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| 912 vs 907 cam towers | Rating: 
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| Posted: 11-01-2008 11:00 am |
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1st Post |
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subwoofer Member
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However silly this may sound: Is it possible to mount the Jensen Healey cam towers on a newer engine? Getting a complete SE engine may be the cheaper and simpler option forgetting a bit more performance, but I would like it to look like it belongs there. I know the old design really is a crap design... Any insight on the matter? -- Joachim
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| Posted: 11-01-2008 04:07 pm |
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2nd Post |
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smcmanus Member 
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The newer towers are certainly improved. They have o-ring seals at the oiling holes and the cam lubrication problems are fixed. I would stay with the new stuff. Good Luck Steve
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| Posted: 11-03-2008 01:50 am |
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3rd Post |
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Judson Manning Member 
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912 / 907 hybrid of mine http://jhppg.com/gallery/album08 912 bottom end / 907 top end...Done that way precisely to keep the "Jensen Healey" name on the cam towers for that 'stealth' appearance. 907 / 912 hybrid belonging to Erik Harkes http://jhppg.com/gallery/album68/907_block_std_2_2L_head_cams_HC_cam_carriers 907 bottom end / 912 top end...Probably a better way to eliminate exhaust cam oil drip if you'd rather have 'Lotus' on your cam covers. Plus no need to modify the front cross member to clear the wider oil pan. To answer your questions...yes...the heads and towers are interchangeable.
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| Posted: 11-03-2008 07:33 am |
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4th Post |
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subwoofer Member
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If I'm going for a hybrid, it will be with the Jensen Healey cam covers, a conversion has to be stealthy for me to do it. I was thinking that if the cam towers bolt straight on the later head, there would hardly be any need to modify any parts at all (apart from the crossmember, but I should be able to do that myself), the head would be better ported than the old, all bottom improvements already done, all I would need is a set of pistons, a 104 cam for the intake and a few gaskets. -- Joachim
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| Posted: 11-03-2008 04:05 pm |
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5th Post |
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Judson Manning Member
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Honestly...for the best fun-to-dollar ratio, stick with 2.0 configuration w/ HC pistons and 107 cams. JHPS, et. al. have all the parts at reasonable cost. That is unless you can find a perfectly good (running) 912SE that you could drop-in. If you are looking for a complete 912, the thing to do would be find an engine and transmission from an Excel SE (which already has the 104/107 cam combo) to get the Toyota W57. Alternatively you could try the impossible and find and Eclat 2.2 with the BMW M3 Getrag transmission. As prototypical and 'rare' as it is, there are plenty of people who've done 907 rebuilds resulting in plenty of reliable parts sources. The 910/912SE is a VERY exclusive club and the main bearings alone are specific to the Esprit = $600US. Another BIG issue is machining the aluminum liners, and no, the aluminum liners do not interchange with the 'easy' to machine iron liners in the 907. 'cheap' and 'simple' do not apply to anything Lotus! only to the Chevy 350!
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| Posted: 11-03-2008 06:44 pm |
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6th Post |
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subwoofer Member
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Let's see (qouting Lotusbits pricing): Alternative 1: 10.5:1 compression ($700, JHPS?), keep the 2.0litre crank, 2 "new" cams (each: £40 for 107, £75 for 104), some porting, a set of Dell'Ortos (£220 inc. manifold), some balancing and honing. Find out if bearings still are up to scratch, or needs to be replaced. New valve springs ($90), MegaSquirt2 for ignition (£250), new oil pump. Alternative 2: Same as above, but with the 2.2litre crank (add £80-150) Alternative 3: SE engine (£1000-1600), gearbox/bellhousing/clutch (£400 or so), modified crossmember, new driveshaft, quite some work... Alt 2 is looking the most attractive, if it doesn't require major bottom end work, a 10-dowel and line bore would add significantly to the cost, I think. Is the 10-dowel needed for 180hp tune? The condition of my engine is still an open variable. I have been finding evidence lately that may have been quite hot, alternatively sat for a long time with old coolant. Also, I know I need new valve guides (at the very least). Getting a complete head from someone like Garry Kemp may be the answer to that, swatting a few flies in one swing. Adding to above cost: 25% VAT for cost + shipping. -- Joachim Last edited on 11-03-2008 06:45 pm by subwoofer |
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| Posted: 11-04-2008 10:27 am |
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7th Post |
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Harkes Member 
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Hi Joachim, with the extra torque you'll be getting from the 2.2L crank, i would not save on the cost of getting the sump 10-doweled. Certainly wth the 107/104 cams or in my case 107/Garry Kemp 104 version your engine will definitely be very torquey. If you have gone this far, i would suggest a std 2.2L head and have it ported for a good flow. This should get you close to 205 BHP. ...and we all love torque :) good luck and keep us posted Erik
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| Posted: 11-04-2008 12:55 pm |
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8th Post |
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subwoofer Member
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Erik, How much do you think the 10-dowel will be, and what downstream costs should I expect? I'll not rebuild this winter, for sure, but probably next winter. This winter is for running gear, interior and some exterior bug fixing, no to mention quite a bit of work on my garage to make it more useful as an all year workshop. May do some ignition work if time allows. ... and indeed we love torque, as long as the revs keep coming! -- Joachim
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| Posted: 11-04-2008 02:23 pm |
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9th Post |
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Judson Manning Member
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Erik, I think we'd all agree The Shark demonstrates there is nothing 'cheap' or 'simple' about your taste! Did you ever get a dyno plot for that engine? I'd really like to see how the curve (not the numbers) looks compared to a dual 107 2.2 configuration. If cheap and simple are the driving factors then the decision really is about how much HP Joachim wants. More HP = more $$ If Joachim wants a 2.2 my suggestion is to source a complete 912/910 engine. 10-doweling a 907 isn't the expensive part, you've got to add line-honing/boring, alternate mains for the x-drilled 2.2 crank, etc. For a RHD car these modificatios to the 907 are much simpler than modifying the car for a 912/910 block. The 10-doweling and line-boring isn't necessary for a 2.0 engine unless you just want a bullet-proof bottom-end and peace of mind. I've done the Chrysler main bearing conversion on a few 907 blocks which tends to run ~$1000US. DBE had at one time a jig to do the 10-doweling on a mill that they rented out. Finding a willing machinist is the real hard part! Judson
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| Posted: 11-04-2008 07:13 pm |
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10th Post |
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subwoofer Member
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I'm aiming for the 180(+) range, which should be doable without too many trick mods, provided I can get it to rev closer to 8k without making it tear itself apart. Pushing 200 and beyond seems to be a victim of the law of diminishing returns, the cost does not (to me, anyway) justify the results. If it's not a torque monster, the bottom end will hold up better, right? The forces on the bottom end should be proportional to torque, not power output, the oil film should actually be thicker at higher RPM due to higher relative velocities, or did I get this all wrong? It's been a few years since university, and I never took the tribology course... All this leads up to another question or two: How crazy will the 2.0 behave with a 104/107 combo? Will the 107/107 combo rev better if set to 104deg lobe centers? CR must come up from the 8.4:1 joke of the federal spec, and the 2.0 is ridiculously oversquare, but how will the characteristics be? Sometimes I do feel a little italian (life starts at 4k rpm...) I do not live in a major city, and I do not intend to use it for driving to and from work, so stop-and-go traffic is not where it will spend most of its time. -- Joachim
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| Posted: 11-04-2008 09:05 pm |
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11th Post |
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Greg Fletcher Administrator 
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I would not call 8.4:1 compression a joke, low yes, but if you're inclined to save some money, it's still totally serviceable. Plus you have the option of running unleaded regular fuel. My JH came with an original engine that only had 27,000 miles on it, so while my 2.2 project awaits additional funding, I'm driving what I think is still a very fun car. I had everything balanced, used new bearings, honed the liners, spruced up the head, added 107 cams, green dot pulleys, mechanical advance distributor and 45mm Dellortos. The 107's give a great rev range throughout and the car feels very balanced. A 2.2 with a big valve head would certainly be much better, but as I said, it's completely tolerable right now. A 104, 107 combo on a stock bottom & head end will not be buying you anything better, I would guess performance would be less dynamic, not more so since you really need the compression and big valves to see some gains.
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| Posted: 11-04-2008 09:13 pm |
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12th Post |
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Harkes Member
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Hi Judson, I have those lying around somewhere. I will dig those up, scan them and send it over to you. It is indeed all about the budget one has and what one prefers (stealthy or not). It also helps a lot if you can do most of the work yourself. I did not dare to do the work myself, to be honest. keep us posted on your decision Joachim..and do you actually have photos on the JHPPG?
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| Posted: 11-04-2008 09:56 pm |
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13th Post |
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subwoofer Member
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Greg Fletcher wrote:I would not call 8.4:1 compression a joke, low yes, but if you're inclined to save some money, it's still totally serviceable. Plus you have the option of running unleaded regular fuel. I think you may have lower octane regular fuel than we do, because my '94 Mondeo (the daily car, although I mainly use a bicycle for getting around) runs somewhere around 10.5:1 and runs perfectly well on regular unleaded (95RON, I believe). The Duratec series runs CRs of 10.6 and 10.8:1, still on our regular. I believe the federal spec 907s run a lower CR than the European ones. Erik: I may well have to post some pics to JHPPG, I try to take some pictures once in a while to document progress. It won't happen tonight, but I'll see what can be done over the weekend. -- Joachim
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| Posted: 11-05-2008 01:16 am |
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14th Post |
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Judson Manning Member
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The 907 was dubbed the 'torqueless wonder' and IMHO that was due to the relatively low c/r and the stock cams having just way too much duration. Greg is correct in that a cost effective rebuild would re-use the 8.4 pistons assuming the liners are in good shape. The 'development' engine in my E-Prod car is a freshened 8.4 with touched-up liners and new rings. ~$1000 in savings. Alternatively, if the liners need more than ~.003" machining then new pistons are in order. With modern gas able to handle well over 10:1 c/r, it's kind of a waste to purchase new 8.4 pistons given the performance increase. From a cam perspective Lotus progressively dropped the duration and overlap with the introduction of the E and 107 cams to boost torque. The dyno results I have from John Cronin's 2.0 with dual 107 cams and 104LC show a wide and flat torque curve with HP peaking at 5,750rpm - perfect for a street car. In the quest to run up to 8000rpm the problem is the mains holding enough pressure to feed the rod bearings. The stock main bearings have a wide and shallow groove with a big hole in the middle - just like a rain tire! To spin that high it's necessary to upgrade to the plain bottom bearings (Esprit or Chrysler) with a cross-drilled crank so that oil film can work undisturbed. Judson
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| Posted: 11-05-2008 09:53 am |
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15th Post |
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subwoofer Member
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Judson, do you have the dyno plots you refer to available for posting? I think a lot of us would appreciate it greatly if someone could assemble a pile of dyno plots for different engine configurations, such as the 2.0/107@104ºLC engine you just spoke of. The problem at high RPM comes with wear, right? Built to factory spec, the pressure should reach the other lube points fine, but the leakage between the top bearing and the crank (as this widens due to wear) causes less oil to reach the rod bearings - at lower pressure, is my analysis correct? While I'm at the diggin': a 912LC engine, does that have the crossdrilled crank and plain bottom bearing? It is a lot cheaper than an SE engine, so it could be used as a 2.2 starting point. -- Joachim
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| Posted: 11-05-2008 01:13 pm |
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16th Post |
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Judson Manning Member
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Joachim, Your theoretical analysis of bearing dynamics mirrors my initial work. What opened my eyes was a technical article I read from Clevitte analyzing the performance of 180^, 270^ and 360^ bearing designs. Then I noticed the progression Lotus' made in main bearing combinations in later iterations. The S1 Esprit essentially used JH bearings, but in subsequent years the middle bottom bearing changed to a plain bearing, then the top bearing changed to a plain bearing and finally the cross-drilled crank of the SE changed every bottom bearing to plain. Lotus' reasoning mirrors exactly what Clevitte said in that article and what every other major manufacturer was doing. The progression of main bearing design further supports the prototypical nature of the 907 and why given the choice (and funds) it's a good idea to up-grade to later specs. To answer your question a 912LC "should" have iron liners (easily machinable) and a non-cross-drilled crank. Iron liners are attractive and if 912SE plain bearings are available at a reasonable cost the crank can be cross-drilled easily. Is buying a 910/912SE worth the extra funds if a 912LC is available? Probably not considering the pain it is to re-plate the aluminum liners....except the crank will be forged steel and cross-drilled, but again that's not important for a <200hp build. Posting dyno plots is a somewhat dangerous thing because the values don't really mean anything. Also the values are totally meaningless unless the same dyno is used for every combination. What ends up happening is everyone starts arguing who's combination has "the most" HP. A more productive posting would be normalizing the graphs to show the relative shape of the torque curves. I have a graphs from various sources including LotusBits.com (focuses on the results of their porting techniques), but my ultimate goal is to get ALL of the various combinations on the same dyno. As a diagnostic tool such graphs can help everyone understand the differences in cam timing, ignition timing, cam duration, header selection and carb jetting. Judson
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| Posted: 11-05-2008 05:03 pm |
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17th Post |
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subwoofer Member
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Judson Manning wrote:Your theoretical analysis of bearing dynamics mirrors my initial work. What opened my eyes was a technical article I read from Clevitte analyzing the performance of 180^, 270^ and 360^ bearing designs. I found some other useful material on the Mahle Clevite web site, but I did not find that exact paper. Do you have a link to or copy of it? What I did find, was a paper showing all kinds of bearing failures, and their causes, and that will come in very handy once or if I start tearing down the engine. The Chrysler bearing conversion, what model/part# should be used, and is that described somewhere? Posting dyno plots is a somewhat dangerous thing because the values don't really mean anything. Also the values are totally meaningless unless the same dyno is used for every combination. What ends up happening is everyone starts arguing who's combination has "the most" HP. I completely agree with you, normalized plots are the way to go, and we should leave the HP race to the turbo boys blowing up their engines...
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| Posted: 11-06-2008 11:23 am |
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18th Post |
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subwoofer Member
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Took a few phone calls this morning to see what I am up against, cost wise. A reputable engine shop in Oslo, Norway indicated the following prices: Cylinder bore + hone: $400 fixed price, all 4 cylinders done Crank + flywheel balancing: $250 fixed price + hourly rate for lightening the flywheel. Line bore for main bearings: Hourly rate only, estimate $7-800. Oversize OD bearings will be cheaper than keeping the OD for stock bearings, i.e. Chrysler bearings is the way to go. The 10-pin process will add hours. I was fearing the line bore would be more expensive, so I may well go that route, unless the 10-dowel itself is a lot more time consuming than the required line bore. -- Joachim Last edited on 11-06-2008 11:24 am by subwoofer |
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| Posted: 11-26-2008 07:10 pm |
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19th Post |
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subwoofer Member
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Just a short update: 1. I have discovered the same as ozzadavies (a small touch of mayo on the dipstick, oil seems fresh after dipping second time), so some engine work is urgent. I also know the engine is burning oil, and there seems to be a bit too much oil mist coming out of the breather tubes. 2. The "while you are at it" stuff does indeed drive the cost of a rebuild dramatically up. Excel is an excellent tool for breaking hopes and dreams. All the small stuff does indeed add up. Add freight to a remote corner of Europe and put 25% VAT on top of that again, and your wallet starts screaming. Although freight to Norway is almost as much as the engine itself, getting a complete 907 engine (ex-Esprit) from Lotusbits is by far the cheapest way of getting a sound(er) engine and just a little bit more oomph. Is 107 cams still the ticket on the Esprit version of the 907? BTW: Mike at Lotusbits said that 4 dowels is enough, and that 10-doweling isn't needed even for quite hot 2.2s. He also claimed that line boring wasn't necessary if the dowel job was done correctly. -- Joachim
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| Posted: 11-29-2008 06:47 pm |
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20th Post |
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Judson Manning Member
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An Ex-Esprit or Ex-Elite 907 'should' be equipped with 9.5:1 c/r pistons and the 'E' cam (~260^ duration vs the JH 'C' cam ~272^). The combination would have more drivability and low-end torque than a Federal or European JH 907. We think of the 107 cam (~252^) as being introduced with the 2.2 engines and VERY necessary for turbo variants. Sounds like indeed the rings are shot and/or the liners are out-of-round leading to the burning oil and excessive blow-by. The mayo on the dip-stick could either mean a cracked liner or a blown head-gasket.....or....just some simple contamination in the sump. The design of the 907 w/ external oil cooling lines and pooling oil in the cam covers, etc., makes is extremely hard to flush the system clean when changing the oil. Elsewhere on the board I've posted a process of repeatively changing the oil to give the rings a fighting chance. I've torn down WAY too many engines with varnish-stuck rings and sludge filling every nook and cranny. Some engines can be salvageable after a good internal purging, and it couldn't hurt to try. Mike has the right idea about the 10-doweling process. I would only add that if you add any dowels to hold the bottom-end in (re)alignment, by definition you'd want to re-surface each half a few thous and then line-hone the bore so it is indeed straight. Last edited on 11-29-2008 06:58 pm by Judson Manning |
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