hanging rpm on dyno
05-11-2014, 11:33 PM
#1
hanging rpm on dyno I finally got the car on the dyno last month and for the most part went fairly well considering it was basically a shake down for a long drawn out build.
I am trying to track down some specifics and I'll do my best to get details from the tuner. Car is running strong minus the rpm "brick wall" on the dyno at 5800 rpms.
Build is as follows:
lme 408
trickflow 6 bolt 235's w/springs spec'd for .700 lift don't have open and closed seat pressures
235/231 621/609 115
twin tc 72's
dual exhaust w/cutouts on the downpipes
jakes perf 4l80e w/ 3200 billet stall single 10.5" lockup
stock ignition w/ tr8's gapped to .028
91 octane (I have methanol injection but it wasn't used on the dyno runs that day)
Car made 746hp and 726ftlbs on 10lbs pulling to 5800 rpm (I'll have to double check dyno numbers on the sheet in the morning)
There was no noticeable breakup on the top end of the rpm range so I doubt that it would be valve float. The engine is just basically broke in and dynoed so the springs are fresh. The car would rev strong up to that point, but would not rev any higher. It would just stay at 5800rpm basically. We are dynoing on a mustang dyno loaded. We dynoed with it unloaded but it didn't really change. Fuel system is up to snuff with -10 feed and -8 return with 90lb fic's with 4303 magnafuel Fuel pressure set at 60 with boost reference of course. What do you guys think it could be? I'll try and post up a short video of a run to show what it sounds like. I'll have to check with my tuner to see if he has any logs saved on the run. Kinda lost at this point. We've come up with 2 possibilities. a. speedo tables need to be scaled so the speedometer is reading double speed and we could possibly be hitting the speed limiter in the stock parameters or b. he thought we might be running through the converter. I question the converter thought since there isn't an rpm rise. It stalls at 5800 rpm. If the converter wasn't holding (locked) it would act like a slipping clutch since that is essentially what would be going on correct? I also question the speed limiter because while I'm driving it on the "racetrack" I hit that speed limiter and it knocks everything down immediately so I wouldn't think that it would just hold the rpms on the dyno. Any educated input would be appreciated. Thanks Chris
I am trying to track down some specifics and I'll do my best to get details from the tuner. Car is running strong minus the rpm "brick wall" on the dyno at 5800 rpms.
Build is as follows:
lme 408
trickflow 6 bolt 235's w/springs spec'd for .700 lift don't have open and closed seat pressures
235/231 621/609 115
twin tc 72's
dual exhaust w/cutouts on the downpipes
jakes perf 4l80e w/ 3200 billet stall single 10.5" lockup
stock ignition w/ tr8's gapped to .028
91 octane (I have methanol injection but it wasn't used on the dyno runs that day)
Car made 746hp and 726ftlbs on 10lbs pulling to 5800 rpm (I'll have to double check dyno numbers on the sheet in the morning)
There was no noticeable breakup on the top end of the rpm range so I doubt that it would be valve float. The engine is just basically broke in and dynoed so the springs are fresh. The car would rev strong up to that point, but would not rev any higher. It would just stay at 5800rpm basically. We are dynoing on a mustang dyno loaded. We dynoed with it unloaded but it didn't really change. Fuel system is up to snuff with -10 feed and -8 return with 90lb fic's with 4303 magnafuel Fuel pressure set at 60 with boost reference of course. What do you guys think it could be? I'll try and post up a short video of a run to show what it sounds like. I'll have to check with my tuner to see if he has any logs saved on the run. Kinda lost at this point. We've come up with 2 possibilities. a. speedo tables need to be scaled so the speedometer is reading double speed and we could possibly be hitting the speed limiter in the stock parameters or b. he thought we might be running through the converter. I question the converter thought since there isn't an rpm rise. It stalls at 5800 rpm. If the converter wasn't holding (locked) it would act like a slipping clutch since that is essentially what would be going on correct? I also question the speed limiter because while I'm driving it on the "racetrack" I hit that speed limiter and it knocks everything down immediately so I wouldn't think that it would just hold the rpms on the dyno. Any educated input would be appreciated. Thanks Chris
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05-15-2014, 12:36 AM
#8
It shouldn't flash if it's locked up though should it? Haven't got a lot of experience with a stalled car. This is actually my first stalled automatic. Could you explain how the car acts when the converter is flashing past it's stall speed?
05-15-2014, 09:02 PM
#10
My car was doing the exact same thing on a dynapak dyno, the shop told me it was my intercooler setup becoming a restriction up top in the rpm band, rpm lvl 7 4l65e with a yank 3400, i now switched to a large frontmount so we'll see what happens now...
05-15-2014, 11:47 PM
#11
Dang, I hope that isn't the case. I have a vertical flow intercooler so I would think that be efficient enough. This is like a "stop it in it's tracks brick wall." If it is getting restricted it should probably still rev to redline though. It won't make the hp that I would expect but the engine is still getting air.