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Discussion Starter · #1 ·
I have a stock 91 HF ... and I would like to swap in an A6 ...

I couldn't really find a thread on this ... but I'd just like to leave everything else in [tranny, exhaust, intake]

what would I need to swap out in order to make this possible and with the least amount of modification and money?

I want to keep my tranny in because its my DD and I'm just a poor college kid who loves getting 40 MPG

Thanks in advance
 

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you don't have to wire anything, absolutely no wiring involved. just get rid of your tired old HF motor, bolt the A6 to your HF tranny, drop it back in. It will be plug and play because both motors use the same sensors and are located in all the same places. You will actually have like 1 or 2 extra plugs left over if you use the A6 intake manifold as there are a couple things on an hF motor that the A6 does'nt use. 1 of them is EGR, i can't remember the other, just leave them hanging, or tape them up.

Your shift light will not work unless you keep your stock HF ECU running the A6 which i really do not suggest, you definately wanna use the PM6 Si Ecu.

Everything will bolt up, your tranny, your clutch/flywheel, your HF dizzy. The only thing is you will not have a Cat on your car after the swap as the HF's Cat is in the manifold, not underneith the car, therefor an HF midpipe is longer than an SI's and goes straight to the Collector at the downpipe. No biggie though, i also drive an HF and i have'nt had a cat since my first swap.
 

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Why do you want to swap in the A6? Is there something wrong with your engine or are you just looking for more power?

Here's the truth of the matter if you're looking for more power:

An a6 bolted up to an hf tranny using the hf ecu will not help you in the power department much. In fact, that might even hurt your low end performance because the hf ecu is designed to work with the internal construction of the hf's 8 valve/shorter stroke/higher compressoin engine, not the a6's 16 valve/longer stroke/lower compression engine.

If you must use the hf tranny to save on cost, the only way to get a noticeable power increase from the a6 engine is to use the intended pm6 ecu for it. Even then, don't get you hopes up too high because afterall, fact remains that the super long gears of the hf tranny severely impedes accelleration.

If 40+mpg is more valuable than anything else and your current engine is fine, then leave well enough alone. If more power is needed, it's not even worth getting into unless you are using a pm6 (aka si) ecu at minimum, plus an si tranny preferably.
 

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godruler said:
The only thing is you will not have a Cat on your car after the swap as the HF's Cat is in the manifold, not underneith the car, therefor an HF midpipe is longer than an SI's and goes straight to the Collector at the downpipe.
Why can't he just bolt his existing exhaust including the exhaust manifold directly onto the si engine?

stnapycnaf said:
I have a stock 91 HF ... and I would like to swap in an A6 ...

I couldn't really find a thread on this ... but I'd just like to leave everything else in [tranny, exhaust, intake]
forgot about this... if you want to retain the stock intake, you cannot use the a6 intake manifold because the throttle body is much too big for the hf intake snorkel to fit around. You could however use the hf manifold on the a6 engine but that becomes a little retarded because it part way defeats the purpose of swapping in an a6 for more power.
 

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Make sure to use the HF motor harness on that A6 motor.

I would totally reccomend using an Si tranny though. and a PM6 ECU.
with my old HF with Si trans/motor i got like 34 mpg
hell with my ZC and Si trans in the HF i get like 29 street and 32 freeway.

And here is my swap article:
http://www.crxohio.org/showarticle.php?id=9

-Henry
 

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... and if you use the PM6/intake manifold, you do need to rewire, as in the "Chassis Notes" section of my article linked in the second post:

Chassis-Specific Notes
There are a couple of little things you need to know/do with the DX and HF models. If you have an Si you're pretty much all set to swap.

The HF has little tiny axles and hubs/brakes. It is recommended that you swap them out for at least CRX Si hubs and brakes. The HF axles will work with other D series transmissions (DOHC ZC aside) because they have the same inner size and spline count, but if you're pulling the axles out anyway, you might as well do yourself a favour and swap the hubs.
With the HF, you also will need to do some minor rewiring to use the FICSV on OBD0 manifolds like the one on the D16A6. Matt Miner provided this information when I did an A6 swap into an HF:

Next is the fast idle control solenoid valve (FICSV), which is mounted on the back of the Si intake plenum, near the EACV. Its plug uses 2 wires: black/yellow and blue. Black/Yellow (later referred to as B/Y) is a 12V + and routes to the B/Y from the EACV plug. The blue wire goes to pin B2 on the ECU. B2 is currently connected to the green/yellow wire from the "shift up light" in the gauge cluster. The plug for this wire contains a green/orange and a yellow/red wire. It is under the driver's side of the dash, connected alongside the fusebox with a white plug. Cut the green/yellow wire from the plug on the harness and splice in the blue wire from the fast idle control solenoid valve, with the new wire going toward the ECU. Don't connect the FICSV wire to the plug under the dash, or weird stuff will happen with your shift light! The "shift up" light is now disconnected (YAAAAAA!!!) and the green/yellow wire on the plug under the dash now hangs bare. FICSV wiring is now complete.
I've actually done this swap, and I can verify that is true. It doesn't matter on Godruler's car because he has a B18, but it does for the A6 with the oddball sensor.
 

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he can use his stock manifold and bolt it onto the A6 but i would'nt recommend it as the HF's exhaust ports are like 1/2 the size of the a6's so the exhaust coming out of the head would hit a brick wall as it tried to flow into the manifold.
 

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Discussion Starter · #10 ·
thanks guys for real

the reason i want to swap out for an A6 is because my HF engine is tired ... and its making sounds ... unreasonably loud ... and because ... well thats really it ... its old ... might as well get something better ...

i'll probably swap an Si tranny in when I get more money ... but my HF tranny seems just fine for now ... I'm not looking for power or anything at the moment ... just convenience

thanks again!
 
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