928 Engine death…..knock….answer. e85 – rennlist – porsche discussion forums electricity grid map uk


With lots of recent discussion about blown race 928 engines it makes me question fuel? E85 has an octane rating above 110 and is nearly impossible to knock. Sure your fuel system must flow around 30% more to support it, but given its cost is well under $3 per gallon and high octane race fuel is over 10 it seems like a viable option for racers, especially those running boosted 928’s

an example a friend has an Apha-N GTR with its twin turbo 3.8L v6. On street 91 it makes 870 awhp….on 100 octane race gas it makes 1040awhp….on e85 it makes 1135awhp…..nice 30% boost on e85 with zero worries about knock… i believe George’s ORR racer is above 500whp now…… not sure what fuel he runs, but 650whp on e85 surely will go faster….assuming his fuel cell holds enough to make it the distance…

i experienced knock on casper, running 91 octane Sunoco at 9-1 cr at 34’ timing around torque peak…..I thought it was a miss…..tried adding fuel…nope….once I got smart and turned spark down at torque peak it ran great….better than ever…..I just wonder how much damage I did while figuring it out…..the engine did run fine for a few more events.. live and learn I guess…. the stand alone ecu on Casper allows unlimited tuning of spark-fuel every 250rpm. Yes it runs crappy at idle and part throttle….but sings at wot

sure I don’t have a dog in this fight as I don’t own a race car now….but if I did I would seriously consider upgrading fuel system and running e85 just to eliminate a well documented failure issue….. e85 costs 70% less that race fuel, but you burn 30% more…well worth it i’d say…..even if your burn rate is 20-25 gallons per hour…..it’s cheap insurance…..Casper at 265whp burned around 10-12 per hour….at track prices of $8…let’s call that $100 per hour. The e85 much more powerful race is around $60 per hour…Casper power level would be at most 16 or $50 per hour.

In my opinion, pure street cars should run on pump gasoline in the US since that allows for convenient fill ups. Hobby cars should run on whatever the owner wants. Race cars should run on the fuel that makes the car fastest within the rules (or at least without getting caught).

In a knock limited 5L turbo car, E85 can be worth hundreds of hp over pump gas. The power advantage is not imaginary in a forced induction setting. Severely knock limited setups may get 1/3 more hp. For a normally aspirated car, the gains are much smaller (of the order if 10%) and there’s arguably more hardware changes required to get there than in a turbo car where you just change the wastegate settings, make sure that fuel system can flow enough, and that the spark has the energy to ignite the cold, wet charge. A lot of the other issues have to already be solved even for a US pump gas turbo car, because they blend in ethanol even to the regular pump gas here.

For a pure street car, I’d run ethanol if I’d live in Brazil. Cold start would not be a problem and fuel would be available everywhere. In the US Northeast, I wouldn’t want to us ethanol because it’s not generally available and cold start is a lot harder with ethanol. Running it very rich when cranking cold is great with gasoline, but doesn’t work that well with ethanol.