DYNO #'s-something aint right!
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
Re: DYNO #'s-something aint right! (ORVette)
I wonder if I was running almost entirely off the alternator yesterday, taking the turn signal thing into consideration. If so, would this be a problem capable of really eating up HP? Thanks again for all the replies guys.
I pulled all my plugs, and they are all light to med. gray on the tips. Just right I think.
I pulled all my plugs, and they are all light to med. gray on the tips. Just right I think.
Since you don't have an A/F reading, can you explain what the graph looks like over 4000rpm? Are the lines really "jagged" as they start to fall off? Or is it a smooth curve, just tailing off pretty quickly? If the graphs are really jagged, then you indeed may have had an ignition/spark problem during the pulls.
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 752
Likes: 1
From: Springfield Oregon
Re: DYNO #'s-something aint right! (WA 2 FST)
Well, I gues it's time to stop grasping at straws and concede that I must just have a crap tune. I'll scan the graphs this afternoon and post them(couldn't get to it last night).
The lines are pretty flat up to 4000-4200RPM, then they start to get wavy, varying up and down 5-10 HP/TQ every 50-100RPM. This is something I just drew up here at work for now. It's maybe a little exaggerated in regard to the jagged lines towards the end, but not much.
[Modified by ORVette, 7:29 AM 8/19/2003]
The lines are pretty flat up to 4000-4200RPM, then they start to get wavy, varying up and down 5-10 HP/TQ every 50-100RPM. This is something I just drew up here at work for now. It's maybe a little exaggerated in regard to the jagged lines towards the end, but not much.
[Modified by ORVette, 7:29 AM 8/19/2003]
Drifting
Joined: Oct 2000
Posts: 1,526
Likes: 1
From: Harrison Township, Mi
Re: DYNO #'s-something aint right! (ORVette)
What are you running for valve springs? I had an issue with mine and I had similar issues on the dyno (I was down about 40 HP over a previous pull, which showed as about 4/10 in my et). My curves also got very erratic as RPM's approached 5,000. We checked my springs and I had less than 100 lbs. force at the installed height. We changed the springs and my power picked back up. Something is also weird with the way your curves intersect. They should cross once, @ 5252 RPM.
I would think a mismatched secondary spring would show up at lower RPM's as you begin to transition. I had this problem as well. It showed up at 2000-2500 as a stumble as I went lean momentarily. We had the benefit of an 02 sensor to pick up the lean condition.
I would think a mismatched secondary spring would show up at lower RPM's as you begin to transition. I had this problem as well. It showed up at 2000-2500 as a stumble as I went lean momentarily. We had the benefit of an 02 sensor to pick up the lean condition.
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 752
Likes: 1
From: Springfield Oregon
Re: DYNO #'s-something aint right! (randy72)
Randy, I have whatever springs came stock on the heads. It is a Gen VI 454HO motor. It only has about 2000mi on it. The graph I posted is just something I drew up on microsoft paint to represent the real one. I wanted to put up something to help describe what it looked like, and I don't have access to a scanner right now to put up the real one. I am going to replace my battery and see about upgrading my alternator to help support the fans. I'll get the real graphs and data sheets up tonight. Thanks.
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
Re: DYNO #'s-something aint right! (ORVette)
I really think its in the tuning. The reason you may not _feel_ it much on the street is b/c the initial transition to full throttle is good and the torque is nice down low.
Randy brings up a good point about the valve springs, since the springs on those heads were meant for a bit smaller cam. But, valve float would be more obvious and the graph would _really_ dive hard from what I've seen first-hand.
There is no way your peak HP/TQ should be that low in the rev-range. Lots of potential left in what you have. :)
Randy brings up a good point about the valve springs, since the springs on those heads were meant for a bit smaller cam. But, valve float would be more obvious and the graph would _really_ dive hard from what I've seen first-hand.
There is no way your peak HP/TQ should be that low in the rev-range. Lots of potential left in what you have. :)
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 752
Likes: 1
From: Springfield Oregon
Re: DYNO #'s-something aint right! (WA 2 FST)
Here's a couple scans of the graph. I called Scoggin before I put in the ZZ cam, and they said it was a good swap and that the springs were fine for this application. The lifts and duration are not that much higher than the stock cam, it's mainly the lobe seperation that makes the biggest difference I think. I will go back to basics and just start checking all the simple stuff first like fuel pressure and coil voltage.
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
Re: DYNO #'s-something aint right! (ORVette)
Not to add insult to injury, but you have to ignore the TQ "spike" at the beginning of the pull. That is common with auto trannies/especially with a decent converter and is not accurate. Your real life peak TQ is ~315 or so.
It's really too bad they didn't have a wide-band A/F monitor on hand. :( That could have really helped give you an idea of where to start. Just by looking at the graphs, it looks like the thing just cannot breathe at all. We know the heads/cam in there are good to ~5500rpm.
Best of luck with it.
It's really too bad they didn't have a wide-band A/F monitor on hand. :( That could have really helped give you an idea of where to start. Just by looking at the graphs, it looks like the thing just cannot breathe at all. We know the heads/cam in there are good to ~5500rpm.
Best of luck with it.
Race Director
Joined: Mar 2001
Posts: 11,322
Likes: 1
From: Living in the Hartland
Re: DYNO #'s-something aint right! (WA 2 FST)
3 things I can think of is the sec aren't opening, you are not getting enough fuel or you are not getting enough spark. I would wire the sec shut and take it for a ride and see if it feels any diff.
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Melting Slicks
Joined: Nov 2002
Posts: 2,231
Likes: 7
From: Fort Pierce Florida
Re: DYNO #'s-something aint right! (ORVette)
That's not too strange. My 383 puts out an adjusted 290 HP and 390 ft. lb. of torque at the rears.
Could explain the 13.07 1/4 at 102 mph :nonod: . Hopefully I'll pick up some HP over the next few months.
[Modified by SuprJames, 9:34 AM 8/20/2003]
Could explain the 13.07 1/4 at 102 mph :nonod: . Hopefully I'll pick up some HP over the next few months.
[Modified by SuprJames, 9:34 AM 8/20/2003]
Drifting
Joined: Mar 2001
Posts: 1,396
Likes: 7
From: Indiana
Re: DYNO #'s-something aint right! (SuprJames)
I think the most interesting thing is the drop between each run. I don't think that the loss of power between subsequent runs is normal. Heat can certainly cause a power loss on following runs, but not that extent. This is exactly the probelm that I had with mine both times I have been to the dyno. I lost 20hp and 10ft lbs by the third run. Even the operator of the dyno was baffled by that. Hopefully the cause of this will also be the cause for the lower than expected numbers for both of us.Unfortunately, I have not yet figured out my problems, but am thinking it could be a voltage problem in the ignition system. With your alternator problems that you mentioned, it could be possible that you are getting weak spark as mentioned before.
Thread Starter
Burning Brakes
Joined: Apr 2001
Posts: 752
Likes: 1
From: Springfield Oregon
Re: DYNO #'s-something aint right! (tsw71)
I replaced my battery today, got my new seperator plate installed in my trans(old one got damaged during reassembly), and I put a screw and nut on my secondary linkage so I could be sure it was opening fully. BIG difference! Trans of course shifts nice and crisp now, nothing to do with HP I know, but the car really pulls hard above 4500 now. Hopefully this was part of the problem, and not just wishful thinking. I measured the voltage at the back of my alt, and it's putting out 14.5V@800RPM's. I will measure across the battery terminals tomorrow with the fans on and the lights on and see what's getting there. Thanks again for all the replies. Dragstrip this Friday, we'll get some more answers there hopefully.
