Just got off th line debating with a mechanic that I know.. First of all, he predicts that my exhaust is too big and does not provide enough back pressure, hence my dismal power figures..

Now for the real Q. I got a custom made test-pipe or as you guys might call it b pipe to replace the cat!. Hypothetically if there is not enough back pressure, I will loose power right??? If I do gain power then my back pressure should be ok!


My engine setup is below. P.S> am trying the no cat option tommorow with my race.. let me know your opinyons!!!

thanks a million- H-T the place to save time, money and learn an absolute **** load.!!!!!!

 

You don't need backpressure for power.... Maybe for more torque at lower rpm. Look at the exhaust of F1 cars...

Just keep the diameter of your exhaust the same as the collector of your header (65 mm) and you'll be fine.

 

I don't think you need back pressure at all to make power. With less back pressure I would assume you could fill the cylinders with more clean air and fuel which would create more power. Correct me if i'm wrong.

 

makes 100% sense to me...

any of you guys notice gains from not running the cat????

 

I thought backpressure was a myth. Generally the less backpressure you have the more power you will gain. Could be wrong. Where's SMSP?

 

It is possible to have too big of an exhaust on a naturally aspirated car. Its not the loss of backpressure that is the problem though. Its the exhaust velocity that is important.
On turbo though, big and free flowing is what you want.

 

Backpressure = bad
exhaust gas velocity = good

you DONT want backpressure. However too large of an exhaust can slow
exhaust gas speeds down and make the system less efficient.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by George Knighton &raquo;</TD></TR><TR><TD CLASS="quote">It's hard to imagine a "dismal" power figure with the modifications you have, even though I don't know anything about turbos.</TD></TR></TABLE>

I can imagine it.
whats this talk of turbos??

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
Your exhaust is not so big that it would cause a problem with back pressure, although this could be affected by how they did your heads and what they expected you would be doing when they did the heads and valves.
</TD></TR></TABLE>

heads... lol

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jansenrw &raquo;</TD></TR><TR><TD CLASS="quote">
Now for the real Q. I got a custom made test-pipe or as you guys might call it b pipe to replace the cat!.

My engine setup is below. P.S&gt; am trying the no cat option tommorow with my race.. let me know your opinyons!!!
</TD></TR></TABLE>

Everyone call it a test-pipe. What kind of cat are you running now? stock cat? Do you have the JDM version of the Mugen header? Is the collector 65 mm OD?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sgT &raquo;</TD></TR><TR><TD CLASS="quote">Backpressure = bad
exhaust gas velocity = good

you DONT want backpressure. However too large of an exhaust can slow
exhaust gas speeds down and make the system less efficient. </TD></TR></TABLE>
What he said.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by George Knighton &raquo;</TD></TR><TR><TD CLASS="quote">
Why do we have a turbo timer if we don't have a turbo?</TD></TR></TABLE>

some offer a nice little A/F gauge with a correction factor , its still a 1 volt based system but its better than nothing...

also , I was thinking of picking one up so I can let my car run in the paddock for a preset amount of time and not have to stand there and wait for it to shut off...

make sense George ?

 

**** have to re-type over again..

first of all the turbo timer does give a/f.
2. my header I'm unsure about, will do exact measurements today. 3. track event is in 4 hours so prepping the car now..

as for my valves, they're spoon stuff so I assume they're same size just lightened.

As for my power figures, here in Aus i'm pushing 110kw atw... sad when i was hoping around the 200whp mark form research. thats about 150kw I think..

hmmm also I'm running penrite semi-synthetic oil (on trnasition to full) anyway its 10W 40 will let you know how it performs..

Jansen

 

oh I'm just running an apparent high flow cat... nothing special!!!!