When I had my truck dynoed the operator claimed my afr was at 12.5:1 and after the dyno I ripped down the street and my afr was at like 10.9:1? could the dyno be loading the truck so much differently that it ran leaner than on the street?

Another question, so I've been dialing in my carb more and more lately since it was runnin rich 10.9~:1at wot and cruising (confirmed by the wide and and the black plugs). I jetted down 4 in the primary and 2 in the secondary. Now my wot is at 12:1-11.8:1 ish. If I got I from the 10.9:1 to say a 12.4-12.7:1 at wot how much power would I pick up on the dyno? They say leaner is meaner but is it a 2 hp difference or 30?

 

Hmm. Where is your sensor located in the exhaust? Is it calibrated? Is the sensor in good shape?

Where did the dyno operator have his sensor? In the tail pipe?

 

My sensor is in the collector and as far as being calibrated I'm pretty sure it's good. The dyno operator was just using my gauge and he said it was 12.5 and when I drove it after the dyno it was only like 10.9 it runs better leaned out like it is but I think I can easially go leaner without issues.

 

That is pretty odd.

 

I don't think he was reading it right or he just said it was 12.5 and didn't know. They were surprised by the numbers that's for sure but now I'm way leaner and am wondering f it would be worth it to dyno again?

 

Running without an air cleaner can make a difference. Also getting the engine really hot.

 

That is true pop...when i was on the dyno, no air cleaner, my numbers were slightly lower.then we put air cleaner back on and did another pull and for sum reason my numbers went up a little....did it vice versa like three times. And numbers changed every time.

 

A good breather base can help smooth the air flow into a carb. I dynode my old 68 Camaro a few years ago and the guy asked if we could do 1 more pull , but without my breather, to see how good my K&N breather top really worked. The pull without the breather lost 3 HP and 5 FTLBS. The guy at the shop has been building brutal engines for years and was amazed that the engine picked up with a quality breather. Every time I see some guy pull his breather off at the track, I get a chuckle out of it. Hey while your at it, throw a few gallons of 108 in the tank of your 9.5 to 1 engine with the 250 at .050 camshaft, LOL.

 

^^^

 

Lol yeah I dynoed the truck with everything on it. It's how I drive it so its how I wanted it dynoed. The engine was gettin hot for the last run but the first pull made the most power. The power dropped with every run as the engine got hotter but they did 3 pulls like hot lapping and printed the best one off. Now I ask again tho, how much power does one gain by leaning out from mid to high 10's to mid to high 12's? Say a average gained by people who tune their fuel on the dyno?

 

I don't do the dyno thing, I am a track guy. At the track, that could be a tenth. Maybe a 1.5 tenths on a street type car. So, I am guessing 10 to 20 hp.

 

I dont know if this is gonna help any but if one jet change only makes 4-1/2% difference in flow its gonna take a few jet changes and spark plug readings to get back to 12.5 from 10.XX i would think.

 

I was at like 92/94 jets specd from pro systems and now I'm at 86/89 and I think I'm gunna drop to 84/88. This is all from memory ill have to check my kit to see what's taken out. That jet kit was a awesome investment, the pro systems carb not so much. Lol

 

I have heard this from many street guys.

 

Not just that they were off on the jets. They misassembled the needle and seat for the float (left plastic from package on needle) almost killed my engine. Was dumping I. Fuel a fast as the pump could supply it. Had to pull plugs a couple times to blow the ga out. Also it sticks so I had to put on 3 extra return springs. The spring on the shaft as wore a groove in the carb body so it hangs up. Kinda odd for a engine with 200 miles on it id say!