redline as the turbo is meant to offer a bit more midrange than top end. The bigger K26/8 gives more to redline with the offset effect of being a couple of hundred rpm slower to build boost. Some people say that an EBC (electronic) should be able to hold it to redline or increase your boost level as rpm continues to rise, meaning you would have 15 down load and the set point would rise from there to help keep any from bleeding off, at least that is how I understand what they are saying with them.

As to how much boost you are holding, if you let off the throttle during acceleration, load drops on the engine and boost WILL go down as the load is less. Boost is not a function of speed or rpm, but both can affect it based on the load of the engine. At a steady 80mph on a level surface you will not have any boost running through the engine, but when you step on the gas and increase the load on the engine it will build boost. This is also why you don't build boost while sitting or rolling with the car out of gear and revving the engine, there is no load to help build boost.

smkn951

i do have the stock turbo (k26), how would i know how much i can turn up the mbc. or should i leave it alone? i've driven it hard a few time not on track just daily driving, and it'll go to 15 psi and not over, if i turn the mbc up higher, will this do and damage to the car, but if the wg is designed to give at 15 psi would it matter if i turn it up?

turbo944

Not sure how you are running your MBC with the shimmed wastegate (Reliaboost perhaps?) but if you have a wideband A/F gauge and you can verify that you have a good 12-12.5:1 ratio under boost, turn it up just a bit and watch your ratios again while you accelerate. Try to stay in that range throughout your acceleration and whatever you can set it to and stay in that range should be good. The v8 Guru chips stated 15-17psi boost and there are some 18psi chips out there now as well. I'm guessing you could probably safely go up another pound or two if your A/F ratios stay in that range mentioned above. If you wanted to run 18psi and your engine is in good enough shape to do it, contact Danno about moving up to those.

smkn951

reliaboost........? i don't have one of those, do i need one?a/f .....there it goes again......how do i adjust this? engine is running well. slight rear main leak, valve cover wetness. but well cared for. i do all routine maintenance on it. oil,plugs filters etc. timing belt needs to be retentioned but aside from that it runs well.
a/f where do you get these numbers from, how do i get them, what can i do to get it close to the proper level/
tia

turbo944

Well, a shimmed wastegate I was under the impression that you couldn't really do a good manual boost controller with. Maybe I'm wrong I do know that the Reliaboost and the Lindsey Boost Controller do let you have that little device that goes under the hood to control your boost. If you bought those chips from Danno, you may be using the Reliaboost. Small cylinder that hooks into your line from the intercooler to throttle body pipe. If you have an MBC of another type that functions then no, you shouldn't need one.

Well, you mention an a/f gauge in your signature You have 2 ways of adjusting it (grossly, not specifically per rpm with what you have) by turning up or down the fuel pressure with your adjustable FPR and also by controlling your boost pressure. If you find under boost that your A/F is 11.5 all the way up, by turning up your boost a bit you could bring that up to 12 or 12.5 to 1 and make more power with more air going into the engine. 14.7:1 is stochiometric and is where all of both oxygen and fuel *should* be consumed. If you want to adjust more accurately, you'd need an SMT6 or a Power Perfect or some device that intercepts the signal from your AFM and lets you tweak the signal being sent to the DME so that you can control your fuel more accurately across the board. That's the big advantage to a MAF under full throttle is being able to adjust it some to match it up.

You'd need to get your A/F ratio from your gauge, something really good is what I have with an LM-1 where I can record wideband A/F ratios (better than just pulling of the stock O2 sensor). See the handheld controller topic on this turbo board right now for a bit more about it.

smkn951

i only got the chip set from danno. the 3 bar nor the reliaboost came with the deal. he knocked some $$ off since i already had the rest of the stuff.
as far as the a/f guage is concerned, when i drive it fluctuates then soon it stabilizes on the low green end. i also have a fuel rail guage and it reads 'bout 36psi( it bounces+-3). so your saying if i turn up the fuel, ishould also turn up boost? won't i flood the car at idle if i do this ,since ican only get boost on load? tia

turbo944

You really shouldn't be turning the fuel up much beyond the 3-bar needed with Danno's chips, but if you found you were consistently running way rich you could turn it down a bit. But you could go up another pound or two if it was needed. Much beyond that and it actually starts flowing less fuel.

Yes, the A/F gauge is really only needed to show you what you are getting when you are getting on it and in closed loop where the fuel is simply sent from a map on the DME. The rest of the time the system is in open loop and the O2 sensor information is used by the computer to figure out how much fuel to give the engine to keep it close to 14.7:1. The computer should be able to account for a bit more fuel by having less injector opening time while in open loop and in closed loop it provides a bit more fuel to the basic number (which goes up in pressure as boost builds as well). I'd be more concerned right now with finding out what your exact ratio is on boost and seeing if you can turn it up another pound or so and stay near 12.5:1 A/F. If you can, then you don't even need to touch the FPR as more boost will be more pressure on it and thus put more fuel in anyway (to a point, but it's not a perfect correlation or you could just turn up the boost and go no matter what). If you don't have a wideband, tuning on a dyno would be your best bet as the stock sensor isn't going to be really reliable to show you where you really are right now on boost if it's between 11 and 12.5.

smkn951

i'm in germany right now, do happen to know where ican have it dynoed and how much? would they make the adjustments?
what is a 3-bar equivalent to?

turbo944

No, unfortunately I sure don't know of anyplace over there to dyno your car. Heck, I don't know of anyplace within 2 hours I could even get mine dynoed. Unless you paid them a good bit of money, they would not make the adjustments to your chips to let you run more boost/fuel. However you can send the dyno chart with your AF logged on it (most do nowadays) and your boost logged (some do that as well) to Danno and he can custom burn chips for you for a reasonable rate since you already have a set of his chips.

1-bar is 1 standard atmospheric pressure unit. 14.75in of mercury or about 369mm of mercury. So 3 would be just 3 times that figure. Gotta run back and do some work....

smkn951

so the 3 bar is set and no adj. is done? would it be better to get that and ditch the adj fp?

turbo944

According to your sig you already have an adjustable one. However if you don't, I wouldn't worry about it. Tune a bit with your boost, see if you can find a dyno in your area and get a few runs to see your AFR, record your boost, etc. and have Danno custom burn you some chips...would probably be cheaper than buying an adjustable FPR...and would likely run better, especially if you wanted to run like 18psi...

smkn951

i do have an adj fpr. just wondering which is better, should i convert to the 3-bar? and have danno burn new chips and get the reliaboost and get rid of the mbc? what are my choice with the current set up?

turbo944

Stick with what you have if it's working fine...no since in changing part of the equation at this point. Same with the MBC...the Reliaboost is just another form of an MBC, just not adjustable from in the cockpit.

If you are wanting to run 18psi of boost, I'd let Danno know what you have and how your boost currently runs as well as what you are seeing on your A/F ratio at several points while you're boosting and see what he's got for you. You may be close enough to stock to get the regular 18psi chips and just use those straight out.

Otherwise, if you just want to try and keep your boost up, you might start looking for an Electronic Boost Controller (EBC). I don't have one and don't know too much about their real operation on these cars, do some searches here as several people have used them and some really like them.

facboy

just a slight correction...under WOT the car runs *open* loop (no feedback), not closed-loop. i think u have the two mixed up turbo944.