Hey!

I have just replaced my seized 14, with a JDM small 16g, and I'm noticing the 16g behaves differently. So I want to know if what it's doing is normal...

I run a boost controller, and I'm tensioning it towards about 15 psi. As of last night, I was peaking around 14psi, so that should be close enough for my question.

In first gear, I get about 10-12 psi quite quickly and then it drops off. I think this is normal.

In second gear, I spike to 14 and then drop almost immediately to 12. The boost slowly drops off to around 10 from there on the way to the high 6000 rpm range.

In third gear, again, I spike to 14, quickly drop to 12, and then ease down to around 10 by the high 6000 rpm range.

I haven't taken the car on the highway yet, so I don't know what fourth gear does. I'll find that out later today.

Now, it could just be wishful thinking, but the Seat 'O The Pants meter says the car pulls harder and more consistently than it did with the 14b. But the 14b didn't spike and drop as dramatically as the new 16g does. So my question is...

...Is this normal behaviour?

Thanks!

Joe

Depending on the boost controller, it could do that.

BTW, there are no JDM small 16Gs.

Big boost leak possibly, check all your connections.

Okay, update...

I turned up the boost controller a bit and went down the highway. What I posted earlier was a slight optical illusion I think, because the car behaves the same way in all gears from second to fourth: It spools up to 15 psi very quickly, then drops to 13. It holds 13 comfortably right up to 7000.

I'm wondering if my wastegate actuator could be the culprit. It IS original.

Also, what do you mean there are no JDM small 16gs? I think you're probably either saying they're all big 16gs, or they're all 14bs.

FWIW, the story on mine is that it definitely appears to be a 16g: It has the double-finned impellers. Chris Tapp sold it to me as a small 16g, and I tend to believe him. He also said that it came off a JDM engine that he had sold without the turbo to a previous customer).

So big 16g or small? I don't know. It looks about identical to my 14b except for the fins. It definitely runs very differently: It's much smoother when it comes on, and definitely pushes with a firmer hand than did my 14b, but it also comes on at about the same RPM range as the 14b (I start to really feel power around 3400 rpm). However, unlike my 14b, the new turbo does not run out of breath over 6500 rpm.

Keep in mind that my 14b was very stiff, and actually appears to have been generating back-pressure at the same time that it was generating boost...

Thoughts?

Joe

The boost controller itself needs some tuning. Ball-spring type boost controllers will do that when the bleed hole is too small.

I meant what i said. There are no JDM small 16Gs.

There's 13Gs, 14Bs, big16Gs, and EVO16Gs.

I'm having the same problem with my 14b, it boosts to 15 PSI, from 2400RPM till 4000RPM, and then, it decreases slowly to 10PSI, as RPM increase from 4000 to 6000RPM. I have a bleed screw on my MBC, so I'll try to open the bleeder more, and decrease the ball&spring screw, as Nick is saying.

Based on your post, I wonder if my "Hallman-type" controller isn't up to the 16g...

The guys at Tapp told me that they often get JDM motors that are upgraded -- although they end up paying more for them. As I said, based on the performance of the new turbo, the twin impeller, and the fact that I can't see Tapp Auto lying about what the turbo was, I DO believe it is a small 16g. But just in case I'm wrong, is there anywhere on the web that you know of that illustrates the differences between the 14b and 16g?

Thanks for the info!

Joe

Joe What Nick is trying to say is that you have a big 16g not a 14b.

Oh!

Thanks for pointing that out Kevin. It's a funny thing: I write for a living, but it seems I can't read...

But my question still stands: How would I know the difference?

Thanks!

Joe

Look here .

Thanks Octavio!

I got so enthralled with this thread that I completely forgot about the FAQs. So you think it likely that I have a big 16g? Is there any way I'd know, performance-wise? Visually, it still just looks like a 16g...

Thanks guys for all your help!

Joe

Bigger turbos have more lag. You'd notice it between your 14b and the 16G, I did, but I don't know if there's that much of a recognizable difference between the small and large 16Gs. The housings are the same, so like you said, visually they will look the same. The difference between the "small" 16G and "big" 16G is in the size of the inducer/exducer, like the site indicates.

But now I'm confused, what do you mean there are no "small" 16Gs, Nick? I always thought there were, by name, and even on the vfaq they have it identified as a "small" 16G

I'll say it again. There are no JDM small 16Gs. In now way does that say there are no small 16Gs at all. It just says there are no JDM small 16Gs.

Small 16Gs exist, but they didn't come on JDM engines from the factory.

Pull the intake hose to the turbo. If the first taper on the inside of the compressor housing is only about 1/4" long, it's a big16G. If the taper is about 3/8" long - 1/2" long, it's a small 16G.

I have a small 16G on my 2G with a home depot MBC set at 14psi. Boost hits 14psi and stays there right through 7k with no drop. I'd start checking for leaks and inspect your MBC like Nick says..he's faster for a reason.

You might be running to lean wich means your car is pulling back timing a lot and at high RPM's the boost will drop.

Alright, Nick, for some reason I was just reading that as no small 16G, my apologies. I think that will clear up Joe's misunderstanding as well, I think he was in the same boat as me.

pulled timing will make the boost drop? that would explain that for me, thanx

Pulled timing will put more energy into the exhaust, and make the turbo spool up MORE.

HAHA, thanks

It's not necessarily a problem or failure with the MBC, it's just that any controller needs to be properly tuned to control a system without it oscillating, or overshooting. Making a controller stable can be very tricky. AN MBC is a mechanical controller, so oyu can't play with the tuning parameters on a computer screen, you have to play with the spring pressures, flow rates, and orifice sizes to tune it. What works for one turbo/wastegate may not work for another.

What worked perfectly on my 16G caused HORRIBLE oscillation and spiking with my T4. The controller i have on the T4 now wouldbe utterly useless on the 16G.

If the bleeder hole on the actuator side of the controller is far too large, it can overboost severely. Slightly too large and it'll overshoot on spoolup. Slightly too small and it can drop off at higher rpm. Way too small and it can oscillate. I like to use MIG welder contact tips as the bleed hole for my boost controllers, because it lets me change through a variety of sizes, and even drill them out to different sizes until i get the right one for the setup.

If by "the first taper," Nick means the short fins on the intake side, then woo-hoo! I have a big 16g! The smaller fins are very short on this turbo.

Also, the boost spikes to 15psi only at WOT and then drops to 13 -- which is more than enough for the moment. At up to 3/4 throttle, I get 13 rock solid through to 7000 rpm. It could be a leak, it could be the MBC.

But the more practical question for me right now is this: Can this behavior be indicative of something that will damage my car? Because frankly, if it's not, then I will work through the possibilities in my usual slow way until I find the problem. But if it could be the harbinger of doom, then I'll park the car and crawl all over it starting now.

I have very little left that I want to do to the car. It needs a fuel pump rewire, a high-flow cat, and maybe a new boost controller. And if that doesn't solve the spiking problem, then I guess I'll check/replace all the plumbing.

I have no interest in taking the car over 15psi right now, because I have a 16-year-old here at home who is just itching for a set of keys (not in my lifetime!).

So I guess my question is: Should I be worried about the spiking?

Thanks!

Joe

Joe, like I said in my emails to you. I suspect the MBC as well.

I'm sure a local Ottawa guy would lend his MBC to you to do a few pulls and just rule out that possibility or narrow it down to that.