Which cylinder head?

[jobberwock]

I recently acquired a 57 convertible and having owned several minors over my maturing years I knew something about the engines....not a huge amount but enough to go down the scrappy and get replacement bits and pieces including a complete engine when needed. The engine number and plate tells me that the engine on the 57 has been replaced with a 1098cc. I also have a receipt for an engine replacement from 1983(oh to go back to those days and the price of servicing!). Anyway I was going to fit a temperature sender to the cylinder head but the port isn't there!? So what cylinder head have I got ? If it's from one of the smaller engines does this affect performance? The car itself seems to perform very well although I wouldn't be surprised if it retained the original gearbox as the torque in 4th gear is amazing....happy to go round roundabouts like an automatic! Also the gear stick looks original...being much longer than the more modern version.

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[chrisryder]

No temp sensor plug does suggest it's not a 1098 head. It's not unheard of for 948 heads to end up on 1098 blocks, whether deliberately or accidentally... There shouldn't be much affect on performance, marginally smaller valves on the 948 head, or marginally worse flow. There's not a lot in it anyway!

As for your good performance, you may well still have the original diff in the back axle. The 948's had a 4.5:1 and the 1098's had a 4.2:1, the later 4.2 allowed for slightly better cruising, with the more powerful engine able to cope with the effective lack of acceleration that changing the diff would have caused.

A 1098 with the early 4.55 diff will accelerate very nicely (and go around roundabouts in 4th!) but you may find top speed somewhat lacking.