Power range of "hot" engine

[Leibinger]

Power range of "hot" engine

I have a beautiful 62 MKII (BN7) Tricarb centershift, which I wanted to give a little more power. For this purpose, I added a few features, that one normally would chose to improve performance. Those are, amongst other modifications:

• DWR Alloy Head, ports polished
• tubular manifold and “open” exhaust system
• replaced (3) HS4 with (3) HD6 carbs, piston springs and jets according to recommendations of UK Healey Club website (see attachment HD6 Tricarb setup )
• Cosworth pistons, compression ratio is approx. 10.5 to 1
• DWR 8 “hot street” 278 degree cam
• adjustable cam sprocket
• oil cooler
• Mallory ignition
• uprated cooling system

When I had the car dymo tested, it only gave a bit more than 150 HP, with torque approx 235 Nm (174 lb/ft). CO readings were fine the entire range, so it seems the carb settings are correct. Ignition is also set well, as far as I know.

My questions: What power and more importantly torque could I expect to get from an engine set up as described? And where can I start looking for the missing power?

Leo

 

[Hangtown Healey]

Re: Power range of "hot" engine

Wow, I did better than that in November with my almost stock BJ8 engine. I will send you my dyno charts. I could tell that mine was sort of running out of breath at a bit over 5000, but I had great torque (180 plus) starting very low down. I would double check your cam timing and calculate if your carbs really flow as much as a pair of HD8's. I think we had best power at 34 degrees ignition timing. I read somewhere that the stock Healey cam timing sprocket was retarded a little bit.

 

[Dave Russell]

Re: Power range of "hot" engine

If the car was tested on a "chassis dyno"/"rolling road" it's generally accepted that measured engine HP would be 15% to 20% higher than this number. 173 to 180 HP.

There are friction & heat losses in the drive train & rear tire to dyno roller losses to consider. Other variables are air density & variations in the dyno itself.

I don't think you really have any missing power. Sounds like a great road engine. A good stock engine, on the same test, would likely show something like 120 to 130 HP at the rear wheels.

A quick check, on any engine, at 5250 rpm, HP & torque are equal. Formula -- HP=(TQ*rpm)/5250. The HP & torque curves will always cross at this rpm.
D

 

[Hangtown Healey]

Re: Power range of "hot" engine

Sorry, I missread. Yes, if the car rather than the engine was tested, the power sounds reasonable.

 

[AJAX50]

Re: Power range of "hot" engine

I have a similar set up except I've got Weber carbs and a John Chatham iron head. On a rolling road it gave 160 at the wheels at 5300 rpm. I'm not sure what loss is typical for a Healey, maybe 20%, so that is 200 at the fly wheel. The engine is quite flexible, but it really flies between 3500 and 5500 rpm, I try to keep below 5500. As mentioned the are other variables such as air temperature and pressure to correct for, but the real test is how it feels on roads you know or in my case will it eat your friends TR6.

 

[Leibinger]

Re: Power range of "hot" engine

To clarify the 150HP figure stated above: I meant 150HP at the flywheel, unfortunately. Had it been at the wheels, I guess I would have been happy ...

 

[GregW]

Re: Power range of "hot" engine

Hi Leo,
I'd think you should be getting more power out of that engine. It's a little out of my league, but the ports being polished have me wondering. The link to the UK forum talks about widening the mainfold inlets to accept the HD6 carbs, which would lower the charge velocity. Were the ports widened also? If so, how much?

 

[Dave Russell]

Re: Power range of "hot" engine

I agree, 150 at the flywheel is lower than expected. Wasn't sure if you were talking engine dyno or rolling road.

The DWR cylinder head has relatively small but well shaped ports for high intake velocity. Any changes to these ports are likely to reduce power. I would expect the intake manifolds to be smoothly tapered from the carb size to the DWR intake port size.

Unfortunately, ALL parts/systems of the engine MUST be optimized to work together. Intake sizing & mixture, ignition timing, cam timing, exhaust tube sizes & lengths, must all be exactly right to get the expected power.

The DWR8 cam requires pocketing the cylinder block for the exhaust valve heads. If not pocketed, there is danger of the valves hitting the block AND exhaust flow will be seriously restricted. Just pointing out one of the seemingly small items that could seriously reduce power.

At this point, I would take the problem up directly with DWR & go over all aspects of your engine build.
D