75 GT4 - US vs Europe engine differences?

It takes a real act of faith to believe Ferraris claims on horsepower and weight. Some are well known to be wildly ambitious and many others are just doubtful. In any event from Ferrari literature the European version GT4 has the same compression, same valve opening and closing times, same maximum advance ignition. The carbs have the same choke size with very slightly different jetting. Yet the EU version has a claimed 250 Hp with 209 ft lbs of torque and the US version has a claimed 240 Hp and 195 ft lbs of torque. The emission control on the US car included an ignition retard system active only at idle, an evaporitive emission system that carried no penalty on horse power, a PCV system, and air injection system that had a 1 or so Hp penalty. and a thermal reactor system that I have not seen in many years.. It probably sapped a few HP. but since they were not installed during dyno runs I will leave it to peoples imagination to figure out where 9 horsepower went.

From having seen a great many Ferraris on dynos and in a few cases seen some of the official actual dyno figures and having driven hundreds or more brand new Ferraris 9 horsepower is less than the spread of identical cars coming of the production line.

There is a general belief that emission control is bad and costs horsepower. 2 out of 4 systems on GT4 were totally passive, one had a very minimal cost and 1 was not very good but had no impact on the factory claims. Technology improved a good deal since then and in the case of the F40 the US version was the most powerful they made.

 

When judging performance between US and EU versions most differences came in gearing, weight and state of tune. The US versions have a weight penalty and in most cases less favorable gearing. I come across few of the carbed V8s that are in a good state of tune.

 

None of the literature I saw showed where Hp was measured. Both had the same redline and with exact valve timing and carb size there is no reason to believe power curves are different. I would question your source.

I was wrong. I looked again. The US version says it was measured at 6600. The EU version does not say. Again, same cams, same carb sizes, power curve should be no different. One thing I have learned from 45 years in the Ferrari business, actually 46 I guess, once someone learns an incorrect fact, no amount of proof will change it.

 

The 91/74 OM shows 250bhp for a 1975 euro Dino 308GT4
The 100/74 OM shows 240bhp for a 1975 US Dino 308GT4

The mechanicals are the same for 1975 models (even the cam timing). The only significant major performance difference is the US version has air injection which puts an air injection nozzle in the exhaust port, partially obstructing it, and driving the air pumps requires a few HP. Of course, many US cars no longer have the air pumps, and those that don't should have the air injector nozzles removed and replaced with an appropriate threaded plug. There are minor differences in the distributors, idle timing, and advance curves, but the total advance at 5000 RPM is very similar. Also, the carbs are 40DCNF on both but are different series (35-36-37-38 for euro vs 45-46-47-48 for US) -- but these are small, changeable internal items (jet sizes, etc.).

The emission items on a US version (fuel evap control, air injection, insulated headers with thermal reactor muffler, etc.) do add a fair bit of weight, but these are often removed/changed, too.

Summary: The differences between 1973-1977 US vs euro are small; the differences between 1978-1979 US vs euro are much larger (as the 1978-1979 US version got a serious detuning, mostly in the cams, to deal with the addition of cats).

 

They didn't do the carbs any favors either.