Looking at the timing maps for a fwd U13 vs a S13 timing maps, the fwd timing maps looks quite a bit more aggressive than the rwd map. Any Nissan experts out there have any ideas why? I believe both are rated at the same HP. The only difference I can think of is the rwd is coil on plug and the fwd has a distributor.
I'm not a Datsun guy, but if one is dizzy and the other is CoP, then there is a big hint. There are probably other differences and they are probably "different generation" engines, so the timing would be different as well. Just dizzy v. CoP is not reason enough for a major timing difference, but the CoP is going to be a later version.
They are concurrent engines and as far as I am aware, same cams, pistons, CR, turbo, etc. Just different orientation in the engine bay and that means different manifolds. The other difference is the rwd has a small side mount intercooler and the fwd has a little bit larger top mount intercooler.
How's the gearing compare between the two?
Other than gears, maybe different fuel specs, differnet cooling system capacity, different intake manifold flow, different total volume of intake, different exhaust/catalyst?
Or heck, maybe they just wanted the cars to sound/feel different from each other.
Muffler is starting to weep on the SE-R which hides the snarl of the engine. Boo. 
Even different weight cars can use a different advance curve for the same motor. And I've had to retard spark when towing, with everything else being the exact same.
bigben said:They are concurrent engines and as far as I am aware, same cams, pistons, CR, turbo, etc. Just different orientation in the engine bay and that means different manifolds. The other difference is the rwd has a small side mount intercooler and the fwd has a little bit larger top mount intercooler.
That last comment reminds of the time a Pulsar GTiR out of Canada showed up to one of the SuperRallycross events in Michigan. After every run, the guy had to drive around the paddock for a while to cool off the intercooler since it would heat-soak so bad.
Getting air out is as important as getting it in, and bolting the intercooler to the valve cover is the last thing you'd want to do.
Relevant to thread, I wonder if the lighter front drive chassis meant that the engine would be less loaded. Or if the Silvia was tuned for people who would bolt the throttle to the firewall and ignore problems. Or, and this is the most likely one, they were tuned by two completely different engineering teams who didn't talk to each other because of intra-corporate rivalry and they arrived at different conclusions.
For reference I have added the two maps to the first post.
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