Had some time to work on my '85 this week...so after getting an alignment done, I took it to a local performance shop for its first baseline dyno reading. The car is a stock set up L98with a Crane comp cam installed before I bought it... and the previous owner was claming 310 HP.

Well...the reality is a bit different Three "pulls" and $60 later, I drove away with: 185 HP and 260 lbs torque @ 3500 rpm. Hmmm...well it was raining today and the car overheated during the test. To make me feel better the tech said that it was a lot better than the baseline of a stock '87 he had just done the day before. Does an automatic trans make a difference in the test result? Seems like it might slip more. But it is still way below the 230 HP stock specs.

Update: forgot to mention how cool it was to watch the dyno procedure. They strapped my car to the floor, over some large textured rollers and then ran it hard through the entire rpm range. I've never taken my car near 5K for that long (simulated speed well over 125) or heard it from the outside at WOT...not to mention 3 times in row. ....Got a major adrenaline rush just watching

 

Net and rear wheel horsepower are two different things.... Stock 230 HP is SAE net, NOT at the rear wheels

 

One, don't believe everything a guy who is trying to sell you his car says about it.

Two, the numbers you got from Modacar are at the rear wheels. No one can seem to agree on the correction factor (to Crank horsepower), but 10 - 15% seems to be an acceptable range.
If you use 15% (for the automatic trans), then your rwhp translates to about 218hp at the crank. Thats only about 12hp from the stock rating. Considering the age of your car, the weather, dyno variations, state of tune, etc. that seems to be in line.

Believe me, few owners are actually satisfied with their dyno numbers!!
Welcome to the crowd.

Now, start planning your mods.

Larry
code5coupe

 

What happened at 3300 rpm? It went lean in an instant and the curves took a dip and leveled out.

I know the stock TPI is restrictive, but looks there like someone pinched off your fuel flow at 3500. Are you sure you're maintaining fuel pressure? Mine felt like a rev limiter at 4000, until I replaced the pump, and picked up 20 lost horsepower.

 

I noticed that too..the HP and torque peak at the same place the mixture dips. The former owner installed an adjustable fuel pressure reglator as one of the upgrades...maybe needs some adjusting?

 

It's actually going from lean to rich at that point, or actually normal value when it gets to 12.5 to 1. I can't read the scale on the right clearly but believe it's 10 at the bottom, 12,14,16. If I'm right it's way lean until that point, then trends to normal for WOT.

With an automatic most people use an 18% driveline loss factor, 15% for a stick. So you are close to stock numbers, but have a strange curve indicating some tune irregularity.

You also could have a high stall torque converter in the car. That sucks a lot of power and makes the curve look weird. Autos don't print nice curves like sticks because of the slop when the TC is not locked.

 

Can't tell you how many times I have heard that before.

Note to all the forum members buying used modded vettes: If the guy tells you he is got a 500hp vette and all you see if a polished TPI setup...just walk away.
At least this guy was conservative at 310!

 

"Crane comp cam"

Crane cams is one company, and they make the LT4 Hot Cam for GM. Comp Cams is another company the the cams are different.

Was that an accurate quote from the Ebay seller? That was a lie if it is what he said.

 

The mixture scale on the printout reads air/fuel and the scale goes from 10 (to 1?) at the bottom to 18 at the top. My car starts at around 15 (air to fuel?) then drops to normal range (13-ish) at the max point in HP and torque. I have been running lower than premium gas lately (89 octane). The tech said it was probably set for proper emmisions in CA and didnt seem to think it was too significant. I think it chip controls that part anyway?

Weird that it develops the most power when it is leanest, and then suddenly gets a richer mixture as it just as suddenly falls off. At best (with adjusting for an A/T) it seems to be close to normal HP ranges..so much for the "hotter" cam...

 

ooops...I typo-ed it is actually a Crane "compucam" 2040 There are a bunch of numbers that came with it like intake@cam 2934, @ valve 440 exhaust@ Cam 3027, @ valve 454...etc, etc.

My guess is that the former owner took the stock H/P and added the specification claims of the cam manufacturer, to arrive at the HP number. I just wanted to make sure if I ever sold the car, I could substantiate it somehow..or just plain know more about the car. I think I do...

 

Is the cam the ony mod on this car? It looks/sounds like to me that the car needs to be tuned.

 

AFPR is snake oil. They only help with major upgrades including intake,larger injectors,radical cam,ported and polished heads and headers.For only a mild cam upgrade stock FPR is more than enough.

 

A stock automatic with several miles on it is possibly loosing closer to 20% at the wheels. Stock torque converters are huge and heavy! That cam with no other worthwhile mods is barely worth 25hp. So, figure 250hp at the crank, minus 50hp (your 20% driveline loss), and you get 200 rwhp. Less than optimal tuning with no special reprogramming explains the other 15hp that went MIA. However, for the money, I believe a decent cam is worth more than any other one or two simple 'bolt ons'. We all know what's next...fuel, exhaust, a chip, and some tuning.

 

Add the dynojet versus the mustang dynos into the mix it even becomes more interesting.... I have heard the difference between the two can give a different in the numbers due to the different styles...

I don't care about the numbers as much as using them for a reference and working up from the baseline... so don't be too disheartened...

Calulcating the lbs/min from my MAF and calculating out the CFM fuel etc.. 10 pounds of boost my engine is putting out around 500 at the crank but on a Mustang Dyno was showing me around 340...The operator let up at about 5500. I was told if it were on a dynojet it would be about 400. Whether that is true, I don't know... once I get my trans back I'll be scoping out a dynojet to see... HEH

It was helpful in dialing in the high rpm fuel though... I was running way rich which is a "good" thing but I was able to get things dialed in much closer...

sure it would have been nice to say I'm making 450 rwhp... but it is what it is...

Mo

 

Mo you are about right. Most cars will show lower numbers on my Mustang dyno. Some go away disappointed, and some will listen to me when I explain to them about dynos and how in theory that they work and how the numbers are computed. Then there are some that just won't accept a lower than Dyno Jet number. As the old saying goes, "you can't please them all"

It is very correct when you said that the numbers vary between the two dynos because of the variances in the way the two operate. Mainly the Mustang takes into consideration the vehicle weight and its theoretical drag coefficient. It does this by using a constant known a Hp@50 MPH. This constant is the theoretical power requirement to maintain 50 MPH for a given car. For my suburban for instance it would take considerably more power @50 MPH than your slippery Corvette. Not to mention the weight differential between the two vehicles. Of course it takes more power to move a greater mass. This is one reason that the DynoJet gives higher numbers, they do not take either constant in consideration. They just take a known mass (the two drums) and with the other constants of aceleration over time and load value on the drum torque arm (via a load cell) they calculate power and torque.

Here are some basic dyno theory:

A dyno uses combination of two laws of physics, force equals mass times acceleration and work equals force times distance, gives us this equation: W=m X a X d. "W" is the work (in pound-feet) the rear wheel is doing, "m" is mass equivalent (the drums), "a" is acceleration (increasing drive wheel speed) and "d" is distance (drum circumference). Once we have the work, we can find horsepower. One horsepower is 550 pounds-feet of work done in one second, so we divide the work number by the length of time measured, then divide the number we get from that by 550. To simplify: we get horsepower by multiplying the mass, acceleration and the distance, then dividing that product by time multiplied by 550. This can be expressed by: hp=(m X a X d) / (t X 550).

Torque can be figured by multiplying the horsepower by a constant, 5252, then dividing that product by the speed at which the thrust force was measured. Generally with rear wheel numbers, axle ratio is not considered in the torque computation. For comparison purposes, this makes more sense. The computer factors out the axle ratio by using engine speed data in the torque derivation.

Also remember that there are some parasitic loses in a chassis dyno. These losses are due to frictional losses in the bearings, frictional losses due to tire deformation and differences in weights of the cars or trucks being tested just to name a couple. These factors are also calculated into the final numbers as well. Boy, its a good thing that we have a PC to do all that damn math

 

tj',

>Mainly the Mustang takes into consideration the vehicle weight and its theoretical drag coefficient.<

WTF
Vehicle weight has nothing to do with engine power.
Of course, weight affects accelertion, like lots of things.

 

"theoretical drag coefficient"........."theoretical power for 50mph"......."weight differential" ???????????????????????????????

I know you know what you are talking about....BUT this just doesn't seem right!!!!!! Why not just use "theoretical" horsepower and skip the dyno test???

And besides that, we are after a horsepower/torque characteristic of engine.....not an overall performance measurement.....what does body drag coefficent or body weight have to do with horsepower????? OK lower drag coefficient, lower weight equal faster acceleration BUT it doesn't really change anything about the motor????

Please explain more??????



So IF we are saying that the Mustang subtracts out power lost to aerodyanamic losses...how can you do this and neglect gear ratios & speed....I am really lost on this one....HELP!!!!

 

I don't think he was implying it has anything to do with power just that certain dyno's takes the vehicle weight into consideration as a rolling mass and adjusts accordingly to calculate HP

 

What he said. If that is in fact true, it's ridiculous. I could understand applying those factors if you're simulating 1/4 mile times (you know, for those dyno queens that don't want to get their cars dirty)

But to use that for just measuring engine output isn't right.

 

That is pretty much correct. It takes more power to move a larger mass than it does a smaller one. What the Mustang does with the simulated load is that it models what the car would do on the actual street. This gives the more accurate data for your cars actual street performance. For instance with this the added data the Mustang Dyne can perform an actual 1/4 mile pass which can give you accurate results to within .10 of a second. I have tested this on my dyne on several cars and trucks and found this claim to be true.

Check out Mustangs website, there is a article done by CHP magazine that explains it well:

www.mustangdyne.com

Click on the "recent articles" link then click on the CHP article.

Boy, I knew I would get in trouble for that answer BTW for the dyno queens I can turn off the compensation and the dyno will give out numbers like a Dyno Jet