I have done some research on the site on these spacers but i have recieved mixed info and also mainly info on "rev up" 05's. I am curious about both plenum spacers, 5/16 and 1/2 spacers. From what i understand, the midrange gains are around 12 hp and 14 hp gains respectively. However, i havent seen any dynos from the 03 model. Also, i am wondering if the 1/2 plenum fits under the stock manifold. What are the differences in performance between the two sizes? Basically, assuming i keep the rest of the car stock, are these mods worth it and which one is the best fit for me? Just whatever links or info that you have would be great. Thanks.

 

get the 1/2'' iso thermal model, you won't regret it.

 

wa he said

 

The G35 will accept any size spacer but the G35 engine cover will not fit with the 1/2" spacer. For maximum performance the MD XL ½" spacer should be used.

For stealth mode modification, G35 drivers should use the 5/16" spacer. The engine cover fits nicely and there is no gap at the oil fill cap. With the engine cover on it looks totally stock.

 

14HP on the 1/2 in. is a bit to much 8-9 is more realistic but is does make a difference. You won't be able to fit the engine cover like stated before so it's just a matter preference at this point.

 

I gained 15HP and 17 FT-LB (dynojet) on my 03 5AT. The only mods I had before the 1/2" spacer and ISO Thermal Kit were a Z-tube+K&N and the Invidia G200 exhaust. A bone stoke vehicle should gain 10HP and 10 FT-LB to the ground.

https://g35driver.com/forums/showpos...&postcount=153

 

My engine cover fits w/1/2" spacer without a problem.

 

03 sedan-the stock engine cover will fit without issues
03 coupe-get any spacer thinner than the 1/2"

as far as power mods, the spacer is one of the best ways to go.