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Discussion Starter #1
Hi all.

I did a 2.5 swap on a Subaru TS which came with a puny 1.6 engine. The improved torque and power was simply amazing,
but sadly according to my mechanic, the stock heads were restricting the exhaust flow, which means that i could only pull my 2.5 to ONLY 4 to 5RPM, after which i have totally no power gains at all.

I am trying now to save for a proper 2.5 head swap, which i stupidly thought was part of an engine swap ( i just got my license 6months ago :p )

Any suggestions how i can improve the flow problem before i can get my heads
Currently I have 1) cold air intake, with stock airbox with Hurrican Air filter
2)STI transmission (the weak stock tranny couldn't handle the power)

3) 2 1/4 exhaust with no cat, custom extractor

I am thinking of exhaust wrap, gravel intake, port and polish. My mechanic suggested a standalone ECU to overcome the head problem.

Any suggestions?

Thanks.
 

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V4 Sti BRP, 98LGT SP, 94SVX PW
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New Mechanic.
Normally when one refers to an engine swap it is just that, a complete swap. Not just the bottom end.

Never seen a 1.6 so haven't a clue as to their heads.
Cheapest solution would be to port/polish and TGV Delete. You can do these yourself. This will free up air BUT will not necessarily allow for more RPM.
FYI - The 2.5 doesn't even make power
until 4250/4500 RPM up to about 5500. From 5500 - 6200 it starts dropping off. And valves float shortly after.
 

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2000 Imp 5 door Sport
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ya WTF is a 1.6?
2.5 heads are not very restrictive and a EMS will have nothing to do with restrictive heads
 

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RS, GF, SSx2, STI GDB
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692 Posts
The 1.6 was the smallest subaru engine to go in the Impreza line. Never was here in the USA.
Guessing you did what a lot of people do and keep your stock heads and intake so the stock computer can still run the set-up. While that may work, adding an extra 66% displacement will run into issues with heads that just are not meant to handle that much extra. ( that and you may be running lean if you are not careful)

I know how you feel. My 2.2T is a SOHC head, and having an 18G on it means I run out of power at 5000 rpms. SO a head swap may be in order, if I want to open up the power up top.
You might want to check out the specs on the 1.6 heads and post them here. That will give us a better idea of the differences on the two.

That will also better help diagnose the issues.

valve sizes and compression ratio before and after would be good also.
 

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Discussion Starter #5
Well, i am using piggy-back E-manage Ultimate to control the 2.5 block now. BTW what is valve float? And what's the torque / power curve like for a stock 2.5RS?

Anyway i just got to know that i am currently running with WRX injectors, anyone can tell me how much more these injectors are running compared to the stock? and does it make a diff?

The reason why i have WRX injectors was because during the swap the mechanic didn't have RS25 injectors only WRX!
 

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2002 Aspen White WRX (sedan)
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Valve float is exactly what it sounds like. Floating valves, which is from weak springs that can't seat them in time.

Dunno about the curves, but you only would need to worry about the injectors if their duty cycle was a smaller amount than the rs, which i doubt it is. They only squirt the fuel commanded by the engine management.
 
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