5.0 engine with Tri-Y headers

GT1966

Member
Sep 26, 2002
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Like many 1st Gen owners, I now run a mildly-built (315hp)1986 roller motor in my 1966 fastback. Of course, the firing order for the 5.0 (13726548) is different from the 289 firing order (15426378). Are there any scavanging / pulse ramifications running a header specifically designed for the 289 firing order on a 5.0 firing order engine, or am I splitting hairs? I swear I hear pulses fighting eachother at 2200 rpm. Or is it that damn Flowmaster 40 drone that's killing me?
 
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rbohm

SN Certified Technician
Apr 12, 2002
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tucson,az
no big deal to run the tri-y's with the late 5.0 firing order. remember that you are just swapping the 5-4 cylinders for the 3-7 cylinders in the firing order.
 

GT1966

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Sep 26, 2002
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no big deal to run the tri-y's with the late 5.0 firing order. remember that you are just swapping the 5-4 cylinders for the 3-7 cylinders in the firing order.
When the tri-y headers were first introduced, they were firing order specific. 1 and 2 are paired, 3 and 4 are paired, 5 and 7 are paired, 6 and 8 are paired. Once you change to the firing order, how can the headers not react differently? I've been running these headers for a few years on this 5.0HO engine, but I'm curious if things would be better with a set of equal length headers rather than the tri-Y?
 

rbohm

SN Certified Technician
Apr 12, 2002
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tucson,az
When the tri-y headers were first introduced, they were firing order specific. 1 and 2 are paired, 3 and 4 are paired, 5 and 7 are paired, 6 and 8 are paired. Once you change to the firing order, how can the headers not react differently? I've been running these headers for a few years on this 5.0HO engine, but I'm curious if things would be better with a set of equal length headers rather than the tri-Y?
you are right, but understand that the headers were designed initially for racing, mostly to boost mid range power given the carb and cam used by shelby in the race models. since this is going to be a street car, any loss of power is not going to be noticed, and can even be mitigated by using a properly designed exhaust system after the headers, an X pipe should do nicely, and if the OP is willing to spend a little extra time, he ccan or have someone install a sub sonic diffuser in the collector.
 

GT1966

Member
Sep 26, 2002
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Maine
you are right, but understand that the headers were designed initially for racing, mostly to boost mid range power given the carb and cam used by shelby in the race models. since this is going to be a street car, any loss of power is not going to be noticed, and can even be mitigated by using a properly designed exhaust system after the headers, an X pipe should do nicely, and if the OP is willing to spend a little extra time, he ccan or have someone install a sub sonic diffuser in the collector.
Well, I have been pretty happy with the 2-1/2" FlowMaster system I installed a couple summers ago, despite the 2200 rpm drone of the Flowmaster 40's. Overall, a bit too loud for this 62 y.o.! For highway, I need to drive at 80mph to get into an rpm range where it's comfortable (the 3.25 gears should probably bump up to 3.5). I am running an H-pipe configuration. This whole discussion was more about the sound / pulse that I'm tuned into at the low, around town rpms that just sounds off to me as I add throttle to get into the working rpm range.