Third Eye

'87 turbo, 38K miles on motor, 145,000 on the car. Performance Mods: A.P.E. Stg. II Chips, TestPipe, Dual Port Wastegate.
Ok, I have ~$700 to 'use' on my car when it get's done w/ some maintanence. I was considering the 3" cat back from SFR, as well as a turbo like 'Luke9583'. Would you all chime in on which you would do if you were in my situation? I plan to do both of these eventually, the question is mainly - which should I do first? These are the pro's and con's that I've thought of so far.
3" Cat Back:
-Quick installation
-Cool Sound, and look.
-~50% less expensive than the turbo I'd want.

Turbo:
-Probably alot more power just from this mod
-faster spool up

-Probably hard as **** to install
-Might need extra little things to go along with it?
-More Expensive

Danno

Go for the turbo upgrade! Only a couple hundred bucks more than your $700 budget but it'll give you 10x the performance increase you'll get out of a cat-back exhaust system. Count on about 4-8 hours to install depending upon the condition of your exhaust bolts. You'll also need to replace the compression seal-rings between the flanges and you should get some new nuts as well.

aka 951

I'd go with cat-back for starters. I'm not sure how much performance you will get (if any). But at least it will sound better (hoepfully not too loud). I've been there and done that with the big turbo thing. This is my third 951 and I plan on keeping my k26 as long as I can before upgrading. You'll have an incredibly hard time finding a turbo with the type of transient response your k26 has on a 2.5L. On the street, transient response is key.

Luke

Big "C",


what up?

my car will be running this sunday if you want impressions on the turbo. Email me if you would like a phone # dawg

Third Eye

Transiet Response?
What does that mean... Also, I thought the Turbo that LUKE had is overall just better, faster spooling up, moves more air, safer...

*Rothmans*

Hey Third:
Get rid of that wee little collapsed two layer downpipe that comes down from the turbo!
Start with a 3 inch there, and work your way down.
If you don't know about this pipe problem then ask some of the boys at Huntley.
I don't care what ANYBODY says. If you put a bigger turbo on it's still blowin' through the same restrictions and your motor is still exhausting through the same factory exhaust.
If you do this your turbo will come on hard and fast with no lag.
The larger exhaust also gets rid of excess heat and your motor will have cooler underhood
temperatures.
I would get a high quality downpipe, and build the rest as you can afford it. Install a 3 inch high flow cat, and your muffler is not a huge issue, just get something to knock the decibels down to your tolerance (and the publics).
Everything else in between is "just a piece of pipe"

Good luck with your project!!!!!
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Luke

[quote]Originally posted by *Rothmans*:
<strong>Hey Third:
Get rid of that wee little collapsed two layer downpipe that comes down from the turbo!
</strong><hr></blockquote>


If it hasn't collapsed, why not stick with it. The ID in the oe Down pipe is the same as the ID of the outlet for the turbine. You would want to keep exhaust velocity high there (ad keeping engine pulses uniform). And have 3in from there on. . I stuck with the oe Down pipe. and my stage 3 turbine is slightly larger than that of a #8 I beleive.?!?! Either way, the DP is larger enough.

Lag characteristics would be more of the cross over pipes fault.

The Biggest fitting pipe is not always the best pipe. (according to Corky)

Danno

The middle catalytic pipe that goes from the end of the downpipe to the cat-back exhaust section is probably the best bang for buck. I noticed on mine where it sweeps under the car, it's gotten banged up on speed bumps enough to be ovalized and is probably the narrowest part of my exhaust. Combined with the cat, this is probably where the majority of the restrictions are occuring. I'm going to get a cat-bypass pipe next and see what happens.

I've run the car with the cat-back section completely removed (making a jig from it) and besides being really loud and putting fumes into the cabin, I couldn't measure any power or speed increases at all. Like Erick said above, gains 'if any' are minimal, but boy did it make the rice boys do a double take as I screamed by (could hear my exhaust echoing off buildings several blocks away). Test was with G-tech using power & 1/4-mile tests, 5 runs, throw out slowest & fastest and average the rest.

Third Eye

So start at the downpipe eh? I guess I'll get a 3" downpipe, then 3" testpipe, then 3" cat back, then Turbo that luke's got.

Luke

There might actually be a loss in performance if you use a 3" dp with a #6 kkk turbo. (seriousLy)

*Rothmans*

You mean that oval inner pipe is the same size and shape of the turbine ? All the ones I have seen are oval, which is the precursor to it collapsing in a bowtie shape because of the tremendous heat caused at that point.
So the solution is putting on a bigger turbo?
I have never heard that before.
Hmmmmm. Interesting.
And why a loss in performance? On other turbo cars, especially 2 litre Talons get amazing performance gains from a 3 inch all the way down.
And amazing boost / horsepower characteristics.
And turbo cup cars have a 4 inch racing exhaust.
Are they running a turbo with a 4 inch turbine
outlet?
I'm trying to wrap my head around this matched size principle.

Luke

pick up a book called "maximum boost" by corky bell. There is a certain speed at which intake and exhaust gasses mustflow around.

My dp was round (perfectly) inside and in diameter of the inner tube was still larger than the diameter of the turbine wheel.

I dont think you wouldn't want the cross over pipe a larger diam. than the dp either ?!?! If you attack it with a perspective on diffusion it makes more sense. High pressure diffuses to low pressure areas.

turbopop

Which Turbo are you considering that is larger, spools quicker, has more power and costs $700.
Typically a larger turbo will generate more power at higher rpms but spool much slower, a small turbo will spool much quicker but run out of breath and drop off at high RPM.
Something like a ball-bearing turbo can achieve both improvements, but will cost more than twice your target price.

Danno

In general, yes turbo-lag and boost-lag are related to turbo-size and flow capacity. But we're also comparing 30-year old KKK technology vs. the latest developements by Garrett and IHI. The compressor wheels are lighter despite being larger and they are aerodynamically more efficient as well.

So you don't necessarily have to experience the age-old compromizes of lag vs. flow. Perhaps if you are comparing the same model turbo, then it would be an easy thing to show.

Third Eye

I see what danno's saying. I really believe what SFR says, if they post it on their site. They said on the stage one turbo upgrade, full boost is typically recognized by 2500 RPM on a stock 2.5L motor. Also, I would just wait longer if the turbo option previaled Turbopop