Twin Cam power outputs

[Spyder fan]

So as not to clutter another topic, could we start a discussion about power outputs for the various twin cam engines supplied with our cars over the years?

I'm particularly intrigued by the hype surrounding the engines that have the "big valve" head and have always been of the opinion that this was a marketing exercise and that the improvement in power over the SE engine would have been possible without the bigger valves and could have been achieved by just using the other improvements such as cams, compression, jetting and exhaust manifold.

The improvement in BHP over and above the SE engine is slightly less than 7%, given that the big valve head was supposed to be a marked improvement I would have expected a greater increase in BHP perhaps to 140BHP when used in conjunction with the other tweaks mentioned above.

Here's an extract from John Smirthwaites web site http://www.jsmotorsport.net/services/lotus-twin-cam,

Power output of the Lotus Twin Cam engine

The power output for roadgoing versions of the Lotus Twin Cam engine are as follows (official figures as claimed by Lotus):

100 bhp (75 kW; 101 PS) Elan 1500
105 bhp (78 kW; 106 PS) Elan 1600, S2, S3
105 bhp (78 kW; 106 PS) Elan S4
115 bhp (86 kW; 117 PS) Elan S2 S/E, S3 S/E, S4 S/E
118 bhp (88 kW; 120 PS) Late Elan S3 S/E
126 bhp (94 kW; 128 PS) Elan Sprint

I'm always willing to learn, and would be interested in what the consensus would be. For instance, was the Big Valve head a better starting point for further tuning?

[rgh0]

The late Mark 2 head castings from around 1968 are all the same and the big valve head was just machining differences to the same basic casting. Head casting condition is far more important than whether it start or as a big valve head or not when rebuilding a head to any specification. Later casting variations were around the twin cam Europa cam fitting and did not change head performance or performance potential

The HP quoted by Lotus for the various engine versions is generally consistent with the modifications made. I have computer modeled a few of the versions and got results that align with the Lotus quoted data allowing for all the uncertainties in what exactly Lotus was quoting and in the inaccuracies in the computer modelling.

cheers
Rohan

[Elanintheforest]

Fords used to quote 105 bhp for the standard engine, and 109 bhp for the S/E, which doesn't sound like an exciting difference!

This little video from Omnitech is worth watching, as it finally explains (to me as least) why one head can be better than another due to the inability to reach down into the inlet manifold properly to exactly match the ports. Whilst the tuning aspect has little to do with your question Alan, it does answer why one standard engine could be so different to another.

https://www.youtube.com/watch?v=PL0kcA2shRk

Mark

[elanner]

This also got discussed here:

lotus-twincam-f39/big-valve-bhp-t33048.html

Nick

[Elanintheforest]

Good stuff Nick, and I think that shows there will never be a definitive answer, except perhaps that they made it all up in the 60s and 70s!

[Spyder fan]

Thanks for the link Nick!

So, looking at Rohan's reply on the previous topic it shows that the Big Valves in the Big Valve head actually contribute just 2 BHP. I have also noted that the head castings are the same (again, thanks Rohan).

I'm not trying to be pedantic and I can see that "Big Valve" is actually a level of specification applied to the base components of the engine which in this case includes increased compression, removal of belt driven fan, revised cam profiles, a better free flowing exhaust manifold and last but not least for those marketing guys, the bigger inlet valves.

All very interesting

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

[stevebroad]

Good stuff Nick, and I think that shows there will never be a definitive answer, except perhaps that they made it all up in the 60s and 70s!

And they don't now?

[Elanintheforest]

I was thinking about claimed power output by manufacturers, but given what has recently been discovered with VW's approach to honesty and integrity, and I doubt that they are the only ones, I do see your point!

[nmauduit]

Thanks for the link Nick!

So, looking at Rohan's reply on the previous topic it shows that the Big Valves in the Big Valve head actually contribute just 2 BHP. I have also noted that the head castings are the same (again, thanks Rohan).

I'm not trying to be pedantic and I can see that "Big Valve" is actually a level of specification applied to the base components of the engine which in this case includes increased compression, removal of belt driven fan, revised cam profiles, a better free flowing exhaust manifold and last but not least for those marketing guys, the bigger inlet valves.

All very interesting

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

not to forget the specific cam cover, which plays a significant role in owner/driver experience (with fins carefully designed along the car direction).

[Mazzini]

not to forget the specific cam cover, which plays a significant role in owner/driver experience (with fins carefully designed along the car direction).[/quote]

Funny!

[Gungebucket]

Aha, Lotus Twin Cam power outputs. Difficult to know where to start really. Firstly there is the "Quoted" power output by the manufacturer, secondly is the question of whether the power was DIN or SAE horsepower, thirdly is where did the information come from and fourthly ..... what do you want to believe! Well, I am going to provide yet another source of information and it is up to you to decide. My information is first hand, i.e. from testing Lotus engines on calibrated dynos and corrected to DIN standards. I apologise if this just sounds like a boast but want to tell you where I obtained my "first hand" information. 1) Working for Tecalemit Jackson fuel injection in the 60s, working at Ford Competitions Dept. Boreham in the 60s, testing engines actually with Colin Chapman at Wymondham, testing engines with John Lievesley and with Brian Hart in the 1970s. OK, the standard production Twin Cam, as in early Elans and Lotus Cortinas, produced 100 bhp when just run-in and 95 bhp after 500 miles. The "SE engines produced only slightly more (can't remember exact figures) and the "Big valve engines" produced 114 bhp on a good day. The works Rally cars in 1967 produced 155 bhp. The best single seater engines in 1967 produced 175 bhp. The Lotus Twin cam was pretty much ignored after the Cosworth BDA appeared but Brian Hart re-looked at it in early 1970 for (damn, I am getting old!) I think it was Formula B. Lievesley did the camshafts and heads, threw away all the old perceived limitations and the 1600s produced 190+ bhp. The last Formula B engines had a pass off requirement of 200 BHP. Now I expect there will be those who will want to dispute what I have said but before they do they need to consider where there information came from.

[Foxie]

........ Lievesley ....., threw away all the old perceived limitations and the 1600s produced 190+ bhp.

What were the old perceived limitations, and please tell us how they produced 190+ bhp !

[rgh0]

Hi Gungebucket
Thanks for that historical data. There is not much first hand information on the engines from around that time so anything else you know would be appreciated

The original published Lotus data was done on the SAE gross basis (edit) I believe as that was the commonly used standard back in the 60's by American and British manufacturers at least rather than the DIN basis and this would explain the difference in the actual dyno numbers quoted above and what Lotus said back in the day. Those DIN basis numbers quoted look good to me and are consistent with all my testing and development work across standard to full race engines. never quite seen an engine to the final Hart formula B level of 200 Hp out of a 1600 twink, but have seen them get close at around 190 + HP running on Carbs with one in a Lotus 7 where you can fit a better exhaust than in an Elan. The cams used were not as extreme as the Hart cams also and with a more modern profile so a little less top end HP but better torque band and driveability for better Lap times in the end

The SAE gross (edit) testing standard is done with no ancillary drives ( i.e. no water pump, fan or dynamo / alternator and with a free exhaust system and no intake filter system. The DIN testing standard requires the engine to be set up on the dyno essentially as it is installed in the car so all those items are required and this substantially reduces the output number for a Twin cam in most circumstances. Clearly a Hart Formula B race car engine set yup as in the car with an good exhaust, open intakes, no fan or alternator would lose less going from SAE gross (edit) to DIN than an Elan road engine

cheers
Rohan

[rgh0]

One of the perceived limitations was head porting and valve sizes. From the Hart heads I have seen the inlet ports were opened up until the broke through into the valve spring seat pocket and then sealed up with epoxy. The valves sizes also went to 1.7 / 1.4 to match the bigger ports and the valves pushed up in the head to fit them in.

The McCoy modified heads with their CNC porting and removable manifolds and the new race heads from Bean / SAS / QED all now have similar port sizes and shapes to the Hart head and can get close to the Hart HP. The porting is not identical as they dont want to break through into the valve spring pocket, as the heads have to last longer these days than the Hart race heads did with their epoxy seal

cheers
Rohan

[Foxie]

Thanks for that info Rohan, now I know where I'm at.

I fitted the QED race head in 2018.

Maybe I should be resting on my oars now !