datsunan Posted July 15, 2005 Share Posted July 15, 2005 So I got my car dynoed today and I am not sure how to feel about what went down. My first dyno was with 91oct, 14.7 psi and timing at what was last set to 20deg. 2nd pull was with 100 oct 14.7 20deg. My 3rd pull I wanted to adjust my timing, what the hell its at like 13deg. I make the correction and increase boost to 16psi. Just as the motor hits max torq the engine revs like the clutch is slipping or the tires are spinning on the dyno. So we try it with two people sitting in the back and it does the same thing, multiple attemps same result. The say althought we don't smell your clutch we think it is slipping. So I take it out, 4th 5th full throttle up hill and no probem with slippage. I come back and they put a O5 corvette on the dyno to test it. No problem, put my car back on turn the boost back down to 14.7 and it pulls the best run yet 286hp and 336ft lbs, nice! So let me try one more time at 16psi, same result, something is giving and it aint my car. They give up and I am still not sure of the the magic #! Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 15, 2005 Share Posted July 15, 2005 What kind of dyno were you on? Really sounds like a slipping clutch though. Quote Link to comment Share on other sites More sharing options...
akeizm Posted July 16, 2005 Share Posted July 16, 2005 Prolly is slipping clutch. I got my car on the dyno (cars only done 500ks) and it would pull hard then slip. So we strapped it down and same thing. But we couldnt smell burning clutch. So it was my clutch. Still got to get it looked it....its a brand new button one too. Quote Link to comment Share on other sites More sharing options...
v8dats Posted July 16, 2005 Share Posted July 16, 2005 well that sucks nice numbers even tho u had problems hope that u get it all figured out. nice car too! Quote Link to comment Share on other sites More sharing options...
datsunan Posted July 16, 2005 Author Share Posted July 16, 2005 Akeizm does your clutch slip when you drive it hard on the street? Mine does'nt. I can't see why it would slip on the dyno and not on the street. I reeeeaally don't think its my clutch. Any who, here are my slips, Quote Link to comment Share on other sites More sharing options...
yo2001 Posted July 16, 2005 Share Posted July 16, 2005 I was messing with a dynojet last night and learned that if the car is strapped down too tight, it'll stress the clutch. I might be just the FWD thing but dyno always seems to over load the drivetrain. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 17, 2005 Share Posted July 17, 2005 If you have a slipping clutch, you WILL see a dip in the power delivery curve. See if JeffP posted his "slipping curve" anywhere. It is very distinctive. When I burnt my clutch up, the thing went, and on the next pull it was worse. It does not get better. Same with Jeff when his slipped. First there was a little smoke. Then a little more, so he called it off. Mine, it was up to speed, they loaded it and POOF! LOTS of smoke. Next run, loaded it and poof! Same thing---would not transmit more than 25HP without slipping. Dyno operator commented "Man, sorry about your clutch. I never seen aturbo come on THAT hard before!" LOL, yeah, thanks buddy! ;^) I don't see that "dip" in your curve. Use wider tires, and load the rear with bags of gravel or sand in the spare tire well. 3 to 400 # of ballast seems to let them hook pretty well. In Japan, it was not uncommon to have five guys hanging out the back of a car on the dyno to make the numbers come up! No liability lawyers there, apparently... Quote Link to comment Share on other sites More sharing options...
akeizm Posted July 17, 2005 Share Posted July 17, 2005 Ahhh ok. Yea mine slips on the street and on the dyno. Quote Link to comment Share on other sites More sharing options...
260DET Posted July 17, 2005 Share Posted July 17, 2005 Got a limited slip diff? If not with that power you need one, as you probably don't need me to tell you Make sure that the fuel tank is full, sticky tyres will help too. With that power its not unusual to get significant dyno roller slip, the back of the car may need to be tied down as well. Nice problem to have though, if the clutch is not at fault. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted July 17, 2005 Share Posted July 17, 2005 I put down 303ftlbs on a dynojet and there were no problems with the tires slipping And I don't have anything even close to sticky tires... $25 all season radials that were on special when I got them. So I'm thinking clutch. And you dont' always smell a clutch that's slipping badly. The clutch in my sentra se-R is on the way out bigtime, it slips VERY badly if I drive agressively, and I've never once smelled it. Quote Link to comment Share on other sites More sharing options...
datsunan Posted July 17, 2005 Author Share Posted July 17, 2005 The straps for this dyno had been burnt in half so we could not strap it down. They did allow me and my buddy to sit in the back 370 lbs. Still had the problem. I was told that they set a "ramp rate" befor the pulls begin, they don't set it when the car is pulling hard on boost so maybe the ramp rate needs to be different for a turbo with significant torq. Maybe the dyno over compensates when it sees the sudden rise in power? Any dyno opperator on this site? If not we need to train someone. I Think Bastaad has the most experience. I do have a lsd diff so its most likly not the tire slipping and my tires were suprisingly warm and sticky. Tony, these pulls I did not have the problem but the ones where I did showed the hp drop staight off. So some people have smelled there clutch burn and others have not, I wonder if it is dependant on the type of disc compound. I am running the Center Force II dual compound, anyone smelt this clutch burn? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 17, 2005 Share Posted July 17, 2005 Allright, you graph cleary shows that your clutch was not slipping. A dyno dynamics unit is sensitive enough to show 1 missed ignition event on 1 cylinder at any rpm. It will show a slipping clutch and there will be no doubt. Do you know what they used for ramp rate? If you can find out, do so. It should be somewhere between "150" and "175" for that car. Any lower than that and they are too low. ("150" = 15.0 km/h per second acceleration) Now, the big questions. Was the mounted in ground or above? Where the knurled rollers in front of, or behind the drive wheels? If they got lazy, or do a lot of FWD cars, they may have had your car on the dyno backwards. That's fine for lower power cars, but usually ~250rwhp is where you'd change over. Maybe they were lazy about it. That combined with the burnt straps (tell them to order new straps dammit, they are just asking for trouble) could have caused your wheel slippage. If the dyno/car is facing such a was that the knurled roller is in front of the drive wheels and not behind, you should be able to turn out 400+rwhp WITHOUT STRAPS on that dyno. Loading up the rear of the car is not necessary in any case if you have straps. Anyway, see if you can find those things out. My guess is they got lazy and put your car on backwards, with the knurled roller behind the drive wheel. (causing your car to unload the knurled roller under power, ever so slightly) That combined with the strap problem likely let your wheels spin a bit... Quote Link to comment Share on other sites More sharing options...
Michael Posted July 17, 2005 Share Posted July 17, 2005 Don't mean to get too far off-topic - but that huge rise in torque between 2400 and 4000 rpm - is that normal for turbocharged engines of this type? Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 17, 2005 Share Posted July 17, 2005 Don't mean to get too far off-topic - but that huge rise in torque between 2400 and 4000 rpm - is that normal for turbocharged engines of this type? Yup, corresponds nicely to the turbo spooling up and boost being made. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 17, 2005 Share Posted July 17, 2005 Don't mean to get too far off-topic - but that huge rise in torque between 2400 and 4000 rpm - is that normal for turbocharged engines of this type? Oh yeah, mine increases by 200 ft-lbs to 420 in under 1000 rpm. That's what a T3 turbine will do. Then it fades as it restricts flow. Quote Link to comment Share on other sites More sharing options...
datsunan Posted July 18, 2005 Author Share Posted July 18, 2005 Thanks Drax some good onfo there. I don't know what the knurled roler is but they do mostly Mustangs and mucle cars, they did not even want to do my car, they said they did not have a tuner for foreign cars, I told them I was going to tune it and they still would not do it till I went in person. Anyways, the rolers in the front had groves in it for traction so I think it was on right. It was an in ground dyno. You don't see any dip or slip on these sheets because they are done at 13.5 psi not 16 where the problems started, I don't have those #s so I can't post them but the hp dropped straight off right when I was hitting max torq. and boost was just hitting 14psi. I don't know what the ramp rate was but I think it was off, like I said they don't do may jap cars, or turbo's either, so they may not know to set it differently. I will try to find out what it was. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 18, 2005 Share Posted July 18, 2005 Ramp rate is chosen purely on power & torque output, to make the run last long enough to get some resolution on the readings, but short enough not to overstress or over heat the engine. If it is chosen incorrectly it likely won’t have negative results, unless it is way off base. If it was an in-ground install, and it’s a RWD shop, then I’d say your roller was likely in the right spot. (the knurled roller being the one with the grooves in it, which should be in front of the drive wheels) From what you describe it still sounds like a slipping clutch to me. It is possible to load the car more on the dyno than you could find on your average street which may be why you couldn’t duplicate the problem. The fact that it occurred at your torque peak would indicate a slipping clutch as well. What kind of clutch are you using? Quote Link to comment Share on other sites More sharing options...
TimZ Posted July 18, 2005 Share Posted July 18, 2005 ...they do mostly Mustangs and mucle cars' date=' they did not even want to do my car, they said they did not have a tuner for foreign cars, I told them I was going to tune it and they still would not do it till I went in person. I don't know what the ramp rate was but I think it was off, like I said they don't do may jap cars, or turbo's either, so they may not know to set it differently. I will try to find out what it was.[/quote'] This, combined with not having any straps and running and charging you for it anyway, makes me think these guys are maybe, I dunno, IDIOTS. Is there some reason you have to go to that shop? They can't be the only dyno shop in San Diego, can they? I guess I've never dynoed my car without having it securely strapped down. I don't think I'd even consider it - I would have thought it would be a safety issue without them - maybe not? Quote Link to comment Share on other sites More sharing options...
datsunan Posted July 18, 2005 Author Share Posted July 18, 2005 I'm running a center force II and did have a problem one night at the drags with it slipping in third gear, but that was last year and I have not had that happen since. I guess if the dyno is capable of producing more load than the road it could be my clutch. It only has like 2k on it, maybe with my new found power it is not enough anymore. What clutch would handle it? I have heard that the Act is very quick, hard and jerky when it engages. I use this as a semi daily driver and don't want a tough clutch, suggestion? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 18, 2005 Share Posted July 18, 2005 My Centerforce 2 only held until I started putting close to 300hp to the wheels. I have a ClutchMaster stage 4 unit now, and it holds the power. Unfortunately I hate the driveability, it chatters like mad in reverse, and it's ON-OFF, so it's smooth at WOT, but harsh anywhere else. It has ceramic pads and a sprung center. I've love to have a CF2 with a stiffer pressure plate, that might work ok... Quote Link to comment Share on other sites More sharing options...
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