Finally got my car back to my tuner.i want to give a thumbs up to Kentucky Speed and Phil Smith (aka BlueCat) for a great job.
the blue line is from last year I was running a stock MSD intake and 1 7/8 headers on 93 octane /and dynomax muffler with 3” turn downs before the rear axles.
today we tried to tune it on E85 the car just did not like it.so this tune is on 93 octane.
with the changes I made I’m satisfied 2” headers and ported msd intake.I’m thinking that if I hadn’t installed 102 nitrous plate and 2 1/2 “ over the axle corsa sport exhaust system on the car .and kept 3” turn downs I would not have lost all that torque.

 

2 inch headers are best for like 418 or bigger. I would think them and the 2 1/2 reducers are definitely the causes of lost torque. Sorry but hope you get things squared away and do better.

 

What was the issue with E85 that your engine didn't like? Definitely odd. Might not pick up much depending on if you were timing limited on 93 but I felt my car drove a ton better on E85 over 93.

 

2" headers are massive. The power difference between 1 3/4 and 1 7/8 on my 402 which made 660+hp was like 10hp at peak after some tuning. I can't imagine needing to step up to 2" headers. Surprisingly the 1 7/8 also had a better TQ curve and better low end.

 

Great numbers and I think with the bigger muffler in the back, there was some more power there especially higher up. It looks like from graph and drawing line out you would still be at 635-640 hp and 480 tq at 7,000 rpm. So very little drop off in power from peak.

 

sorry I’m not a tuner all I can say is the car is running 19 degree of timing( I think) with 93 octane. I think that Phil normally add 4 degree of timing when going to E85.anyway the motor did not like it.my compression is 11.84.1 so there’s no good reason why it shouldn’t have made at least 10 hp with E85.that said sometimes things just don’t work .Phil did pay me a compliment about my engine he said that my engine rev as fast as a dirt late model engine (that coming from a man who tune lot’s of Ls engine’s)
as much work as I have put into this car it makes you feel good , to hear your tuner giving you a thumb up.i hope to get it to the track next month

 

thank you for the kind words Lewis I can’t wait to see how your engine preforms.
I’m thinking that they will mirror each other.your right about the exhaust I know it’s holding me back about 20hp ,but it’s sure nice riding around without losing your hearing.
i know with 3” turndowns/electric water pump/and that 102 nitrous restricter plate out of the intake the car would put down 670hp to the rear wheels.
but with all the trouble I have had with lifters in the past year,I’m just going to drive it and enjoy. I know that the horsepower is there if I want it,and then there’s my nitrous bottle.

 

Looks great on that wheel setup

 

Jayyw thank you for the compliment,I hope you’re up an running soon.i have to say Phil done a great job of tuning the car. I got the car out yesterday and drove it about a hour and half.for a big cam car it drive pretty good (and no I wouldn’t want to be in a big city every day and drive the car)without the 3.90s in rear the car would definitely be harder to drive.and with a big cam I’ve come to the conclusion that you would be better off running .80 .60 gearing in transmission (aka ZR1)fifth and sixth . If your running a big cam and it being a weekend cruiser.I’m thinking if the car doesn’t get into the high 9s this time it want be the car fault.

 

I agree, the headers are too big for your application.

 

you are probably right for the NA application.but when I turn the bottle on then it becomes a different story.thank you for your input.

 

Without knowing for sure what engine you are running (yes, I can see the GS labels blacked out but the engine could be anything), I will say this: at your power level, 2" are NOT too big. Most of those same people also think you need back pressure...no. Now, if you bump to bigger exhaust WITHOUT tuning, you will typically see it fall a bit flat but once you tune it, you virtually always pick up everywhere. If not, you got a bad tuner or have other issues that cropped up. People told me years ago that 1 7/8 were too bit for a stock LS1 but they were wrong - engine picked up hp and tq all across the band WHILE adding heavier rear wheels and tires. Plus, I was set for upgrades so when I threw in a cammed LS3, it was already good to go. This same principle will apply even more to rec/sq port heads. Tuned properly, it's hard to go too big because these engines love to breathe. You clearly did it just right.

 

jimilz28 it’s a 450 cid RHS block /TFS 260 ls7 heads ported by Greg Good (2.250 intake/1.615 exhaust (286cc intake runner)
MSD intake ported by Greg Good
Cam Motion LLSR 255/269 114+4.5 intake 702/exhaust 683 /with stainless steel crower shaft system
Pac 1237x Valve spring setup for 750 lift /175 @seat 565 open/ setup .105 from coil bind
I’m with you about the 2” headers .if I would have left the 102 nitrous plate off and left my 3” turn downs on this car would have put down around 670 rwhp NA. and that’s thru 3.90s .that said if you look at the graph all it done was move the power band up 500 rpm. (the ported intake and 2” headers)
I have to say BlueCat done a great job on drivability for such a big cam.

 

Looks like a weapon!

I've played around with my C5 & C6, my C5 started with a goal of 500rw LS1. Almost made it, 496rw, 1 3/4 LG pros catted. The 3" over axle power gain was substantial, the initial package was 2.5". I don't remember the exact gain, it was very worth while.

Engine Masters has a video where the laid out an exhaust replicating a full chassis exhaust. They used 2.5" & 3.0" mufflers & exhaust comparing that to open headers. This was done on an engine dyno, the 2.5" killed torque in the area of 35ftlbs. The 3.0" mufflers & exhaust was much closer to the open headers.

Eventually the LS1 puked & a LS3 stroker was cobbled together with 1 7/8's ARH retaining the 3.0" over axle which were LG's btw. That was spec'd by a well know LS guru & can only be described as a total failure & nightmare. After three camshafts swaps & completely different cylinder heads it was running nearly 610rwhp with 4:10's

I kinda sorta wrecked that car....whoops. That same motor is now in my C6, the headers were destroyed. I had LG pro's for the C6 with 3.0" GHL over axle. The best rwhp with this exhaust combination barely broke 550rwhp. I did have the motor freshened between swaps because it had a bit of an oil usage problem & the impact was hard enough I wanted it checked. After it was freshened I checked the cam timing prior to install.

Very sure the headers were choking it I had a couple of good conversations with Nick @ ARH. I had debunked the low rpm torque loss with large tube headers long ago & struggled with 1 7/8 vs 2.0. I'm buying headers, so which ones? The idea of picking a few extra pushed me towards the 2.0 headers.

Now I'm seeing 577rwhp with torque improvement thru out the torque curve.....no loss done low, better. It's carrying the power better up top however it is still low. Another difference between the C5 & C6 is the E38 computer, it is much more sensitive to KR. Comparing the timing curves the C6 is 2-3* less from peak torque to peak HP. This motor had an oil leak after being freshened so it ended back in the shop & I ran out of time this season to get back on the dyno.

Long story, sorry. Just wanted to debunk the header tube size with my first hand experience in the Vette chassis.

 

ctd that’s useful information for anyone just starting to build a car.
and as far as a C6 goes the 2” ARH headers seems to do the best job
to me it’s a no brainer if your looking for performance NA buy the 2”

 

Went back and redyno my car yesterday with just the 3”x pipe and 3” turndowns.taking off 2 1/2 over the axle pipes and corsa sports . getting ready to take the car to the track I pull the muffler and passenger seat. I went ahead and had the tune checked ,he had to add a little fuel in the mid range . I got my mid range torque back.still on 93 octane

 

Very nice build, keep us posted on track results

 

Good results and gives us an idea what the over the axle part can do for power at different rpms.

 

good results for the power bad results for the ears .double 06 I hope your project is going well best of luck

 

huge gains. do you run a dedicated fuel system for the nitrous? If not, i would try to get the E85 tune dialed in. Would pick up even more power on nitrous.