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 Post Posted: Fri Nov 30, 2007 5:18 pm 
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Phil don't confuse the "T" slot feed with the "Intermediate" (third) circuit!  If you're having problems with an off idle rich condition then it's likely the intermediate and possibly the "T" slot with it.  With the throttle blades closed you should just barely be able to see the bottom of the "T" slots from the bottom side.

As far as finding out what condition you have goes, if the plugs are sooted up then it's rich, but then again, most 1050 3 circuit carbs will do that anyway?

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 Post Posted: Fri Nov 30, 2007 5:45 pm 
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I have been reading here and have any of you got the ARF on gas at 12.5 or so and got an EGT reading????

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 Post Posted: Fri Nov 30, 2007 6:13 pm 
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Haven't used the O2 sensor on gas Barry as it belongs to a friend and the life of those sensors is limited on leaded gas.  Slowpoke (Donee) has done that I think so maybe he will post his findings.  He's got an Innovate Data Logger on his car with 8 EGTs and 2 O2 sensors so he should know.

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 Post Posted: Fri Nov 30, 2007 9:16 pm 
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Barry,

I'm running a NA 427 BBC

I haven't finished my tune-up yet, and I am still seeing about a 200 degree spread between my coldest and hottest cylinders.  The four corner cylinders are generally hotter than cylinders 3, 4, 5, & 6.

With my AFR's in the mid 12's, I'm between 1260 & 1460.  But that will change drastically, roughly 100* hotter, by just changing the timing from 42* to 38*.  Changing the timing can also change what the O2 sensors are seeing, which affects the AFR "reading".

I am using the AFR info to try and get a consistant AFR reading, say 12.5 from starting line to finish line.  Once I get that, I'll use the EGT's to help balance out the fuel to each cylinder.  Then go back to the AFR and try it richer, then leaner, to see what it likes.  Then move the timing around.

After it's all said and done, I'll have an AFR reading I like, and an EGT reading to shoot for when trying anything different.

I basically look at  AFR's and EGT's like I do total timing, the actual number doesn't matter, as long as you know what the number is where it runs best, it's just a reference.  You can have two identical engines and one will run better with 40* timing while the other will run best at 38*.  I think the same apllies to AFR's and EGT's.

I know I can make 2 runs with different AFR's and timing, and the EGT's will be the same, but the ET's will be way off.  If you add fuel the EGT's normally get colder, but if you retard the timing the EGT's come back up. So if you had a good tune to start with, you would end up with less power but the same EGT's.

This is the way I see the relationship between these numbers, I'm still learning a lot from logging this info, with a lot left to learn.

Donee


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 Post Posted: Fri Nov 30, 2007 10:23 pm 
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Donee, I run a BBC also and don't have a o2 to look at but do have an EGT and it seemed to always run it's best ET and MPH at around 1350...

To be honest it repeats very well although Im still working on short times to be more constant =;

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 Post Posted: Mon Jan 28, 2008 7:00 am 
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FAO Ken + Tuner

Pulled my carb and looked at the jet sizes on my 468 . The Idle and Int bleeds  I could not see a No on them. Worth noting was the Intermetiate bleed had already been drilled out by the previous owner of the carb, presumably in an effort to cure part throttle richness, which probably explains why the main jet size needs to be so big.

My MAB is .023. In an earlier post, you wrote the following

"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 certian 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!  "

Now I need to decrease the MAB size to richen my top end. When you state .005 in jet size, I assume this is actual jet diameter and not Holley numbering for jets. If so, how do I work out the size of a 98 main jet so I can calculate the correct air bleed sizes to effectlivly jet this up by 1 or  2 jets sizes ?

As a refresher, I'm trying to richen my top end as my lambda reading was around .95 and a little on the lean side. I'd like to get it on the richer side for peace of mind. Main jet is already 98.

Thanks

Phil

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 Post Posted: Mon Jan 28, 2008 7:47 am 
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I found this site about Holley Jet sizes

http://www.angelfire.com/fl4/pontiacdud ... yInfo.html

assuming the jet No to size is correct. I calculate the following

98 jet at 0.125

so

0.024in bleed and 98-0.125 jet = 0.130 jet size = 4% increase in jet size
0.025in bleed and 98-0.125 jet = 0.135 jet size = 8% increase in jet size
0.026in bleed and 98-0.125 jet = 0.140 jet size = 12% increase in jet size

given I only have available metric micro twist drills, the only sizes of use would be 0.6mm and 0.65mm giving me 0.0236in and 0.0255in

so this kind of equates either a 2% or 10% increase in jet sizes

anybody got any thoughts on this. Are my calculations correct ?

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 Post Posted: Mon Jan 28, 2008 8:57 am 
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If you'd like to buy this set let me know.  He only ships to the USA but I'll get them for ya and send them myself.  You can send me payment any way you want.


http://cgi.ebay.com/Qty4-20pc-NUMBER-DR ... dZViewItem

RE:  Your figures?  I'm not sure I know exactly what you mean.

The sure cure for this carb problem is a 2 circuit conversion!  What you are experiencing is the same problem that hundreds, if not thousands have had with this carb design, ie, stupid rich down low and falling off lean up top.  

Scott Smith just went thru his because he was having the same problem.  I don't think that more jet is going to cure the top end leanout because of the design of the 3 circuit block and the resulting restriction in the mainwell.  

Anywho, there is a guy that sells Holley parts on fleabay that has the 4150 blocks you need for about $25 each last time I checked.  BPTCarbs is his user name if you want to check.  Those metering blocks, some drills like the ones I showed you above and a couple more added to it and you can permanently fix that problem that's been biting you in the ass for a long time now.  I would offer to do the carb for ya but you're not going to learn anything if I do that!  Old saying is that if you give a man a fish, you'll have to give another each day but if you teach him to fish, then he can feed himself.  Our goal here on MSV is helping ppl learn to do stuff on their own if they want and I think with what knowledge you've acquired in recent months, you're ready to tackle this on your own! ;-)

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 Post Posted: Mon Jan 28, 2008 9:32 am 
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Hi Ken, just spotted a flaw in my original figures, I've increased the air bleed size, when I should have decreased it. ](*,)

I get what your saying about the 2 circuit mod, but I don't understand what the restriction is without seeing it.  Other problem is I don't have a logger to measure the affects. My readings came from my original dyno session, and at the equivilent of $800 a day....I can't afford another session for a little while...I guess I could go by the plugs and times but we don't get a lot of testing time over here.

thanks for the offer on the drills, but I think if I'm able to richen it slightly (if Tuner chimes in ? ) I'll have a friend do it on his lathe. With hindsight I don't think my pillar drill will do it.

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 Post Posted: Mon Jan 28, 2008 10:05 am 
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Smaller MAB will richen the top end by .000 amount.  Larger does the opposite.  My old style 8896 has an .026 MAB and 89/94 jets and is a little rich.  When I gave you the .001 to .005 ratio I was speaking of inches as that's what we use for alky carbs.  Sorry.  

If you'll notice, some Holley jets with different numbers will have the exact same .000 diameter?  They change flow rate with the length of that orifice.  Longer orifice might = less fuel flow for a given diameter, or it may be the opposit but that's how they get the flow number they use.

That $800 dyno session would have bought you a nice entry level Innovate logger with O2 here in the States.   ;-)

The restriction, say IDLE FEED TUBE, in the main well takes area away from what the jets will flow.  There comes a point where the area of a jet will overcome the area available to flow fuel in that mainwell.  YOU'RE THERE NOW!  No matter what jet you put in, or even take the jet completely out, there's probably not enough room in that main well to increase flow past a certain point.  Leaning out that third circuit just aggravates this condition even more.  The two circuit blocks have the idle circuit OUTSIDE the main well!

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Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

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 Post Posted: Mon Jan 28, 2008 11:00 am 
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so basically I can only lean and not richen my top end with bleeds as the main well won't flow any more ?........am I right in thinking I could put an 1150 or 1250 on and it'd make no difference as the required cfm remains unchanged ?

$800 is around what it costs over here, I got my motor dyno'd for free by the guys who built it, I wasn't paying till it made the pony's they said it would !. I have considered a logger but I need to check my class rules and keep saving my pennies....

Aside from the 2 circuit mod, would the only other bolt on option be a dual carb set up ?

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 Post Posted: Tue Jan 29, 2008 5:11 pm 
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OK, so I emailed Holley tech to see from their perspective what i can do to even out my AFR throughout the rev range. I detailed my motor to them and they basically came back and said a 1050cfm was too big for a 468 ?

I got 2.19in inlets, 1.94in exhaust in Edelbrock Performaer heads flowed further but not sure on flow figures, with a single plane Edelbrock 454R, 4 into 1, 2 3/8 headers.

Would a 4150  950cfm allow me to achieve the same performace and even out the AFR without strangling it ?

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 Post Posted: Tue Jan 29, 2008 10:15 pm 
 
Hey Ken, I don’t know why you think casting aspersions in public will inspire me to post, what’s up with that, I haven’t told anyone any of your dirty little secrets.  [-X

Sounds like Holley is taking the same party line as the rest of the carbufornicators out there, “If it doesn’t run right your engine is (pick one), too small, too big, over-cammed, under-cammed, over revved, too full of oil, you have stale gas, you have stale ignition, it’s the wrong combination, you lost the combination, you have reached a number that is no longer in service, please look up the number and try your call again, whatever it is – it’s your fault – our carbies are perfect until you take them out of the box, etc etc…..”

I don’t understand why they would say a 1050 is too big in a 1 X 4 application when it’s listed in the catalogue as such and they would no doubt suggest two of them (or 1150’s) on a tunnel ram at the slightest hint of interest on the customer’s part.

Enough of the editorial, the bottom line is the 3-circuit metering block is so restricted in the main well by the idle tube it won’t work in most applications, especially engines that flow a lot of air.  In many applications the high RPM AFR doesn’t get any richer beyond jets in the low 90’s but at low RPM and part-throttle insult is added to injury because it’s already too rich with any main jet and just gets worse with bigger jets.  Ken is giving you the straight scoop, use 2-circuit metering blocks and do some simple drill and tap exercises and you can have your cake and eat it too.  In the last 35+ years I have never seen a 3-circuit carb run really well.  I’ve seen some people who thought theirs did but they also think, “fouled plugs are normal for a race engine, and radical engines are supposed to blow black smoke and blubber and fart, that’s how you can tell how radical they are.”

See if this makes any sense.
http://www.innovatemotorsports.com/foru ... ostcount=4
Chase the whole thread. http://www.innovatemotorsports.com/foru ... php?t=7546
I think Scott is pleased with his tuning effort so far.  The weather hasn’t been kind to him lately but he got a few passes on it a couple of weeks ago.


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 Post Posted: Tue Jan 29, 2008 10:55 pm 
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Tuner wrote:
Hey Ken, I don’t know why you think casting aspersions in public will inspire me to post, what’s up with that, I haven’t told anyone any of your dirty little secrets.  [-X


"Cast aspersions on someone/something, ie, to say that someone's character or work is bad."

Didn't say that at all!  Procrastination is more appropriate I think.  I did speak highly of your work as that's where I got the tuneup for my carb! =;

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Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

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 Post Posted: Wed Jan 30, 2008 12:45 am 
 
I thought you were sprinkling me with holy water. http://en.wiktionary.org/wiki/aspersion


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