1.8L

Dang lag. The forum is a 5:1 compression 2 liter motor with a big rig turbo on it. laaaaaaag. By the time I got over the 5k word limit, someone made some of my points...

Hello,

Part 2

4. Relative volumetric efficiency is a measurement of the amount of air entering the engine compared to the total volume of the engine.

4a. Ignoring super-high dollar NA engine design, NA engines in theory can peak at 100% VE, meaning the 2.5 liter engine draws 2.5 liters of air every two strokes. To get there requires very specific parts designed to operate at peak efficiency. Designers must chose a specific RPM range at which to reach that peak efficiency, because a part designed to be efficient at one engine speed will not be as efficient at another speed.

4b. Superchargers and Turbochargers can create a relative VE of well over 100%. A 2 liter motor running 14.7 pounds of boost at peak efficiency could in theory draw 4 liters of air every two strokes (200% rVE). Even at 50% VE, the relative VE of that system, compared to an NA system, will be 100%.

This explains why it's so easy for turbo motors to make more power than NA motors. Notice that a WRX makes more torque than a 2.5 by 2000 RPM. (or maybe earlier, even?) Sure, the 2.5 is a "torquey" motor, but its peak is way below that of the 2.0 turbo.

As for tranny-killing, that seems to be a function FIRST and FOREMOST of the driver. Then it seems to be torque related. A 2.5 turbo has far more torque than any 2.5 NA motor (street cars, obviously ignoring mega-0buck purpose built race motors. And this is because of the much higher VE even at low RPMs). A high powered 2.5 turbo makes far more torque than an even more powerful 2.0 turbo.

And since the first poster was asking about NA power as a prelude to turbo power, don't forget the part above where NA parts have to be designed with specific RPM ranges in mind. A good example is Cobb's "wild" or "spicy" or whatever he calls those cams. They have a large amount of overlap to help with scavenging, fully replacing the gas in the cylinders, etc. These things are important to improve VE at high rpms. These things "waste" some VE to gain overall VE. You loose some good intake charge in order to get a nice full cylinder. Well, add a turbo to the system and when the valves first open up, there's boost sitting right there. And it flows right through the engine and out the other side. The overlap will cause a HUGE loss in VE for a boosted car.

Now, note that a welcome fact comes from emissions laws. Emissions laws require cars to have very little cam overlap at the low RPMs tested. That makes for clean burning. In cars that don't have some VTEC mechanism (which simply introduces a higher overlap cam profile at higher rpms), there is only one cam profile - a low overlap profile. Perfect for forced induction. Emissions cams are great cams for FI.

Anyway, the cam example is an extreme example, but if the NA parts you are considering are well designed for NA use, they can detrimentally affect your future FI use.

Oh and lastly, N/ABeast, your comment on spending $7k on an NA 2500 pound Impreza versus $7k on a heavier turbo Impreza (on which car were you meaning?)... for what purpose? Street racing / drag racing? I'd take you up on that any day if that's the case.
How many 10 second non turbo Imprezas are there?
How many 11 second non turbo Imprezas are there?
How many 12 second non turbo Imprezas are there?
How many 13 second non turbo Imprezas are there?
Spend $1k on a WRX and you have a 13 second car (Vishnu Stage 0). Spend a couple grand more and you're in the 12 second range. Shoot, spend $7k on your Impreza and you can almost pay i-Speed to drop a bone stock WRX motor into your Impreza and you can run 13s. Put a turbo kit and a TEC-III into your Impreza for about $7k and you can run 12s and 13s, too.

Joel

ImprezaRSX

iTrader: (1)

Thanks Joel.
I tried to answer BAN SUVS question, but this thread turned into a hijacked fantasy thread.

Hey BAN, I talked to Tom at Ludespeed. He said his stage III kit runs GREAT on COBB Cams (street/mild) and Borla Headers. If you support the Turbo with something other than the headers you shouldn't have any cracking problems.

Until then, N/A, You'll get about 45HP with Cobb Heads/Cams, Headers, CAI, exhaust. When you change over, the CAI has to go and the turbo back exhaust should be AT LEAST 2.5" (3" is optimal)

Other than that.... I didn't get cobb heads, just the cams and I love 'em. IF you ever come to Hawaii look me up and I'll give you a ride.

Kevin M

iTrader: (12)

Yep, I read the tech page on Cobb, and decided to eventually do cams based on their better performance with turbos. Before that I hadn't really planned on ever doing anything but pure bolt-ons. And, since Minnam seems to have fallen off the face of the earth since the SCC project car and Vishnu appears to be a WRX-only shop now, I plan on going with the Ludespeed kit. Eventually, considering the cost of a converting my '01 GM6 to a 12-13 second EJ25 is approximately equal to the down payment my lender told me I need to get a house. In the meantime, $2000 spread out over several months will make for a nice N/A street car that will hold its own on an autocross course.

Thanks for the replies guys, my questions have pretty much been answered. Actually, most of it verified what I had already figured out or been told and chose to believe.

EDIT: Oh yeah, I forgot, I'm not doing the heads at any point. Not nearly enough returns for the money considering I won't be doing any real competitive racing. So, I figure maybe 30-35 hp from the other stuff- which will put me right on the threshold of 200, right where I'd like to be.

KGB

Isn't that a 6 cylinder though with higher displacement? What's the stock power figures on that engine? percentage wise, pushing our motors to 250hp at the crank is a good 50% increase, and doing it in N/A can be kind of freaky...

Kevin M

iTrader: (12)

That's about 50% for the Bimmer 3.0 I6 too. Sweetest motor on the planet in a car most people can reasonably afford at some point.

Kevin M

iTrader: (12)

bump

Tattoo Collecto

Here is a list of mods that I am doing now and in the future to my 98 2.5 RS.
-11:1 Forged JE pistons, wrist pins, rings
-port/polished heads
-valve springs with titanium retainers
-Cobb Spicy Cams
-polished/overbored throttle bodies (yes, that's plural)
-custom made intake manifold (doing it myself so it might not work)
-at first I am going to run it with the stock intake manifold and 1 throttle body. Then when I get some money I am going to do 2 throttle bodies and if that works, i might try 4
*note* I am doing all of the mods except for the dual throttle bodies at first.
-Stand alone ECU (Motec, Tec-II, Haltech, something?) I don't know if I am going to need it at first. I hope not!
-Fidanza Flywheel
-Vitek 4 Puck Carbon Clutch
-STI engine, tranny and pitch mounts
-some kind of air intake
-higher flow fuel pump and bigger injectors (if/when needed)
-I am going to be balancing and lightening the crank & shot peening the rods.
I am doing all of this work (machining, assembly, fabrication) myself, so this is goign to take a few months because I still have to work, take classes and try to make enough money to pay off my thousands of dollars in debt.
If you guys have any suggestions, let me know.

Kevin M

iTrader: (12)

With all the other stuff you are very definitely going to want a TEC-III or equivalent fully tunable system to take advantage of all the flow. The stock unit will either severely underutilize the VE of your motor or simply fail to work at all. Plus, you can build near 100% reliability in any motor with good tuning. You'll find plenty of help around here when you get deeper into this project, a ot of us would love to see what that motor would be like.

ImprezaRSX

iTrader: (1)

is the fidanza flywheel the aluminum one? I have heard a lot of sketchy history of this flywheel. Your best bet is a lightened ONE Piece (not two or three like the aluminum flywheels) chromoly flywheel. they are stronger and more reliable.

Kevin M

iTrader: (12)

"Lightened" is a misnomer. A true 'lightened' flywheel is an evil piece of junk, where somebody takes a stock flywheel (usually one that already trashed) and shaves it down and drills the snot out of it to make it lighter. But a good one piece flywheel should be ok if you aren't abusing it. Chromoly is definitely best though.

Tattoo Collecto

What ECU do I need to run everything and how much am I going to have to spend. Like I said, I am not doing the independent throttle bodies right now. That will probably be a summer project. I might not even be able to afford the cams yet. Can someone please help me??? BAN SUVS, you seem to know quite a bit about this, please help. I am so used to old hotrods that have no computers or fuel injection. This is new territory to me. I understand that this ECU is going to cost me, but I don't want to spend $3000 on it! What about the TEC-II, why won't that work? I thought that was a stand alone ECU also? How about the Link? I was also looking at Haltech and Motec. Which one is going to do what I need for the best price, and whom do I buy it from to get the best price?

Nathan

ImprezaRSX

iTrader: (1)

You're going to have to shop around. Prices fluctuate alot. Generally, you can get a base standalone for around 1500. when you start adding features is where the money is. For example, a TEC III with a Suby Harness and necessary hardware is about 2250. That's a really good system, but a lot of work.