performance question
Thread Starter
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Freshman User
Joined: Sep 2002
Posts: 49
Likes: 0
From: Nanaimo Canada
performance question
Hi all,
Just looking for some advice from the experienced members. Here is the situation. Just replaced the old exhaust manifolds (broke two bolts in the heads… ouch) with headers, built 2.5” diameter dual exhaust system. Here is the problem, the truck idles fine (the rpm dropped after header install) however it is sluggish when accelerating and seems to lack power at higher rpm. It has a weak backfire in the headers after sudden rpm drop. I suspect it might be running to rich or lean, I have checked the timing and it is where it should be. The truck is a 1969 4wd, standard, 390 2bbl, pertronix ignitor ignition and high performance coil. Thanks in advance.
Just looking for some advice from the experienced members. Here is the situation. Just replaced the old exhaust manifolds (broke two bolts in the heads… ouch) with headers, built 2.5” diameter dual exhaust system. Here is the problem, the truck idles fine (the rpm dropped after header install) however it is sluggish when accelerating and seems to lack power at higher rpm. It has a weak backfire in the headers after sudden rpm drop. I suspect it might be running to rich or lean, I have checked the timing and it is where it should be. The truck is a 1969 4wd, standard, 390 2bbl, pertronix ignitor ignition and high performance coil. Thanks in advance.
Hotshot
Joined: Oct 2002
Posts: 18,488
Likes: 22
From: The Big, Oregon
The increase in flow is making it run a little lean, most likely.
You might also want to add a crossover pipe just behind the transmission to balance the exhaust flow and allow it scavange the cylinders properly.
You might also want to add a crossover pipe just behind the transmission to balance the exhaust flow and allow it scavange the cylinders properly.
Elder User
Joined: Jan 2004
Posts: 731
Likes: 0
From: in the springs
sounds like it is running lean to find out definatively you could always purchase and install a fuel mix sensor they aernt very expensive when you look at the cost of fuel these days knowing the truck is burning at an optimal level is good piece of mind.
Thread Starter
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Freshman User
Joined: Sep 2002
Posts: 49
Likes: 0
From: Nanaimo Canada
Thanks for the help folks. I reset the carb to a richer mix and it runs better. To get the performance I am thinking of the 2 bbl will probably have to be switched to a 4 bbl. The idea of a fuel mix sensor is interesting, if its an easy install and not to expensive I'll try it. If anyone has installed a fuel mix sensor gauge system in these old trucks it would be interesting to hear the details.
Last edited by cies_69truck; Aug 29, 2006 at 11:38 AM.
Elder User
Joined: Jan 2004
Posts: 731
Likes: 0
From: in the springs
i installed one and it owrked great but i was running way too rich and burned out the o2 sensor all that is required is welding an o2 bung into a collector, and supplying a power wire for the controll box and routing the wirees.
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Check into AutoMeter's narrow band gauge, to run a wide band it will cost you app $350. I run the narrow band switchable left right bank, this will add to the cost having two O2 sensors.
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