L.Williams
soundcloud.com/lwilliamsmusic
why could this be ? the gears just draaaaaag now, usually with old standard exhaust, used to pick up speed thru the gears pretty quiclky and nicely, now sports exhaust is on, its slow and sluggish
sports backbox installed, now slight power loss?
- Thread starter L.Williams
- Start date
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
lmao yeah, but why would it actully lose slight power? i mean.. i can deffo feel itit sounds quicker tho eh
frank
Club Member
thats quite an achievement
bum dyno,s are notoriously inaccurate LW, do a couple of timed vids, and compare them
You running a decat?
Enuo
Glorified Electrician
If it were me I'd check stupid stuff before I blamed the exhaust setup. Make sure you've not sucked leaves into intake or something daft, fuel filter isn't almost blocked... Then maybe check fuel pump isn't worn and is generating enough fuel pressure?
You'll lose power at the low end with lower back pressure but expect to gain some towards the top end, If the filters/pump can't deliver enough air/fuel to run well at the top end you'll lose power everywhere...
You'll lose power at the low end with lower back pressure but expect to gain some towards the top end, If the filters/pump can't deliver enough air/fuel to run well at the top end you'll lose power everywhere...
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
hm,mm all good info guys, and checked my air pipe, nothing, relocated it so better air flow, bit quieter but not much power gain compared to stock pipe, and no decat, and im running a powerflow backbox off SulUR check his page somewhere, pics of it on there
Bit of a stupid one, but are you actually pushing the pedal down hard when accelerating? i know it sounds like a stupid one, but the thing with louder exhausts is getting used to the "new" noise it makes, the louder it is the more your brain thinks the noise is assosiated with speed so you may be subconsciously holding off. If not, it could be as said, a lack of back pressure, did you seal the join with paste? is the the box damaged? ie got an obstruction in it? have you moved the rest of the system and pulled a join or cracked a weld? Also, with just a back box, you will be lucky to gain even half a HP, if the gain is less than 10% you will never feel that gain anyway. The pitch change will make it sound different and therefore may "feel" slower, so you really need to time the before and after, but tbh i bet it will be the same.
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
think its most likely you have lost power. if you've put a different back box on then the exhaust will be less restrictive, creating more free flowing exhaust gas. however, the backpressure does have a significant effect on the car. i'd suspect you've got 2 or 3 bhp more right at the top end, but a loss of power and torque in the midrange.
LOL, this is probably my fault for the joke, but engines loosing power due to having less back pressure is a total fallacy...
Most cold air induction systems actually suck in hot air. Backboxes make a nice sound and in a situation where the car retains the standard manifold & downpipe etc, it will make no more power.
You're probably right. The cynic in me says, back to back the car probably makes less power now than standard in certain areas.
Most cold air induction systems actually suck in hot air. Backboxes make a nice sound and in a situation where the car retains the standard manifold & downpipe etc, it will make no more power.
You're probably right. The cynic in me says, back to back the car probably makes less power now than standard in certain areas.
sorry mate but its true. exhaust systems are calculated to be of a certain tuned length, designed to work specifically at a set revs. if the exhaust system is too long, you'll lose power, but will also lose if its too short. we tried a kawasaki zx-10R with and without a tuned length exhaust. there was 8bhp increase from 6000rpm to 14000rpm with the tunes system.
frank
Club Member
backpressure is just an unwanted consequence of creating flow in the pipe tom
skymera
Brutal Honesty
I've read quite a bit about the "backpressure myth"
Apparently it's about the speed/velocity of the exhaust flow with minimal backpressure.
This was a good read. I'm not an expert in exhausts though.
http://www.hondacivicforum.com/forum/header-intake-exhaust-12/backpressure-myth-why-its-wrong-3064/
From what I remember it was a good read, a simple Google will yield further results.
Apparently it's about the speed/velocity of the exhaust flow with minimal backpressure.
This was a good read. I'm not an expert in exhausts though.
http://www.hondacivicforum.com/forum/header-intake-exhaust-12/backpressure-myth-why-its-wrong-3064/
From what I remember it was a good read, a simple Google will yield further results.
N'ah, it's just one of those things that's been circulated around for long enough it's become part of the furniture.
It stems from people fitting headers that were too large a diameter to a vehicle, (since this was the rule of thumb a while ago). This spoils exhaust gas flow velocity and thus ruins scavenging, particularly at the low end. In some cases it can really ruin a build and result in total disappointment.
Since effective scavenging actually stems from a carefully timed low pressure zone at the exhaust port, (i.e. your example above), it's the drop in exhaust 'back pressure' that aids cylinder filling. Tune the exhaust to give a high pressure zone and you will induce reversion, dilute your intake charge and lose power.
If you are still running everything standard other than the backbox it will make no difference at all purely because it's getting slowed down way before the backbox. You won't really notice a difference till you get a full system i.e 4-2-1 and full sportex system...
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
only other thing to do with power is a cold air feed with a cone filter, which is not gonna effect it highly, that i know, any upgrades you reccomend for the time being? bit short on cash right now
If you are gunna do it, do it properly. What I have learnt is to save up and buy the proper parts instead of wasting money on bits which don't actually make a difference!
Save up buy a proper 4-2-1 and full system till then if performance is your outright goal it's not worth doing unless it's done properly!
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
okay mate, but wont a 4 - 2 - 1 increase emissions or something ? i read it on here before and he failed MOT for it
But so will hollowing out the front cat. Your not going to make any difference as long as you have a cat. I recommend finding someone who will bodge your emissions results for you... But if your not gonna change that, don't expect to notice a change in anything other than noise
OP
OP
L.Williams
soundcloud.com/lwilliamsmusic
so a 431 manifold wont increase emissions, if i keep the cat? if i remove cat, it will ovo increase, and fail mot ?But so will hollowing out the front cat. Your not going to make any difference as long as you have a cat. I recommend finding someone who will bodge your emissions results for you... But if your not gonna change that, don't expect to notice a change in anything other than noise
You have the facelift so also only have 1 cat in the manifold. Therefore if you replace the manifold with a 4-2-1 it won't have a cat and hence will not be to correct emissions...
pollyp
Club Member
a cat will only work efficiently within a certain temp range (measured the rear end of the secondary cat must reach at least 178C to work).
too cold (too far away) and it barely cleans up the emissions. too hot (very rich unburnt fuel or too close to a hot turbo) and it begins to melt n damage n restrict permenantly.
the primary cat was close enough to the engine to get upto temps and does most of the cleaning job imo.
a 4-2-1 header will remove the primary cat nearest the engine and leaves the secondary cat (if fitted) to do the work.
but i find the secondary cat is wayy too far away from the engine that it has a hard time getting upto operating temp to clean the emissions (even on my turbo setup with heatwrapped exhaust) nor build up heat fast enough cos MOT guy is only allowed to hold the revs for afew secs.
so leaving just the secondary cat will not guarantee a MOT pass.
other solution is to annually:
swap back to a stock manifold or
lean out the afr at the 2-3k rev (fuel reg or ecu tuning) to reduce CO but may increase HC due to likely misfire
too cold (too far away) and it barely cleans up the emissions. too hot (very rich unburnt fuel or too close to a hot turbo) and it begins to melt n damage n restrict permenantly.
the primary cat was close enough to the engine to get upto temps and does most of the cleaning job imo.
a 4-2-1 header will remove the primary cat nearest the engine and leaves the secondary cat (if fitted) to do the work.
but i find the secondary cat is wayy too far away from the engine that it has a hard time getting upto operating temp to clean the emissions (even on my turbo setup with heatwrapped exhaust) nor build up heat fast enough cos MOT guy is only allowed to hold the revs for afew secs.
so leaving just the secondary cat will not guarantee a MOT pass.
other solution is to annually:
swap back to a stock manifold or
lean out the afr at the 2-3k rev (fuel reg or ecu tuning) to reduce CO but may increase HC due to likely misfire
