BW 8374 Boost Creep Check
 

So, I've tried everything I can think of and can't control boost creep on my 8374.

Car is a basic set up for track use: Small street port, Turblown IWG 8374 kit, stock coils/twin power, NGK 9/9 plugs, open exhaust, PFC, FFE Step-up kit w. ID2000's, 044 pump.

Speed 1 tuned it, and claimed to be able to hold 15 psi on the dyno, but when I put it on the street, it was 17.5 in 2nd/3rd gear. I took all the pre-load out of the medium canister, and it may have helped a little, then swapped to low boost canister and from a GReddy Ti to a PFS exhaust (more restrictive), that yeilded nothing.. car will hit fuel cut at about 6500 in third. I can see it creeping on the boost trace.

I'm nowhere close to 11-12 psi on spring pressure. I've disconnected the trailing coils to confirm the ignition is working.

For others with the internal gated turbo who are able to control boost, could you post your set ups? Trying to determine if there's anything unique in my setup that would contribute to this, but I'm really convinced it is simply wategate size, and isn't able to waste enough exhaust.

Whats your downpipe and exhaust size? What are you running in the exhaust for restrictions?

Im a bit worried about this.
Ive got the same turbo coming to me, and a turbosmart actuator. Planning on running 3.5" downpipe into 3" exhaust with straight through mufflers. Want to be able to run less than 10psi if i want - should i be worried?

It's a 3" downpipe, 3" midpipe with a magnaflow, and a 3" PFS catback (was an 80mm GReddy Ti).

I'm really interested in the set up of other cars who've managed to control boost. I'm wondering what I've done wrong (or too right) here.

Ok, also, have you checked the Wastegate actuator arm preload?

Yes, as noted it's at zero preload, which should theoretically allow it to open the wastegate as far as possible.

how are you controlling boost? Through a boost controller or are you off spring pressure on the wategate actuator?

Spring pressure, which will theoretically be the lowest it can be.

I'm less interested in analyzing my set up (although it's helpful) so much as hearing from others who have the this turbo and are able to control boost, and get details on the rest of their setup/tuning to see where differences lie.

I'm less interested in analyzing my set up (although it's helpful) so much as hearing from others who have the this turbo and are able to control boost, and get details on the rest of their setup/tuning to see where differences lie.

I understand you want to figure out what the others are doing to prevent boost creep that you aren't doing, but first we have to know what you are doing to compare set-ups.

Post pictures and specs on your streetport (intake and exhaust) and post your data logs with AFRs and timing or at least dyno with AFRs.

I chased boost creep for years on a set-up.

Porting and rich AFRs with too conservative timing are big contributors to boost creep.

Just having a good set-up can cause boost creep compared to a 100% stock engine/intake manifold with single turbo slapped on with an IC.

I know its frustrating, but you can always just put a reducer gasket between the midpipe/cat back to fix the boost creep.

A 2" hole is a good starting point (that plus a straight through 3" midpipe flows slightly more than stock cat section, but less than 3" highflow cat section).

Here's the dyno sheet. Car was tuned by Dave at Speed1, on a PFC. I don't have logs of it, nor pictures of my port, but it's a conservative/small port that has passed VA emissions with TTs (I recall Ray at PFS showed me two street ports, and I chose the smaller of the two). It was tuned to mid 11's and I can confirm that's what it blows on the street.

There's literally nothing remarkable about my car's set up or the tune. Note, the "13 psi" run listed here was done at part throttle, the 15 psi apparently held on the dyno, but on the road it was 17.5 before I backed all the preload out of the actuator.

There's no way I'll run a restrictor. I didn't built the car for that. I could have just done a cheaper setup. I'll sell the car first.

^ Nice graph.

Just to be annoying - have you checked all the vacuum hoses? Can confirm wastegate opens all the way? What did the guys who tuned it say? - appeared to hold 13psi ok that day.

Im watching this with interest - got a bad feeling mine is going to overboost its face off.

Stupid question: Can the wastegate be ground out bigger at all on these things? Put a bigger flap on somehow?

As noted, the "13 psi" run was done at part throttle.

I'm not sure how the vacuum system could be off, it's pretty simple. I'm not even using the boost control so it's literally just a line to the actuator. I don't know how I could confirm if the wastegate open, other than shrinking myself to 8" tall and hanging under the car while someone drives it. I guess I can try removing the actuator entirely and wiring the door all the way open, but that eliminates the spool aspect.

Serious question for those who understand big turbo systems better than I do. I know exhaust and the WG itself have the biggest impact on Boost Creep. I can see low AFR, and certainly porting having an affect too.

My assumption is that inlet restriction should also help control boost? For instance a smaller intercooler or smaller intercooler piping between the turbo and throttle body? Could that make a marked difference? This one has be a bit worried because i'm moving to an 8374 IWG as well. I also track my car a lot. But, i have a relatively small intercooler.

Nobody seems to have any real answers. Dave @Speed1 though I needed the lower boost canister because the spring was too stiff, but the lower boost canister made zero difference.

The spring only influences when it opens, so my gut tells me both are opening as far as they'll go—that's why taking pre-load out helped the medium, but not on the low. the arm reached further.

I can try it with the actuator open, but the lack of spool up on the turbo then might hide the true dynamic.

No i mean visually inspect the wastegate action while feeding the actuator compressed air - although the shrinking down to 8" would be better.

Where am I going to get that kind of compressed air?

Did you ask Elliot?

Yes

....and....?

Nobody seems to have any real answers. Dave @Speed1 though I needed the lower boost canister because the spring was too stiff, but the lower boost canister made zero difference.

The spring only influences when it opens, so my gut tells me both are opening as far as they'll go—that's why taking pre-load out helped the medium, but not on the low. the arm reached further.

The WG spring most definitely does not *just* influence when the WG opens, but also how far the WG opens as the boost pressure increases.

I went through this as well with my boost creeping set-up.

I finally ported out the WG passages huge (bigger than the turbo runners) and had a HKS 60mm WG on the set-up.

Still with the standard (12.8psi to 18.5psi) spring the WG would indeed crack open around 10-12psi if I had the adjuster screw backed off all the way and hold that till ~ 6,000rpm, but then boost would seemingly "creep" up to 18.5psi.

If I tightened the adjuster all the way in the WG would crack open ~15-17psi and still just boost up to 18.5psi.

I put the lowest rated spring in (8psi to 14psi) and with the adjuster screw backed off all the way the WG would crack around 8psi hold 10psi to around 6,000rpm where it would "creep" to 11psi.

With the lowest rated spring and the adjuster screw tightened all the way tight it would crack around 10psi and hold 13psi to around 6,000rpm where it would creep to 14psi.

I finally ended up loosening the WG adjuster all the way and putting in a Hallman Pro RX manual boost controller for solid boost (varying 1psi across rpms) from 11psi to 14psi (whatever boost I chose with MBC). I actually had to drill out the bleed hole a bit to get boost to come on super smoothly.

Anyways, you can see there was a lot of variables even with a simple WG and spring and then even more once I added the MBC.

13psi?

Here is a good article. I havn't read the whole thing yet. Pretty much just skimming to read Jacob Cartmill's posts.

https://www.google.com.au/url?sa=t&r...psqvdwK26_oCGA

That makes sense. Springs always are force over distance so to get the gate to open up enough to flow more the boost has to creep at higher RPM. So it seems like a pretty straight forward solution is to put a lower spring-rate in then use a boost controller.

Morale of the story is that you really dont want to select your spring based on the boost you want to run at the low end of the spring range. If you want 15 psi it might make the most sense to use a 8-14 or 10-15 psi type spring and use a boost controller to achieve the level you want. Rather than a 12-18 psi spring?

The down side is if you want to run (and hold) higher boost with the car, the lightest spring may be overcome and start to bypass too much gas thus drop boost at higher rpm.

That's what the stocker did on my car. The spring would be overrun at high RPM. Because it's not just static pressure on the gate but velocity pressure at that point (which does not show up on your boost gauge).

It's nice that there is an adjustment on the aftermarket turbos as well to preload the spring.

I do not have an exact answer why Peter's car does not run " low boost". My inital answer was ignition related( anti-lagging in the manifold from low timing as BlueTII has mentioned).

Most of our customers are able to run 11psi. Some 10 psi, but most run 11. My EFR 9180 iwg FC was able to hold 8 psi, but that was with a 2.5" catback. There is another guy on here who cannot hold even moderate boost either..

I have emailed a few people to chime in on this thread.