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Discussion Starter #1
Hello everyone, first off I'd like to thank all the people here who have given me advice for my projects after all these years. My current build is a 1966 Bronco with a 429/ZF 5-speed. I'm getting custom stainless headers built for it soon and I was wondering about what exhaust pipe diameter I should go with. Then I saw magnaflow has a full bolt in dual 2.5" system with an x-pipe:

Performance Exhaust 15344

Looks like a beautiful exhaust system. I've had a full kit from them before and I really liked it. My issue is that the pipes may be too small as most people on here run 3" systems. Here's a breakdown of my engine combo:

429cid (0.060 over)
11:1 compression (flat tops with SCJ valve reliefs)
FRPP SCJ heads (Intake valves backcut)
Solid roller with 239.5in/244ex (@0.050) and 626In/654Ex Lift
Performer RPM Air Gap converted to EFI (Ports matched to SCJ height)
And if it matters 3.73 gears with 33" tires

This will primarily be a fun street toy. Will the 2.5" system work or will I be giving up a lot to use it?
 

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Your combo looks like it's gonna be a breather. Regardless of it being only 429ci, I'd go the extra mile with the 3". It's there if you ever decide to stroke that bad boy in the future. Actual hp loss I don't know and being that it is not a race engine I understand you not all to concerned maybe, but imo, do the 3".
 

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Discussion Starter #4
I'm not concerned about future upgrades. I just want this thing up and running. I have a blower intake in my basement, so if I actually do upgrade, 3" won't be enough.

It's interesting that the 2 replies I got on this site say go bigger cause of future upgrades. The 2 replies I got from the 'other' site said 2.5" is good for a street truck. Different mindset of groups maybe?

Either way, I do appreciate good advice from all. I'm 90% sure I'll be pulling the trigger on the Magnaflow kit unless I get a VERY good reason why it would be detrimental to my Bronco. My Tcase sits 3" further back than the stock bronco and is about 1" lower than stock as well. That could make interference problems with the Xpipe. We'll see.
 

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You will find that with the 2.5" system tip in and transient response as well as light throttle torque production everywhere under the torque peak RPM will be better. The top side charge to max rpm will be down a bit.
The 3" will pull harder about the last 1500 rpm to peak hp and past but give up average power below peak torque.

I love the 3" full mandrel exhaust with H pipe and magnaflows on my LTD. It added a few hundred usable rpm at the top but hurt light throttle cruise response and torque on the street at low rpm. It simply wasn't as sharp down low. Even with a 3,450 stall converter.

Having said this the fact that old girl will pull like a freight train to 6,700 rpm still makes the hair on the back of my neck stand up :D




S
 

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Discussion Starter #6
I'm thinking for my intended purpose of just a fun hot rodded toy, the 2.5" will be fine. I do have a universal 3" X-pipe kit on my shelf. I could take my time in the future and make a nice 3" exhaust if I thought my truck needed it. I would already have the blueprint to go by.:) My only real issue is the location of the X-pipe in relation to my driveshaft. My tcase sits a litle lower than stock as well as 3" further aft. I've got to sit down and really size up where it would sit on mine and also if I could trim a bit to move it aft. I'm sure it wouldn't be a problem though.
 

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I think you knew your answer before you asked. 2.5” will work just fine for your build. You likely won’t run it all that hard anyways.
 

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Discussion Starter #8
I think you knew your answer before you asked. 2.5” will work just fine for your build. You likely won’t run it all that hard anyways.
Well I did and I didn't. Reading multiple builds here had a preconception in my mind what I should shoot for. I just needed to ask the question to those in the know before I went and spent $1000cad on an exhaust. This is not the only site I posted on and with the answers I was given I am sure the 2.5" will work fine. If someday I need to go bigger, I'll deal with it then.
 

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All my street vehicles have 2.5 inch exhaust and cutouts off the headers if I really want to make some noise at the track.

My car makes 550hp and if you have it wide open throttle on a public road, well, you are either losing traction, or going waaaaay too fast by the time the exhaust is a restriction. Super fun for the 0-60mph blast, but really in order to keep it on the road max rpm is probably only 5500-6000rpms.
I am 100% certain that 3inch looks better on a dyno, but if it's a real street car, dyno's lose their relevancy.
Heck of a lot easier to package 2.5 and it is much easier to keep the drone done.

Do whatcha want. We are all just tossing out experiences so you can make an informed decision either way.
 

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Discussion Starter #11
Well tdotperformance.ca had a big magnaflow sale. Then they had 10% off for Black friday. Then free shipping. So I had to do it. a 2.5" mandrel bent exhaust with an x-pipe for $877cad. If it installs half as easy than my last exhaust I'll be happy.
 

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So with a 2.5" mandrel bent exhaust and magnaflow straight through mufflers, what size headers should i build?

1 7/8" would suffice. Unless building your own you are going to have to settle for what is available.

I have the FPA mid length headers on my LTD with 1.75" primaries which are just fine at 560+ hp.



S
 

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Discussion Starter #14
1 7/8" would suffice. Unless building your own you are going to have to settle for what is available.

I have the FPA mid length headers on my LTD with 1.75" primaries which are just fine at 560+ hp.

S
I have no choice but to make custom headers. I did a ton of research and quite a few guys have put big blocks in their early broncos. Everyone needed custom fenderwells. One guy told me L&L fenderwells fit his. I bought them and they hit in all the wrong places.
 

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I have no choice but to make custom headers. I did a ton of research and quite a few guys have put big blocks in their early broncos. Everyone needed custom fenderwells. One guy told me L&L fenderwells fit his. I bought them and they hit in all the wrong places.
Building your own headers will also allow you to make sure the flanges are not blocking any area of those SCJ ports. I decided to build my own headers for my TFS 325 CNC ports. I have now purchased 3 sets of flanges and none of them will work as a pure bolt on. To my surprise the best fitting flange is sold by speedway as a speedway flange. (still needs fine tuning) I don't know who the manufacturer is. Hedman was the worst. They all need grinding on to make the port right even for a 18 Gauge 2" primary. If you are building all stainless you might look at 'Patriot'.
 

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Discussion Starter #16
Building your own headers will also allow you to make sure the flanges are not blocking any area of those SCJ ports. I decided to build my own headers for my TFS 325 CNC ports. I have now purchased 3 sets of flanges and none of them will work as a pure bolt on. To my surprise the best fitting flange is sold by speedway as a speedway flange. (still needs fine tuning) I don't know who the manufacturer is. Hedman was the worst. They all need grinding on to make the port right even for a 18 Gauge 2" primary. If you are building all stainless you might look at 'Patriot'.
Thanks for the heads up. I'll look into Patriot.
 
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