ORVette

I went up to a free chassis dyno day and here are the results.

Max HP-259.8
Max TQ-387.9

??? Here's my motor setup

454HO-425HP-500TQ
ZZ502 cam (224/234-.527/.544)
Low rise LS-6 intake
Holley 3310-750 (80508S) 72/75(metering plate secondary)
Mallory Unilite-12*/35* total by 2600RPM
2" primary headers
TH400
3.70 rear

The thing ran sweet. I made three pulls back to back, and the motor stayed nice and cool and never let out a bit of smoke on the way up or down. Pulls 2 and 3 showed even worse figures, like 230/330. I just don't get it. I caravaned home 100 mi. or so down the expressway with a friend in a 347 stroker '90 Mustang LX that runs 13.9's. He couldn't touch me. We'd slow down to like 40-50 and run up to 90 or so, not even a race. I'll scan the graphs and post them later.


[Modified by ORVette, 8:25 AM 8/18/2003]

Eddie 70

I was surprised by my numbers also. I was expecting more HP and TQ but never got it. I made the same 3 pulls like you did. But I did make 254 HP and 300 TQ. I must have a pretty good restriction in my setup.

Sorry I have no answer for your numbers though.

ORVette

Here's another thing. The graphs show my car making, within 10-15HP, the same power all the way from 3600 to 5800. There's also a chart that lists all the info in 100 RPM increments. For gear ratio info, it says 51.68 RPM/MPH. Does that mean for every 51.68 RPM, my car is turning 1 MPH? If so, that is way off. Also, it says my speed maxed at 112MPH at 5800 RPM, that is way off too. I just don't understand this stuff. Help!


[Modified by ORVette, 5:33 AM 8/18/2003]

GrandSportC3

That's not a surprise to me.. I had a 450 HP stroker engine in my '69 Vert (sold) and I only got around 300 RWHP... I was told that the main reason was the TH400 that eats up lots of HP..

WA 2 FST

What is your rear tire diameter (measured, not theoretical)? With 3.70 gears, and a non-lockup converter, I bet 51.68rpm is pretty close (this figure always varies slightly from pull to pull, believe it or not). My Z06 registered 46.06rpm and it only has 3.42 gears. The key would be the actual rolling height of the tire. Sidewall flex will certainly result in a shorter tire, and will lower the top-speed per gear. Assuming an actual rolling diameter of 26.5", 5800rpm with 3.70s should give you 123mph @ 5800rpm... but that's assuming a converter that is locked in high gear. If you have a typical non-lockup converter, you still get some slippage and the rpm will be higher per a given mph.

As far as your power not varying much b/w 3600-5800rpm, that's not atypical of your combo w/ an auto trans. Mine wasn't much different with the stock 454 HO setup. My driveline is setup differently than yours so it will show more power given the same combo of parts (334rwhp/384rwtq with basically the same setup).

Your friend with a 347 Mustang that runs 13.9... that is slower than most relatively stock 5.0 Mustangs. A properly set-up N/A 347 will make 350rwhp easily in mild tune on pump gas and run mid, low-12s.

WA 2 FST

Another ?. Did they record the Air/Fuel ratio during the pulls? This would give you an idea of where you stand tuning-wise. There might be some more ponies in the top-end of the rev-range if its running too rich.

ORVette

WA2FST-No A/F ratio, just pulls. I am going to try to get up to the dragstrip this Friday for some time slips to compare with these dyno sheets. I was really bummed I couldn't get at least the same #'s you did with your stock setup. I'll keep messing with it. Those horses have to be in there somewhere!

WA 2 FST

Don't fret. First of all, you have a solid torque figure. This means the _average_ HP for your entire rev-range is very good. Another car that makes 275rwhp, but has a really peaky curve will not run as good of times as yours will. :) Good acceleration times are not measured by _peak_ HP or TQ, but a combination of both. Average HP in the rpm range where you race is what is most important.

And I bet there is another 20-30rwhp in b/w 4200-5500rpm. It's probably a bit rich up there and is another reason you don't see a dramatic increase in power above 3600rpm. I guess I'll retract my earlier statement... it should be climbing more than 10-15 hp.

ORVette

I was just looking at these graphs again. Those 260/390 #'s they printed on the results aren't right. They are the peaks of the lines on the graph down around 3500RPM before the pull even started(the best I can tell). The lines are high around 3500-then drop down to around lower #2,3 pull readings. So, according to the data charts, my RWT reads highest at 314@3600RPM point where the pull started, and falls off on a pretty steady decline from there to 203@5700. The HP #'s peak at 230@4500, and fall steadily to 221@5700. This CANNOT be correct. There was a ragged out 75 Nova with a 350 target motor w/headers,intake,crb that put out 200. Same with a stock '87 5.0L that put out 195. You mean to tell me that my BB only puts out 30 more RWP than that Nova? I am TWEAKED!!! :mad


[Modified by ORVette, 8:42 AM 8/18/2003]

Fevre

What spring are your running in the carb for the sec? You may not have been getting enough load to open them fully. Get a 750/850dp and you won't regret it.

ORVette

I installed the lightest(white)spring I had. I also switched to a 5.5 power valve a while back. I did it because my idle vacuum was around 11-12 inches. Maybe I ought to go back to the 6.5. I just need to get on one of those A/F readout dyno's. At least if I knew that was right, I'd know the rest was an equipment problem.

Fevre

Yes do get a a/f meter and use it in conjuntion with a vac gauge to determine your pv rating(s). I am running mine lean on the mains and then using 2 diff power valves so I don't get too much fuel at once with my little 350. I am running the first pv about 2 to 3 lbs below my vac at idle so it gets the fuel when I start off then I have the second pv just below where the vac drops when taking off under light acceleration. It is really nice to see both the a/f ration and the vac at the same time.

WA 2 FST

Ok, well something is not right...that's for sure, but the dyno looks fine. You reference the stock '87 5.0... those indeed tend to put out ~190-200rwhp.

On my old combo, very similar to yours except for the cam, peak HP was at 5400rpm. So for your peak HP to be at 3500 and then drop off from there... something in the tune is not right. There's a LOT of power left in there if you're peak # is at that low of an rpm.

Matt Gruber

http://community.webtv.net/MATTGRU/D...eat/index.html
.
maybe my article will help :cheers:

ORVette

Thanks Matt. Great article! Here are a couple pics. The Blown BB shown only made 440RWHP@6500RPM. I thought that setup would go at least 500. Also, I noticed on the way up to Beaverton that when I was idling at a stoplight w/my turn signals on, they would barely flash until I brought the revs up to 1500 or more??? Could be I have a weak alternator or something. On the way home, I actually was unable to get it to start after shutting it down for a pit stop and had to get a jump. It was hotter than heck, and my fans were on almost all the time. Could this have messed with my ignition(dumb question I guess).




[Modified by ORVette, 5:05 PM 8/18/2003]

PRNDL

You mentioned you are going to the dragstrip. That would have been my suggestion! :) Of course, if you don't get traction results will be inconclusive. Try to weigh your car at the strip also (they should have a scale). In general (this is a BIG generalization.. :lol: ) dynos are better as a relative tuning tool than an absolute measure of HP tool. Most dynos can give you an accurate reading of how much hp you gain by tweaking carb or making other changes between pulls, but to compare your 250 rwhp on that dyno to what someone gets on the east coast is probably meaningless. MJ

WA 2 FST

What's more meaningless is to compare your strip times to that of someone who runs on the east coast...where we all know the density altitude is below sea level and the tracks are slightly downhill (kidding about the last comment)! ;)

Seriously, if the chassis dynos are set up right, and the operator does not fudge on the weather info input into the computer before the correction factor is taken into account, then the difference should be +/- 1 or 2%. There are several types of chassis dynos out there, and they will have a larger variance for sure.

Granted, I can go to 3 different Dynojets here in the Dallas area and they may all vary 5-6 hp across the board. But then again, you may can see a 2-3hp difference b/w pulls on the _same_ dyno.

You can "cheat" on a dyno by inputting incorrect data in order to get a wild positive (high) correction factor, but that doesn't benefit anyone. Just like icing your intake in b/w runs (common practice on EFI engines), etc.

Corey_68

I'm starting to question the dyno. Your numbers and the Blown BB #'s are very low!! :eek: :eek:

ORVette

I was wondering about tire slippage. There was a 440 Challenger there that put down 438 peak HP with a single 4bbl and no power adder. It was stout, but the guy drove it home. Anyway, he switched to slicks before he ran. The blown BB in the pic was in a tube frame Riviera, but on street radials(BFG TA's).

Another thing, I just went out this afternoon and tried to start my car, and the battery was dead. I put the charger on it,and now 2 hrs. later, it is still dead and won't take any charge. 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.

WA 2 FST

While I agree that the blown BB #s are weak... we _all_ have seen ****-poor tunes in a number of cars. Or maybe the guy has a low-po BB he slapped a mild blower on top of? Who knows?

I see several "knowns" to me in this report. 1) the baseline of the old stock 5.0 Mustang tells me the dyno is reputable. 197rwhp is within 2-3% of every stock 5.0 I've seen ... and that is from a decade of my experience racing and tuning SBFs. ;) 2) ORVette says his peak HP and TQ occur right after the operator stood on the gas and rpms jumped up to ~3500+. This makes sense b/c the converter will flash and will show a nice peak TQ figure there... but the HP should continue to climb to at least 5300-5500, since my old combo was almost identical and that's where it made peak HP. My TQ didn't start falling off til past 4400rpm. It was over 370rwtq from 1800-4400rpm, so the curve for his combo should be extremely flat, and its not. 3) I know my old combo was tuned as close to perfect as I could get it. A/F ratio was 13.0:1 at WOT on 93 octane, no sign of detonation, and the plugs looked great.

It's always best to assume the dyno is right. I'm not saying they cannot be screwed up b/c they can be. If _everyone's_ graph looked the same (meaning after they stood on the gas, the #s peaked and then fell off), or if all the cars' #s were out of line, then it might be possible to question it. While the blown BB owner had to be extremely disappointed in his #s, it doesn't surprise me one bit that his #s are low. Everyone expects their #s to be way up there, and are usually disappointed.

As far as tire-slippage and how that affects the readings... it certainly will, IF indeed the tires are blowing off on the rollers. I've seen this in a few cars in my experience (900+rwhp), but only a very few. My 600+rwhp Mustang didn't blow the tires off and I had radials on it. Slicks will keep it from spinning, but they also create more drag, so the #s will be slightly lower usually compared to if the same car was running a radial tire with a stiff(er) sidewall. My two Vettes don't blow off the tires and you can see where they stand power-wise.