Boost spike..One of these again

[killab443]

I have a 92 fwd turbo, mods are: FMIC, 1g slow release bov. FP Td05 20g. Turbo is ported in wastegate passage. Bigger wastegate door, completely ported by FP. FP is even stamped into the housing. EVO o2 ported as well into a 3in exhaust. No leaks in the system at all. I'm setting boost at around 15psi and it spikes way to 21psi and then falls back to15psi and holds steady. Ive changed boost controllers still have the same problem. Also have changed wastegate from 2 other 14bs. still have the same problem. Ive also ran just wastegate and it doesnt spike. But it creeps to 16 psi from stock wg psi. Any ideas?

 

[kenamond]

Does it spike less in higher gears and more in lower gears? If so, my understanding is that the small bleeder hole in the MBC isn't big enough for your level of boost. The ball/spring MBC is actually still kind of a bleeder MBC. The ball cracks but the air leaks out of the bleeder hole. Eventually the leak past the ball overwhelms the bleeder enough to open the WGA. So the bleeder acts as a bit of a warning to the WGA. A larger bleeder will need a lower ball cracking pressure (lower spring preload) than a smaller bleeder to hold the same level of boost, but the larger bleeder will be less prone to spike, because the WGA has a bit more warning and starts to open sooner. A smaller bleeder gives the WGA less warning, and in lower gears (when things are happening faster), the WGA doesn't open fast enough and you spike. But if you go to a larger bleeder, you fix spikes in lower gears, but boost hits less hard in higher gears (when things happen more slowly).

That's my understanding of the matter. One idea we tossed around was adding a tee between the MBC and WGA and running that through a bleeder-style MBC. If you close the additional bleeder all the way, the MBC operates normally. If you open up the extra bleeder, it acts just like making the ball/spring bleeder bigger. If the spikes bug you enough, it might be a pretty cheap thing to try. Dial the bleeder open bit by bit and see how it helps with low-gear spikes and hurts high-gear boost response. Find something you can live with. If you open the bleeder, you'll also have to loosen the ball/spring MBC a bit or your stable boost will go up. Note: the bleeder idea is just an idea. But if it works or not, post your results and/or PM me.

Good luck.

 

[killab443]

Its worse in the higher gears. Its very bad in 3rd gear and higher gears, thats where I start to get knock from this. This actually makes some sense to me. Both boost controllers I tried are turbo XS. One is the regular unit the other is the HP unit. Both MBCs have the same body so the bleeder is the same size. It does bother me enough because I can only run 15psi on my 20g "safely". If I run it at 21-22psi like I want, I'm looking at 27psi spike, sometimes higher.So its the opposite of what you said.

 

[haioku-rocket]

You mentioned that you had the larger flapper door? 34MM flapper I presume? Even for the 20g I think that is still a bit on the small side. Thats why you get boost creep to 16 psi. The wastegate is just too small for the boost you are running.

I do have a solution that you might not want to hear for your spiking.

1. Weld the flapper door shut and go external mounted off manifold to atleast a 38MM+
2. Get an 02 mounted external, remove the flapper door, and bore the sh%t out of the wastgate passage hole.
3. Or get a good electronic boost controller that can control the gain. The gain tells when the electronic solenoid when to start opening the gate. You can set the gain a bit conservative to open sooner which can control spike. However opening the gate sooner hurts full boost/spool up slightly. your choice here.
4. Or you could try a quality ball/spring type like hallmans, Joe P. My wife runs the Joe P and I run the hallmans. Both great boost controllers. On evo 3 16gs with 28MM flappers we weren't seeing more than 2-3 psi spike, and on our 50/60 trim To4E with 38MM internal gates we only see 1-2 psi spike.


Good luck. Honestly I think you should go external/02 mounted wastegate. That would solve boost creep problem, and your boost spike problem. I have also ran the XS power wastegates and can say they are actually quite good quality. I would use them again. But thats my opinion. Good luck.

 

[kenamond]

I like all of the recommendations made above, but this doesn't sound like creep, because the boost settles back down. The exception might be if the boost only settles down on the top end which might be creep that is eventually countered by flow restrictions on the top end. Does it spike and settle down early or just up top?

I like my JoeP IL MBC. It holds 15psi with 1psi spike, but this is on a FPBig28, not a 20g. A better-flowing WG will probably help with spikes, because the WG can quickly divert a lot more exhaust than the small internal WGs. I have no experience with EBCs, but I'm beginning to think that they could help a lot with spikes. The EBC gain sounds exactly like what the bleeder setup I mentioned would do. But I've read a review of EBCs that showed that a ball/spring helped spike just as much as an EBC...but that was a fairly old article testing on a E3B16g and was only one article.

By "slow release" BOV, do you mean you did the dodge-garage mod and left the added nipple open?

 

[killab443]

Its a 34mm door. Im going to retro fit a t3 actuator to it. somemething with a longer throw and stronger spring. Also gunna try anothe mbc. I have a bullseye housing for td05 turbos that i was going to sell. thats got a 38mm internal gate in it, maybe ill try that if none of this works

 

[killab443]

Yes the inner port was drilled into from the side of the base of the bov. jb welded the set screw into the bottom of the port. The port now sees atmospheric rather then boost

 

[killab443]

Just as an update, I installed an additional bleeder between the boost controller and wg actuator. It didnt help. I went ahead and ordered the Forced Performance Evo 8/9 Wastegate actuator. Its the high pressure one they sell. It was 115 shipped from FP, its not the OEM unit, its the FP unit. Opens at 17psi. Evos with stock turbo housings run this actuator to 23-25psi with no problems. I retrofitted it to my setup. I took the mount off of an old 14b wga and mounted the FP WGA to it. The FP WGA bolts to the mount. I simply drilled the one from the 14b after hacking it off the 14b wga. I belt the fp wga rod several times to get it to fit on my setup. I had to shorten the overall legth of the rod about a 1/2 inch. I also had to rethread the rod to make up for the 1/2 inch I took off. I redrilled the hole in the arm to fit my flapper arm. Evos have a bigger post of the wga arm it appears. The hole i drilled is right next to the hole that it came with. Overall Im very pleased with the way it came out. Ill have to post pictures for those wondering what it looks lilke. Boost now holds solid at what I set it. The wga is complete adjustable via the threaded wg arm. It allows you to add preload very easily but removing the cotter pin and turning the rod in or out to increase or decrease the flapper preload. VERY happy with it. The hardest part was hacking the mount off of the old 14b wga.