Race Engine Forum UK

I have a 125T which although road registered is used mainly for track and sprint work. Since owning the car for approx 3 years I have not even had to take a cam cover off, with the engine giving 93 HP at the rear wheels, enough for a first time track driver. However it is time to upgrade and put this engine and gearbox away as a spare unit. Over the last couple of years I have been collecting parts for the 1608 and have finally started the build, my aim has been to do a good engine as a whole unit and do it once. I have resisting the temptation to add bits and pieces to teh existing engine along the way. I am not building the engine myself as I travel a bit for work, and to be honest I do not have the skills to do the job right the first time, so have asked someone in the car club I can trust to do the assembly. I expect it to be finished by the end of May.
Block has been machined and lightly skimmed
Crank has been ground down 0.010"" and balanced, you can do this on a 1608 crank.
All plugs removed , a LOT of material cleaned out and grubs screws inserted I was lucky enough to buy a GC 1608 head and a set of L2 cams. The head is almost too nice to install, worth buying one to keep on the coffee table as a work of art

Picking up new clutch and flywheel today and check on progress.

Update

Have been away for work but progress has been made by the builder.

Head has been assembled, lots of "fettling" to get head, cam boxes, cams all from different sources and ages to fit as they should. Cam boxes have been powder coated. Have received new locally manufactured rods from a reputable source. Weight of 550gms versus approx 800 gms. I spent a great deal of time trying to decide if I could justify the cost of new rods, but in the end I decided I could not justify not using them. Already the piece of mind is reassuring even if it delayed the build by six months while dollars were saved. Pistons need to be trail built and machined Block partially assembled, will be running a 1 inch cam belt I have also sourced a close ratio four speed gearbox that had been built for a log booked local Abarth Spyder. It has been built into a 125 casing with ratios of 2.33, 1.78, 1.33, 1.0, should make a big difference on the track.
The engine builder is on holidays for a few weeks , but there will be a lot of progress when he gets back !

Be sure to cut off the fuel lobe on the aux driveshaft and plug it, the 1608 is one of the 'at risk' units - can hit no. 2 conrod.

GC

Good stuff.

Now, it may just be my eyes but in the top 2 photos it looks like the block isn't flat - curved down at each end?? (its probably the camera lense playing tricks though)

I'm sure it's a trick of the light!!


G

That's a wide-angle lens artifact most likely, yes. Remember all the close-up photo's where your nose looks so big? That is what is probably happening here.

Yes a trick of the camera, reckon even I would have picked up the block being that far out !!

Fuel pump lobe has been removed and crank unplugged and a LOT of junk removed.

More pictures please! This looks like a very nice build.

What ignition are you intending to use. As it is going into a 125 you cannot use the distributor in the cambox unless you reposition the booster and I notice you have the hole in the block for the distributor fitted with the blanking plug. As an aside if you use the blanking plug that can be found in some camboxes in the block the oil pump drive gear can be pushed up until it no in contact with the gear on the auxillery shaft.

Well noted, I am looking at putting a straighter inlet manifold on so will be using a MegaJolt Ignition system, with the idea of be able to get the best possible tune out of the Dyno. If I decide to log book the car later and need to go back to distributor at least I will know exactly what curve needs to be set. Another advantage of the MegaJolt is thw ability is store two ignition curves as I am keen to explore E85 ethanol fuel in the future. The engine builder is currently on holidays in Europe for a couple of weeks so progress slowed till the end of the month.

More progress at last, everyone has finishd their overseas travels. The pistons have been machined to suit, the cams have been dialled in and the trial build completed. The machinist measured and then calculated the compression ratio and worked out a real 10.4 to 1, so may look at running 100 Octane to keep everything working. Happy with that result, as I understand it is hard to get compression out of a twin cam in real life.

Engine assembled this week and hopefuly into the car in next week or two. Plan after that is to get a set of headers made, going to use the "standard formula" as per the book for a set of 4 -2 -1 , but any advice of ID size of of the primaries and secondaries appreciated. Finally going to see if some sort of air box and remote air intake can be made, again really hard on a 125 due to lake of space, before the dyno tune.

Watch this space to see what numbers are produced, any guesses any one??

What carbs/venturis are you planning on using? Knowing that, would make guessing the power output figure a bit more "scientific".

Fair Comment. DCOE 40's, 36mm choke, may have a 38mm option if needed and jetting as per Guys recomendations.

4-2-1 - here is my best advice:

1. The collectors must not be considered part of the lengths - they are merely the open space that generate the reflections.
So you can make them as long as you like and internal taper optimum is 14 deg included angle or less to minimise turbulence.
2. Overall sum of primary and secondary pipe chord length (measured at pipe axis & not incl collectors) should be typically 34-36". The min acceptable py chord length is 27" (no less!) thus with 27" py the sy chord should be 7-9". You could equally as well run 28" & 8" or 29" & 7". Etc etc. You can go longer overall, say 37 or 38" but don't go below 2&" py and don't lengthen beyond 34-36" unless available space dictates that's needed. The py pipe is measured from the head face and the pipe chords must be of equal length to +/- a few mm. Py pipes are paired 1& 4 and 2 & 3 and no other way!
3. Cannot predict the effect of various lengths suffice to say the torque won't suffer (nor power) but the position of the spread of torque will alter up/down the rev band. And no more than that!
4. Py pipe ID should be such that the final py pipe internal area is equal to the valve throat area (x 2 if a 16v head) or the area of the port exit region - whichever is the larger. Invariably on a 16v the port area will be bigger than the combined valve throat area (which after all is the controlling section) and on in fact an 8V unit I tend to make the py pipe ID same as valve throat diameter plus 5mm which works well in practice and has been proven in simulation to be effective. You can go bigger - but it may not work so in general terms avoid! There is little point making ex ports huge in relation to that valve throat (s).
5. Make the sy pipe diameter 25% bigger than the py.
6. The tailpipe - which is the bit from the sy collector to the silencer (muffler) make same as sy internal diameter. As a rule of thumb no 8v TC tailpipe should be bigger than 2" bore and frankly 1.75" will suit any 1600 & 1800cc unit.


Hope this helps,

G