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Old 07-06-2009, 09:55 PM
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glowing headers and backifiring HELP!!

hopefully you guys can help me

i just finally got my car back together and running my problem is that my header glow when i hold the engine at a certain rpm above idle i held it at about 3000 and they started to glow also i get a backfire if i hit the throttle to fast when i open up the butterflies fast form idle it backfires

here are some specs maybe they will help

sbc 350
weiand 177 blower
msd
holley 750 double pumper
488 cam
edelbrock rpm heads
fuel pressure is at 6 psi
cam is installed straight up
timing is at 10 deg btdc

it seems to run way better when i put more timing in it but weiand recommends not putting any more that 6-10 deg of intially timing. Does that change is i have a strictly mechanical advance distributor as opposed to mechanical and vacuum advance?
the engine holds 15 hg/mg at idle just fine
thanks in advance for your help

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Old 07-06-2009, 10:15 PM
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It's either lean or retarded timing or both, right? You need some sort of boost reference for enrichment.

If it's a new engine, then yeah they run hot at first also.
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Old 07-06-2009, 10:28 PM
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the engine is new what would you do to fix the problem i can put more timing in it but how can you put more fuel in it with a boost reference carb
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Old 07-06-2009, 10:42 PM
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I think you need a little of both timing advancement, and larger jet's in the carb.

Right now you are at 12 degrees base timing, what happens when you advance this to 16 degrees, maybe 18, or 22? Does it cool down?

As far as the carb jetting, run it up to 3000 rpm, and induce carb spray, or a propane mist over the carb. Watch your headers to see if they start to cool down. This will let you know if the carb is too lean. With this test, I'll bet the rpm's will increase by a whole bunch.
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Old 07-06-2009, 11:40 PM
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do you think 16 18 and 22 is to much base timing? and what do you mean by induse carb spray
great help keep it coming
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Old 07-06-2009, 11:47 PM
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Quote:
Originally Posted by Pupsvette76
do you think 16 18 and 22 is to much base timing? and what do you mean by induse carb spray
great help keep it coming
Spray it into the carb's airstream to richen up the A/F charge.
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Old 07-07-2009, 01:56 AM
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You do not have enough initial timing. Roots blowers love initial timing and it is very important for performance and cooling. In most cases you will need to be in the 18-20* range initial. This may require you to recurve your distributor to limit total timing. You don't want the total to be more than ~34* max and will probably end up around 32* depepending on how much boost you're making. You will notice much crisper throttle response, very responsive.

I have no idea why Weiand would tell you to retard the timing that much. I'm sure they are trying to be conservative, but that's not going to work with a roots blower (as far as timing), I'm sure they are worried you will have too much total.

Set your initial at 18* and see how it runs there, but don't go out and jump on it just yet. Come back and check your total timing which should be all in by 3200RPM so rev it to 3200 in park and check your timing. Make sure it's not over 34* MAX. You can tune from there. Once you set your timing you will need to go back over your carb tuning as well.

Your lean condition is a separate issue and will have to be tuned as well. Are you running a power valve? If so what rating is it? If not (powe valve plugged) make sure you jetted up the secondaries 8 - 10 sizes.
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Old 07-07-2009, 11:06 AM
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when i had the car running the yesterday i played with the timing and it ran much better at about 18

my carb have a manifold referenced power valve

does boost ony come under load or would i make boost when stationary in neautral i know with turbos there must be a load to make boost but what about blowers my boost/vac gauge hasnt ever seen boost

so you think jump up a few jet sizes in the secondaries?

great help thank you
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Old 07-07-2009, 11:47 AM
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Boost will only come on under a load.

You will need to play around with the jet sizes, primary and secondary, so that your spark plugs will look a dark grey in color. It is necessary to run it a little on the rich side.

You may need to go up 8 jet sizes, to achieve this. It is better to start the rich side, then drop it down a couple of jets if it is too rich.
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Old 07-07-2009, 12:54 PM
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10 more degrees of timing will cool the headers.

And you need a boost retard system (msd).
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Old 07-07-2009, 05:12 PM
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As mentioned you will only see boost inder load and you will only see full boost under load and WOT. It is very possible to drive a blown car around all day and never see any boost. That doesn't mean you're not making power, it just means there is no back-up in the intake.

Rich is good and that's where you want to start. Lean will break stuff.

Make sure you check your total timing or you might be asking for trouble.

A boost retard may be needed, but that will depend on how much boost this combination makes. anything over 8lbs and I would start dialing back the timing. I have mine set up that way.
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Old 07-08-2009, 12:16 AM
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i have heard of these boost retard systems but what are they what do they do does it replace a spark box or work in conjuction this is my first boosted car so bear with me thanks for your patience lol
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Old 07-08-2009, 07:48 AM
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A boost (timing) retard box works in conjunction with the control box. It has a vacuum hose connection, which gets hooked up to a intake manifold connection. I strongly recommend using small zip ties at the ends of this hose connections. When you get under a boost situation, the intake manifold switches to pressure, thus the 'boost'. This is adjustable from 1-3 degree retard per pound of boost.

As already pointed out, blown engines need a lot of base timing, and it is best to lock out your mechanical, and vacuum advances. Set your timing between 34-38 degrees.

As an example of the function of a boost retard box, say you have your timing set to 38 degrees, and the retard box set to 1 degree, and you are under 10 pounds of boost. Your timing will be retarded by 10 degrees, making it 28 degrees.

This helps to keep the bottom end together, even more so when running cranking compression ratios of 9.0-1 or higher.

Hope this helps.
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Old 07-13-2009, 11:47 PM
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ok so today i finally got a chance to put so timing tape on the balancer and put so more timing in it

well it definitely idles better and the headers arent glowing anymore but if i hit the throttle fast it still backfires

the timing is at about 16 degrees... also when i hold the car at anything higher than 3000 rpm it seem to me than i am getting some dentonation

not really sure ive nver actually heard detonation is it loud? is it really high pitch? does it sound like a bell jingle?

how can i keep the car from overadvancing?

your guys help is really helping this car come together thank you
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Old 07-14-2009, 04:01 AM
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Quote:
Originally Posted by Pupsvette76
well it definitely idles better and the headers arent glowing anymore but if i hit the throttle fast it still backfires
Can you define "backfire"? Are you referring to a pop through the carburetor, or a bang from the exhaust? If it's through the carb, it may be a lean pop, caused by insufficient accelerator pump duration and/or shot volume. Try a bigger shooter and/or a bigger pump cam.

Quote:
when i hold the car at anything higher than 3000 rpm it seem to me than i am getting some dentonation

not really sure ive nver actually heard detonation is it loud? is it really high pitch? does it sound like a bell jingle?
What indications are you seeing (hearing?) that make you think the engine's detonating?

Usually, you wouldn't expect to have detonation at a steady-state, no load/no boost condition unless the timing was really excessive. Under no boost, the engine is going to behave much like any NA engine would be expected to behave. The only real difference will be that there's not as much timing as a NA engine would like to have, but that's a necessary evil when using analog timing.

That said, at 3000 RPM the mechanical advance is likely all in, so you need to know what the total timing is at. If it is still able to advance more if the RPM is increased above 3000 RPM, lighter centrifugal weight springs need to be used.

Quote:
how can i keep the car from overadvancing?
The methods vary w/the type of distributor you are using. An HEI has a slot and pin arrangement that limits total advance, aftermarket distributors can use bushings to control total advance, etc.

A couple thoughts:
Weiand's limiting of initial to 10 degrees is OK, as long as the mechanical advance will come in quickly- all in by 2500 RPM. But I wouldn't hesitate to use more initial timing- as long as the plugs look good, the carburetion is on the rich side and that the total timing isn't excessive.

Don't forget the plug heat range. Too hot of a plug will have you chasing detonation problems that seem like they shouldn't exist.
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