ka24det confusion over different turbos

[nissan240boy]

So I'm running my kat with a cheap ebay t3t4 turbo for drifting a few times a year at events. Now ive had this turbo on for over a year now turbo's still running strong. But oil is starting to leak into the intake side which I'm fine with. Anyhow lets get to the point. Is the turbo I have a good turbo for this engine. My main confusion which ive seen in other threads is about different size turbo's making different flow rates but same pressure and how some turbo's will blow a motor and some wont. When I think bout it my opinion is 8 lbs of boost is 8 lbs of boost no matter what turbo creates it. If u have 8lbs in the intake you have 8lbs in the combustion chamber so how can different flow rates make any difference if in the end u still get the same pressure from the turbo. The wastegate stops the pressure from rising. The only difference I can think u could get between different turbo's is lag time and maximum boost pressures that turbo can create.

[pepesilvia]

i've often kinda wondered this myself.... which is why i took my turbo off, because i clearly didnt know enough about turbo's to daily one aftermarket hahaha

[Jmoore124]

There are a lot of reasons. Biggest I can think of is air displacement matching where you determine flow rate for your motor and make sure you are not over turboed (wasting potential and creating lag etc) or under where your not flowing enough air to make your horsepower goals.
Just to name one.
http://www.automotivearticles.com/123/T ... tion.shtml
This is a good article to read, may clear some stuff up.

[daemonyk]

When I think bout it my opinion is 8 lbs of boost is 8 lbs of boost no matter what turbo creates it. If u have 8lbs in the intake you have 8lbs in the combustion chamber so how can different flow rates make any difference if in the end u still get the same pressure from the turbo. The wastegate stops the pressure from rising. The only difference I can think u could get between different turbo's is lag time and maximum boost pressures that turbo can create.

Here's why flow rate matters. Imagine a bicycle tire and a car tire both inflated to 50 psi. Even though they're both at the same pressure, there's physically alot more air molecules in the car tire than the bike tire. So lets relate that to turbos. A t25 vs a t4 lets say. Both can be set to 10 psi, but the larger compressor can move more mass of air at the same pressure than the small compressor. So it's like filling up the engine with air with a shot glass, versus a bucket.

If you have a small displacement engine with small cylinders, then lower flow is useable. But if it has large cylinders, then it needs more air, at the same pressure, to fill them. So a small flow turbo, on a large cylinder car, even set at high boost, may not be able to fill the cylinders efficiently. And a large flow turbo on a small cylinder car may over pressurize the cylinders because although its still the same pressure, its a higher volume of air being forced in, which can cause problems.

Imagine trying to use a regular air compressor to run boost. A regular craftsman 5hp compressor can easily output 30 psi. But not at a volume of air that will do any good. Same idea.

Hope that made sense

[mechanicalmoron]

I'm not a turbo guru, but my scientific sense tells me....

Yes, if you run a little turbo on a big motor, it won't be able to keep boost up.

But if you run a bigger turbo than you need, the only problem will be more lag, or other spooling problems.

It can't over pressureize the cylinders, because no matter how much it flows, if the pressure rises too high, the wastegate will just flow more, to keep the pressure correct.

Obviously, if you didn't have the right wastegate, you would boost too high. But not because of the turbo size, just the turbo/wastegate size ratio.

Think of it like so: if you have a tire pump with a wastegate set to 30psi, and you pump up a car and bike tire, they'll both get to exactly 30psi, even though a bigger pump will get the car tire there faster.

[nissan240boy]

Thank you mechanicalmoron. We both have the same concept of how this works. If were wrong someone please clarify that has fact to back it up. I cant see what a bigger turbo would hurt an engine running low boost other than creating longer lag time to spool up. The wastegate maintains the correct pressure no matter what volume size of air is flowing. The only way it wouldn't keep up is if it was a smaller wastegate and u were using an extremely big turbo then I could possibly see it overboosting. But anyhow yea as far as I understand flow rates would only be important if u were concerned with getting the least amount of lag time so u could use the perfect flow rate and size turbo for that setup

[daemonyk]

Sorry, by "problems" that "can" happen, I meant things like running 30 psi on a too big turbo with a too small intercooler or piping generating backpressure - I tend to get carried away in theoreticals like that...

Anyways, you are right, the pressure will be whatever its set at. The flow rate matters to tuning the setup to run well in a right-tool-for-the-job way, is what I was trying to get at.

[nissan240boy]

OK thanks I'm glad I understand now I apprreciate the info