Dyno-testing a newly rebuilt engine??

[Dick G.]

I finally got my 65 running, late August, last year. I have only 375 miles on the car. Is it too soon to run this engine on a dyno with only 375 miles?? She runs great on the road. I just found out tonight there is a dyno in town hungry for business. This car has it's original 327/350HP engine. Should I wait till she is broke in or not? $10.00 for one run. $100.0 for 3 runs is the norm. Thanks DG

[Duke W.]

Re: Dyno-testing a newly rebuilt engine??

No, assuming a moly faced top ring set was used the engine should be broken in, but make sure you've made at least a few WOT runs to redline through a couple of gears.

Ten dollars for one run and 100 for three? That doesn't make sense. How about 100 bucks and hour so you can do some tuning? You want at least two back to back pulls within two percent to verify the veracity of the readings? A good OE L-79 should make around 220 SAE corrected RWHP in the mid 5000 range.

Please start the pulls at no more that 1500 or even 1000 because you really should be able to use the engine at those speeds. The typical "dyno pulls" that start at 3000-3500 tell you NOTHING about the low end torque and the RPM range where the engine spends a substantial amount of time. Testing race engines from 3000-3500 makes sense, but road engines should be tested from barely off idle.

Verify that your dwell is right on and initial timing is at 6-8 degrees, assuming the dist. still has the OE 30 degrees of centrifugal. Are the springs OE or are they lighter to bring in the centrifugal earlier?

Is the engine a pure OE rebuild with no head massaging or other than OE equivalent replacement parts?

Do some WOT road runs from 1000 revs in third gear. It should pull smoothly to redline or something is amiss - basically verify that the engine is in optimum tune with the usual checks and road testing.

Dyno pulls are not very hard on the engine. Assuming it's an inertia dyno, like a Dynojet, pulls from low revs to redline take about 15 seconds - roughly equivalent to pulling in third gear (although the dyno pulls should be in fourth) Fill the rear tires to the maximum cold pressure placarded on the sidewall for the test to minimize tire hysteresis loss.

There should be plenty of external fan flow and allow a minute or two dwell between pulls. This will help prevent the fan clutch from tightening, which could cost up to 15 HP at the top end.

Make sure you understand what if any correction factors are used. The most common is "SAE" which is the same as used for SAE net power on modern engines, so your flywheel data is the corrected RW data divided by 0.85. Of course, the dyno operator must have a "weather station" and it's best if the temperature probe is placed near the air cleaner inlet so actual inlet air temperture is recorded.

If the pulls are on a Dynojet, get copies of the raw data including temperature, pressure, and humidity by email or bring a diskette to copy the data if the computer does not have an external link with email. You can then download some software from the Dynojet Web site to facilitate data display, use different correction factors, etc.... plus you have a permament digital record.

It's tough to get full, IN CONTEXT dyno data. Too often the pulls start at too high revs and context (observed, corrected, or what correction is used) is not known so the data is worthless for comparing to known full rev range full context data.

Now if I can only get some full, in context chassis dyno data for the Special 300 HP engines....

Duke

[Tom L.]

Re: Dyno-testing a newly rebuilt engine??

Just last week my engine builder finished the motor, did the initial break in on a dyno, changed the oil, tweaked the mixture, timing and dwell and did a few pulls. I was initially concerned about this, but the machine shop said that this is commonplace now. So much for going easy for the first 500 miles.

I was pleased to learn that the mostly stock LS-5 motor made 440.2 hp and 555 ft/lbs of torque.

[Paul K.]

Re: Dyno-testing a newly rebuilt engine??

Duke
That is some great information, I also have a 66 L79 i was thinking of a dyno pull done
What does WOT mean

Paul Klemetson

[Duke W.]

Re: Dyno-testing a newly rebuilt engine??

Observed? Corrected? STP? SAE? Headers? High compression or low compression version of the LS-5?

That's a lot more SAE gross torque/power than Chevrolet ever got out of even the high compression '70 LS-5 on a lab dyno - more like a '70 LS-6, but even more torque; 555 lb-ft of torque sounds like a stroker to me.

So what was done in the rebuild to improve torque/power?

The numbers look and sound impressive, but like I said, data without full context is worthless.

Duke

[Duke W.]

Re: Dyno-testing a newly rebuilt engine??

Duke
That is some great information, I also have a 66 L79 i was thinking of a dyno pull done
What does WOT mean

Paul Klemetson

Wide open throttle

Here's a quick checklist to use that you should discuss with the dyno operator before you commit. I will assume we are dealing with a Dynojet inertia dyno that is the most common available type.

1. Dyno operator has a good external fan arrangement

2. Dyno operator has a weather station that measures temperature, pressure, and humidity

3. Dyno operator will start the pulls from 1000 to 1500 revs to the limit you specify, which should be no less than tachometer redline for an OE or OE equivalent engine.

4. Car owner has verified that the engine is in good tune and the engine pulls on the road from low revs (1000-1500) to redline in third gear. (Optional: Owner has optimized spark advance map by changing springs to bring the centrifugal advance in as quickly as possible without detonation and total WOT advance, the sum of initial plus full centrifugal, is in the range of 36-40 degrees)

5. Car owner brings a diskette to copy test data for later display on his computer. This data can also be emailed to other interested parties. Display software is available at no charge from the Dynojet Web site.

5. Car owner inflates rear tires to the maximum cold pressure placarded on the sidewall.

(Warning - pulls to redline in top gear results in tire speeds of 120 to 170 MPH depending on gearing and redline. A 3.08 axle and 6500 revs will yield about 170 MPH in top gear. Typical S-rated tires that lack the nylon cap belts of "H" and above rated tires may be subject to tread separation and catastrophic disintegration, which can lead to consequential vehicle damage and personal injury. Briefly exceeding the speed rating by 20-30 MPH should do no harm, but running S-rated non-nylon cap belted tires to 170 may be risky. If this is the case, use third gear. Flywheel power can be estimated by decreasing the direct drive (fourth gear) driveline efficiency from 0.85 to about 0.81. In direct drive (fourth) the transmission efficiency is 98-99 percent, 94-96 percent in the intermediate gears when power is routed through the countershaft.

Duke

[Tom L.]

Re: Dyno-testing a newly rebuilt engine??

Duke,

I assume SAE, but I'm not sure. I'll pick the motor up on Friday, it comes with the print outs, so I should know more then.

It's from a '70. I kept the C/R at 10.25:1. The only modifications are 1) a roller hydraulic cam with a little more kick than the stock piece 2) the size of the intake and exhaust valves were increased and 3) there was some polishing of the heads starting at the valve seats and extending about an inch up. The motor was bored .030 over, but I wouldn't think that would make a noticeable difference. The stroke was not changed.

The dyno runs were done with headers that are set up to hold the temp and other sensors. I expect to lose a little with the factory exhaust.

Tom

[Duke W.]

Re: Dyno-testing a newly rebuilt engine??

Typical lab dyno tests use STP (standard temperature pressure) correction, and hopefully the data sheets will indicate the type of correction used.

Once you have fully in context lab dyno data, I hope you do some chassis dyno pulls. In this case use SAE correction.

Using a driveline efficiency factor (typically 0.85 for manual transmissions in direct drive, 20 percent for non-lock up torque converter autos) you can derive a good estimate of SAE net at the flywheel.

About 4.5 percent of the difference between the lab test and computed SAE net af the flywheel is STP versus SAE correction. The rest is "as installed" losses, which are primarily the exhaust system and front end accessories. The fan is a wide card - probably no more than 1-2 HP if you can keep the clutch from engaging will lots of external fan flow, but as much as 15 HP if exit air off the radiator is hot enough to fully engage the clutch.

Duke

[Tom L.]

Re: Dyno-testing a newly rebuilt engine??

Duke,

A chassis dyno pull for comparison is a great idea. Unfortunately, at the less than impressive rate of this project, it might be a while.

Tom

[Duke W.]

Re: Dyno-testing a newly rebuilt engine??

My median life expectancy is about another 20 years, so I should still be around when you get 'round to it.

It's taken years to build up my current data library, but I'm like Alan Greenspan - data, data, data - I can never get enough data.

Duke