203 cylinder head on 403 block ?
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  1. #1
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    Default 203 cylinder head on 403 block ?

    A question for Graham W or any other expert. Will a 203 head fit onto a 403 block to give the appearance that it is still a 203 motor , if yes can larger inlet valves be fitted and should the head be planed to get a better compression ratio ?

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  2. #2
    Fellow Frogger!
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    It is exactly what we have done for Carolyn's 203. We had a fully restored and balances 403 block with new sleeves, pistons, camshaft and etc. and a brand new 203 head so we put the two together and put it in her 203. The only thing that we really notice is the induction noise when the engine is running. We have tried all sorts of carbys and carby jets to try and reduce the noise all to no avail. It would probably disappear with a 403 silencer and aircleaner but that would be difficult to fit to the 203 rocker cover.

    It gives much stonger running with the bigger capacity, cruises comfortably between 60 and 65 mph and pulls up most hills in top (over-drive) and we get a consistant 32 to 34 mpg at those speeds. Does very little running below that as we only drive 1/2 km out the drive and we are in a 100 kph zone. If Carolyn sits at 50 mph it returns 35 to 37 mpg.

  3. #3
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    It will give the same compression ratio as the 403 head, the 203 pistons are domed, 403 flat.
    You could take 40 thou off the head I did this with my 403 and it still runs on 91.
    Can fit bigger valves, the 203 rockers are different, although the same as early 403s so shouldn't be a problem.



    Quote Originally Posted by Restorer View Post
    A question for Graham W or any other expert. Will a 203 head fit onto a 403 block to give the appearance that it is still a 203 motor , if yes can larger inlet valves be fitted and should the head be planed to get a better compression ratio ?

  4. #4
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    Thanks Flash Car 76 and Graham Wallis , all food for thought - will look into 403 air silencer issue.

  5. #5
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    Re the induction noise, this is one of the first things I noticed when returning to 203 driving after some 40 years. As far as I can see it is endemic to the design of the oil bath air cleaner. This is probably why the silencer was fitted to the 403.

    I can only assume that the problem does not exist with he (French) domestic market paper filters. Incidentally, the 403 paper filter has the same format as the silencer. Possibly the easiest solution is to fit a 203 paper filter. There are a few of these around having been fitted to Australian 1949-50 models. You could first try a generic paper filter to see if my theory stands up.

  6. #6
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    I put a paper elament from a Suzuki (?) in the oil bath air cleaner, yes I drained the oil and cleaned it and sealed the paper element with gunk so air wouldn't leak past it, and it made barely any difference. Didn't try an early 203 configuration but I seem to think that on the 1949 I owned it wasn't that "silent' either. A few years ago and I know that the grey cells are declining but I don't think I am that bad yet.
    FLASH

  7. #7
    1000+ Posts Mike Tippett's Avatar
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    A 404 KF2 Injection with a K&N is unbelievably noisy!
    1966 Peugeot 404 Coupé Injection post-restoration reassembly underway!
    Register your 404: https://recensement.leclub404.com/submit.php

  8. #8
    Fellow Frogger! Commerciale's Avatar
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    Does this imply that Peugeots suck (loudly)?

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