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Discussion Starter · #1 ·
Made my own exhaust by cut of all the original mufflers and re use the piping welded together with 2" universal muflers
The rear muffler are made by welding together a splitpipe and using 2 paralell 2" mufflers with 3" DTM style tips
The sound are great a low rumble at low rpm rising to a damped roar at 4000rpm over 4000rpm the sound turns to clean higth tune.
But i have some conserns i`m suspecting the backpressure are to low since it comes out a lot of soot. Infact the DTM tips whos directs the exhaust slictly upwards causes the rear end of my car to get coated with a thin layer of soot
and at a time i had apart the front mufler from the front pipe i found some black goo in the joint i belive it are caused by the low backpressure allowing air/gas to reach the exhaust manifoild before the exhaustvalves closing
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88 626 sedan 2,0i 16v
ZKW ligthgrille
Hella fogligts
7,5x16 alu rims with Michelin MXM 205/55-16 tyres
Alpine head and signalprossessors
Rockford subs and mid
Macroom highs
3 rockford 4 channel amps
 

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Maybe your engine is running too rich? How is your 02 sensor?
 

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Discussion Starter · #3 ·
No o2 sensor

My Co2 are 1.2% the service manual says 1-2%
Do you mean the lamdasond when you refer to the o2 sensor
in that case i can tell you the 88 model of the FE3 engine
has no lamdasond and no cat(thank god).
of course the problem Can be worn valve seals or pistonrings (mileage 340000 km)but i havent seen this before i buildt this exhaust system
 
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low back pressure

Trust me unless your running 3.5" straight pipes with no restrictions back from huge exhaust manifolds and downpipes we will never see the daylight of low back pressure problems arising. And even in this drastic a case it's the fuel system, air/fuel mixtures, sensing and timing that needs to be addressed. It's all a question of balance and pro-tuning. Is it just me or has there been a lot of talk about low back pressure problems. It's a myth I swear. Balance the in and out of air and burning of fuel matched with timing and as long as your engines compression is good and not burning oil there should be no problem.
I have this funny story, I had a rough transition in my AT from 1st to 2nd, and I for sure thought I had transmission gremlins at work. I took my car too a few professional transmission mechanics which said I had to have it rebuilt or replaced, or atleast nothing could be done with out opening it up. Turns out it was a bad motor mount that was throwing the whole transmission-engine alignment off and putting pressures in abnormal areas of the trans and body. Crazy I tell you.
 
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exhaust

Why would anything unburned make it through the exhaust valves if timing is tuned correctly, or else compression is exceedingly high for the engines internals and under the circumstances. By then you'll need an upgraded computer and a reground camshaft. I don't know maybe I'm just a little mixed up in the head. good stuff though!
 

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Discussion Starter · #10 ·
Re: exhaust

My teory:
The cams has some degres overlap on intake and exhaust valves.Result when the when the exhaust phase are finished the exhaustvalve are open a little bit into the intake phase. Another faktor my be the VICS intake system (some kind of inertia loading system)who can create a low boost in the intake. the third factor are the scavenging effect of my home made exhaust system.

Summary:
The speed of the air sucking in to the sylinders has create a small amount of boost in the VICS intake.When the intake valve opens the air are rushing in to the cylinder,since the exhaust valve still are open some of the air/gas mix will be sucked out in the exhaust manifoild by the vacum created by the exhaust system`s scawenging effect.
Some of the gases burns in the manifoild creating soot and when i shut down the engine some of the reminding gases condense in the exhaust system,who when it cools causing the black goo, whos probably a mix of water, fuel and soot.
If my exhaust system had a higher back pressure it would force the gases back into the cyl causing a higher filling ratio and no soot or goo. Any comments?
 

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Thats impressive!

In fact there IS a considerable overlap in the valve timing. Your theory seems to make sense. VICS stands for variable inertia charging system... it IS an inertia based cylinder filling system. It forces air through a longer intake runner so that the inertia of the air flowing through the runner helps charge the cylinder at lower RPMs... then when the RPMs are really high, (above 4000 or something) then they shorter runners open up as well to help reduce intake restriction.

This is off-topic, but I think that this head is great for turbo-charging when you think about it... at low RPMs the turbo turbine is spinning slowly and the wastegate is closed completely, therefore manifold pressure is relativly restriced from leaving out the tailpipe end freely. So if you 'floor' the car, there is no exh. scavenging due to the closed wastegate and slow spinning turbine, then as RPMs rise so does the turbine speed and the wastegate begins to open, thus reducing high RPM restrictions in the exhaust while the VICS also allows a more direct route for boost to reach the cylinders... and with the overlap, the engine can breathe REALLY freely because the boost will help clear spent gasses while providing the turbine with a maximized amount of exhaust for spool-up.

I could be missing somethig.. so let me know if I'v said something erroneous!!

[Edited by mazda-head on 03-04-2001 at 05:58 AM]
 

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Discussion Starter · #12 ·
Make sense

Everything you wrote make sense to me.I`ve thinkin the exhaustsysrem are perfect for turbocharging to ,but now when aim still running N/A it seems like this causes loss of power,fuel economy and of cause its pretty anoying to have my rear end (the cars not mine) cowered with soot shortley after spending 10$ in a washing place

[Edited by FE3T on 03-05-2001 at 06:25 PM]
 
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