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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc |
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![]() Tom,
Re overboring cylinders whilst keeping the external dimensions of the block the same - I think that you will have insufficient sealing area between the bores. The original engine is already marginal in this area! The other issue, as correctly pointed out by Geoff Dowdle, is that a substantially overbored block from say 66 to 75mm diameter would encroach/erode your main bearing area of your block. In short, if you increase your bores to enable 2.5L or more you need a new longer block casting and crankshaft. Hence my TR 2500 engine block and crankshaft suggestion earlier. Can I suggest that you have another look inside any block and you will see what I mean. I guess you could design a "modular" engine with different stroke crankshafts and vary the rod length. Unfortunately the 6cyl Bristol motor is already substantially undersquare and thus increasing the swept volume by increasing the crank throw and fitting shorter rods would be a backward step in efficiency. I think that most designers just set out to optimise the bore to stroke ratio and allow say, a 3mm overbore capacity. Regards, Brett |
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![]() I must admit that I've been thinking of selling the motor and gearbox from my 401. Then possibly installing a 2.4 Jag motor, which I have. Hopefully not much weight added, as the 2.4 is lighter than a 3.4, though I have no info as to how much less.
Then the 401 would be driven more, with less chance of being stolen and gutted for a fake Ace, etc. |
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![]() Kevin
The clue is in the word "pattern". My (serious) suggestion was to consider using 3D printing to make a pattern of the needed part in plastic, not the part itself. Then use this in a mould to cast the part in iron or aluminium, using the lost wax process. Must be vastly cheaper than constructing a pattern using traditional processes. The Jag 2.4 is a straight 6 in the XK series. Fine design for its time, long stroke, a bit limp compared with its 3.4 and 3.8 litre brethren. You may be thinking of the small V8 that Jaguar fitted in the 250 and Dart. Nice, compact, but I think you may be right that it might be a bit tricky to slip into a Bristol. But maybe it's been done. Selling off the original Bristol engine and replacing it with another unit sounds sacrilegious to me. But if it must be done, why not emulate AC, and slip in a 2.6 litre six cylinder Ford unit from a Zodiac. It's what they did with the later editions of the Ace and Aceca. So not that awful, and there is a distinguished precedent. |
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![]() The 2.4 is a short stroke 3.4 straight 6, and is almost 2" shorter, so should be lighter also. Nice looking engine and I already have one, with triple 1/1/2" SU's!
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![]() InRacing in Nottingham seem to be energetically using new technology to simplify the manufacture of replacement parts in all kinds of impressive ways, so they might well be using 3D printing to make patterns. They do make new 2-litre heads and blocks already. The fitter who showed me all all this didn't know how much a new block would cost. It might be a matter of 'if you have to ask the price, you can't afford it'.
Hugh |