My question is this. Can you detect a slipping clutch during a dyno run?

 

Interesting question...If it's slipping enough you'll get the fairly distinctive smell of burning clutch- but I'll bet you knew that. Without that or visible smoke I'd think that if you looked at the readout & saw a dropoff or flattening of the power curve before your parts combo should be peaking, you'd have reason to suspect slippage. That's assuming the rear tires weren't losing grip on the rollers. A good dyno operater may be able to tell by ear too- it could be an audible change in the rate of RPM increase.
What makes you ask?

 

Les,
Thanks for your response.
I am asking because, the car just doesn't have the numbers that it should.
I am searching every conceivable option I can think of.
The clutch didn't smell or smoke on the dyno, and the guy said he couldn't see any slippage, but I am using a stock BW unit and have used it hard over last couple of years.
The engine peaked at 5,300, on a cam that should do 6,000.
The GM springs they use on ZZ4 with .525 lift, and I am under that.
Thanks for your help,
Bud

 

Bud - What were your numbers and what was the rated hp of the ZZ4 you have?

 

i'm not familiar with all features of a dyno, but...
a dyno measures the angular acceleration of the drum. uses the known mass to compute force, then torque, and plots vs engine rpm to get horsepower, correct?

well i would assume the dyno drum sensors can measure the drum rpm (or integrate the acceleration vs time). can you plot drum rpm vs engine rpm? any variance is slippage somewhere, either clutch or tires, and it would probably colinear until a certian rpm, then breakaway and diverge. also, you know your gear and axle, so you could use the final drive ratio to calculate theoretical drum rpm.

this would depend on how accurate and fast the speed senors are, as well as what amount of clutch slippage is realistic (1%, 15% ??)


[Modified by Turbo-Jet, 11:31 AM 11/15/2001]

 

Turbo,
Your about three feet over my head!!! I have no idea what you are talking about, but I wish I did.
My only response is that I ask the question is the gears ratio affected the dyno results and was told only that the lower gears 3.9 (mine) require a little more hp & torque than say 3.23 would. Not an amount worth worring about.
Thanks for your response,
Bud

 

Mark,
That is my biggest problem! They are not on a ZZ4 block, but a rebuilt old L82 .
Trust me when I say I sure wish they were!
265.8 @ 5,300 with max torque 306.8 at 3,800.
Thanks,
Bud


[Modified by bud snyder, 2:04 PM 11/15/2001]

 

Bud - You may not have clutch slippage at all. I don't think your chassis dyno numbers are so bad for a stock L82. Keep in mind, what you are looking at is rear wheel hp. They are not to be compared to GROSS (at the flywheel with no accessories hooked up or drivetrain) hp numbers of pre 1970 cars or the now standardized Net (at the flywheel with accessories and belts in place but no drivetrain) hp numbers that the auto makers are using. Also, the crate engines are rated at Gross as well and assume headers and 4bbl carb is in place to get those numbers. Whenever you see HP ratings of the newer cars, they are stated as net, not gross. For example, this means that
when you compare the new C5s (380 - 405 NET hp for the new Z06s) with the older BB cars (390, 400, and 435
GROSS hp), the numbers are not the same. In reality, the new C5s are pushing more hp than the old stock BB
cars were. I've witnessed and run against C5s at the strip with slight mods running in the low 13s and struggle to keep up with
them. When I chassis dyno'd my 425 GROSS hp 454, even the stock C5s were putting out more rear wheel hp
(my 303 vs their 320 - 372 for a modded 01 Z06) than me or the other mid year BB car (under 300rwhp) there at the time (Now as
far as seat-of-the-pants rear wheel torque, there was no comparison! - my 415ftlbs vs 372 for the same Z06
). I was dissappointed also until I started looking into this further. I am always skeptical of any hp claims on the forum since many make the mistake of quoting crate engine claims, desktop dynos or flywheel dyno results as compared to chassis
dyno results which IMHO is the true indicator of performance. The key point here is that I don't think your numbers are that far off for a modded L82 SB. Just
my .02!


[Modified by Marks69BB, 2:41 PM 11/15/2001]

 

Mark,
You may be right. I am just disappointed at the results. I used all good parts and they just do not jive together right.
God I wish I had a ZZ4 bottom end!!!
The car seems to run much better than the numbers, but facts are facts.
In all honestly I don't have the capability to use the engine's output anyway.
My traction with street tires is terriable. I broke the tires coming off the line on Sat. at 3,200 and stayed in it, all the way through 1st and part of second.
0-60 time 2.93.
It doesn't seem logical that a car with those numbers could achieve that.
Thanks again,
Bud

 

Bud - To reverse the math: chassis dyno 266 'rwhp' + est 18% loss of C3 vette drivetrain = 324 'net' hp + est 15% for belts/accessories = 382 'gross' hp. A ZZ4 crate is rated anywhere from 365 to 385 'gross' hp depending on the cam and heads selected. As a comparison, my numbers would be: 303 'rwhp' + 18% = 370 'net' hp + 15% = 435 'gross' hp. My pump gas 454 bowtie crate engine was rated at 425 'gross' hp when new in 91. On mine the mild cam and low 8.5-9cr is what is holding it back from the higher 500+ 'gross' hp of the newer ZZ502 BB engines. The 15% and 18% losses are based on what I've read and been told regarding gross>net conversion and the vette's independent rear with all of the u'joints respectively. BTW, I checked your sig and you've made some excellent mods with great stuff!

Re the 60ft times, I have to come off the line at about 1500rpm and nail it when she hooks up to get low 2s - any higher rpms and I smoke the tires off the rims! My 1/8 times are in the upper 8s but the problem is my launches with street tires, shift points, and the 3.08 rear; not the engine. In other words, the vette is saying





[Modified by Marks69BB, 5:30 PM 11/15/2001]

 

Mark!
I feel a little better after reading your post. Thank you! 382 hp is ok, but the point is I think that it should be better. Last nite at the speed shop I talked to one of the guy who works there and races also. 350 sb 590-600hp with 750 Holley. There are pictures of the car on the wall. 58 Corvette, 10.6 regularly.
Unforginately he roller the car at Atco, NJ last Sat. at 120 MPH. Engine gave out and locked up the drive train.(rear wheels) He wasn't hurt, and the car only suffered basicly cosmetic damage. wow was he luckey!
It has been a pleasure talking with you and take care,
Bud

 

Bud,
I understand what you are saying about using all good parts and nothing fitting together right. I just built a 383 C.I. small block, and spared no expense, I used a proven combo that many others have in their cars, and I have never seen the amount of trouble that I had with EVERY part I put in the motor. As far as your numbers are concerned, I have no dyno slips but I owned a 69' BB that was heavily modified, and a stock 86' and the 86' could run rings around the 69'. Torque now is a different story.
Good luck,
Joe :yesnod:

 

Another question is what kind of dyno was it? Most are a Dynojet and not so common is a Mustang.

Reason I bring it up is I dynoed my "stock" LT4 and came away with 260 peak Rear Wheel Horsepower!? Car is fine, will exceed 170 MPH and runs 110 in quarter so power is there.

But this number is around 40 hp off what most get for same car/engine-they use a dynojet set up which simply reads higher most of the time. Even comparing Dynojet dyno to another Dynojet dyno (or Mustang to Mustang) isn't the most accurate. Most say best use of a dyno is to try changes and run on the exact same dyno to give accurate data.

Bottomline-you could be making as much as a LT4 which is pretty respectable. BTW-my brothers 461 CI Caprice made only 323 RWHP (runs easy 13.50 in a 4400 pound package).