Jump to content
SAU Community

What Is Flat Spot?

lingeringsoul
 Share

Recommended Posts

lingeringsoul Grand Master

lingeringsoul

Posted
  • Author
Posted (edited)

is it just in certain rev range or does it happen in differnt gears?

reason I'm asking is, my car pulls hard like a school boy with a stack of porno in first second and third gear, all the way up to/close to redline. The fourth gear and fifth seems a little lacking in torque. I pu the foot down and the car sound like its suffocating when reving higher. I'm wondering if thats a flat spot or if it is just because of the standard dump/front and cat restricting the air flow when the boost is increased.

Edited by lingeringsoul
Liz Grand Master

Liz

Posted
Posted
oh well, no big deal anyway, once I order the split dump/front pipe and put on the high flow cat, I'll give it another test and then get it tuned properly. Thanks for all the info guys

yeah i'd put it down your exhaust restriction!

you should have just asked me what a flat spot was! I was talking about mine all the way to newcastle the other week! lol

someonestolecc Grand Master

someonestolecc

Posted
Posted
reason I'm asking is, my car pulls hard like a school boy with a stack of porno in first second and third gear, all the way up to/close to redline. The fourth gear and fifth seems a little lacking in torque. I pu the foot down and the car sound like its suffocating when reving higher. I'm wondering if thats a flat spot or if it is just because of the standard dump/front and cat restricting the air flow when the boost is increased.

That's not a "flat spot" per se.

A flat spot would be if your school boy in 2nd gear stopped for a little while between say 3000-3200rpm before going hard again. That would be a flat spot.

What you're doing is underloading the engine. To see even the middle top of 5th in my car you're doing around 250kmh+ so if you whip out 5th and it isn't down the hill and you're doing 80 you're not going to have the response when you're in boost in 3rd.

yeah i'd put it down your exhaust restriction!

That's really not it. See above. If it WAS exhaust restriction it would be RPM dependant and it would be a gradual curve/taper in restriction. This is because the restriction would be directly relative to the volumetric output of the engine at that RPM/load. So you wouldn't experience this as a flat spot, unless for some reason your exhaust was changing in diameter as you accelerated.

By your description in your first post it seems normal - if you're worried get on a mountain/racing bike and see what happens when you pedal at a low gear, then at the same speed click it into the highest gear. When you pedal at this point you'll notice you're expending more effort to move the bike - that's the same thing.

Either way a good exhaust will free your engine anyway :woot:

Liz Grand Master

Liz

Posted
Posted
That's not a "flat spot" per se.

A flat spot would be if your school boy in 2nd gear stopped for a little while between say 3000-3200rpm before going hard again. That would be a flat spot.

What you're doing is underloading the engine. To see even the middle top of 5th in my car you're doing around 250kmh+ so if you whip out 5th and it isn't down the hill and you're doing 80 you're not going to have the response when you're in boost in 3rd.

That's really not it. See above. If it WAS exhaust restriction it would be RPM dependant and it would be a gradual curve/taper in restriction. This is because the restriction would be directly relative to the volumetric output of the engine at that RPM/load. So you wouldn't experience this as a flat spot, unless for some reason your exhaust was changing in diameter as you accelerated.

By your description in your first post it seems normal - if you're worried get on a mountain/racing bike and see what happens when you pedal at a low gear, then at the same speed click it into the highest gear. When you pedal at this point you'll notice you're expending more effort to move the bike - that's the same thing.

Either way a good exhaust will free your engine anyway :P

oops, i thought he did say it was rev range specific! Nevertheless you explained some things I didn't know before!

btw.. I know who i'll be pming when i need help with my car!

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing


  • Similar Content

  • Latest Posts

    • Matvei27
      WTB noltec r32 front upper (camber) arms

      By Matvei27 · Posted

      I have offset Nismo brackets so the fact the gktechs can pivot is less important to me. I have 170mm JIC arms with bushings - but they provide no adjustment and I'm not sure whiteline eccentric bushings will fit them (I don't want to ruin the bushings currently in them to find out). Ideally I want something with bushings + adjustment; hence why I'd like to find a pair of these. Unfortunately they aren't easy to find.
    • Murray_Calavera
      Brake pad Compound suggestion

      By Murray_Calavera · Posted

      @Vee37 How much do you really care about finding these pads again? If your pads are quiet, work well and produce minimal dust, really isn't that enough? If you are set on finding the exact pads again, I suppose I'd do something like this -  Visit your local Jax, find out what brand of pads they carry. If the Jax workshop you previously went to had the pads on the shelf, then you can almost guarantee it will be of said brand.   I'm guessing you don't have the receipt for the previous work and pads. Can you visit a Jax workshop and see if they can look up your previous job to see what pads were fitted?  Still no luck? Put your stalker hat on, find the staff that used to work at the Jax store and ask them. Talk to local workshops, try to find out where the mechanics went to. Talk to Jax workshops, maybe they relocated to another workshop. When it comes to mechanics, its a small world. You'd be surprised how easy it is to track someone down. If these ideas don't work, shit will start getting crazy very quickly.... You could find out every brand and model of pad that fits that car... and try them individually ticking each off the list if it wasn't the one you were looking for.... If you go down this path your going to want to learn how to swap pads yourself, it is very easy, takes minimal tools and space. If you have room to park the car you have room to swap the pads. Plus you have the advantage of making sure all the brake hardware goes back in so they won't squeal! 
    • MBS206
      Beers and skylines Fatz style

      By MBS206 · Posted

      You miss spelled bearings...
    • Kinkstaah
      Help Understand GTT Boost Setup

      By Kinkstaah · Posted

      Just putting it out there, that's a decent list. You would be better off *not* doing *any* of that and buying someone else's modded car. Like mine. Or anybody else's. Yes it's lotto dependent and all this and that but that 70K (remember, double your guesses) could go elsewhere. Keep it stock, save your money, go lowball @Dose Pipe Sutututu :p
    • GTSBoy
      Brake pad Compound suggestion

      By GTSBoy · Posted

      Does not mean what you think it means. The continual rising coefficient is the coefficient of friction that continues to rise with increasing temperature. Not "rising during a single stop", except inasmuch as the brakes should get hotter during a single stop. The RR would not be the best choice for a streeter. Yeah....no it's not. JAX would rummage around in the "shit pads we use for all shitboxen that come in here" and install those.
×
×
  • Create New...