Once all my parts are installed, for mods I'll have:
-wai, 2.4l intake man, balt ss injectors, 68mm TB, 4-2-1 tsudo header, tuning tuning tuning

My exhaust is still stock, and will have to wait until I do the IRS (Olds Olero independent rear suspension/disk brake swap, jbody swap to get rid of torsion axle) as the exhaust will be routed differently..anyhow, been pondering 2.25" or 2.5".. right now I'm building NA but i MAY get a GMPP supercharger kit in the future, so I'm leaning heavily towards 2.5"...I've also heard there is not a lot of low-end loss running 2.5" for city/daily driving. Opinions?

 

With a 2.5 exhaust and a 2.4 IM there will be a significant reduction in the low end. But if you are supercharging later it might be a good thing to have the bigger exhaust for later.

I'm not sure that you will need the 2.0 injectors though. There is no point in putting those on your car if they aren't needed.

A 68mm TB is likewise not needed.

 

if you are wanting or thinking of the SC kit, i would go with the 2.5 i wouldnt think there would be too much loss in daily driving

 

The 2.0 injectors are not only needed but mandatory with the 2.4L intake man...unlike balts, the jbodies don't have a MAF sensor and do not adjust to the intake man correctly and lean out/detonate due to the air/fuels... this can be fixed with tuning, but the 2.0 injectors help the problem as well are needed once past the basic breathing mods. Why is the TB not needed? The 2.4 intake will be pushing more air, and a larger TB will no doubt help, combined with the header and other breathing mods.

 

i think he is going of cobalt knowledge, i dont know how the j's work but good luck with that, and iw ould go 2.5, i have that on my balt and its jjust fine

 

Your going to lose power with the larger throttle body. You may see a few hp difference in the high end but your low and mid range is going to suck. Why might you ask... Because your increasing the side of the air inlet, decreasing air velocity, causing you to require higher revs to make more hp. So in turn, your low and mid range suffer. Honestly i wouldn't change the TB size. I also wouldn't go with 32lb/hr injectors when you have no need for them. If your getting a tune, you really have no need for them. Even the LE5's dont need them with full bolt ons putting down 185+whp and i doubt your going to exceed that.

Also on the exhaust size, the 2.25" will be perfect for both applications. 2.5" will suck for NA and make a minimal difference on just the basic M62 kit. Now if you plan on exceeding 250whp then yeah 2.5" would be good but your not going to see that on the stock pulley. Stick with 2.25", it will treat you right on your current mod list, and future.

 

ya i have a 2.5, and 2.4 intake many i like it

 

Sorry, disagree and I have past experience running larger TB's, if you go too large then yes it's a problem, 68mm is a small upgrade. Or if you put a larger TB on a car with stock breathing mods. The injectors are needed, not going to argue there, already seen many have to use them, remember I don't have a balt. And I'm going with 2.5" exhaust... the feedback I've gotten here and on jbody/saturn sites is the eco engine already has good low end so the 2.5 does not effect it that much (provided you don't remove the cat or run a highflow cat). I always get custom compression bent exhaust so it won't be a true 2.5" anyhow, it will be somewhere in between

 

I know how you feel on that compression bend. That's all the guy here in town does, but it's cheaper and as long as he knows about how big to do the piping he can normally do a pretty accurate job.

 

i also run a 2.5" and its no prob

 

So your telling me your going to be flowing more air then a fully bolted LE5? You do realize the LE5 aka 2.4 runs the same injectors as the L61(at least on the cobalts). So by adding a 2.4 intake manifold your going to be magically flowing more air then the 2.4? I dont think so... Thats why im telling you the injectors are not needed. Who cares if the 2.4 leans your car out, that has nothing to do with the injectors and everything to do with the tune. It doesnt matter if its a cobalt, its still an 2.2. The injectors are not needed at all is what im saying, but if you want to spend the money, go ahead

 

Regarding injectors you have no idea what other plans/mods I have for the car...and "who cares if it leans out"? I care, quite a bit actually One of the first jbody guys that installed a 2.4L intake man without tuning or larger injectors toasted his engine.... BIG mistake but he didn't realize the differences between MAF and MAP...there's a few guys building up 2.2's and they all needed the larger injectors and dyno tuning proved it. You should think outside the box a bit more.