Geboe

Assuming size matters, I have a stock 2003 and I am starting to add some performance enhancing bolt-ons, like headers, CAI, and a tune.

I want to know if a new larger throttle body is recommended. What size is stock an what size is recommended?

Thanks,
Gary

kp1

Not necessary with the add-ons you're talking about.

Rob 02

On a stock 2003 I don't see the throttle body to be a bottleneck. Unless you have made substantial modifications to the engine I don't see much benefit. A larger TB will require the mouth of the intake manifold to be ported witch may help at WOT.

A CAI and a tune will yield HP gains (20-35HP). CAI alone (10-15HP). A freer flowing exhaust may be good for (10-20HP). These are just estimates. People will argue with me but I don't see headers really adding any HP to a stock LS1. The stock manifolds work fine on the 405+HP of the Z06. I would go with a cat back exhaust and possibly gut the pre-cats.

tblu92

I agree---Unless you plan on running your engine consistently over 6500 RPM's OR have larger than stock cubic inches a larger T-Body will NOT give you any HP advantage and will create some drive ability issues unless you get a re -tune---
Your best option is to get your STOCK T-Body professionally ported----There are several companies that can do this for you--Typical cost is between $150 and $250----This is all you really need A ported T-body most always adds about 7-10 RWHP however the throttle response really wakes a drive by wire throttle wake up---AND no tuning is required--------If you go to a larger aftrmarket like a BBK 80 T-Body it will require tuning otherwise you may go backwards in HP--------

Geboe

From what I've been reading headers add horsepower. But you are saying the exhaust might be restricted beyond the manifold. I bought the car with aftermarket exhaust but I am not sure what they are yet, but they have a great sound. I will try to determine what type this is soon.

Rob 02

Headers help more after other HP making modifications.

Gordy M

Any cat back system you buy is for the sound, The Z06 TI added about 3 hp to the Z06 according to the GM head Powertrain engineer who spoke to our club several years ago. He mentioned that other than the Corsa TI straight pipe or similar, you will not gain anything noticeable in power gains. If you add a true CAI you will need a good tune to realize any HP gains 10-15hp, otherwise, without a tune, you might actually lose hp (The incoming air is denser-more oxygen-and the many fueling tables may not be able to supply optimal air/fuel mixture). Also the TB is drive-by-wire and a good tune will also eliminate some of the delay associated with it.

tblu92

There is no magic in ANY aftermarket cat-back exhaust system-----Typically most all brands will only add from 3-8 RWHP
Sound in the major reason to choose one brand or design over another-----Everyone has different tastes in what they like----

Rob 02

Exhaust and intake's don't add HP they restrict it on some level. Weather or not it makes a difference for your set up depends on a lot of factors. On a stock LS1 I don't see much of a gain from headers alone. What HP is gained is most likely from the freer flowing cats. When you start making more HP the exhaust starts wanting to breath more.

With 350HP you may see a 3HP increase with headers but at 500HP You may notice a 35HP gain for example. The stock manifolds aren't that restrictive for a stock application. Some people have reported a 20HP gain with a tune and headers, but a tune alone can get you 10-15HP.

People do like headers though, and kind of expect them.

grantv

CAI getting 10-15 is a push from what I've seen, more like 5-10?
Free flowing exhaust; buy for sound not power. Maybe 5HP gain on a stock LS1.
And while the stock manifolds are fine, headers and a tune are an easy 25-40 depending on motor. Not arguing, there many internet posts with proven dyno results.

Geboe

If not headers after CAI with a tune, what would you suggest as being next.

Geboe

Based on the differing responses it seems like a personal choice thing. So you feel adding CAI, headers and a tune could add 25 hp or more?

grantv

I wouldn't say it's personal choice, more a matter of research. Google Super Chevy LS1 header install test (can't recall the link) for example. They did an install and dyno test which gained IIRC around 25HP from headers alone, another 15 from a tune to maximize the effectiveness = 35-40HP total. And the torque curve proves more important, power across the board.
The remainder of the factory exhaust is very good, you might gain 5HP from removing/gutting cats, another 5 usually from a cat back if lucky.

Rob 02

The stock air box is restrictive. I think you could get 20 with just CIA and a tune. The mods you are talking about are so common that there is a ton of information on this if you do a search. You will get multiple results on the exact mods you are considering.

Rob 02

I could provide a link to a Super Chevy test but it was on an LS6. There was no substantial gain with headers alone until they tuned it then about 20HP. Again the tune is good for about 15.

http://www.superchevy.com/how-to/050...te-motor-test/

I cant imagine the LS1 needing the headers any worse.

I am not a fan of the pup cats/ pre-cats either. They are probably responsible for 3-5 HP.

Mike 92LX

Headers make a big difference on an LS1 even a stock one.


For your needs a stock ported throttle body is fine. Attack what is in front of it. Callaway and Varam make the best C5 systems in terms of power. Not easy to install though

alxltd1

So what it comes down to is the question of whether or not there is a sequence of mods that give you the most bang for your buck. Maybe. It depends on so many variables that no two cars will react the same to similar mods. There are mods within the threshold of the stock LS1 even with bolt-ons, that will achieve increases in HP/TQ to some level. I would recommend that you look at a bigger picture remembering that you need to have a balanced approach. That is, if you look at the engine as a big air pump, increasing input without increasing output does you minimal or no good, or even worse degrades performance. There are tons of threads on different combinations, as well as experts you can go to who will advise you based on your goals and their experience. Or you can just do a power adder such as NO2 or turbo or supercharger. Most will come in a package with a known HP/TQ increase. Whatever you do is up to you and your budget. Enjoy the journey and research will help you avoid at least major mistakes in the process. To the original question regarding the TB: absent any other mods, other than what you mentioned, porting the existing TB would probably yield you the most improvements.

Rob 02

Also take into account your driving needs.

If you are just having fun on the street then the stock low end torque is nice. Some of the mods only show yields at high RPM's or at WOT.

A lower rear gear may be what you are really looking for.

Mike 92LX

Lower rear gear is a major pain to install on these cars...plus you need to go in the tune to correct the speedometer