VP - C25 vs C12 or C14

[Bob Nottingham]

In going from C12 or C14 to C25, how much larger jet is usally required in a holley 750 or similar sized carb. It seems about 2 sizes may be in the range, any throughs or comments appreciated. Thanks Bob

[Dyno]

I found 2 jet sizes worked on the dyno going from 14 to 25.

[Mike Croley]

Originally Posted by Bob Nottingham

In going from C12 or C14 to C25, how much larger jet is usally required in a holley 750 or similar sized carb. It seems about 2 sizes may be in the range, any throughs or comments appreciated. Thanks Bob

When changing fuels, the general rule of thumb is to change one jet size for every .10 change in specific gravity ( Fuel Density).
For instance,
switching from a fuel SG of .720 to a fuel of .725 SG wouldn't require a change in jetting.
switching from a fuel SG of .720 to a fuel of .730 would require a change of 1 size in jetting.
And switching to oxygenated fuels will usually require up to four jet sizes higher to start.
Start out easy and let the plugs ( read all of them, not just a couple ) be your guide for further changes.

[art leong]

I tested C25 against C12.
Found it gave me 1 mph but lost .05 overall. Lost .10 in the sixty, .15 in the eight, but picked up .10 in the second half of the track.
This was just make 3 runs, change fuel, make 3 runs, back to original fuel make 3 runs.
I believe the C25 would be beneficial if I can do some tuning. But 9 runs in a day was enough. Later I might put the C25 back in and do some tuning. If I can get it to leave like the C12 it will be overall quicker. But so damn expensive.

[CWhitney]

Bob give me a call or shoot me an e-mail and I will talk to you about C25. Are you trying to switch to C25 for your Fairlane?

[randy wilson]

Did anyone's timing change with C-25?

[M&M Motorsports]

Run one - two degrees less timing.

[randy wilson]

Thanks. I've seen as much as 4, and as little as 1 degree difference. Just wondering if I was seeing right.