Race Engine Forum UK

Dear Mr. Croft,

Last year i writed you asking some advise how to get more power from a 1608cc engine that i am using in a Fiat 125 in the chilean historic car champioship. Following your advice i change the chokes (from 32 to 36) for the same carbs (twin 40mm IDF Webers) and in addition i changed the emulsion tubes (i have now F2 instead F11) and i went to electronic ignition (fixing the timing 36‚° in advance) and now the engine is well for around 128hp (from 118) at the rear wheels.

I am not sure of how many bhp the engine loss from the flywheel to the rear wheels but seems that 15% is a fair %, so i can think that my engine is pumping now around 147hp. The engine reaches the max. power at about 6900-7000 RPM

I am planning now to change the carbs for new ones Weber 44 IDF that I already have (chokes 36mm) and change the cams too. I‚´ll be very grateful if you can give advise about what kind of cams to put in.

My engine now has the following paramethers:

1. Bore 81mm; stroke 80mm.

2. valves size: in: 43,5mm (Lancia 2,0 valves); ex: 36mm (standard)

3. Carbs: 2 weber 40mm IDF ; venturi 36 mm; jets: air170 and fuel 135 (i have from 155 to 140); emulsion tubes F2 .

4. Cams: made by Crespo (from Argentina); the valves open up to 10,5‚° and the permanency is 296. The paramethers that Crespo gave me was inlet cam open at 43 and close at 73 and ex. cam open at 38 and close at 78.

5. the header is hand made 4-1 .

6 . The head was worked from a chilean specialist that included: polishing it, bigger admision ducts and seats, he changes the seating angles to 35‚° (from 45‚°) and worked the valves guides.

7. forged piston from IAPEL (argentina) and special rods from SAENZ (argentina too)

8. Compresion ratio 11,6:1

I think that maybe you can advise about new cams with more lift (12‚° would be better?) and new valves springs (i think yours triples would be great)

Sincerely,

Daniel

Daniel wrote:

1. Bore 81mm; stroke 80mm.
2. valves size: in: 43,5mm (Lancia 2,0 valves); ex: 36mm (standard)
3. Carbs: 2 weber 40mm IDF ; venturi 36 mm; jets: air170 and fuel 135 (i have from 155 to 140); emulsion tubes F2 .
4. Cams: made by Crespo (from Argentina); the valves open up to 10,5‚° and the permanency is 296. The parameters that Crespo gave me was inlet cam open at 43 and close at 73 and ex. cam open at 38 and close at 78.
5. the header is hand made 4-1 .
6 . The head was worked from a chilean specialist that included: polishing it, bigger admision ducts and seats, he changes the seating angles to 35‚° (from 45‚°) and worked the valves guides.
7. forged piston from IAPEL (argentina) and special rods from SAENZ (argentina too)
8. Compresion ratio 11,6:1
I think that maybe you can advise about new cams with more lift (12‚° would be better?) and new valves springs (i think yours triples would be great)

Well, you could certainly try my full race circuit cams 12mm lift approx, but they have no distributor drive. You might be better to try the 44IDF first. My springs are certainly a good idea, drop me an e mail to order croftengines@aol.com
I am not sure about the 35 degree valve angles, my experience is that shallow valve angles only give improvement at low lift. But as I did not prepare and flowtest the head I better not comment! I suggest that the best emulsion tube for the 44IDF is F11 or the richer F9, I do not know the characteristics of the F2, sorry, never used them.

If I saw the inlet flow graph of the head it would give me a much better understanding of the cam situation. (It might be an idea to just change the inlet cam). I asume the man who prep'd the head has a flowbench and has given you the data? You could email it to me.

Some engine photos would be a help here.

GC

Mr. Croft,

thanks for your answer and tyour advice....


I already proved on the Dyno with the 44 IDF (installed on a new machined inlet manifold) and the power went down 12 bhp!

Now i turned back to the originals IDF 40 and the power arrived to th original 128.

About your cams; my problem would be what to do with the distributor because we are not allow to use those modern ignition system without distributors; any idea?

thanks again and i wait for your answer,

Daniel

Daniel, hi

it may be that the cams you have simply do not provide sufficiently high flow and strong enough pressure wave effect to run 44IDF, the air velocity is just too slow to fill the cylinder. I assume that you examined the mixture thoroughly with the 44s before taking them off.
This 'gig carb' thing is quite a common problem, I myself have tried 48s against 45s on the 2 liter and 1800 and found the same when the cams were not powerful enough. I have often run 45 DCOE (even bigger than 44IDF) on 1600 engines with great success.
128bhp is not a bad result for a 1600, but it is nowhere near the limit. That engine - by me - is capable of well over 155bhp. .but I am not building or preparing it.

As I said before:
If I saw the inlet flow graph of the head it would give me a much better understanding of the cam situation. (It might be an idea to just change the inlet cam). I asume the man who prep'd the head has a flowbench and has given you the data? You could email it to me. I'd also like to see the lift by cam degree map of the cams. Without this information I cannot make any expert judgement about improvements.

GC

Mr. Croft,

The problem is that the person who worked the head has a lot of experiece but he hasn't got any flow graph (I will try to talk to him any way).

When return to my city i will send you the cam degree map that i received with it.

Thanks and talk later,

Daniel

@guy: Which manifold do you use for double weber on ohc engine (1.6 tipo engine)? In germany you get the hoermann (=alquati) manifold and winz manifold but this manifold is divided into two parts (for each portpair).
The alquati has a bigger radius in the port, difficult to explain... but the winz is cheaper... what costs such a manifold in UK? For DCNF? I will use DCNF 36 with throttle body from the 40 or 42 DCNF because it's the same (but you have to change the throttle etc.).