Problem: Backfire

JSE · Postby **JSE** » Fri Apr 20, 2007 11:50 am

My car seems to be backfiring a lot. Not massive ones but definately loud enough for others to hear. What is the problem? Bad batch of fuel? I did fill up with 91ron for the first time ever (usually use 98 bp ultimate). any other things that could be causing this?

GP · Postby GP » Fri Apr 20, 2007 1:09 pm

91 isnt the best for your car always.

That's strange, It's such a low compression engine 91 should suit it fine. Mine runs sweet on it

davamb · Postby **davamb** » Fri Apr 20, 2007 4:16 pm

GP wrote:That's strange, It's such a low compression engine 91 should suit it fine. Mine runs sweet on it

Really? What's the CR for the NA6?

JSE · Postby **JSE** » Fri Apr 20, 2007 4:19 pm

it happens alot when the tank is almost empty. I run 98ron always, this is the first time i have fille dup with 91. The timing is advanced to 14 also.

Sheck · Postby **Sheck** » Fri Apr 20, 2007 5:29 pm

the lower the RON the better it burns, the reason you make more power with a higher RON rated petrol is because of its lower combustibility (also longer burn time) which lets you run more boost and/or more timing before detonation sets in. ie it wont detonate as early because its harder to burn.

Also from what i've heard most backfires are due to leaning out, not too much fuel. I think you need to have megga amounts of fuel to get a backfire and when it goes it will be bloddy loud!!! and make a nice looking flame

Dave

GP · Postby GP » Fri Apr 20, 2007 5:35 pm

Really? What's the CR for the NA6?

I'm sure my manual states that it's 8.5-1 but a google search returns 9.4-1. Confused

Sheck · Postby **Sheck** » Fri Apr 20, 2007 5:43 pm

8.5 would be the B6T 9.4 is the Na6 manual 9.0 is the Na6 auto.
:mrgreen:

zoomzoom · Postby **zoomzoom** » Sun Apr 22, 2007 12:34 am

Sheck wrote:the lower the RON the better it burns, the reason you make more power with a higher RON rated petrol is because of its lower combustibility (also longer burn time) which lets you run more boost and/or more timing before detonation sets in. ie it wont detonate as early because its harder to burn.

Also from what i've heard most backfires are due to leaning out, not too much fuel. I think you need to have megga amounts of fuel to get a backfire and when it goes it will be bloddy loud!!! and make a nice looking flame

Dave

Sounds spot on to me mate, the higher octane burns slower and is less combustable, and being such low comp for an NA engine the 91 should be fine, the only advantage of the higher octane fuel is it allows you to run more timing, so for the love of your mazda, if you advance your timing, DONT USE 91 OCTANE!!!