Can somebody explain to me why the F40 in most videos shoots flames and backfires when the accelerator pedal is lifted. Clearly it has to do with turbocharging. Is the ECU dumping too much fuel ? Is it usually attributed to aftermarket straight exhaust and decat pipes ? Is there ECU tuning involved ? Thanks
I'll take a shot at this but am far from an expert. When I had my F40 in for service I talked with the mechanic about additional HP. He said that you could tune it for higher HP but that would entail enriching the air/fuel ratio in the throttle bodies and hence deleting the cats and going to straight pipes. I'm sure there is a lot more to it than that. But armed with that information, I think you need straight pipes and over enrichment to get the situation you are talking about. Again, just my guessing. Drew
When you lift the throttle on a Ferrari without pneumatic exhaust valves, you create a partial vacuum in the exhaust as the flow decreases. This causes an intake of fresh air, which ignites the relatively rich, hot mixture in the tailpipes. On most Ferraris with open tailpipes, this results in the mild popping that sounds so good on deceleration. On cars running a relatively rich mixture, this can result in flames out the exhaust pipes. On Ferraris with pneumatic exhaust valves, unless you are at very high revs, as soon as the throttle is lifted, the valves slam shut, keeping the popping to a minimum.
Here is my thought. Turbo car is moving more air because, turbo. That means it takes more fuel. Shut the throttle and the air is cut off but it take a time for the fuel to reduce. That fuel ends up in the exhaust and gets burned off when it hits the air at the end of the exhaust pipe. Old carb 308s are more prone to popping on declaration because they tend to have a rich mixture. I am sure you could tune a naturally aspirated car to "shoot flame" with enough fuel, it just won't run as well. I was told by a rep when I was at the dealership that the F40 was delayed on it's US delivery because the feds didn't like the flame out the back on decel. As a kid starting his dream job with exotic cars, I didn't really see the problem.
As a kid starting his dream job with exotic cars, I didn't really see the problem.[/QUOTE] I really like your reply. Good chuckle to start the weekend. Drew
I have had loads of cars that blow flame. Best story: I was in my 1978 930. I had hopped it up to 441HP (that was a big deal in year 2000) and was headed over to a pals house at 4AM one morning in route to a car event. It was pitch black as I cruised down a four lane supper highway alone. But as I crossed a ridge I saw a line of red taillights in the slow lane. I cruised up to the line nice & easy and took note that it was a pack of Camaros doing the same as me (heading to a car event no doubt). I rolled up past the last in line and continued along in the fast lane passing what seemed to be a dozen or so... Then I noted one of them pulled out of line & roared up to my tail. We both passed the front Camaro while in tandem and then he ziped along next to me. Now remember it was pitch black except for our headlights... Next I looked over and the Camaro guy sorta reved up his engine. So I dropped a gear & simply laid into the throttle then immediately let off. HUGE kernels of flame poured out of my custom dual exit pipe. The scene around us two lit up like a lightning strike. I looked over at the guy, then the Camaro backed out of his stance & pulled right back in line - assuming his prior position. I rolled on peacefully. Moral of the story... Flame is boss. Image Unavailable, Please Login