Quick Way of Checking Engine Power

[david.g.chapman]

My +2 engine is running OK, but I am not sure how much power it's producing.

Compressions are all in the 160-170 psi region, as I have a low compression head (the car was originally for the federal market).

I am running CPL2 cams on a Stromberg head with a low level balance pipe. The exhaust manifold is standard narrow bore flowed design (not cast).

I don't want to go to the trouble of a dyno test, and 0-60 times are a bit hit and miss - I tried recently but only got 10 seconds with a lot of clutch slip, or the engine bogging down. Not something I want to keep trying.

Are there any other acceleration figures worth using in your experience? Or another way of measuring engine power?

Dave Chapman.

[david.g.chapman]

Thanks for looking everyone.

I suppose its best to rely on the acceleration figures from an old road test, find a straight level road somewhere on a still day and just do it....

The only other thing I thought of was to use the dyno apps on a smartphone - looks rather inaccurate to me.

A few years ago I found out about very low power output (due to burnt exhaust valves) going up the steep hill to Maldon high street in Essex. I had to go into second gear to make it!

Dave Chapman.

[mbell]

I was going to post about phone apps but held off to see if any one had any other suggestions.

Getting consistant results probably difficult but if you can find an app that plots speed v time and do single gear pulls it might give something useful. Other people maybe able to share plots for there car to compare with.

[Andy8421]

I have an old engine tuning manual that suggests a timed run in 3rd gear up a hill is the best way to build a 'home dyno'. The book suggests finding a hill with constant slope, and rarely used by other traffic (book was written in the early 60s). Choose a couple of landmarks prior to the run, enter the run at a given number of revs, floor it, and time how long it takes to get to the second landmark. Distance to second landmark chosen so that car is still flat out, and toward top of rev range.

No good for absolute measurement unless a friend with a similar car with a known performance will offer to run the test to give a benchmark, but very good for comparative tests. Do the run, fiddle with something then do the run again. By entering the run at different revs, it is possible to figure out where in the revrange the changes are having an impact.

Avoids heroics trying to pull away from stationary for a 0 to 60 run, and also avoids gear changes. Doesn't hammer the driveline either.

[rcraven]

The problem with using old road test figures is whether you can rely on them. They generally seem optimistic to me. Weren't they sometimes given specially prepared cars? I think I've read some writing about cruising happily and steadily at 100+ mph for long periods, which has always seemed unrealistic to me in a two-seater Elan except on virtually empty roads.
As to the mobile phone app, it seems a good idea, but I've not got it to work yet. You probably need a passenger for safety.
So Andy's method is a good practical one if you've got somewhere suitable to go and have done it first when the car was working properly.

[david.g.chapman]

I have a level section of road that I have been using for a rough 50 to 70 time in 4th.

I have been counting "elephants". I takes about 1 second to say elephant normally

It takes between 4 and 5 elephants to get there! Anything more than 6 elephants and its time for a compression test.

I will have a look at other scenarios. A hill would be great, but I do not have anything to compare against. Suppose we say a level stretch of road, and 50-70 in 4th or 30 to 60 in 3th. If someone has a recent dyno record, could they do a run with proper passenger timings and post it?

Dave Chapman.

[rgh0]

A phone app that allow you to put in weight and some form of air drag factor and measures acceleration should be able to give reasonable HP at rear wheels estimate. Not as good a a decent rolling road dyno but good enough for most purposes.

cheers
Rohan

[alan.barker]

"I have been counting "elephants". It takes about 1 second to say elephant normally "
Is that white Elephants or pink Elephants.
Alan

[david.g.chapman]

Definitely pink elephants, Alan.

There are other words you can use - bol**cks takes about a second as well!

Dave.

[AdrianSi]

If it's bogging down, then it would suggest that it's not running at its optimum... you can wet finger it in the air, but the time and money would be best spent getting it to somebody with a Rolling Road and having it jetted to suit the L2 cams.

[collins_dan]

For my stromberg head with L2 cams, I found B1BT to be the ideal needles. Dan

[alan.barker]

Imho the only way is a rolling road where you get facts and figures on a graph.
Or go to an area meeting where there will be someone with another Lotus to compare with
I know in the past with Club Lotus track days at Goodwood just to see a car accelerate from standstill on the straight gave a good idea. Without racing of course
Alan

[david.g.chapman]

Thanks everyone. There food for thought there....

I decided to have a go at a phone app - aDyno, available at the Google store.

I secured my old HTC phone to the dashboard with blu-tack, fired up the app, entered my car profile including weight, frontal area, rev range, pitch characteristics at 2.00 degrees per g (a default guess), conservative drive train losses at 15%, rolling resistance at 0.015%, cd as 0.3, and min and max speed for 3rd gear.

The results are very spiky, as the phone was probably vibrating and producing waves on the accelerometer output. However, I have hand drawn a line through the points for torque and bhp (same scale on the y axis), to give a stab at an average reading. The orange line is torque, and the blue bhp.

The results are not too stupid, although the pitch characteristics guess worries me. I might try a few more runs sometime and post them if there is something to say.

Cheers,

Dave.

[denicholls2]

Late to the party, but the only required collection device is knowing the speed at start of run and at end of run and using an accelerometer (in all smartphones). The rest is math.

There was a device available before smartphone apps came into vogue that was a little box about 2x1x1.5" with an LED display and a couple buttons on it, still living in my basement somewhere. Cost maybe $25? You input vehicle weight using the buttons, started rolling and started it when you hit something like 20mph (to avoid the "off the line" problem.) I forget whether you had to tell it to stop too when you hit 60 or it just figured it out from weight and acceleration. I think it figured it out for you. Anyway, at the end of the run it displayed its BHP estimate. Which I found to be remarkably close to expectations.

A phone app can do the same thing, might be harder or easier to press the right buttons.

Dynos are good for tuning but if you search discussions here are often not very accurate at providing true power readings because customers really want to see bigger horsepower numbers than reality and customers are (almost) always right. I remember going to a local Lotus club dyno day and there was a guy there expecting something like 550hp from his Maserati Biturbo. He clocked something around 300 and nearly took a nutty. The operator explained that he calibrated his dyno for accurate horsepower vs. the common practice of bragging rights.

On that dyno, my Hermes Europa-Renault returned something like 88hp at the wheels. My power was comparable to (a bit above) a tired-looking LoCort (ex Alan Mann) running with no airbox and brought in by the owner of GKN-47D who had recently acquired it and wondered whether it might still be packing a race-prepped engine. So I figured the dyno numbers were in fact about spot-on. (Stock Twinks around 105 at the flywheel, Hermes kit marketed at something like 110 at the flywheel, add 20%-ish to the power at the wheels.)

[david.g.chapman]

The aDyno App also does not require a standing start. You can set the start rpm to something like 2000 (with the corresponding speed in your selected gear), and when you start the dyno function nothing happens until you reach this speed. It just tells you to drive.

There is therefore no need to time the software start with anything physical, or look down at the phone. You keep the throttle planted until the target speed/rpm is reached and just exceeded (which you entered earlier in the App).
Then ease back and brake to a stop - your run will then be complete and can be stored.

If you try it just be careful on public roads....

Dave Chapman.