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Thread: General tech questions...

  1. #1
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    Default General tech questions...

    Hey guys i have a few questions...
    I couldn't find any pleasant answers myself.

    I have technical understanding, i work as a technican at a car dealership,
    but if you want to get super mega scientific, i'm out...
    If there are generel formulas or calculations i can go from there...

    I hope everything is clear and understandable.

    Thanks a lot i advance!

    __________________________________________________ ___________

    1)

    If i do a electrical fan conversion, how do know what fan i need?

    I thought "bigger is better".., if it overheats, cool it down fast.
    Or is a slow cool down better?

    E.g. 1: One big fan that can move 1600m/h air.
    E.g. 2: Two which move 1000m/h each, one starts at 95C/203F the
    other at 107C/225F.


    The engine is NA, 2 litre, 8V, inline 4 with 115hp, cooling system is about 6.5l/1.6 gal.
    The radiator is an oldschool top to bottom flow type thingi, with a belt driven visco fan.
    Thermostat opens at 93C/200F (fully open at 107C/225F).
    System pressure is about 1-1,3bar/14-18psi, boiling point about 125C/257F.
    Car is daily driven...



    2)

    How much can i lighten the rotating mass of the engine.
    I want it it to rev a bit better but still maintain a healty amount of rotating force
    for a daily driven car.

    If i toss (e.g.) 3Kg/6.6lbs off the crankshaft (via a lighter pully and by removing
    the visco fan and lighten the flywheel) would it rev to the moon or still be a pig?

    Car is rwd, if that makes a difference...



    3)

    I want to build an exhaust systen, how do i calculate what diameter i should use.

    A bigger diameter means the gas flows slower, but you have less back pressure.
    The same or smaller increase the flow but also the pressure.
    Is it better to have a better flow or to have less back pressure?

    Or should i keep the stock diameter (50mm/2") and just reroute the exhaust for better flow.
    I thought to go with 57mm/2.25" or 60mm/2.35" from the exhaust manifold back...

    Also i thought about v-band claps, are they worth the hassle/money?

    The engine is NA, 2 litre, 8V, inline 4 with 115hp at 5200 rpm,
    170nm/125pft at 2600rpm.

  2. #2

    Default

    Are you racing this car? Personally think you are over thinking this little 115hp daily driver. I had a mk3 2.0 gti and did an intake, exhaust, 260 cam, bored the throttle body, and chip. That was one free rev'in son of a bitch after all that, but at the end of the day is was still a slow piece of shit. Couldnt even beat a mazda 3. I say keep daily drivers stock. If anything put an intake and a muffler on it and lower it call it good. Spend your money on your fair weather car.

  3. #3
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    Default

    The car IS a slow pos, that's kinda the point...
    There is literally no aftermarket for this car, especially for the small 4 banger...
    Got an intake already, Exhaust manifold too. Lowering is in the works,
    custom.., because nothing available...

    That's why i'm asking.., doing this for fun/experience, not gain in hp or whatever...

  4. #4
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    Default

    Quote Originally Posted by OrangeBlue View Post
    Hey guys i have a few questions...
    I couldn't find any pleasant answers myself.

    I have technical understanding, i work as a technican at a car dealership,
    but if you want to get super mega scientific, i'm out...
    If there are generel formulas or calculations i can go from there...

    I hope everything is clear and understandable.

    Thanks a lot i advance!

    __________________________________________________ ___________

    1)

    If i do a electrical fan conversion, how do know what fan i need?

    I thought "bigger is better".., if it overheats, cool it down fast.
    Or is a slow cool down better?

    E.g. 1: One big fan that can move 1600m/h air.
    E.g. 2: Two which move 1000m/h each, one starts at 95C/203F the
    other at 107C/225F.


    The engine is NA, 2 litre, 8V, inline 4 with 115hp, cooling system is about 6.5l/1.6 gal.
    The radiator is an oldschool top to bottom flow type thingi, with a belt driven visco fan.
    Thermostat opens at 93C/200F (fully open at 107C/225F).
    System pressure is about 1-1,3bar/14-18psi, boiling point about 125C/257F.
    Car is daily driven...
    Generally bigger is better, assuming that you control your fan speed effectively. Bigger will allow you to accommodate more heat rejection at higher temperatures. Of course after a certain point it may just be unnecessary.

    You want a strategy as follows:
    1.) Your thermostat needs to be full open for awhile. You don't want your fan fighting the thermostat. Then you get wild swings that will wear out fans, thermostats, and radiators.
    2.) Increase fan load as temperature goes up.
    3.) You need to be all out on cooling capability before your max useable temperature limit. That is to say the kind of temperature that would trigger a yellow light, but not necessarily a red light and shutdown.
    4.) When the fan is on, it should run for awhile, but should kick off well before the thermostat starts to close.

    And generally you want your fan ramp rate (if applicable) to be steady. Not so steady that it lets your temp run away before you control it, but it shouldn't be so quick that it causes rapid cycling that fails components.

    2)

    How much can i lighten the rotating mass of the engine.
    I want it it to rev a bit better but still maintain a healty amount of rotating force
    for a daily driven car.

    If i toss (e.g.) 3Kg/6.6lbs off the crankshaft (via a lighter pully and by removing
    the visco fan and lighten the flywheel) would it rev to the moon or still be a pig?

    Car is rwd, if that makes a difference...
    Of course you can lighten it up. The biggest ones without digging into the engine block are the pulleys, fan drive, and flywheel. Go to an aluminum flywheel and smallest (diameter) clutch possible.

    That will give you a small bump. It won't be very big though. You might gain a few hp and a little quicker rev, but it won't change your redline. For that you're talking engine internals and balancing, along with making sure your valvetrain/ignition/fuel system are up for the task.

    3)

    I want to build an exhaust systen, how do i calculate what diameter i should use.

    A bigger diameter means the gas flows slower, but you have less back pressure.
    The same or smaller increase the flow but also the pressure.
    Is it better to have a better flow or to have less back pressure?

    Or should i keep the stock diameter (50mm/2") and just reroute the exhaust for better flow.
    I thought to go with 57mm/2.25" or 60mm/2.35" from the exhaust manifold back...

    Also i thought about v-band claps, are they worth the hassle/money?

    The engine is NA, 2 litre, 8V, inline 4 with 115hp at 5200 rpm,
    170nm/125pft at 2600rpm.
    There's calculators out there you can use to calculate effective flow rate and base your selection off of that.

    Now backpressure is a bit of a misconception. What you're really talking about is flow restriction and velocity. Ideally you want high velocity for scavenging (getting exhaust out of the cylinder) and low restriction, which means you can flow more air through the engine, and make more power. It is after all an air pump. In reality they're usually inversely related, and you have to optimize what configuration gives you the best trade off.

    For instance if you run a huge 5" exhaust on a little 4 cylinder, you'll have next to no restriction, which is good for high power and when you're spinning it to the moon. But when you're puttering around at low load and low RPM where you're not moving much air, your velocity is going to be extremely low, reducing scavenging and giving up power/torque. Same if you go the other way. Then you lose out on top end due to too much restriction. It's all a balancing act.

    Realistically if you've got a pretty stock 2L NA engine, 2" is probably adequate. If I remember correctly from my Neon days, most NA guys, both with the 2.0 and 2.4 usually ran 2.25" exhausts, 1.5" primaries on the headers, and that was plenty for the extra displacement of the 2.4, along with the extra power of cams and higher compression. Depending on your particular installation, select replacement of components like manifold, cat, and muffler may be your best bang for the buck.

    As for V-bands, I'm not a big fan of them. They're usually a pain, and that's even on stock systems. Slip fit always seem to leak. 3-bolt flange are a bit of a pain with their gasket, but not near as bad as V-band (half or full marmon.) Ball and socket type joints have given me the least issues.
    I Have No Idea What I'm Doing

  5. #5
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    Default

    I'll bring this up to the current state...

    Thanks a lot guys for helping me out.



    As for the e-fan upgrade...

    Accordingly the info i got, i went with the following...
    As my thermstat is fully open at 107C/225F, i got a thermoswitch which
    kicks on the fan at 117C/242F, and stops it at 107C/225F,
    as the boiling point is about 125C/257F at 1-1,3bar/14-18psi system pressure.
    I'll wire it directly to be batterie via a relay, so when i park the car the fan is still on,
    maybe i'll wire it to the ignition or get a extra waterpump...

    I think it should be ok.., but testing it out shouldn't be to hard...


    About the lighten of the rotating mass...

    I found a alloy crankpully which is about 1kg/2.2lbs lighter then the stock one.
    Also the visco fan will be gone, maybe i'll mod the pully of the powersteering and
    if that's not enough, i get a smaller (read race) alternator.

    Then a lighter flywheel, i don't want to mod the one i have, as they are hard
    to come by in the rwd version if i don't like the "feel" of it...


    The exhaust system...

    I've read some threads about this.., well seems to be trial and error with this engine
    in my platform...
    Most fwd people go with 60mm/2.36" as a catback which should be up to the task,
    as i plan to get a cam later down the road...

    As for velocity and scavenging i think the stock cat from the Fontera Sport
    (same engine, smaller cat, metal cat), 1 muffler (60mm, straight throuh),
    a cleaned up piping (also 60mm) and a backbox with 60mm inlet and
    two 1.87" outlets should do the trick...

    Also i got another question.
    I bought two exhaust manifolds, more to just have them and because they are rare,
    then to use one of them..

    One is a 4 into 1, the other one is a 4-2-1...
    I couldn't find out which does what, iirc an 4-1 is for better rev,
    and a 4-2-1 if for more power...
    But if i get all thie exhaust stuff right a 4-2-1 creates a better vacuum in the runner to
    cylinder next to it then the 4 into 1, which each runner has to create for 3 runners...
    So a 4-2-1 is better for scavenging the cylinder...

    If some can shread some light here it would be greatly appreciated!


    Thanks a lot for reading!
    Last edited by OrangeBlue; 05-12-2015 at 02:56 PM.

  6. #6

    Default

    Bookstore, there's a book on fabricating exhaust systems and components I'm reading at the moment. For most I6/V6 to V8 applications it's going to be 2.5" to 3.5" depending on the kind of flow your looking for, too big and you lose back pressure, too tight and you restrict flow

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