Tony Posted October 14, 2006 Report Share Posted October 14, 2006 An inquisitive question if anyone can help..... All the cars have the same engine profile (V8) and i assume they are all under the same fuel octane/mixture regulations so i wonder this? As the train of some 20 cars decelerate for the bend why is it that only some have flames coming out of the exhaust There are only milliseconds between them so the breaking/throttle reactions must be mirror images.. I am curious why only some cars display this since the conditioning is the same Quote Link to comment Share on other sites More sharing options...
Mark H. Posted October 14, 2006 Report Share Posted October 14, 2006 Perhaps its down to the drivers driving style and something that some do and some dont. Or perhaps some run higher fuel pressure and perhaps run richer. Quote Link to comment Share on other sites More sharing options...
discount tyres dan Posted October 14, 2006 Report Share Posted October 14, 2006 yeah i know they have adjustable mixture settings in the car, so i recon if they are running richer they would get more of a flame Quote Link to comment Share on other sites More sharing options...
Bazza Posted October 14, 2006 Report Share Posted October 14, 2006 they got the chavtastic flamer kits Quote Link to comment Share on other sites More sharing options...
Tony Posted October 14, 2006 Author Report Share Posted October 14, 2006 they got the chavtastic flamer kits 'Chavtastic' Quote Link to comment Share on other sites More sharing options...
TDIPLC Posted October 15, 2006 Report Share Posted October 15, 2006 The flames are caused by unburnt fuel in the exhaust system. This can be a consequence of some forms of anti lag systems (on turbocharged cars), or uncalibrated deceleration fuel cut off. Most race car owners have completely different priorities regarding engine management calibration. They are normally only concerned about WOT (wide open throttle) calibration, whereas road cars need to be optimised for all conditions. Personally I like to see race cars calibrated for all conditions too as this helps with getting off the line and any sort of transient acceleration. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 15, 2006 Author Report Share Posted October 15, 2006 Personally I like to see race cars calibrated for all conditions too as this helps with getting off the line and any sort of transient acceleration. Now i am bothered? Why don't they follow this sort of understanding if it's so obvious? If the calibration assists off the line and forms part of the transient acceleration then why allow the car to be over-fueling on deceleration, it doesnt make sense..... This must leave a void in the engine mapping, violating the overall result?.... is it that obvious or am i missing a verse somewhere Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 15, 2006 Report Share Posted October 15, 2006 Because its not that important. Yes in an ideal world the thing would be fully mapped, but other things doubtless take priority. Ask yourself this, why do all these race teams turn up at a circuit then seemingly rebuild/assemble their car. Why not do it before you arrive in a nice workshop? Or arrive at a 24 hour race with no headlights, then spend most of the day fabricating a lamp bar? It gets dark most nights! I'm new to track support, but we unloaded the car we had repaired and prepped, prior to its race, stuck the numbers on, checked the fluids (again) then looked around and wondered what we were failing to do! Still came second in class. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 15, 2006 Author Report Share Posted October 15, 2006 Because its not that important. Yes in an ideal world the thing would be fully mapped, but other things doubtless take priority. Ask yourself this, why do all these race teams turn up at a circuit then seemingly rebuild/assemble their car. Why not do it before you arrive in a nice workshop? Or arrive at a 24 hour race with no headlights, then spend most of the day fabricating a lamp bar? It gets dark most nights! I'm new to track support, but we unloaded the car we had repaired and prepped, prior to its race, stuck the numbers on, checked the fluids (again) then looked around and wondered what we were failing to do! Still came second in class. Your answer belays the question. tdiplc has suggested a reason and this reply confuses me.... Your new track support reply also confuses me? The fully mapped remark surely is vital toward the overall track position (over or under fuelling) Team preparation prior to any event is irrelevant to this thread, although vital on the actual race. I feel the visible question regarding fueling is valid since there are obvious discrepancies between cars and set-ups, so far i don't feel totally satisfied with the answers..... To understand more sometimes the reply needs to be examined further Anyway what does this 'second in class' mean? Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 15, 2006 Report Share Posted October 15, 2006 The control of fuelling on the overrun is not that critical. If its overfuelling, then largely its just a waste of fuel. On your road car no fuel will be entering the engine at all during overun with the throttle totally off. The reason i reference the track support/prep issue, is it seems clear to me that many cars that are racing are far from fully prepared. In other words they have run out of time, money, skill etc to fully complete the task. If you are pushed for any of these, then tuning your engine under full throttle takes precedence over its behaviour in the overun. It also removes the need to concern yourself with the transition from zero fuel back to fuelling when the driver commands power. As tdi say, it has potential to be an advantage, but releatively small in the overall objective. The car we were supporting had totally inadequate alignment set up, but the focus had been totally engine based until now as that was the area demanding the most attention. Second in class, refers to where several different classes race in the same race, in this case the Porsche open. Overall it was 15th or similar, but the the other classes operate different criteria such as greater power. Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 15, 2006 Report Share Posted October 15, 2006 Your answer belays the question. tdiplc has suggested a reason and this reply confuses me.... Your new track support reply also confuses me? The fully mapped remark surely is vital toward the overall track position (over or under fuelling) Team preparation prior to any event is irrelevant to this thread, although vital on the actual race. If i can add further, the reason IS team preparation. If they all had unlimited time, money, skill etc, all the cars would be optimized to the same level. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 17, 2006 Report Share Posted October 17, 2006 For what it's worth guys I was with a group of other engine tuners recently and a similar question came up. It turns out it's quite deliberate and actually all about combustion chamber cooling. Bearing in mind that the only reason to run any air fuel ratio's richer than stoichiometric (14.4:1) is to use the excess fuel as a thermal managment media these guys are simply choosing to run a very rich afr during very low intake manifold pressures (only reachable in throttle closed over run) the aim is to cool down the piston crowns and exhaust valves. It's apparently thought to enhance reliabilty over a race distance but some very experienced and highly respected people there that day think it's totally un-founded and a simple case of monkey see monkey do around the V8 supercar paddock Quote Link to comment Share on other sites More sharing options...
Mark H. Posted October 17, 2006 Report Share Posted October 17, 2006 I wondered if it may be for cooling, as you generally wouldn't burn extra fuel and thus have extra fuel weight on board for no reason. I'm pretty sure someone said the 1/2jz-gte engines are set to run rich by 5-10% at times to help keep them cool. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted October 17, 2006 Report Share Posted October 17, 2006 I wondered if it may be for cooling, as you generally wouldn't burn extra fuel and thus have extra fuel weight on board for no reason. I'm pretty sure someone said the 1/2jz-gte engines are set to run rich by 5-10% at times to help keep them cool. It's true of almost all engines actually, once you move to air fuel ratio's richer than 14.4:1 any extra fuel particals will find no oxygen to combine with so they go through unburn't... Most modern engines can tolerate stoichiometric ratio (14.4:1) up until around 50-75% load. During the last 50-25% of the throttle pedel engines generally need the air/fuel ratio to richen too approx 12:1 (varys alot from engine to engine) at full load, the additional fuel is added purely as upper cylinder coolant. This V8 supercar phenom of "lift off over fueling" is just an extention on that theme Quote Link to comment Share on other sites More sharing options...
Roger440 Posted October 17, 2006 Report Share Posted October 17, 2006 Agree with the cooling theroy. GM use this technique on the stock engine map on the cars we do when air intake temps get very high. Not convinced of the benefits though. Quote Link to comment Share on other sites More sharing options...
IS1000 Posted November 18, 2007 Report Share Posted November 18, 2007 For what it's worth guys I was with a group of other engine tuners recently and a similar question came up. It turns out it's quite deliberate and actually all about combustion chamber cooling. Bearing in mind that the only reason to run any air fuel ratio's richer than stoichiometric (14.4:1) is to use the excess fuel as a thermal managment media these guys are simply choosing to run a very rich afr during very low intake manifold pressures (only reachable in throttle closed over run) the aim is to cool down the piston crowns and exhaust valves. It's apparently thought to enhance reliabilty over a race distance but some very experienced and highly respected people there that day think it's totally un-founded and a simple case of monkey see monkey do around the V8 supercar paddock Stoich is actually 14.7:1. They run rich to prevent detonation which is needed in their high comps motors. Quote Link to comment Share on other sites More sharing options...
Sam@TDi Posted November 19, 2007 Report Share Posted November 19, 2007 Yep your correct on both counts, good spot on the 14.7 When I talk about thermal management please don't think I mean engine temperature. What I was getting at was the influence that rich afr's have on controlling the combustion process through it's initial slow burn phase. Which as you correctly point out is crucial to controlling the combustion speed and therefore keeping detonation at bay. Quote Link to comment Share on other sites More sharing options...
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