Lotus Elan

Headers

PostPost by: Davidb » Wed May 20, 2020 2:06 am

My engine is still fitted with the headers it acquired in the sixties. They are well made, normal 1+4 and 2+3 into collector. I have enlarged the engine to 1720cc and it has 420 cams. Should I be fitting larger, more modern headers? How much more power could I expect?
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PostPost by: nmauduit » Wed May 20, 2020 8:25 am

This would be largely depending on head porting (not only valve size), and max revs the engine can take : if more or less stock (e.g. standard big valve no porting, 6500 redline) I would say 5-10hp max above perfect tune : no need for 45 carbs then either.
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PostPost by: pharriso » Wed May 20, 2020 10:40 am

Equals Exhaust Manifolds

Let me translate that for you :)
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PostPost by: Davidb » Wed May 20, 2020 3:19 pm

Phil, I am afraid you will have to translate!

My engine has "regular" big valves and I did the porting as per David Vizard/David Bean-to keep the torque at low rpm. I suppose my rev limit is about 8K rpm with steel crank and rods but I drive only on the street so I have never been anywhere near that! (I got a terrific deal on an old Formula Atlantic crankshaft and had it refurbished).

I was really thinking out loud last night--would I just be wasting money?
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PostPost by: pharriso » Wed May 20, 2020 3:47 pm

Davidb wrote:Phil, I am afraid you will have to translate!



Headers = Exhaust Manifolds in the UK... :D
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PostPost by: nmauduit » Wed May 20, 2020 5:16 pm

Davidb wrote:My engine has "regular" big valves and I did the porting as per David Vizard/David Bean-to keep the torque at low rpm. I suppose my rev limit is about 8K rpm with steel crank and rods but I drive only on the street so I have never been anywhere near that!


you're much more likely to get exhaust limited at high revs then, and your engine is likely a good candidate to make the most of a bigger bore header, but if you "never" get there then it's a matter of your assessing the chances of the odd track day where you'd regret a bit more to take over a buddy... The regular twink is usually considered as intake limited, but now you have alleviated that to some extent with the porting, plus more flow to account for due to the increased capacity...

As per the best bang per $ for a given setup, it's always a bit subjective and depending on accurate situation (e.g. has it been fine tuned on a dyno/rolling road?)

Awaiting for other opinions (e.g. Rohan's, who's put quite a few thoughts on that matter), in that situation I would be tempted to fit an intermediate header (e.g. "fast road" version from TTR - no affiliation - supposedly good up to 160hp), but for sure the justification for this is still high revs (the higher, the more need for flow). It's not cheap though (esp. adding shipping) - would require a small chassis mod for confort, but would fit reasonably easily. It's certainly worth looking possible american alternatives (Dave Bean ?) .
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PostPost by: Davidb » Wed May 20, 2020 5:33 pm

Phil, thank you! It is 47 years since I left the UK and I sometimes forget the smaller differences.

To be clear, my car is fitted with tubular headers/manifold piping with an o/d of 1.25 inches.

They look like they should do the job and as nmauduit says new headers ain't cheap.
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PostPost by: ecamiel » Wed May 20, 2020 11:35 pm

I switched to Tony Thompson big bore race headers from stock headers. No other change on a near stock motor and had big, noticeable gains in mid range power, Total surprise.
Others have told me that even stock motors benefit greatly from the big bore headers.

I tried both sets of pipes on a race spec Hart motor and had significantly more power throughout the range with the big bore set.

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PostPost by: rgh0 » Thu May 21, 2020 1:53 am

It really depends on how good your current headers and exhaust system are. If they are the original small bore Lotus 4/2/1 setup then something like the TTR road system would definitely give you a benefit of around the 5 to 10 hp you suggest. If you already have a well designed and built larger bore set of headers the benefit may be less. In terms of what you can fit through the standard location in an Elan then the TTR design appears to be the best I have seen. I doubt you would see any benefit going to the TTR race headers versus TTR's road headers with the slightly smaller pipes and you may even find a loss of mid range torque with the race headers in your engine versus the TTR road headers

If you change the headers then a rolling road session to get the carbs and timing set right will ensure you get the full benefit of the new headers. Ensure also that any new headers are well matched to the ports, a small step up from the port to the header diameter is OK but not a step down and no offset.

What cam timing did you use with the QED 420 cams as the QED recommend timing is a little strange and appears to be based on maximum top end power at the expense of mid range torque which is what it appears your looking for in a big capacity road engine

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PostPost by: Davidb » Thu May 21, 2020 2:44 am

Thank you Eric-that is good information.

Thank you Rohan.

The cams I have are Newman 420-32/68 and 68/32 but I set them with 4 degrees advance on the intake from the recommended 108 degrees--So I set the intake at 104 degrees and the exhaust at the 'normal' 108 degrees. I notice the engine idles much more smoothly than it did with the previous cams which were .385 gross lift but more duration--35/70 and 70/35. The exhaust header pipe is 2 inch back to a large transverse muffler with 2 inch tailpipe. I have not driven the car with the rebuilt engine and new cams yet!

I suspect that the headers I have are original Lotus from the sixties so fifty years, at least, of development should see some improvement. Next year though...
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PostPost by: rgh0 » Thu May 21, 2020 3:51 am

Davidb wrote:Thank you Eric-that is good information.

Thank you Rohan.

The cams I have are Newman 420-32/68 and 68/32 but I set them with 4 degrees advance on the intake from the recommended 108 degrees--So I set the intake at 104 degrees and the exhaust at the 'normal' 108 degrees. I notice the engine idles much more smoothly than it did with the previous cams which were .385 gross lift but more duration--35/70 and 70/35. The exhaust header pipe is 2 inch back to a large transverse muffler with 2 inch tailpipe. I have not driven the car with the rebuilt engine and new cams yet!

I suspect that the headers I have are original Lotus from the sixties so fifty years, at least, of development should see some improvement. Next year though...


The Newman cams should be much better than the previous ones - twinks love lift ! 280 degrees duration is about as long a cam as you want in a road car also above that you start to get a hole in the mid-range torque curve. 104 inlet is really a power setting for the inlet cam and for a road car a 106 to 108 inlet probably more appropriate with exhaust in the 108 to 110 range. To narrow down those numbers you need to do your own dyno testing with your specific engine as the cam manufactures timing is normally just generic recommendations for that type of grind unless they have done dyno testing in specific engines ( in which case they should give you details of that testing to confirm its relevant)

A 2 inch tail pipe and large transverse muffler should be good but the skinny original Lotus headers will be costing you some engine output. There will also be a step up at the outlet of the old headers to the larger tailpipe unless the Y piece has been changed and this may have some strange effects also.

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