I have been noticing what seems to be backfire sounds coming from the exhaust and I was wondering if there was more then one reason for this. I know that running rich will be a cause for backfires but can ignition advance or camshafts overlap also be possible causes (or something else).
I seems to happen mostly when upshifting from 6000+ rpm or when I am at 6000+ rpm and lifting the gas pedals for a few seconds. The exhaust will "puff" two or three times and then everything will be fine.
It sounds very "cool" ( I think I am to old to use this word) but is this the best set-up performance wise.

Thanks for any advise

 

I thought backfire happens on the intake side....

 

Well my definition of backfire is the ignition of unburned gas mixture in the exhaust system. If this is not correct please put me back on the right track

 

I`m not sure if you mean backfiring..

I would describe the sound of my exhaust this way:

low rpm and leaving off the gas pedal causes a deep "blubb, blubb, blubb" a few times....

And a kind of "bang" when vtec kicks in under full throttle. Just like opening a bottle of champaign......

 

Officially, backfire happens in the intake manifold or airbox when unburned mixture is ignited by the sparkplug while the intake valve is not fully closed.

http://www.raetech.com/Manifold/manifold%20test.pdf


[Modified by DutchITR1689, 4:19 PM 7/16/2002]

 

I don't think it is anything as drastic as the intake manifold backfire described on that page.

I beleive it is more the deep "blubb, blubb, blubb" elequantly described by ITR1858 ( ) that I am noticing. But there is no loud bang under hard acceleration ot when vtec kicks in. The "blubb"is only when I upshift at high rpm.


[Modified by JPP, 10:59 AM 7/16/2002]

 

The bang is caused by the x-over of my cams......

But why does the exhaust "blubb" ?? I never wondered...

 

Due to big cam overlap the exhaust gasses will pull a part of the intake gasses out of the cylinders and that intake mixture will burn in the header. I don't know the name for this effect, maybe it's callled exhaust backfire?

 

If it's a mild "popping" rather than a violent backfire, I'd say that's perfectly normal and is a result of a relatively high-flowing exhaust.

 

when i shift at around that rpm...my car will make a little popping noise..thats due to not having a cat and running a test pipe i love the sound too.......

 

as soon as I put my new exhaust on, I got lots of popping, burping, and burbling. It happens to most any car. If it really bothers you, get a fuel controller and tune the burbling out.

 

Thank for all the replies. If it is only a consequence of big cams and high flow exhaust and no arm can come from it, then I will keep enjoying the rumbling sound.

 

called "overscavenging".

JP is it because of the cam gear settings we did at Yoshio's or did you try the settings that made a bit more torque?

 

Wow! That took some time...

 

BTW it is very difficult to overscavenge on N/A cars as you can see from the Pressure values in the intake port , chamber, and exhaust port at cam overlap:



I'm guessing that you are running rich from Yoshio's habit of running extra rich on his programs and some extra unburnt fuel is going in the exhaust.

I wish Stephen could have joined us up in Toronto at Yoshio's so we could hear is approach. I suspect he runs much leaner than Yoshio. On Yoshio's computer, the injector duty cycle loop tables showed us the duty cycles as the rpms climbed and Yoshio was hesitant to lean out further at higher rpms. Any comments on this would be much appreciated by people who know their Hondata or EMS tuning....

 

been kinda busy....a B18C rebuild and a 3 day course at the Bridgestone Racing School in Reynard F2000 formula cars at Mosport have kept me "occupied" these days.....gotta love my Home Depot tear away strips with the blue EZ peel masking tape used by painters as my pull tabs..LOL







[Modified by Michael Delaney, 12:11 PM 8/5/2002]