blow thru tuning
blow thru tuning hi everyone! im a noob to ls1 tech anyone having luck w blow thru carbs? ive been tinkering w my home modded carb and have had some luck and some questions as well. drilling the pvcrs how big is to big? im up to .136 pvcr w 74/94 jets still lean under boost. 15 psi boost. i wanna push 18-20 psi to make around 700whp. although i dont want to effect cruise afrs as they are borderline rich as of now. thanks for your help!
have you changed your hi sp a/b's? .136 is getting way to big on the pvcr, most guys dont need to go much beyond .090 or even less
what is your idle vacume-are you sure the p/v is opening
did it have a p/v ck ball (blowout proof)
what size n/s's are you using, at least.120-.130, soild floats? jet ext's?
your jetting is in the ballpark if its a 750, the hi sp a/b's will help richen up the fuel curve, usually stock ones are .031-.033, you can drop them down to .023 to help-also annular boosters help out to
what is your idle vacume-are you sure the p/v is opening
did it have a p/v ck ball (blowout proof)
what size n/s's are you using, at least.120-.130, soild floats? jet ext's?
your jetting is in the ballpark if its a 750, the hi sp a/b's will help richen up the fuel curve, usually stock ones are .031-.033, you can drop them down to .023 to help-also annular boosters help out to
Last edited by forcd ind; Mar 24, 2009 at 11:15 AM. Reason: =
have you changed your hi sp a/b's? .136 is getting way to big on the pvcr, most guys dont need to go much beyond .090 or even less
what is your idle vacume-are you sure the p/v is opening
did it have a p/v ck ball (blowout proof)
what size n/s's are you using, at least.120-.130, soild floats? jet ext's?
your jetting is in the ballpark if its a 750, the hi sp a/b's will help richen up the fuel curve, usually stock ones are .031-.033, you can drop them down to .023 to help-also annular boosters help out to
what is your idle vacume-are you sure the p/v is opening
did it have a p/v ck ball (blowout proof)
what size n/s's are you using, at least.120-.130, soild floats? jet ext's?
your jetting is in the ballpark if its a 750, the hi sp a/b's will help richen up the fuel curve, usually stock ones are .031-.033, you can drop them down to .023 to help-also annular boosters help out to
What are your boosters, HSABs, Needle and Seats, etc
x3
smaller hsab's and annular boosters are your friend.
It will keep the fuel curve nice and rich under boost, but not overly rich at cruise.
With a .136 pvcr, you have probably maxed out the flow of the feed passage to the booster.
That HP goal will be a challenge on a home modded carb without poor low speed metering.
Give the boys at CSU carbs a call.
The will save you a bunch of headaches modding yours.
I think that a stock 750 (non-HP series) may not have big enough main well/booster passages to flow the fuel you need.
What fuel pump are you using?
I assume the f/press regulator is boost referenced right?
Is it lean at the hit of the throttle, or steady state wot?
smaller hsab's and annular boosters are your friend.
It will keep the fuel curve nice and rich under boost, but not overly rich at cruise.
With a .136 pvcr, you have probably maxed out the flow of the feed passage to the booster.
That HP goal will be a challenge on a home modded carb without poor low speed metering.
Give the boys at CSU carbs a call.
The will save you a bunch of headaches modding yours.
I think that a stock 750 (non-HP series) may not have big enough main well/booster passages to flow the fuel you need.
What fuel pump are you using?
I assume the f/press regulator is boost referenced right?
Is it lean at the hit of the throttle, or steady state wot?
blow thru specificatons Thanks for your help guys. i apologize if my forum ettiquette is incorrect. ok my carb is a holley 850 w a proform main body. i have size 26 hsab and 70 lsab. .130 n/s 4.5 pv pv plug in the back. i have changed the hsab the original didnt have a # on them so i dont know what size they were. pv protection has been removed. the boosters r not annular thats for sure. the main wells have been drilled to .180 so they should have adequete flow. the floats r stock plastic i need to put the nitrophyll ones in but theyve been holding up so far! float levels r fine boost referenced fuel system on the hat and im running an aeromotive a1000 -10 lines feed and return. i think thats everything lol as i said i can just jet the thing up and itll be fine but my cruise afrs w suffer. i dont wanna cruise down the highway w 10.0 afrs. its already around 11-11.5. the idle however is fine 14.3 and i can tune it flawlessly on idle. thanks so much for help guys. ill post pics when i figure that part out!
thanks again!
383sbc
afr220cc heads
8.5compression
240/246 custom turbo grind 4 7 swap solid lifters
turbonetics t72 turbo .84 a/r
font mt intercooler
procharger carb hat
best of 11.66@124 10psi
thanks again!
383sbc
afr220cc heads
8.5compression
240/246 custom turbo grind 4 7 swap solid lifters
turbonetics t72 turbo .84 a/r
font mt intercooler
procharger carb hat
best of 11.66@124 10psi
im going to try and block the hsabs. its going lean at wot but its also pig rich at at tip till the boost picks up. i really need to do some work here butif i can at least get it safe at wot first, then i can try to tune it for cruising. ive got it up to about 15psi boost now w afrs hitting low 13s its a little lean for my liking but hauls ***! 4th gear wheelspin at 55mph w the stickies on! oh one question. does anyone ever mod the back metering block? i figure the seconday pv should give some extra fuel right? i currently have a pv plug in the secondaries so the pvcrs dont do anything right? just a thought. thanks
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im going to try and block the hsabs. its going lean at wot but its also pig rich at at tip till the boost picks up. i really need to do some work here butif i can at least get it safe at wot first, then i can try to tune it for cruising. ive got it up to about 15psi boost now w afrs hitting low 13s its a little lean for my liking but hauls ***! 4th gear wheelspin at 55mph w the stickies on! oh one question. does anyone ever mod the back metering block? i figure the seconday pv should give some extra fuel right? i currently have a pv plug in the secondaries so the pvcrs dont do anything right? just a thought. thanks
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