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Old 02-22-2001, 10:42 PM   #1
cvalle-sd
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Post Does size matter (for turbos, silly!)

I was just wondering - could you choose a smaller turbo to decrease lag and impose some theoritecal cap on boost? say I wanted to run only 5-7 pounds; could I choose a smaller turbo without overtaxing it? How much larger or smaller are ones exist than what comes on the EJ20 or EJ22? - for that matter, how might a US legacy T set do on the EJ25 - Is that what Tim Prudence did?
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Old 02-22-2001, 11:12 PM   #2
8Complex

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An IHI turbo (the one in the JC Sports group buys actually...) will run 5-7psi well and has very little lag. It's about the right size if you're looking for that kind of boost. For the rest of us, there are T28's and T3's.
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Old 02-22-2001, 11:49 PM   #3
RallyKid
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YES!!! Ohhh, 4 Turbos, well, still YES.
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Old 02-23-2001, 12:20 AM   #4
Michael
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size do matter to a certain point but...tuning the car properly will have a better result
you can look at it this way...
big turbo with a crappy tune job will be slower than a small turbo with a perfect tune job...
plus a better tuned car will last longer too
michael
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Old 02-23-2001, 04:34 AM   #5
Pipercub
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I have the JCS IHI turbo and with the exception of the BOV not sealing up snappy anough there is virtually no lag. If the BOV were sealed all the time when it should be there would be no lag. It feels like it has a big non-turbo engine.
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Old 02-23-2001, 09:15 AM   #6
HamFist
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Wow piper...you actually sound like you're praising JC Sports .

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Old 02-23-2001, 09:18 AM   #7
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Cool

so the IHI is a good daily driver eh? thats what i would like.
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Old 02-23-2001, 09:39 AM   #8
MattC
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Spool up isn't going to be a problem with any of the turbo kits sold right now. As I've said before I can get 5psi by 2300rpms and 10psi by 2600rpms. This is with the "gigantic" T3/T04. I really wouldn't want it to spool any quicker.

A good, properly sized, exhaust system can do wonders for reducing lag. I saw big decreases in egts, and much quicker spool up with my 3" exhaust.

I would definitely get the biggest turbo you can afford. Afterwards you'll be able to run more boost, have a killer top end, and be able to show off your bigger than a 20g turbocharger. Yes, a T3/T04 turbocharger is bigger. Andy@Rallispec measured my inlet turbine, and looked up a 20g inlet. The T4 turbine turned out to actually be slightly larger


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Old 02-23-2001, 10:30 AM   #9
Skidd
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For quite a while, I was wondering the exact same thing. Lag, vs, Boost, vs, size, vs...ect...

I want a turbo that will give me about 8lbs of boost. I have NO intention of going past 10lbs. I want No lag... You know, the usual wants.

Well, after reading pretty much every post on this message board, and after reading Maximum Boost, I've decided that the T28 is the turbo for me.

Here is one of the many good posts I've found here. Personal Turbo Size Experience

Good luck!

[This message has been edited by Skidd (edited February 23, 2001).]
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Old 02-23-2001, 10:46 AM   #10
SHADOWES
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WHAT ABOUT A SUPER CHARGER....THEIR ARE ALOT OF THEM THAT RUN AROUND 5-10 PSI WITH NO LAG.
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Old 02-23-2001, 11:01 AM   #11
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You're a newbie...we'll forgive you . No one has made a reliable supercharger yet for our cars. JCS ran one of their turbos against the supercharged car and slaughtered it only running 8psi. I'd like to see a centrifugal supercharger for our cars instead of a roots blower. Maybe a whipple charger, even. But, the efficiency of a turbo is hard to beat. VERY hard. Believe me, I've been trying very hard.

Gary
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Old 02-23-2001, 11:07 AM   #12
Skidd
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I was planning to go the SC route. I'm a big fan of the old school, Big Displacement, Big Blower setup. I've done alot of playing with SmallBlock Chevs and 671 Blowers. But 2 things helped me change my mind to the Turbo setup.

1. The fact that the TB for a SC setup _should_ be moved to be before the SC, and not left at the intake. If you leave the TB at the intake, then you get a bit too much pressure on the front side of the TB from the SC. Not really a big issue, but a bit of a hastle.

2. No lag on a SC, true, but the Turbo is simply a more elegent solution. It provides power bassed on howmuch throttle you are providing. If your just cruzin' down the highway wih the trottle open a hair, then the turbo isn't really working all that hard. But an SC would be building boost, and if you still have the TB in the stock position, then, you can see what I was trying to get at with #1.

hehe. Good luck making any sense of this. Why is it so hard to copy and paste ones brain to the screen?

(P.S. Woh, sorry for all the TLAs)
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Old 02-23-2001, 01:22 PM   #13
edekker
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Guys,

I still think there's a misunderstanding about the meaning of 'lag'.

There had been a discussion about this a long while back where I've had expressed my opinion, but please let me reiterate:

The term 'lag' is not so much about where, in terms of RPM, the boost starts to build up (although arguably lower is better), but rather how quickly the boost builds when a switch is made from light throttle (steady-state high manifold vacuum) to WOT. This transient response, where the onset of boost follows the step change in throttle, is what ought be called turbo lag.

The virtual zero lag is what's great about the supercharger (and my reason for choosing it);

Take just one example, where you're on the road and you're stuck between two cars fore and aft, and you're eager to pass. You are waiting for that window of opportunity, ready to bolt out of there. But while waiting for that window - it is entirely possible, likely in fact, that the manifold vacuum remains very high even as the revs are kept high, ready to mash the throttle.

Once the throttle is mashed, the instant power made available is a thrill to behold. This phenomenon is a bonus in the autocross and even in daily city driving, because it allows you to power dart in-and-out at the very play of the throttle.

For me anyways, this is what makes supercharging so great. It more than makes up for the fact that the t/c will edge out the s/c in the straights for the same given boost level.

Regards,
Ed.


[This message has been edited by edekker (edited February 23, 2001).]
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Old 02-23-2001, 01:35 PM   #14
edekker
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Skidd,

You are wrong about the s/c.

The driver has exactly as much control over the power as if it were stock. There is no perceptible difference, except that it feels as if the motor is larger.
The boost doesn't start to rise until the throttle is made heavy enough. As the throttle as modulated more heavily, the boost modulates automatically resulting in a seamless and linearly controlled power delivery.

Ed.
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Old 02-23-2001, 02:09 PM   #15
MattC
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Ed,
After 3000rpms boost is literally instantaneous, in my car. This is not your average 2 liter 8:1 compression motor. Boost comes on very fast, in my case too fast. I have gone to great lengths with my tech boost controller just to stop boost from spiking at over 3500rpms. When I set a standard restriction across the rpm range I was getting up to 3psi of boost spike after 3500rpms. As you know in our motors this is a lot! Thank god the tech has an overboost cut. It saved my ass more than once.

You also have to remember that we really don't run that much boost. Spooling up to 7psi takes a lot less time than spooling to 20psi.

Another thing is that we have fairly short gearing. I'm doing 70@3000rpms. At this speed I hardly ever downshift to pass. If I do, its not because of lag but because the car pulls so strong all the way to my 6500 rev limiter.
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Old 02-23-2001, 02:24 PM   #16
edekker
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MattC,

If it's spiking, that detracts from the very drivability I enjoy.
That fact that your boost is too instantaneous may have something to do with that.
My s/c is as instantaneous as could be, with good control of power delivery no spiking or any anomalies whatsoever.

Ed.
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Old 02-24-2001, 12:06 AM   #17
SHADOWES
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I belive that some manufactures such as remmer (if they are still in business) use a valve somewhere in the system that re-directs the air when under vacuum. I am a nubie to Subaru and I am planing on building one up very soon, I have not herd of the supercharger problem but I do know about the TB problem from other cars. What is the problem with reliability, I was under the impression that a SC was more reliable than a turbo. Also what about using a twin turbo setup to avoid lag?
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