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Dumb Question Thread!


Jambun

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Ok 2 dumb questions to start the year first one . I changed my front springs for some reason every time I turn the wheel it grinds/knocks have I instslled them wrong? Second one my car hesitates a lot when cold once it warms up its sweet any help please

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BG5 Legacy here:

I cleaned out my BBOD solenoids/lines with carb cleaner, after doing the wheel-well boost control solenoid earlier (all while cycling solenoids in test mode, also gave the actuators some WD-40).

I think the ECV duty solenoid freed up, because I didn't notice it clicking before I cleaned it, but now I get no primary boost at all. This is after driving while having the diagnostic connectors connected. Does the ECU have to re-learn safe boost from nothing? Does it need another reset? Could I have some carb cleaner trapped in the system somewhere (pesky differential pressure sensor?) stopping it from working?

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Maybe you didn't plug it in again, or it was stuck open to start with

hen you say "none at all: do you mean "zero psi" or just it feels flat

It does not have to "learn" safe boost, it should run normal levels right away, all it will do is run *less* if there is a problem

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Given the car it is, it's likely an air leak or more likely a faulty AFM. They go bad if you look at them sideways and quite often won't throw a CEL - it normally shows up with poor or no idle and random cutting out (feels like a boost cut?) at full noise

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 boon said:
Different air density when it's cold.

And time for my dumb question, can you explain how you conclude your ECU is worn out? It's an electrical device with no moving parts, I'm not sure how this would happen.

EDIT: On the TMIC/FMIC spooly business thing - I have given this much consideration and done some maths on it.

Let's say you use 2.5" intercooler piping and a Perrin FMIC. For argument's sake we'll say you have 3 metres total of intercooler piping.

The piping has a volume of roughly 9.5L or 0.33 cubic feet.

The intercooler core has a volume of 0.52 cubic feet - that's total, in reality it's probably about half this in terms of actual air passage size but whatever.

So you have ~0.85 cf of volume.

A VF22, flat out, flows about 420cfm, or 7 cubic feet per second.

This means it takes about 1/8th of a second for a VF22 to pump enough air to fill your intercooler piping.

Ok so on a TMIC setup that's probably going to be more like 1/16th of a second but who cares.

And with regards to distance, well, the intake port velocity of a turbocharged vehicle at high RPM is usually around MACH 0.5 - maybe 150m/s - again, with 3 metres of intercooler piping the air is covering this distance in 1/30th of a second.

Conclusion: other than the pain of having to cut the front and make the piping fit, the spool/boost threshold/response/blah argument around TMIC vs FMIC is purely a mathematical one, because in the real world you are unlikely to notice, and this is reflected in what a lot of people see when they install one.

Extra conclusion: I'm installing a FMIC.

So far less volume in the exhaust side which feeds of the intake filling at 1/8th of a second. Whats the hot side science?

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Exhaust port velocity approaches supersonic and the volume of gas is considerably larger due to thermal expansion.

Having thought about it a bit more, the problem with both the hot and cold side maths is that in each case you effectively have an enormous "leak" - on the cold side this is the engine consuming air and on the hot side it's the turbo and open-ended exhaust. So the rate at which you can fill/compress these spaces is actually defined by the surplus being produced by the compressor (or products of combustion) over what is managing to exit the space.

Say at 3500rpm a 2L Subaru is probably chewing through roughly 200cfm of air, so that only leaves 220cfm from the turbo to compress the inlet tract. Even then you're still looking at only 1/4th of a second.

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Just make sure you use gl5 and quality. If plate you need lsd oil. Gl5 is more of a diff spec takes a lot more punishment where gl4 is kinder with regards to synchro wear etc. In sub where the front diff/trans is shared its better to use a gl4/5 rated oil no idea if penrite do one and doubtful anyone at repco will be able to tell you so check bottle.

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Do fans HAVE to come on when bleeding coolant? I have no a/c, top left of rad is hot same witg turbo water feed, bottom right is cold, (slowly hole thing going hot) its at 90 deg and holding but NO fans have kicked in at all? Can v7 fans be changed to turn on at a lower temp in ecu? Getting slightly paranoid thats it wasnt just a leak....

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So I currently have a 3" Catback installed with the stock up pipe and downpipe but I'm looking to ditch the cats and restrictions and install a catless aftermarket up pipe and downpipe. The intake is stock.

I know that it would be stupid not to get a tune with these mods so that I can squeeze some more power out, but is it needed? As in is it safe to drive without a tune for a while?

And as for the tune, is it possible on the factory ECU or is an aftermarket/piggyback needed?

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 chulozumo said:
Do fans HAVE to come on when bleeding coolant? I have no a/c, top left of rad is hot same witg turbo water feed, bottom right is cold, (slowly hole thing going hot) its at 90 deg and holding but NO fans have kicked in at all? Can v7 fans be changed to turn on at a lower temp in ecu? Getting slightly paranoid thats it wasnt just a leak....

Nah - I was in the same boat. Car was at temp, fans blowing hot air, fans were going, no more air bubbles and the bottom rad hose was still cold.

I went for boost, came home, popped the boot and the bottom hot was hot as, shortly after the fans kicked in.

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 Authentic said:
So I currently have a 3" Catback installed with the stock up pipe and downpipe but I'm looking to ditch the cats and restrictions and install a catless aftermarket up pipe and downpipe. The intake is stock.

I know that it would be stupid not to get a tune with these mods so that I can squeeze some more power out, but is it needed? As in is it safe to drive without a tune for a while?

And as for the tune, is it possible on the factory ECU or is an aftermarket/piggyback needed?

Will be fine, just run rich and you won't get the benefits from your mods.

Is your car a 2001 WRX STi as per your signature? V7 STi? Then you can get the factory ECU reflashed.

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 Authentic said:
So I currently have a 3" Catback installed with the stock up pipe and downpipe but I'm looking to ditch the cats and restrictions and install a catless aftermarket up pipe and downpipe. The intake is stock.

I know that it would be stupid not to get a tune with these mods so that I can squeeze some more power out, but is it needed? As in is it safe to drive without a tune for a while?

And as for the tune, is it possible on the factory ECU or is an aftermarket/piggyback needed?

There is no cat in an STI up-pipe and it's a bastard of a job if you've never had it off the car before so don't bother. The stock item is actually pretty good.

With a free flowing exhaust you will get boost spikes to ~21psi but the car will handle that more or less OK.

Get a decent fuel pump and a reflash and you'll get good power, also way way better spool.

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 Timmah']Will be fine, just run rich and you won't get the benefits from your mods.

Is your car a 2001 WRX STi as per your signature? V7 STi? Then you can get the factory ECU reflashed.

Yeah its a V7. Sweet, I've seen a couple of users mentioned on here so I'll get in touch. Any recommendations?

[quote name='boon said:

There is no cat in an STI up-pipe and it's a bastard of a job if you've never had it off the car before so don't bother. The stock item is actually pretty good.

With a free flowing exhaust you will get boost spikes to ~21psi but the car will handle that more or less OK.

Get a decent fuel pump and a reflash and you'll get good power, also way way better spool.

Is that the same for the V7 too? I swear I read about the V7s having a catted up pipe and it was the later models came without one as they were prone to failure.

I'll definitely get a tune/new pump in the future but its a daily driver so the mods will have to be done one at a time. And I'm a poor student so my funds run pretty thin!

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 Authentic said:
Yeah its a V7. Sweet, I've seen a couple of users mentioned on here so I'll get in touch. Any recommendations?

Is that the same for the V7 too? I swear I read about the V7s having a catted up pipe and it was the later models came without one as they were prone to failure.

I'll definitely get a tune/new pump in the future but its a daily driver so the mods will have to be done one at a time. And I'm a poor student so my funds run pretty thin!

The Wellington guys should be able to help with who to get your car reflashed with. I think STM?

I also think it was the Singapore Spec Version 7's that got the catted up-pipe. We got the JDM models here which don't have the cat in the up pipe.

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 Timmah said:
The Wellington guys should be able to help with who to get your car reflashed with. I think STM?

I also think it was the Singapore Spec Version 7's that got the catted up-pipe. We got the JDM models here which don't have the cat in the up pipe.

Oh wicked. I won't have to worry about changing that then.

Cheers guys!

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