The FD is considerably faster than the FC but somehow manages to maintain a similar fuel economy. My question is: are there certain modifications that can be done to an FC that would improve its performance to the point of being comparable to an FD while still keeping a reasonable fuel economy or does the FD engine just possess inherent improved technologies that cannot be easily replicated through modifications?

 

get a standalone and a really good tune

 

weight and aerodynamics. They may also use slightly different gearing

plus peak power has nothing to do with cruise efficiency

 

they're basically the same engine. remember the turbo isn't in use while cruising.

 

FD has equal or less weight, with taller gearing.

 

the fd weighs more my FC is 2650 and my FD is 2775 the difference is in the port on the FD. u can make an FC run like a stock FD with a port job and a retune.

 

completely depends on the options for each model. s5 T2 is significantly heavier than an FD, over 100 lbs. 86 base non turbo is over 100 lbs lighter than FD. s4 T2 is similar in weight depending on whether it had power steering. FD touring package had rear wiper, sunroof, and Bose wave system which added about 50lbs to the car

 

I thought the gear ratios were the same

 

They're most definitely not, having driven T2, s4 n/a, s5 n/a, and FD transmissions plenty. The FD has taller gears and higher top speed, not to mention a higher redline than the FC. The s4 T2 has the shortest gear ratios of series 4 - 6.

 

s5 and s6 turbo are the same gear ratio (US) and have the same 4.10 rear end. the difference in the s5 n/a gears is negligible.

 

The chassis and suspension design between the FC and the FD is HUGE. If you want an FD, just wait and save up and get an FD. Enjoy your FC for what it is.

 

Thanks. I know what transmission i want now!

Short ratio ftw. Screw mileage.

 

The FC S5 has 200 Hp, the FD has 255 hp factory. The twin turbo setup was designed to spool at very low rpm with a small turbo, then just before the first turbo ran out of air, the second small turbo opens up. Boost pattern stock is something like 10 psi-((first turbo fully spooled)8 psi-(second turbo opening up) 10 psi( second turbo fully spooled). The control system was very complicated and became troublesome with age.

Closest you can get with a single turbo would be something ball bearing like the Garrett Disco potato GT2860R (GT28RS). This statement will start an argument.

The big turbo guys will say this turbo runs out of breath at higher rpms-they would be correct, especially compared to some of the T4 turbos in use in the rotary world. But the T4's that give the high Hp won't spool nearly as quick. Depends on what you want, response or max Hp.

But don't ask me...

 

I was also under the impression that they were the same at least between the S5 Turbo and say, a '95 USDM

Sources:

I don't know how valid that 2nd source is, but if you can shed some more light as to what the ratios for the 3rd Gen are, that would be much appreciated.