Technical How hotrod fiat 128?

[matza64]

I recently bought a fiat 128 sedan. It has a 1100 engine with just 55hp. I was thinking of fitting in a 1300 engine instead. From what i have read there is a 1300 engine with 70 hp. I assume that engine can serve as "baseline".
Donator car?
I was also thinking of having the cyl head ported. No race job, just for street application.
Do i need to change cam, suggestion, where can i find one?
Is it possible to use Weber 36DCD or Weber 32/36DGV? On which intake manifold?
Which exhaust manifold can be used?
Suggestions are welcomed since i have not worked with Fiat engines before and do not know which parts to use.
I am aiming somewhere around 95hp on the flywheel.

 

[fiatfactory]

1116cc engine is around 55hp, comes with a single barrel carburettor and manifold to suit, and a single outlet exhaust manifold.

1290cc engines came in the 128 rally (around 70hp) and the 128 coupe and 3P (around 75hp) ... the main difference between the rally engine and the coupe engine is the twin outlet exhaust manifold. The compression ratio, carb (2 barrel), cam timing, ignition advance etc are the same between the coupe/3p and rally, it's the ex manifold and front pipe that make around 8hp difference.

Most 1290cc and 1495cc engines have 2 barrel carbs and manifolds to suit (32dmtr / datra and some have 32/34 dmtr variants, and some have 34dmtr variants) 32 and 34mm being the butterfly sizing, but there are also variations in choke sizing which will affect driveability/economy and performance of the chosen carb.

1495cc sohc engine came in regata / strada / ritmo ... rated at around 85hp depending on model and market.

1581cc sohc engine comes in Tipos etc ... rated at around 90hp for the single cam version.

Find a 1495cc engine and slip that into your 128, more torque and power, easy fitup (block is only slightly taller) and enjoy cruising for minimal $$ outlay.... or a 1581cc sohc engine would also drop straight in.

If you can find a 128 coupe there are a lot of donor parts that suit the sedan (like suspension coil and rear leaf springs) and will improve handling (lower and slightly firmer)

Bigger brakes from later models (like the 100s regata) will fit the front, giving a much larger front rotor (257mm) but this will require 14" wheels.

Another popular swap is an Uno turbo engine (105hp)

I have a lot of SOHC engine info @ www.turbo124.com/forum

SteveC

 

[matza64]

More questions, How hotrod fiat 128?

Hi again,
thanks Steve for your replay.
My car is already lowered with springs from a X1/9 in the front and distances between the leaf spring and its "bracket" (do not know the english word) in the rear. I´m planning for a front sway bar from an "estate/wagon".
Engine:
But, someone adviced me to not exceed 1300cc displacement due to the 128´s quiet weak chassie. Too much torque. I do not want to start to weld in the sheet metal in order to reinforce the car (if it isn´t absolutely necessary). So therefore i was thinking of a 1300. I also think it would be interesting with "spicing up" a quiet small engine.
My questions are: Are there kind of a "standard recepie" for the 1300´s that has been proved to work well?
Which parts to use? Steve listed several carbs for instance, any preferable? I would like to stay with a single carb (might be a two barrel) to keep the costs down and to leave the original heating system as it is.
It seems like 1100´s cyl head can be used on a 1300 shortblock to increase comp ratio, true or not?
Any preferable cams to use?
Anyone with experience?
Is it too optimistic to aim for 90-95 hp from a 1300 with a single carb and with the use of relativeley std components (exemptions: cam and ported cyl head)?
All ideas and experiences are welcomed, thanks in advance.

 

[fiatfactory]

Well what parts to use will largely come down to what your budget is, what parts you have available locally, and how much time you want ot put into sourcing the parts (and the suitable machinist) for a build up....

The largest stock bolt pattern style carb that bolts straight onto a standard 128 style 2 barrel manifold is a 34DMTR (or variant of) with 25/27 venturi sizes. This carb originally comes from a 2litre Lancia that made around 120hp, so that tells us it will flow sufficient air for around 120 HP...

Other cars come with progressively smaller venturi sizes (Ritmo 105TC, Lancia sedans, A112 Abarth etc etc) and smaller butterfly sizes, including some that have a 32mm primary throttle plate and a 34mm secondary throttle plate... and others that use 34 or 32mm throttle blades on both primary and secondary venturis... which are suitable for different rates of airflow.... at wide open throttle...

The trick with changing / upgrading a carburettor is finding one that flows enough air to produce the desired result, but not going too large so as to slow the air speed through the carburettor down and reducing low revs and off idle response...

If you decide to go all out (on a stock 2 barrel inlet manifold) and get a 34DMTR with the big 25/27 venturis, then you will need to equip your 1300 with the ability to use the air flow capacity ... and expect to rev it high enough to achieve the air flow the carb is capable of as well.....

A Weber dmtr . datra . etc etc are all variants of the same thing with differences regards choke actuation (water heated / manual / electric) and minor fuel vapor recirculation / emissions stuff, as well as fuel inlet / return tail orientation...

If your prepeared to source a different inlet manifold then either a single or a pair of Weber DCNF style carbs would be the next logical steps ... these are syncronous dual throat carbs (not like the progressive style dmtr / datra etc) which have much greater tuning potential, as they have removeable main venturis which let you adjust the airflow to suit a particular application.

These DCNF style carbs dont fit onto the standard manifold as the stud spacing is different, and they also require a different throttle shaft and float pin orientation to function optimally...

I have twin DCNF's on my 1970 128 sedan and I still have the heater box, and am still able to run a (standard skinny) spare tyre under the bonnet... as I run offset aircleaner assemblies to give the spare tyre enough room.

Single DCNF manifolds are probably more difficult to find than a twin carb manifold, but they do come up on ebay occasionally... a single 36dcnf / dcnfa / dcnva (again variants of the DCNF style with different choke / cold start enricment and fuel tail orientation differences) works very well on a mildly warmed over 1300. Both Alquati and Sprint made these single DCNF style carb manifolds... but long ago now ... as far as I know no one makes these new anymore

Alquati also made manifolds for the 128 to suit the DCD style carb too... again a syncronous opening (usually 36/36DCD's were used) 2 barrel with removable main chokes... but getting harder to find tuning parts for these days...

Twin DCNF manifolds are easier to find, but that will require the purchase of two carburettors and also all tuning components in multiples of 4 (jets/chkes/emulsion tubes etc etc) and this can add up in $$ terms very quickly.

Again it all boils down to how much air do you expect to flow through your engine? (ie its capacity and the revs it will be doing)

You need to realistically decide what your budget is, and then see whats available ...

SteveC

 

[matza64]

How hotrod fiat 128, more questions...

Thanks again Steve for sharing your knowledge.
To be honest, i don´t know how much air the engine shall flow (and i don´t know how to calculate it). I have had a few Volvo pushrod engines that have been tuned in various levels. Here in the country of Volvo´s these engines have been tuned for many years and the speedshops can guide you pretty much into which parts to use. When the engine is finished you may have to change a few jets and work with the igniton to get the best out of it. Of course these are not pure race engines, but still perform well (typical from 2 litres: 170 hp with twin 45 dcoes or 130 with a 36 dcd (different cams and heads)).
But, when it comes to Fiat...
However, my presumptions:
1300 cc
95 hp on the flywheel
Single two barrel carb (from my experience it´s not as expensive as twin Webers). I have a few 36 DCD´s on the shelf and i was thinking i might as well use one of them. Furthermore you can change venturis, acc pumps etc on them. Maybe it´s possible to use a fiat intake two barrel manifold and rework it to match the footprint of the DCD.
Use a two barrel exhaust manifold from a Ritmo?
Let a headporting shop fix the cyl head. Which core to be used, 1100cc?
Buying a cam from Kent or Piper, recommendations? Here i don´t know the max lift that is possible to use with std pistons.
Maybe its the wrong way to go.
Steve or someone else, have you built a 1300 cc engine in the 90-100 hp range and would you mind sharing the "recepie"?
How do your twin 36 DCNF´s perform, what kind of an engine, power output, driveability, etc?
regards Matza

 

[fiatfactory]

DCD needs to sit at 90 degrees to the standard 2 barrel carb... a dcd alquati manifold is shown in the group of pictures I posted.

Of course you could make up some sort of adaptor plate to mount onto the standard 2 barrel manifold, but the flow would be less than ideal.

You could machine the top plate off a standard manifold, and then make a new one and reweld it on .... but by the time you do that it will work out $$ wise pretty close to a secondhand DCD or DCNF single manifold .... unless you have your own milling machine and TIG welder.

Ritmo/strada/regata/X19 dual manifolds are all much the same, but they are slightly different to a 128 coupe manifold (longer to the 4 bolt flange)... if you used a 128 coupe one you could find a standard front dual pipe section to suit your car ...

Look at turbo124 like I suggested, I have a stack of sohc head info over there .... I dont feel like reposting it here ... so go and take a look and search for my posts .

the trouble with your suggested build is you haven't adressed any increase in the static compression ratio .... apart from the 1100 head solution, which IMO is the worst way to achieve any increase...

The reason is the 1100 head shrouds the valves very badly, the combustion chamber only extends out to around 80mm (the 1100 bore size) which only leaves a couple of mm around the valves periphery. The 1300 head extends to around 86mm across and has a lot more flow potential because of this.

The 1100cc head will run out of flow around 6k due to the valve shrouding ... and it is a fact of physics that if you cycle a four stoke engine higher (rev it harder) AND maintain volumetric efficiency then you will produce more power ... but the 1100 head drops the VE above 6k massively ... to deshroud it you would end up with a chamber that looked just like a 1300 chamber with the width taken out to bore size...you need to rev a sohc to get it to make good HP.

The best way to achieve a compression increase is to increase the swept capacity of the cylinder by over boring... and while your at the rebore, there are pistons from other Fiat models which have higher compression heights (CH is the distance from the gudgeon pin centreline up to the top face of the piston - excluding any dome or dish) and these will give another compression increase....

The standard CR is around 9.2:1 for a 1300 ... to get up to around 100 crank HP you need at least 10:1.

Same with the camshaft ... camshaft selection should be based on the static CR of the engine (as well as other factors)

Increasing the cam duration and not increasing the static compression ratio could be detrimental to performance ...as the DYNAMIC compression ratio is a factor of cam duration ... ie if the inlet valve closes later after BDC on the compression stroke then there is a lesser swept volume that is going to be compressed ...as the inlet valve is still open and the piston is further up the bore when the valve finally closes..

I have twin 40's on my 128, around 10.4:1 CR, 40/80 10.4 pittatore camshaft, kent vernier cam wheel, standard valve sizes but reworked and throated seats and ports, a 128 coupe exhaust manifold and 2.25" (63mm) exhaust system, electronic ignition (plex201 from a regata85), lightened flywheel ... it will rev to 8k in 4th gear quite easily ... my estimate would be around the 110hp mark at the flywheel... and has a surprising amount of torque and pickup at lower revs (I kept the port size smallish to keep airspeed thru the ports high)

1500cc engine is much easier to get a decent compression increase (I have a 1500 X19 which makes 99 rear wheel HP and still uses a standard single carb manifold and standard exhaust manifold), it also has much stronger conrods (forged as opposed to cast)

Which 1300 are you going to use? (55.5 x 86.4 or 86.0??) as some have higher static CR standard (9.5:1) ... so you might be best to start with one of these instead of a 9.2:1 engine.

SteveC