Terry Keeley
Well-Known Member
- Joined
- Jul 24, 2002
- Messages
- 7,201
Absolutely! Andy put me on to cutting the water back long ago and I've added to it over the years with the hot plug and high C/R stuff. A good piston/sleeve fit is also critical for top performance and therefore proper break-in is also important.
1. Around 70%, follow this and you'll be in the ballpark: https://www.intlwaters.com/threads/on-line-head-volume-calculator.74796/
2. Flat with sharp corners.
5. I've only used 7075 aluminum.
6. If you run hot the piston grows, less than about 0.010" and I start to see the squish band imprint on the piston.
7. Standard.
8. Yup!
9. Double yup!
If you try to burn 60%+ nitro what's happening when you don't do the above is most of the charge is still burning well past TDC. We have to advance the timing way before TDC but can't time the spark so have to do it with heat, plug temp, C/R etc.
Look how far in advance a Top Fuel motor lights the charge:
Nitro Racing Ignition Timing
Ignition timing is a tuning tool for professional Top Fuel drag race engine builders. The spark advance in a 10,000+ hp nitro-burning engine is typically as follows:
Idle/staging is typically 55 degrees to ignite the cylinders with a rich idle mixture.
Launch typically 50-53 degrees adjusted for an optimum power at launch.
Sudden drop of the timing to typically 36 degrees, approx. 1 second into the run, to instantaneously reduce power for reduced traction from tire growth.
Bring the timing back to typically 50-57 degrees for the remainder of the run to restore power.
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