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Old 07-05-2008, 05:12 PM
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SBC Questions not pulling hard up high

Ive been working on my 327 for quite some time now and just cant seem to get it to run the way it should.The motor is a 327 with trw pop top pistons,edelbrock 70cc alum heads,rpm intake,lunati roller rockers,4150 750 holley,msd 6al,msd pro billet distrib,536/554 solid lift camshaft and a th350 3500 stall.The problem is it just doesent pull very hard up top but has great low end...we have pretty much had the timing everywere with little or no diff on the high side.The msd pro billet distrib has had the vac advance blocked off and other then that its the way they come out of the box..could it be from the advance being blocked off or possibly the weights or springs in the distrib being wrong?Also the truck has a full 3" exhaust with flowmaster super 44 mufflers and over about 4000 rpm it will make like a kackel sound not like lean pop but like it has cherry bomb glass packs on it maybe that will help because it seems strange to me.Any help would be greatly appreciated Thanks

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Last edited by Highmarkx; 07-05-2008 at 05:19 PM.
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Old 07-05-2008, 05:24 PM
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What are your initial and total timing #'s? Which springs and what color stop bushing is in the distributor? What does the fuel system consist of? What kind of exhaust?
IIRC the distributor comes with a 28 degree bushing in it from MSD-perfect for grandma's sunday to church car' but not at all right for a performance engine.
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Old 07-05-2008, 05:29 PM
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Timing is at 32 deg.exhaust is full system 3" super 44s ceramic coated longtubes.fuel system 16 gal fuel cell holly blue 8an braided line summit fuel filter
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Old 07-05-2008, 05:47 PM
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Same answer I gave Cutty.....rig up a temporary fuel pressure gauge, mount it on the cowl and monitor it through the windshield while making a pass. The motor may be running out of fuel at the top. My first thought was valve springs, but I assume the heads are new.
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Old 07-05-2008, 05:48 PM
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Quote:
Originally Posted by Highmarkx
Timing is at 32 deg.
If that is the TOTAL Mechanical timing, it is way low. Bump it up to around 38 degrees.
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Old 07-05-2008, 05:57 PM
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Do you know the specs on the valve springs? How old are they? Timing at 32, is that the total or the initial? Rest of what you listed sounds good.
Do you know the actual compression ratio, accounting for gasket thickness, deck height, dome volume?
What is the fuel pressure set at?
What kind of plug wires?
Just trying to eliminate things from the picture.
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Old 07-05-2008, 06:00 PM
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We're also a little crippled here without cam duration specs. You might just have a cam that is wimping out before the rest of your components do.

Also, can you tell us where its wimping out? 5000 rpms? 6000?
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Old 07-05-2008, 06:08 PM
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Since I have never used a MSD module, I looked it up. Here is what I found.

"MSD 6AL, PN 6420
The 6AL shares the same proven circuitry of the 6A with the addition of a built-in adjustable rev limiter. The combination of powerful sparks with the safety of a Soft Touch Rev Control is what makes the 6AL the most popular ignition control in the world.
MSD first developed the Soft Touch rev control to prevent overrev damage to your motor in the event of a missed shift or driveline failure. The rpm limit is adjustable in 100 rpm increments with MSD?s plug-in modules. When the engine reaches your selected limit, the Soft Touch circuitry begins dropping the spark to various cylinders. On the next cycle, these plugs are fired again to prevent fuel from loading up in the cylinder. The result is a smooth and accurate limiting action without backfires or roughness.
The Soft Touch Rev Control also opens the door for you to add rpm accessories such as a Two Step Rev Control. A Two Step allows you to set two rpm limits, one for a holeshot rpm and another for overrev protection.
The 6AL is supplied with rubber shock mounts and modules for 3,000, 6,000, 7,000 and 8,000 rpm
."

My question to you at this point is which module do you have installed? If too low, that could be your problem. I strongly think your power falling off at the lower (4000 RPM range) figure is either ignition or fuel related or a combination of both.
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Old 07-05-2008, 06:24 PM
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The heads are brand new same as the springs i bought them complete.If i go any higher then 34-36ish it starts real hard but even set there it still doesnt pull right in the 4000 up range and still kackels in the higher rpms like a set of glasspacks...it will still pull in to the high rpms just not hard like i should.The motor never smokes a bit ever nt in start up not wot.....plugs look good....engine has msd wires ngk plugs...7000 rev chip...and it never really isnt wimping out it has a good low end romp but about 4500ish its just a dog but if u just flash the converter it will just torch the tires but from a roll just gettin on it u can really notice how bad it is even if you slam down a gear and nail it it just kind of falls off and kackels

Last edited by Highmarkx; 07-05-2008 at 06:40 PM.
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Old 07-05-2008, 07:10 PM
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What is the compression ratio and what fuel are you using?
Check to see if the coil pos+ and neg- are wired correctly.
Lets make sure we understand you- is the timing figure you are giving us total, initial, or locked at that #?
What rear gears? What does vehicle weigh?
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Old 07-05-2008, 07:15 PM
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total timing i think im setting it at above 3000 rpm? its a 76 shortbox chevy so weght not sure 4850 im thinking.10.5 to 1 compression 456 rear end ratio running 93 oct pump and i have ran turbo blue 110 once before didnt change a thing smelt real real good lol
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Old 07-05-2008, 07:28 PM
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Just checked coil orange to pos black to neg just like the instructions say I was hopeing it was backwards....also i have a 21 degree bushing in the distrib

Last edited by Highmarkx; 07-05-2008 at 07:53 PM.
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Old 07-05-2008, 08:11 PM
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Will it pull clean to redline in first gear?
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Old 07-05-2008, 08:17 PM
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Better then the 2nd and 3rd but not clean still kcackels and falls off a bit
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Old 07-05-2008, 08:25 PM
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Back to techinspector's idea, fuel pressure at WOT. Have you checked it?
Is this a 4x4?, if fuel pressure checks out it may just be "too much weight too little motor" at 5000 lbs.
What are the cam specs? What brand? I'm still thinking valve springs may not be strong enough.
What Edelbrock head?
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