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Old 04-25-2007, 12:48 AM
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Engine falls over above 5000rpm

Here's the problem,
The car a 540Ci powered BBC producing just under 600hp on the engine dyno and just over 400 at the rear wheels. It is leaning out badly at around 5000 revs, it runs a nice 13.7 Afr up to that point then leans out sharply, if you come off the throttle for a second then stand on it again it makes power to 5k revs again then falls over again.

Fuel system,
Tank outlet at the bottom rear of tank,
1/2 line to Areomotive fuel filter,
1/2 line to 170gph Holley black mechanical pump,
1/2 line to Areomotive dead head fuel regulator (set at 7 psi),
3/8 line to fuel bowls (4150 series 950 Holley).

The fuel pump maintains 7 psi pressure even when the motor leans out.

I have tryed an electric pump feeding from a fuel can with on improvement. It was set up as follows.

fuel can on bench above carby height,
1/2 line to pump,
1/2 line to regulator,
the rest as above.

Could I be correct in suspecting that the fuel level is dropping in the fuel bowls. If so what are your thoughts on correcting the problem?

Would replacing the 3/8 carby lines with a 1/2 inch setup and allowing the regulator to feed one bowl per reg outlet increase flow enough?

Are there any high flow needle and seats available that may help?

Another thing, the engine is happy to rev to 6000 rpm in first and second at the strip but falls over in top.

Thanks for advance for any help/ideas you may have.

Happy tuning

PINKO351

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Old 04-25-2007, 06:38 AM
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Dead head regulator sounds like it's causing your troubles. Read this as to why.
Lots of good info here, but the stuff at the end would be of the most interest to you I think.

http://www.centuryperformance.com/fuel.asp

Hope it helps.
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Old 04-25-2007, 04:10 PM
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Uh... Has the carb been jetted for this size engine...? If its just the factory jetting then its most likely to small on the main jet size...?
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Old 04-25-2007, 05:48 PM
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I would also investigate the air bleeds. If they are tunable you can use them to taylor your fuel curve. I am also curious what you are using to determine AFR. If it is a WB02, then I think you are good.
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Old 04-25-2007, 06:36 PM
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Thanks for the reply's,

I believe the jet size is correct as it is fine up to 5k (it also works fine in the lower gears), and the AFR was repeatable on both dyno's. When origanally on the engine dyno I don't think RPM was sustained during the power pulls, hence the leaning out was not found till we run it at the strip. And to answer your question the carb is not out of the box, It has been tuned for the engine.

As for AFR, this was obtained be means of stuffing the prob up the exhaust pipe, name of such device not know to me. Once again repeatable on both types of dyno.

As for the dead head reg being the problem, we chose this reg as it is used on engines at the track. They are the same Ci and develop more HP then our engine. The difference is they are running Dominator carbs. We will be back at the dyno on Monday night with a borrowed 1150 demon.

After searching the WWW. I think we need to increase bowl size with bowl extensions, fit high flow needle and seats and up grade reg to carb fuel line to 1/2 inch. Or if the 1150 works we may get our own 4500 Dominator 1050/1150 carb. Easy way out but more money!

For anyone wondering why the dyno guys can not help? Our engine builder (engine dyno) is currently in the state's working for GM and the Chassis dyno guy is a 4's and Rotor injected freak. The Chassis dyno is handy to home and he's happy to allow us to play after hour's on his dyno!

Thanks again

PINKO 351
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Old 04-25-2007, 11:25 PM
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Doc here,

What Ignition system are you running?

Doc
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Old 04-26-2007, 07:21 AM
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If everything is flowing properly you should not have to run bowl extensions, or fuel line from your regulator to the carburetor. We routinely work on engines producing two to three times the HP you are without bowl extensions, and with 3/8 lines from the regulator to the carburetor. A dead headed regulator system can handle this very easily on a drag race car if everything is plumbed and working properly.

Pressure, and volume are independent of each other you can have 7lbs of pressure flowing 50 GPH, or 7lbs of pressure at 400 GPH. The first thing to do would be to flow test your fuel system to see how much volume it is flowing.

Does the car break up at 5000 RPM in each gear or just in one or some? If it does this at a specific RPM in each gear its most likely ignition related not fuel related.
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Old 04-26-2007, 10:13 AM
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Top end lean out is pretty common. There's lots of things to fiddle with the Holley jet's, air bleeds, emulsion tubes, boost venturis, and power valve.

I'd first want to be sure the power valve comes in. Then you might want to richen the secondaries a couple sizes to see how it reacts.

One needs to consider that under acceleration the fuel runs away from the secondary jets.

This of course assumes the valve springs aren't crapping out at 5000. when this happens the engine just tends to lay down till the revs drop.

Oh, Oh, Oh! I just went back and reread your original input where you said the engine holds up in the lower gears. Yeah this might be just not enough gear ratio, you've just reached the point where it's done pulling in the top cog. You want to go back in the rear gears and use a ratio that puts the engine going thru it's horsepower peak revs as it passes thru the traps. That will have it pulling as hard as it can all the way through the quarter.

I presume you're running an automatic, if so what is the stall. What are the cam and compression specs?

Bogie

Last edited by oldbogie; 04-26-2007 at 10:28 AM.
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Old 04-26-2007, 08:21 PM
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Thanks again, more info as asked,

Ignition, is a MSD Billet Disy, MSD 6AL, MSD Mega Blaster Coil, Eagle 9mm HT leads and NGK plugs (Can't remember Pn but new and all firing).

Drive Line, Hughes 3500/3600 Stall, Full manual T400, mini spooled 4.11 nine inch and 29*12.5*15 slicks.

Engine runs if memory serves me correctly 10.5 comp, runs on Australia BP 98 RON with octane booster. We use BP fuel and Winn's booster all the time.

Cam specs not at hand. It is a roller with plenty of valve lift and duration, will find spec over the week-end.

Please remember we are talking about the Holley 4150 series 950 carby, which has secondary jet extensions and it sill leans out on the chassis dyno. Hence G loads are not a factor. Please refer to original post for fuel set up.

Engine is happy to rev to 6000 in first and second, however it is only there for a fraction of the time it is held in top.

If it was ignition I would have thought it would go rich as there would be unburnt fuel passing thru the cylinders, any thoughts on this?

I still think it is the fuel level in the bowls dropping to a point where the carby can no longer meter a suitable mixture, Comments?

I have looked at the power valve and it is serviceable, however it is a 8.5 valve and the engine has about 4-5 inches of vacuum at idle. This would lead me to think it is open all the time, unless decelerating.

Looking forward to your thoughts - there is a simple fix for this just need to pin point it!

PINKO351
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Old 04-26-2007, 09:42 PM
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An 8.5 power valve with 4-5 vac at idle? First thing, your power valve should be about a 2.5 with 4-5 vac at idle. It is open all the time as you suspect. Change the power valve and bring along some larger jets to the dyno as youre going to be needing them to get your afr back up to where it needs to be when under 5000 rpm. Also you may be pushing 7psi with the fuel pump you have but that doesnt mean you are pushing enough volume to keep the bowl full and the jets covered. Could be that the pump is undersized or just wore out and the pump arm is floating at higher rpms. If it were me id straighten out the pv/jets and do a couple pulls on the dyno and see if your problem persists. If it does, replace the pump with one rated at a higher volume of flow. This would be the logical first steps if it were me having this problem.
Edit: After rereading your posts, the pump you have should be plenty as far as volume goes. Could still be a weak spring on the pump arm allowing it to float or even a pin hole in the diaphragm.
Mike

Last edited by kane583; 04-26-2007 at 09:50 PM.
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Old 04-26-2007, 10:01 PM
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Just to add to my last post,

With the power valve you have installed, it should be dumping fuel at idle causing the engine to run overly rich at idle. Im not sure that you could even lean the idle circuit enough to compensate. I doubt it. Is it showing a rich condition on the dyno at idle? Have you looked down the throttle bore and noticed excess fuel dumping in the carb? Once you have that straight I would think you are going to need to jet up around 8 sizes in jets to richen the system back up to the correct afr.

Mike
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Old 04-26-2007, 10:33 PM
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I don't claim to be an expert ... but I am under the impression that a power valve is used to provide additional fuel in the transition stage ... until venturi vacuum is established and fuel is drawn through the main jets. At 5000 RPM, this should be WELL established, shouldn't it?

Also, at WOT there should be almost zero vacuum, and the power valve (regardless of rating) should be wide open anyway ... right?
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Old 04-27-2007, 12:05 AM
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Doc here,

In addition to any fuel issues your checking out...

Is the Dizzy an 8365 Pro-built Billet Dizzy?

AND do you have a built in Rev limiter? It may be out of adjustment.

Generally Speaking,under optimum operating conditions, stock Ignitions good to 4500/5500 RPM, Performance Ignitions Good to 8000/8500 RPM's, And CDS and Mag type , good to over 10,000 RPM's..

Running a performance Ignition with a "Weak" module could kill top end..as well as any other "WEAK" part of the system. but still run good at lower speeds..

A Mal~Adjusted Rev limiter WILL kill the top end If set too low..IF you have one check adjustment..

Internal Cap Cross fire can cause a top end dead spot (but you should have other noticeable problems like spit back.)

An otherwise Good coil, may be weak under FULL load..you might want to swap it out with a known good one (blasters do have their problems.)

Check your wire to your Coil..under gauge wire will current swamp the coil..(turning current into heat in the wire doing NO useful work and making a performance Ignition run worse than a stocker) Most don't think a Coil will draw that much current, believe it only draws an amp or two..and that is where they go wrong..a stocker can draw up to 15 to 20 amps!

A performance Coil (Blaster) WILL draw up to 48 amps..Just apply a little OHMS law ..
  • Coil primary resistance = .3 OHMS,
  • Working Voltage = 14.4 Volts..
  • Current draw will be :48 AMPS (yes I said 48 amps!)
  • At 691 WATTS! (About 1/3 The Wattage of an electric Space heater in your shop!)

Under FULL load..THAT wire should be at least 10 gauge, not a puny 14 gauge supplied by the stock harness. At top end , you MAY be current swamping the coil.

IF it were falling off at top end and over~fueling the cylinders, I would assume the burn Return would be so quick that it would leave no noticeable traces..at least at those RPM's..You MIGHT see "Puffs" of smoke out the back (like a fueler with not all the candles lit..but I doubt you'd notice it..)

Just some Electrical things to look at..Induction is not my Fortay..There are more here Way better qualified at that then I..

Hope it helps a bit , at least in including or eliminating a problem.

Doc
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Old 04-27-2007, 06:13 AM
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Quote:
Originally Posted by Pinko351
Thanks again, more info as asked,

Ignition, is a MSD Billet Disy, MSD 6AL, MSD Mega Blaster Coil, Eagle 9mm HT leads and NGK plugs (Can't remember Pn but new and all firing).

Drive Line, Hughes 3500/3600 Stall, Full manual T400, mini spooled 4.11 nine inch and 29*12.5*15 slicks.

Engine runs if memory serves me correctly 10.5 comp, runs on Australia BP 98 RON with octane booster. We use BP fuel and Winn's booster all the time.

Cam specs not at hand. It is a roller with plenty of valve lift and duration, will find spec over the week-end.

Please remember we are talking about the Holley 4150 series 950 carby, which has secondary jet extensions and it sill leans out on the chassis dyno. Hence G loads are not a factor. Please refer to original post for fuel set up.

Engine is happy to rev to 6000 in first and second, however it is only there for a fraction of the time it is held in top.

If it was ignition I would have thought it would go rich as there would be unburnt fuel passing thru the cylinders, any thoughts on this?

I still think it is the fuel level in the bowls dropping to a point where the carby can no longer meter a suitable mixture, Comments?

I have looked at the power valve and it is serviceable, however it is a 8.5 valve and the engine has about 4-5 inches of vacuum at idle. This would lead me to think it is open all the time, unless decelerating.

Looking forward to your thoughts - there is a simple fix for this just need to pin point it!

PINKO351

You may be dealing with a fuel delivery problem, but I'll ask again have you actually flow tested your system to see how it's performing?

Has changing your main jets helped when the car starts to break up, or affect your 60' times at all? This information is helpful in determining if it's fuel delivery or not.

Actually though, if you have a fuel system problem it's usually more apparent at the top of first, and second gear (right before you shift) because that is when the engine has the most load on it due to transmission gearing.
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Old 04-27-2007, 06:39 AM
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TECH @ BG,
I intend to complete the flow test as soon as I get a chance, will report the results some time over the week-end.

Thanks again to all and i intend to check all things mentioned.

PINKO351
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