Absolutely would be the first thing I would check for. No cost checking for an exhaust leak.
exhaust backfire
- Thread starter Jbarker
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Absolutely would be the first thing I would check for. No cost checking for an exhaust leak.
OK you have pretty much ruled out mechanical problems at the engine.
Let's try to figure out if the backfire is happening from the head down to the H-Pipe, (before the H-Pipe).
Or if the backfire is happening after the H-Pipe?
There again is the backfire happening before the mufflers or after the mufflers.
As loud as you say it is to make babies cry, would it be after the mufflers?
Let's try to figure out if the backfire is happening from the head down to the H-Pipe, (before the H-Pipe).
Or if the backfire is happening after the H-Pipe?
There again is the backfire happening before the mufflers or after the mufflers.
As loud as you say it is to make babies cry, would it be after the mufflers?
Maybe uncap the headers and see if it does it.
I like this idea ^^^^^.
Process of Elimination
My thought was to put a stock manifold on the passenger side and see if it still backfires. But uncorking the headers could provide the same results.
Process of Elimination
My thought was to put a stock manifold on the passenger side and see if it still backfires. But uncorking the headers could provide the same results.
512Stroker
We are all here because we are not all there.
Can you try a different box?
yellow rose
Overnight Sensation
I know you have a HyFire. Which one is it??? There are several part numbers. I doubt it’s the box, but I’m curious what you are using. And the coil.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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induction crossfire?
That could happen with a Single Plane intake manifold.
Inertia
Well-Known Member
That'd be post #3 .
How many thousandths of backlash are you setting for your intake and exhaust valve backlash settings using a feeler gauge, with a cold engine?
Popping in the exh can be caused by rich condition, unburned fuel in the exh system igniting. You often see this on race cars when they lift off the throttle; causes high vacuum & pulls extra fuel which goes out the exh....
Why Cars Backfire - Afterfire - Explained
(Fuel Injection or Carb, same theories.)
More than likely rich unburned fuel in exhaust system, air introduced to it. That allows it to burn and backfire (afterfire out the tail pipe.)
The mixture in the exhaust is rich enough that it can not burn, introduce oxygen then it burns. Bang !!!
Would like a look at your spark plugs to see how they are burning. Bet they are more carbon black than they are white and clean.
@Jbarker
(Fuel Injection or Carb, same theories.)
More than likely rich unburned fuel in exhaust system, air introduced to it. That allows it to burn and backfire (afterfire out the tail pipe.)
The mixture in the exhaust is rich enough that it can not burn, introduce oxygen then it burns. Bang !!!
Would like a look at your spark plugs to see how they are burning. Bet they are more carbon black than they are white and clean.
@Jbarker
Jbarker
Active Member
Hey guys- you have asked a lot of questions that I haven’t answered yet. I’ve been working too much the past 24 hours. Still stuck at work now, but I can look up those cam specs and backlash tomorrow. I am running an Edelbrock performer RPM intake manifold
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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My opinion;
I'm gonna say rich.
Unless you have synced your transfer ports to your mixture screws, to your idle timing, the throttles will be too far up the transfers, and she will idle rich, and too fast. But just slow enough for the headers to pull plenum charge across the top of the piston during overlap. Your engine may not be running rich, but your exhaust system is rich with unburned fuel AND air from the plenum, just waiting after the merge somewhere, to explode. All it needs a lil flame to catch and Boom!. If air gets into a single primary pipe, it will pop right there.
Somebody talked about this, already,
Fix your sync, so you can close the throttle further, to reduce the header inertial tuning pull, and the popping should go away.
I'm gonna say rich.
Unless you have synced your transfer ports to your mixture screws, to your idle timing, the throttles will be too far up the transfers, and she will idle rich, and too fast. But just slow enough for the headers to pull plenum charge across the top of the piston during overlap. Your engine may not be running rich, but your exhaust system is rich with unburned fuel AND air from the plenum, just waiting after the merge somewhere, to explode. All it needs a lil flame to catch and Boom!. If air gets into a single primary pipe, it will pop right there.
Somebody talked about this, already,
Fix your sync, so you can close the throttle further, to reduce the header inertial tuning pull, and the popping should go away.
Jbarker
Active Member
Hyfire 6 AL
Jbarker
Active Member
No carb spacers or heat shields under the carb. No exhaust crossover. (Edelbrock performer RPM)
Jbarker
Active Member
Hughes cam STL4650BS3-08
Valve lift with the 1.5 ratio rockers I have is .576 on the intake and .588 and the exhaust. Duration at .050 is 246/250
Jbarker
Active Member
That’s a really good thought, but my understanding is that with an iron block and aluminum heads, valve lash will open up slightly as the engine warms up. If I’ve got this confused, please correct me.
Valve lash closes as the engine warms up. Pushrods lengthen, adjustable rockers and their bolts expand, valve stems lengthen.
When you do not have enough valve lash it will start holding the valves open when the engine comes up to temp.
The exhaust is almost always set looser because of the expansion due to heat.
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Here is what one B Body guy is setting his at:
I am running the same 590 mp cam as you in my 383 street monster, I run the .028/.032 spec that the designers from ma mopar said to use.
If you are setting them at .010/.012 ths you are probably running them too tight. Your exhaust valves are going to open up first when too tight because of the heat.
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Set them, then start up and warm up the engine good. Shut the engine down and pull the valve cover quick and measure the lash again. If you cannot get a feeler gauge in you know they are too tight.
yellow rose
Overnight Sensation
Is the part number 685 and does the box have digital display on the top, or does it look like an MSD box.
I doubt it’s the box, I’m just trying to determine what you have.
And it’s probably a bad exhaust valve or it’s pig rich at idle.
yellow rose
Overnight Sensation
NO! Valve lash increases with engine temp. Even with an iron block and iron heads. They always get loose.
Here is what Huges recommends for his solid camshaft valve lash after the engine has warmed up Hot:
Intake .010
Exhaust .012
Intake .010
Exhaust .012
yellow rose
Overnight Sensation
512Stroker
We are all here because we are not all there.
YR doesn't .010/.012 seem tight for a hot lash?
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