Lotus Elan

Rolling Road Tune with QED 420 cams

PostPost by: mark030358 » Thu Mar 28, 2024 6:46 pm

So as part of the ongoing drive to make my car run as good s it can do, I booked a Rolling road session with “Mikeanics of Congleton”.

I booked this session based on reputation of the tuner who has been in business many years and is particularly clued up on carbs.

Attached are two dyno plots, one from a bench dyno, the other from the RR tune. Interesting to note that the tuner said the engine was losing power at the top end due to the air box/exhaust, whilst the engine dyno had no air box fitted and had a much larger exhaust (I have the video).

Anyway, I’m very happy with the results which gets me some way towards my goal.So with QED 420 cams and a ported head we ended up with 55 idle over 0.9 air corrector, 145 min over 180 air corrector while the ignition was 31 dregs at 4000 rpm.

No off idle stumble, no 3200 rpm bog, drives really well.

Cheers
Mark
Attachments
IMG_3944.jpeg and
IMG_0283.jpeg and
Last edited by mark030358 on Thu Mar 28, 2024 7:32 pm, edited 2 times in total.
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PostPost by: 661 » Thu Mar 28, 2024 7:02 pm

Can't see anything attached, but it's what it's like to drive, and being safe ( fuel mixtures) that's more important for a road car.
Well done.
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PostPost by: SimonH » Thu Mar 28, 2024 7:05 pm

That is a mistake that race Dyno operators often make. Run without the vehicle airbox or exhaust then wonder why it’s flat at the top in the vehicle. Good that you got the results you wanted though
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PostPost by: mark030358 » Thu Mar 28, 2024 7:19 pm

Just added the plots, apologies for missing them off.

Cheers
Mark
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PostPost by: 2cams70 » Fri Mar 29, 2024 12:49 am

Thank you for posting. That is good information and you’ve done the right thing by having it professionally tuned on a dyno rather than guessing. Set It right at the beginning and there’s no further need for gadgets such as 123 ignitions and air fuel ratio meters. What size chokes did you you settle on?
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PostPost by: rgh0 » Fri Mar 29, 2024 4:03 am

Yes I have seen a 4 to 5 hp loss with the standard airbox and the restriction it causes with the No4 cylinder in a 160 hp engine. You data seems consistent with that though hard to read the graphs axis numbers in the photos.

cheers
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PostPost by: mark030358 » Fri Mar 29, 2024 10:59 am

@Rohan/2 Cams

uploaded again with clear number, apologies.

Chokes used were 34. In fact the chokes were the only item of the carb that were as QED spec, mainly because I didnt have any others.

thanks
Mark
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PostPost by: Craven » Fri Mar 29, 2024 1:45 pm

Maybe of some interest, historical power output curves from a Twincam back in 1960’s
Note BHP at 4500 rpm is around 110 appox same as the 420.
P1030154.JPG and
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PostPost by: Lotus54 » Fri Mar 29, 2024 2:32 pm

I do not understand why it would completely drop out at ~5500 rpm? Like it hit a rev limiter or something.

Mine (S/E big valve specs) is still pulling hard at 6500 where I have the rev limiter starting to kick in (soft limiter).
I have stock airbox/filter, stock exhaust size with SJ head pipes.
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PostPost by: disquek » Fri Mar 29, 2024 3:44 pm

Lotus54,

Unless there is a rev limiter, that's simply where the dyno operator chose to lift off. Which I see as a bit early. Typically dyno operators will lift off as soon as they see the curve flatten out. Rarely do curve flatten and pick back up.

I'd bet that this guy was just being cautious.

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PostPost by: Lotus54 » Fri Mar 29, 2024 3:51 pm

Ok, I didn’t think of that.
With the engine graph, I’m sure it was still making more power, with a redline of 6500, seems strange to stop at 5500? (Well, first couple pulls that makes sense)
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PostPost by: mark030358 » Fri Mar 29, 2024 10:10 pm

disquek wrote:Lotus54,

Unless there is a rev limiter, that's simply where the dyno operator chose to lift off. Which I see as a bit early. Typically dyno operators will lift off as soon as they see the curve flatten out. Rarely do curve flatten and pick back up.

I'd bet that this guy was just being cautious.

-Kyle


Hi Kyle,
I asked the tuner the exact same question.
You are correct in saying the tuner took his foot off around 5500 RPM, hence the sudden drop off. The engine will rev very safely given the work to a standard 6750 and a bit more actually but the power and torque was falling off. I'm not inclined to change the air box, or fit TTR manifolds and big bore exhaust but I'm happy with the way it pulls and runs. I fitted the car with an electronic rev limiter some time ago, set to around 6800 from memory.

Also, has anyone had any issues with the current crop of dizzy caps? During setting the ar up mine started to fail, poor spark etc. I had what I hope is a "Lucas" cap with me, and when replaced all OK. He mentioned he gets this a lot with the repro brands, especially Cosworths when they get hot. On the one that failed I could see a small brass ring around the centre section, but on another cap I have this is not present. So wondering who sells what now.

cheers
Mark
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PostPost by: h20hamelan » Sat Mar 30, 2024 12:00 am

I have had nothing but problems with newer Lucas, and have binned the lot.
Finding NOS Bosch is near impossible, but there are some still out there now fetching big bucks.

While 2cams may be correct about set and forget, and forget about all the fancy gadgetry. Those of us 1000’s of miles away from any such rolling road of course can not.

So with the lack of quality ( knowing Distributor Dr and others can supply) there seems to be some real issues with quality. As 123 supplies new and likely not as problematic, how else can you be assured of issues without some modern gadgetry?
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PostPost by: David1953 » Sun Mar 31, 2024 5:30 pm

This looks similar to my experience, The engine dyno used the QED setting for the carbs which was very rich, around 10:1.
In the car with the carbs set and stock exhaust the power is flat at the top end. But as a road car I do not need any more.
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PostPost by: tonyabacus » Sun Mar 31, 2024 7:32 pm

The airbox on a twin cam is usually tapered towards the rear and so the rear two cylinders can show as running different to the front two, as the volume of air is reduced by the shape of the standard airbox. I noticed a guy on ebay that is manufacturung airboxes which have a different depth to the factory fitted box and has apparently seen good results from this modification. It looks very much the same as the standard box and is a straight forward replacement for the original.

He only makes in small batches so you need to keep an eye on the site under Lotus Airbox, unfortunately I cannot recall his name, but his last advert was about six weeks ago and may possibly be located through the eBay advanced search box using the above title in the recently sold section.
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