1984 Bronco build thread

[StraightSix]

John,

Your Bio has a offy intake and Motorcraft carb what you using for a air filter?

The factory 300 one will not fit the carb.

I also dont see how the factory v8 housing that fits that carb will clear everything?

So how will you have a snorkel for the hot air and or cool air from in front of the radiator support?

I think if you have a housing that will fit the carb and clear everything then to get the hot air from the exh manifold would be easy. Have you tried driving the truck with out it to see what happens?

Dose your choke use hot air to open it and if so hot did you over come that?

I would hit the junk yard and look at older cars & trucks that run a carb and see if you can rob their metal that might work for you. I want to say I have seen older Toyota's with with exh manifolds close to the shape of that front one you have that may work.

I also want to say it would not be to hard to make something if you need to.

Sheet metal on the back & front to make a pocket around manifold. The 2 sheet metal parts can be bolted together and have it hold tight to the manifold so it dose not make noise.

A tin can that fits the paper hose. cut the bottom out and slice it up about an inch all the way around making it like a fan if it it was bent out.

Find a place on the outer sheet metal to make a hole for this can to fit and the hose to reach.

Bend every other "wing" out from the end you sliced.They will be the stops when the can is put in the hole. Put the can in the hole up to the wings with the others inside the hole.

Now bend them up to the sheet metal. The can should now be held in place by the wings on either side of the sheet metal.

You can use epoxy (JB Weld?) around the can & sheet metal to make it air tight if you want.

Bolt it to the manifold add the paper hose and filter and you are done.

I am using EFI manifolds with the factory Carter carb & air filter and I did not make anything to heat the incoming air. I have driven the truck when in the 20's with out any issues. I also have the cool air to snorkel for when the door opens, if it dose?

I used copper tubing wrapped around the rear manifold for the choke hot air asst.

I only had to make 1 adjustment when the temp got down to the 20's as the fast idle did not come off.

I wrapped header wrap around manifold & copper so I would not lose heat and it has been fine since.

I also run hot water to the stock intake manifold to heat it are you going to do the same?

Dave ----

Hi Dave!

Sorry, I need to update my signature. Im using an offy C, and EFI exhaust manifolds. I have recentry installed a holley 390. For an air cleaner, Im using a home made number made out of a mix of parts from my original 300 air cleaner and the factory set up off of an 85' 302. The air cleaner body and filter are from the 302, the snorkel and all sensors are from the 300. The air cleaner is oriented in such a way as to use a convenient feature of the air cleaner to help avoid the water core box. Even with this, I still needed an aluminum spacer between the carb and air cleaner to clear everything. In effect, I have a mostly stock style air cleaner set up.

I think there are more details on my air cleaner earlier in this thread, I built it in march or april to sit atop my 2150, which is now replaced with the 390.

All this time, Ive had a dry rotted air damper motor, and a hard time finding a replacement. Just today, I was able to install a new cx120 and start the system up for the first time.

My "cold weather modulator" seems to be an open leak to atmosphere. I took it out of the circuit so that vacuum ran from the manifold, to the bi metal sensor, and then the vacuum motor. The motor emediatly pulled closed to only allow hot air. After 4-5 minutes of run time, the damper slowly opened all the way to the "cold air" position. Seems about right? The ambient temp here is 65F tonight.

As I understand it, the cold weather modulator is little more than a check valve calibrated to function below a certain temperature. In the mityvac documents in the documentation section, they make mention of the system operation on as little as 7inhg. My power valve is an 8.5, so Im not sure if I care if this system fails to operate below 8.5 inhg. If anything, my power valve causes the engine to run too rich. Perhaps I dont need a cold weather modulator?

As for operation with cold air and a true cold air intake - I have found that if I want to keep cruise between 14:1 and 15:1 on the wide band, a set of jets is only good for about a 35F ambient temperature swing. I get nervous about cruising any leaner, I have a lot of DCR for 87 octane gas. Plus, it drives like a wet sock when it gets that lean. Im hoping that the hot/cold air factory style intake will make my tune last a little longer through weather fluctuations and seasonal changes. Im also hopeful that it will help the engine cold start and warm up a bit more gracefully. Mine is pitifully cold natured and slow to warm up in cold weather. I do have water piped to the pocket under the intake.

My choke is purely electric.

Thanks for the heads up on toyotas! I like your fabrication advice. Ill probably start by making cardboard patterns?

[Gary Lewis]

Hi Dave!

Sorry, I need to update my signature. Im using an offy C, and EFI exhaust manifolds. I have recentry installed a holley 390. For an air cleaner, Im using a home made number made out of a mix of parts from my original 300 air cleaner and the factory set up off of an 85' 302. The air cleaner body and filter are from the 302, the snorkel and all sensors are from the 300. The air cleaner is oriented in such a way as to use a convenient feature of the air cleaner to help avoid the water core box. Even with this, I still needed an aluminum spacer between the carb and air cleaner to clear everything. In effect, I have a mostly stock style air cleaner set up.

I think there are more details on my air cleaner earlier in this thread, I built it in march or april to sit atop my 2150, which is now replaced with the 390.

All this time, Ive had a dry rotted air damper motor, and a hard time finding a replacement. Just today, I was able to install a new cx120 and start the system up for the first time.

My "cold weather modulator" seems to be an open leak to atmosphere. I took it out of the circuit so that vacuum ran from the manifold, to the bi metal sensor, and then the vacuum motor. The motor emediatly pulled closed to only allow hot air. After 4-5 minutes of run time, the damper slowly opened all the way to the "cold air" position. Seems about right? The ambient temp here is 65F tonight.

As I understand it, the cold weather modulator is little more than a check valve calibrated to function below a certain temperature. In the mityvac documents in the documentation section, they make mention of the system operation on as little as 7inhg. My power valve is an 8.5, so Im not sure if I care if this system fails to operate below 8.5 inhg. If anything, my power valve causes the engine to run too rich. Perhaps I dont need a cold weather modulator?

As for operation with cold air and a true cold air intake - I have found that if I want to keep cruise between 14:1 and 15:1 on the wide band, a set of jets is only good for about a 35F ambient temperature swing. I get nervous about cruising any leaner, I have a lot of DCR for 87 octane gas. Plus, it drives like a wet sock when it gets that lean. Im hoping that the hot/cold air factory style intake will make my tune last a little longer through weather fluctuations and seasonal changes. Im also hopeful that it will help the engine cold start and warm up a bit more gracefully. Mine is pitifully cold natured and slow to warm up in cold weather. I do have water piped to the pocket under the intake.

My choke is purely electric.

Thanks for the heads up on toyotas! I like your fabrication advice. Ill probably start by making cardboard patterns?

I like that air cleaner! Should do a good job and help the warmup significantly. And hopefully it will let one tune last across a wider temp range, but please report back on that.

As for the cold weather modulator, I’ve not had any problems without them.

And that approach is called CAD - Cardboard Aided Design.

[StraightSix]

I like that air cleaner! Should do a good job and help the warmup significantly. And hopefully it will let one tune last across a wider temp range, but please report back on that.

As for the cold weather modulator, I’ve not had any problems without them.

And that approach is called CAD - Cardboard Aided Design.

Myself and many other whipersnappers call my dads hand sketches "Randy CAD". We are all fairly comfortable with autodesk or other similar programs, but hes a bit more old school. Its always good for atleast a chuckle.

I cant imagine how it wouldnt help with cold weather warm up, and so long as it does everything it's advertised to do, I imagine it will greatly cut down on seasonal tuning. Somehow, they configured these things so people who wouldnt know a caeburetor if it hit them in the face could drive them year round without much hassle. Perhaps part of my problem is that this is the only non-EFI vehicle Ive ever had, maybe my expectations are off base.

In any case, this all seems like a big step in the right direction.

[StraightSix]

Myself and many other whipersnappers call my dads hand sketches "Randy CAD". We are all fairly comfortable with autodesk or other similar programs, but hes a bit more old school. Its always good for atleast a chuckle.

I cant imagine how it wouldnt help with cold weather warm up, and so long as it does everything it's advertised to do, I imagine it will greatly cut down on seasonal tuning. Somehow, they configured these things so people who wouldnt know a caeburetor if it hit them in the face could drive them year round without much hassle. Perhaps part of my problem is that this is the only non-EFI vehicle Ive ever had, maybe my expectations are off base.

In any case, this all seems like a big step in the right direction.

Hi guys! I drove the bronco in to work today at 39F ambient. I think cold warm up may have been slightly better today, but its hard to say. When I got to work and checked the position of the diverter in my air horn at idle, I was surprised to see that it was in the fully open position. Perhaps there is enough heat in the engine bay that the system isnt blending at 39F ambient?

[Gary Lewis]

Hi guys! I drove the bronco in to work today at 39F ambient. I think cold warm up may have been slightly better today, but its hard to say. When I got to work and checked the position of the diverter in my air horn at idle, I was surprised to see that it was in the fully open position. Perhaps there is enough heat in the engine bay that the system isnt blending at 39F ambient?

Yes, behind the radiator the air is frequently pretty warm. Most of those systems were set to just over 100F and if your thermostat has opened then you are dumping pretty warm water into the radiator.

And yes, a constant inlet air temp greatly stabilizes the AFR. Which is why I just shake my head when people pull a well-engineered air cleaner system and install an open-element cleaner. Now they are pulling cold air in the winter and hot air in the summer into the carb. And since the vast majority of carbs don't compensate for inlet air temp, that drastically changes the AFR.

[StraightSix]

Yes, behind the radiator the air is frequently pretty warm. Most of those systems were set to just over 100F and if your thermostat has opened then you are dumping pretty warm water into the radiator.

And yes, a constant inlet air temp greatly stabilizes the AFR. Which is why I just shake my head when people pull a well-engineered air cleaner system and install an open-element cleaner. Now they are pulling cold air in the winter and hot air in the summer into the carb. And since the vast majority of carbs don't compensate for inlet air temp, that drastically changes the AFR.

Hi Guys!

Its been quite a while since my last update. Between moving and a new much more demanding job time has been slim. The bronco is still around and we are still making modest progress!

Last Summer I developed a miss at idle. I suspected ignition but decided to run a compression check before going too wild with the volt meter. As it turns out, cylinders 1, 2, 3, 4, and 6 all made between 145- 150 psi while cylinder 5 made 0 psi. I started the truck up and drove it into the workshop where I discovered that unplugging the #5 plug wire with the engine running caused an immediate reduction in idle speed, quality and vacuum as well as causing the wide band O2 to show leaner - so cylinder 5 was indeed combusting and doing something. I repeated the compression check and found that cylinder 5 was still making 0 psi. From there I decided to pressurize cylinder 5 with both valves closed to see which side the air came out through - there was a small puff of air under the paper towel covering the carb inlet, then a clicking sound, and then the cylinder started to build pressure. A subsequent compression check showed 150 psi like the other cylinders.

I tinkered around with every component of the valve train, even going so far as to disassemble the lifters on Cyl 5. The lifters, pushrods and rockers all looked fine. from there I decided it was either a bent/sticky valve or a valve seat issue (this head has pressed in seats). since I had pesky water and oil leaks I decided to pull the entire block instead of just pulling the head in the truck.

I never did find the root cause of my miss at idle, the valves were straight and felt very good in the valve guides, no apparent seat issues.

oil pressure had been low in this engine since I had it rebuilt (8-10 PSI at hot idle) so I decided to search for the source of my low oil pressure while I had the block on the engine stand. Turs out that my main and rod bearings were trashed with deep gashes in the bearings and the journals.

I spent a few frustrated weeks trying to decide what to do and settled on having the 300 block rebuilt again with a few upgrades. presently, Im 0.040" over, 8.8:1 static compression, about 7:1 dynamic compression, Custom ground cam (204@0.050, 270@0.006, .448 gross valve lift), ARP main, rod, and head studs, and a Promaxx performance cylinder head with efi style stock stamped rocker arms. The head is a virgin casting with the EFI style chambers, 12 hardened seats, 1.94 and 1.60 valves, and it is CNC ported in the runners and chambers from Promaxx. Im hoping for a good street engine with slightly more power for motivating this heavy vehicle up and down steep north Ga hills.

The engine came home Monday and is on the engine stand. Im dressing it this week and hope to have it installed in the truck by early next week. With any luck it will be running by the end of next week. It will go back together with a recurved DS2 distributor, factory DS2 ignition box, EFI exhaust manifolds, Offy C intake, the Holley 390 and my home assembled 4V factory style intake.

It has been nearly two and a half years since the original engine went out, hopefully Ill soon be focusing my efforts back outside of the engine bay! Ill keep you all posted on startup and tuning.

[ArdWrknTrk]

Hi Guys!

Its been quite a while since my last update. Between moving and a new much more demanding job time has been slim. The bronco is still around and we are still making modest progress!

Last Summer I developed a miss at idle. I suspected ignition but decided to run a compression check before going too wild with the volt meter. As it turns out, cylinders 1, 2, 3, 4, and 6 all made between 145- 150 psi while cylinder 5 made 0 psi. I started the truck up and drove it into the workshop where I discovered that unplugging the #5 plug wire with the engine running caused an immediate reduction in idle speed, quality and vacuum as well as causing the wide band O2 to show leaner - so cylinder 5 was indeed combusting and doing something. I repeated the compression check and found that cylinder 5 was still making 0 psi. From there I decided to pressurize cylinder 5 with both valves closed to see which side the air came out through - there was a small puff of air under the paper towel covering the carb inlet, then a clicking sound, and then the cylinder started to build pressure. A subsequent compression check showed 150 psi like the other cylinders.

I tinkered around with every component of the valve train, even going so far as to disassemble the lifters on Cyl 5. The lifters, pushrods and rockers all looked fine. from there I decided it was either a bent/sticky valve or a valve seat issue (this head has pressed in seats). since I had pesky water and oil leaks I decided to pull the entire block instead of just pulling the head in the truck.

I never did find the root cause of my miss at idle, the valves were straight and felt very good in the valve guides, no apparent seat issues.

oil pressure had been low in this engine since I had it rebuilt (8-10 PSI at hot idle) so I decided to search for the source of my low oil pressure while I had the block on the engine stand. Turs out that my main and rod bearings were trashed with deep gashes in the bearings and the journals.

I spent a few frustrated weeks trying to decide what to do and settled on having the 300 block rebuilt again with a few upgrades. presently, Im 0.040" over, 8.8:1 static compression, about 7:1 dynamic compression, Custom ground cam (204@0.050, 270@0.006, .448 gross valve lift), ARP main, rod, and head studs, and a Promaxx performance cylinder head with efi style stock stamped rocker arms. The head is a virgin casting with the EFI style chambers, 12 hardened seats, 1.94 and 1.60 valves, and it is CNC ported in the runners and chambers from Promaxx. Im hoping for a good street engine with slightly more power for motivating this heavy vehicle up and down steep north Ga hills.

The engine came home Monday and is on the engine stand. Im dressing it this week and hope to have it installed in the truck by early next week. With any luck it will be running by the end of next week. It will go back together with a recurved DS2 distributor, factory DS2 ignition box, EFI exhaust manifolds, Offy C intake, the Holley 390 and my home assembled 4V factory style intake.

It has been nearly two and a half years since the original engine went out, hopefully Ill soon be focusing my efforts back outside of the engine bay! Ill keep you all posted on startup and tuning.

30 month gestation?

Wow! You have sure come a long way since your last update.

Should be good for another 300,000 miles!

[Gary Lewis]

30 month gestation?

Wow! You have sure come a long way since your last update.

Should be good for another 300,000 miles!

Wow! That's a lot of work, and worry. I hope you get it started up with no problems and get to enjoy what should be a very strong engine.

[StraightSix]

Wow! That's a lot of work, and worry. I hope you get it started up with no problems and get to enjoy what should be a very strong engine.

Thanks Guys! 30 months, wow! Ill try to get some photos posted tomorrow!

[StraightSix]

Thanks Guys! 30 months, wow! Ill try to get some photos posted tomorrow!

Hi Guys! here are some photos to go along with the story from yesterday.

bearing damage - I suspect machining debris from the original rebuild was captive in the crank or block at first fire of the engine in early 2022.

The new Engine

I ported the intake, I only have this before photo showing the alignment issue between the spacer and the inlet flange.

The new heads intake and exhaust ports - I was really pleased with these.

Finally, the Holley 390. this carb has a few upgrades to include a rear metering block, a quick fuel adjustable vacuum canister (white spring installed), and a mechanical choke. I dont recall my jetting at the moment, but its somewhere in the neighborhood of 54s in the primaries and 58s in the secondaries. Ill try to verify. Its running an 8.5 power valve. The carb was running great when I pulled the engine. I took it apart and cleaned everything up at that time so it should be ready to drop on and run. hopefully the new cam wont play too much havoc on tuning.