FCD question
 

Are S4 and S5 FCDs interchangeable?

I don't think they are.

seconded. you might find a store that sells one for each and see if they're the same or not (part number, or send support a question....). Racing Beat might sell them.

Racing Beat lists them differently but HKS (albeit eBay) lists them together. I found an S4 one to use so I'll be fine, but maybe good to know for future reference.

Most of them are interchangable unless explicitly stated.
(This info is probably outdated, since I haven't messed with FCD's in years.)
The older Racing Beat ones (metal case) could be used on any model?
The only one that I know that doesn't work is the Trust / GReddy one - this unit is specifically listed as a Kouki FC turbo only application.
Trust me, I tried - I slapped one on my old set-up on my 1987 Turbo II, and it didn't prevent the overboost fuel-cut with the stock ECU. :P


-Ted

Good info.

That's really weird considering how they work. I would think that if one worked, they all would. Perhaps the voltage is slightly different, e.g. 3.6 S4 and 3.7 S5 and the Greddy one activates at 3.65v or something. :dunno:

It's probably due to the design of the FCD itself...

The older Racing Beat units were just resistors inline of the signal.
This basically shifted the overboost fuel-cut point to a higher boost level.
I think I was able to hit it *with* the older Racing Beat FCD at around 18 - 19psi.

Most of the new ones are voltage-clamp design, which just keeps the signal at a predetermined maximum *if* the input voltage exceeds that level.
Since the overboost fuel-cut boost level is different between the FC turbo series, this is why you see specific applications explicitly stated.


-Ted