GC99TA

iTrader: (30)

Did some testing with a 63n/53f set up on my carb'd LY6 this weekend. Set up is an NOS Big Shot plate with the above jetting at 950psi bottle pressure and 5.5psi flowing fuel pressure. Timing was 24 degrees. Plugs are NGK BR7EFs. The plugs were from cylinders 4 and 7 which have proven to be my richest and leanest cylinders respectively. The plugs were swapped in the staging lanes and the car was pushed to the burnout box. Did my burn out, made a pass, killed the motor on the big end and pulled the plugs in the return road.

In the first pic, number 7 (leanest cylinder) is on top. They are marked on the boxes in the second pic.





My take on this is the tune is pretty clean, if not just a touch lean. Plug 4 shows a little more fuel shadow than 7, but it is my richest cylinder. #4 also shows no visble timing mark on the strap but 7 does. Again, #7 is usually my leanest/hottest. What do you guys think? Am I on the right track?

Traction was limited because it was COLD and my slicks are on their last leg, so I only got to make two nitrous passes, so no fuel or timing changes were made between passes. Where would you go with this? I think it could take another degree of timing based on the #4 plug but does it need a little fuel to go with it based on how light #7 is?

03EBZ06

What is your gap?

GC99TA

iTrader: (30)

its .030

speedtigger

iTrader: (16)

No real clear defined timing mark.

03EBZ06

I would like to see a little more carbon on the base ring, ie a little more fuel, maybe 0.5psi. The discrepancy between 4 and 7 might later be solved by putting a colder plug in 7.

I would also check cylinder 4 and make sure compression is good just as a sanity check.(though I suspect it is based on photo)

ATVracr

iTrader: (5)

Good advice!

The colder plug will also let you put a little timing in it = faster.
Because you are on a plate and do not have the individual timing control that we have a colder plug is about your only option to help even the cyl's out.

If it was fuel injected you could flow the injectors and put the highest flow in the hot holes. (not sure if there is something you can do like that with a carb)

GC99TA

iTrader: (30)

Thanks for the input and advice guys. I think this tune up will be fatter next time out as-is because this time around it was COLD outside!!! 36-39* to be more specific. And I can't see myself trying to run the car in weather that cold again. But I'll also try adding some fuel pressure as well to see what it likes.

I was also thinking, in addition to/or instead of a colder plug in #7, I may try to stagger my carb jetting by putting a one size larger jet in the barrel closest to #7. It's not as precise as using a higher flowing injector would be since it's not specific only one cylinder like an injector, but it should get a little more fuel to that cylinder and probably number 5 as well.