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 Post Posted: Thu Mar 20, 2008 5:40 pm 
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I decided to try the conversion on a 80533-1 1250 HP Dominator. I have 2 circuit Demon blocks to work with. My current settings are as follows:

Original Idle jets removed, 6/32 set screws with .040 holes.
Original .080 TSJ's removed, 10/32 set screws with .054 holes.
Angle channels @ .159
Outer bleed holes plugged
IAB's .065 in center holes, was .053
MAB's .026 in inner holes

Primary PV restrictors went big to .081 matching factory blocks. I did this prior to the 2-circuit info being finished. I can swap the front & rear and re-drill if needed as the rear is not drilled and plugged.

PMJ's are BLP 102, approx 90 Holley.
SMJ's are BLP 120, approx 98 Holley.

The first issue is idle. When I get the idle speed adjusted as low as possible, I have the mixture screws out only 1/4 turn to get it clean. When I load the engine, it looks like AFR is at low 14's, hitting high 13's occasionally. When I first started it with the mixture screws out 1 turn, AFR was more steady 13's but idled bad. I have no holes in the primary plates to allow air through. T-slots looked good, almost square with the plates all the way closed. Do I still need to drill holes to close the plates up? I started with 3/4 turn in on idle speed screws, but had to go a couple turns each to get the speed up. This is a 1250, where am I off?


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 Post Posted: Thu Mar 20, 2008 7:17 pm 
 
Hi Mark,

When you say “When I load the engine, it looks like AFR is at low 14's, hitting high 13's occasionally,” How much load are you referring to?  If that’s at WOT it’s too lean but if it’s in the area of the T-slot’s influence, like a little load on the torque converter, the load is small enough so that as lean as it will run smooth is what you want to do anyway.  Do you mean it runs poorly or the number is alarming?  If it runs smooth and it’s not at heavy load, it’s OK.

The number of turns out on the mixture screws is somewhat irrelevant.  I know everyone chants a mantra of “1&1/2 turns” but what is really important is if the screws are able to control the mixture so as to get a good idle at all.  In other words, be able to be adjusted both too rich and too lean and to the sweet spot.  Admittedly, if they are only open as little as you describe they are more sensitive than if the sweet spot is further open.


A lot depends on just how much slot is below the butterfly when the idle is adjusted the way you want it.  If too much slot is exposed it’s delivering fuel the curb idle screw would be so the screw can’t be open as far as if there were less slot.  That sounds like your situation?  Adjust the idle the way your want it and take the carb off and look at it.  You have plenty of initial timing, right?

If you want it to go richer as you open the throttle up the slot you would use a smaller IAB.  Because your idle mixture screws are open so little you would need a smaller IJ or larger IAB, both of which will lean the T-slot more that it is already (provided that’s what you mean in your description of the AFR).  With smaller IJ and larger IAB, a larger TSJ will get you back to square one in the t-slot.

I need to know how much slot you have showing below the throttle at the desired idle speed.  4500’s usually don’t need holes drilled in the butterflies because they are large enough the airflow is obtained without opening the throttle too much, but if the engine is really large and the cam is really wild and the T-slot is too low, etc???

When the speed screws are backed all the way off and the butterflies are touching the bores, look through them at a light and see how much light leaks around the edges.  Perhaps you can loosen the screws and shuffle things around and get a better fit so they close lower in the bores.  

Engine details?  Initial timing?  Is the idle jet at next to the PV or is it at the top of the block?  It’s better at the lower position.


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 Post Posted: Thu Mar 20, 2008 7:57 pm 
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OK,
Engine is a 447 SB2 head small block, 27 total timing. Idle jet moved down and top one removed.  I didn't think about it being part throttle, that helps a little. WOT isn't possible without disabling the 2-step. At current idle adjustment, front t-slot is about .065, back is about .090. It's currently in a trailer, I am trying to get the carb close for the dyno session on Monday. I have the old style 9375 1050 we made initial runs with, the AFR's were in the 13's during the burnout and run. I am working with a FAST AFR(sorry) and while I can record a run, I can only play it back real time. Reading AFR at idle is impossible, the #'s jump all over to make it unreadable. The car also came with a Red Alert EGT and is plumbed but isn't working and haven't had time to figure it out. I also have an 8896 I will convert after this one gets worked out. I do want to know if my initial jetting and primary PVCR is close for the 1250 or do I need to make any changes? Also, The factory blocks feed the idle circuit separate from the mains, where the 2-circuit draws from them. Any issue with that?


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 Post Posted: Thu Mar 20, 2008 10:45 pm 
 
Is the car the dragster in your ST avatar? The O2 sensors can’t function well at idle with the short header collector such cars have.  Usually OK at WOT but the idle and part-throttle is unreliable info because of the backwash of fresh air into the collector.  The miss-fire on the 2step makes that info junk.  You don’t have to be sorry for using a counterfeit AFR meter; it’s not the meter’s fault, just the nature of the situation.  The advantage in the Innovate stuff is the LogWorks software for graphic analysis and playback at any speed you like.  Are you familiar with it?

The time slip and plug reading have the final word, I think.

Your jetting scheme sounds OK to me.  Just don’t make fun of me if it isn’t.  I would have used a .025” MAB though.  No matter if first dyno pulls tell you the AFR is rich, jet larger to confirm it looses power before going any leaner.

How many and what size are the E-holes in the BG metering blocks?  Do you mean the factory Holley or BG blocks feed the idle separate form the mains?  I think they both feed the idle from the tube in the main well and the intermediate circuit is separate.

So, you mean it has 27° locked, idle & WOT?  If so, OK.

I know when you compare the area ratios of the primary MJ/PVCR to the secondary MJ it looks rich in the front but it `taint necessarily so because of the length of the PV passage.  There is reason to believe jetting richer in the front of the manifold will give a better average AFR because it compensates for acceleration, similar to jetting a circle track car richer on the left side.  I don’t really know what size PVCR to suggest because it seems to be a real application specific deal.  You’re about in the middle of the zone on the PVCR size.  You just have to kiss it first to see how it tastes and do what it likes.  If you can get co-operation from a dyno operator to play with the part-throttle tuning it should be easy.  Some of the folks I know think a dyno is for “pulls” and have a hard time using one for tuning light load.  After a couple of lessons they get religion and it was their idea all along.  (Why is that?)

You can plug the PV and jet it square but it will be rich at part-throttle again that way, not as bad as the original though.  When you dyno with 8 cyl’s of EGT or if you have that in the car with a data system, that’s a good way to find out how much or if you need to stagger jet, percentage wise, and you can carry that over into the PVCR sizes.  I have some 600 DP’s in spec road race applications on 180° manifolds that have 4 different size PVCR’s.

You might have to put holes in the butterflies if closing them will significantly reduce the amount of T-slot showing.  I know that sounds ambiguous but it depends on how much T-slot is showing when the butterflies are closed tight in the bore.  Some 4500’s of recent manufacture have the T-slots too low in the bores and that’s a tough deal.  I hope you don’t have that problem.


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 Post Posted: Thu Mar 20, 2008 11:24 pm 
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It is the same dragster, and I suspected without a long collector or muffler O2's would be an issue. I do wish I had opted for the Innovate, but hopefully I can still get info from it. I will drill the plates to get the T-slots covered more. And BLP is on my way downtown tomorrow, I can pick up some 25's and 24's to play with. 5 E-holes 1 & 3 are .031, came that way in the blocks. 2, 4, & 5 I plugged. Should I pick up .026? I didn't look close, probably is the intermediate feed next to the jets. I have a Digital 7, timing is 29 to 1500 RPM then goes to 27 locked. Hope to get a usable curve to program from the dyno. I always did wonder if running fatter up front on a drag car would help, I'll have to get my EGT's on the car working.

Thanks,


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 Post Posted: Fri Mar 21, 2008 12:55 am 
 
If the E-holes are already threaded and easy to change, yes, get some bleeds.  I think shrink them to .026” or .028” but don’t take my word for it, ask the engine.  You’ve been studying, eh?  The boys at BLP are gon’na love this.

While you’re there ask them if they have 45146 down leg boosters (140”).  I need some to fix an old 715 Shelby carb that’s been on fire.  Why do people have to use an entire truck full of extinguishers on one little carb?  It never did anything to them.

What kind of dyno is it?  A buddy has a dragster we tried to get on a chassis dyno and the tires are too close together.  We’re doing an engine dyno session, hopefully tomorrow.  Part of the windage tray came out on the magnet on the drain plug and they’re working on it right now.

You can get an idea of a trend in timing over a range, like if it wants to advance as the RPM climbs past the torque peak and over the power peak. or not, but if the dyno load (weight of the roll) is different than the car it wont be the same as on the track.  Your scoop will change the carb and the timing too.


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 Post Posted: Fri Mar 21, 2008 9:17 am 
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E-Holes are threaded. Pulling the engine out for an engine dyno, it's our 1st SB2 so we want to get the tune right and find the powerband to buy the converter. The dyno owner/operator is local comp racer Glen Treadwell, and he has some SB2 experience. I'll find out about those boosters.


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 Post Posted: Sun Mar 23, 2008 12:24 am 
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Wouldn't it be better to drill and tap an idle air bleed near the air filter stud on top of the carb rather than drilling the throttle blades. Seems to me if this didn't help the problem you could plug it a lot easier than fooling with the blades. #-o

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 Post Posted: Sun Mar 23, 2008 9:12 am 
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Mark if memory serves, if you absolutely have to have those holes they need to be near the T slots if possible.  It helps with fuel distribution at idle.

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 Post Posted: Sun Mar 23, 2008 1:13 pm 
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Ken , check ur PM

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