well i was just wondering if anyone has run into this issue yet, i was comparing some dyno graphs i had laying around and was noticing a couple different things.

the most significant hing was my turbo civic (b16) mademore power with exhaust on it than with an open downpipe, anyone else seem to havethis issue???

 

my car lost 30whp by taking off my 3" custom exhaust.

 

its all about the tuning, so depending which way your tuner went, your car could either lose or gain power

 

okay so im not retarded! My car just seemed soo much faster and made boost alot kwiker with my full exhaust on.

we need more info on this

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mrbsponge &raquo;</TD></TR><TR><TD CLASS="quote">okay so im not retarded! My car just seemed soo much faster and made boost alot kwiker with my full exhaust on.

we need more info on this</TD></TR></TABLE>

very intresting...I want to know more too...

 

its something to do with back pressure,try puttin a smaller muffler on

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dabig1 &raquo;</TD></TR><TR><TD CLASS="quote">its something to do with back pressure,try puttin a smaller muffler on</TD></TR></TABLE>

No it isn't.

 

it would probably be because u had ur car tuned with exhaust on it, when u unbolt the exhaust it throws ur whole tune off.. it u want to do that u should have ur car tuned with open downpipe then u can bolt ur exhaust up to run on the street..then u will be fine

 

You didn't give any details (i.e.: Dyno graphs with A/F, etc.) but here is a valid theory:

Because your open down pipe will give you less restriction your A/F mixture will be leaner (more air can pass through the engine while it supplies the same amount of fuel for a given given throttle angle/RPM/manifold PSI). If the A/F mixture is lean enough the engine may knock (detonate), even though it may not be audible, causing your drop in power either from the knock itself or from the ECU pulling back the ignition timing. I am not sure what sort of knock control your car has if any, I tune BMW's not Honda's (although I've been owning/working on Honda's for 15 years). To properly tune for the down pipe you would need to richen up the A/F mixture at wide open throttle.

That's just one theory, any rebuttal is welcome

-Scott Tucker

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AutoEng2002Si &raquo;</TD></TR><TR><TD CLASS="quote">You didn't give any details (i.e.: Dyno graphs with A/F, etc.) but here is a valid theory:

Because your open down pipe will give you less restriction your A/F mixture will be leaner (more air can pass through the engine while it supplies the same amount of fuel for a given given throttle angle/RPM/manifold PSI). If the A/F mixture is lean enough the engine may knock (detonate), even though it may not be audible, causing your drop in power either from the knock itself or from the ECU pulling back the ignition timing. I am not sure what sort of knock control your car has if any, I tune BMW's not Honda's (although I've been owning/working on Honda's for 15 years). To properly tune for the down pipe you would need to richen up the A/F mixture at wide open throttle.

That's just one theory, any rebuttal is welcome

-Scott Tucker</TD></TR></TABLE>

Man people get sooo technical for simple questions....

anyway, It could be possible your seeing more low end torque and just all around better responsive ness from the car. When I was open Dp it made more hp on the dyno but when the exhuast was on..(3in) it made more torque and my car seemed faster. you could be mistaking it for that as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by HybridcivicLS-T &raquo;</TD></TR><TR><TD CLASS="quote">

Man people get sooo technical for simple questions....

anyway, It could be possible your seeing more low end torque and just all around better responsive ness from the car. When I was open Dp it made more hp on the dyno but when the exhuast was on..(3in) it made more torque and my car seemed faster. you could be mistaking it for that as well.</TD></TR></TABLE>

Open DP should yield more hp AND torque. period.
aka the less restriction/larger piping, the more power you will make.

 

actually i just plain dyno'd my car WITH exhaust, i did a little tuneon the vafc with uberdata and exhaust.

THEN

we tuned open DP with hondata.

b16a2
8.5:1 je
crower rods
880cc inj
aebs manif
darg turbo kit
big intercooler
hondata

it just felt like my turbo spooled up soo much faster, it actually showed on the dyno how much sooner the boost came in, i actully layed them over each other and i DID make more power with hondata, but i/we were wondering why it took so long for boost to come on????

nothing is wrong with the turbo ie: shaft play or broken parts, i think its just loss of low end torque.

AF is 12.5-12.7 under full boost to redline of 9000. the tune is amazingly great

 

Not to open a can of worms (ie. Uberdata vs Hondata), but you're talking about two different tunes. Are the ignition values similar? Step retard under boost, or linear retard?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by m R g S r &raquo;</TD></TR><TR><TD CLASS="quote">

Open DP should yield more hp AND torque. period.
aka the less restriction/larger piping, the more power you will make.</TD></TR></TABLE>

That's not true, throwing a bigger pipe at it is not going to give it more power unless it's tuned properly, he didn't give much data at first

 

So what you are saying is that with the full exhaust on the turbo spooled much quicker than with the downpipe? And you are using two different fuel/ignition management systems? Did you make any runs with, all else being equal, just the down pipe swapped out?

 

my main question was would the exhaust cause a spooling issue or no, thats all

as far as the tune, i have the exact same values as far as ignition retard per boost, just set up with higher injectors, nothing too fancy

 

The speed of the turbine is proportional to the volume of exhaust gases going through it and since the down pipe is less of a restriction than the full exhaust the turbine should spool up faster.

 

funny thing is it doesnt...........

me, my tuner, the dyno operator, where all wondering why it comes on sooo late with an open DP

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mrbsponge &raquo;</TD></TR><TR><TD CLASS="quote">my main question was would the exhaust cause a spooling issue or no, thats all

as far as the tune, i have the exact same values as far as ignition retard per boost, just set up with higher injectors, nothing too fancy</TD></TR></TABLE>

You say that it has the same ignition retard per boost, but can you be certain that both wide open throttle spark maps are the same? Turbo cars are very sensitive to ignition timing and even a few degrees would be enough to make a noticeable difference.

 

This in an age old issue. If you look at the 5.0 Mustangs, guys back then (when I was in high school) were wondering why they lost a lot of low end punch when they ditched their cats by going with the "offroad h pipe".

To put it simply and generally, open exhaust is going to be best for all out top end horsepower, but for around town driveability some kind of exhaust will typically yield better results. If you're going for all out high rpm power, you'll lose bottom end hp and tq. This is usually made up for with the use of shorter diff gearing to get the car into the high rpms as quickly as possible, and to keep it there.

On another note, I just cut the magnaflow 3" cat off my exhaust I took from my old Civic, and it's hollow now...I didn't do that, wonder how it happened? Anybody seen that before?

 

I find that kinda hard to believe that I could have made my turbo spool up quicker with an exhaust on my car..

Make more low end trq and hp with an exhaust on? With the same air/fuel ratio? Don't know about that.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Smashback &raquo;</TD></TR><TR><TD CLASS="quote">This in an age old issue. If you look at the 5.0 Mustangs, guys back then (when I was in high school) were wondering why they lost a lot of low end punch when they ditched their cats by going with the "offroad h pipe".

To put it simply and generally, open exhaust is going to be best for all out top end horsepower, but for around town driveability some kind of exhaust will typically yield better results. If you're going for all out high rpm power, you'll lose bottom end hp and tq. This is usually made up for with the use of shorter diff gearing to get the car into the high rpms as quickly as possible, and to keep it there.

On another note, I just cut the magnaflow 3" cat off my exhaust I took from my old Civic, and it's hollow now...I didn't do that, wonder how it happened? Anybody seen that before?</TD></TR></TABLE>

It sounds like you are talking about naturally aspirated exhaust tuning but he is wondering why it takes so long for his turbo to spool up when he's running the down pipe. Basically what I have been trying to say is his dyno comparisons are not really valid since he was running two different fuel/ignition management systems . . . unless he can show that the WOT spark curve is exactly the same and the A/F curve is exactly the same on both runs and the only difference is the down pipe. It seems he is comparing apples with oranges. If he had done some runs with the full exhaust then swapped out the down pipe (and possibly made some tuning corrections) and did more runs and compared the results they would be more accurate and he would know whether it was specifically the down pipe that caused it or not.

He thought that an open down pipe should make more power than a full exhaust and he is right - all else being equal, but he has made other mods to the car that he didn't take into consideration so it's not necessarily the down pipe that is to blame.

If he it is really bothering him and he has the money to spend he can take the car down to the dyno with the exhaust on, do some runs, put on the down pipe, do some more runs, and then he will have valid results.

 

the main reason my car lost so much power was b/c the air fuel went off the charts rich. i had already been tuning for 3 hours at that time..so i didnt feel like starting all over again.

 

Can you post the two dynograph's? The same thing happened w/ my car and a friends car after we changed from open dp to full exhaust. We never had it on the dyno but the "butt-dyno" it felt faster. Kinda odd.