Ok, this is really strange..I use the stage 1 wastgate spring(5-6 psi) on the turbo, and use a Hallman MBC..NOw, if i set boost to around 8-9 psi, boost is great, very steady, NO spike at all. Now, i'm trying to tune for 15 psi,and that sucker will spike to like 18-19 psi! It's only for a second though, and boost falls to 15 steady..Its pissing me off becuase the 034 EIC does not like the spiking very well..making it a PITA to tune..motor will detonate for a second at the spike, or misfire/studder..then runs fine..I'm am starting to wonder if using a MBC to run a much larger boost pressure, over the rated wastgate spring pressure, is causing this spike? I think i read somewhere that you should not run twice the amount of boost as the rated spring pressure..it makes sense, since its spiking over a 10 psi setting...Anyone have any input to this? I've tried all diff boost sources for the MBC also...

I've heard the saying not to run double the boost of your wastegate spring also. My wastegate spring is only a 3 psi spring. Well I've had 2 mbc a turboxs one and a hallman. Both for some reason I couldnt get to settle down at above 8 psi. They would hold 6 easy as hell but once i tried to make it 7-8 it would spike to 10 then go down to 8 or whatever. So I finally said screw it and bought an AVC-R I love it so far. I have settings for wastegate @ 3psi, setting B @ 6 psi and setting A @ 8 psi. I really like this thing. It's just a bitch to setup at first but once you get the tuning down you'll like it I guarantee.


1998 Eclipse RS-T
Aim= masterkoronor
Email krwadd02@louisville.edu

The AVCR is nice, I use it in my 2gnt as well. Throw the auto mode out tho, it does not work very well. I picked it up after my MBC would not hold 16 psi very well.

On a side note the avcr can modify boost per gear. I'm running 10 psi in 1st, and 7 psi in 5th. That makes it great for launches at the track and highway driving.

Yah I love the avc-r. I have all different settings for what I plan on doing. If i just wanna have a little fun I'll just throw it on 3 psi and just have a little fun without owning my gas :) But when I wanna get down put it to setting A and push 8 psi and have some real fun! hehehe Mr. Mustang GT and Civic SI last night can tell you how fun 8 psi is heahehea.


1998 Eclipse RS-T
Aim= masterkoronor
Email krwadd02@louisville.edu

you have a boost leak. not a spike.

do the usual things.. check all vacum lines, intercooler pipes.. check your exhaust manifold for leaks.

Originally posted by siueclipse
you have a boost leak. not a spike. do the usual things.. check all vacum lines, intercooler pipes.. check your exhaust manifold for leaks.

Checked it already..only really small leaks at throttle body plate shaft, and very tiny leak at the comressor housing C clip area..def not enough to cause any issues, and are pretty normal...I rigged up the old bleed valve off of the SFMU I had, right after the MBC oulet, to bleed off pressure from the wastegate, to kind of make it a pressure regulator of sorts..It works much better now, but still spikes 2 psi..I'll prob end up getting the 10 psi wastegate actuator, as I really dont plan on going lower than that..I talked to HRC today, and the dude said that you shouldn't run more than 10 psi past the spring setting..and also, spiking is a normal trait of a MBC..I was going to get the Greddy Profec B Spec II EBC, but I'm not sure how well that will be able to control pressure too, using a 5 psi spring..I think the problem is the 5 psi spring just starts to open the wastegate too early, since its rated for low pressure. Wastgate starts to open prob around 3 psi or so I would imagine without using a MBC..just not a strong enough wastegate spring, esp trying to run high boost..

I ran a 5psi spring in my car, and 15psi on the MBC. No spikes. Spiking is not a trait of MBCs. it is a trait of bad MBCs.

Originally posted by DarkOne
I ran a 5psi spring in my car, and 15psi on the MBC. No spikes. Spiking is not a trait of MBCs. it is a trait of bad MBCs.

What he said... a bad MBC will cause spikes... You've almost proved it to yourself by bleeding air off...

Originally posted by DarkOne
I ran a 5psi spring in my car, and 15psi on the MBC. No spikes. Spiking is not a trait of MBCs. it is a trait of bad MBCs.

Yeah..you also use an external wastegate too, which is much better for precise boost control..Could be the MBC i suppose..I have done some searching on the net about spikes, and have read that as you increase MBC tension, spiking can worsen. Spiking is more common on smaller turbos, where the turbo can spool up very quickly(which mine does), and the time it takes for the MBC to open up, pressureize the wastgate atuator, and start to control boost,the boost can spike, then settle down(which its doing). It just can't react fast enough, since the MBC is keeping all pressure from the wastegate, until its set to open. The spiking is the worst when i am on the highway, in 5th, at 70 or so, then drop to 4th and go WOT. Boost is instant, and it just makes sense that the MBC cant control the wastegate fast enough..causing it to spike for a second. Found some interesting info on Saab forum, where someone took an adjustable air pressure regulator, tapped that off of the comressor boost source, then teed the output of that to the MBC's oulet, so both outputs of the APR and MBC go to the wastegate. This lets an adjustable amount of air pressure going to the wastegate actuator, to *slightly* pressureize it, not enough to open it, but enough to pressureize it, then when the MBC opens, boost does not spike at all, since you have decreased the amount of pressurizing time to open the wastegate..sound interesting to try..although the easiest solution is to get the damn EBC haha..trying to Macgyver something is more fun though :)

Originally posted by XtremeRS

Originally posted by DarkOne I ran a 5psi spring in my car, and 15psi on the MBC. No spikes. Spiking is not a trait of MBCs. it is a trait of bad MBCs.

Yeah..you also use an external wastegate too, which is much better for precise boost control..Could be the MBC i suppose..I have done some searching on the net about spikes, and have read that as you increase MBC tension, spiking can worsen. Spiking is more common on smaller turbos, where the turbo can spool up very quickly(which mine does), and the time it takes for the MBC to open up, pressureize the wastgate atuator, and start to control boost,the boost can spike, then settle down(which its doing). It just can't react fast enough, since the MBC is keeping all pressure from the wastegate, until its set to open. The spiking is the worst when i am on the highway, in 5th, at 70 or so, then drop to 4th and go WOT. Boost is instant, and it just makes sense that the MBC cant control the wastegate fast enough..causing it to spike for a second. Found some interesting info on Saab forum, where someone took an adjustable air pressure regulator, tapped that off of the comressor boost source, then teed the output of that to the MBC's oulet, so both outputs of the APR and MBC go to the wastegate. This lets an adjustable amount of air pressure going to the wastegate actuator, to *slightly* pressureize it, not enough to open it, but enough to pressureize it, then when the MBC opens, boost does not spike at all, since you have decreased the amount of pressurizing time to open the wastegate..sound interesting to try..although the easiest solution is to get the damn EBC haha..trying to Macgyver something is more fun though :)

Jesus, this is like having sex with my eyes. Such a welcome read after reading from idiocy-riddled srtforums.com for the past hour. :bowdown

I'm having the same problems Matt. This is my 4th boost controller. You figured a 90 buck turboxs boost controller wouldn't do that. But it will all eventualy do. I'm going with the dual next. If that fucks up, I'm going all out electronic. Wastegate spring is not a big factor. Afterall it's still being fooled by the boost controller no matter what spring you have.

Whooo hooo! I think I fixed it..with a little internet help and searching..Somone on a Saab forum figured out a way to prevent boost spikes or "overshooting". Basically, you use an adjustable Air Pressure Regulator, getting its pressure input from the compressor. You use manifold pressure for the MBC inlet. Then, on both the APR and MBC outlets, you tee them togheter and run to the wastegate. So what does this do? Well you set the APR to "prime" the wastegate with a few psi of air pressure, whenever there is boost. Then, when the MBC's ball/spring mechanism is lifted off its seat at your set pressure, it makes the wastegate much, much more responsive. The spike is caused by a delay really. Since this turbo spools so quickly, esp using a MBC, the MBC cannot react fast enough to open the wastegate to not get any overshoots in pressure. Now, with the wastegate being slightly pressurized, the time it takes to open it, is greatly reduced, and no spikes. I tried it out tonight, and preliminary testing reveals it works, and works quite well. I didn't have much time to play with it, but a little tweeking gave excellent results. This is a very good read, if anyone wants to get more info on the setup. Its called a "MBC Anticipator"

http://www.saabnet.com/tsn/bb/9-3/?bID=73160

http://www.saabnet.com/tsn/bb/9-3/index.html?bID=69576

http://www.saabnet.com/tsn/bb/9-3/index.html?bID=84683

EXCELLENT find.

I forget that not everyone runs a manly turbo with an external gate. :shrug

Originally posted by DarkOne
I forget that not everyone runs a manly turbo with an external gate. :shrug

Heh, give me a bit, I'll be there soon enough. :P

+7, 8?? for MBC suckage.

I doubt its a boost leak if your holding that 15-16 steady after the spike. Normally w/ a boost leak you will fall off a psi or two and its really unpredictable.

Sounds to me like you are in the realm of EBC land. A nice EBC will anticipate and learn the charactaristics of the boost curve, and would actually anticipate such a spike. It would know to open the solenoid before that spike, pressurize the wastegate lines. Also, a bleed style MBC might work better than a ball and spring MBC with these boost levels. A Ball/Spring type MBC will keep all pressure out of the wastegate until the ball-bearing pops up and opens the valve (peak boost), while a bleed valve will constantly pressurize the wastegate lines, but bleed off a certain ratio of air pressure to achieve higher boost.


1996 Eclipse RS / 5-Speed / Aerogear Body / Coated in Magnetic Red Metallic rev.2 / T3 Turbo Intercooled @ 8 psi / More at http://home.insightbb.com/~mgalyan/
Mark Galyan - Indianapolis, Indiana