Having never put one of my own cars on a dyno (not kidding- NEVER done it before) I was kind of excited to see what it put down.

It's my super-mild 383 with AFR heads, modest cam, low blower compression and Weiand 142 blower pushing 5 PSI into the motor after sucking it through a home-tweaked QJet carb. It's in my 78 Malibu (my Grandmother's old car with 35K original miles!)

Dyno is your typical Dyno-Jet spin-the-big-roller deal. The kind that seem to be everywhere these days. Made 3 runs but with my tall gears getting it to hold top gear when I nailed it from 80 MPH was.... problematic. So I later did it in 2nd gear, despite the fact that I was given stern warnings about running it in anything but 1:1.

The numbers, as you can imagine, were all over the place with the gear selection issue so I basically consider them meaningless but for what it's worth here they are:

HP (take your pick): 367, 389, 407

Torque (take your pick): 412, 464, 526

I never went beyond 6000 RPM, which might have been a bit too soon. HP was flattening out but not totally flat at that point. Torque looked flat as a Kansas wheat field from 3000 to 5200 and then gradually sloping down beyond that.

What are the REAL numbers??? Good question. I'd say, factoring out the shift weirdness and the torque converter "flash" peaks, that it's really around 390HP and 410 Torque to the back tires. BUT HOW CAN IT POSSIBLY BE RIGHT IF THE TORQUE AND HP LINES DON'T CROSS AT 5252 RPMs????? BY DEFINITION THEY MUST!

As many of you know, I have estimated this motor at a "legit" 450 at the crank many times on this board and others. I'd say that's probably about right if you factor out the losses through the converter, trans and rear end. 450 HP Vipers usually lay around 390 to the rollers on this rig. A stock LS-1 usually around 290-300.

One guy layed 370HP to the rollers but with 510 ft/lbs in a N/A 383 with a lumpy cam. I noticed his torque curve started at the peak- his stall RPM of 4500- and then went straight down at a 45* angle until he let out at 6700. So he made 20 fewer HP but 100 more torque. Weird. I attribute that to the high stall converter. He claims to run 12.7 @ 112 on street tires, which would roughly line up to my car's 12.5 @ 115, also on street tires.

Almost all the "race cars" with high stall converters had curves that looked like that. They start and peak the torque curve at stall speed and then a line goign straight down from there.

This is why I HATE dynos. It's hard to know what the numbers really mean. Someone care to explain the inner mysteries of a DynoJet to me?

 

That peak torque spike at intial flooring of the throttle is meaningless with regard to true flywheel torque. That is the result of the stall torque multiplication. The shop that does my car will not even plot torque on high stall, non-locking converter setups.

You say your torque and HP curves don't cross at 5,252rpm. Well, the lines may not cross, but HP and torque should have the same numerical values. Usually, if you look at the dyno graph, you will find they use two different scales on the left and right axes for torque and HP. This means the torque and HP lines will not actually cross on the graph at 5,252prm, but if you draw a vertical line up from 5,252rpm, and at the point where it intersects the HP curve, read the HP on the HP scale on one side, and then at the point where the vertical line intersects the torque curve, read the torque on the torque scale on the other side, you should get the same numbers.

 

It's difficult to get good reading from a chassis dyno with a loose converter. High gear helps. I can run mine in high, what exactly happened when you ran in high?

Rich Krause

 

Injuneer- I'm embarassed that I missed that. You're absolutely right- the left and right sides don't have the same number scales on them. Factoring them out..... yep, pretty darned close.

I know what you mean about "spiking" the torque momentarily when you nail it. That's why I'd NEVER tell anyone I put 526 ft/lbs down, even though I have a piece of paper to back that claim up. It's clearly a meaningless number, which is why I factored it out when I gave what I beleive to be my "real" numbers of 390 HP/ 410 Tq.

BTW- I've been thinking about the guys with high stall converters who made runs and their odd "straight down" torque curves. I suspect that the dyno is measuring torque converter multiplication as much as it's measuring actual engine output. The converter is probably still multiplying torque even well beyond stall speed, but less and less so as RPMs climb. Hence, the straight-down shape of the torque curve.

Krause- What I did to get 3rd gear was to delay activating the data capture. I punched it, it dropped 2nd, revved up, dropped 3rd and thats when I started capturing data- so that I got a true 3rd gear only set of numbers without spikes from the shift or from "flashing" the converter. That's when I got my 389 HP (middle of the 3 runs) and 412 Tq (lowest of the 3). The graph also looked considerably less "wiggly" than when we took numbers in 2nd gear. Nice smooth curves all the way up.

 

Your car was damn impressive for being a modest machine.

I think if you didn't have that tranny down shift issue, you would of had more accurate #'s. And you are totally correct about the looser converters having inaccurate TQ readings.

I on the other hand still have engine issues that you already know about.
Let me know when we can start testing on it.

By the way, here were my numbers...

Run1- 290.5 HP 378.8 FT/LBS
Run2- 296.2 HP 401.4 FT/LBS
Run3- 308.6 HP 403.2 FT/LBS (open cutouts!)

NOTE!!!- HP curve stopped rising and started dropping at 5000 rpms on all 3 runs!!

Heavy

 

Mark, I'm thinking that your torque converter is STILL having some torque multiplying effect even as high as 4500, even though your stall is at only 3000. ALL of the graphs of high-stall combos looked similar to yours. I'd expect the peak HP numbers to be higher that what you got, as you and I have talked about many times since Saturday, but that's work for another day.

That guy in the 2nd gen Camaro had a combo almost exactly like yours and put down 370. But his idle was SOOOO much lumpier than yours I just can't beleive that your cam is as simalr to his, even though we think it should be, which, of course, we've also talked about.

Before we get to actually breaking out the dial indicator and measuring your cam I though of something simple we should try first- measuring manifold vacuum at idle. If you're pulling 12-14" there's no way you've got the cam in that motor the builder told you it's got. No way a cam with 250 duration on a 110* LSA is gonna pull any meaningful vacuum at idle.

 

OK. sounds good to me. I like simple checks.

Hey, did you do a burnout in your Malibu for their burnout contest? Someone said there was a white Malibu that did a huge nuker!

 

I can not tell a lie. T'was me who chopped down the cherry tree.

I'm still 16 at heart.

 

COOL! I hope they got a pic of that. LOL

 

I think they were too busy diving for cover. I was VERY sideways.
Probably looked dangerous from outside the car but I never got anywhere near out of control.