So i just got a response from japanparts.com about the spring rates for the Impul's, here they are after my conversion.
It's:
Front= 8.7kg/mm--->(my conversion) = 487lbs/inch
Rear=8.5kg/mm---->(my conversion) = 476lbs/inch

now if these are the rates for:
G35 sedan's with non sport
Front: 283 Rear: 308,

wow those are some aggressive rates...if my conversion is correct than I'm really surprised that those with impuls are not experiencing bouncy ride.
Actually these rates seem to be stiffer than the eibach pro kit

 

That's really not "that" aggressive. JIC's run 12k/8k for their COs, so the Impuls should be fine. Except for the price that is.

 

well, if you compare it to the eibach pro it, which lowers the car more, yet it has less aggressive spring rates, the impul's rates seem strange.

Also, the 480 spring rate definitely puts the Impuls beyond the 10% +/- rate threshold, which determines premature shock wear.

 

well, these came in today, and now i am stuck.

should i do it ( i still don't have enough consensus on these springs)

or do i turn yellow?

 

Put them on!!!!!!!

ill take em off your hands if you dont want them....

 

which springs did you order? There drop down menu is a little confusing. I have an 2008 3.5L. They list a 2.5L and 3.5L as the same, then list a 3.7 with and without 4 wheel active steer, then the coupes

 

if you don't have active steer this is the option you need to select:

SEDAN 3.7L without 4WAS

btw, when you order, they will contact you and double check what car you have and whether you have active steer or not. Their customer service was very good.

 

ive been emailing Yuki over there about this and I am still confused. He seems to think I should go with the 2.5L/3.5L bc I have a 3.5 V36. I am leaning towards the 3.7L w/o 4WAS. My question is were there any suspension changes from the 08 3.5XS and 09 3.7XS?

 

It's just springs, and i doubt anything was changed that would jeopardize spring fitment.

Are you saying that they have an application for V36 3.5L? if they have one for that I would order what Yuki is suggesting. If anything they might have different spring rates due to weight increase of the G37X

 

for the V36 drop down box they list the 5 options...

2.5L or 3.5L
3.7 w/4WAS
3.7 w/o4WAS
coupe w/4WAS
coupe w/o 4WAS


IMPULs website only shows one application and thats for a V36 2WD, which is what japanparts.com site used to say. From what I remember, a X member ordered and installed the V36 2WD ones without problems. Now that there isnt an option for that, Im just a little confused.

You may be right though on the spring rates for the weight difference. why do they list a 2.5 and 3.5 as the same??!?!?!

 

that is confusing, for my 3.7L it was much simpler.

Hmm, strange i'm sure there's a weight difference between 2.5L and 3.5L and yet they have the same version for both.

I guess with this info in hand to be safe i would go with:
3.7 w/o4WAS

There's no way suspension components were changed, also the eibach pro kit fits both 3.5 and 3.7, which to me suggests that nothing was changed.

 

Nothing with the suspension changed other then spring rates because of the extra ~100lbs of the VHR

 

I was told the spring rates (and dampening rates of the shocks) did change slightly between the 08 and 09. Nothing else on the suspension changed.

Eibach has different versions for the 08/09 with different rates. I can also add that I am running 08 Eibach's on my 09, and they drop the front of my 09 more than they do on the 08 FWIW....

 

Impul only have 3 sets of springs.
Two sets for G37 coupe:
SF-77 & SR-77 (with 4WAS)
SF-79 & SR-79 (w\o 4WAS)

And one set for V36 SKYLINE SEDAN 2WD Models (G35 & G37), also can be used on X models:
SF-76 & SR-76.

It doesn't depend on the engine type. 2.5, 3.5, or 3.7.

 

Thank you, thats what I needed.