MBC question

vrg3 · Post by **vrg3** » Tue Oct 26, 2004 12:14 am

Would you say it sounds like the engine is being strangled?

Is your exhaust stock? The stock exhaust is very restrictive...

magicmike · Post by **magicmike** » Tue Oct 26, 2004 2:08 am

it sounds very weird, it almost sounds like something is about to break or something. Its weird. I did notice that it only does the sound at WOT under hard accel. Under normal acceleration all you here is the turbo spooling. It is very loud even for the factory exhaust. It sounds like its creating crazy ass horse power but then the car isn't moving that much. Thats the best I can explain it. Maybe its fast but driving my infiniti daily makes it seem slow to me. Oh at about 90 on the highway I think I hit fuel cut, the car suddenly lurched forward for a second. My MBC is not very consistant...

vrg3 · Post by **vrg3** » Tue Oct 26, 2004 2:19 am

Do you think maybe it's an intermittent boost leak?

You have an intercooling setup, right?

When you were on the highway did you exceed about 13 psi for more than about 3 seconds?

magicmike · Post by **magicmike** » Tue Oct 26, 2004 3:54 am

I do have an alluminum saab setup yes. I dont think I have a boost leak. I'm almost thinking the loudness has something to do with my header. I know my honda civic got really loud when I installed a header in it. I'm sure I exceeded 13 for more than 3 sec I was accelerating at a steady rate. I cant tell for sure because I was trying to read it under my map light ( I havent connected the back light on the gauge yet) To me it sounds alot like the balls to the walls WRC cars but at the same time something does not sound right. I need to jack my work's camcorder and take a video tomorrow or the next day. you really need to hear the sound for yourself.

Warp3 · Post by **Warp3** » Tue Oct 26, 2004 3:05 pm

-K- wrote:We are on my subject now: Home Depot Racing
My bleeder cost a little over $3
I also have a Home Depot Racing intake for my airbox

Yeah, at least on my RX I spent more time buying "mods" at Lowes and Home Depot than I did car parts places...

magicmike · Post by **magicmike** » Thu Oct 28, 2004 2:08 pm

well I've hit fuel cut a few times so I lowered the boost down a litle. My mbc is a little shitty and not very consistant. If I accelerate slowly it will max out at 12 psi but, if I floor it and it drops a gear and goes to redline the boost reaches 13 to 14, for a split second. Its very hard to read the gauge. When I'm on the highway and cruising at say like 70-80 and I just slightly step on the gas to go a little faster you can see the boost rising rising until it hits full boost then the car accelerates. Its weird. its like the engine on its own is doing nothing. like the turbo is driving the whle thing or something. I dont know how to explain it, its just weird. I really need to drive a stock leg turbo to get a comparison, or meet up with one of you guys maybe in CT who has one. Hopefully my CES will help

vrg3 · Post by **vrg3** » Thu Oct 28, 2004 2:44 pm

Yeah, a lot of MBCs seem to behave differently in different gears... I'm not sure I fully understand why.

Our engines do rely heavily on boost... they bumped the compression ratio down to make boost more reliable, but that does make it kind of sluggish off boost.

Are you running the stock turbo-back exhaust right now? That's horrendously limiting at the amounts of airflow you're seeing. You will definitely see a big improvement with the CES system.

magicmike · Post by **magicmike** » Thu Oct 28, 2004 10:04 pm

heres the thing though, it sounds like I have a ton of air going through the trubo as it is loud as hell when its spooling. I'm surprised that I can hear alot going on but not much movement of the car can be felt. could be that I'm not getting enough fuel into the engine for all the air? or is that what fuel cut is?

vrg3 · Post by **vrg3** » Fri Oct 29, 2004 12:40 am

Fuel cut is very different -- it'll feel like hitting a brick wall.

It's possible that you have a leak, so the turbo's pushing lots of air but it's not all getting into the manifold.

Are you monitoring fueling somehow? You should be able to at least do a sanity check on your fueling by looking at the oxygen sensor's signal. EGTs can also tell you.

magicmike · Post by **magicmike** » Fri Oct 29, 2004 2:31 am

I have an autometer a/f guage but I havent hooked it up yet. I'm working on a custom gauge setup for my dash with a hidden panl so the gauges are hidden when the car is off. Its pretty cool but it needs more work before it can be installed in the car.

vrg3 · Post by **vrg3** » Fri Oct 29, 2004 3:03 am

Hmm, so you have absolutely no idea if you're getting enough fuel or not? I'd fix that ASAFP....

magicmike · Post by **magicmike** » Fri Oct 29, 2004 4:39 am

hum....thats a very good point, I guess I didn't figure that I could not be getting enough. perhaps the bad sound I hear at WOT is some mild detonation. or does detonation happen when you have too much fuel? I forget

vrg3 · Post by **vrg3** » Fri Oct 29, 2004 5:03 am

Lots of things can cause detonation, but insufficient fueling is one of the more common causes. Usually on boost running a bit too rich is okay. It does reduce power, but doesn't hurt the motor. In fact, it's possible that you're making less power than you ought because of how rich you're running -- Right at about 200 grams per second of air, the MAF sensor maxes out and the ECU just fuels as much as it can, so at that point the mixture is about as rich as it can get. As you start flowing more air than that, it actually comes back down a bit -- until you go too far and exceed the injectors' capabilities.

You really really should be doing some monitoring... a VF-34 at 12 psi could be getting close to the limits of safe operation with stock engine management. I think you should get a real air/fuel ratio meter and also an EGT gauge.

Do you have a high-flow fuel pump? If not, you should get one.

-K- · Post by **-K-** » Fri Oct 29, 2004 6:32 am

Sounds more like a bad cat in the crappy DP to me. Makes a huge improvement and with the price you can get a DP for ($150 for the HKS) or almost nothing for a stock WRX take off nobody should be running the stock DP.

magicmike · Post by **magicmike** » Fri Oct 29, 2004 2:11 pm

-K- I have a full DP back CES in transit as we speak

And vrg3 what is a real a/f meter?

vrg3 · Post by **vrg3** » Fri Oct 29, 2004 3:10 pm

Something that uses a wideband oxygen sensor so that it can measure air/fuel ratios. The system consists of a wideband sensor and a control unit that has to be installed in the car (it needs to be connected to reliable ignition-switched power). The sensor will thread in place of the stock one, and most wideband controllers have an output that simulates a narrowband signal so you can connect that to the stock ECU. The control unit typically also has some kind of display that lets you read off the ratio.

magicmike · Post by **magicmike** » Fri Oct 29, 2004 7:53 pm

hum interesting....

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MBC question