hanknmorgan

How's it going. I purchased my first FD about a month ago and I have a question about my boost pattern. First off, I know it should be 10-8-10. Is it possible for a boost guage to be incorrect? Mine seems to run about 10-(6-7ish)-10 most of the time. It will however sometimes in third gear boost to like 12-13, according to my guage then come down to 10 or so after a few seconds. That scares me. My car is completely stock except for a modified Adam C intake with K&N. I had the K&N before and it still had the same problem. Should I be worried? Everything runs great. I had a rotary shop check everything out and said the turbos look good and everything runs well after their test drive/inspection. I have a VDO boost guage that was put in by a previous owner. What could cause this overboosting? I know people often run into a problem like that with a midpipe, but I have stock everything including precat. I want to put on a downpipe for reliablity but I'm scared to do anything with it boosting like that. The engine was rebuilt about 20,000 miles ago or so and there are no other concerns about the car. Any advice would be appreciated. Thanks.

mad_7tist

get a profec-b installed. and you should be fine with a few mods. it will keep the boost at 10psi

Ibumar

I've been tuning my Profec B spec 2 for the last couple weeks, and noticed some patterns regarding boost spikes on the primary turbo.

It seems that the spikes are related to the rpm you're turning when going WOT. On my car I get slight spikes when going from right around 3k rpm. I've been using third and fourth gear for tuning purposes, those seem to be the ones causing the most spiking.
If I nail it from around 2500 or 3500 I don't have that spike, or at least it's quite a bit smaller. The spikes themselves only last for a fraction of a second and seem to register at aroun .5 to .8 psi over steady boost.

I had the same spikes occur before I put my dp on and installed the bosst controller, though they seemed to last a bit longer than they do now,

I tried any conceivable setting to dial it out without any success.
I wonder how many people have the same problem...

FWIW, my mods a dp, a CB straight pipe and K&N drop in.
My current setting are.
Set 18%
Gain 31%
Set Gain 65.

Limiter is set to 10.3, and spikes are about 10.5. They're short enough that they register, but the limiter never even kicks in.

adam c

iTrader: (2)

Hi Hank,

You should definitely install a boost controller before putting in your downpipe. Electronic boost controllers are nice, but can be expensive. I use a manual boost controller, and like it very much. It is very simple to adjust, and will not need to be readjusted until you do another mod. Here is a link for a manual controller that will cost you around $10 for everything you need. Install it now if you are really worried.

http://www.rx7turboturbo.com/robrobi...controller.htm

If you choose to install this controller, DO NOT install the pre spool controller.

With no other mods, I would not be concerned right now. The reason the cars detonate is too much air flowing thru the system, and not enough fuel. In your case, the car has so many stock restrictions for flow, that it is virtually impossible to flow enough air to run lean.

hanknmorgan

Thanks for the help guys. Are those $10 home depot controllers reliable? I dont want something that will potentially cause $5000 worth of damage because I didnt spend $350 on a boost controller. Also, why would I be running that high with so many restrictions? Dont most people run several more mods without much problem? Would there be any other benefit of going with an electronic boost control other than adjustability? Also, is VDO a decent guage. I see most people use autometer or defi or something like that. If it's not a good company, I would like to replace it as I am getting a water temp guage as well which I would like to match. I dont want two crappy guages. Thanks again for your help guys.

adam c

iTrader: (2)

The boost controller is a needle valve that lets in a certain amount of air, depending upon how much you open the valve. It costs about $5. The extra hose you will need will cost about $5. When you set the valve where you want it, it stays there. There are no moving parts, and no electric signals that it has to pick up. Because of this, it is the most dependable controller you can get. Other controllers offer more features, but none are more dependable.

VDO is a "good" quality gauge. They are OEM in many Porsches. There are other gauges that are better quality, but are more expensive. Your gauge is probably correct, which is all that is important. You could easily hook up another gauge to see if yours is right.

FlameThrowingRotary

is it cold? before I got my profec b, it would be 10 psi all the time but if the temp dipped down to the 40s and 30's i'd go as high as 15-16ish because of the denser air.

hanknmorgan

It has been a bit colder here. 60's. Northern California. It makes sense that colder air could cause a bit of an increase. I think I will look into a MBC to keep it down to be safe. Would electronic boost controls correct themselves based on the temperature? Do temp changes really affect boost pressure enough to worry about? I want reliable and cheap, but I dont want to run any risks or sacrifice performance on account of my attempt to budget. Thanks.

adam c

iTrader: (2)

Any boost controller will be effected by changes in temps. Thats why you hear people saying that their boost is "around" XX psi. Boost pressure changes a little bit when the intake temps change.

hanknmorgan

Cool deal. Thanks Adam. So an electronic controller offers no real benefit other than ease of adjustment and extra features such boost readout, etc. Performance and function wise they are the same though is that correct? I would prefer to not spend hundreds on one and I dont really need a hi-lo setting or anything like that. How about manufactured MBC vs. $10 homemade options? Are they comparable in reliablity or performance?

adam c

iTrader: (2)

Some people like the Hallman controllers, and claim that they work better. I have not seen a test of this. I have seen them fail, but that is very infrequent. They have moving parts, so there is a higher probability of a failure. They are not cheap.