Hi all, I have posted this question at another forum. (ls1lt1.com) But not many responders..
However here is whats going on... at around 2500-4000 rpm the car hesitates and stutters...note, this only occurs when under load. Will idle and rev up just fine...It has been running rich.

Fully rebuilt motor ~15k ago. professionally built top end with custom heads by Springfield Custom Auto Machine with Comp CC306 cam and matching valve train, BBK shorty headers, SLP exhaust. 6 speed manual.
the opti, plugs, wires were replaced at engine swap..
It is still an LT1 engine.
I have cleaned the MAF, replaced the cat and performed several other maintenance tasks without any real improvement.

-F-Body Central in Baltimore, MD. Lloyd at Springfield Custom Auto Machine did all of the machine and valvetrain work.

-hesitation started to occur after the engine was rebuilt.

-Starts and idles fine. The idle is lopey due to the big cam.

-Car revs freely and perfectly fine

-Accel 26lb/hr.

-No codes thrown

So with all this being thrown into the engine, Do you all think my last step is to simply get a tune? or is there a sensor or something that is bad causing this hesitation? Also, being I live in BFE There are pretty much ZERO speed shops within a reasonable milage to me, The best tune I could get is a box tune bought offline, what should I do?

 

Does it clear up after 4k, or keep stuttering until you let out?

I would check your fuel pump, if it is stock it could be on its way out. Mine waited until a H/C swap to start dying, wasting a trip to my dyno tuner.

 

I highlighted the parts that concern me.
Are you saying you drove the car 15K miles on the same valvesprings with larger than stock injectors on questionable programming? Please explain "box tune". Have you swapped the gears?

 

Recently purchased car, this is what is done to it. and with valvetrain work I do assume springs were changed to something stiffer. And "box tune" is simply buying a pre tuned pcm online, sorry I bring some terminology from my old forums over.. and I'll take it out tomorrow for a cruise and see if it stutters past 4k..Usually its just the mid rpms. I'm not to savvy on the internals of engines, but different lift profile and bigger injectors on the stock computer...wouldn't that cause the computer to throw too much fuel, which would explain the rich condition, but If that was the case wouldn't it stutter in neutral as well? Also, what are the stock injectors for a 95 lt1? 22lbs? Is there any need for more lbs per hour with stated engine work?? Its an m6, so gears shouldn't matter right?

 

Stock 95 are 24lbs so yours aren't much bigger. Gears definitely do matter with a cam like the cc306. What brand is the new optispark?

 

When did you buy the car? and has it been stuttering since you bought it? For starters id get a dyno tune. Theyll also let you know if youre maxing out the injectors.

 

Hook up a fuel pressure gauge and see what's going on with that.

Also, if the car isn't tuned, it certainly needs that.

 

I think your avatar has expired.

 

Car is getting better..Ran a can of seafoam right into the engine till it died, waited 10-15 min and ran the **** out of it,..Most of the hesitation is gone. Put another can in the gas and a 1/4 or so in the oil, hopefully with luck upon my side it will all smooth out in a hundred miles or so and another tank of gas..Maybe the injectors where a little clogged?

 

If running a can through the TB or vacuum line made it better that is a sign of a BIG problem like massively wrong tuning causing carboning or something.

A mailorder tune is not necessarily a problem IF you give a good tuner good information.
Given the build list and information given though I would question the quality of the information and the tuner that would have been picked.

 

Check the o2's also