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Old 08-08-2000, 06:45 PM   #1
Trey
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Join Date: Dec 1999
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Post Air flow data - Cylinder Heads

Here's some data I know a few of you have been waiting for. This data is not to be reproduced without my authorization.

I've posted air flow graphs comparing the intake and exhaust port flow of the following cylinder heads:

Stock 2.5L SOHC
Ported 2.5L SOHC
Stock 2.5L DOHC
Stock 2.0L Turbo DOHC (WRX)
Stock 2.2L Turbo SOHC (Legacy Turbo)

They can be found at the following url: http://www.cobbtuning.com/impreza/en...nderheads.html
Just click on the graphs to enlarge them.

Since this is a technical board, I'd like to note that this web page is commercial in nature but the data included is unbiased and scientific. Flow tested was carried out on a calibrated Superflow flow bench at 28".

I will have a seperate page documenting the differences in the heads, in detail, in the near future.

Questions, comments, anything...let me know.

Trey
CobbTuning.com
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Old 08-08-2000, 08:46 PM   #2
ColinL
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Thumbs up

I would like to say...

I'll be damned. The WRX heads you tested (from what version?) outflowed the 2.5L heads at low lift on the intake side but ended up being no better at .400". On the exhaust side they were equal at low lift and were inferior at high lift.

And the Legacy turbo heads stink.

Were you surprised that the DOHC 2.5 heads flowed very similarly to the SOHC ones considering the differences in valve angles? Was this similarity likely caused by similar runner volume and port shape?

Oh, and will we see dyno results of the porting? Any forthcoming packages with your cams installed in the ported heads?
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Old 08-08-2000, 10:32 PM   #3
CNC84
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Thumbs up

Pretty interesting stuff kinda throws the idea of putting the wrx heads on the 2.5 out the window not exactly a whole lot to gain from that move. I wonder why the legacy turbo heads were so crappy in comparison to all of the others was there anything that stuck out about the 2.2 heads as opposed to the 2.0 and 2.5 that was so much different that would restrict things that much?
Chris
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Old 08-08-2000, 10:42 PM   #4
MPREZYA
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I can just see Jay UK clamoring for a set of 2.5 heads to swap in . I just wonder about the 2.2L N/A heads.
Rich
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Old 08-08-2000, 10:51 PM   #5
Jon Bogert
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95 993 C4, 71 911, 04 STI

Question

Um, did you just post the camshaft page, too? How about some more details on the camshafts, for example: How much power do they make? What do they do to the low end? Can you match them with a piggyback ECU and raise the redline a bit? Are you going to incorporate them into your power packages?

I'm real close to buying a turbo kit. Talk me out of it with stories of free revving NA power!
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Old 08-09-2000, 12:03 AM   #6
Turk
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Great Job!!!!!!
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Old 08-09-2000, 02:10 AM   #7
Jay_UK
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LOL

I will stick to my nicely flowing modified STI IV heads...

Trey nice work...

But what model do you mean by WRX ? the Euro/Oz wrx ? or the Jap WRX ? and what year ?

J.
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Old 08-09-2000, 07:04 AM   #8
SteveS
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Trey ~~ Please keep up the excellent work and articles! This is the type of thing that really benefits the aftermarket community.

SteveS (* 20K turbo'd miles *)
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Old 08-09-2000, 07:21 AM   #9
Matt
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Ok, step one : read Trey's mods and dream
Step two : Rob bank

Why oh Why am I so #&^% poor ?!

Oh well. Got to dream about something I guess.
 
Old 08-09-2000, 07:35 AM   #10
Trey
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Post

Regarding the WRX heads, to be fair, these were an older, hydraulic lifter version. They're off a closed deck EJ20 but not a STi version. The newer WRX heads are likely better in flow (we would hope).

The Legacy Turbo heads are so poor I think due to a horrid port design coupled with small valves (1.222" IN / 1.105" EX). The best thing for a Legacy Turbo would be to put heads off a later model car, or WRX. I wouldn't waste money on modifying them as it would take alot of work just to bring them up to par with the stock EJ25 or WRX heads.

The WRX heads I tested had a smaller intake valve compared to the EJ25 heads (1.310" vs 1.420"). Exhaust valves are marginally larger (1.250" vs 1.240"). There are definite differences in port designs between them. The EJ25 heads also have better quinch area design (which again, might have been addressed in later models).

I'll work on getting more data up in our technical section as I also have flow data on intake manifolds, throttle body, etc.

And yes, we will have dyno results for everything soon and build packages from those results.

Thanks,
Trey
CobbTuning.com

P.S. If anyone has any heads I haven't tested (ie: 2.2L NA, later model WRX, etc) I'll flow bench them for you at no charge so I can collect more data.
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Old 08-09-2000, 01:14 PM   #11
Marco
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Thumbs up

Guys & Gals (SubieGal that is),

I have been following the progress of these upgrades, basically bugging Trey over the phone, emails and at his shop.
I'm impresed. He has invested a lot of effort and countless hours in getting the heads, cams and all the other goods he's working on to work right. I guess I don't need to tell you this, but I feel that he deserves a lot of credit for making parts and performance upgrades that actually work.
I think he is an example of how aftermaket tuners should work and present their products.

Keep up the wonderful job you're doing, Trey!!!

Cheers,
Marco

[This message has been edited by Marco (edited August 09, 2000).]
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Old 08-09-2000, 02:05 PM   #12
SCOOBYSHAG
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Wink

Trey Cobb yooooouuuuuur my heroooo...
(in my best Ferris Bueller voice)

just kidding! keep up the great work Trey!
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Old 08-09-2000, 05:13 PM   #13
CNC84
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Marco I can't agree with you more I just wish some of our other tuners were a little more interested in doing thier own research than in simply repackaging things sold over-seas but hey what can you do there is a place for both types of "tuning" Trey's way is just so much more exciting. I mean he shows us what's going on every step of the way instead of just saying I have this product so come and buy it he gives charts and graphs and explanations as to why he has great products.

***Matt you find the bank and I am game gotta get those heads.**** (just kidding)

Chris
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Old 08-09-2000, 06:40 PM   #14
S.Damery
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Thumbs up

Trey,
Interesting reading and nice work! You said that you designed your cams to work with the stock ECU, would they effect emissions? Would your cylinder heads work okay with the factory ECU as well (not that that would be smart, I think Shiv's Tech-II kit would complement this setup nicely). What kind of HP would your Headwork and Cams make? Just curious.
-Shawn
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Old 08-10-2000, 07:12 AM   #15
Trey
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Post

Shawn,

Yes, the cams work with the stock ECU, though adding a piggyback or Super AFC to correct the A/F ratio is highly recommended. We hope to have the cams dyno tested next week when the dyno we use (RX7.COM) becomes available.

The heads might work with the stock ECU but to see full benefits, a TEC-II, Haltech, or something similiar would be HIGHLY recommended. I'm going to try and dyno the heads/cams with stock ECU but we're also installing a Haltech E6K on the car to show the full gains. We'll also have another cam profile available (later on) for those running a stand- alone computer which will take advantage of a higher rev limit.

Thanks for everyone's patience. We've got many things in the works but we'll try and get the results for these cams and our heads very, very soon.

Best Regards,
Trey
CobbTuning.com
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Old 08-10-2000, 09:48 AM   #16
cOz
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Trey is doing the really important work for our cars and is doing a great job with it. Hats off to him for going to the plate for something he enjoys doing.

He is making it really difficult to decide on forced induction or NA. Time will tell...

PS whats up Marco! Trey my cars running great although it is getting the power bug.

Robert cOz-art
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Old 08-10-2000, 11:38 AM   #17
Turk
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Everything sounds great, thank you for your hard work. But I was wondering are you also going to make Cam Gears for the cams?
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