Supercharged 383 backfire, bog
Thread Starter
2nd Gear
Joined: Aug 2008
Posts: 2
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Supercharged 383 backfire, bog
Hello, I'm new here. I am finishing up an 89 Vette with a 383 (low comp), AFR heads and a Paxton Supercharger. It had a TPIS intake, big injectors, blah blah blah on it but I got tired of the computer so I took the FI off and put on an Edelbrock Torker 2 intake and a Demon pressurized carb for blow-through set up. (Not a box enclosure carb) I put a carb hat on it and finished it off with a mechanical advance distributor and an Aeromotive 1:1 boost referencing fuel pressure regulator.
It runs fine in the garage, has crisp throttle response, and will rev up high without problems. Blows a little unburned fuel smoke, but thats kinda expected. Need a little more tuning. The problem comes up while I'm cruising along at part throttle (in any gear) and give it more than one half throttle. It bogs, backfires through the carb and hesitates. By the way: 6spd manual trans.
I checked the plugs and although they were black, they were not fouled. Timing is set at initial advance of 10 degrees. Fuel pressure is 6psi at idle. Factory 4 wire coil probably needs to go away but I can't imagine that the coil alone would make the car suck so much.
What am I overlooking? Thanks!
It runs fine in the garage, has crisp throttle response, and will rev up high without problems. Blows a little unburned fuel smoke, but thats kinda expected. Need a little more tuning. The problem comes up while I'm cruising along at part throttle (in any gear) and give it more than one half throttle. It bogs, backfires through the carb and hesitates. By the way: 6spd manual trans.
I checked the plugs and although they were black, they were not fouled. Timing is set at initial advance of 10 degrees. Fuel pressure is 6psi at idle. Factory 4 wire coil probably needs to go away but I can't imagine that the coil alone would make the car suck so much.
What am I overlooking? Thanks!
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 59
From: Fremont Oh
Sounds like it is leaning out when you punch it ( something going with the accelerator pump) (?). Do you have a fuel pressure guage ( see if it is dipping from not enough supply) and or a WB O2 to see whats going on ? Remember under boost it is going to lean out fast....
If you do not have a logging program I would suggest one then incrementally run it up so you can handle things without blowing it up from detonation...
Hope this helps,
MO
If you do not have a logging program I would suggest one then incrementally run it up so you can handle things without blowing it up from detonation...
Hope this helps,
MO
Last edited by Mo_Bandy; Oct 21, 2008 at 03:18 PM.
Thread Starter
2nd Gear
Joined: Aug 2008
Posts: 2
Likes: 0
More timing
I advanced initial timing to 13 and it ran LOTS better. I then changed the medium springs in the mech advance distributor to the light springs and even more improvement was noticed. Changing the 21 degree bushing to the 28 degree bushing helped even more. Haven't been able to really hammer on it yet.
Thanks for the input on fueling..... I really want a wideband O2 but thats probably going to be next month. Still reading plugs for now.
Doesn't that seem like a crazy amount of advance for a blown motor? No pinging (yet).
Thanks for the input on fueling..... I really want a wideband O2 but thats probably going to be next month. Still reading plugs for now.
Doesn't that seem like a crazy amount of advance for a blown motor? No pinging (yet).
Advanced
Joined: Jul 2007
Posts: 89
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Wideband O2 should have been first on the list, why be in the dark ages reading plugs when you can buy something that will tell what you are actually doing in terms of a/f ratio so then you can adjust accordingly instead of guessing. WBO2 will get you tuned so much faster and more accurately. I have tuned efi for many years and would never think about not using wbo2 sensor because it just makes the process extremely fast and pretty damn accurate period. Also how much psi are you running and do you have a target afr you are shooting for?
Melting Slicks
Joined: Dec 2000
Posts: 2,719
Likes: 59
From: Fremont Oh
They are really" inexpensive these days... the 300 dollars or so they cost is very inexpensive life insurance...A rough rule of thumb is pull a degree for every pound of boost you are running.
I would seriously look into a means to monitor your spark knock as well.
I can't really speak for the carb, but with most of the vortech SC's with EFI they generally are making boost as low as 2000 RPM. Are you running an intercooler?
We all are only trying to help you from prematurely grenading your engine
regards,
MO
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