Fiat sohc: (domed) piston options

[hermanno]

Dear Guy,
dear all,

since this is my first post to the illustrious circle a word of introduction: I'm about to build a Fiat X19 racer according to the old Group-4 regulations for historic races. The whole project is quite a bit cumbersome, bodywork takes time and many useful things from struts to chassis-bearings are just not available easily....

My thoughts about the short engine are:
- X1/9 1500cc block with
- either 1500cc crank or 1600cc (tipo) crank
- H-shaped conrods from arrows or +-shaped ones from pauter
- Domed pistons for a cr of 12.5:1, max 13:1 that allow a 5.5mm lift at TDC

Questions:
- The compression height for 1500cc (stroke=63.9) and 1600cc (67.4) pistons should be different since those engines have equal block height/equal rod length. Would it be possible to use a 1500cc domed piston together with the 1600-tipo crank and compensate the 1.75mm with a thicker head gasket?

- Where can i get domed pistons for this application, do i need a custom production?

- Can the h-shaped arrows rod handle speeds up to 21.5m/sec?

Your comments are apriciated!
Armin

[Guy Croft]

Armin, hi

rods from any reputable source, Cunningham, Pauter, Arrows can easily handle that rod velocity, in fact they could handle twice that speed, 38+m/s, comfortably with either stroke. Race pistons too, properly designed and made.

Everyone wants to shop around for the cheapest but FWIW (since I own the site) I myself have beautiful piston designs for either unit (and dozens of others), just had some made for Gunter Pitzer's Tempra with low comp ht.

Gunter's set shown are to 87mm bore with race rings, weight piston 337gm, pin 90 gm, rings 23gm, as they stand that GC design (which is on my cad so can be readily altered) they will accept X19 or Tipo 36-37.5in, 33mm ex valves with plenty of radial clearance. Lift to contact valve-piston at tdc is 7.85mm inlet, 7.44mm based on head with 10 thou removed for cleanup, 1.5mm thk gasket. They are not cheap, they are expensive, see list in GC V/W. Are they in stock? No, mostly my pistons are made to order and they are about month to get it from order although I can genuinely get them in a week with a surcharge.



GC

[hermanno]

Thanks Guy,

for your advice and the great pictures.
I run my own racing team with the following staff menbers: Head of engineering, CFO, driver and unskilled worker. Unfortunately i have to implement all positions by myself (unskilled worker is most busy)! Your pistons are probably the benchmark for this engine and i will certainly consider them as an option. Hopefully the finance guy will not veto....

Armin