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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
I currently have the Victor Jr intake that has port size 1.10" x 1.90 where the ports on my AFR cylinder heads are 1.31" x 2.21." Im porting and polishing the intake to match them up. My question, has anyone done this simple upgrade and will it require any carb adjustment to fully benefit from said upgrade? Thanks in advance
I've currently got 437rwhp @ 5600, anyone want to help guess what benefits I would yield?
Last edited by 25thannivZ28; 07-16-2016 at 06:38 PM.
If anyone wanted to take a stab in the dark on what my gains would be, I guess you'd need to know what else I've got. its a 406 Dart block, 10.4:1 compression with AFR 1054 heads. Hooker headers, two 3's into a single 4" Mufflex exhaust system into magnaflow muffler.
i've noticed better throttle response by port matching. IDK if it would make much HP increase? thing is, obviously not to have smaller ports at the head or the gasket interfering in any way. having a slightly smaller port size on the intake could actually help produce a venturi effect and prevent reversion in a way. JMO.
this was the before, the guy who gasket-matched it was able to take about a 1/4" off the top of the port. Got it together this morning, making a few tweaks then i'll get back to the Dyno.
i've noticed better throttle response by port matching. IDK if it would make much HP increase? thing is, obviously not to have smaller ports at the head or the gasket interfering in any way. having a slightly smaller port size on the intake could actually help produce a venturi effect and prevent reversion in a way. JMO.
I've been getting a lot of the same feedback. I'm still holding onto hope, I'd be happy to get to the 450rwhp mark around (low-mid)6000rpms. With combination of this gasket match and leaning out my carb. My AFR was 11.2 - 11.5 on my 437rwhp run above.
Wish me luck, i'll post results once they are available.
Honestly the best port work comes from just cleaning up the straight wall and raising the roof. On a typical sbc the WIDEST you can go in the push rod pinch is 27-28mm or 1.07-1.09 in width. Try to keep the path as straight as possible
Honestly the best port work comes from just cleaning up the straight wall and raising the roof.
That's funny, the guy who ported it said the same thing. His words were that 90% of the air travels at the top, so the more you take off the top the better we're off. In which, he took off about .25"
The results are NOT in yet (on paper at least) but I've got it put back together. HUGE difference on higher end, almost felt like a turbo kicking in around 4700 - 6k. Not much loss feeling on the bottom.
I've got a question though here for you Carb experts. On the DYNO run I posted above, I have 88 Secondary Jets, 82 Primary jets. My Wideband O2 gauge read mid-upper 12's, hence the reason for staying with those jets. BUT, the dyno results came back with 11.2-11.5 average AFR.
I've decreased my jets in both front and rear 2 increments at a time and test drove, it didn't "Feel" any different and my Wideband gauge hasn't moved any leaner. Its still in the 12's (but if the Dyno said 11.2-11.5 when my gauge said 12's) i'm convinced the AFR hasn't changed.
I'm down to 74 fronts and 80 rears. Any suggestions to lean it out some? If you were in my shoes, what would you do next? Thanks in advance!
Last edited by 25thannivZ28; 08-02-2016 at 09:09 PM.
i dont think i'd lean it out. i'd be scared to burn it up.
how many pulls are you going to do and can you make a few changes?
i've seen significant changes just by trying different carb spacers.
but if you want to see how much the gasket match/port work was worth, you wont know if you make other changes.
i guess 1 thing at a time?
There are 3 fuel circuits in a Holley carb. They aren't independent of each other...but close to independent. Idle/part throttle, main circuit (the jets) and the WOT circuit (the power valve and the associated power valve channel restriction jet). At cruise, it is likely you are running mainly off of the idle/part throttle circuit. The jet changes wont have a huge impact on that portion of the fuel curve. In your case, I would be looking to lean out the idle feed restrictors.
i dont think i'd lean it out. i'd be scared to burn it up.
how many pulls are you going to do and can you make a few changes?
i've seen significant changes just by trying different carb spacers.
but if you want to see how much the gasket match/port work was worth, you wont know if you make other changes.
i guess 1 thing at a time?
Yah, it would be hard to pinpoint what JUST the port matching would do. I got it assembled and it was a noticeable seat-of-the-pants difference. It would have been neat to get it on Dyno before I do any carb changes, to see what that alone did, but time is not working in my favor. Knowing what I know with my previous dyno AFR readings and what my current Wideband gauge reads on the street, I'm in process of making some changes, recommended by Quick fuel Tech Support. Dyno to come hopefully sooner than later.
I've got a question though here for you Carb experts. On the DYNO run I posted above, I have 88 Secondary Jets, 82 Primary jets. My Wideband O2 gauge read mid-upper 12's, hence the reason for staying with those jets. BUT, the dyno results came back with 11.2-11.5 average AFR...
Keep in mind that the density of the air, or the lack thereof, will also impact your air/fuel ratio, so be sure to compare your intake air temperatures from when you did your datalog against when the dyno did theirs. With no O2 correction being a traditional carb, it is what it is when it comes to IAT and AFR. I'm assuming your datalog was out on the road when a cold air intake would be put to use as opposed to an in house dyno...
07-16-2016, 05:31 PM
