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Old 03-22-2013, 10:43 AM   #1
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Default Autocross turbo setup - mitigating lag

My FM2 kit with GT2560r on non vvt 1.8 is not cutting it on response time. It is awesomely responsive and reasonably powerful, but I want more. I actually want faster response more than I want more power.

The goal:

I want substantial boost pressure within 8 ft coming off the slowest corner I'll ever encounter. That means about 200 ms (0.2 second) from trailing throttle to substantial/full boost at 3000 rpm in second. I figure I need response down to about 10 ms by 5000 rpm, which seems far less challenging. The present setup almost does that, with a poorly repaired FM DP. I don't want to give up any more top end power than I already do with the GT2560r.

To encourage spool with valve timing:

1.8 with vvt. Stock high compression (not building the engine yet).


To encourage spool on the exhaust side:

I'm using a port matched, short, small diameter runner manifold with semi-tangent collector. I'm doing a DP with taper from the turbine outlet diameter up to 3" into a 5" 100 cpi cat, through a 3" perf'd core straight through muffler.

To encourage spool on the intake side:

I'm doing a 9" barrel AEM dryflow with a 6" velocity stack into a 3" pipe, with a long taper transition into the compressor inlet. I'm planning on 2" OD pressure side intake plumbing, small water to air intercooler, most direct route possible, and maybe water injection too.

I've looked at various types of two turbo setups to get good response and good efficiency over a broader rpm range. Obviously this will be a lot of money and a control system nightmare in the making, but it is still a possibility.

I'm looking at anti-lag with a small-ish frame, large-ish ar turbo. If I had anti-lag setup so it engages partial misfire with retarded timing and throttle bypass solenoid in a narrow rpm range and low but not zero throttle position, I could have the system only beat up on the engine/turbo when I intentionally pre-position the throttle just before going WOT on corner exit. I'm still concerned that this is going to murder my exhaust valves and turbo.

Should I go smaller on the pressure side intake piping? Think the GT2560r will get me where I want to be with just a little anti-lag? A little anti-lag is a lot less bad than a lot of anti-lag, right?

Thoughts?
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Old 03-22-2013, 10:52 AM   #2
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the vvt will help a good bit
the higher comp should a bit too
the least restrictive hotside and exhaust setup will help

So yeah, your plan sounds legit.
Not sure about antilag, never used it on a miata, but should help too.

You could also switch to a tubular fm replacement log like Tim makes, that's a significant improvement over the cast log.

Switching to 2" ic piping and the smallest ic to achieve your goals would also help.
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Old 03-22-2013, 11:27 AM   #3
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Efr6258?
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Old 03-22-2013, 11:42 AM   #4
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ha I was going to say that too, but he's wanting to get it spooling faster, and iirc the efr spools about the same just provides a ton more power
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Old 03-22-2013, 11:59 AM   #5
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I assume you are using EBC? Since you are talking about setting up anti-lag I assume you are already using EBC, but just want to make sure.
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Old 03-22-2013, 12:03 PM   #6
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Since when is ebc>mbc when discussing spool? I thought they were equal

I ask because I see in multiple threads lately people telling other people to switch to ebc for better spool, and I just don't get it: ball/spring mbc is closed til desired pressure is reached, and afaik they would have the turbo spool just as quick as an ebc.
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Old 03-22-2013, 12:03 PM   #7
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The only thing I can add is that I was under the impression "anti-lag" likes to eat turbos.
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Old 03-22-2013, 12:27 PM   #8
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18psi, The adjustable bleed MBC is probably what they are talking about as opposed to the ball and spring MBC. I still think an EBC will be more effective because it doesn't open as gradually as the ball and spring does.

Very short and small diameter manifold tubing sounds good because of the reduced volume. Likewise, reducing the intake volume, shorter runners, including intercooler and piping may help. But shorter runners can effect low RPM torque.

Lighter weight rotating and reciprocating parts are a big plus for responsiveness. If you are serious, you already have looked at the lightweight dual plate clutch, an aluminum driveshaft, a tubular front subframe, lightweight brake rotors, shim under bucket lifters with lighter springs, titanium spring retainers, etc. Forged rods are much heavier weight than stock, so be careful when you upgrade.

If you want more torque and responsiveness down low, have you advanced your cams yet to shift your torque curve down the RPM range? That should help the lower RPM spool as well.

I understand that retarding your ignition timing in the spool ramp up cells can aid in spool by causing expansion of exhaust gasses to continue to occur in the exhaust stroke and into the manifold, but doesn't that also impede acceleration? I'd like to see the differences on the dyno.
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Old 03-22-2013, 12:37 PM   #9
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I see. I had no idea people still used bleed-type mbc's lol.

I don't think anti-lag can even really be tested on a dyno unless you do hard shifts to simulate real world conditions and log pressure recovery time (as OP kinda talked about).

They use it in wrc and other types of racing with great results, I'm sure there's merit to it.

Another completely random idea is to eliminate the bov altogether. If you're gonna be hard on the turbo I don't think that's any less damaging to it than anti-lag.
This way you get minimum pressure loss in the intake side during shifts or throttle transitions.

Just a thought

PS: oh and definitely do not shorten the IM runners. That is for sure going to hurt your lowend
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Old 03-22-2013, 03:13 PM   #10
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Ditch intercooler and go with meth/water injection so you can run the pipe straight from the turbo to the intake?

(I don't know if this is a good idea or not)
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Old 03-22-2013, 03:44 PM   #11
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Quote:
Originally Posted by 18psi View Post
I see. I had no idea people still used bleed-type mbc's lol.
I actually have no idea what the difference between the 2 types of MBCs are, despite being on this site for 7 months now. Because nobody talks about them here anymore.

In my defense though, OP didn't specify any boost control, so it could have been wastegate only (though I doubt it).
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Old 03-22-2013, 05:38 PM   #12
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Ditch intercooler and replace with air/water cooler... fill with ice water before each run
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Old 03-22-2013, 07:14 PM   #13
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supercharger.

Bring on the hate!
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Old 03-22-2013, 07:58 PM   #14
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Quote:
Originally Posted by thenuge26 View Post
I actually have no idea what the difference between the 2 types of MBCs are
I've played with both. One is stupid, one is not.

Bleed types: Only pro for these guys is you can adjust it from the cockpit with some models. But the line is constantly open to the wastegate, you're just bleeding off some of the pressure, so it opens a little later. You'd achieve the same effect by cutting holes in the line going to the wastegate. Spools sucks cause technically the wastegate starts to open at .000...00001 psi.

Ball/spring types: Can't adjust from the cockpit unless you run long lines into the cockpit, but that seems stupid. Spring/ball design keeps the line shut until close to target pressure, where your boost is strong enough to push the ball out of the way and open the wastegate. HUGE pro to these guys is that you spool the turbo with the wastegate clamped shut.
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Old 03-22-2013, 08:14 PM   #15
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even the ball/spring type is inferior to EBC because once the pressure is enough to overcome the spring, the ball/spring MBC turns into a bleed type until target boost is reached.

EBC holds the wastegate shut until the very last moment.

How about left foot braking and keeping your foot on the gas a bit to load the engine and keep turbo spooling? A-la brake boosting
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Old 03-22-2013, 09:41 PM   #16
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Quote:
Originally Posted by 18psi View Post

Another completely random idea is to eliminate the bov altogether. If you're gonna be hard on the turbo I don't think that's any less damaging to it than anti-lag.
This way you get minimum pressure loss in the intake side during shifts or throttle transitions.

Just a thought
when i read this .. i tought of that ...i will use a photo because my engilsh is bad bot the idea is that the trothel body move at the same time.I really dont know if it doable just an idea
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Old 03-23-2013, 02:03 AM   #17
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Quote:
Originally Posted by 18psi View Post
iirc the efr spools about the same just provides a ton more power
You recall wrong. It spools faster, responds SIGNIFICANTLY faster, and provides far more power.

The OP wants an EFR6258.
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Old 03-23-2013, 02:10 AM   #18
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Quote:
Originally Posted by 18psi View Post
ball/spring mbc is closed til desired pressure is reached, and afaik they would have the turbo spool just as quick as an ebc.
Incorrect. An 8psi wastegate spring begins to bleed pressure at ~5psi, which slows spool. An electronic valve that provides no pressure to that wastegate until ~7.9psi is going to spool faster for obvious reasons. This has been proven in dyno pulls (IIRC Soviet has some pulls in his build thread that illustrate this very clearly).
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Old 03-23-2013, 10:52 AM   #19
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Quote:
Originally Posted by Savington View Post
Incorrect. An 8psi wastegate spring begins to bleed pressure at ~5psi, which slows spool. An electronic valve that provides no pressure to that wastegate until ~7.9psi is going to spool faster for obvious reasons. This has been proven in dyno pulls (IIRC Soviet has some pulls in his build thread that illustrate this very clearly).
This is correct.
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Old 03-23-2013, 12:39 PM   #20
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I came in here to give some advice, but sixshooter beat me to all the points I would have suggested.

You may consider some cylinder head work. It wakes up the BP everywhere.
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