Big Valve BHP

[Mick6186]

I have been reading the book ' Lotus, the Elite, Elan, Europa' by Chris Harvey and have found a passage which I hope somebody can clarify. In a section regarding the release of the Big Valve engine the passage talks about the valve sizes, cams & carbs of the engine and states " In this form it gave 126 bhp at 6500 rpm when measured at the propeller shaft ( rather than at the end of the crankshaft), which compared favourably with the SE engines 101 bhp at 6250 rpm when taken at the same source".
Bearing in mind transmission losses through the gearbox ( which I believe can be in the region of 8-10%) this passage suggests the Big Valve engine produces considerably more than the accepted 126 bhp when measured at the crankshaft.

[rgh0]

Yes a strange set of comments.

I have always thought based on published data by Lotus and reinforced by limited testing of standard engines I have done:
standard 1558 cc engine B cam - 105 hp
SE engine C cam - 118 hp
Big Valve Engine D cam - 126 hp

This is SAE standard measured HP at the flywheel - SAE HP includes no engine ancillary such as alternator and water pump losses If I recall correctly

Why you would test an engine at the propeller shaft after the GB but before the diff I don't know and it is certainly not normal practice. Loss in the gear box at full power would be around 2% to 4% in the intermediate gears and less than 1% in 4th gear so it depends what gear you tested it in.

In general 125 to 130 hp at the flywheel is a good number for a standard big valve engine depending how well it is built and tuned and carb and exhaust details.

cheers
Rohan

[pharriso]

This is SAE standard measured HP at the flywheel - SAE HP includes no engine ancillary such as alternator and water pump losses If I recall correctly

Why you would test an engine at the propeller shaft after the GB but before the diff I don't know and it is certainly not normal practice. Loss in the gear box at full power would be around 2% to 4% in the intermediate gears and less than 1% in 4th gear so it depends what gear you tested it in.
cheers
Rohan

I was in Engine Test at Ford Dunton (UK) for 5 years (1980-85). The Dyno is/was attached to a propshaft driven by the Gearbox. Always tested in 4th gear.... I seem to remember some of the gearbox innards being removed to reduce losses.

How could you test without water pump losses?

[john.p.clegg]

Drop the drive belt off and use an external pump in the coolant tank??

John
( guessing )

[pharriso]

Drop the drive belt off and use an external pump in the coolant tank??

John
( guessing )

Technically you could... we did not!

[elanner]

I too have had 105hp stuck in my head for several decades. I think most manuals say "Max BHP @ r.p.m.: 105hp @ 5,500 STD; 108hp @ 6,000 S/E" - three hp obviously being a useful selling point in those days!

But in what must be one of the last manual editions printed by the factory (part number X036 T 0327Z) - "Revised Reprint, October 1974" the power had mysteriously dropped by a mere, ahem, 14%:

The word "net" appears after "Max BHP" too, suggesting that the measurement is further down the drivetrain or with ancillaries.

By this time the marketing department presumably didn't object to dropping the power below the magic 100hp number because it helped sell the newer cars!

Nick

[oldchieft]

Drop the drive belt off and use an external pump in the coolant tank??

John
( guessing )

Technically you could... we did not!

If I was doing it I would get a electric motor with a pulley on it and mount it next to the engine.

Jon the Chief

[rgh0]

I guess Lotus potentially changed the standard used from gross to net in line with the changes described below. Maybe a standard engine with its relatively restricted cast iron exhaust manifold does drop to 90 hp at 5500rpm I don't think the belt driven accessories would make up the full 15 hp loss from the originally quoted 105 hp. Maybe the revs that maximum power was reach under the different test conditions also affected the power produced. Lots of variables and marketing number games back then as there is now.

i.e. taken from the wikipedia so it may not be totally correct!

"SAE gross power[edit]

Prior to the 1972 model year, American automakers rated and advertised their engines in brake horsepower (bhp), frequently referred to as SAE gross horsepower, because it was measured in accord with the protocols defined in SAE standards J245 and J1995. As with other brake horsepower test protocols, SAE gross hp was measured using a stock test engine, generally running with few belt-driven accessories and sometimes fitted with long tube test headers in lieu of the OEM exhaust manifolds. The atmospheric correction standards for barometric pressure, humidity and temperature for testing were relatively idealistic.

SAE net power[edit]

In the United States, the term bhp fell into disuse in 1971?72, as automakers began to quote power in terms of SAE net horsepower in accord with SAE standard J1349. Like SAE gross and other brake horsepower protocols, SAE Net hp is measured at the engine's crankshaft, and so does not account for transmission losses. However, the SAE net power testing protocol calls for standard production-type belt-driven accessories, air cleaner, emission controls, exhaust system, and other power-consuming accessories. This produces ratings in closer alignment with the power produced by the engine as it is actually configured and sold.

cheers
Rohan

[elanner]

Wow, God Bless Wikipedia. Amazing stuff, as usual.

I realized after my earlier post that while the non-Sprint numbers had dropped 14% the Sprint numbers had not! So those Big Valves are good for 36hp, or 40% more power, guvnor.

Trust me, I'm in marketing.

I am too, but at a software company, and we all know that software does exactly what the blurb says.....

Nick

[seniorchristo]

My take on this is Lotus wanted to inflate relative HP figures to help market the Sprint. Maybe owners who have driven both versions have an opinion.
When referring to the "deratings" listed in the Lotus Workshop Manual,The Original Lotus Elan by Robinson and Ross page 66 states
"These apparent deratings appear to have occurred sometime after the introduction of the Sprint engine, when Lotus were anxious to justify their much publicized claiam of a 25% power increase for the new big valve engine".

[rgh0]

In Lotus Elan Gold Profile page 132 in a road test of PLus2S 130 a graph of HP for SE and Big Valve engines are shown with both SAE nett and gross curves .

The nett curves show 101 hp for the SE engine at 6000 rpm and 126 hp for the Big Valve at 6500 rpm.

The gross curves show about 111hp for the SE engine and 136 hp for the Big valve.

Thus "substantiating" the 25% power boost claim which is mentioned in the article on a nett hp basis if you believe the data provided. To me the gap appears to be to large. The curves are "edited" as both the gross and nett peak numbers occur at the same RPM but in practice the nett HP peak would occur at a lower rpm.

cheers
Rohan

[rgh0]

I have been doing some more playing with my engine simulation program ( Dynomation version 5).

Varying the individual engine differences in the simulation and using my best approximate estimates where items are not covered by the simulation in detail (e.g. the exhaust system modelling in the simulation is approximate and no modelling of the engine fitted fan) and I get the following:

Standard to SE engine:

Camshaft ( 264 versus 272 degrees) = 5 HP
Exhaust System ( cast manifold 4 to1 versus cast 4 to 2 to 1) = 5 HP (approx.)

Total 10 HP which matches the originally quoted Lotus difference

SE to Big Valve engine

Inlet valve size (1.53inch to 1.56 inch) = 2 HP
Valve cam lift ( 0.35 inch to 0.36 inch) = 1 HP
Compression Ratio (9.5 to 10.3) = 3 HP
Belt drive losses (engine driven fan versus electric fan) = 2 HP (approx.)
Exhaust System ( cast 4 to 2 to 1 versus tubular 4 to 2 to1) = 3 HP ( approx.)

Total 11 HP which matches the originally quoted Lotus difference

The 105 HP Std / 115 HP SE / 126 HP Big Valve numbers all appear to me to have been done on the same SAE gross basis. SAE Net HP would be maybe 15 HP less for the Standard engine, 12 HP for the SE engine and 10HP for the Big Valve engine. The variation is due to the different exhausts as installed in the car ( the worst exhaust loses the most going from Gross to Net) and no engine driven fan for the big valve ( so it loses less from Gross to Net). I personally believe Lotus marketing played with Gross versus Net numbers quoting Net for the SE and Gross for the Big valve to get the claimed 25% power increase.

Rear wheel HP for a standard Big Valve Elan is around 95 HP. This equates to a flywheel SAE Net HP of around 115 to 120 HP as the SAE Net HP is roughly the flywheel HP of the engine as installed in the car. This then matches roughly the quoted 126 HP on a SAE gross basis.

In the end though its a lot of guessing on what was going on to try to make the numbers add up and make some sense


cheers
Rohan