Ive read post after post to the contrary,what Ive read is theres no notable increase on a stock efi 300 vs efi manifolds,unless the motor has been built with a bigger cam,ported head,roller rockers,and so on,since efi manifolds flow way more exhaust than a carbed 300,On a carbed 300,with non efi manifolds,I can see where there may be a little to be gained by installing headers,,you may see a increase in power,
Im not making this up,its on these forums,maybe I seen it on Fordification.

 

yea i mean just from what ive been told, for big trucks with bigger engines work good with a larger diam single exhaust. ive already got 3" on my 300, but ive still got both stock cats and and a muffler so its not gonna die haha

 

I cut pipes off right at cat bought bulk 2" pipe at O'Reillys cherry bombs also tail pipes for f-250 with 460 hung tailpipes chrome tipes to boot "Advance Auto I think" with CB's slipped on measured distance cut bulk pipe to length had engine ends xpnded to slip over stock down tubes DONE! Price 4 everything including clamps just under $90.00 tax included 3-5 mpg gain n sounds GREAT!! Hope this helps,GOOD LUCK!

 

What?






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If they were talking about dual exhaust using efi manifolds "stock" on my sons "300" 91 bronco info in last post tells how i did it cut exh B4 cat= catyltic converter CB= cherry bomb,tailpipes for 84 to 96 f250 with 2 tailpipes"hung from stock rubber hanger"exiting 1 muffler xpnded="expanded" if not i misunderstood post SORRY!

 

is anyone that was originally involved in this thread still on here?

I have a '91 ford (efi 6-banger...that's toast) that I am going to put a '96 efi 300 into. as they have split manifolds, but go to one cat and do have o2 sensors, is there a 'best' suggested way to get the best fuel economy by modifying the exhaust?

 

Well I'm still here, but you see how controversial my posts became.

From experience and study I KNOW that long tube headers provide a more significant gain than even a really good, free flowing manifold or shorty header system. The reason is that a properly designed header system allows the flow of the neighboring cylinders at the collector to scavenge or suck the charge out of the cylinder.

In the mid seventies, I had a 200 six cylinder Mustang, '66 model with a three speed. I used it as a commuter for a mostly highway, 100 mile round trip daily commute. I found a set of tri Y headers and dual exhaust system in the paper and bought it for $50 or something like that.

I keep records on all my vehicles including mileage/gallons/trip etc. so I can always tell you how fuel mileage is going down to the hundredth of an MPG. The header system with no other modifications, improved my fuel mileage significantly.

Later at rebuild time I ported the head and opened up the carb port to the size of a carburetor from a 300 truck six along with a mild cam. That little thing ran like stink and sounded like a V8. I could outrun even four barrel Mustang V8's occasionally and ALWAYS put it on two barrel V8 Mustangs.

Problem was I wore out the hood hinges opening it to prove that it was a six.

If you're on a budget, I would think that the exhaust from the donor truck could be made to work really well for your purposes. If you have lots of extra money or have the equipment and welding skills, Find a good set of long tube headers and weld in bungs for the O2 sensors and I think you would reap the reward, but there's no guarantee that it would return the money in gained fuel economy.

Hope this helps.

 

after listening to that, reading some other stuff, etc...unless I hear anything better, as I do have the exhaust from the 'donor' for the implant engine, I will probably install that. the donor was wrecked...122k miles.

not that I am doing anything fancy, just getting a little rig running so I have a run around truck. I wish it was the newer 92-96/7 body style, but whatever I guess for now. Thing is...when this project ends, from my leftovers I will have a rebuildable EFI 300-6 with the wiring harness and PCM from the '96, albeit the donor had an automatic.

thanks.

 

I thought I would throw in my experience with a Hedman header. I bought it new and installed it on a newly rebuilt 300 with a modified head. I used grade 8 studs and crimp nuts over the oem thick washers. I had to put the oem washers, that are about 1/4" thick, on a bench grinder to compensate for the different thicknesses from intake to header flange. I also used the double gasket that came in the engine kit, not the Mr. Gasket #260 that everyone on the forum raves about.

I applied the ultra high temp RTV around the exhaust ports, both sides of gasket, and installed by torquing to 1/2 called for amount, starting in the center and working to outside in a counter clockwise spiral. Then torqued to full amount in same fashion. After break in run I let the engine cool completely, then retorqued. I did that two more times, then forgot about it.

I believe it has been ... more than three years and I have never had an exhaust leak. Oh, that's a lie. The bolts at the collector came loose and one fell out. I had to replace it. I love the header, but the engine compartment does get hot.

 

Having a rebuildable 300 after the project is definitely not a bad thing. In fact, since it is an EFI engine, it might be easily rebuilt with bearings, rings and a valve job.

Since modern engines last so long and rarely get rebuilt, the skill of evaluating an engines condition is not as common as it used to be. I love doing engine work and have done a number of them. If you decide to tear it apart for analysis, let me know and I'll help walk you through it if you have never done that kind of thing. For all I know, though, you have rebuilt more of them than I have.

I think your decision to go with the exhaust you have on hand is a very practical decision for your purposes.
Larry

 

thanks for that. no, I have only ever built one engine, that was back in '95, but it was a go-er. an old 4-bolt main chevy 327 .030 over with some pretty cool stuff on it.

BUT, I am getting back into that game kinda. I have some projects to get out of the way first. I actually have 4 300-6's on hand right now, two good, two toast; a 460 that needs over hauled and an old '61 unibody with a 223 that I'd like to upgrade to a 331 stroker or 393W. Really, if I could find one, for the nostalgia, I'd put a 406 tri-power in it.

A guy can always dream big, can't he?