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Discussion Starter #1
Looking for some help on finding a direction to go with my set up.
81 Malibu , s480 turbo, BBC 402 w/2 speed glide.
Running a msd 6al programmable, looking for guidance on the boost map, right now atmospheric pressure is 7.5 so pulling 1° per 1lb after 2lbs is made and also guidance on jetting and power valve sizing.
Right now Primary has 72 jets. 6.5 pv
Secondary has 72 jets and pv eliminator. (Was n/a on something else when I got the carb)
Right now at idle fully warmed up 185/190 degrees afr is at 11.5 when in gear and slowly accelerating up to the converter at 2300rpm AFR is at 10.0 once on converter I floor it and it makes 1 or 2 lbs of boost , AFR gauge goes to 14.5 for a split second and then 16.8/17 for another split second and then doesn't read from being maxed out and Also spits back through the intake. All within seconds. id like to stay low 14's at idle and mid 11's at wot.
 

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Encase this helps my set up is 402 BBC bored 40 over, forged pistons ,oval port heads, 240/253 Duration at .050". 113 Degree Lobe Split / 0.575"/0.595" Valve Lift, high rise single plain intake, 950cfm Wilson carb converted to blow through per the hanger 18 write up, s480 turbo with twin 38mm wastegates and twin 50mm b.o.v's, backed by a 2speed power glide and a 12bolt with 3:73 gear and 28x10.5 qtp's.
 

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Holley black pump and a Holley reg with a vacuum port with 1:1 ratio.yes I have tested it , and it is obvious the engine is getting way too much fuel just looking on where to go with the carb jetting
 

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The AFR values say it's going way lean. Just FYI you cannot correctly read AFR if it's on the 2-step.
 

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If it goes 14.5 afr then higher and spits back, it's obvious, it's not to much fuel. Your wide band will go high if it gets rich enough to miss fire. But imo that's not the case. Holley "black" pump is not going to cut it!
 

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How will that pump not cut it when all I'm trying to do is make 2psi with it right now in my driveway? The pump is not the issue right now. you haven't asked and I haven't said the psi or hp goal yet either?..
I'm going to run 8lbs of boost and that fuel pump makes 14 psi. It will be pushing the use of that pump but it will work. The carb needs addressed not the fuel pump,
 

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Not sure if you mean running it in gear against the converter or just in gear on jack/stands. You can't tune it without loading the engine properly. Just running it in gear without additional load is like highway cruise or less loading. IMHO it's very difficult to tune a blow-thru combo without any kind of datalogging. Haltech VMS / VMS-T is the most bang for the buck but anything that can give you AFR vs Time or AFR vs RPM will get the job done.
 

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Not sure if you mean running it in gear against the converter or just in gear on jack/stands. You can't tune it without loading the engine properly. Just running it in gear without additional load is like highway cruise or less loading. IMHO it's very difficult to tune a blow-thru combo without any kind of datalogging. Haltech VMS / VMS-T is the most bang for the buck but anything that can give you AFR vs Time or AFR vs RPM will get the job done.
Its on the ground in the driveway. Also drove it around the block with the same results as to the AFR leaning out to 10.0 then richening to 14.7/16 followed by a split through the carb
 

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When I get to a point when I run out of fuel pump I'll talk to you. I'm not here to argue either just want help with my carb tuning
10.0 is rich 14.7 is lean. Not having fuel delivery will keep you from tuning the carb. Just trying to help save ya from chasing your tail.

As Turbo II said AFR to time and RPM is valuable. I used an AEM data logging gauge for years.
 

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Discussion Starter #14
Data loggers sound expensive, ohnestly haven't looked into one. but if I spend anymore money it will be parts to tune the carb and a bigger fuel pump. Just want it to drive right now with what is has done 😭
 

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They are cheaper than engines. I have rarely seen anyone do their own carb conversion and tune the engine without hurting it at least once before they get it sorted out. Carbs and turbos are not the best combo. Much more difficult to get sorted out safely compared to a supercharger where X RPM == Y Boost. Turbos are primarily load driven. Carbs are reactive to air volume and velocity with a ton of dead time so bad things can happen before they can respond adequately to avoid damage. The timing map is just as important as the fuel curve as well. Generally speaking, if you short shift to high gear with a supercharger rpm goes down, boost goes down and load goes up some. No big deal in most cases. Now short shift a turbocharged engine, rpm goes down, load goes up and it pisses off the turbo and boost goes up violently in most cases. If the fuel curve isn't in range and/or the timing map is not correct in all areas it can lead to damage from lean condition or detonation from lean or excessive cylinder pressure. I'm not trying to bash any combo or anyone for that matter, I'm trying to help you avoid some expensive lessons. Just my $0.02
 

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Discussion Starter #16
In which direction with jetting, power valve size, etc. do I need to go to get my car close on the carb side of things.
 

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Its on the ground in the driveway. Also drove it around the block with the same results as to the AFR leaning out to 10.0 then richening to 14.7/16 followed by a split through the carb
you are incorrect in your statement. it is not "richening" from 10.0 to 14.7/16
it is becoming leaner as the afr moves from 10.0 to 14.7/16
 

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On another note the cam is not helping matters either. A lot of reversion going on with that much duration split. Good chance it is screwing with the signal to the carb, especially at lower rpms. 13* of split is a lot for a turbo application. Its more in line with a street/strip blower/N20 application.
 
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