Restrictive exhaust, how does it affect performance
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From: Culpeper, Virginia
Restrictive exhaust, how does it affect performance
I posted almost two years ago about poor performance. My truck (79F1504x4w/4604spd) will run fine, but seems to lack power even for a tired motor. Stock motor, in pretty decent condition, good vaccum, good tuned carb, fresh tune-up, yada.
In my other post we came up with a million reasons why or what could cause lackluster performance. Crappy exhaust was a possibility. So my truck has stock exhaust maifolds, run into a Y, then into a big single mufflet, thing must be 5 or 6 inches around in circumfrence, then turns down about 6 inches past the end.
I have a cat, but never pulled it off to see if it was clogged.
What could I do to see if the exhaust is restricting the motor, simply unbolt and run it? Thanks.
Blair
In my other post we came up with a million reasons why or what could cause lackluster performance. Crappy exhaust was a possibility. So my truck has stock exhaust maifolds, run into a Y, then into a big single mufflet, thing must be 5 or 6 inches around in circumfrence, then turns down about 6 inches past the end.
I have a cat, but never pulled it off to see if it was clogged.
What could I do to see if the exhaust is restricting the motor, simply unbolt and run it? Thanks.
Blair
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From: Rio Rancho USA
Compression good? Any blow-by? Depending on mileage, possibly a worn cam or stretched timing chain? Never saw the old thread, so Im probably just repeating what has already been said.
A good way to check backpressure is to get a pressure gauge and measure it. Just weld on a O2 sensor bung or whatever you can get and attach an air line into it. Bring the gauge inside the cab, hook it into the air line and run the engine. Anything more than about 1psi at idle or 3 psi and 2K is bad. Then you can start looking at the different parts of the exhaust system to relieve the backpressure.
I think if you try this method, you would find the cat, being that old will be a pretty restrictive part of your system. Better yet, with that kind of age and miles on it, I would either remove the cat altogether or get a high flow one to replace it. IMO, a good straight-through muffler would be a good idea also.
A good way to check backpressure is to get a pressure gauge and measure it. Just weld on a O2 sensor bung or whatever you can get and attach an air line into it. Bring the gauge inside the cab, hook it into the air line and run the engine. Anything more than about 1psi at idle or 3 psi and 2K is bad. Then you can start looking at the different parts of the exhaust system to relieve the backpressure.
I think if you try this method, you would find the cat, being that old will be a pretty restrictive part of your system. Better yet, with that kind of age and miles on it, I would either remove the cat altogether or get a high flow one to replace it. IMO, a good straight-through muffler would be a good idea also.
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From: Culpeper, Virginia
Thanks.........
Thanks for the reply.
Compression was OK, been awhile since I did that, but I don't remember anyone here saying my numbers were horrible when I posted them.
I've put on a new double roller chain and gears when I forst got the truck.
As for blow-by, she doesn't burn any, ony leak I have is from the drain plug.
How could I diagnose a worn cam? I don't remember that being put out there before............
I was thinking about dropping the cat and old muffler anyway, I have no plans for true duals until many other things are taken care of. At the Y should I be stepping up to a bigger exit pipe? Like a 3" or 4".............
Thanks,
Blair
Compression was OK, been awhile since I did that, but I don't remember anyone here saying my numbers were horrible when I posted them.
I've put on a new double roller chain and gears when I forst got the truck.
As for blow-by, she doesn't burn any, ony leak I have is from the drain plug.
How could I diagnose a worn cam? I don't remember that being put out there before............
I was thinking about dropping the cat and old muffler anyway, I have no plans for true duals until many other things are taken care of. At the Y should I be stepping up to a bigger exit pipe? Like a 3" or 4".............
Thanks,
Blair
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From: Rio Rancho USA
Yes. IMO, for stock 2.25" into a 3" Y pipe would work great. The best way to go is with some mandrel bent pipe pieces and an aftermarket Y piece and put your own together. Stock Y pipes are usually pretty bad for flow (even new ones), the only idea the factory had was to join 2 pipes together, and the point where the 2 pipes join is not thought out very well.
A worn cam is unlikely, it was just thrown out as one more thing to check since all the other alternatives have been taken care of. A miss in the exhaust is the easiest way to tell. Overall, I would put my $$ on the cat being the problem.
A worn cam is unlikely, it was just thrown out as one more thing to check since all the other alternatives have been taken care of. A miss in the exhaust is the easiest way to tell. Overall, I would put my $$ on the cat being the problem.
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From: Culpeper, Virginia
Thanks for the replys. I'll do the vac test, I'm going to tinker with the carb a little, make sure it hasn't fallen out of adjustment. I'll take a look at the exhaust next.
Thanks again,
Blair
Thanks again,
Blair
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From: Culpeper, Virginia
I have a post in the carb forum to help me be sure the carb is tuned.
Vac readings...
15 steady at idle, idle is set a little low...
18 at around 1500
20 at around 2200
both steady....
a pic of the exhaust on the truck.........
[IMG]
[/IMG]
Vac readings...
15 steady at idle, idle is set a little low...
18 at around 1500
20 at around 2200
both steady....
a pic of the exhaust on the truck.........
[IMG]
[/IMG]
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i like single myself, build a nice single 3 inch system to get more performance....check out my gallery i used 4 inch cause my motor is a little built
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Thread Starter
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Posting Guru
Joined: Oct 2001
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From: Culpeper, Virginia
This will sound super ignorant, but where can you go get some 3" or 4" stuff off the shelf. I'd love to buy it myself, but in a small town with just a Advance Auto, not many choices. Would a hot rod shop carry that stuff on the shelf?
Thanks. Like your rig too..............
Later,
Blair
Thanks. Like your rig too..............
Later,
Blair
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Post Fiend
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From: "Islander"
There are several places that sell mandrel 180 degree tube, I buy thru a company in Oregon as they have 14 ga. not your Summit 16 or 18 ga.
Try, magumforce with www. before and .com after, they have bends up to 4"
.....=o&o>.....
Try, magumforce with www. before and .com after, they have bends up to 4"
.....=o&o>.....
