holley 800 Jets
 

Hello All,

I have a 98 gen 6 502 with dart iron eagle heads and a crane731 cam, the timing is set at 14 degrees , been playing with the jets most people here are running mid 80"s primary and low 90"s on the secondarys . I tried many jets in this area but the engine is running way to rich according to the plugs, I ended up with 74's in the front and 87's in the back with a 5.5 front power valve no rear power valve . The carb is a holley marine 800 why would I run much smaller jets than most others. The factory holley jets are 72's and 87's. The motor runs awesome this this set-up. Thanks

If that was a factory HP500 the jets should have been the following:

Primary/ Port 81
Primary Stbd 75
Power Valve Front bowl / 6.5
Secondary/ Port 93
Secondary/ Stbd 89
Power Valve Bock off

This was from the factory and a baseline to start.

I run AFR heads with the Dart 6200 intake and a Crane 168741 cam and use the following setup:

Primary/ Port 78
Primary Stbd 72
Power Valve Front bowl / 6.5
Secondary/ Port 88
Secondary/ Stbd 84
Power Valve Bock off

Runs a little fat, but not too bad the plugs have good color.

AFR's from the dyno were between 13.12 (4500 rpm) and 12.62 (5800 rpm).

Hope this helps!

Dave

I will try to take a shot at this, this is what I was just told 2 weeks ago, anyone correct me if I'm wrong. I just built 2 469's that made 590HP. I used my Barry Grant 750's that were on my Merc 425's I ran 77's in the front 6.5PV, and 87's in the rear PV blocked and plugs looked great. I put the new engine on the dyno and the O2 and the BSFC were saying I was running really fat with the old jetting. I jetted down to 76's in the front 6.5PV and 82's in the back. I asked why it was running rich and they said with the better flowing heads and more cam that it was pulling more fuel than the carb would allow air to flow. In another words my carb is to small. That was limiting me to go over 600hp.

I'll take a guess at it...Merc likes to run their motors fat from the factory. Second, the better flowing heads are more efficent. My guess!

Notice the difference between my jetting and the factory, plus I'm making 650hp!

Dave