briann510 Posted March 4, 2005 Share Posted March 4, 2005 These runs were done on a Mustang Dynamometer and NOT a Dynojet for those looking at the numbers only. Most people were expecting higher results achieved on a Dynojet machine but these numbers we got are usually a solid 15-20% less than a Dynojet dyno if you want to compare to other peoples results who used a dynojet. This facility is a couple blocks from our house and very convenient to go back often for testing after changes, so this will be it from here on out. when all is tuned and satisfied we will go find a Dynojet facility just to have both sets of numbers for the curious... these first runs were just to get a baseline and AFM numbers for jetting changes etc.. so for all you people that were looking for a Dynojet readout RWHP number just add approx 40 hp to get 258 RWHP on a Dynojet machine to compare. The jetting is went pig rich when the main jet comes in at 3K and we still have the bad stumble off idle we need to take care of. have another pig rich point at 4900 also and another rich at 6500. we did not try different timing changes this time out and just left it at 32 degrees total. we also want to make 2 runs back to back with air cleaners and with stacks only to see if that changes anything. we were going to do step testing for the a/f ratio monitoring but will hit that next go round after some carb tuning. this will be a good baseline to start with. current jetting is: 180 fuel jets 210 air jets 34mm chokes 55 idle jets 50 acc Our 73z with 3.2 stroker with pictures and videos Chassis dyno run video Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 4, 2005 Share Posted March 4, 2005 I think your pilots are too small and your mains are too big. I'd expect you'd end up with a mid 60's pilot and a 160 to 170 main fuel and a 180 to 190 main air. Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 4, 2005 Author Share Posted March 4, 2005 yes we know we are off in several places and thats exactly what the runs with the AF results are for. Luckily we can run on the dyno as much as we need to. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 4, 2005 Share Posted March 4, 2005 yes we know we are off in several places and thats exactly what the runs with the AF results are for. Luckily we can run on the dyno as much as we need to. Lucky you! Someday I'll find time and money simultaneously to check my #'s. Someday... The jetting is pretty pig rich when the main jet cuts in at 3K and we still have the bad stumble off idle we need to take care of. once the rpms get up to the power range the jetting isnt too far off for max power. This is your small pilot for sure. Quote Link to comment Share on other sites More sharing options...
Clifton Posted March 4, 2005 Share Posted March 4, 2005 Wow, that's pretty good for an N/A motor. Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 4, 2005 Author Share Posted March 4, 2005 ok, here were the carb settings on the dyno runs as i wasnt positive on them before when people were asking: 41mm chokes 210 air jets 175 fuel jets 67.5 idle jets 50 acc nozzles 50mm velocity stacks 32 degrees total timing what we need to address is the off idle stumble at anything more than half throttle. we of course have a under hood heat issuse we need to address which is part of the problem even though we run the cowl hood. we need to get more air to the carb side of the engine compartment. the cowl hood at speed is a stand off i belive and no air is going out the opening, not is any going in at speed. Tnaks all for your suggestionsand comments. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted March 4, 2005 Share Posted March 4, 2005 A smaller choke would help the stumble but would hurt the top end. I'm running 37's and still have a little stumble. I have 34's but don't want to sacrifice the top end to use them. At some point it boils down to trying to make a racing carb acceptable for the street. The Webers have a lot more parameters to adjust than the Mikunis, and you can get that part throttle driveability nailed down perfect. I've never known anyone with Mikunis that totally irradicated the stumble that you're struggling with, but they all said once you get the right pilots it all comes down to the choke size. Looks to me like you have the right pilots... Quote Link to comment Share on other sites More sharing options...
briann510 Posted March 4, 2005 Author Share Posted March 4, 2005 we just removed air cleaners just now and the stumble has pretty much dissapeared. we reserved all of next thursday afternoon for dyno time and have a whole assortment of jets until we get it right. gonna do step fuel curve testing and timing runs as well. it will get dialed in this next go round! Quote Link to comment Share on other sites More sharing options...
heavy85 Posted March 5, 2005 Share Posted March 5, 2005 we just removed air cleaners just now and the stumble has pretty much dissapeared. I once had a late 70's 550 honda motorcycle when I was a poor college kid. It needed a new air filter bad and I couldn't spend the, what seemed like at the time, rediculous cost for a new one (like $30 or $40 if I remember). So I just threw the old one away and thought - that'll make 'er run. Well all it did was created a bad stumble just off idle. So I got clever and decided to take an old tee-shirt doubled over and use that as an air filter. Well then it was a pig - just no power at all. So then round three I used only one layer of tee-shirt and it ran better than ever. I would have never believed it if I had not experienced it myself but no filter = bad stumble, two layers of tee-shift 'filter' = dog slow, one layer of tee shirt 'filter' = yee hah. I guess my point is engines can be very sensitive to what air filters you run. Cameron Quote Link to comment Share on other sites More sharing options...
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