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Horsepower and the joys of old machinery

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57_BN4

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I have built an engine test rig in my old Healey chassis by installing a Clayton waterbrake absorber where the diff used to be. This way I can easily and relatively safely run the engine and gearbox under load and check that all is well before installing it into the car- a job I'd prefer to do only once. The old Clayton dyno is modernised with a loadcell that transmits RS232 data back to a Labview program which converts rpm and torque into hp and record it into a log file.

The problem is that I'm only getting 80hp at 4600 rpm (claimed 102) and 114 lb-ft torque at 2400 rpm from an advertised 142lb ft. This particular engine is from an A105 sedan and is as it left the factory except for having hardened exhaust seats installed at some time in the past and a Pertronix in place of the points. Mechanically it is in excellent condition with fully rebuilt carbs and runs an AFR of about 14:1 at full throttle.

Does anyone have information on how the 2639cc engine were rated at the factory? Is the 102hp under optimised conditions with no generator, water pump or fan? What is a realistic true hp output given the conditions?

Differences to the way the factory may have measured hp are:
*the A105 sedan engine is mechanically identical to the BN4 except for dished pistons. The 102hp figure is used for the sedans as well as the Healey which is a bit of a giveaway to the accuracy of the factory spec since lowering the c/r must reduce the output.
*The measured figures include losses in the gearbox which is in 4th gear, without OD. I don't think these losses will amount to much though and the gearbox is barely luke warm after testing
*The exhaust system is not the original one but is in reasonable condition.

Soon I will be swapping out the sedan engine for the freshly rebuilt Healey one so it will be interesting to compare the low vs high compression engines.

Has anyone tested a 'real' Healey engine against factory spec and obtained similar or different results?

Andy.



zwaterbrake.JPG


zengine.JPG
 
Very clever!

Disclaimer: I'm not a dyno expert, but I've been researching this topic over the years. Please refute if I'm wrong; I'm still learning (I know you will!).

Horsepower ratings were changed by the SAE a while back (many years, actually) from 'gross' to 'net.' The former were ratings without dynamo, power steering, etc. (maybe even without water pumps). The latter was output at the flywheel with all necessary accessories attached and working. The original rating is almost certainly 'gross;' that would explain at least some of the difference.

Also, ratings were at the flywheel (no drivetrain). Rolling road dynos--which measure at the rear wheels--usually allow for about 15% drivetrain loss. Your rig is somewhere in between; I'd guess you could allow at least 5% power loss driving the clutch, transmission and gearbox.

Output will vary based on atmospheric conditions. Does your app have inputs for air temperature and pressure, maybe even humidity? Original HP claims were a marketing tool so were usually given under ideal conditions.

All considered, your readings are probably in the ballpark. Do a compression check; if results are nominal and all other parameters (timing, etc.) are correct I'd say 'good engine' but, again, I'm not an expert.
 
Bob

I think you might be right, because Jaguar claimed 265 bhp for the E Type in European tune, yet in his ambiguously named book A Climax in Coventry, Walter Hassan, who designed the XK engine and later the V12 states the the latter gave 270bhp and the former 170, so that's a 95 bhp discrepancy.

I was a friends of Steady Barker's who'd edited the Brit Mag Autocar in the sixties and I remember him saying how miffed he was when they discovered that the review E Type was a hotted up special and 25 mph faster than the customer's version.

To be fair to Austin, they were more conservative than Sir William, so a discrepancy of 20 bhp seems reasonable.

Ash
 
Thanks for the replies. I had a read of the previous dyno posts a while back and came to the conclusion that I couldn't decide how accurate original specs were as some ppl were getting the same as factory spec, others above and others below.

Bob- I can pretty much put any inputs into it but since I mainly set up the rig to test/run in the new engine I didn't get too scientific about it at this stage. I live a short walk from the beach so altitude compensation isn't really an issue here.

This week I'll swap over to my spare head which has had some combustion chamber reshaping and 45 thou skimmed of the face. Maybe I can claim back some of those precious 102hp before the neighbors call out the noise police.

So far the rig has proved its worth as the new synchro cones I got from AH4H don't work on 3rd and 4th gear. 2nd is ok but if I hold the stick towards 3 or 4 with the engine idling it baulks weakly then pushes the cone aside. Kind of like the ramp angle is not quite right. Gearbox will be coming apart again one day.

Andy.
 
Hi Andy, interesting rig you have there. I have no experience/knowledge with dynos, but I think the real value is using a dyno to evaluate changes, in other words its value is in relative performance. The absolute HP and torque are not as important as the changes made by swapping parts and changing tuning. look forward to your progress getting your Healey on the road.
 
Andy,
Love your dyno! The dished pistons are going to reduce the HP a fair amount. Also, peak horsepower is usually reached at the higher RPM levels. The factory motor HP peaked at 4600 RPM. Did you rev your motor past 4600 RPM to see where your engine's peak HP was achieved? Even using OEM parts, the cam timing can vary from engine to engine and peak torque and Hp will be found at different RPM levels.
 
I'm impressed with your rig, great job!

I note that you are testing an early bn4 engine with the two port head. The Healey's were never happy with this unit, wouldn't be surprised if they over rated it to make it look like an improvement over the 4 cyl 100 -- even though many books report that the car was slower than the 100 in most respects. So maybe your 85 hp is a reasonable number for this engine.

I am sure the later 6 port head would do quite a bit better, especially the BJ8 engine.
 
I did a few more runs today, just wanted to record a baseline before swapping the head over. I figured the neighbors didn't like me so much today as they put on some loud music in protest.

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Quick video from today


After fixing up an exhaust flange leak and adding two heat insulator shims in the carb mountings the power has dropped to about 76hp and torque 109lbft.

Agree that the BN4 head is a real crapper but I'm determined to stick with it for the sake of... yeah I don't really know why.

Andy.
 
Why did you stop at 4650? The engine was continuing to make horsepower when you pulled the plug. Apparently you did not read my earlier post. Why didn't you go to 5000 RPM to see what the power curve actually looked like? Also, why didn't you hold the throttle open at 4650 for at least a few seconds? Was your engine at full operating temperature when you made your pulls?
 
Hi Richard,

actually I did read your post but it isn't what I'm trying to achieve. All I want to get out of this is to see how different the actual vs 'factory' hp figure is, see if I can get close to the factory figure and to run-in and set up the Healey engine and gearbox so I don't have to pull them out once the car is assembled. The factory figures are taken at 2400 and 4600 so those are the only two points I'm interested in.

The redline for the earlier engines is 4750 too which is probably inadvertently carried over from the four cylinder engines but either way, I'm standing right next to a 54 year old engine that still has the original pistons and rods untouched from the factory. If I over-rev it and one of them jumps out of the block and chops lefty off then I'll be very upset.

The hp figure doesn't increase if I hold it there, actually it drops slightly after about ten seconds.

Last night I pulled the head off and each piston has a small puddle of oil in the dish so I think the oil rings aren't as good as they could be. Compression is an even 140psi on all of them and crankcase fuming is minimal so I'll swap on the other head tonight and see what changes.

Andy.
 
Last week I did some more power runs with the other cylinder head installed to see if there is any improvement. Looks like not much but the good thing was it didn't run on at all which was the primary reason for modifying the head. I reshaped the combustion chamber to remove most of the peak between the valves and then machined 0.045" off the face to increase CR to 9.5 with flat top pistons. This old engine has dished pistons so isn't a very good comparison.

Other changes were to replace the generic muffler-shop exhaust system with a NOS pair of front pipes and NOS BN4 single-outlet muffler. It was considerably noisier than the generic system but no real power gain. If anything the torque has dropped off at low rpm, possibly because the front exhaust pipes are now quite a bit bigger diameter than the previous ones.

It does tell me that the factory ratings of 102hp and 142lbft were almost certainly made up numbers...

torque.PNG


power.PNG



Next run will be done with the Healey engine which is fully reco'd and has the correct flat top pistons.

Andy.
 
I'm sure you've checked but I'll mention it anyway. Is the camshaft still in spec. They are worn out on most old engines I rebuild.

Ash
 
Hi Ash,

no haven't checked anything on this engine, it is just as it left the factory in 1957. This engine is from an Austin A105 which I got to test that is all working correctly before firing up the newly recon'd Healey engine.

Now that you mention it, I will check the cam specs on both engines.

Andy.
 
The camshaft makes the biggest difference to power output, so it'd be worth popping one from a BJ8 in your engine, though you may also need to change the distributor cross shaft as well.

Ash
 
EV2239 said:
The camshaft makes the biggest difference to power output, so it'd be worth popping one from a BJ8 in your engine, though you may also need to change the distributor cross shaft as well.
Click to expand...

And triple Webbers, a stage three head, lightened flywheel, nitrided crank and bore it out to the max. Should just about do it. :banana:

:cheers:

Bob
 
Did you try a richer fuel mixture? 14:1 is pretty lean for WOT. I'd go with 13:1 at the leanest (shoot for 12.5), and around 36-37 degrees total timing on that engine, at least for dyno testing. Add 10-15% to correct horsepower lost through the tranny.
 
John Turney said:
:iagree:, although SUs make for easier mid range driving.
Click to expand...

I agree! just the camshaft, the higher compression and otherwise standard with probably give 30+ more horse power and no loss of torque. Re-profiling the existing cam and facing the tappets is inexpensive.

The icing on the cake would be the late BJ8 Spring diaphragm clutch on a lightened and balanced flywheel. Smoother and with a nice light clutch.

Triple Webers and a fancy head with bigger valves would be extremely expensive and add another 10 bhp if you were lucky.
 
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