Ive got a 2003 EVO 8 with dynoflash, hallman pro MBC, and buschur intake.

I have a terrible boost spike that im afraid will damage something if it continues when i get a better tune. I think the only thing saving me now is running so rich that the cylinder is staying cool. When im in 5th gear or actually just about any gear under 4k rpm and i floor it, the boost spikes to about 24 psi for a few seconds then it drops steadily and ends up at 21 psi at redline.

I have my boost controller going straight formthe turbo nipple to the wastegate nipple. I trie splicing into the BOV line, but that had the same result. I have a fairly small ID line running to and from the MBC, and i heard that getting a larger ID line will help some. Anyone know of the validity of this statement? I'd like to hear form anyone who hits 21 psi and it stays there till redline.

Also, i went to the drag strip and was going to use some race gas, but no matter how high i turned my boost controller up, it would only hold 21 psi. I disassembled the boost controller and made sure all my fittings and connections were tight. But no matter what i tried, nothing over 21 psi. Anyone think this might be the cause of my spike? Overcompensation with the boost controller?

Any aftermarket wastegate i could use? Or has anyone ported the stock wastegate?

 

Also, im thinking about buying this, anyone think it will help?

http://www.turbosmart.com.au/boost_c...electronic.htm

 

probably wastegate spring causing boost spike?

 

Figure out your boost problems before looking at the EBC. Easier to isolate a problem with simple measures in place. Has your car always done this? What was added last to cause this? What are your other mods? Down pipe, exhaust etc. Need a tad bit more info to help.

 

I thought it was ok to spike in the mid range rpms and then taper at redline. In fact, don't some ppl do this on purpose?

 

its fine to spike up to 24 psi in the midrange and then taper down. I see no problem there. most EVOS spike including mine I even spike to 26 psi but i have a bigger turbo. If I were you I wont be worried..

 

This is pretty much normal for an EVO. On stock cams you can hold over 20 psi to redline after a midrange spike up to 24 or thereabouts. With HKS 272's and lots of good flowing parts you actually outflow the turbo at a lower psi, so you spike to 24 and drop to 19 or 20 instead of dropping to 21 or 22.

Keith

 

I got the Hallman Pro also, and I spike 20psi and then fall to 17.5psi, in the same manner you described.

 

5th will always spike especially in the cold. I run 22psi and spike to 25psi in fifth. The only to stop it is to downshift and then wack it. Otherwise it will spike. Don't waste your money on EBC I have a $20 MBC works fine. Set and forget

 

ya its cold now. I am getting pretty high reading and my oil takes about 35~40min to warm up.

 

Why is more boost in the midrange okay? Our motors make max torque in that range, which means max cylinder pressure in that range and maximum risk of detonation, right? A I missing something? I don't have a very good understanding of what is safe and what is not on pump gas I guess. And why is more boost safer on a larger turbo? Cooler air from the larger turbo?

 

Its not where our engine makes power the most its on which RPM.... if he said 24 PSI (pump) @ 7K RPM I would have been worried. but 24 psi in the 3K to 5K area in this cold weather is nothing to worry about except if he hits fuel cut. The possibility of detonation and misfire at higher RPM is a greater than the low RPM..

 

Look at it this way. Your engine is basically just a large air pump that happens to burn fuel to power itself. When it is reving at say 3500 RPM it will pump something like half the air it is pumping at 7000 RPM. Now with a turbo car you have an additional air pump in the form of a turbo.

First a quick review of how turbos work. The turbo gets it's power from pressure and heat generated by the motor that in turn is used to pump more air into the engine. Turbos are limited by the maximum gases they can flow on both the turbine (hot) and compressor (cold) side. Another limiting factor is the minimum flow that it takes to get the turbo spinning at a useable speed.

Now to understand the answer to your questions you also have to realize that turbos aren't perfect. The closer to their maximum airflow they get, the less efficent they become, and the more unnecessary heat they will create. In addition to that, the air will heat up just by the act of compressing it, this is part of the Gas Law equation.

Now consider your engine and turbo as air pumps feeding each other. At mid engine revs the engine doesn't require too much air from the turbo. That means the turbo will operate fairly efficiently and can easily supply the volume of air required to maintain a particular PSI. But at redline the motor will need something like twice the air as I said earlier. To keep up the turbo will have to work much harder an much less efficiently heating the air much more than at mid range. Heat as you may know can create pinging, detonation, and other forms ignition of the air/fuel mixture due to heat or pressure and NOT spark. Higher octane fuels buy you more resistance to this, but can only go so far.

A bigger turbo compared to a smaller one can supply the same PSI more efficiently (and cooler). You can turn up the boost more on a bigger turbo because it will reach its performance limits (efficiency and air flow) at higher PSIs. Of course too big of a turbo and the motor can't supply enough exhaust gases to spin the turbo up quickly enough. This is where excessive turbo lag and sluggish low end perfomance come in. Therefore it's important to match the turbo to the motor and intended use. Too big and you get all or nothing performance, too small and you have a severe drop in top end performance. There is such thing as too big of a turbo!

 

Thanks for the tips guys, this makes me feel better now.

 

CHeck to see that your Intercooler piping, BOV tubes, and everything are very tight. Also get a leak test done..see where u might be loosing boost... Mine barely spikes.. Also the stock BOV is a piece of crap.. its leaks like crap all the time.. I bet if you found the source of your leak.. it would barely spike and hold pretty solid to redline..