Lotus Elan

Head and Camshaft advice

PostPost by: Donels » Tue May 08, 2018 7:42 pm

I am just about to start an engine rebuild on my +2 130S engine. I want a tracktable road engine that will run on unleaded fuel, so the first thing is to get the head fitted with hardened valve seats. So while getting this done is there any advice on other head work, gas flowing etc. Also any advice and experience on cams and good workshops who know what they?re doing?
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PostPost by: promotor » Tue May 08, 2018 8:18 pm

Contact John Smurthwaite @ JSMotorsport - he's a Twincam specialist. He's local to you and does a very good job.

Have used him and his work is top notch.
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PostPost by: MarkDa » Tue May 08, 2018 11:47 pm

I too have used John, he is very thorough and the end result was first class.

He does a lot of race engines and generally has up to 10 twinks on the go at any one time.
My big valve engine turned out c140 bhp on his dyno after a few hours running in with no upgraded parts but plenty of new bits because it had been stood and seized for a long time, we did balance the bottom end.
This output is probably down to his FIA manifold rather than production 4-2-1 and also a 40 thou overbore gives another 40cc. Which is 2.5% more capacity so could be worth 4 bhp in itself.
The engine is very tractable - presumably they always were if you set them up right?
No doubt aided by complete strip, clean and rebuild of carburettors which I had done separately.
If your carbs are 50 years old and haven't been made good as new then budget ?400 and 6 weeks lead in. It will definitely be worth it.

His standard rebuild price is pretty good but parts can soon run the bill up.
They are competitive because he is a volume buyer but given his racing background he buys quality.
He gets very busy especially during the summer so be prepared for a wait to get in and a fairish time in the workshop.

I was impressed that he didn't try to sell extra power. For a road engine he pointed about that youl spend a minute amount of time using an extra 20 bhp above 6250 rpm but an awful lot of time mid range where you want smooth response and decent torque.

Are you sure that you only need head work?
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PostPost by: Foxie » Wed May 09, 2018 12:40 am

Donels wrote:I am just about to start an engine rebuild on my +2 130S engine. I want a tracktable road engine that will run on unleaded fuel, so the first thing is to get the head fitted with hardened valve seats.


Twincam heads are already fitted with alloy steel seats. When unleaded fuel was introduced a lot of unscrupulous engine shops made a lot of money unnecessarily replacing good valve seats. :o
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PostPost by: Donels » Wed May 09, 2018 7:27 am

No I?m not sure it?s just head work, however I have rebuilt several crossflows so may do the bottom myself using Coventry Boring for the machining.

I did wonder about the valve seats. Clearly they?re not aluminium so needing to replace them for unleaded is an urban myth?
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PostPost by: MarkDa » Wed May 09, 2018 8:43 am

If you are competent and confident enough then rebuilding an engine that's in good running order now then getting it back to factory specification is theoretically a DIY job.

JS sub-contracts much of the machining, if you have contacts in that field so much the better.
However the great advantage of using an engine builder is that they have the tools and measuring devices to check crank and bore diameter/ovality. They will pressure test the head - mine had a couple of cracks that needed welding.

They will also have the experience to know whether a head has been 'messed with' and how to correct it. JS measure and adjust combustion chamber volume for balance and compression ratio for example which isn't exactly DIY.

John replaced one of my conrods because of a big end irregularity that was 'in spec' but more than he was happy with.

All in all these small details add up in producing a smooth running and ultimately tractable engine. But at a price - you pay your money and make your choice really.
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PostPost by: rgh0 » Wed May 09, 2018 11:54 am

The standard sprint cam profile is about as good as you can do with a standard road engine and the standard valve components. With this cam you can do a bit better than the standard Lotus big valve torque and power curve to get around 135 hp with a better exhaust, a little higher compression and a little more aggressive ignition advance curve and a good quality engine build doing things like matching combustion chambers, boring to 1600cc and a lot of other small build details.

Much more is possible in a road engine with a 6500 rpm limit with short duration high lift cam i.e. less than 285 degrees seat to seat and high lift in the 0.41 to 0.44 inch lobe lift range . This sort of cam can give you more torque and more power over the standard rev range with a peak of around 150 hp in a near standard head and a 1600cc engine. This build requires a complete new valve train design in terms of valves, springs, followers, cam base circle etc to fit it in. The cost is actually not much more if doing a total rebuild that requires these to be replaced.

More is possible still with a bigger capacity and / or high rev capability bottom end that is still very road tractable. it really depends on how much performance you want and how much you are prepaid to pay. You can build road engines that will be better mid-range and will deliver 180 hp+ at 7500 rpm without the need to put a Zetec in the car.

All of this is possible in your own garage if you have the knowledge and some basic hand fitting, machining and measurement capability and can specify and outsource the specialist machining. This takes time and effort to develop so hard to justify for a single rebuild. If you have a specialist twin cam workshop locally who understand all of this and will do a good job and not rip you off to much based on your lack of knowledge compared to them then you can work with them to build the engine you want.

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