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today's attempt was just another adventure in overboosting.

however, i did make it to 5200rpm instead of 4600 this time. and i think the mid range boost is a bit better that solely relying on the 4psi spring.

i'm having trouble wrapping my head around how this 2 port manual control is supposed to be any better than just plumbing the controller inline with single port control. either way, you're just creating a variable boost leak in the wg signal line.

what i really need is just a boost referenced switch fully open/closed to the wg, or even better, and electric wg. screw the pneumatics.

anyway, i've raised the boost fuel cut to 15psi, adjusted k/tim to hopefully account for the load, and added a little bit of fuel to a few cells that were reaching the upper 12afr's.

if i can't stay under 15psi, i guess the only move i have left is to try direct control on a spring that's in between 4-10psi. if that doesn't work, i guess i'll have to live with the 4psi spring and a lazy mid range for the remainder of this year, and go back to the drawing board next winter.

i don't get it... still overboosting. the boost controller is venting as much as it's capable of, from the top of the wg.
if i drop down to 3rd and pin it, it goes over 15psi+. 4th gear seems to hold, but i don't have a safe enough stretch of road to hold 4th right to 7000rpm. why would 3rd overboost, but 4th hold?

k is currently at 354, tim at 680. i made this adjustment to account for the possibility of holding 14psi. seems to be about the right scale for the moment.


what am i doing wrong here guys?

38mm wg, recirculating to the downpipe through a 1.5" pipe. aside from the quality of my welds, do you see anything wrong here?

my next move is to try removing the boost controler again, and run on the spring alone. if that doesn't work. i'll try no spring at all, and see if this wategate even has any hope at all in this scenario.

OK, best you do some really basic tests. So first you need to work out if your WG is capable of bypassing enough exhaust gas to control boost. I've only done this on internal WG systems as external systems tend to work better. With IWG you just remove the actuator from the WG flap arm and go for a drive. This should give zero boost. If your boost rises significantly with RPM then there's a fundamental problem with your turbo/WG sizing. It happens all the time with IWG setups.

With external WG it'll be a bit trickier. I'd assume you could remove the spring so the WG is open all the time and achieve the same thing?

Once you've done that, assuming you didn't get more than 2 or 3 psi boost you should be able to fit whatever spring you have and connect the diaphragm direct to boost source. That should give you whatever boost the spring is. Approximately anyway.

PL

thanks pl. i was already wondering if that would be a good test, so hearing it from you got me motivated to try.

with no spring at all, top port open to atmosphere, bottom port run directly to the boost reference.
i was climbing a gradual hill, which i figured would be a pretty good way of testing the limits.
it made ~0psi (cancelling out the engine vacuum) up till 4200rpm. after that, boost rose exactly in step with rpm, from 1-13psi at 6600rpm.

so i'm guessing that if that rate of rise continued linearly, i'd be at 15psi at 7000rpm. i could live with that for now. i'm assuming that's where i'd be if i just put the 4psi spring back in, no attempt at adding control to the top port. i assume i'd get back a little bit of mid-range, but it's probably going to hold 5-6psi till 5000rpm, which is leaving a lot on the table. sure would be nice to get that 12-15 psi sooner.

just throwing an idea out there- what if i restricted the top port's flow to atmosphere? slow down the rate that the wg opens, but don't restrict it from fully opening?

OK, that tells me your WG flow isn't ideal but it's good enough if you're happy with 17psi up top.

Yes a 4psi spring is gonna make it feel pretty lazy for sure. Can you fit a stiffer spring? 12 or 14psi spring would be nice - and then just run spring pressure for now. Nothing worse than trying to tune the engine at the same time as sorting your boost control. No fun. Particularly when you're still learning.

I'd fit a stronger spring (or add some pre-load to your existing spring if possible) to get boost up a bit. Then run with just boost source to bottom port and top port open. Get you tune nice and then start playing with boost control again.

Tip: tune so you're leaving some headroom for more boost. So adjust your K Const/load scales so you're hitting 2 or 3 columns (of fuel and IGN maps) from the end. Then when you add boost you won't be banging into the last column as soon as you get full boost.

PL

Thanks once again.

When I tried the 10psi spring combo, it was just straight to the moon with boost. I guess I could try something in between 4 and 10, but if that raises the top end at all, I’m afraid I’ll be up against another problem...

After reviewing my last 2 logs, I’ve been adding a bit of fuel at the top of the map. Still a bit lean though, and the injectors are approaching 100% duty cycle. Makes me think I’m at the limit of the fuel pump now that i’m able to rev above 6000rpm.

Thanks for the tip on the load scaling. On the runs that I’ve hit 15psi I’m just touching 160, which is the end of the fuel map scale. (Timing scale goes to like 208 or something) 12psi is more like 144, or 2nd to last column. I’m guessing that if I ever get to the point where I can hold 15-17 to redline, I might need a touch more, right?

Speaking of which, any idea where the limit is for the stock head gasket? Am I getting close there, or do I have some headroom?

Hmmmmmm. That's a bit weird that the 10psi spring gives unlimited boost. Even if the WG doesn't flow as much as it should up top, you should still see 10psi down low. Was your top port open to atmosphere???

Try carefully feeding compressed air into the WG lower port and see at what pressure the valve starts to move - if you can see it. Easy with IWG but bit harder with ext WG. An ext WG will tend to leak past the "guide" too. They often don't seal 100% like an IWG but don't let that bother you. The point where the valve cracks off the seat will be your boost pressure.

Rule of thumb for stock HG is around 20psi max. Above that you're in the danger zone and should be ordering a metal HG ASAP. Naturally it's not just about boost - it's about cylinder pressure. But we tend to use 20psi as a rough guide.

PL

yeah, i tried the 10psi springs twice. i think it's actually worse now with the new maf housing.

i'm probably exaggerating a bit. it just hits my 15psi limiter, and i let off. in reality, if i could stay into it long enough, it would probably spike then settle down.

i have bench tested the wg a few times, and it operates. unfortunately i don't have a regulator that can reduce the pressure low enough for me to reliably say where it's cracking at. but i do know that it works, and i haven't found anything wrong with the diaphragm.

i think this combination is just a bit too free flowing to control boost this low. i'm sure it will eventually be fine for my end goal of 400hp, but i was hoping to make a couple stops along the way. it's a big deal from me to go to a tuner. we're talking about hours of driving, and overnight in a hotel.

looks like a fuel pump is in order now, but that's going to have to wait for a while. i'm out of time for big projects.

the only other thing i can try in the short term, is maybe covering up part of my air filter. like i said, the new maf housing seems to have made it easier to overboost. perhaps reintroducing a bit of restriction could slow it down a bit.

i also like the idea of using the 4psi spring, but installing a restricted orifice for the top cover atmosphere vent. slow down the opening, but don't restrict it's finishing spring rate. gain some mid range without raising the top end.

great news about the 20psi threshold. that's a relief. thanks again.

Yeah you might just have to hold it down and see what boost does. Bear in mind that they'll tend to overboost more in low gears when boost comes up super fast. So if you have a nice safe piece of country road you could try rolling on in a higher gear.

Another thing I like to do is have a "safety column" in my IGN map. So fill the last column with something like 5 degrees. And tune so you never hit it. Then if you do get an overboost for some reason you won't hurt anything. Nissan actually do this in some of their factory tunes. That's why simply turning up the boost on a stock R33 won't get you far - cos you run into the "safety column" of the IGN map.

It sounds like you're quite capable of tuning this thing yourself (and have plenty of patience), so hopefully won't need to take it anywhere. And you'll learn a lot in the process.

PL

thanks for the vote of confidence! haha

this is actually very similar to what i do for work- troubleshooting and commissioning equipment. the big learning curve has just been learning the acronyms and getting familiar with the software. definitely feels like i'm getting to know the process now.

yeah, i do notice the overboost problem more in 2nd and 3rd gear. 4th is much better, but yeah i run out of road pretty quick around here at that rate.

i like the idea of the safety column in the ign map. i'm going to do that for sure. thanks.
speaking of which, do you find it odd that the fuel load scale only goes to 160, but the timing load scale goes to 208? 3 extra rows... unless that the factory safety columns. they are definitely low values.

i hope to get that 4 psi spring back in there tonight. i'll report back again when i've got some new data. thanks.

Yeah some of them have different scales for fuel and IGN. Not sure why. It's certainly good to have a bit more resolution on the IGN map. Fuel doesn't really care if you run into the end column.

PL

so i did some more testing, running direct boost signal to the bottom wg port (4psi spring), top port open to atmosphere.

boost holds pretty decent till 5000rpm, then creeps up in step with rpm until 2 things happen- afr starts to go lean at ~12psi, and in some cases, boost can continue up till it hits the 15psi limiter (6300rpm if i remember right).

so obviously i will need to upgrade the fuel pump. 255lph drop in replacement seems to be a tried and true route. does that sound right, for a long term target of about 400hp?

next up is boost control. the current setup just isn't going to stop building boost, is it?
as well as you guys, i've also been bouncing this issue off of the tial customer support guy (who has been awesome). one option he recommends is, if my current boost response is good, i could go up a size on the turbine housing, and that should be more controllable for the mvs 38mm.
current size is .83ar (gtx3071r g2). i seem to be into the positive boost at 3200rpm, and hitting my 4psi (wg spring) by 3600.

but after a little googling, it appears the the turbosmart gen-v compgate 40mm, is a direct replacement for the tial mvs 38mm. slightly bigger, and they also claim to have superior flow capabilities. should that be something to consider?

going to a bigger wg entirely would mean pulling the manifold back off to weld on the bigger flange, and then re-fabricating the recirc tube/downpipe. probably the right thing to do, but a setback and a big task.

or... considering that i'm most likely looking at boosting till 17psi at redline with the 38mm gate, do i just do the fuel pump, and hope that the best the 38mm can do, is going to be enough to keep me from needing a head gasket?

All good points there.

I'd just go Walbro 255. Hard to go wrong for your HP goals. Just get a genuine one from a reputable seller. Lots of China fakes about.

Yes the bigger rear housing would fix the problem but I fear it would add a ton of lag and you wouldn't like it.

The 40mm TS comp-gate sounds good if it really does flow more. That's probably all you need.

Yes, you could just go with what you've got and just be careful that you don't lean out of detonate up top. Your choice there.

PL

ok thanks!

yeah i really didn't like the thought of giving up response.

if the comp gate 40 truly is a drop in replacement, that's easy enough to try. i'll get that and the fuel pump on the way.

been quite a while, so i thought i'd do a quick update here, of where i left off for 2021...

the turbo smart compgate 40 is almost a drop in part.... the outlet v-band flange is opposite from the tial.

so instead of a male/female connection, it ended up being a female/female connection. not ideal, but the v-band clamp still fit. i figured that would be good enough for a test run at least.

tried it with a 7psi spring. it does indeed work better. instead of just instantly overboosting, it would hold 7psi up till about 5000rpm, but then creep up to 12 at 5600rpm, and fuel cut of course.

i ran out of patience for it at that point. just decided to enjoy the ride for the remainder of the year, and go back to work over the winter. the v-band connection seemed to be holding fine, so i left the comp gate 40 in place.


so i now have the walbro to install. i'm also pricing out radium fuel rail/regulator/damper/ etc to clean up the engine bay.

over the course of the summer though, i did notice a couple of odd things with the tune.

after driving more than 20 mins on a hot day, it would be hard to restart. i would have to step on the gas pedal a bit to get restarted.

also, sometimes just for the sake of my own amusement, i would let the engine rev a bit longer that normal in 2nd gear so i could enjoy the sound of the exhaust. not driving hard at all. just a low load rev to say 4200rpm, maybe 1/4 throttle. in these instances, i would notice the afr going lean. i figured that wasn't good, so i stopped doing that. but i guess it's something i'll have to revisit in 2022.