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 Posted: 08-10-2005 01:31 am
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Leshok
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Can someone post the stock cams specs of the 907 engine? Along with the 104, 107? Just to help with my cam selection.

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 Posted: 08-10-2005 04:02 pm
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Greg Fletcher
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I think Kurt Housh/Judson Manning may have posted this on the old message board:


Stock JH cam (sometimes called 'C' cam):
~.340" lift & ~272^ duration, ~224^ with 0.050" lift. MOP 115^ for early engines, 110^ for later ones, and IN105/EX110 for the last, smogged, engines.

Lotus 'D' cam (Lotus only, but rumored to have been in a couple of 1975 UK JHs. 1 groove on nose end):
~.350" lift & ~270^ duration, unknown at 0.050". MOP typically 110^.

Lotus 'E' cam (Lotus only. 2 grooves on nose end):
~.344" lift & ~260^ duration, unknown at 0.050". MOP typically 102.5^.

Lotus 104 cam (Lotus only. 444 on nose end):
~.420" lift & 272^-280^ duration, unknown at 0.050". MOP typically 104^.

Lotus 107 cam (Lotus only. 777 on nose end):
~.388" lift & 252^ duration, ~224^ with 0.050" lift. MOP typically 104^.

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 Posted: 08-10-2005 08:20 pm
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Leshok
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I know how you guys talk about the 104 getting its power late in the Rpm range, but cant that be fixed by changing the lobeseperation angle or have the cam ground a few degrees in advance?

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 Posted: 08-11-2005 04:10 pm
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Greg Fletcher
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It's not like lots of grinds don't exist already. There are a plethora of grinds, but as I, like many others, have experienced first hand that these grinds don't necessarily offer what one might expect. On my old JH, I used a profile from Camonics in Los Angeles (other parts suppliers out there are using these guys) and their 107-like cam falls short. It just doesn't have the same torque and lift combination that original 107 or 104's for that matter have. There's a club member down the street from me that runs 104 cams and he claims they are perfectly driveable around town. He runs high compression pistons and a big valve head and that's really what 104's want to get the most out of them.

Otherwise, a 104 inlet and 107 exhaust combination is supposed to be a great match in the Lotus 907 head. Garry Kemp described this to me once as more dynamic flow through the head (from the lift ratios) with a result that you end up with a bit more torque without costing you any top end power.

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 Posted: 08-11-2005 11:11 pm
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Leshok
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I just was reading the specs on the cam and saw that it was rather small (104) To get the most out of your cam I agree, is compression to cam. Just that 230 duration at .050 is rather small. Just because you extend duration with the cam does not mean the powerband shoots way up. you can have the cam ground a few degrees in advance or have the lobe seperation angle a little lower (110 and 108 would brind more TQ lower in the powerband).

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 Posted: 08-12-2005 04:30 am
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Jensen Healey
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Just get some adjustable cam pulleys and change away! Lotus used to supply a wide variety of pulleys but they are getting scarce.

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 Posted: 08-12-2005 11:13 am
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Harkes
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the 104 cam has 272/280 duration, not 230... and that is rather large.

if you are looking for great torque throughout the whole rpm range than the 104 inlet/107 exhaust is what you are looking for, but you can also use a custom cam for the inlet, but i would use the 107 for exhaust.

i should have my dyno results of my 2.2L high compression (1:11) engine, made by Gary Kemps. He used a custom inlet cam with a little more lift than the 104 and a little less duration than the 104 i thought. For exhaust he used the 107.

i could find out more about it if you want..

good luck with your engine

erik harkes 15175, netherlands

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 Posted: 08-12-2005 08:03 pm
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Leshok
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i dont think you understood what duration I wrote. Greg posted that the cam is . 280 duration at seat to seat. the typical rule is to subtract 30 to get a rough estimate duration @ .050. so being that 230 @ .050 is fairly small. nice option would be a 246 duration @ .050 with lift about .430-.440, 106 lobe seperation for torque. have it ground 3.5 degrees in advance to bring the RPM power down. Dont mean to offened anyone just stating an opinon.

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 Posted: 08-12-2005 10:29 pm
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Mark Rosenbaum
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The '30 degree rule' is generally a pretty fair approximation, for most cam grinds.  However, using that rule, 280^ seat to seat works out to 250^ at 0.050" lift, not the 230^ that 'Leshok' wrote.

In any event, some of the 'standard' cam designs mentioned above were intended for use with turbocharged engines, and the fact that they also work fairly well with normally aspirated ones is probably sheer good luck.

As the valves in a 907 engine can hit the pistons if things go badly awry, I'm not sure that really high lift is a particularly good idea.  The valve train mass is so low that you might get better overall results with less lift and a fairly abrupt cam profile.  One must also consider the side forces that are applied to the cam followers; these can not be allowed to get too high or wear will increase tremendously and you might even lose more power than was gained from the greater lift.

As far as the MOP is concerned, as was noted, one can set any MOP within reason using adjustable cam gears.  Lotus apparently chose the MOP to comply with emissions regulations, and back in the late 1960s and early 1970s, no one really understood how all the various engine design parameters inter-related  -- they just knew that they had to meet the specs in order to use their engines in cars sold in the US.  In any event, the 907 engine was developed first for racing, and supposedly just happened to be a fairly low-emissions design.  (Or, which I personally think is more likely, the designers were brilliant enough to accomplish both.)

 As somebody knowledgeable once said, decades ago, "You can do anything you want with an engine if you just want to start the race.  Finishing it, well, that's another matter."


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 Posted: 08-13-2005 12:49 pm
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Leshok
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Cool mark. thanks!

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