Exhaust Silencer Internals

[malcolm]

Robert reported that changing the exhaust silencer on his R4 from a random aftermarket one to a Bosal one improved performance. Just for fun we cut one apart this morning to see what's inside. It's a restrictive design - couple of perforated tubes passing through rockwool in the end chambers and crimped at the ends in the central chamber.

Wondered if anyone had noticed any performance improvement by swapping the exhaust silencer (or whole exhaust)? Thinking it could perhaps be the next restriction after the carburettor.

 

[ade]

exhausts

the exhaust is almost certainly very restricive...its always the first thing to go for on older cars....i doubt the Renault engineers knew much about tuned exhaust lenghts etc (as i don't), but i think its always worth keeping the length of standard bore pipe, before going into a larger free-er flowing silencer, so that exhaust gas speeds are kept high, thus aiding the scavenging effect (sucking out remaining exhaust gases)...this is what i've done on my Mini, anyway...ade

 

[malcolm]

I might try an experiment at the weekend and remove the exhaust altogether. The Hennessy hot up kit has really suped up the low speed performance (torque) on my R4, but whatever I do to the timing there's nothing to be had in actual top end power. Still doesn't go very fast.

I've worked a little in this area. Forget tuned lengths - they have a relatively small effect and are more about smoothing power curve than getting the power in the first place. Main things will be exhaust diameter and silencer restrictions (back pressure being a bad thing despite what some say). Shall report back when I've tried the car on my performance test strip without any of this back pressure.

 

[Steve Hennessey]

I would be intersted in the results Malcolm. I did manage to get 90mph from my 4 after fitting the hot up kit but I did enlarge the main jet!!

 

[mr-reno-139]

as this is now the go faster santa pod thread
i might as well comment as well ,seem to recall that compression ratio and camshaft is different on R4 engines compared to R5 (and R6)
remember fitting good second hand R4 head to R6 years ago( after head gasket failure )
to get car back on road , to find it was absolotely useless and no amount of fiddling around would get performance back to standard
customer was not impressed until i refitted original
closer inspection side by side showed combustion chamber depths to be deeper on r4 head
just a thought

back to topic again i also fitted R4 rear silencer (genuine) to R6 with loss of power
R6 1108 has an expansion box under wing and straight through type rear mounted box but is same diameter pipe as R4
ps just rememberd i have got another 1289 r5 engine with a KENT cam in my garage that used to be in my grass track R5 race car -maybe i should put it in the 3 wheeler DKR kit
paul

 

[ade]

exhausts

after the silencer and induction system, the obvious next thing to go for is work around the valve seats to improve flow- i'm sure someone must have played with a few heads in their time...Mr Reno, do you offer a go-faster head conversion?..perhaps someone has got the ideal spec for a cam for an engine modified in a specific way ( as all these mods are supposed to complement each other)..ade

 

[angel]

Paul the head you describe could be from an F6 as they had lower compression ratio.
The R4 engine, especially the 1108, is tuned for maximum low end torque and economy. It has a very mild camshaft and small carburettor (and quiet rather than effective exhaust). I doubt that any work done in the ports and valves without first fitting a wilder camshaft and larger carburettor. I stay tuned to Malcolm to see how restrictive the silencer is! (I guess too much...).

 

[mr-reno-139]

hi ade
sorry my experience with tuning R4 s is fairly limited, as 15/20yrs ago when most of customers had R4s and mk 1 5s
they where happy just for car to work at all !
as i am self employed day to day work is now clios and espaces lagunas etc
i am still an R4 fan (just got a 1975 845) and enjoying this forum
and happy to help with advice and ideas
my memory is fading fast but do still have quite a few bits still around from being a bit of a hoarder so feel free to ask
as for whats in my friends barn !!??

hi angel
yes you are right it was f6 head !!
as to the best combination of parts i think it depends on personal requirement and also what is available on location and budget

paul

 

[malcolm]

Didn't get a chance this weekend to test the car without the exhaust - too busy building a little house for my air compressors. (They are going outside to save space and I'm planning to pipe the air into a couple of workshops.)

I'd thought the cam profile was common between the R4 and R5 engines. Certainly the timing is the same - is the lift different? Mine feels a bit restricted, and timing has no effect at all, so it doesn't feel like mixture to me. A really low tune cam could do it I guess.

We shall know more when the exhaust test is done. Mine is a random aftermarket one. I've been testing acceleration time uphill on a stretch of road where I used to get exactly the same terminal speed as at the end of the Santa Pod quarter mile (about 60mph). I'm only 3mph up with the new carb - sure there must be more to come.

 

[Steve Hennessey]

Malcolm, are you using the R5 air filter on your 32IF?

 

[entwistlecymru]

A few months back we bought a couple of tuned 1300 R5 engines in bits, one of them built by Mark Fish. The 'Fish' head had been ported with the inlet manifold done to match. The other was standard so we compared the 2 side-by-side.

The ported one had had a serious amount of metal taken away and was supposed to be putting out 95hp on a standard twin choke carb. The standard one looked very restrictive compared to the tuned one.

Interestingly the inlet valves on both were the same size, but the exhaust valves on the ported head were 2mm bigger, suggesting the exhaust side of a standard head is restrictive (probably to aid torque)

We've since fitted the ported head/manifold to the F6 with a 1400 bottom end and standard cam. I'd expect to get a drop in torque with the head ported as seriously as it is, but hopefully the extra 100cc and mild cam will make up for that. We've used a 28/36 Weber carb (off a mk2 Escort?) on an R5 TS manifold which should supply enough mixture.

As for the exhaust it consists of a standard diameter R5 downpipe with one stainless centre silencer exiting from the side, just in front of the rear wheel. This might be a bit too free flowing so if the car seems a bit flat low down I'll try an underwing silencer.

It hasn't been driven yet so we'll wait and see what this freak will run like!

Any of the findings we make will be posted up as the ideas could be transferred to the 1108 engine, albeit on a milder scale.

Another suggestion would be to look at the specs for a Gordini/Turbo camshaft. The turbo cam will probably be tuned for torque and might make a good mod for a daily driver.

 

[angel]

Timing of a turbo cam is another story, as it should have little overlap and late exh. valve closing to enhance exhaust gas velocity (so as to decrease turbo lag). Therfore I doubt that it will be suitable for a n/a engine.
Also theory says that, as exhaust gases have significant pressure in the combustion chamber, it is no problem for them to get out, so we don't need a bigger exhaust valve actually (maybe the 1300 exhaust valves are really small?).
It will be very interesting to know the results of testing these bits on the R4!

 

[mr-reno-139]

now we are getting really technical
just to add when i built my r5 race engine which was supposed to be standard!! for my class
(except camshafts were free) had a good idea use gordini cam in 1289 block using duplex chain etc

until on assembly realised that inlet and exhaust valves are not in same sequence due to gordini being crossflow type head

ah well ,then had kent grind me a special cam only to find the valves opened so far that although spring didnt bind up top cap came down and hit top of guide
2mm off top of guide with grinder sorted

fast enough to beat 1660 escorts till i rolled it
oh yes did use 5g turbo ex system about 50 mm bore


EDIT
found an old photo probably 1993 (thought i had engine pictures )
have still got engine though
now you know what the 139 on my user name is about

paul

 

[ade]

tuning

just a couple of thoughts to slip in:
i have fitted larger exhaust valves (with reverse flow restriction)and increased exh tract flow on my '67 Mini, the reason to reduce pumping losses, because power is used up to expel exhaust gases.
i've just come across an old Retro Cars article on the C1J engine, quoting 350 bhp from a fuel injected Group B R5 Maxi Turbo from about '86, and referring to a company called BB Performance Tuning in Colchester, who have quite a bit of tuning experience with this type of engine.
does anyone know if there's an easy route to fuel injection on our engines?...perhaps a bike throttle body with just the right sizing/ hole centres etc....probably, injectors from these new injected scooters may be sized best?
ade

 

[angel]

The R5 Turbo 2 had Kugelfischer mechanical injection, something like a low pressure diesel injection.
As far as I remember it worked at around 2,5 bars boost pressure, thus these HP figures.
I think fuel injection would not be too difficult to be fitted on the C1E. If you want to have individual throttles they can be made or better (but more expensive I guess!) fit throttle bodies from a motorcycle, they are individual, not paires, so their spacing can be altered very easily.
But of course you will need an engine management system with a blank ECU. I think the cost of the whole project would be too high to be justified... however take a look at what I found in my photo archive:

 

[mr-reno-139]

very impressive Angel
non cross flow ,probably based on 5gt turbo (and with no distributor to play with )
have you any more info ?

PS the 5 turbo 2 used gordini type engine not C1J but still 1397 .am sure i saw a website somewhere a few years back where someone was building a mid engined turbo R4 or was i imagining things??

are we far enough off topic yet malcolm? i thought we were originally discussing easy bolt on BHP mods

paul

 

[malcolm]

Exhaust test results are in. I've been very scientific checking terminal speed over a length of road from a roundabout.

Yvette the R4 would reach an indicated 65mph.
Ermintrude as standard only managed an indicated 64mph.
The R5 carb and a little ignition twiddling increased that to around 68mph.
Tried removing the exhaust at the front floor connection today - 70mph! So the exhast is a little restrictive.

My car was fitted with a Bosal exhaust. Cut one open to look inside and it's different from the one in the earlier photos - no crimped ends of pipe, but the changeover section looks very small.



I modified mine to make it straight through (not very pretty)



Next filled it back up with stuffing (and a little stainless wire wool around the pipes to help stop the stuffing blow out)



Welded a cover plate on to seal it back up and went for another performance test. 70mph again - success! It sounds a bit funny though - perfectly quiet, but there's an entertaining rasp on acceleration and over-run.

 

[Deauville]

I regularly get nearly 110 from our R4 with no mods whatever

 

[mr-reno-139]

how fast !!!

very optimistic R4 speedos have you verified this with a speeding ticket ?
i find that most sat navs have the option to display current speed and probably more accurate
mind you theres always Santa Pod , any dates yet malcolm ?

 

[malcolm]

Should imagine 110 is on the km/h calibration - French car I'm still struggling to cruise at more than a real 83mph on a flat road with no wind. Very annoying.

No dates for Santa Pod yet - the current job should fizzle out in the next few weeks leaving a little more time for organising such things.

I'll thrash you all - mine is running very nicely at the moment - some exhaust porting in the head while it was off the car seems to have made an unexpected difference.

Won't start for some reason though which may move some of the advantage to the opposition.