Bonneville America Forums Forums Technical Forums Performance Mods BB Dyno results

Here's the results of my first dyno run.

Mods so far:
-Airbox removed/ K&N filters

-Idle mixtures screws 3 1/2 turns out, TBS needles w/1 shim, 155 mains/ 42 pilots

-904cc BB kit

-BUB slip-ons with no baffles(they'll be going back in when I get some more rivets-louder than I thought it would be).

Clearly I have some more tuning to do. The first thing I think I need to do is even out that dip in the A/F ratio from 3k-4k. I think that is a too rich condition(10:1), so I was thinking of removing the one shim I have on my TBS needles. It's a stupid question(but I'll feel even dumber if I don't ask), but is 10:1 rich or lean?

Thanks,
phil

10:1 is richer,,,the base line being 13 parts of air to 1 part of fuel,,,,,so if it is 10:1 there is the same amount of fuel (1 part) but less air (10 parts) making a rich mixture,,,,and vicy versa,,,,say it was 16:1 there is the same amount of fuel (1 part) but there is more air (16 parts) making it a leaner mixture..

Hope this explains it and doesn't confuse you more..

3K is about where the slides start to open. At that point, you are running on both needle jet and the transition jets. The way you read the A/F ratio is pounds of air per one pound of gas, so at 3,000 to 4,000 rpms, you are burning one pound of gas for each 10 pounds of air passing through the engine. This is very rich and the dips in the other curves tell you that it is costing you power. Depending on how your gas is formulated, you need 12.5 to 13.0 pounds of air to 1 pound of gas to make maximum power.

OK, I'm done. Yes, it looks like it would be a good idea to remove the shims.

Definitely remove the shim.

So that dip right there is a graphical representation of "the flat spot" that people experience eh? It's been my experience, and observation, that not many people run shims with the TBS needles.

yes it's much like the one I have that I talked about before except opposit direction and not as pronounced.