Motorsports Village

Page 3 of 5

Author:  nomad [ Mon Sep 13, 2010 8:30 pm ]
Post subject:  Re: Emulsion

The last two runs in the elimination sessions are where I had to slow to avoid breakout. One I scrubbed off 1 MPH and the last 3 MPH.

Author:  nomad [ Mon Sep 13, 2010 8:43 pm ]
Post subject:  Re: Emulsion

I have saved only the smoothed logs.

Two areas concern me most. 1. That it's so fat in the burnout (4k or so RPM). 2. That there is a rise and a dip in AFR right at the shift.

Author:  shrinker [ Mon Sep 13, 2010 8:50 pm ]
Post subject:  Re: Emulsion

So as your lifting your foot a little bit its going rich?

Author:  nomad [ Mon Sep 13, 2010 9:21 pm ]
Post subject:  Re: Emulsion

Do you mean at the end of the run, shrinker? Yes on the last two passes.

At the shift point I don't lift as it's PG car. I suppose I could have lifted sooner on that second to the last pass. There was two seconds between us and I did catch him pretty quick.

While I can't say for sure but, I wonder about the level of fuel in the main well at the point where I shift.

What I'm getting at is these are BLP blocks with .028 orifices in the 1 and 3 e-hole position. Perhaps, at the shift, the fuel level in the main drops below the lowest (#3) e-hole and richens the mixture? Would another orifice in the #4 position flatten that out?

Author:  shrinker [ Mon Sep 13, 2010 10:44 pm ]
Post subject:  Re: Emulsion

You have 2 separate issues. It goes lean on the shift and it goes rich in the burnout. The lean on the shift is the fuel re filling the air well. When the booster demand drops due to engine RPM drop the air pulled in via the main air bleed to the emulsion drops too. So the fuel level in the main well back flows into the air well. While its doing that its not going out the booster so it runs lean. Once its stabilized the level in the air well again the main jet supply all goes to the booster.
The burnout is also the same problem with the top end. when your lifting the foot slightly its going rich, so its rich at part throttles. Thats because there is too much main jet flow. The main jet is not performing its function as the sole jetting device. If the main jet is too large the transfer circuit can pull too much fuel through when you back off a little bit. The main jet is supposed to control the fuel flow by referencing the pressure on the outlet side of the main jet with the bowl side pressure. The booster and t-slot combine to provide the outlet pressure upon the main jet and the fuel level in the bowl provides the inlet side pressure. If you have a problem with inlet flow lowering the level in the bowl too much, the main jet will have to be larger to get the AFR right at high demand then when the throttle is backed off the extra vac present at the T-slot is able to pull on the too large main jet and get the fuel easily. So they richen up. Correct booster design and emulsion and t-slot pressure control is what is needed to stop that. If the booster can provide good depression at high demand then the t slot is stopped from functioning. All the fuel goes to the booster and nothing comes out the T-slot.
Some of the problem with the leaning on the shift could be from booster design as well.

Author:  shrinker [ Mon Sep 13, 2010 10:47 pm ]
Post subject:  Re: Emulsion

It depends on what your requirements from the carby and engine are but running a smaller carby will smooth out these issues your mentioning. How much power is this engine? And why is it a race car running on pump fuel? Dare I say that if its got low comp for the cam then its always going to be wrong in some regards. Race cams need compression ratio and that needs appropriate fuels.

Author:  shrinker [ Tue Sep 14, 2010 5:20 am ]
Post subject:  Re: Emulsion

nomad wrote:
Would another orifice in the #4 position flatten that out?

When air is correctly used as a density and viscosity modifier the lower down the well you introduce the air the richer the mixture will be. The air doesn't enter down at the lowest bleed unless the pressure in the main well is sufficiently lower than the pressure in the air well. Where the air enters, is purely pressure balance stuff, when you have a row of bleeds say 5 of them the top bleed will flow air at very low booster depression. As the booster depression increases, the main jet and fuel level in the bowl interact to fill the fuel well. The resultant pressure in the fuel well then determines the air pressure needed in the air well to flow air through successively lower e-bleeds. If you change to a larger main jet the level of fuel in the fuel well will be higher at every measured point of the carbys CFM flow so the E-bleed influence is changed. The main jet restriction is the reason why the level in the fuel well drops, and that drop is the reason why the various ebleeds may or may not become active.
The main air bleed restricts the flow of air into the well so that the fuel well isnt overcome with just air. It also influences the pressure in the air well once air flow starts. For instance if the main air bleed is made larger then more pressure exists in the air well at any point in the carbys range. That causes air to commence flowing through each successively lower E-bleed at a lower carby CFM flow. The E-bleed sizes can be adjusted so that different positions receive different percentages of the total flow that's controlled by the main air bleed.
If the main air bleed is removed for instance, a large amount of air will flow through the E-bleeds at very low booster depression and the air flow will take the fuel with it so the booster will supply high fuel flow rates at low depressions. If you do this as an example test you will hear the engine fuel up that bad that it floods it as soon as the booster starts. If you block the main air bleed with a ballpoint pen and then rev the engine up you will starve the booster of fuel until it reaches high enough depression to lift the solid liquid fuel to the height to get across to the booster, so the engine will have a big lean flat spot.
Do those tests and you will understand that air blowing towards the booster from the air well actually encourages fuel flow. When you then extend this thought to high CFM flow and lots of booster depression you will realize that its the job of the main air bleed to act as the brakes on how much air gets flowing through the wells at flat out. The position and size of the E-bleeds effects where in the CFM rate the flow of air from the air well will enter the fuel well and blow towards the booster thus carrying fuel with it.
If you are into your own tuning then you need to do experiments to discover exactly what having an E-bleed in position 2 does verses position 5 etc.
The concept of E-bleeds is that the air should be sufficient to add tiny bubbles to the fuel well but not be so excessive that its becomes one large air blob at any point in the carbys range.
The rule to learn is' the lower down you introduce the air the lower will be the pressure on the outlet side of the main jet so more fuel will flow as a result of that.'

Author:  nomad [ Tue Sep 14, 2010 6:51 pm ]
Post subject:  Re: Emulsion

How much power is this engine? And why is it a race car running on pump fuel? Dare I say that if its got low comp for the cam then its always going to be wrong in some regards.

This engine made 818 HP@6600 and 717 ft lb of torque on BP 93 octane. Until now I've always bought my race fuel by the drum and because of the difficulties in handling drums alone i always bought two at a time. Then there's cost. So it's best now that I use 93 octane swill.

The cam is an off the shelf grind from Bullit that John Partridge recommended. it's low compression about 10.2:1. This is an all parts from a catalog engine and will be the last I build from scratch. I'll freshen and maintain but, no more new directions. It's as fast as I want to go. I never expected to make this much power. My target was 675 to 700HP or so.

What you've just posted above makes sense even to me, so thanks. Lots to think and consider.

Author:  nomad [ Mon Sep 20, 2010 10:03 pm ]
Post subject:  Re: Emulsion

This weekend's logs. I don't have the notes in the logs but they are unsmoothed.
The car went 5.840 for the first two passes, 5.848 for the third, then 5.811 and 5.816. Time trial 2 log is not here, I forgot to turn on record #-o
It ran clean all day and was a tick leaner than last week. I reduced the PMJ by .002 and TSJ and PVCR by .004 over last week. It'll start with just a touch of the starter where I see others grind away to start.

Tuneup is as follows and the same for entire day.

P&SIJ .040
P&SIAB .065
PVCR .0.059 front only
P&SMAB .028
P&MTSJ .0.055
PV 4.5
e-holes .028
Metering blocks are of BLP manufacture
angle channel .157
.500 center 12 hole billet booster inserts (flat bottom) and .980 boosters banjos.
The last pass I pedaled it the others all full passes.

Logs first 5 sessions are last weeks runs unsmoothed.
For shrinker to see.

Author:  shrinker [ Tue Sep 21, 2010 1:10 am ]
Post subject:  Re: Emulsion

Well it all looks good. if you could get the burnout a bit leaner you would be happy huh? try a smaller IFR for a start. I also think your main jet is little on the large size, is that a number 100 main jet or is it .100" diameter that your listing.
In any case the main jet is obviously not the focal point of control in the burnout so its possibly a bit on the large size but if you made it smaller then the engine would run too lean up top so it might be a booster vacuum generation thing. Hard to tell across the net and its something that you really need to experiment with and see for yourself.
But if you go down to maybe a .038" IFR that will start to clean up the burnout without much effect at the top end. So some experimenting is needed. You will get the feel for the tuning as you go.
One thing to be careful of with O2 sensors is that the AFR answer they provide is not always accurate. They are predominately affected by the CO content of the exhaust. If the CO is high for whatever reason, say not optimum timing coupled with a little too much fuel at moderate load like in the burnout, then the AFR reading will be really high. So when you change the jets etc and the AFR doesn't change in line with the jetting areas then it possible that you have high CO stuffing up the readings. This is a trap that many people fall into, they need to use gas benches or even an old fashioned CO meter and not WB's.
With experience you can tell if an engine is making CO from the sound of it. If its dull and bassy then its probably CO city in there. If its crackly then its not. Sharp cracking exhaust sound is generally normal CO levels with correct CO2 relationship.

Author:  Slowpoke [ Tue Sep 21, 2010 8:03 am ]
Post subject:  Re: Emulsion

I leaned out my burnout by opening the PVCR to .089 and ended up with an 84 Holley Jet in the Primary (Secondary jets are 92 Holley Jets)

My Carb is an 8896 1050, 3 circuit (converted to 2 circuit) with annular boosters

Pri & Sec IFR .039
Pri PVCR .089 with 6.5 PV (Hi Flow)
Sec PVCR .069 Plugged
Pri & Sec angle channels .159
Pri main jets 84
Sec main jets 92
Pri & Sec T-Slot jet .052
MAB .025
IAB .076

That's what works for me.

Author:  nomad [ Tue Sep 21, 2010 2:08 pm ]
Post subject:  Re: Emulsion

Shrinker, thanks for your input. You, too slowpoke. I use BLP jets and parts as they are 20 miles away.

A 100 BLP jet is the same orifice as a Holley 88 jet (.100) I believe. I understand they're not the same in flow, however. Fortunately BLP rates thier jets in lb per hour. Holley is ccs so it'll be just a math conversion.

I was a little confused on the AFR in the water box being rich. There, we have a fair amount of RPM, 4000 or so, but, very little throttle opening needed to maintain that. I was pretty sure the TSJ is still in control at that point. Maybe, as mentioned there is more main jet working than I thought. It's not rough in the burnout, just not as clean as I'd like it.

I had thought about an .039 IJ to lean that circuit. I'll also work on that PVCR also. I can see now that it works.

The best 60ft that night was 1.28. not bad for a 33" tire and a 4.10 gear. I've run 5.67 before and have had a 1.25 60 ft. However, that was in drive it off the cliff weather last January.

Author:  Slowpoke [ Tue Sep 21, 2010 5:25 pm ]
Post subject:  Re: Emulsion

Bruce, if you want to check it out before you drill out the PVCR just bring your engine up to your burnout rpm in neutral or park (not against the transbrake) while logging and compare your AFRs to your burnout AFRs. They should be very close. Then start taking primary main jet out of it, and see what effect it has on your AFRs. If it makes it leaner, you're working on the right circuit. Don't put a load on it while you're leaning the main jets. If it doesn't affect the reading, try leaning the T-slot jet or the idle jet. My money is on the PVCR.
You can get it real close this way and have a good idea how big to go when drilling the PVCR.
Good luck!

Author:  nomad [ Sun Oct 03, 2010 8:47 pm ]
Post subject:  Re: Emulsion

Should I be reading these logs using the Lambda scale?

Author:  nomad [ Wed Oct 20, 2010 8:39 am ]
Post subject:  Re: Emulsion

Data from recent Div 2 race. Note that these runs are on a throttle stop. Weather details are on second session. The weather did not really change the whole day.

Page 3 of 5 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group