Renault Fuego 2.2L project

[Alejandro]

Dear Guy and forum members,

I'm doing a head preparation in a 1990 Renault Fuego GTA. The car has a 114 HP, 2.2L aspirated engine, fed by a double body carburetor. It develops 198 km/h and accelerates from 0-1000 meters in 31 s. My intention was to update the engine a little bit, and to gain some extra torque and power. Theory predicts that after preparation the engine will have between 135 and 140 HP at 6000 RPM. However, the preparation has been very conservative and the car is intended for street use.

I'm in the mounting process and I will leave some pictures soon, but in the mean time I'll explain in general the head preparation:

• Compression ratio increased, from 8.7:1 (factory standard) to 9.5:1
  Modified inlet ports in order to induce swirl (swirl motion of the fresh charge)
  Some minor modifications of the combustion chamber
  Replacement of the original 30° inlet valve, for 45° inlet valve
  A new camshaft, with 280° of duration and a 10.30 mm lift
  Installation of a low pressure drop air filter
  Hi power ignition coil, special spark plugs and spark plug wires.
  Some work done to the carburetor (updated fuel-passage diameter because of the extra air-flow, and work in the diffusers)

However, I have not yet decided what to do with the exhaust system, and most of the literature I have read does not provide me with all the answers. The cars original exhaust is a cast iron 4-2-1 header (a short 4-2, and long 2-1), and three mufflers. There are several sport exhaust system available for this car, which include a 4-1 header and only two special mufflers (low back pressure), but I'm not sure if this systems are what I'm looking for.

I know that in general, a 4-1 exhaust will give better performance in the high RPM range, but it comprises torque at low RPM, so a 4-1 is closer to a competition car than it is to a street car. All vendors talk about more top end speed and power, and this doesn't surprise me because it is expected in a 4-1 header, but they don't mention anything for the low and middle engine regime. Low regime torque is a good feature in a street intended car, I don't expect to drive at 5000 RPM at all times. Also, I known that sometimes back pressure is a wanted feature at a high regime, because it produces gas retention and prevents the loss of the fresh charge that just entered the cylinder by the exhaust scavenging action.

What are your experiences or suggestions? Should I keep my 4-2-1 or upgrade to a 4-1? Will I fell the lower torque at the lower regime? Should I replace the mufflers only? The car will be put in the dyno when its finished, and maybe I can test a few alternatives.

Thank you all,

Alejandro

[Alejandro]

Hey Guy and dear forum members, I leave here some pics of the head preparation of my car. These are just a few of all the pictures I took. I hope you like it.


Disassembling the engine in an elevator (the Fuego is low car and this is the mos comfortable way to work with the engine in order to avoid back problems)



The cylinders and a piston...covered with carbon, and the casted exhaust header in the back



The cylinder head, with carbon also...before the clean up



The car's original camshaft and its gear



The rocker arms



The intake manifold and the double body carburetor (Solex 34/34 TEIE, with progressive opening)



The cylinder head, already cleaned trough sandblasting



The combustion chamber ceiling



The cylinder block, cleaned up



These are the inlet valves, the two at the left are originals with 30° seat (the most far left is covered wit carbon, and the one in the middle is already cleaned), and the new 45° seat valve is at right.



The same but with exhaust valves...the two at the left are originals (the most far left is covered wit carbon, and the one in the middle is already cleaned), and the new one is at right. In this case, the old ones and the new ones are 45° seat angled.



Machining the valve guides in the exhaust ports and preparing for the new guides






Machining the intake port in order to promote swirl









The right side of the port is clearly larger than the left side, allowing more flow trough this side of the port, and this crates a rotating movement of the charge (swirl).



Machining the around the spark plug, but only the side near the wall...this is in order to open the flame front towards the wall of the chamber






Machining the bend radius of the valve seat



The final sand process with very thin grain sand paper



The cylinder head work is finished, and this is the result after a second sand blasting process






Machining the new seats in a high quality Serdi machine



Before measuring the contact between the valves and its seats...the contact is perfect



The adjustable cam gear



A few moments before measuring the combustion chamber volume (in order to determine the static compression ratio)



Filling the combustion chamber with hydraulic oil. The volume turned out to be V = 55 cm3.



The new camshaft, machined over the old one, with a darker color after the phosphate treatment



A detail of one of the cams



One of the old iron casted rocker arms



This is the reason I replaced all of the rocker arms, fatigue causes pitting (erosion) of the rocker arm paddle, with a later camshaft damage



The new syntherized iron rocker arms installed (with the same rocker arm ratio as the old ones)



Installing the new valve viton gaskets



Compressing the valve springs before installing the valve cotter


Releasing the spring after the cotters are installed



The cylinder head already assembled



The cylinder block with the new competition gasket



Verifying with the angular torqometer the 5 Kgm adjustment previously done with the automatic torqometer



The cylinder head, intake header, and carburetor installed on the engine



Starting the final assembly process, installing the last parts



The new, 4 electrodes spark plugs



In order to make things easier at the time of adjusting the cam gear, I cut part of the belt cover. This will allow me to adjust the cam gear with out removing the radiators and the front of the car...



This is the part I cut off the belt cover



You slip in the right side...



...then the left side, and the cover is closed again



Adjusting the two bolts secures the top part and finishes the process



The distribution completely assembled



The new spark plug wires, with separators and numbers



A detail on the wire numbers



The new air filter cover



The low pressure-drop filter



And finally, the engine completely finished












I already have a reservation on the dyno, for two weeks from now. I will show some results at that time. Greetings,

Alejandro

[Guy Croft]

MODEL POST!

WOW!

GC

[Alejandro]

Thanks Guy. I leave here a few more pics. This is the valve-lift profile measurement process. There is an interesting paper called "Back to Basics", written by Prof. Gordon P. Blair where top power at maximum engine speed is related to the area under the graph of valve opening area (the valve lift times the seat perimeter). I verified the equations in that paper with this measuremets...and surprisingly the error is as little as 1%. So, I used Prof. Gordon's method of areas under the graph to create my new camshaft and to compute the engines top power with it.


This are the elements I used to make an approximate measurement of the original valve lift profile, with minimal disassembling of the engine. You can see the 10 mm stroke comparator. Again, this is approximate, but later measurements with the cylinder head on a bench sowed minimal error. In order to place the angular measurement instrument, I used a distributor rotor.



The angular measurement instrument attached to the distributor rotor. A fast and effective tool.



Reading the scale and centering the angular measurement device.



As the cylinder head and block are made of aluminum, I had a hard time placing the magnetic support of the comparator, and I had no other alternative but to locate the comparator measuring tip at the rocker arm regulator. The error committed was very low ... 0.04 mm.



About to start the measurements...



And finally, the valve lift profile curve (with the original camshaft)...its the lift vs the crankshaft rotation angle. This curve verified the engine's original 114 HP at 5500 RPM, with a maximum error of 1%. Maximum lift is 9.05 mm. Duration is 260° at 0.20 mm running clearance.



Using the equations in the paper of Prof. Blair, I tested some camshaft alternatives, each of them with their valve lift profile. Each of them showed some interesting results. I decided for the ones that offered a street behavior of the engine.


The new valve lift profile curve...maximum lift is 10.30 mm and duration is 280° measured at 0.0 mm running clearance (no clearance). With this profile I make an extra 7 / 8 HP at maximum engine speed.

[Guy Croft]

I would be for using either:

4-1 of primary bore valve throat +5mm length (equal length pipes) anything from 33"
4-2-1 py bore as above, sy bore 1.25 bigger, py length 24" sy 9"

The overall pipe (not including collectors) length of the 4-2-1 will be the same as the 4-1. You can vary total py/sy lengths and really run with anything from 29-38" but keep the same ratio of sy to py ie: 9/24. In other words you could have, with 38" overall, 14.25 sy and 23.75 py. Hope you understand that. 4-2-1 will definitely give a better spread of torque and it is by no means always true that 4-1 will give better top end. In fact, with the cutting-edge data I get access to these days I can say there are no 'hard and fast rules' anymore! However on 4-2-1 the py should always be way longer than the secondaries. Remember that the pipe length is the chord (axis) measurement.

Tailpipe bore 2", single muffler with bore (2.25") straight-through like the one shown.

[Alejandro]

Hey Guy, thanks for your reply and explanation. That is true, I've read that modern exhaust systems are hybrid combination of the 4-1 and 4-2-1, and the general conclusion is that the adage that 4-1 means more peak power with a loss in mid-range torque and 4-2-1 means more mid-range torque with less peak power is an obsolete idea.

It's interesting to note that the car's original exhaust header is a 4-2-1, with short primaries, and long secondaries (the opposite of the header you detailed in your reply). I've read somewhere that this configuration of short py gives better performance at high RPM, and the long sy gives more mid-range torque, so the combination of both would be a compromise between them. I'm I correct?

I'll start planning the header following the 9/24 sy to py ratio, and the bores you detailed for each pipe. As this is a street driving car, I'm more interested in an engine that has a better spread of torque rather than high peak power.

Thanks for the reply and the explanation was very clear,

Alejandro

[Guy Croft]

I wouldn't read too much into the OE setup with cast header. They're used because they are cheap to produce and no other reason..

Obviously a cast unit with long pipes is going to be prone to fracture - so you'll never find one. And if the overall length (py + sy) is too short, ie: less than about 2ft, you can get chronic cylinder to cylinder pressure wave interference that prevents the engine from a) idling stably and b) picking up - even off load. So you'll generally find relatively long sy pipes on a cast header.

The optimum lengths of py, sy depend on the total inlet tract length and cam timing primarily, but there are so many other real variables, like CR, combustion efficiency, valve lift and overlap that it's quite impossible to generalise about what happens if you shorten or lengthen those pipes, except to say that, for a given header setup, if you lengthen the inlet tract (with longer manifold or rampipes) the torque will come in lower down but at the expense of the top end power.

GC

[Alejandro]

Obviously a cast unit with long pipes is going to be prone to fracture - so you'll never find one.

That is a good point Guy, cast headers are fragile. A longer cast header wouldn't resist an everyday use for a long time.

And if the overall length (py + sy) is too short, ie: less than about 2ft, you can get chronic cylinder to cylinder pressure wave interference that prevents the engine from a) idling stably and b) picking up - even off load. So you'll generally find relatively long sy pipes on a cast header.

Yes, in order to compensate for the total length, the sy pipes are made longer. It's the only alternative with short py.

Indeed, the optimum header design should be done considering all the other variables, but it would led us to a header design for one engine only, which is quite expensive, and the overall gain is not as significant as the cost of the entire process...and it may not be worth it. However, this general guidelines are very useful for a primary header design.

I have a reservation on the dyno for next Friday afternoon. I'll like to try different settings of the adjustable cam gear, and a nozzle design that a friend and I made to place on top of the carburetor (to compensate for the height lost when the new air filter was installed...in order to close the hood, It was necessary to lower the carburetor. This causes some loss of speed of the inlet flow).

We are doing the final adjustments to the carburetor, a double body Solex 34 TEIE. this are the actual settings:

Engine:

• CR: 9.5:1
  Bore: 88 mm
  Stroke: 89 mm
  Inlet valve size: 43.8 mm
  Inlet valve lift: 10,30 mm
  Inlet valve duration at 0.05": 272°

Carburetor:

• First body:
  Main jets - 125
  Air corrector jets - 145
  Idle jets - 45
  Emulsion tubes - 175.000

• Second body:
  Main jets - 125
  Air corrector jets - 125
  Idle jets - 47.5
  Emulsion tubes - 174.000

• Accel pump jets - 45

What do you think of this values, would you recommend any change before the dyno test? Thanks and I'll add more as soon as I have news,

Alejandro