What Is Flat Spot?

[lingeringsoul]

Just wanna ask people what does it mean by flat spot in when tuning engines. What does it feel like?

[Big Rizza]

Flat spot usually refers to an unusual lack of torque over a speciffic RPM span - basically the car won't pull like it should!

[godzGtR]

flat spot in tunning is like a lag, which the enigne is having problems, such as when you take off the engine feels like its not pulling at all than out of no where you get the car pulling

[lingeringsoul]

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 May 13, 2006 by lingeringsoul

[evil_weevil]

hmm....thats no good james!

My car had a flat spot around 5-5.5k in all gears....my mechanic sorted it out and was all good

[WazR32GTSt]

flat spot is rpm dependent, not a matter of gears

yours sounds like a normal car in that at such a high engine output things are jsut being restricted (eg stock exhaust)

you shouldn't really be seeing that side of 5th gear anyway...

[lingeringsoul]

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

[Liz]

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]

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

[lingeringsoul]

yeah....getting exhaust done this week.......should sort all this out

Edited May 16, 2006 by lingeringsoul

[Liz]

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

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!