Upgrading a 300 carb Straight Six. (Pics) - Ford Bronco Forum
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post #1 of 154 (permalink) Old 03-23-2009, 02:59 PM Thread Starter
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Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd NP-435 manual. 32" tires.
Upgrading a 300 carb Straight Six. (Pics)

Hey everyone, this is my first writeup on here. Seems that most everyone has the 302, 351, or a EFI 300, so I thought I'd give some eye candy to the carb 300 enthusiasts.

The stock carb 300 has about 120hp and 255tq. The engine is known to be a tank, and you definitely can't stop it. Unfortunately, you can't exactly get it going very quickly either.

Last summer I swapped out my stock log exhaust manifold for the dual manifolds from a stock fuel injected 4.9. (I'll have to dig up my pictures and put them in here too). The 1bbl exhaust had a 2" outlet, which is about a 3.1 square inch exit. The EFI manifolds have two 1.75" outlets. Together, that's about 4.8 square inches. About a 30% gain. I also went from the stock 1 7/8" exhaust to a high flow 2.5" exhaust. Not to mention the cat was original and was so plugged I was blowing manifold gaskets. The difference was amazing. Est. 145hp/270tq. Total cost from engine block to tailpipe: ~$400

This spring it was time for an intake upgrade. The stock Carter one barrel on the 300 is about 180 - 200cfm (heard quite a few different numbers). It does well up until around 3000 RPMs and then gives out. With the stock setup, you can't get it up much over 3000 anyway so this is okay. However, with a much higher flowing exhaust, it was time for some more carb.

After doing about a year of research (might as well since I had the time, not the money), the Offenhauser dual port intake with a Holley 390 was agreed to be a very good upgrade. I found one used from a guy who threw a rod in his engine for much less than new. Normal price was about $800, picked his up for about $300.

The hardest part was making an accelerator bracket for the engine since the stock bracket bolted to the stock intake. Just took some ingenuity.

After wading through and removing the stock tangle and mess of vacuum lines and removing the stock intake, I bolted the new intake in and connected the carb. It fired up nicely and after a little tuning we took it for a test drive. Even with a 3.00 rear end, it snapped the RPMs right up to around 4000 and definitely wanted more. Without some head building, I probably shouldn't be taking it much higher than that, although it seemed like it certainly wouldn't care. My easy going 300 has suddenly become a force to be reckoned with. I couldn't believe the difference, it basically felt like I just removing 1500lbs from the vehicle and it felt as light as a toy.
Est: 170hp / 290tq.

The new intake, prepped and ready to go.


Fitting on the Holley carb to check for accelerator bracket alignment.


Comparing the old Carter 1bbl with the new Holley 390.


Here's a comparison of the venturi sizes. No wonder...


My brother working away with the grinder making the cable bracket.


The mostly stock engine bay, just ready and waiting.


Another view of the engine bay.


Here's a view of the previous intake and exhaust. Gotta love the mess of vacuum lines.


A view of the stock carb on the engine. It's put in some good work, but it's time to go.


A cleaner view of the intake/exhaust with all the lines out of the way.


A clear view of the dual exhaust manifolds from the fuel injected 4.9. Those things are sweeeeet.


The new intake set in place on the engine. No work required, it fits perfectly.


Here's me working away, torquing down the manifold bolts.


My Bronco with my brother's Jeep. Another awesome straight six. (4.0L high output.)


The finished custom accelerator bracket. Simple, effective, and hidden from sight under the air cleaner.


Hooking up the necessary vacuum lines and hoses. There were so few, it took me a moment to believe it.


The final touch. Tuned, and ready to go.


Next on the list is a distributor recurve. This moves the distributor's vacuum advance from an emissions oriented curve to a performance curve and will really wake this whole setup right up. The kit cost $4 and is sitting on my work bench. After that, it's a head P&P (maybe this summer), and a cam. From what I've read, this should be setting the engine right around 210hp/325tq. Should have come like this from the factory...


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #2 of 154 (permalink) Old 03-23-2009, 03:04 PM
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Nicely done. I was planning to do an offy intake/Holly carb on my 77 but I've decided to just do a FI swap one day. Now put a 3G on it and a saginaw out of a E series w/ a 300!

Want to sell that Carter YF?

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post #3 of 154 (permalink) Old 03-23-2009, 03:12 PM
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This is a great write up. i agree, 3G and saginaw pump would set it over the top, search though the threads and u should find a bolt on saginaw pump thread.

questions i didnt see answered for others. which y pipe did u use, and muffler. have u rejetted the carb or played with anything else?

also, dont forget for now u can swap to high lift rocker arms instead of the cam swap.

1993 F-150 XLT 4x4
-300/E4OD/SA D44/8.8/BW1356
1988 F-350 Custom 4x4
-7.3IDI/ZF/D60/10.25/BW1356
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post #4 of 154 (permalink) Old 03-23-2009, 03:14 PM Thread Starter
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Quote:
Originally Posted by justin View Post
Nicely done. I was planning to do an offy intake/Holly carb on my 77 but I've decided to just do a FI swap one day. Now put a 3G on it and a saginaw out of a E series w/ a 300!

Want to sell that Carter YF?


Thanks. Driving to work this morning was a whole new experience. I loved it.
I thought about doing the FI swap, but I didn't like how finicky the stock computer was, and this was much more in my budget. Besides, this is much more unique. :)
A 3G is definitely on the list but first is a Saginaw! After all this work, I'm looking forward to one day being able to hear my engine over the sound of the power steering pump whining.



As for the carb, I have some parts carbs if you need some things, but I need to hang on to this one. We do have emissions here and I might need to swap it back in. There's no visual, so I'm clear there. But I figure if I can get an emissions oriented 1bbl to pass emissions with flying colors with NO emissions equipment whatsoever, I should be able to tune a 4bbl to pass our lax emissions laws. If not, I'll probably need to swap it back in to get it to pass.

Quote:
Originally Posted by Optika1 illushun View Post
This is a great write up. i agree, 3G and saginaw pump would set it over the top, search though the threads and u should find a bolt on saginaw pump thread.

questions i didnt see answered for others. which y pipe did u use, and muffler. have u rejetted the carb or played with anything else?

also, dont forget for now u can swap to high lift rocker arms instead of the cam swap.
I used a walker converter pipe made for the 4.9 EFI manifolds and it bolted right on perfectly and was dirt cheap. WLK-45166 The muffler was a turbo dynomax muffler and it sounds awesome. Here's a video of the exhaust with the 1bbl on there (haven't updated yet): http://www.youtube.com/watch?v=sHTK3Twq2Vo

JUST got it running last night. Haven't messed with jets or anything yet. That'll come next. Already drives great, so it's pretty close fortunately.

And I've heard mention of the higher lift Chevy rocker arm swap but I think I need different rocker studs on my head.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #5 of 154 (permalink) Old 03-23-2009, 03:15 PM
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Nice writeup and neat engine. Ive had an inline 6 in an 86 bronco before.

Mine was stock but I hear of some peps working these engines for impressive
numbers. Ive also seen a carbed Jeep with a worked inline that made some
impressive power and the exhaust sounded good too.

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post #6 of 154 (permalink) Old 03-23-2009, 03:19 PM Thread Starter
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Yeah, there's a guy over on fordsix.com that had his professionally built and rebuilt. It's pushing out around 300hp/400tq.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #7 of 154 (permalink) Old 03-23-2009, 03:27 PM
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I work at an emissions shop, and if you want the best chance of passing, install a zero-backpressure cat, if you haven't already. Use one with a Cali CARB EO number cat, as those are generally used by racers in Cali (there are eight-second EFI Mustangs and Camaros out in Cali) so that they still pass emissions. The 390-cfm has a very good chance at failing without a cat to back it up; and a zero-BP cat should not affect your numbers.
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post #8 of 154 (permalink) Old 03-23-2009, 03:31 PM Thread Starter
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Quote:
Originally Posted by Handy_andy_cv64 View Post
I work at an emissions shop, and if you want the best chance of passing, install a zero-backpressure cat, if you haven't already. Use one with a Cali CARB EO number cat, as those are generally used by racers in Cali (there are eight-second EFI Mustangs and Camaros out in Cali) so that they still pass emissions. The 390-cfm has a very good chance at failing without a cat to back it up; and a zero-BP cat should not affect your numbers.
Thanks for the info. Right now it has a high flow cat on it. (This one to be exact: Cat ) I guess by no emissions equipment, I meant in the engine bay, like a smog pump and EGR valve and other components that effect how the carb itself operates. The cat is brand new as of last fall.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #9 of 154 (permalink) Old 03-24-2009, 01:49 AM
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By the time your pushing 300tq you'll want to start using forged parts. I think you may be fine though, but I'd ask FTF.

Btw, where did you get the recurve kit? And did they have one for the EFI dizzy?

Bruiser - '90, SCLB, 300 sixer, M5R2, 4x4, smorgasbord, down for surgery.
Enterprise D - '90, CCLB, 7.3L IDI, ZF5, Dually, Western Hauler, 2wd for now
Bronco (unnamed) - '92, 300 sixer M5R2, 4x4, almost ready for the road.
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post #10 of 154 (permalink) Old 03-24-2009, 01:51 AM
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why? the engine will only see 5,000 rpm at the most and forged isnt really needed.

1993 F-150 XLT 4x4
-300/E4OD/SA D44/8.8/BW1356
1988 F-350 Custom 4x4
-7.3IDI/ZF/D60/10.25/BW1356
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post #11 of 154 (permalink) Old 03-24-2009, 02:26 AM
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Originally Posted by Optika1 illushun View Post
why? the engine will only see 5,000 rpm at the most and forged isnt really needed.

-Ryan

Check out my youtube page. Many bronco videos.
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post #12 of 154 (permalink) Old 03-24-2009, 10:13 AM Thread Starter
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Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd NP-435 manual. 32" tires.
True, right now its probably at it's peak hp at 4000 - 4500 RPM and peak torque around 1500 - 2000. I doubt I'll rarely take it to 4500 unless I'm just in the mood. Plenty of go down low. 5000 would probably scare me.

I got the recurve kit at summitracing.com. Either way, it's a Mr. Gasket 925D. As for working on an EFI, I really don't know for sure. Mine already says "for a Ford '55 - '70 distributor", but it's the one everyone says to go with.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #13 of 154 (permalink) Old 03-24-2009, 12:39 PM
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I'll have to dig through the threads on the FSP forums and findout if I should use the same. And if 5k is going to scare you then you'll be fine with the stock cast pistons. Just remember that they like sheding their skirts, unlike most girls I went to high school with...

Bruiser - '90, SCLB, 300 sixer, M5R2, 4x4, smorgasbord, down for surgery.
Enterprise D - '90, CCLB, 7.3L IDI, ZF5, Dually, Western Hauler, 2wd for now
Bronco (unnamed) - '92, 300 sixer M5R2, 4x4, almost ready for the road.
1/2 million miles!
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post #14 of 154 (permalink) Old 03-25-2009, 01:44 PM Thread Starter
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The thing you may need to look out for with the EFI is throwing off the computer, those things are sadly finicky. That would be what I'd worry about.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
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post #15 of 154 (permalink) Old 03-25-2009, 01:51 PM
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btw justin nice write up. if anyone finds info on the recurve kit for the efi post it up. i am deffinatley interested in one. another cheap mod for the six is doing a 302 throttle body swap. I have been working on this for a while unfortunatley i have the expensive tps the one without the whip which is bigger and won't work on just any 302 throttle body. if you have the tps with a whip on it. it's a direct bolt on. I recommend doing a little boring on the upper intake.

I miss my bronco!!!!

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post #16 of 154 (permalink) Old 03-25-2009, 02:01 PM
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Bronco Info: Bruiser - 1990 Ford F150, 4.10's, 10.25 Rear, TTB Front, 37x12.50R16.5's, awaiting SAS
My build will consist of the 302/351 TB and a mild port n' polish job on the intake, but I'm doing that build to a complete drop-in for my wornout stock 300.

I want to go Megasquirt sometime down the road, after reading through the Megasquirt section on the FSP forums I still don't understand it completly though. I just hope my build won't send my stock PCM on the fritz!

Bruiser - '90, SCLB, 300 sixer, M5R2, 4x4, smorgasbord, down for surgery.
Enterprise D - '90, CCLB, 7.3L IDI, ZF5, Dually, Western Hauler, 2wd for now
Bronco (unnamed) - '92, 300 sixer M5R2, 4x4, almost ready for the road.
1/2 million miles!
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post #17 of 154 (permalink) Old 03-26-2009, 12:15 PM Thread Starter
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Bronco Info: 1981 300ci 6cyl w/4bbl conversion. 4spd NP-435 manual. 32" tires.
If anyone is curious, I added all of the pictures from the exhaust upgrade I did last fall.


http://www.supermotors.net/registry/media/717393


Some highlight pictures for people just browsing the forums:

The pre-made pipes. These were a great buy. The tailpipe was 2.5" mandrel bend made just for the Bronco, and the Y collector was a 2.5" performance upgrade pipe made just for the 300 EFI manifolds. Saved me TONS of money and time. About $150 for the pair.


The dual EFI 300 manifolds, courtesy of LandTortise (and his help removing them). Says one thing about EFI vs. carb. 5 hours to take them off the EFI, 30 minutes to put them on the carb (including removing the original).


The stock and super restrictive 300 exhaust and EGR pipe.


A clear view of the 300 intake/exhaust ports with the manifolds removed. So easy working on an engine with everything on one side and out in the open.


New vs old. I couldn't believe how HUGE the stock cat was.


New pipe size vs. the stock pipe. 2 1/2" vs 1 7/8". It may not look like much, but one 2 1/2" exhaust pipe is almost as big as two 1 7/8" pipes. Quite a difference.


The original muffler. That's chunks of guts that blew out of the cat. So once exhaust got past the completely and horribly plugged cat, it had to work it's way around MORE cat that was in the muffler. No wonder I was blowing manifold gaskets.


New exhaust all installed and tightened. It sat SO nice and solid. I could lift myself off the ground with it.


I've seen some premade tailpipes that hang pretty low. This one was nice and snug under the body. I was very pleased.



The pictures were taken with my phone instead of my digital camera so the quality isn't as clear. Also, the link has more pictures and more writeups of the project.
Let me know what you think.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
Supermotors Pics
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post #18 of 154 (permalink) Old 03-27-2009, 01:08 AM
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Was that snake skin or braided metal?!

Bruiser - '90, SCLB, 300 sixer, M5R2, 4x4, smorgasbord, down for surgery.
Enterprise D - '90, CCLB, 7.3L IDI, ZF5, Dually, Western Hauler, 2wd for now
Bronco (unnamed) - '92, 300 sixer M5R2, 4x4, almost ready for the road.
1/2 million miles!
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post #19 of 154 (permalink) Old 03-27-2009, 07:30 AM Thread Starter
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Quote:
Originally Posted by crash-harris View Post
Was that snake skin or braided metal?!
lol

That was a sleeve of factory heat insulation.


March 2016 FOTM
1981 Bronco. 300 I6. 450cfm QuickFuel 4bbl. BFG A/T KO2 32x11.5" tires. NP-435 trans. EFI exhaust manifolds. 2.5" Exhaust. DUI performance ignition. Redhead steering box.
Supermotors Pics
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post #20 of 154 (permalink) Old 03-30-2009, 03:59 PM
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Where did you order the walker pipe from?
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