dyno insight
Thread Starter
Burning Brakes
Joined: Aug 2004
Posts: 849
Likes: 1
From: Dallas TX
dyno insight
hey guys,
i need some help figuring out the dips in the tq and power curve of my dyno graphs. run 6 is a motor pull which does not show any dips. however, when i spray a 100 shot on run 8 there are two noticable dips in the curves. anybody care to explain what causes the dips?
fyi, bottle pressure was approx. 1100 psi, bottle had a fresh fill, plugs are tr6's gapped at .035, it is a single nozzle nx setup. the car was tuned at speed inc. and the dyno results were almost identical. the graphs had spikes and dips. the funny part is when you graph against speed instead of rpm the graph is totally smooth. i looked at the plugs after the pulls and they looked great. no sign of fouling at all.
graph located at
http://www.casadenico.net/gallery/vi...80&id=untitled
i need some help figuring out the dips in the tq and power curve of my dyno graphs. run 6 is a motor pull which does not show any dips. however, when i spray a 100 shot on run 8 there are two noticable dips in the curves. anybody care to explain what causes the dips?
fyi, bottle pressure was approx. 1100 psi, bottle had a fresh fill, plugs are tr6's gapped at .035, it is a single nozzle nx setup. the car was tuned at speed inc. and the dyno results were almost identical. the graphs had spikes and dips. the funny part is when you graph against speed instead of rpm the graph is totally smooth. i looked at the plugs after the pulls and they looked great. no sign of fouling at all.
graph located at
http://www.casadenico.net/gallery/vi...80&id=untitled
Racer
Joined: Aug 2003
Posts: 304
Likes: 2
From: North Vancouver BC
Are you running a FPSS (fuel pressure safety switch?) You might be hitting the fuel pressure threshold that the switch is set to on all 3 dips. If you are running this item, you could try bypassing it for a run (you can let off early at 5500 RPM to be "safer" at the top end).
Thread Starter
Burning Brakes
Joined: Aug 2004
Posts: 849
Likes: 1
From: Dallas TX
yes i do run a fpss. that's definately a thought. also forgot to mention i've got a msd digital window switch. one of the runs the spray did not cut off at the correct rpm. i guess that could point towards a misfire if the misfire occured at the cut off rpm?? if it is a misfire, wouldn't it show up on the motor pulls as well? neither motor pull shows the dip like the spray pulls.
another wierd occurance is, if i open the run files in winpep 7 which is downloadable on dynojets website, the graphs are very choppy. there is approx. 1000 rpm cut outs where the dips are on these graphs. the graphs posted are displayed using runviewer. this is driving me
also, last year before the cam, i was picking up 139 ft/lbs on the same 100 shot on the same dyno. this year after the cam i'm picking up 113 ft/lbs on the same 100 shot. are the dips in the tq curve causing the overall number to be lower this year? i think tq is a calculated figure on dyno jets right??
another wierd occurance is, if i open the run files in winpep 7 which is downloadable on dynojets website, the graphs are very choppy. there is approx. 1000 rpm cut outs where the dips are on these graphs. the graphs posted are displayed using runviewer. this is driving me
also, last year before the cam, i was picking up 139 ft/lbs on the same 100 shot on the same dyno. this year after the cam i'm picking up 113 ft/lbs on the same 100 shot. are the dips in the tq curve causing the overall number to be lower this year? i think tq is a calculated figure on dyno jets right??
Last edited by creighton; Jul 24, 2006 at 07:37 PM.
Racer
Joined: Aug 2003
Posts: 304
Likes: 2
From: North Vancouver BC
I bet it's your FPSS then... I had similar dips in my nitrous setup. Fuel pressure in our cars is very sensitive to changes in fuel delivery rate due to the returnless style system. You can either calibrate the FPSS to cut at a lower pressure threshold (which reduces its intended effectiveness), or remove it entirely from the system after ensuring your fuel pressure is consistent and tuned for.
Collections Hold
Joined: May 2003
Posts: 3,520
Likes: 2
From: Tacoma WA
Tire slipping on the rollers. Look at the corresponding dips in your fuel. going rich from less demand on the rails for a sec. That's my speculative guess, as I had a similar problem when 2nd stage kicked in.
Robert
Robert
Thread Starter
Burning Brakes
Joined: Aug 2004
Posts: 849
Likes: 1
From: Dallas TX
i will turn the fpss down a little and see how it feels. i don't want to take it out of the system completely. i've never really calibrated it real well. i've keyed on and used a voltmeter to check continuity while turning the screw. once i lost continuity i backed it off about 1/4 to 3/8 of a turn.
i'm not positive but shouldn't i be making more power before having wheel spin issues on the dyno?? maybe i just need to put a 2 step on and lessen the initial hit
i have noticed though, if i cruise at a low rpm (ie 5th or 6th 12-1500 rpm) when i give it an initial punch it seems like the car has a bog or mis down low.
i'm not positive but shouldn't i be making more power before having wheel spin issues on the dyno?? maybe i just need to put a 2 step on and lessen the initial hit
i have noticed though, if i cruise at a low rpm (ie 5th or 6th 12-1500 rpm) when i give it an initial punch it seems like the car has a bog or mis down low.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Former Vendor
Joined: Oct 2004
Posts: 2,592
Likes: 0
From: FI Performance : Norwalk Connecticut www.FIPERFORMANCE.com
On Dynojet's plot Gear Ratio vs. RPM. No slip equals straight line
Brian
PS email me the run file and I can post it: brian@icsperformance.com
Brian
PS email me the run file and I can post it: brian@icsperformance.com
Thread Starter
Burning Brakes
Joined: Aug 2004
Posts: 849
Likes: 1
From: Dallas TX
emailed the run files to you brian. thanks for hosting them!
i plotted gear ratio vs rpm and it was not a straight line. the dips in the graph correlated to the dips in the tq vs rpm graph. thanks for the help!
i plotted gear ratio vs rpm and it was not a straight line. the dips in the graph correlated to the dips in the tq vs rpm graph. thanks for the help!
Former Vendor
Joined: Oct 2004
Posts: 2,592
Likes: 0
From: FI Performance : Norwalk Connecticut www.FIPERFORMANCE.com
From what we are seeing in this graph, my tuner has the following to say
"Looks like a bit of knock or misfire..." The roller speed at the point of knock/misfire remains sort of constant of which when the HP/TQ dip, the roller drags on the tires, then car picks up again in power but in a slip state, cathing up with the roller So its already slipping. Knock or misfire again towards the end of the run, less agressive bump, but a slip in the same sense.
Lost base run graph info on the TQ, from what looks like the inductive pickup not reading correctly all the time, thats when you use "speed" to fill in the plot. Portions of the inductive pickups can be broken where cracks develope causing jumps/dips (HUGE) or no data at all. We replace ours every year some times more when people don't pay attention and drop them.
Whenever you can and if your local Dynojet house has optical pickup, use it, the dyno actually counts each revolution based on return signals from reflective tape on the crank pulley. If anyone has dyno related questions, don't hesitate to ask.
Last edited by Brian@FI Performance; Jul 27, 2006 at 10:13 AM.
