Engine back firing

pablo · Post by **pablo** » Tue Sep 09, 2008 5:08 pm

Need to understand what went wrong.

The old engine in our car started to backfire and spit flames out the exhaust at around 4500rpm, it came on boost at 3500rpm. We thought at first that the plugs were knackered but after changibg them it still did it. Also if you revved it whilst stationary it was picking up 5psi of boost.

Any ideas as to what may have happened would be very useful as we are thinking about building another one next year to be Alan's daily drive / occasional track day.

duncan · Post by **duncan** » Tue Sep 09, 2008 5:13 pm

Do you monitor EGT / fuel mixture?

pablo · Post by **pablo** » Tue Sep 09, 2008 5:19 pm

No we didn't :oops:

Gerry H · Post by **Gerry H** » Tue Sep 09, 2008 7:42 pm

Was also thinking of over fuelling.

pablo · Post by **pablo** » Wed Sep 10, 2008 6:15 am

cheers guys now what would cause the car to pick up 5psi of boost whilst revved stationary.

duncan · Post by **duncan** » Wed Sep 10, 2008 6:36 am

Mine gains boost when stationery Pablo when I sit with LC on.

Gets to just under 1 bar

Gerry H · Post by **Gerry H** » Wed Sep 10, 2008 7:09 am

pablo wrote:cheers guys now what would cause the car to pick up 5psi of boost whilst revved stationary.

Unburnt fuel burning in the exhaust manifold.

pablo · Post by **pablo** » Wed Sep 10, 2008 4:57 pm

Thanks gents that answers some nagging questions.

tomcat · Post by **tomcat** » Wed Sep 17, 2008 2:08 pm

I had a lot of misfiring problems when I went over 16psi boost.
I tried everything to solve it -fueling,new coil, leads,plugs etc.
solved it in the end by reducing my plug gaps from 0.8mm -> 0.7mm
Not 100% ideal, but without replacing my stock ignition, I think the only solution.

pablo · Post by **pablo** » Wed Sep 17, 2008 3:50 pm

Thanks Scott... we did that and it did allow the car to rev higher by about another 750 rpm. That and a drying track meant that Alan was able to knock 20 secs. off his lap time