Ported Throttle Body and higher idle??

[Midnight02]

Just got my car back from the shop last night after the SFC install and I also had my stock throttle body ported (along with the bump stop mod).

I’ve noticed that the car is a bit more responsive to the throttle and seems to rev a bit quicker (a good 5 rwhp according to the seat of the pants dyno!), however I’ve noticed that once I let out of the gas and move the shifter to neutral (6-speed manual) the idle is a bit higher than it used to be. It used to idle in neutral around 800 RPM, now it hangs around 1,100 RPM. Of course, that number is lower if you put it in gear and just let the car creep along.

I know when I was working on my L98 Corvette that I needed to reset the throttle adjustment cable each time after working on the throttle body (because the RPM would hang up if you didn’t). Do our LS1’s also have a throttle adjustment cable that should be adjusted or do you think the higher idle is simply a result of the throttle body being ported along with the bump stop mod?

[BlackLT1Z28]

Don't have experience with a stock vs ported TB yet, but I think the higher idle is the result of the porting. Your letting more air in with the same angle of the throttle blade. That's what I think.

[Ripper415]

first, you cant "feel" and extra 5 hp on a 350 hp engine. it's just a placebo effect in your mind. second, after i got my tb ported the idle was actually about 100 rpm LOWER than before, so i dont know what to make of that. third, the bump stop mod has no effect on the idle because it's only being used at wot. so any time the gas is pushed down less than like 99% it has no effect at all.

[Midnight02]

first, you cant "feel" and extra 5 hp on a 350 hp engine. it's just a placebo effect in your mind. second, after i got my tb ported the idle was actually about 100 rpm LOWER than before, so i dont know what to make of that. third, the bump stop mod has no effect on the idle because it's only being used at wot. so any time the gas is pushed down less than like 99% it has no effect at all.

I stand corrected. I guess the PLACEBO effect distorted my mind and made it FEEL like 5 extra horsepower. So if the dyno indicates that the car gained 5 rwhp would the argument still be that my mind was tricking me into thinking that I feel a difference? Guess so. Switching to a 3.90 gear certainly made my car feel considerably faster, and the gain on that one was ZERO hp. I guess saying that it "feels like 5 HP" was a bit presumptuous on my part, however I wouldn't think it's a stretch by any means to say it "feels faster".

Thank you for the second and third part of your post, that was helpful! I guess I'll look into this a bit further.

[Ripper415]

I stand corrected. I guess the PLACEBO effect distorted my mind and made it FEEL like 5 extra horsepower.

yup.

So if the dyno indicates that the car gained 5 rwhp would the argument still be that my mind was tricking me into thinking that I feel a difference?

still yes.

Switching to a 3.90 gear certainly made my car feel considerably faster, and the gain on that one was ZERO hp.

changing the gears on a car substantially alters the drivability and performance of it so of course you'd feel a difference. just as if you found a way to remove 500 lbs from the car somehow, while it wouldn't produce more power it would certainly drive and feel different than before.

I guess saying that it "feels like 5 HP" was a bit presumptuous on my part

correct again!

Thank you for the second and third part of your post, that was helpful! I guess I'll look into this a bit further.

no problem, glad i could help