Box Stock

Running Lean on Spec Jet

Your right I do not know .
Dosen't change the fact the tech person should not be giving out details on anyones engine , that was legal . I applaud you for what you do . Tech is a totally Thank less job . Pass or fail some one , your either great or a rip off depending on which side of the fence your on .
I don't know if that person was involved I appoligize for my assumtion .
That they were .
 
The reason I gave the jetting was due to the fact that I am flooded with questions about this engine. Many questions pertaining to what are the factory jets. If any track is running an out of the box engine, then by me posting the factory jetting, some of my calls and e mails and texts might slow down. Know, I am a firm believer that a tech should not kiss and tell so to speak. Any engine teched other than the predator Should NEVER have information shared. When asked the answer should always be " all I can share is that the engine was either legal or out of spec". Like I said, this predator is a different situation only because of the out of the box rule. I even have a DVD made showing exactly what to look for on the hemi.
 
.031 is a good jet for a predator but I don't think it is stock.I drill a lot of jets to .031
 
Of the 10 I have disassembled using my calibrated pin gauges the low side is .0155, .0165, and the main is .030, .0315. I haven't seen any smaller or larger.
 
Just to give you an idea of how much change in jet hole size area there is between the numbers you gave.
jet size 4.jpgjet size 4.jpg
 

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Drill bits are not going to give the needed accuracy when tuning .
This drill chart shows very little definition of change .Screenshot_20191003-093152_Google.jpg
Screenshot_20191003-093152_Google.jpg
 
Like I've said before, when I worked for Bob Truax we had 200 jets made for a rocket engine. They were made on a Swiss CNC lathe. Flow testing them found about 15 different flow rates.
I've never understood how people can "drill" jets and hope to get the right size and rate of fuel flow. Using reamers, you get a more consistent hole finish, and I would think, more consistent flow rates. Even then, flow testing the jets, and marking them accordingly, would be the best way to find consistency in performance.
 
Yes even with a pin vice you can not hold it parallel , leave a burr or mark and funnel it on either end .
Same as when you have too small of a drill bit. You wobble the hole out till whatever fits .
 
Under the rules you are running the low speed jet is no-tech. Open the low speed jut to .031 or remove the lower oring. This will help.
 
Got on the dyno today. Stock out of the box hemi predator with wienie pipe no governer.
29.62 baro
66.4 temp
52.6 dew piont
air density 1017
1.034 correction factor (uncorrected power was about .2 down)
7.26@4400
6.94@4750
6.08@5000
4.79@5250
tq 10.13@2750
jet was drilled to .031 (stock jet was about .2 down)
 
When I put my stock out of the box hemi on the dyno a check it to calibrate my Dyno, I get real close to the factory rating of 7 h.p.@ 3600 rpm. Mine actually was 6.95. when I turn the rpm to 5500 my peak h.p. is always around 4800/4900 @ 7.9/8.4. put the factory exhaust back on as an experiment and see if your h.p. gets better. just sayin
 
What does the plug look like? Sounds like the timing is late, flame in exhaust as well as the backfire is an indication,


I always considered those things a sign of the engine being rich when I was racing. Of course we were racing 2 cycles with oil mixed in the gas.
 
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