Hold off on the IAB and try the IFR changes. Factory orafice was .031. I found .025 works to clean up my idle and provide good cruise in the 14's AFR. The IAB is more of a fine tuning tool you may not need.
Cross Ram Jetting and Tuning
- Thread starter 540 XRAM
- Start date
JDJG
Well-Known Member
Any guidance on those IABs? Im assuming you had to increase the size? Any estimate on how much % wise?
JDJG
Well-Known Member
Ok! My factory IFR was 0.41- I moved down to .031 and have some 0.25 in the mail
I will report progress! Thanks very much for the details
Here are the factory specs on the Crossram Holley Carbs - Right Carb - primary jets - 75 (tag side) vacuum pod side and 80 (linkage side) accel pump side, factory IFR's .030 (measured)
Left Carb - primary jets 76 both sides, factory IFR's .031(measured)
Original IFR's are located in lower portion of metering block
The driver side factory IAB were #47 bit (.0785) reduced to #48 bit (.0760). The passenger side factory IAB were larger at #44 bit (.0860). I ended up squaring both carbs with #42 drill bit IAB.
Left Carb - primary jets 76 both sides, factory IFR's .031(measured)
Original IFR's are located in lower portion of metering block
The driver side factory IAB were #47 bit (.0785) reduced to #48 bit (.0760). The passenger side factory IAB were larger at #44 bit (.0860). I ended up squaring both carbs with #42 drill bit IAB.
I would suggest you sneak up on the IFR as you don't want to go too lean. I'm running NGK GR4 plugs in ported iron heads, solid FT cam .252 dur. Every combo varies so use my specs as a guide only.
As for the primary jets I swapped the #80 jet for a #75 in the right carb and left the #76 in both sides of the left carb. My plugs read aboout the same color so the asymetrical jetting wasn't needed. If you have the clearance (I only have 1/4" spacers) adding carb spacers tends to help the fuel mixture travel easier through the intake.
Also, I installed 10.5 power valves. I have 17- 18" vacuum at cruise and they work well.
JDJG
Well-Known Member
Thanks VERY MUCH for sharing all those specifics- that was super generous of you and I owe you a beer x 3
I will let you know how I make out on the next test session!
No Problem JD. Let me know if you need anything else. We crossram owners have to share our tuning tips.
Ernesto
Ernesto
JDJG
Well-Known Member
Hi Ernesto
I got a set of precision pin gages in the mail today and measured my IFR in the metering blocks in those carbs. The size ranged from .041-.055”. I was surprised at the size and the variation in the size. No wonder this was running rich!
I got a set of precision pin gages in the mail today and measured my IFR in the metering blocks in those carbs. The size ranged from .041-.055”. I was surprised at the size and the variation in the size. No wonder this was running rich!
These were designed for all out racing. I assume you have original Holley carbs. I have the Holley repos so perhaps they sized them smaller. I forgot to mention, I also drilled and tapped the pvcr (Power Valve Channel Restrictors). Let me know if you need any more of factory vs. modified data.
JDJG
Well-Known Member
Yes you are right! I also spoke to Gary Williams and his initial comment was that these cars were usually pushed to the starting line, did the burnout, ran the 1/4 mile and got towed back to the pits to prep for the next round! In short, idle and cruise characteristics were waaaay down the list of requirements!
I do have oscillation at times during idle but I live with it. I have a DIY air flow meter to sync the carbs but with the AFR spot on, the plugs look good and she drives great so I am leaving well enough alone.
JDJG
Well-Known Member
Looks great!!
JDJG
Well-Known Member
Badazzz. My next favorite B body. I'm feeling the color combo too.
JDJG
Well-Known Member
Hi Ernesto!
Just back from a ‘neighborhood test n tune evaluation’.
I think youre right on with those higher value power valves. I noticed cruise values for vacuum on mine 12-17 depending on grade/gas pedal pressure etc.
My idle vacuum with this cam is quite low 7-10 but I wouldnt think having a power valve around 10 would affect that since the throttle blades are closed at that point and not pulling fuel out of the main circuit.
any thoughts?
Just back from a ‘neighborhood test n tune evaluation’.
I think youre right on with those higher value power valves. I noticed cruise values for vacuum on mine 12-17 depending on grade/gas pedal pressure etc.
My idle vacuum with this cam is quite low 7-10 but I wouldnt think having a power valve around 10 would affect that since the throttle blades are closed at that point and not pulling fuel out of the main circuit.
any thoughts?
From all the reading I've done and from my experience power valves have no affect during idle so the idle vacuum does not matter. Here is what I did and it worked. I took my cruise vacuum and with my wideband, I drove a steady cruise speed 70mph. When I approached a grade or needed to gradually speed up I noticed my AFR would go way lean and my vacuum would drop to 6.5 before the additional fuel was added via the power valves. (this is with 6.5 power valves). This lean condition lasts too long and is not engine healthy. This led me to install the 10.5 power valves as once those same conditions occur I am lean for a moment before the condition is back to normal. The thing about the wideband is you can use it as a tuning aid and then remove the gauge and plug the threaded bung. I would not have known the lean condition was occuring so often and for so long without it.
What is your idle timing and rpm? Vacuum advance?
I have a very good article that member Fran Blacker sent me. Although the Hemi in the article has the inline 2x4 intake there are very good details about tuning 2 4bbls. PM me with your email address and I will send it to you.
Similar threads
