Yeah I did change the whole exhaust system, but I can assure you that most of the gain was from the headers. My previous exhaust had a cutout and was 3" diameter except for the y-pipe.
I will give you another example: I've got two local buddies with internally stock LT1 F-bodies. Both installed the Hooker 1-3/4" long tube headers and nothing else, and both picked up 2-3 tenths and 2 mph. Both cars dynoed around 285-295 rwhp(one 6speed the other auto). Explain why an internally stock ci LT1 likes the long tube 1-3/4" headers? Also, we install long tubes after long tubes on LS1 F-bodies(stock or modified) and they all usually pick up around 18-20rwhp(more if its modified). Again, it really depends on the setup, but most all 350+ci will benefit from the larger tube, unless the intake is restrictive or the cam is tiny. This has been an ongoing debate, and this is all my opinion.

 

As I said above I had the same results moving from 1 5/8ths shorties to 13/4ths long. I looked over your Website David ,and I really like your car, Our motors are very simular. I just installed AFR heads on my car (190cc) did you get the street cnc job or the competition? also what springs did yours come with (not to get off the header subject) I was just wondering if the springs are good for that cam?
Perry

 

Yeah David...I see your point...although the stock LT1 cars do have restrictive manifolds, so switching to any headers would improve things.

I think that in this case, there has to be something with this engine combo and it preferring 1 5/8" headers to make 490 HP...

Who knows...

 

Thanks! I have the basic 190 package(street porting, standard springs and retainers). I just swapped the springs for some Comp 987 and Ti retainers. I was getting valve float at 5800rpm with the standard AFR spring and this camshaft. Should be all fixed now, really haven't had a chance to test it though. The last time I raced before the spring swap was 12.07 and short shifting at 5700 and letting off right before the traps. I'm figuring 11.8's at 115 in some good weather.

 

Thanks David, I'll look for some springs to replace these then. with my LT1 homeported heads with bigger valves (work done by me) I ran a best of 12.29 @112.7, I am hopping these heads gave me at least 2 tenths as the chip wasnt even programmed for the cam and heads I had...lol
Later.
Perry