1. Seafoam. Since I was doing oil change, plugs etc, tried seafoam first. Got the can with the throttle body funky bendy tip. Sprayed 1/2 can as per instructions. let soak for 5. Started up and followed instructions. Smoked like crazy as expected. Took it for a drive to clear out residual. Did I feel any difference? Nothing earth shattering or identifiable. What I did notice over the next 3 days while driving back and forth to work was a noticeable difference in fuel consumption. I have 19k(12m) each way to work. I am lucky to not have to go through city traffic and I use a major highway most of the time so I do not baby it. 35-40 liters a week on average. (10 -12 gallons). After seafoam, I used 28 liters the next week. I am"not"an advocate of seafoam for fixing all sorts of engine ailments but I did get better gas mileage.

2. MD 5/16th's spacer with copper iso for colder climates. Good packaging/material, but generic instructions that pissed me off. Had to decipher 350z, G35, Iso, Copper, etc. It's all there but that is the problem. Not specific for your application - be prepared to read numerous times for your car. Quality product. Cleaned plenum while apart. Have above average car knowledge but still took 3 hours due to deciphering (and insuring) proper install.Also installed 2006 coupe airbox (larger venturi). Reset ECU via the instructions provided (typical key on, insert key 5 times within 5 seconds etc) Car started right up. Took out and ran hard after listening for problems. Seat of pants dyno feels good but I do not think 13-15 whp? Not convinced. Maybe 5?

3. Fluids and plugs. Rear diff - drain, fill with OEM, tranny -half *** (the 3 quarts out and then back in exactly what was removed) and Amsoil engine oil. Same time changed out plugs at 80k miles, NGK G35-6619 Irridium. Overall car seems smoother and way better gas mileage. As far as improved TQ/HP, no way that these type of mods/tunes are going to show any "big" results. Will keep your car running better, but you will not be able to change it into a GTR so get over it. Realistically when I take it over to the chassis dyno, I will expect 230-235 whp as opposed to the stock 215-220 whp (Don't go ape **** you few, advertised hp/tq was 260 at the flywheel). Cheers and hope that this in some small way helps.

 

If you did the plugs at the same time as the Seafoam, it may have been the plugs that got you the better gas mileage. That would be my guess.

 

No surprises there. You're not likely to 'feel' 5-10-15hp even if that's what you netted. Same dyno, same day, same conditions is the only true measure.