Lotus Elan

Bigger Holes in my Head

PostPost by: JonnyPlus2 » Sat May 06, 2017 1:11 pm

Hi,
My head has the puny 39mm (all sizes approx.) stock valves. Since I am building up a 1760cc engine I would like to go up to 41mm valves. Can the current seats be machined out to take the bigger valves? Thanks.
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PostPost by: promotor » Sat May 06, 2017 1:37 pm

Valve seat insert outside diameter is approx 41.23mm so you would be just on the outside limit.

What's the need to go bigger? FIA race Lotus Cortina's and Elans manage circa 175bhp on 39mm valves.
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PostPost by: JonnyPlus2 » Sat May 06, 2017 1:57 pm

175 bhp with 39mm valves. Who wudda thunk it? That is interesting. I shall think about that .

My engine will have a redline of 7K and it will be almost 1800cc. I am hoping it ends up producing as much torque as a standard Elan below 4K with a *lot* more power in the 5-7K range. This will give the car a Jekyll & Hyde personality which, as my sons would say, is how I like to roll. :-)

Thanks for this.

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PostPost by: rgh0 » Sat May 06, 2017 11:26 pm

Whether you need to go to bigger valves really depends on the rest of the head modifications planned, cams your going to use and your target HP.

A standard head with little or no porting and standard "big valves" benefits from an increased lift up to around 0.42 inch hence the popularity of the QED 420 cam. A 1760 twin cam with get a lot more low end torque with this cam as well as top end power at 7000 rpm over 150hp if built right.

Lots of porting ( expensive) and bigger 1.625 inch inlets and 1.4 inch outlets and a.44 inch lift 285 duration cam and bigger carbs and exhaust will get you up around 170 hp at 7000 rpm in a 1760 cc engine with as good low end torque as the QED 420 and smaller valves.

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PostPost by: JonnyPlus2 » Sun May 07, 2017 1:05 pm

Hi Rohan,

Thanks for laying out the landscape for me. Your answer reminds my of why my Plan A was a Honda S2000 engine! lol This is a Semi-Low Budget Production but since I only have Stromberg heads I'll have to send one to McCoy (hence the Semi-Low Budget) for a makeover. From what you and promotor say I think that I'll either stick with the my standard 1.53" valves or go to the Huge Valve (TM) 1.625" option.

One of the many things I liked about my old Plus 2 S/E was that it felt a like a cooking engine when I was just potting about but if I dropped down a gear or two it would turn into Godzilla Jr.! It never got old!

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PostPost by: rgh0 » Sun May 07, 2017 8:31 pm

Hi Jonny
If your getting McCoy to do a conversion for you talk to him about what you want and your budget as he can build the converted head to whatever spec you want at not much incremental cost and supply you with suitable cams /valves /springs etc

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PostPost by: JonnyPlus2 » Sun May 07, 2017 9:21 pm

Hi Rohan,
I shall do that although I must say that getting my cams reground to Q420 spec @ 85 quid a pop appeals to me a lot more than McCoy's cam prices. :-)

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PostPost by: 2cams70 » Mon May 08, 2017 12:39 am

Interesting about those FIA engines - so that's 175HP, 39mm inlet valves and 1600cc !

I know a lot of the specs are probably secrets but can anything further be divulged? what sort of cam spec's are involved? lift, etc? What type of carbs? 45's I presume. Do they run on normal high octane pump fuel?

What is tractability like at low RPM?
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PostPost by: rgh0 » Mon May 08, 2017 7:24 am

2cams70 wrote:Interesting about those FIA engines - so that's 175HP, 39mm inlet valves and 1600cc !

I know a lot of the specs are probably secrets but can anything further be divulged? what sort of cam spec's are involved? lift, etc? What type of carbs? 45's I presume. Do they run on normal high octane pump fuel?

What is tractability like at low RPM?


Not that hard to get 175hp from a 1600 twink even with 1.53 inch valves these days. The new heads with their much bigger inlet tracts or John McCoys converted heads enable much better porting than was historically possible. A 290 to 300 degree duration .46 lift cam will then produce that sort of HP at around 8000 to 8500 rpm and have a good torque spread and be quite tractable at lower revs. Much better than the older style 320 degree duration race cams especially in an Elan or Cortina. You need a good exhaust and 45's running 36 or 38mm chokes and around 12.5:1 comp ratio on Avgas or racing fuel and also have everything else built right. You will get a bit more HP in a Cortina as you can fit a better exhaust than you can in an Elan.. In a light open wheeler with good gear matching to the circuit you can probably go for a bit more power still and less torque by going to a slightly longer duration and slightly higher lift cam.

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PostPost by: promotor » Mon May 08, 2017 9:44 am

2cams70 wrote:Interesting about those FIA engines - so that's 175HP, 39mm inlet valves and 1600cc !

I know a lot of the specs are probably secrets but can anything further be divulged? what sort of cam spec's are involved? lift, etc? What type of carbs? 45's I presume. Do they run on normal high octane pump fuel?

What is tractability like at low RPM?


Un-related but even more astounding - I will be looking over a 1600cc BDR this week - that is 250bhp! Rev's to about 9500rpm I believe. 16 valves help though!
Last edited by promotor on Mon May 08, 2017 12:54 pm, edited 1 time in total.
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PostPost by: rgh0 » Mon May 08, 2017 9:56 am

More than 200 hp per litre appears to be achievable in a normally aspirated engine but you don't get much torque below 12000 rpm :lol: . See what the 1000cc GP motorbikes do e.g. Honda RC213V 230hp

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PostPost by: promotor » Mon May 08, 2017 10:31 am

rgh0 wrote:More than 200 hp per litre appears to be achievable in a normally aspirated engine but you don't get much torque below 12000 rpm :lol: . See what the 1000cc GP motorbikes do e.g. Honda RC213V 230hp

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Absolutely - apparently the BDR has only got circa 150 lbf ft!
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PostPost by: 2cams70 » Mon May 08, 2017 1:02 pm

I always thought those F20C Honda S2000 engines from the early 2000's were an amazing piece of kit. 240HP @ 8,600RPM out of 2.0 naturally aspirated liters. All whilst being 100% reliable, emissions compliant and running normal pump fuel.

Had the pleasure of driving one once. Tame as a garden variety Honda Civic when pottering around town but sounds like an angry whipper snipper at full noise.

Still love those classic BD series Cosworths of course but have utter respect for Honda's engineering capability when it comes to engines in particular.
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PostPost by: holywood3645 » Tue May 09, 2017 12:01 am

2cam70
The F1 guys would strongly disagree with your Honda engine comments! :D
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PostPost by: 2cams70 » Tue May 09, 2017 3:05 am

I'm not necessarily talking about recent events but historically Honda engines have always been beautifully engineered. They have a long racing history that the other Japanese manufacturer's don't have. I've pulled apart quite a few of their lawn mowers and brushcutters and even those engines are works of art!. Once I had an air-cooled Honda 1300 coupe from the early 1970's (Soichiro Honda's pet project). Flawed yes (was a learning curve for them) but fun to drive, unique (unlike most Japanese cars of the time which were just carbon copies of British designs) and great engine. Almost as much power as a standard Lotus Twin Cam but 1300cc.

If Honda's 1960's DOHC F2 engine wasn't as good as it was Cosworth might never have developed the FVA. We might never have got the BDA either. Honda's DOHC F2 engine was more competitive than the single cam Cosworth SCA hence Cosworth had to develop the FVA to stay in the game.

And no - I don't work for Honda !
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