WOW our car's tuning is very similar !

On my 98- for cold or warm starts--I have a 16.12 commanded into "open loop"--- it really helps it start and run nicely--no surging or idle hunting-------In closed loop I never could get precisely back to 14.68--as the Stock 02 bungs on the 98 are like only 12" from the exh port !! and my LT bungs are 36" back from the stock bungs !!! Having the stock bungs so close makes the stock swithing point table "goofy" I had to lower mine to 340--- Also I have tried messing with the Commanded Stoich.--Changing this table doesn't help much as ALL 02's are callibrated to "center" around .450 millivolts which is precisely 14.68--- I got a small improvement by changing to .340--tried even lower but with no change---Installing a permanent Wideband 02's in the stock locations would be the absolute fix and running your C/L off them
Also---having your VE table callibrated well really helps when trying to get back to 14.68---It just takes more time and data logging--The more tuning you do in your VE table--the better the results--- I settled for around 14.4 and called it good---doesn't suffer much in mileage--and I'm not concerned all that much with mileage anyway---

 

now i ain't all that familiar with these cars yet, but with the trucks, the factory manifolds flow almost as good as a shorty header, so the only reason people use shorties on the trucks is to pass CA smog tests. is this not the same on these cars? i know when i put LTs on my 5.3, my hwy mileage @ 65 went from 18.5 to 21.5 untuned. around town went from 16 to 17. i just got my new PCM in last night, so i ain't had a chance to check mileage after tuning yet.

i've a set of 1 7/8" ARHs with a 3" catted x-pipe for the car sitting in the living room waiting to go on, so i can't really offer first-hand experience on corvettes yet.

 

Just did a cam install and my tuner did a nice job of getting the 14.3-4 and 12-6.8 at WOT. I still manage around 25-27 highway....but my city is now around 15mpg

 

TNSTAAFL

 

On a 2000 coupe I have Patriot heads - basically the 243's cnc'd by them-300 cfm w/double gold springs -if not cnc'd why put them in?
LS6 intake is necessary for our older cars - that is one end of the "straw!!"
The other end is the exhaust - the shorties will save mpg but you are taking your fingers and squeezing the straw at this end!!! Seems to be a big waste of time to do all the other stuff and then "squeeze the straw" at the other end!!! I have Kooks 1 3/4" headers through xpipe into corsas-Yank SS3600 converter - 3.43 gears -
I get 28 mph on the highway with 90K miles on a daily driver -
Oh yes, don't forget your catch can!!!!
Yes tune is the key - luckily I had probably the best tuner in the country do mine!!!
Performance?? Not bad - 11.83 secs/117mph in the 1/4 mile with 1.67
60 foot time on M/H 17" drag radials

 

and I've picked up several good tips from your well written and thought out posts.

I hope the OP is still going to go ahead with his mods even after hurting his Dad's transmission recently

 

My theory is that it was going to happen on the street eventually anyway. I only made two passes and both were clean...12.5 at 116 then 12.4 at 116. Not like I missed a shift or anything lol.

The heads are going on first...AI ported and milled 799s with an ls6 intake. They are already there, I Just need to send them the money.

 

as far as mpg with headers, Installed the xspower headers with 3" hiflo cats and a street tune and the mpg are still the same as before(21-22 city 26-27hwy). Im using the original 200K mile front O2 sensors. The rear O2's are tuned out and sitting in a toolbox. With the street tune and headers I made 355whp/359rwtq sae. The mpg's are all in the tune. I have a 00 FRC and plan on doing stock LS2 243's and a small cam with 28lb injectors. Don't expect much of a loss in cruising fuel economy.

 

I was planning on throwing some XS Power LT and X Pipe on but I got the non catted ones. Will that hurt my MPG and decrease my performance without a tune? Or will I just be throwing codes?

 

ANYTIME YOU CHANGE THE AIRFLOW THRU THE ENGINE,,,, you should tune. You will see an increase in power but,, you will leave some power on the table without a tune. It will not hurt the engine but you will NOT get the most out of the Mod without a tune and you will loose some fuel economy.

With a tune you will gain in both areas.

 

I'm alittle over 420rwhp and depending on how I drive it in the city I can go 6-15mpg and on the not so flat I15 I get around 27-28mpg at 75-80mph.

 

FWIW when cam-only @ 373rwhp (MTI Stealth II, headers and cats) with stock gears and stock sized tires I could still knock down over 30mpg and went 11.9@119

 

I have the same setup as IW but with 3.73 gears and I also get 28mpg on the highway.Car is a 02 with 80k on it.We have the same tuner and he realy is the best as IW said.I am also running 11.2 C.R. and I am sure that helps a little also.

 

here's my post-header update...
31.5mpg with the cruise set on 73. if you're going off the dash calculator instead of miles/gallons, it was somewhere around 33

that's a stock 2000 - just rolled over 45k today with an LG CAI & the catted ARH's... untuned

 

After my header install I've been wondering if the cats help hold the heat in the headers and keep the O2 sensors working better. I can see a big difference in the heat the pipes see before and after the cats, and the O2 sensors need the heat to work right (they really are lazy until they are hot enough). I haven't seen any loss in fuel milage with my XSPower headers, LS6 intake and Vararam. I can pull >30mpg at 60mph.

When you cam watch the overlap. I'd expect a large overlap will likely hurt your power. Don't go too big for the rest of your combo either. I see some examples of huge cams with stock LS1 heads and it may sound cool but really - gaining 5 or 10 more HP for such a loss in the driveability?

I have noticed that the mileage really does depend on the weather. I can drive the same stretch 2 days in a row at the same speed and the DIC will show 4mpg difference.

Peter