Souping-up 782cc engine

[angel]

A friend of mine with a 1975 French-spec R4 (still with the 782cc engine and 26 DIS-5 carb) asked me about what can be done to increase performance. He, being used to modern cars, feels that the bottom-to middle rpm torque is low.
Although the engine runs great (and is in good shape), it feels underpowered, similar to my '71 with average-condition engine. The solution would be to go to a bigger carb. I was thinking of 32 mm combined with the later vacuum advance distributors, which, from my experience, works wonders on the 845cc engine.
Has anyone tried this on the 782cc engine? I'm between two thoughts: One, that 32mm throttle bore would be too much for the small engine, and the other that, since both 845cc and 782cc engines share the same camshaft and head, why should a 32 mm carb not perform equally well on the 782?
One fact puzzled me more. In the mid -70s Renault changed the camshaft timing (on the 845cc engine) and made it hotter, while keeping the carb down to 28mm. Then in 1984, they returned to the initial camshaft timing, enlarging the carburettor to 32mm and altering the ignition curve (I think a bigger carb would suit better the hot camshaft)...
So I'm waiting to hear your comments/experience...

 

[mr-reno-139]

hi angel
cant really help but just to comment that very few 782 cc engines in uk ,as not officially available here except i think the very first 1962? cars were available as 747cc

all uk r4s i have seen had 28IF carbs ,only seen 32mm carbs on base model R5 (845)and R6L (845)
have never stripped any 3 bearing engines down far enough to notice any reall difference in port/valve sizes or measured cam shaft duration

did have a renault 4 turn up some years ago with an SU carb on (off a reliant robin!!!)
which went very well, but the head had been skimmed as well

think i may have 32mm 5L manifold at barn (if it didnt go in the last scrap metal pile )

paul

 

[entwistlecymru]

If your friend is after more torque, has he thought of a supercharger?

 

[angel]

Paul I can confirm you that on contemporary 782 and 845s the camshaft and heads were the same.
Slightly off-topic, I admire the SU carb for its simplicity,tuneability, and efficiency. I was thinking seriously of fitting one just for try on one R4 (when I have enough time...).
If you still have this manifold, I am interested!

 

[DaveP]

Just stumbled across this from ages ago. Angel, your post seems to imply that a late 70's cam fitted to my '84 tl might give a small (but they all count) power boost. Might have to raid the scrappie again

 

[angel]

Ages later, this particular car I was talking about has just been converted to 1108cc :-D

This cam should work very well with the 32mm carb and vacuum advance distributor normally fitted on an '84 845. I have also found a (new) 782 R5 camshaft, that I suspect to be hotter than the R4 one. Does anyone have info on its timing?

 

[DaveP]

I'll try to get hold of one of these and let you know how I get on, cheers