| Moderated by: Greg Fletcher | ||
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James Wilson Member 
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I'm considering getting a tubular exhaust manifold: But I'm wondering whether the improvement is worthwhile. How much benefit is this likely going to be over the stock manifold. I'm rebuilding the engine to a high compression (10.9:1) specification with a 2.2 crank and 104/107 cams for a street car... Other modifications will be a Lotus/Toyota 5 speed and uprated suspension (bushes, springs, shocks). I'm inclined to pass on this... suspecting that the difference between it and the stock set up (which looks pretty good by comparison to most cars' cast iron manifolds) won't be significant for the street... But any comments? |
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Greg Fletcher Administrator 
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I'd say it's worthwhile. A header is always an improvement over the cast iron manifold that the late cars came with. You didn't say who make this one, but chances are that it is an improvement. If it's made by Monza in the US, then I would pass- their JH headers were poorly made and didn't fit right. |
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James Wilson Member
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The one shown is made by Tony Law in the UK, its actually for the Sumbeam-Lotus but they make them too for the Jensen-Healey which look similar to the one shown. Its a 4:2:1 design. The company seems to be pretty well known and respected here; and my car already has an exhaust system from the manifold back that they supplied to the previous owner. My car is an early one with a factory tubular manifold like that shown on page 3 of the Martin-Robey catalog: http://www.martinrobey.com/filestore/jensen.pdf It looks a lot more effective than most of the cast iron Lotus ones I've seen that I presume are like those fitted to later J-Hs. But it has one tube bend forward and then back so it can't be as efficient as after-market ones that run straight... but I'm not sure whether the additional benefit will be there for a less than all-out modified engine. I've since spoken to someone here and their considered opinion is that the Tony Law one shown is more suitable for a competition or more highly modified engine, with what may be a little too big a bore for what I'm doing. I suspect that the expense (think £500 ~ $1000) would be more beneficial elsewhere in engine or suspension upgrades.... |
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Jensen Healey Super Moderator 
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I agree with your assessment. The stock JH exhaust appears to be an "extractor" with each tube the same length to keep the pulses flowing smoothly. Without dyno testing there is no guarantee it will provide the bang for the buck for a street car. You are going to have plenty of power!!! I think the money would be well spent on transmission, suspension and steering upgrades! Kurt |
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