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OverdriveGear Member 
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I came across this head some years back and I was looking at the JHPG and noticed a comparison between the early 907 heads and the later ones. I put the calipers to it and calculated the later head's intake ports to be roughly 30% larger. I'm not sure what model this head came from (esprit, JH, otherwise) but it does have the smog ports. I'm guessing that this head would be a nice upgrade from the earlier versions and perhaps would amplify the benefits of performance cams. There are numbers on opposite sides of the head reading: K1 26FDA16 and on the rear: 14302 Attachment: MVC-002F.JPG (Downloaded 79 times) |
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Ron Earp Member 
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Actually, I think just about any of the later Esprit heads are larger. I remember getting my 907 head off and looking at the ports - tiny! So, I bought later model instake gaskets for the Esprit and port matched them on the intake and exhaust side - 10 hours later I had a nice looking head with some big ports. I think the best thing would be the big valve Lotus head, called the Zeus head, which is now the only thing that JAE offers for head replacement. It had, if I recall correctly, 1mm oversied intake valves when compared to a Lotus Esprit SE head, but, I don't know how a Lotus Esprit SE head compares to a 907 head except I know the ports are larger. Ron |
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Mark Rosenbaum Member 
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I did some research early last year which sheds a bit of light on this. First of all, as far as I have been able to document, all JHs used the same head casting, A907E0311Y, which would have had the smaller ports. As far as I've been able to discover, the B907... head was never put into production. The C907... head was introduced sometime between engine number 12020 and engine number 14302 as reported by 'Overdrive Gear' above. (FWIW, each 9xx engine had its serial number stamped on the head, block and bearing saddle.) A point which may be of particular interest to those racing their JHs is that two versions of the Stromberg intake manifold were used. The earlier version, which has no casting number but which apparently is A907... or B907E0250Y, has small ports measuring about 1.688" wide and 1" high. Manifold C907... appears to have been introduced fairly early, perhaps even before the changeover to the later block, and has larger ports measuring about 1.875" wide and 1" high. I'd expect that the significantly larger port area of the later manifold would give a noticeable increase in torque throughout the rpm range. The C907... manifold was used, with minor machining differences, on both the JH and Lotus cars with Strombergs, and thus ought to be readily available. Attachment: Stromberg Manifold identification.jpg (Downloaded 59 times) Last edited on 06-11-2005 10:54 pm by Mark Rosenbaum |
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Judson Manning Member 
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The head in the pic with the larger intake ports is the very one I'm currently running on the 907/910 hybrid with a hotter version of the 107 cams. After this pic was taken, I did some additional port matching (my Dellorto manifold didn't need any work as it was bigger than the gasket!). The gasket in the pic is the currently available 910 gasket available from the usual sources (the original 907 gasket IS smaller AND available as a special order from DBE, so Ron, wink wink nod nod...). This particular head has the air injection fittings on the exhaust ports. Additionally it had a water spigot behind cc #4 which tells me it came from a non-JH vehicle. As Ron points out, the IT rules allow 'port matching' 1" from the gasket. A novice can't screw up too badly by doing this mod to an earlier head by themselves. To get some serious power, send it to an expert like Richard at WCRCH for a full porting job. I don't know how the head in the pic and an authentic JH5 head compare, however, come to think of it...I do have an authentic JH 1974-1/2 head in my bone pile...hmmm |
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Ron Earp Member
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Wish I had one of the larger instake manifolds, but likely it makes no difference for my application. I enlarged the ports on the intake to preceisely match the gasket and the head, so it is large now. And, internally the intake was large as well, stock, so it doesn't suffer from the "snake swallowing an egg" sort of look. 1" in huh Judson? I might have shot over that a bit...... Now, as far as gaskets it is okay if the small 907 is still available. Gaskets are free in IT, so, I got the largest I could find!!! All I really need is some sort of documentation that the original JH cams are no longer available and have been superceeded by some 104s or similar. Anyone have any info on this, I heard it was true......... R Last edited on 06-12-2005 02:09 pm by Ron Earp |
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Judson Manning Member
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From the 2005 GCR: 17.1.4 Improved Touring Category D. Authorized Modifications 1. Reciprocating Engines l. Manifold & Cylindr head port matching is permitted. No material may be removed further than one (1) inch from the manifold to cylinder head mounting face(s).... Of course the IT category has always been a hotbed of 'differences of opinions' and those that aggressively interpret the rules. My motto: It's not illegal until you get caught (just make sure whatever you do is worth it)! LOL |
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Ron Earp Member
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Yeah, I know, I'm just saying that it could be my die grinder might have slipped a bit. Don't worry, we've got to get this thing on the podium at the AARC before we get torn down and that is a long ways away!!!! |
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