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Discussion Starter · #1 ·
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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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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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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Discussion Starter · #8 ·
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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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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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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Discussion Starter · #12 ·
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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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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Discussion Starter · #14 ·
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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Pupsvette76 said:
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.

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.

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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Discussion Starter · #16 ·
my distributor is strictly mechanical advance and my initial timing is at 16degrees but i should use lighter spring

in order to fix the lean condition what should i do increase jet size, float height?

should i bring the timing back down from 16 to 10 it idles better at 16

as far as detonation goes i thought i heard some jingling noise really quiet though i just never heard it before so i dont know what it sounds like it may not have been detonation at all
 

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Pupsvette76 said:
my distributor is strictly mechanical advance and my initial timing is at 16degrees but i should use lighter spring
If- when you look at the total timing w/a timing light- you see there's still advance coming in over 3000 RPM, I'd say yes, lighter springs (or heavier weights).

in order to fix the lean condition what should i do increase jet size, float height?
IF there's a lean condition, larger jets will make it richer. Float height will also bring enrichment in sooner.

should i bring the timing back down from 16 to 10 it idles better at 16
As long as the total timing- as read w/a timing light- isn't over the maximum allowable total, 16 is fine, IMO.

as far as detonation goes i thought i heard some jingling noise really quiet though i just never heard it before so i dont know what it sounds like it may not have been detonation at all
Put it like this: If the engine's detonating at a steady 3000 RPM, no load and no boost to speak of, it will be terminally detonating under load.

That said, if the total timing- as read w/a timing light- isn't over the maximum allowable, and the plug heat range is correct, and the carb's jetted rich enough, and the octane's high enough, and the engine's not running too hot, the engine won't be detonating. ;)

But back to your specific deal.

See what the total timing is, and at what RPM it's all in by. From there, you can figure what you can get away with, AFA how much initial, and whether you can run lighter springs or heavier weights on the centrifugal advance, etc.

At some point, you're going to have to actually take it out on the road and load the engine in order to get a plug reading of some sort, unless you have an exhaust analyzer.
 

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Discussion Starter · #18 ·
i have a question

which is true?

do smaller squirter bring fuel sooner with a longer duration?
and do larger squirter bring more fuel at a slower rate?

what is the differeance between jets and squirters?
 

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Pupsvette76 said:
i have a question

which is true?

do smaller squirter bring fuel sooner with a longer duration?
and do larger squirter bring more fuel at a slower rate?

what is the difference between jets and squirters?
The size of the 'squirter' only changes the quantity of fuel, not the 'timing' at which it is supplied.

The accelerator pump adjustment changes the 'timing', as far as, when it starts, and ends. This is accomplished using different pump 'cams'.

The jets are 'sized' to the amount of fuel passed through them. They are the main source of fuel used during full throttle, or steady throttle events.

The 'squirter's' only function during acceleration events, to add additional fuel.

Hope this helps.
 

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Discussion Starter · #20 ·
so if i get a carb pop off immediately off idle that means there is not enough fuel getting to the engine faster enough and i will want to change accelerator pump cam does having a mechanical advance distributor contribute to this problem
 
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