turbo tech questions

[jonbig]

ok just a few questions i have about turbos.

1. do turbos really need backpressure? people always tell me that turbo nees a little bit of back pressure. as a noob i may be wrong but in my mind that makes no sense to me. to me it seems like the turbo would run best with out any kind of exhuast at all? maybe im wrong.

2. my second question is about turbo lag. i recently saw a video where an evo raced a rented fiat in 6th gear and the evo was at full throttle for over a mile and never could catch the fiat which was in 6th also (kind of like a geo). in the vid they said it was lag but that seems stupid to me, surley a normal person would just downshift? juust need some clarification. thhanks


-jon

 

[Super Matty P]

turbos <3 no exhaust- or as large as possible

the video you saw was stupid....i saw it also. he was showing that the turbo was too large for that car for street driving...in order to be in it's powerband you'd need to downshift. No'one with an EvoFQ400 is not going to figure out the downshift!

 

[505zoom]

ok just a few questions i have about turbos.

1. do turbos really need backpressure? people always tell me that turbo nees a little bit of back pressure. as a noob i may be wrong but in my mind that makes no sense to me. to me it seems like the turbo would run best with out any kind of exhuast at all? maybe im wrong.

2. my second question is about turbo lag. i recently saw a video where an evo raced a rented fiat in 6th gear and the evo was at full throttle for over a mile and never could catch the fiat which was in 6th also (kind of like a geo). in the vid they said it was lag but that seems stupid to me, surley a normal person would just downshift? juust need some clarification. thhanks


-jon

1. Best exhaust for a turbo car is no exhaust... same with the compressor intake. The benefits you get from a larger exhaust far outweigh any that you might get from scavenging. Where you don't want to go too big is on a exhaust manifold. That is where you want to keep velocity high with a smaller ID pipe, until you reach the HP level where you need to go bigger.

2. Not sure about that, if they were just putting it in high gear at low speed/RPM's and then punching it, then that seems logical to me. Stupid way to test acceleration if you ask me though.

 

[jonbig]

thanks guys, yea that video didng make sense to be to be sure thats not lag but jsut..i dont know the engine itself? i thought lag was when you were at like 3k rpm and the second or so it takes to hit full boost

 

[Super Matty P]

lag is the time it takes for the blower to start building boost.

turbo's are quick, superchargers are instant.

 

[pluto316]

lag is the time it takes for the blower to start building boost.

turbo's are quick, superchargers are instant.

I am not going to rag on you, but I seriously don't understand why people put 's after plural words on this forum.

Turbos is plural, turbo's would show ownership.

 

[pluto316]

Ok, after I am done being a gammar nazi:

ok just a few questions i have about turbos.

1. do turbos really need backpressure? people always tell me that turbo nees a little bit of back pressure. as a noob i may be wrong but in my mind that makes no sense to me. to me it seems like the turbo would run best with out any kind of exhuast at all? maybe im wrong.

This is when you decide when it's best not to talk to someone about cars anymore. Anyone who says a turbo needs backpressure obviously has no idea what they are talking about. Not only will backpressure increase the time it takes for the turbo to spool property (or at all) it will also trap head in the turbo it's self. This will decrease the life of the turbo and could raise under hood temperatures. If you wanted the best possible solution you would have nothing after your turbo. Living in the real world you're pretty save with a 3" pipe with as few bends a possible with a high flow cat and exhaust.

2. my second question is about turbo lag. i recently saw a video where an evo raced a rented fiat in 6th gear and the evo was at full throttle for over a mile and never could catch the fiat which was in 6th also (kind of like a geo). in the vid they said it was lag but that seems stupid to me, surley a normal person would just downshift? juust need some clarification. thhanks

I am pretty sure you are talking about the Top Gear episode where they review the EVO FQ 400. I KNOW I have the episode on my harddrive someplace, but I can't find it. Anyway, it was to prove the point of how Mitsu has over engieerned the car to get to that 400bhp mark. Getting 400bhp out of a 2.0L engine (from the factory so they had to do it right, and not run some crazy emissions stripped monster car) takes a very large turbo. From a roll in 6th gear the EVO is going to be incredibly slow. The engine runs on low compression pistions and is nothing without that huge turbo huffing into it. The idea wasn't to downshift, but to show the EVO's engine is showing it's age and maybe a 400bhp production car isn't really what Mitsu should be trying to push out of the current EVO chasis. There's no reason to buy the FQ400 over the FQ300. You pay much more to the factory than it would take you to do on your own.

 

[pluto316]

Oh, and buy this book.

https://www.amazon.com/dp/ (commissions earned)

 

[peepsalot]

Comparing two cars by going 30mph in top gear is just plain idiotic. You are lugging the engine at that speed, and I would never drive that slow in fifth even with the MSP's relatively short gearing. I highly doubt the gear ratios were even close between those cars anyways.

 

[pluto316]

Comparing two cars by going 30mph in top gear is just plain idiotic. You are lugging the engine at that speed, and I would never drive that slow in fifth even with the MSP's relatively short gearing. I highly doubt the gear ratios were even close between those cars anyways.

You are still missing the point. The EVO FQ 400 has a lot of turbo lag, it was a demonstration of it. It's hard to just say THIS CAR LAGS A LOT, and was more effective to show it comparied to an otherwise underpowered car.

 

[MSP #167]

ok, about 2 weeks ago my friends and i were bored and we decided to take off my exhaust....we unbolted it from the front of the downpipe, after the s pipe.

Now it was loud as **** and the turbo spooled fast but you know what.....the car was slower with no exhaust. It was really weird. Also i am running 10psi.

I'm assuming it needs some type of backpressure.

 

[pluto316]

ok, about 2 weeks ago my friends and i were bored and we decided to take off my exhaust....we unbolted it from the front of the downpipe, after the s pipe.

Now it was loud as **** and the turbo spooled fast but you know what.....the car was slower with no exhaust. It was really weird. Also i am running 10psi.

I'm assuming it needs some type of backpressure.

It was slow because you were missing your catalitic converter and you were throwing a CEL. Your ECU retarded the timing and was dumping too much fuel into the combustion chamber. YOU DO NOT NEED BACK PRESSURE FOR A TURBO.

 

[MSP #167]

It was slow because you were missing your catalitic converter and you were throwing a CEL. Your ECU retarded the timing and was dumping too much fuel into the combustion chamber. YOU DO NOT NEED BACK PRESSURE FOR A TURBO.

I have a catless downpipe...so i have no cats anyway, and i run a MIL.

 

[pluto316]

I have a catless downpipe...so i have no cats anyway, and i run a MIL.

So your butt dyno said the car was faster? Explain to me how backpressure makes a turbo charged car faster.

 

[low_psi]

Explain to me how backpressure makes a turbo charged car faster.

I would also like to know.

 

[KyRaceFan]

lag is the time it takes for the blower to start building boost.

turbo's are quick, superchargers are instant.

Superchargers lag too, based on pully speed. There are 2 kinds, roots and centrifugal. Im too lazy to explain more, but look on howstuffworks.com for the difference.


In regards to the evo video, that is an EXTREME case. If he had been in a lower gear the car would have spooled up much faster. In fact, that evo was keeping up with a ferrari or lambo, dont remember which one.

In todays cars however, especially on smaller turbos, lag is negligible. Even a decent sized turbo with dual ball bearings can spool at very low rpms.

There are just too many other factors to really explain it all, like gear lenght, head flow capability, turbo size, etc etc etc.

 

[t3ase]

Just to contribute, I've run opened S-pipe for quite a while and the difference is night and day. While very low end torque (~1-2k) in 1st was noticably less, anythhing over that was a great increase.

Turbos need to backpressure. Your mom's Camary may.