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 Post subject: Lambda to AFR ?
 Post Posted: Thu Nov 22, 2007 12:01 pm 
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is there a significant enough correlation between Lambda readings and AFR to determine one from the other using a formaula ? If so anybody know it ?

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 Post Posted: Thu Nov 22, 2007 4:12 pm 
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Fuel ........................ AFRst ........ FARst ....... Equivalence Ratio ... Lambda
Gas stoich ................ 14.7 .......... 0.068 ................ 1 ................... 1
Gas max power rich .... 12.5 .......... 0.08 ................. 1.176 .............. 0.8503
Gas max power lean .... 13.23 ........ 0.0755 .............. 1.111 ............. 0.900

How about this?

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 Post Posted: Fri Nov 23, 2007 4:12 am 
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thanks Ken, so if I have a Lambda reading of 0.95, this gives me a AFR of 13.96-1 ? slightly too lean ?

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 Post Posted: Fri Nov 23, 2007 9:24 am 
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Yeah Phil, that's the way I read it!  From what I've read, on gasoline you want to be in the 12.5 to 12.7 range on afr.

So tell me, is this the 8896 Dominator carb you're running now?  If so, then it's exhibiting the usual fat down low and lean up top condition that these things are known for.

Can you say "two circuit conversion" boys and girls?  I knew you could! =;

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 Post subject:
 Post Posted: Fri Nov 23, 2007 10:58 am 
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yeah it 's an 8896, just wanted to be able to interpret my dyno lambda readings in AFR terms. I guess it could do with fattening up in the top end a little more, I don't plan on running it hard but getting it onto the safe side for peace of mind and reliability would be nice

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 Post Posted: Fri Nov 23, 2007 1:26 pm 
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Yeah Phil, I'd think that at near 14 to 1 you're approaching the detonation danger zone, depending on how much total timing you have in it.  Richer fuel mixtures are somewhat more tolerant of timing than lean ones.  My engine was detonating at 30* and a little lean and now it's fat and at 30* it isn't showing anything on the plugs.  

Shame you are so far away or I'd loan you my 2 circuit gas Dominator to see how it compared to yours.

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 Post Posted: Wed Nov 28, 2007 5:59 am 
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whats your thoughs Ken on going up to an 1150cfm ? I run the 1050cfm with 98 jets and no power valves, do you think having power valves would help flow more up the rpm's ?

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 Post Posted: Wed Nov 28, 2007 9:42 am 
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PSweeney wrote:
whats your thoughs Ken on going up to an 1150cfm ? I run the 1050cfm with 98 jets and no power valves, do you think having power valves would help flow more up the rpm's ?


Phil the power valve circuit is part of the mainwell.  That being the case, it will just add insult to injury to try to flow more thru that same mainwell with too little area.  Normally you decrease the high speed or main air bleeds (MAB) to richen up the upper RPM range.  I think most of the Dominators come with an .026 in'em cuz that's what mine are on my 8896.  I've run my 1150 alky carb as small as .020 but with your afr being damn near 14 to 1 I don't think you can get to 12.7 with the MAB alone.  

Not exactly sure what the 1150 gas carbs have for metering blocks but they probably have the same s**t that the 1050s do, which would be S. S. D. D.  ;-)

Remember, I do have a tuneup for that carb with 2 circut blocks!  ;-)

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 Post Posted: Wed Nov 28, 2007 9:59 am 
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How about going richer and taking out the IAB's? That would lean the intermediate and then jet it to suit... I did the primary on my 8896 to two circuit, I don't have an AFR setup yet, but the car picked up over the 9375 I had on it.


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 Post Posted: Wed Nov 28, 2007 12:05 pm 
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I see what your saying Ken, If I recall from the dyno session, jets are up at 98, 99 is apparently no jet installed, ie a 99 jet is same size as the passage with no jet installed.  MAB was also smallest usable I beleive, I'll check out the size tonight.  I guess it's either a case of run it where it is ?, or go up to an 1150 and try to lean it out lower down ? I'm running 34 degrees overall and getting no detonation and it's running real strong but I'd just like to run it a bit safer for consistency. I might back the timing out to 32 too be safe.

Mark, I guess that would work if I could jet up to compensate, but I'm on the limit already

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 Post Posted: Wed Nov 28, 2007 1:38 pm 
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Question.  Did you try any jets larger than the 98s?

When I built this 8896 I used some regular 4150 metering blocks I had in "junk" parts!  Main jets in that 8896 carb now are 89 and 94 with a 6.5 PV in the front and it's rich.  Only problem I've seen so far is that the corners are a little lean, but that's not the carbs fault and hopefully the spivies will take care of that next time out.

As I said before, I don't know if the 1150s would be any better.

If you have access to some drills, taps and patience you can probably do the 2 circuit modification yourself.  The Idle air bleed holes (IAB) must be drilled and tapped for a screw in bleed.  If you can find metric brass set screws over there in a 4mm size then they would work just as well as the 10x32s and you wouldn't have to buy them from the speed shops.  10x32s are .190 OD and 4mm would be near .160 OD, which is plenty big for what you are doing.  You could also use those in the "T" slot jets (TSJ) as well.  Power valve channel restrictors (PVCR) have to be drilled out as well as the idle jets (IJ) but they don't usually reqire the drill and tap stuff since they are already smaller than what you need them to be.

FYI, none of these mods you do to this carb will make it so you can't go back to where you were!  Just replace the IAB with the proper size for the intermediate thats in there now and pull the TSJ out.  Put the other stuff back on and viola, you're back to where you started.

Did I talk you into it yet?   ;-)  =;

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 Post subject:
 Post Posted: Wed Nov 28, 2007 7:51 pm 
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Phil, check the main air bleeds to see what size they are.  Some of those carbs had main air bleeds as large as .040 so this may be part of your problem.

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 Post subject:
 Post Posted: Thu Nov 29, 2007 6:47 am 
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Ken, jets are up at 98 already, was told the carb/ metering block will only flow up to a 99, ie for a 99 jet, you may as well run with no jet in there.

Drills and taps cane be bought, patience on the otherhand is in short supply !

Pretty sure my idle air bleed are already screw in ? Where are the T slot Jets ???

Couple of questions; How small can you go on the Main Air Bleed ? and when running with no PV's, does the metering palte require any mods

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 Post Posted: Thu Nov 29, 2007 5:33 pm 
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PSweeney wrote:
Ken, jets are up at 98 already, was told the carb/ metering block will only flow up to a 99, ie for a 99 jet, you may as well run with no jet in there.

Drills and taps cane be bought, patience on the otherhand is in short supply !

Pretty sure my idle air bleed are already screw in ? Where are the T slot Jets ???

Couple of questions; How small can you go on the Main Air Bleed ? and when running with no PV's, does the metering palte require any mods


Phil the main air bleeds in my 8896 are .026.  I'm running an .020s in my alky carb.  You need to check yours to see exactly what you have.  As stated in the previous post, some of those carbs have .040 main air bleeds in'em so if yours are that large, then you can remove them, drill and tap the mains and make them whatever size you like.  

Rule of thumb is for every .001 you change the main air bleed, you richen the circuit about .005 in jet size.  That ratio will change once you cross over a certain point going smaller but understand that a change in the main air bleed could have a profound effect on overall afr.  In other words, make small changes!

If you don't run a PV then all you need to do is plug the hole it screws into.  It's been my experience though that a PV in the primary side can be good!  Helps make a clean running engine at part throttle, ie, around the pits and such.

"T" slot jets aren't there unless you put them in.  Some carbs do have a metering orifice in that location but on mine, I put in a set screw with a hole in it to act as a jet.  If you take your carbie apart and look where the "T" slots are and follow that straight back to the main body flange where the metering block mounts you will find that hole.  Like I said, I tapped mine and put in a set screw that was drilled as a jet.

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 Post subject:
 Post Posted: Fri Nov 30, 2007 6:56 am 
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thanks for th info Ken, I may try a PV in the primary as I get a little stumble going up on trans brake which I'm not totally convinced is shooter related, not sure wthether its a lean or rich stumble, any way to ID which it is ?

T Slot Jets sound like a great idea given the typically rich condition low down with this carb.

Will get my air bbleed sizes over the weekend, cars buried under stuff in the transporter at momment........

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