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Old 07-24-2006, 04:18 AM
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SBC misfire

I have a misfire problem with my car, I've got a shoebox nova with a sbc/muncie 4 speed/ 4.11 9" combo.
Engine has-
forged bottom end, 9.3 static compression(91 octane)
solid flat tappet cam 490 lift 240 degrees @ .050
sportsman 2 iron heads
pertronix billet distributor
speed demon 650
super comp fenderwell headers
327ci

The car is real light, and the engine run's real strong on the low end. Problem is around 5000+ RPM's there is a random misfire, I shift as soon as I feel it, but I believe the setup has got to make max power around 6300-6500RPM. Initial timing is set at 16 degrees. A lot of people I've talked to have told me that the pertronix dist. is capable of high RPM's out of the box and that an ignition box isn't required, but it's one of the only things that hasn't been covered. I'm planning on running nitrous in the near future and will run a box then, but is it needed now?

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Old 07-24-2006, 06:51 AM
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Either your running out of fuel or out of spark. Check both the fuel system and the ignition system. One way of checking the ignition is too look at the spark, if it`s yellow it`s weak, if it`s blue it`s okay.
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Old 07-24-2006, 07:02 AM
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One of the best diagnostic tools is a fuel pressure guage. Mount it at the cowl so you can monitor fuel pressure under load and at the rpm the miss occurs. You want 5-7 psi, any less may cause problems. What kind of fuel pump are you running and what size fuel lines.

Steve
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Old 07-24-2006, 07:47 AM
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A 327 with a 240 @ .05" cam should have a power peak well in excess of 6500 rpm, ours is above 7000. Have you checked the valve springs?
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Old 07-24-2006, 07:59 AM
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I'm thinking springs also.
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Old 07-24-2006, 08:40 AM
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miss

You listed your initial timing but what is the total timing set at???

What fuel pump is on it???

Is that distributor what they call a stock replacement??? If so the stock style HEI modules all but quit right around 5500 rpms...

Do you have a true 12 volts to the distributor????

what spark plugs are in it??? when was the last time you changed them??


Keith
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Old 07-24-2006, 11:40 AM
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welcome to the site

I'll take a complete MSD system anytime.

As an observation I would like to make a general comment. We see this all the time on this site as well as at the strip and the cruises.

Not being mean, just observant for many years.

Too many people want to build a high performance engine and then cheap out on the valve train and the ignition systems.

They would save themselves a lot of anxiety and $$$ by spending the extra on an excellent proven system at the very beginning.


www.readershotrods.com
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Old 07-24-2006, 12:25 PM
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Quote:
Originally Posted by xntrik
welcome to the site

I'll take a complete MSD system anytime.

As an observation I would like to make a general comment. We see this all the time on this site as well as at the strip and the cruises.

Not being mean, just observant for many years.

Too many people want to build a high performance engine and then cheap out on the valve train and the ignition systems.

They would save themselves a lot of anxiety and $$$ by spending the extra on an excellent proven system at the very beginning.


www.readershotrods.com
I'm 24, had this car since I was 19. Not one person in my family is remotely into cars, besides my younger brother with his dodge demon. The car is a complete project that's finally starting to see some street time. I make no money and have no resources, this is the best I can do.

I'd give anything to have some family that could point me in the right direction, but until then i blow up motors, thats how i learn.

BTW every kid around here has a full ignition setup, valvetrain, heads and all that and is frying 1 tire down the road thru a 3.08 open diff. It is MY observation that people like to cheap out on suspension, rear end, and brakes.



.....and my spring seat pressure is 140 lbs, i've got 1 piece chromoly push rods, guide plates, roller rockers all the goodies, i wouldn't say i "cheaped out" on the valve train,
carter high flow mechanical pump- 6 psi, 1/2 lines( yeah i know, im upgrading to a electric unit soon)
it does have true 12 volts to the coil, and has autolite AR-13 race plugs, brand new

the distributor is not an HEI style,but i do believe it is a stock replacement, with a billet housing. I haven't checked total timing, i've always just adjusted the base timing and gone from there, i guess that's next to check.

Thanks for the replies, ill keep this thread updated until the problem's solved
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Old 07-24-2006, 01:12 PM
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miss

Well we are not getting into the valve train until we go through the basics first.....lets not put the cart before the horse guys....

So it's a points style distributor??? or an electronic like a msd with a remote coil???

If you have 12 volts at the coil your one step closer to solving the problem.....

We really need a total timing figure before you go any futher.. It would be not be smart to keep guessing at the problem if you only have say 25 degrees of total timing...

Keith
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