Hero to zero in 2 runs. LOL Pictures inside

You take the actual percentage of OD change and add the same amount of fuel.

25 over to 30 over is not 5%. It's actually more like 8.3% more.

25/30=.83

This is what i was shown by Les Davenport and it hasn't failed me yet.

 

% of change

I agree with JRB about adding same fuel as % of change, but I don't agree with the math.
1.3-1.25 =.05 .05/1.25=.04 that is a 4% change. Always done it this way also no problems. Also .83 =83%

zero260in1, in your example of 9.1 gpm
9.1 X 1.04 = 9.464 you added .3 gallon which is very close to what I would do, but a different way to get there. Don't know if your example works in all situations.
Also remember changing overdrive changes cylinder balance and if 6 was on the edge before it could have gone lean. If you want to be safe you could be like JRB and put twice the change in %. That's one way to cover your #@$

 

I'm on my phone, a bit tougher to proof what my fat fingers are typing. Lol

Your way makes some sense, but to each his own. Do what works for you..

 

I have been watching this one for a few days so you could get expert feedback before I threw my theory out there and muddied things up

When I look at your first post,

1. Safe looking plugs, car repeated performance from 08 even with less compression and same GPM
2. Found one cold cylinder, ( cylinder 6 ) and took 2 sizes out of that hole
3. Spun blower from 25over to 30over, added .30 of a gallon to tune up
4. Two runs with 30 over, and this was the result to cylinder number 6


It made me think that 2 and 6 are the holes that get the least fuel on your engine, since you left the fuel alone, when you went down on compression spacing out the fuel droplets ?, it pushed #6 over the edge into a lean misfire at idle so the plug showed less heat causing you to take two out of that hole.

When you upped the overdrive without adding enough fuel these two jugs took the brunt of the beating particularly 6 since it was 2 sizes down and was the leanest already.



Like I say that's just my theory, any feedback will be appreciated.

 

25 times what equals 30.

25 times 1.2 equals 30

thats a 20% increase in OD

close to Mr. Davenports rule

 

Did you run water the time before?

 

Ok, everyones opinion is on here already so let me put mine in.

It doesnt matter what the % change in overdrive 25%-30% = whatever %. Its simply a matter of how much more air you can pump. A 5% increase in OD is worth alot more on a good 14-71 that it would be on a weak 8-71. In my opinion the only way to figure how much extra fuel to throw at it, is to know your air output.

Then there is the intake temp rise going from a 25% to a 30% OD.

 

25% OD to 30% OD is not a 5% change. You have to use full numbers when dealing w/ %'s.

IE-25% OD is actually 125%, 30% is 130%, etc

Underdrive would be 85% for 15% under, 95% for 5% under, etc.

so 125% times X = 130% where X is % increase

130/125= X

X=1.04 which is 4 %

So 25% to 30% is a 4% increase in OD.

Confused? me too

 

Flyboy is correct. The numbers are 1.30/1.25 = 1.04 or you can do the math like this (1.3-1.25)/1.25 which yields .04 or 4%. But again - the change in air needs the right amount of fuel. If you figure .3gpm per # of boost increase that should keep you safe.

If we have the time we will make a 1/8 mi. and 1000' pass to verify we are safe before we run it out the back on a blower change. Read the plugs and verify the distribution hasn't changed and overall tuneup is fat before the 1/4 mi. shot.

Troy.