zippy Posted September 1, 2005 Report Share Posted September 1, 2005 most buying a 408 don't care about the fuel, but it does make a difference. a huge difference over a blown application. espeically when considering a radix. a radix with a smaller pulley such as a 2.8-3.0 will produce boost around 37-42% of throttle. when i say boost i mean at that low of throttle you can see 5psi come in at around 1800rpm. the downside to this is that in everyday driving you tip into the power enrichment constantly. with a stock pulley on a radix this isn't as bad, but anybody driving one with a small pulley can tell you this. pulling out into traffic, passing, etc. just about all driving gets you into the power enrichment. this just doubles if you put a trailer behind that same truck. now you're into p.e. on a regular basis. the other downside is that without having a 2 bar map system, you have to feed the truck for your max boost. you set the p.e. to run what you want it at for say 9psi. well, at 4-5 psi if your'e just tipping into it, the computer has no idea what boost you're at. it see's it's max of about .7psi and runs the same v.e. and p.e. table from there on up. this means that you spray an a/f ratio of around 9:1 on that same setup at say 50% throttle when you aren't even into it that hard. at it's peak boost that same fuel spray is around an a/f of 11.7:1 or so (depending on how you have it set). if you tow at all with that same truck your goal then would be to pull without getting into boost using say a 2.8 pulley. good luck with that. the 408 doesn't need to go into power enrichment until considerably later. stock setting is 90% and i have matts at 75%. i could easily run it at 90%. this is where the main difference is between a well modified radix truck for example and a truck that simply has more cubes. with more cubes you can pull that trailer up a hill at 60% throttle at 14.7:1 afr and just keep pulling like it's nothing. the radix truck would come into boost, go to power enrichment and pull like it's nothing not requiring a downshift either. whether you've went to 5psi or 9psi though, you still spray heavy on the fuel at what would be around 10:1 or so. this same thing happens around town driving and highway. next time you're out crusing around anyone, think of how often you've went past 40% throttle. if you can log, take your average drive and see how many times you go past 40% throttle. i can tell you have have two trucks up here, one that we just pulled the radix off and matts with the 408. in everyday occasional heavy driving the 408 kills the radix in fuel economy. if you were to drive them both at 35% throttle and less, i'm not sure which could get better milage except that the 408 doesn't have to spin the blower as an extra accessory. the 6.0L doesn't have to feed the cubes. the fuel saved with the 408 is all in how often you go into power enrichment, no two ways around it. it has nothing to do with it being a 408. since the subject has come up, one other thing to add about the 408 VS. radix. just for the point of it i made 3 passes back to back to back with nobody in line at the last dragstrip outing. all 3 passes were within one tenth, yes .1 of my best pass. try that running a radix with a small pulley. they get heat soaked running on the street let alone wide open passes back to back. Quote Link to comment Share on other sites More sharing options...
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