Bad tune, or engine at its limit?

[Dirtybob]

do you know what the density altitude was? (it can be approximated from the time/location of your pass)
could you post the timeslip info?
400 hp isn't necessarily weak considering that mild cam....
assuming you were into the low/mid 12s with that mph?
how many rpm at the shift (you need to rev to make big hp #s)?

[90Vette]

Looks like the density altitude was 1,697 feet. I'm new to drag racing, but that doesn't sound too bad. According to another calculator I found, with that DA my HP should be 100.5% of rated HP.
I was actually at 13.4. Granted, that was my first time going to the strip, but on that run I felt like I had a good launch and fast shifts. I'm running street tires and wasn't launching too hard, so that might contribute to the slow ET. Honestly, I was mostly shifting just by ear and feel, but I think I was shifting around 5200 rpm. It's hard to say because my tach is a bit off.

By the time I figured out the basics, bracket racing had started, so I didn't want to mess with my launch RPM or shift point (no regrets, I somehow ended up second). From what I've read though, 2000 rpm is a decent launch for street tires, and 5200 is right about where a Super-Ram 383 with a small cam should be shifting. Am I off on that?

R/T	.064
60'	2.104
330	5.792
660	8.758
MPH	83.66
1000	11.314
E.T.	13.436
MPH	106.23

[Dirtybob]

I don't think a 1700' DA equates to "100.5% of rated HP". I would expect it to calculate out at around 96%. Are you sure which barometric reading you used (corrected vs. uncorrected)?
Cant speak to the power curve of your motor but you may be able to squeeze more rpm out of it (good heads & intake might carry the hp past peak for a while), try raising the shift points and see what happens.
60' times are abysmal unless you're running hockey puck (aka all season) street radials. Get some better rubber and/or practice your launch. You will probably find that your mph will drop (but ET will be much better) with improved 60' times. I would be looking for 1.8 or better 60'.
When using ET/mph to calc hp, just remember that the numbers are really only good for comparison. Say you put gears/stall converter/drag shocks/slicks on your car and it picks up 7 tenths and loses 2 mph? HP did not change but your numbers did...

[90Vette]

I pulled that number from this calculator, which appears to use an SAE standard. Corrected for what? Temperature? The linked calculator takes temperature, altitude, barometric pressure, and humidity into account, so I assume it's making corrections.

I was under the impression that even the old AFR heads are pretty good? And unfortunately the Super-Ram is my only option for a smog-legal intake. Next time I hit the strip I'll try some runs with a bit higher shift points.

I know I suck at launching, I guess I was just hoping to have a higher trap speed with all the work I've done. But my spark and fuel curves look decent to you?

[Dirtybob]

Most weather stations report corrected (to sea level equivalent) barometer. You need to uncorrect that reading or factor in for track elevation.

I would say you have good heads, unfamiliar with the superram but it's got to be better tan the stock long-tube tpi. Wouldn't suprise me if your car pulls close to 6k before laying down. My stock (iron headed) LT1 with the wimpy little cam turns 5500+, I went as high as 5750 but no improvement vs. 5500 (shift completion rpm - auto trans).

13.1:1 afr and 30 deg timing has worked well on my car (apples vs. oranges), yours may like more timing.

[90Vette]

Hmm. Well, the track was only at 70' elevation, so I can't imagine that correction would have thrown stuff off too much. But good to know for the future.

The Superram is waaay better than TPI, but it isn't meant to rev high. On a 383, everyone I've seen is shifting in the 5000-5500 range.

Did you tune that with a dyno, or have you tweaked it with trial and error at the track? I think mine could take a bit more timing, but on the street it's hard to see if changing timing or fuel helped or hurt. I'm also a bit paranoid about knock - as a newbie, I am not familiar with what it sounds like (I've watched videos, but it's not the same). I've been getting lots of knock counts at lower RPMs which I've attributed to false knock, so it's hard for me to tell if knock counts at WOT could be false knock or if it's the real deal. I don't want to risk adding in timing, datalogging a run or two, and hurting my engine from detonation.

[Dirtybob]

Did you tune that with a dyno, or have you tweaked it with trial and error at the track?

I baselined it with the butt dyno and then finished tuning at the dragstrip.
I saw more kr on the street than at the track (varying conditions vs. WOT all the time). Going from light throttle cruising in 3rd gear around 50 mph to full throttle downshift (into 2nd) will still carry a bit of kr beyond burst knock - sometimes. Was able to run timing up to 35 deg with 93 octane and no (WOT) kr, ran the same ET/mph/60' as 30 deg advance on 10% ethanol 87 octane (also kr free). Car is a daily driver so cheap gas is a bonus. Worth mentioning that w/e pos opti I have is probably not indexed correctly from the mfr. - there are some timing light discrepancies. I quit worrying about it and just tuned it for what it wants. Small amounts of kr had no effect on ET/mph/60' but I tuned it kr free to be safe. Progressively leaned out PE afr as far as 13.5:1, sweet spot appeared to be about 13.1:1.
stock 178k mile motor '95 Roadmaster, 3.42s/posi, ebay headers. 4450# as driven. 14.66 @ 92.5 - 2.045 60', 1800' DA. Needs more power (and a diet lol) plus a real (not a 12") torque converter...
http://magic-photos.com/2011/Fri%20F...s/DSC_0306.JPG

I would say if you can't hear it rattle (assuming your car isn't obnoxious loud), and the knock counts are minimal, you are at low risk to hurt anything. Have you tried higher octane to see if kr is reduced?

Edit: headers will amplify valvetrain noise - but you probably already know that...