Lotus Elan

L2 Cams And 33mm Chokes ?

PostPost by: sk178ta » Thu Jun 03, 2004 4:37 pm

I`m running L2 cams and 33mm chokes on Webers and there`s not much happening low down. What can anyone recommend?
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PostPost by: brian wilson » Thu Jun 03, 2004 11:01 pm

Try some Viagra, if nothing happening down below!!!
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PostPost by: types26/36 » Fri Jun 04, 2004 6:42 am

try some viagra
:D :lol: :D :D
But seriously try some smaller chokes....may be 32--30's
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PostPost by: cdraper » Fri Jun 04, 2004 8:00 am

I found my car much nicer to drive with 30mm chokes rather tthan 33mm - have been told I? may be losing 3 bhp at over 7000rpm - so what!
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PostPost by: rgh0 » Fri Jun 04, 2004 8:38 am

I dont thinks the chokes are the real issue with poor low down torque with this sort of set up.

The L2 cam is designed for high revs and works best with very high compression ratios because of its long duration, it inherently has a hole in the torque curve low down.

On the other hand there is no problem getting good low speed torque with up to 36 mm chokes in a 1600 twin cam provided you have the right carb setup to go with the chokes. Of course finding the right setup get harder as the choke size goes up as other factors become more critical but it can be done.


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PostPost by: elj221c » Fri Jun 04, 2004 9:08 am

I agree with Rohan. I don't have a spec sheet for L2s but I do have a Cosworth Mk 12 sheet with the carb info for L1s. It reads as follows; Choke 33, mains 130, air correctors 160, slow running jets 50f9, pumps 35.
Specs I have also for QED 360 and Sprint (big valve) cams aslo say 33 chokes. I originally had BRM phase 3 cams when I bought the car and they had 34 chokes. A really free reving engine, that, and I don't remember it lacking 'low down'.
The main difference with the specs seems to be with the air correction and emulsion tube and I would think you would need a trip to the rolling road to get that sorted.Roy
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PostPost by: rgh0 » Fri Jun 04, 2004 10:06 am

Out of interest I have done some playing with the Kent L2 cams ( 302 degrees duration, 102 degrees max opening point, 0.350 lift) on the Dyno Sim program I use and that I have setup to give me good correlation between the dyno tests I have done and the Dyn Sim program output, so I believe its good for doing comparisons such as a cam change. I presume the cams you have are equivalent to these but I have seen slightly different specs quoted for "L2" cams from different suppliers

It shows that at 3000 rpm the L2 has around 70 lb/ft of torque compared to around 100 lb/ft for a standard sprint cam engine with the only difference in setup being the cams. Certainly this would be seen as lacking down low ! The dyno sym program assumes perfect air fuel mixture for max torque so you dont need a carb problem to generate the lack of torque low down.

In general adding duration to a twin cam camshaft specfication is less important than adding lift ( read the Dave Bean catalogue which supports this also). The 302 duration on the L2 is excessive unless you are trying to build a 9,000 rpm engine and even then you need to combine it with much higher lift and a high compression and lower duration will still give you a better torque curve. It certainly does not work on a road motor.

I have never understood why you would go for an L2 or why it was orginally made as it performs worse than the standard D type sprint cam. It appears to have come from the "more duration is better" school of selling performance cams which has never worked on the twin cam with its good breathing and head design and probably does not work on a lot of other motors either. Increasing lift costs money for head off valve train rebuilds but increasing duration you can bolt in with a new set of cams so the cam sellers prefer to promote this approach as they know people will buy the easy route to what they think will give better performance and thus its easier to sell cams. !

Rohan
(A very biased advocate of short duration high lift cams in twinks for road or race application.)
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PostPost by: types26/36 » Fri Jun 04, 2004 11:26 am

A quote from Burtons "L2 a good fast road cam, simlilar to BLL14 but not so tractable in lower rev range." Valve timing 46/70/70/46. Duration 296 degrees
Lift .345 (8.76mm) inlet full open @ 102degrees
I always understood the "L2" was a Cosworth designed cam profile, I had a Cosworth spec sheet at one time (had the above specs) but alas its not at hand.
I did use L2's a long time ago but dont remember the jetting and the car was quite driveable.
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PostPost by: john-c-elan+2 » Fri Jun 04, 2004 4:02 pm

I must be real stupid as I thought dyn sum was Chinese food ??
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PostPost by: sk178ta » Fri Jun 04, 2004 4:24 pm

John C and Brian W should get together. How their sides will split !!
Thankyou so much to everyone else, and any more thoughts will be much appreciated.
Jim
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