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Discussion Starter #1
Wow I was at the subie dealership and we were showing the chrysler people how its done ;). I revved it up and the look on my g/f's eyes were priceless. She was like, did you know your engine moves when you rev it, im thinking well duh its got a lot of power being shoved into it and no where to put it. So I get out to watch it (thinking its just going to move a little) and she revs it up just as I did and the thing like slides from one side to the other lol. I was like HOLY CRAP, Im assuming this is normal, but man, talk about wierd, I've never seen an engine move so much. I guess it does this because its an H4 engine and instead of just shifting up and down a little, it'll slide side by side? lol definitely an eye opener though for people who dont expect it.

Robert~
 

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I think part of the reason the engine moves so much is because of the cylinder firing order. Imprezas and STi's fire 1-3-2-4.... So the engine fires down the driver's side and then the passenger's side....
 

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Actually... there is, but you don't get as smooth of a power distribution...

If they fired the cylinders 1-4,2-3, (or 1-2,3-4, assuming the pistons are numbered how I think they are....) with no firing for 2 of the four cycles, there would be counter-firing cylinders at every revolution and the block wouldn't vibrate hardly at all.
 

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I'll be looking into stiffer engine mounts. . . . I know the car will shake more, but the gains off the line are definitely there for most cars. :D
 

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I dont know if this is true for the Sti but Honda VTECS such as the S2000's are specifically built to move. They are bolted to rockers that purposly do this. This might be the same for the
 

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the motor would move no matter what you did to the firing order, because you have a crankshaft and flywheel rotating. that's where most of the inertia comes from...
 

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ever see a small block chevy motor move when it reved? my Camaro had solid motor mounts and you'd think it was going to rip itself off the frame. i'm pretty sure that the motor moving is nothing more than power that is being lost so i too will be looking into the possibility of a using stiffer motor mounts. too bad i'm not sure exactly how the Subie motor mounts being an ex-chevy guy.
 

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Personally I think you guys are worrying about this too much. How much power are you 'losing'...anyone know? You are never going to get the car to respond instantaneously to engine input, so why worry about this? Engines are allowed to do this not just for smooth power delivery, but to give the whole driveline a place to let shock dissipate. Think about it....

Hard accel, hard decel....every component (or the new weakest link rather) in the drivetrain has these massive forces being slammed against it. How long to you think it will be before something breaks?

IMO....the engine mounts aren't an area for huge improvement. Stiffer ones for smoother shifting, maybe. But using the displacement of the engine movement under load as the determining factor to start welding the engine to the frame......not a good idea IMO.
 

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Discussion Starter #13
heh ya, i just posted this out of amazement ofseeing an engine move like it did, not to start a hp loss argument ;)... just dont worry about it fellas, make up the HP in other areas.

Robert~
 

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in my experience, again mostly with chevy V8's, the main reason for "solid" motor mounts is to control power. a built chevy V8 could destroy stock motor mounts. i'm sure the stock mounts on the STi can deal with a stock STi motor, but what happens when we start uping the power output? if you're looking to make more horsepower and torque i suggest looking into stronger mounts as well. i don't think any of us want to accelerate hard only to find that you broke your motor loose.
 

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crashsti said:
in my experience, again mostly with chevy V8's, the main reason for "solid" motor mounts is to control power. a built chevy V8 could destroy stock motor mounts. i'm sure the stock mounts on the STi can deal with a stock STi motor, but what happens when we start uping the power output? if you're looking to make more horsepower and torque i suggest looking into stronger mounts as well. i don't think any of us want to accelerate hard only to find that you broke your motor loose.
Ok, but does stiffer=stronger? Just because you get a stiffer mount doesn't neccesarily mean that it is any stronger than one that has some movement.
 

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Ok, but does stiffer=stronger? Just because you get a stiffer mount doesn't neccesarily mean that it is any stronger than one that has some movement
in most cases a "solid" motor mount is made of steel. it eliminates any rubber from the mount. it rigidly mounts the motor in the frame. effectively transferring the shock of a sudden application of power from the mounts to the entire frame and suspension of the car. i'm sure the stock motor mounts on the STi are plenty strong to handle stock power levels but like i said, if you start making alot more power it'd be wise to look into a more ridgid mounting system. a motor mount can easily be a weak link in a high power car. best to eliminate it. besides i can't imagine that "solid" motor mounts for the STi would be expensive, assuming someone makes them. for a small block chevy they run about $60.
 

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With the engine turned off take a look at how much the engine moves when you grab the front tire and shake it. When we did the tech inspection at Willows it took 5 minutes for everyone to come over and look at the engine shake during the front bearing check - too much fun!
Don't know for sure - but we were guessing that the motor mounts are fluid filled to minimize vibration transfer. When I go to pick up the car after the new engine is installed - I will ask the techs what is there.
Bill
 

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crashsti said:
fluid filled motor mounts? wow, that would be something. let us all now what you find out.
The mounts on my jetta are fluid filled...that is the mounts I haven't replaced with solid polyurethane :)
 
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