Sorry if this has been covered, I searched but found mostly FD sequential twins and FC fuel cut defenser problems...

Ive got a stock port 88 13BT, Garrett TO4E, HKS cast manifold, HKS 40mm standard wastegate, 3.5 inch V-band downpipe, wastegate dumping back into downpipe (right where the exhaust is pointing straight back, a very smooth merge), and a large NPR intercooler with 2.5 inch charge piping. And a Greddy Profec B spec II.

My problem is boost dropping off a few pounds by 7k. I have an 11 psi wastegate spring. With no boost controller I get 11 psi at around 3600-3800, it will hold (and sometimes rise to 12-13 psi in cooler weather) until about 5500 where it will fall to 10, and by 7k its around 9 psi. I figured an EBC would solve this problem, and I wanted to crank up the boost anyways, so I recently bought a new Profec B.

Now the boost is higher, but the pattern is the same. It will jump to 17-18 psi, hold breifly, then gradually fall to about 11-10 psi by 7k. Ive tried adjusting the Gain function, which helped a little (held 14 psi till almost 6k), but its still frustrating as hell.

I think the real issue is a cheap Ebay 11 psi wastegate spring I bought for it. When I bought the wastegate it had the purple 20 psi spring in it. I didnt want to run that as a minimum so I got the cheapo spring.

So is the yellow HKS 14.2 psi spring the solution? Any input would be appreciated.

 

Which To4E do you have?

 

The solution is to ditch the HKS 40mm wastegate altogether as it is undersized and will cause you nothing but problems. Myself and J-rat have gone through this, we both ran the HKS manifold with HKS 40mm and had to give up on that wastegate. The whole spring issue aside, your boost pattern will constantly change because of the weather.

 

If anything, with too small of a wastegate he should be having creep problems, not boost falling off. Have you tried changing the source for the wastegate? Check for leaks in your pipes too, a boost leak will cause the turbo to run out of breath as it's trying to move more air then it can handle. what is the rest of the exhaust? Converter in the path? It's hard to imagine the spring being the issue unless it's like a 4lb spring or something really soft.

 

If boost creep isn't out of control these are the exact symptoms. It also sounds like your ebcs gain (I believe thats their wording for attack) is set too low.

 

I don't see how you can have boost creep and boost falloff at the same time? Sounds like an oxymoron to me. If you have boost falloff, it would either mean the wastgate is diverting too much exhaust energy away, or the turbo just can't flow enough air, either by being too small or the pressure being bled off somewhere. It could be the gain is set too low, though on a proper setup you shouldn't have boost falloff even without an EBC in the picture.

Boost creep means the pressure goes up with rpms and too much exhaust is still flowing through the turbo, usually due to an improperly sized wastegate or manifold design.

Weak springs usually create fluttery boost response due to the target boost exceeding double the spring pressure.

Obviously there are exceptions to all of this but this is what I've seen with various setups.

 

Im not exactly sure which Garrett turbo I have, please see this link https://www.rx7club.com/single-turbo-rx-7s-23/can-you-name-garrett-turbo-829610/

Its close to a 60 mm compressor wheel, and the turbine A/R is 1.00 with a 3.5 inch v-band outlet. Just going by these stats I feel the turbo itself is not the issue.

The pressure source is coming right off the turbo compressor, and the rest of my exhaust is a Apexi N1 single. With no cats, there should be no restrictions.

Ive tried playing with the Gain function (and other settings) on the Profec B, Ive had it cranked up fully and it was better, but still falling off.

A boost leak does seem likely based on these symptoms, Ill see what I can find. Thanks for the replies so far!!

 

So do you have any update about your problem? I have a similar problem with my FC.

 

I don't see how you can have boost creep and boost falloff at the same time?

Like he said, this happens when you have boost creep but you don't have run away boost creep.

So you have boost creep up in the upper mid range and then in upper rpm range the boost falls back down to where it is actually set on the boost controller.

You thought you had set the boost controller to the peak boost you were achieving, but that was actually boost controller boost + boost creep.

 

I rigged up a pressure checking setup a couple days ago, welded some 2.5 inch pipe to a flat steel plate on one end. Made two, one for the turbo side and one for the TB side. I drilled and tapped a 1/4 inch pipe thread on one of the caps, and installed a male quick disconnect. Took couplers off the turbo and TB cap, installed test caps, turned regulator down to 0, and hooked up the air hose.

After turning the regulator up to 5 psi, I heard MULTIPLE whistles. Apparently even though I have some heavy duty T-bolt clamps, and nice, tight fitting silicone couplers over the pipe, I have a few boost leaks. At 5 psi!!

Some of my clamps are Vibrant Performance, and they are sealing great. I ended up with a few others (Mikalor I think, from a hydraulic shop) that are actually a wider clamp, but Ive noticed they form a slight "D" shape when torqued down. I cannot get a good seal. I should have some replacements soon, Ill make another update. And pressurize the system to at least 25-30 psi!!!

Anyone recommend some good t-bolt clamps? Vibrant seem to be good...

 

Had this problem before I got the boost controller, just running off the WG spring.

 

I had the same thing, boost trailing off at high rpms, turns out my exhaust was to restrictive. Change my catback and solved the problem.