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Cams 107 with 104  Rating:  Rating
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 Posted: 05-05-2008 04:08 pm
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Tim Knowlton
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I am considering a cam upgrade and would like some advice on the 107 exhaust and 104 intake combination as a set. I have done som research and am told that this combo is the best of both worlds. Pulls strong through the 7000RPM range with a very strong low end also. I have dellortos 40's and stock bottom end crank pistons etc. Any advice is welcomed. Also where to by the most reliable set. As always thanks for the advise.

Tim Knowlton

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 Posted: 05-05-2008 08:29 pm
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Scott Robinson
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Hi Tim.

That has been my plan as well after lots of consideration, especially since Tim Engel has recently amplified that 2 107s are wimpy above 5 grand. I have a nice pair of real Lotus 107s I haven't installed--have been waiting for someone with 104s to say they were interested in a trading one 104 for a 107. The JHPS store sells cams as does Dave Bean Eng., Delta and JAE. If you buy a set of 104s I would be happy to trade a 107 for a 104.

Scott Robinson

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 Posted: 05-05-2008 10:44 pm
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Tim Knowlton
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Scott,

Thanks for the reply. I hear that with the 107/104 combo a 2 litre with dellortos really pulls strong through the entire RPM range give powerfull low end off the line and top end should improve. Would you agree with that. Any other thoughts or suggestions???

Tim

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 Posted: 05-05-2008 11:10 pm
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Jensen Healey
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Remember that the 104 requires the performance valve springs.

You can slap a pair of 107's in there and be driving after a few weeks of valve shimming. ;-)

Kurt

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 Posted: 05-05-2008 11:39 pm
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Tim Knowlton
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Do I need the performance valve springs on the 107 or just the 104?? What is your opinion trgarding the performance of this set up?

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 Posted: 05-06-2008 10:45 am
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Harkes
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Hi Tim,

i wouldn't advice using a 104 in a 2.0L engine. In a reconditioned 2.0L engine i would use 2 x 107's. In a decent compression (10.5:1 or higher) 2.2L engine the combo 107/104 is the ticket.  I, for one, have this (engine done by Garry Kemp).

Then the question is about 40's or 45's dellorto's and this is mainly determined by venturis you plan on using. In my 2.2L i run 38 venturis which I think is not possible in your 40's.  If you are running 2.0L with 2 x 107's then the 40's should be fine as I think you'd want 34 or 35 venturis which should work with your set.

good luck

erik

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 Posted: 05-06-2008 02:32 pm
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Judson Manning
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Tim,

The 104IN/107EX represents the results of ~15 years of evolution for the 907/911/912 engine family.  Keep in mind the 907 was really a prototype with little product development when delivered to Jensen in 1972.  As time went by and Lotus received a lot of customer/racing feedback they made applicable changes to the engine (not just the camshaft).

'The Shark' built by the Master Gary Kemp takes that evolution a bit further as Erik was interested in something quite wild.  Gary began with the Excel SE (912 104/107 + 35mm chokes) platform and added things like the latest Lotus Zeus head casting found in the post 1995 Esprit.  Erik CAN use 38mm chokes precisely because the head + cam + 2.2 crank CAN flow that ridiculous amount of fuel+air.

Kurt does make mention of alternate springs to which I will add the need to do substantial head porting to take advantage of the additional lift of the 104.  Take a look in the gallery to see the differences in intake port sizes from early to late JH engines.  The later Esprit heads make the JH head look tiny.

Also take into account the 107 evolution put it running a 104^ lobe center vs. the stock 110^ lobe center.  Slapping a set of 107s on stock JH cam sprockets will chop-off breathing over 5000rpm, but it will be a low-end torque moster for around town.  Spring for a set of HTD sprockets with the 104^ 'green dot' if you want higher end breathing.

If all you want to do at this stage of the game is put in a new set of cams, I'd buy and install the 107s on your stock cam wheels and feel the difference.  If you are not happy with the results dish out another ~$300 for green dot sprockets.  Assuming that is still not enough, spend $1,500.00 on a full porting job and install the 104 (with green dot sprockets).

IMHO installing a 104/107 combination on stock JH sprockets (110^ LC) and a stock JH head might not be the best solution.

Judson

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 Posted: 05-06-2008 04:51 pm
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Brett Gibson JH5 20497
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Judson, what would be the benefit or would there be to just sticking the green dot sprockets on a completly stock engine, and would the dizzy sprocket have to be swapped out as well.

It was told to me that if I put the dizzy sprocket on a cam, (dizzy sprocket equals a green dot, yes/no) the stock cam sprocket on the dizzy, and then bought one green sprocket, I'd have a bit more powerful engine.

True or false, and why.

Brett.

Brett

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 Posted: 05-06-2008 07:00 pm
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Judson Manning
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Brett,

There may be an explicit part number for the accessory housing sprocket, but I'm not aware of one.  From memory all I've seen is just another cam sprocket mounted in that location.

The 1975 Spec 4 JH used a 100/110 timing mix while later Spec 6 & 7 kept with 110/110.  In 1980 the California Spec 8 went to 102/110.  My guess is that the 100 & 102 mixes were specific efforts to increase intake overlap to meet certain California NOx emission requirements with the original 'C' camshaft.  Installing a blue-dot sprocket on Intake alone would yield similar results.

The guys at lotusbits.com posted dyno results of two 104 cams (same duration as the JH 'C' camshaft) utilizing 104^LC (blue-dot) sprockets.  Comparing their dyno results to others suggest peak power moves up from 6200rpm to 7200rpm.  Of course the lotusbits guys were running a fully ported head.

On an otherwise stock JH, switching to 104^LC sprockets would shift power potential up 1000rpm at the expense of low-end torque and drivability.  Concurrently, the increase in valve overlap decreases the dynamic compression ratio.  Without switching to higher compression pistons there would be a net loss across the entire rev range. 

Judson

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