Opinion on X pipe design

[Schurkey]

Well it does seem peppier now (shocker). But my old problem of pig rich mixtures at wide open throttle still remains. I think I may try a new AVS2 650 cfm Edelbrock and see how it responds. The 750 QF and an 800 Edelbrock seem just like they are too much, regardless of jetting changes.

One would think that the larger carbs would be easier to lean-out, since bigger venturis make for less booster signal; all else equal.

What kind of air cleaner are you using? Any chance you have a restricted snorkel? How much vacuum is on the clean side of the filter at WFO?

[motormonkey]

What's your combo, vehicle weight and gearing to start with.
What jets your plugs look like.
Basics first.

[Belgian1979]

What a mess. I made my own, by using 2 90° bends, where I cut a section out of the outer part of the bend and welded them together. Works like a charm. I'm not a perfect welder by all means, but it was a lot better than what you have there. Over here they have a Dutch expression which roughly translates as 'it has been shit together instead of welded'.

[shoedoos]

OP, please define "pig rich" in A/F numbers, also was this a momentary "pig rich" or a permanent "pig rich" at WOT? Have you played with the air bleeds? Confirmed the choke plate ain't hanging closed/semi-closed on you?

[MadBill]

...
where it is joined at the X could be full of slag for all we know,only one way to find out.
i can see the restriction causing more back pressure leading to combustion contamination etc,i would cut the system off and start again.

Wow, 'X' ray vision Steve!

[GARY C]

I always start with the Jegs universal kit, Summit has one as well.
https://www.jegs.com/p/JEGS/JEGS-Univer ... 2/10002/-1

[In-Tech]

Hiya,
With higher overlap, the exhaust can go either way based on pressure differential. Think EGR affect causing the richness. None of that non-mandrel bent tubing is helping. If you HAVE to use those exhaust manifolds get the pressure differential lower past the manifold.

[steve cowan]

Thanks for all the responses. I was confused about what I had said earlier. A clogged exhaust or high back pressure can cause a wide band to read rich. But Shurkey is correct in that a misfire will cause a lean indication.

So far I’ve gone through a brand new Quick Fuel 750 SS that came stock with 72/80 jetting and went all the way down to 64/68 jetting and it still ran pig rich at WOT. Same behavior with a brand new AVS2 edelbrock 800. Even after going down 2 stages lean on the primary metering rods and 2 stages lean on the secondary jets.

I’ve come to the conclusion that my issue HAS to be this x pipe or either the position of my o2 sensor is causing it to read faulty under wide open throttle. I have the AEM wideband that says to install 18” from the head. I didn’t follow this and put the o2 in the factory bung in the manifolds I had to use which is closer than 18” to the head.

not sure how much time and money you are prepared to spend but i would square jet that carb (750) and install a rear powervalve and PVRC jets.
74-74 jets
depending on cam and vacuum 8.5'' - 10.5'' power valves front and rear
need to road test with vac gauge and check manifold vac.
start off 58'' PVRC jet.
understand if you dont have carb parts etc,just a starting point thats all.

[In-Tech]

not sure how much time and money you are prepared to spend but i would square jet that carb (750) and install a rear powervalve and PVRC jets.
74-74 jets
depending on cam and vacuum 8.5'' - 10.5'' power valves front and rear
need to road test with vac gauge and check manifold vac.
start off 58'' PVRC jet.
understand if you dont have carb parts etc,just a starting point thats all.

Good numbers for a starting point. I normally use 72 jet with downlegs and a .065" pv jetting, then for safety test, start with a 10.5 pv. Totally depends on app. Good call Steve.