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As promised I would do a write up on my header install. As a follow up to my original "My Crossfire Odyssey" thread (https://www.corvetteforum.com/forums...m-odyssey.html) I've have installed a pair of Doug's D350 headers. The purpose of this thread is to get some information out there on headers and a bit data rather than the it feels better.
To start off I settled on the Doug's D350 headers. From looking at pictures of C3's undersides with headers the Doug's looked to have the best ground clearance (actually better). They also had a thick flange, 16 gauge tubing, and positive fitment reviews. At first I was a bit unhappy with the welding of the flange and was ready to send them back. Jebby in a post looked at the pictures and said I'll be okay with them. To be fair the factory manifolds/headers were just as bad. So off came the stock manifolds and y-pipe. To install the headers it necessary to disconnect the motor mounts and remove the spark plugs, starter, dip stick tube and AC compressor brackets. The headers came with some decent looking composite gaskets so I use them. Originally I thought spark plug wires would need to go over the headers I was able to keep the stock routing. I bought some 3/8id x 2 inch spacers and cut them down to refit the AC compressor brackets. The factory y-pipe is a interesting piece. It consists of a 2" pipe going into 2.75" pipe with with individual section of 2.5" pipe inside of it. I cut the y-pipe about 12 and 16 inches back from the reducers and welded in some 2.5 pipe. Melting two pieces of metal together is good therapy also. A bung was also welded in behind the left side reducer to read the A/F ratio. I also wrapped the piping and replaced the stock starter with a Powermaster #9100 starter. I also bought this thing called Dragy to be able to do some tuning. Now here's a live and learn lesson. I broke the rule of making more than one change of a time. I'm not going to bother with posting all of the Dragy density altitude corrected ET's times. While I was installing the the headers I also change my timing table to get 34 degrees in by 3200 RPM's. So after adjusting the A/F ratio and Dragy testing I saw no improvement. Thought to myself "man that was a waste of time and money". Guess what I need is a true dual exhaust system. A few weeks when by. While laying on the couch watching some Family Guy, I thought "why don't I try putting back my before headers timing table". Well that Dragy test put a big smile on my face! For what ever reason my car doesn't like the traditional all in by 3200 RPM's or or anything near that aggressive timing. Before I get to my actual ET here is a few other numbers. The before and after decibel readings @70mph, windows up was 81db. No change there. Although the headers are ceramic coated I did get a slight increase in under the hood temperature of from 128 to 136 degrees. I measured this by pointing a infrared thermometer at the master cylinder. Exhaust back pressure behind the left side reducer is a max of 3 psi. Yesterday I went to Gainesville raceway and ran a best of 14.906@90.67mph. The temperature for that run was 81 degrees with a density altitude of 1784. My previous best was 15.223. Unfortunately I don't have a temperature or da for run however Dragy da corrected ET's shows about the same improvement. I know the 3psi of back pressure is leaving a bit on the table. So the final chapter will be something with the exhaust system. Marc
Last edited by Fly skids up!; 12-12-2021 at 06:38 AM.
Nice writeup and interesting results and data. You can probably pick up another tenth or two by going to full duals and low restriction mufflers, like Magnaflow.
I know that you are familiar with the impact of DA changes on ET and MPH. You can easily compare your actual times for any run to another rum, at a different DA, by going to dragtimes.com. / tools / DA (Select Track on left)
Look up DA calculator for the track and date/time of run and hit the correction button. It changes your data to a DA of zero so it cancels the DA difference effect on your times.
Nice writeup and interesting results and data. You can probably pick up another tenth or two by going to full duals and low restriction mufflers, like Magnaflow.
I know that you are familiar with the impact of DA changes on ET and MPH. You can easily compare your actual times for any run to another rum, at a different DA, by going to dragtimes.com. / tools / DA (Select Track on left)
Look up DA calculator for the track and date/time of run and hit the correction button. It changes your data to a DA of zero so it cancels the DA difference effect on your times.
12-12-2021, 06:07 AM
My Crossfire Odyssey, part 2, the header install
