Ok, the car did get slower, but I intentionally used a catchy title to get people to come inside. Here's the deal: 11-03 car ran a 11.8 @ 118 mph. I just ran it last week after the long tube install and it went 11.95 @ 114. I verified the a/f ratio with my wideband. There was a major issue in that the motor would not rev much past 5800 rpms. Usually I would shift it at 6200. It was almost like it was shutting down past 5800. I pulled a few valve springs and pressure checked them to within 2 percent of brand new ones on my Rimac. Questions:

Could the new headers contribute to valve float?
Could I have lost alot of top end coming from edelcrap shortie headers?
What could be the issue?

 

What headers do you have now (dimentions) and what did you used to have (dimentions)?

What changes to the rest of the exhaust did you make when changing your headers?

 

I have 1.75 hooker long tubes. I went from 1 5/8 edelcrap shorties. I had a single 3 inch with a dump, now I have a single 3 inch with a dump but the dump is a few feet further back.

 

I doubt its your long tubes, but maybe the new y pipe. Did you change to a different muffler?

 

Double check your ignition timing. You may not have enough timing. I found that with my MiniRam, the motor runs best with very aggressive ignition timing (38 degs.). The LT1 manifold should be pretty much the same. You stated that you monitored A/F ratios, what were they? Also, it is not uncommon for valve springs to become weak. For your Hyd. Roller, I like the Comp 987-16 springs shimmed to 1.825".

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Nothing else changed but the exhaust?

The long tubes shouldn't slow you down, although they in my trials, they aren't worth much HP over decent shorty headers with a GOOD exhaust system.

With the bigger headers, are you sure you're not running a tad lean now?

Have you tried giving it a bit more timing?


Headers shouldn't contribute to valve float...they either are or they aren't...floating that is.

 

One possibility is that the larger diameter tubes have reduced the low end torque, which could result in higher ET's.

While choosing the right size for the engine is tough, I would assume that 1 3/4" for a 406 is not "too large".

I would look at timing also, the engine may be able to run more with lower back pressure.

 

few things:

A/F ratio is 12.5-12.8 across the board.

I run 987 springs set up at 1.8 inches with ti retainers. I checked the springs on a rimac to 321 pounds @ 1.200 inches. This is nearly identical to new ones.

I ran a dump with both sets of headers so muffler isn't an issue.

I run 38 degrees of total timing.

The only other thing I changed was ignition modules. I went to a DAP one. Any experience?

Could the fact that the motor is revving higher contribute to valve float? The motor just hits a wall at 5800 and didnt do it before with the smaller crappy headers! Thanks

 

If you still have your old ign module pop it back in and see if it makes a diff, ign module can diff cause high rpm problems if faulty.

 

GoFaster - It sounds like you have covered all the bases. When the motor falls on its face after 5800, does it pop and sound like a miss? If not, it's probably not the springs.

Try leaning your fuel out a little. My 406 seems to run best 12.8-13.0.

 

Check your plug wires.

 

itd suk if all u did was fry a plug wire, but thought the longtubes would always give u a lot more up top especially upgradin from the edelcrap