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 Post Posted: Mon Dec 14, 2009 8:41 am 
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Hi guys

First post from me. Looking for some experienced input.

Here is what I have. The motor is a 632" Big Chief, 11.25:1, cam is a 279/292 .730lift 115lsa 115icl. Sheet metal tunnel ram with two side mounted 9377 dominators that are currently being converted to 2-circuits with a PV in the primary side. The intake also carries two fogger systems. The motor is backed by a two speed auto with a brake and very tight nitrous converter.

This all is in a 3400lbs car that runs hard at the track and also sees a fair amount of street driving. The engine is actually pretty mild when it comes to idle and low rpm response. It idles just fine at 800rpm in gear and pulls like a train from idle and up. Has been running this with a singel dominator on a cast singel four intake for three years. Now looking to step up to a higher power level as well as getting a little of that fear factor maybe =;

So I need a basic tune up for the two dominators to start with. Main jets, transfers slot jets, main air bleeds, idle air bleeds idle jet.

I have a broad band O2 sensor and gauge in the car to help a little but no data aquisition.

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 Post Posted: Mon Dec 14, 2009 4:44 pm 
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If you check out the conversion section, I would start with the regular calibration for a 2 circuit Dominator. It will be close enough to start, using the O2's to dial it in from there. Not sure if anyone has a 2 Dominator setup to get you any closer, although the thought has crossed my mind.... :-$ :-$ :-$


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 Post Posted: Tue Dec 15, 2009 2:43 pm 
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I have read the conversion section three times but did not find a tune up for 2-circuit 1150 carbs. You mean I should try the same settings as a 1050 carb?

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 Post Posted: Tue Dec 15, 2009 7:15 pm 
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Most everything will be in the ballpark except main jets, 95 would be OK to start with.


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 Post Posted: Wed Dec 16, 2009 4:04 am 
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Ok.

Did some research and found that a 4500 list7320 is a 2-circuit 1150 model too. It has the following base tune up
MJ 95
MAB 28
IAB 53
Prim nozzle 31
Sec nozzle 35

I did not find out what the 7320 carb is designed for but I guess that it can serve as a baseline to work from. With the additional info in the conversion section about TSJ and IJ I think I have a base tune up covered for the 1150 carb list 9377 converted to 2-circuits as follows.

MJ 95
MAB 28
IAB 53
TSJ 65
IJ 40
Prim nozzle 31
Sec nozzle 35

I´ll take it from there and find the best main jetting at the track. Then add the PVs and PVCRJ.

Thanks for your help :-$

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 Post Posted: Wed Dec 16, 2009 7:18 am 
 
Sorry I am late to the party. Standard disclaimer, every engine is different, your results may vary, etc., etc. You have to fine tune your engine but this should run well enough to get you started. Because a street driven car usually has a unique combination of mufflers and tailpipes, the idle circuit is harder to predict.

Because there are twice as many idle circuits (with 2x4's vs. single), delivering the same amount of fuel to a similar manifold vacuum at a given small HP (therefore same amount of air flow), they don't need as much area in IJ's as a single carb. I have used as small as .025" IJ in 1150 2x4's on a Roots supercharged engine. The 2x4's seem to work better with small IJ's and smaller IAB's to get the necessary fuel at the upper end of the slots, than with larger IJ's and larger IAB's to keep them from getting too rich at the top of the slots. I hope that makes sense. IJ in the .040" range, like a single carb needs, will be slobbery rich at moderate acceleration and may get a level road blubber that you can't get rid of without a huge air bleed, that is then too lean further up the slot. That is my opinion this week, say tuned.

IJ .035"
TSJ .059"
IAB .052"
MJ 85-90
PVCR .078" -- .089"

I would expect the .035" IJ to be a bit rich, but start there and see if it doesn't want a larger IAB. If it gets beyond about .063" in the IAB and still is too rich in the T-slot throttle positions I would try a smaller IJ.

I realize you are tuning 1150's, but the last set of 1050's I highway tuned were down to #80 MJ and I though they could go smaller. However, those carbs had .093" PVCR's which seemed too big for that particular application. It was too rich at WOT so we dropped the jet to 80 trying to deal with that and it ran better at intermediate throttle too. The situation will be resolved next spring with some new (old school Holley) metering blocks with adjustable PVCR's and some dyno time. The car is in chassis shop jail for the winter and the carbs have been powder coated so the tune-up is starting over. The IJ was .031" with .059" TSJ and .052" IAB. The street cruising on pump gas did not foul #9 NGK's. Cam is a roller, 276-284 @ .050.

Street driven 4500 2x4's are sensitive to the location of the bottom of the T-slots in relation to the closed butterflies. It is best if the slot is just barely visible (.005" or less) below the closed tight in the bore throttle plates. Before modifying slots, loosen the screws and fit the plates if they are not close to being light tight or show uneven light leakage around the perimeter.


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 Post Posted: Wed Dec 16, 2009 9:48 am 
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This is what I found on what this 7320 carb is designed for...
Brand Holley
Manufacturer's Part Number 0-7320-1
Part Type Carburetors
Product Line Holley Model 4500 Dominator Carburetors
Summit Racing Part Number HLY-0-7320-1

Number of Barrels 4
Carburetor Flange Dominator
Choke None
Fuel Gasoline
Secondary Type Mechanical
New or Remanufactured New
Fuel Inlet Dual
CFM 1,150
Carburetor Finish Dichromate
Ford Kickdown No
Booster Type Annular
Throttle Linkage Type Universal
Quantity Sold individually.
Notes Designed for single 4 barrel set ups.

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 Post Posted: Thu Dec 17, 2009 3:56 am 
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Thanks to all for the feed back.

Tuner. Your comment on the idle jet makes perfect sense to me. Also, your comment on the transfer slot is highly appriciated, it makes sense to me after thinking about it for a while =; Thankyou.
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 Post Posted: Tue May 18, 2010 7:12 am 
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Update.

The basic tune up for the two circuit converted 9377 Holleys (2x1150) was:
IJ 036
TSJ 059
IAB 052
PMJ 85
SMJ 90
PVCR 078

Street tuning:
This proved to be way fat on the idle circuit. Rather than mess with the air bleeds I went straight to a smaller IJ 032.
Now the idle mixture is tuneable. Actually, I think I got it pretty good and the WB seem to agree. Runs and drives fine on the street. Real calm manners I would say.

Problems now: Idle rpm is a little too high. I´m working on that ( I suspect it might be a linkage issue and/or vaccumleak). Transfer slot not tuned yet- but I know there is no slot visible with the plates closed.


Track tuning:
Runs real fine on wot and jetted 90 square (no PV). I picked up 2 tenths in the 1/8 mile over the previous singel carb setup. But is way too rich at part throttle AND idle. I wonder why the idle circuit is affected?
I then tried it with a PV and 85 PMJ in order to have it run cleaner at part throttle and idle. This time it bogged big time when I mashed the pedal (on the trans brake). Must be a lean hole there but I dont understand why it it did not happen when it was square jetted. I think maybe smaller IAB can do something to help?

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 Post Posted: Tue May 18, 2010 8:36 am 
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Sorry Tuner is not around, been MIA as of late, but I will try to help.
As far as the idle speed, are there holes in the butterflies? if so, replace the blades. If not, make sure the blades are all closing completely, you may need to loosen them to let them square up in the bores and then tighten them back down. Last would be a vacuum leak.

What power valves did you use? You need to look at your engine vacuum when cruising, then go down 1-2 on the PV rating. If you go down too much it won't respond quick enough and leave a hole. T-slots may be OK as long as they are at the edge of the butterflies on a dual carb setup. If afterward you still seem rich at idle and LIGHT throttle, try going to .030's on the idle jets. If idle is OK and just rich on light throttle go down on the t-slot jets a couple at a time.


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 Post Posted: Wed May 19, 2010 2:17 am 
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No holes in the butterflies and I have already tried to position them in bores.

PVs are 4.5. Vacum at idle are 11". Don´t know what vacum is at cruise. But I see your point there. I may just stick in a set of 6.5 and see if it cures.

Thanks Mark.

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 Post Posted: Wed May 19, 2010 3:58 pm 
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Man I didn't pay attention to the dates and got all excited because I thought Tuner was back. [-(


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 Post Posted: Wed May 19, 2010 10:36 pm 
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Got me too!!! =;

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 Post Posted: Thu May 27, 2010 2:51 am 
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Ok. So I found a vacum leak. The t-ram top wasnt flat and it was sucking air at the base of the rear carb. After fixing that I now have 12" of vacum. But now the idle is hard to get clean. The idle mixture screw are out only 1/2 turn.
So, I might try go up a little on the IAB. But I suspect that will not be enough. Next step down for the IJ is .030.

Also tightened up the primary pump arms as they were a little loose.

The PV is now 6,5.

But the bog is still there if I hit it instantly on the t-brake. I can creep up on it though but that is not exactly how I want it on the starting line.

BUT the current main problem is the idle rpm. With the primary (and of course secondary) blades completly closed the idle still runs at about 13-1400 rpm. If I force the throttle lever by hand to close the blades even more the idle comes down. When I get some time for it I will try to reposition the blades to see it that helps with this situation.

And of course, the transfer slots are not even close to the blades.

The race series starts on saturday so the street tuning is canceled for a week or so.

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 Post Posted: Thu May 27, 2010 5:21 am 
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Some random thoughts.

Since the bog didn't show up until you went with PVs then that's what you need to work on.

Higher # PV might help. If you're pulling 12" HG at idle then you might be able to go as high as an 8 or a 10 on the PV to allow that circuit to come in sooner. This was once a common practice "back in the day" on the old 780 Holleys. Remember, if you got 12" at idle then at 2500 RPM it's likely going to be higher than that until you get closer to WFO.

Another thing to consider is that if you go to a smaller PVCR you will need more MJ and since that MJ will come in before the PV, that might help also but I do think I'd try the PV change first to see how it reacts to that.

If you open up the IABs that may lean the T slots at the same time. Leaning the transition circuit may make that bog worse and if that part works well for street driving now then you might not want to mess with it until you eliminate the PV stuff.

Dropping the IJ will have some effect on that also and may require a slightly larger MAB to compensate up top. The wide band will tell you whether this is the case or not.

Half turn on the mixture screws may not be THAT big of a deal as long as you CAN tune it there. I've read where several have had carbs that fall into this category.

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