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I was just about to slap a set of fender well headers on my 66 cj 6 with a 225 and it seems I have heard quite a few folks say they prefer the stock manifolds. I intended to move up to a 4 barrel intake and Holley 390 at the same time. What is everyone's opinion on this matter?

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Hi, Stefan...Thanks for joining the forums!

I have a range of concerns around headers and the Jeep/Buick 225 engine's particular needs.  Also important is the safety of your vehicle's occupants.  Your desire to improve the performance of your Jeep CJ-6 is fully understandable.  I'd like to begin with the positives around adding headers, a performance 4-barrel intake manifold and a four-barrel carburetor:  

1) The 225 Buick/Dauntless V-6 engine will perform better with headers, as the stock 225 exhaust manifold design is highly restrictive.  More directly, a flipped over cast iron exhaust manifold at one bank was Kaiser/Jeep's hasty way of fitting the 225 V-6 into an F-head four-cylinder engine bay.  

2) Headers, if tuned properly and not just designed to fit okay and look good, can offer less restriction and better exhaust scavenging.  Seek out performance (preferably dynamometer chart) results for the headers.  Headers can be a distinct boost in power output, typically in the mid-range to high rpm range.  Headers generally do not make much, if any, performance difference at lower engine speeds unless the OE exhaust system is badly engineered.  We know the stock exhaust layout is marginal.

3)  A Buick 225 V-6 in the earliest CJ chassis looks like a conversion engine.  Jeep Corporation was struggling to fit the package into the F-head four-cylinder engine bay.  On your '66 model, a set of headers will look good and inevitably perform better than the stock exhaust system.

4)  The four-barrel intake manifold distributes fuel more uniformly than the stock Rochester 2-barrel (2GC type) intake.  Cylinders receive a more uniform air-fuel charge with a four-barrel manifold, although a V-6 engine does better with a two-barrel carburetor than a V-8 engine does.  (The worst case for uneven fuel distribution is the Jeep inline sixes with either one-barrel or two barrel carburetion.)  A dual-plane versus open plenum intake manifold is another question we can discuss. 

I do have several concerns and biases related to modifying your odd-fire 225 Dauntless V-6:

1)  Carbureted engines require warming the intake manifold as quickly as possible to facilitate proper combustion of air/fuel when the engine is cold.  It is desirable to warm the intake manifold when the engine first starts and begins to warm up.  Once a stock 225 V-6 engine is warm, the intake manifold is also warm and no longer needs an auxiliary source of heat (in this case exhaust back-pressure flow) across the intake manifold.  The heat riser opens, which dramatically reduces the exhaust flow across the intake manifold.

Note: Your planned aftermarket intake manifold for the Holley 390 may not have an exhaust crossover passage to warm the base of the carburetor.  This leads to incomplete combustion when the engine is cold.  The passage in the stock iron manifold is the typical head-to-head cast port that runs beneath the plenum.  On a bright note, aluminum dissipates heat rapidly, and the aftermarket manifold would warm up quickly once the engine block, heads and coolant begin to warm.

2)  You may have a hand choke on your Jeep's carburetor.  If, however, you have a heat stove or bimetallic spring choke, you need heat across the intake manifold and at the choke's heat source.  On the Buick 225 V-6 and other period engines, a heat riser valve is used to create exhaust back-pressure and flow hot exhaust through the crossover passageway beneath the intake manifold.  When you install headers, the headers' collectors are usually too far from the engine to efficiently operate a bimetallic spring heat riser valve.  Stubby headers might be close enough for a heat riser.  

Note:  One remedy would be a vacuum operated heat riser like later emissions carbureted engines use. the signal coming by way of a thermal vacuum switch (TVS) threaded into a cooling port on the heads or intake manifold's coolant passage.  Without a heat riser, like with most header systems, there will be no hot exhaust passing across the intake manifold when the engine is cold—which also means that there will be insufficient heat to operate a bimetallic spring choke.  At the least, you would have to live with a balky engine when cold and during the engine warm up phase.

3) If you have a pristine '66 CJ-6 and want the body to remain stock, make sure the headers do not require fender/well cutting or extreme modifications.  Fender well exit headers have been popular and require sheet metal modifications that you may not be willing to make.  At least know the fitment requirements before starting the project.  Make your judgment call.

4) In the day, headers were often accompanied by side exit exhausts and short mufflers.  Not sure where you plan to go here.  I can only say that side exit pipes on a Jeep CJ (81" wheelbase vintage CJ-5 or even the 20" longer wheelbase CJ-6) are a very bad idea.  I always run exhaust pipes to the rear of the vehicle, emulating the stock approach, either with a single, larger diameter exhaust pipe or with dual exhausts of the right diameter each.  Carefully fitted, you can get dual exhausts beneath your CJ-6.  It takes a competent muffler shop and a lot of precise bends to avoid the chassis, axle, brake and other components!  An experienced shop can determine the right size exhaust tubing and muffler inlet/outlet sizes.

5) Side exit dual exhausts or open headers can make vehicle occupants sick. Crawling on rocks or idling, with typically rich fuel mixtures roiling up from the tub sides, will flood the cabin with toxic and noxious fumes.  While an open top would seem like the worst situation, a cloth top or hard top can lead to accumulation of fumes and lethal (i.e., odorless CO) gas mixtures.  If you jet that 390 CFM Holley four-barrel for sea level, I guarantee that by 2500 feet elevation it will be running rich, and the condition will worsen proportionately as the altitude increases.  This overly rich air/fuel mixture, whether you find it acceptable or not, needs to exit the rear of your Jeep.

This may seem like a blunt view of headers or the Holley square-bore carburetor design.  In fairness, headers and a Holley 390 square-bore, four-barrel carburetor with aftermarket manifold have been a chosen path for many Jeep 225 V-6 owners.  If you're satisfied with this approach, I understand.

My personal carburetion choice, however, would be either a Carter AFB (genuine Carter from a specific OE engine application, I can offer particular AFB model numbers) or a Quadrajet from a small displacement GM engine as close to 225 cubic inches as possible.  

Note:  The altitude hypersensitivity of "high performance" 4100 square bore 4-barrel series carburetors and even the universal 2300 series two-barrel Holley carburetors is a consideration here.  Objectively, manufacturers like International Harvester and Ford did have success with properly tuned and equipped OE versions of both the 2300 series two-barrel and 4100 series square-bore four-barrel carburetors.  As for the off-the-shelf aftermarket "universal" Holley carburetors, unless you have Holley tuning experience and know Holley jetting, power valve requirements, accelerator pump and float tricks, you might be much happier with a blueprinted OE Carter AFB or small GM-application Rochester Qjet carburetor.  

Many would suggest that your best bet is a TBI (Throttle Body Injection) conversion.  This is a highly beneficial option, however, cost could be an issue.  TBI/EFI does not require a heat riser and would respond nicely to headers...We can discuss various ways that OE or aftermarket TBI could be retrofitted. 

I'd like to know more details about your engine, its overall condition, the Holley carburetor (part number) that you have in mind, and the type of headers you have considered.  Also, what is your current ignition distributor type and firing voltage?  Camshaft profile?  Compression ratio (stock or otherwise)?

Do you need a 390 CFM four-barrel carburetor?  The 2G and 2GC Rochester two-barrel series is highly reliable, these are predictable carburetors.  They were found in a wide variety of applications.  In the late 'sixties, I rebuilt large 2GC units that fueled standard compression 389 Pontiac V-8s and other big GM cars equipped with base engines.  I have rebuilt and tuned tri-power systems that benefited from 2G and 2GC carburetion.  From the mid-'fifties onward, the standard compression small-block Chevrolet V-8 truck and passenger car versions, units similar to your 2G or 2GC, were popular.  Your carburetor is easy to service and will deliver excellent performance in return.

I unearthed these figures courtesy of Doug Roe's classic work, Rochester Carburetors (HP Books, page 108) for approximate CFM flow on various 2G series carburetors.  We could look into your carburetor's dimensions and weigh what you currently have in flow rate:

1-1/4" flange, 1-7/16" bore x 1-3/32" venturi = 278 CFM

1-1/2" Flange carbs each have 1-11/16" bores:

1-3/16" venturi = 352 CFM

1-1/4" venturi = 381 CFM

1-5/16" venturi = 423 CFM

1-3/8" venturi = 435 CFM

All ratings @ 3.0 in HG

It would be great to see our vintage Jeep CJ 225 V-6 forum members jump into this discussion!  Please share your experiences with Stefan...

Moses

Edited by Moses Ludel

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I swapped a 225 into my 59 cj5. I went with a set of Sanderson headers, sort of a block hugger style, only because my stock manifolds were junk. My brother did the same swap, on same year jeep and stuck with manifolds. I think his drivers side manifold was from a commando or something, it actually points to the back. There is zero difference between the two performance wise. Mine is louder for sure.  I'm certain his manifolds will outlast my headers. I went with raw steel finsh and painted them myself with high temp header paint, about a hundred coats, wich is all gone replaced by nice looking rust. We both considered doing a holly 390 with a offenhauser intake, but it was going to be pretty expensive. That was what stopped us. Also Rochester 2gc carbs are literally everywhere..easy to work on and cheap too.

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Thank you Moses for the in depth reply. Let me tell you what I am looking to gain and perhaps you can make some suggestions. I have a 66 cj6 that currently is bone stock with a buick 225. I have been parts collecting for the past year and plan on getting the build started this summer. As a novelty, I would really like to keep the major components of this jeep as jeep factory items so I have a th400 and dana 20 from a commando, a postal rear end and a narrow track dana 30 front end waiting on the shop floor to be swapped in.  I am looking to make a weekend beach/camping family vehicle out of her and want to build the motor to get myself up in the 175-180HP range without getting exotic with it. I am not one to do burnouts or punch the gas un-necessarily but would like to keep up with highway traffic and have enough on ramp power to merge without scaring my wife. I would like to be able to tow a small trailer with her on occasion as well. Honestly 80% of my driving will be on road and I was trying to get the performance I was looking for through induction and exhaust. I wouldn't mind gaining some power through a cam upgrade as well but i haven't gotten that far in my plans to know what is available our how it would compliment my potential set up.  I plan on running a mild lift with either 32 or 33 inch tires and 4.10 gears. The motor that is in the jeep now has the stock ingnition but I have a spare motor that has an HEI set up that I was planning on using. I live in North Central Florida where everything is flat and we probably never get above 750ft of elevation. I wouldn't mind a TBI system, what is out there? Perhaps I am barking up the wrong tree? Maybe I should be trying to build that power internally? Let me know what you think! 

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Stefan L...This is helpful, thanks for clarifying your Jeep CJ-6 equipment and goals.  Here is my take on each of your points:

4 minutes ago, Stefan L said:

As a novelty, I would really like to keep the major components of this jeep as jeep factory items so I have a th400 and dana 20 from a commando, a postal rear end and a narrow track dana 30 front end waiting on the shop floor to be swapped in.

I'm on board with preserving a pristine CJ-6 body and frame.  Your proposed changes should not have a large impact on the chassis if done properly.  Good plan, does the narrow track 30 have disc brakes?  The postal rear end should have decent size drum brakes, the combination would work.  Ditching the OEM brakes is wise for your family's safety and modernizing the vehicle's handling.

6 minutes ago, Stefan L said:

I am looking to make a weekend beach/camping family vehicle out of her and want to build the motor to get myself up in the 175-180HP range without getting exotic with it. I am not one to do burnouts or punch the gas un-necessarily but would like to keep up with highway traffic and have enough on ramp power to merge without scaring my wife. I would like to be able to tow a small trailer with her on occasion as well. Honestly 80% of my driving will be on road and I was trying to get the performance I was looking for through induction and exhaust. I wouldn't mind gaining some power through a cam upgrade as well but i haven't gotten that far in my plans to know what is available our how it would compliment my potential set up.  

Understood that this is a family, multipurpose vehicle.  Drivability is a key issue, you have good plans, and the 101" wheelbase does help with handling.  A Saginaw power steering conversion with one-piece tie rod (see Advance Adapters) would surely be a consideration if you still have the Ross TL steering gear...Engine wise, with the gearing and tire diameter proposed, and without overdrive in the THM400 transmission, I would build the engine for strong low-end and mid-range power.  For me, this translates as an RV camshaft or a grind with very mild duration increase and an emphasis on more valve lift than stock for bottom end power.  You need to move this vehicle along, and especially for light trailer toting, higher rpm power is not the goal. 

For a multipurpose 4x4, my camshaft mantra for decades has been the CompCams 252 grind or equivalent.  Fortunately, this grind is still available for the 225 Buick V-6.  Here are details at Summit Racing, you may find more at the CompCams' site:  http://www.summitracing.com/parts/cca-cl63-234-4/overview/make/buick.  If your engine is in top condition, you can change the camshaft and lifters in the chassis, add a Cloyes timing sprocket and chain kit and Melling's high volume oil pump kit, additional gains while you're at it.  If you are interested in judging the engine's condition, follow the cylinder leak down testing I describe in the General Repairs forum and elsewhere at these forums.

With the 252 camshaft or equivalent, you could run a set of headers or simply maintain the stock manifolds and split the exhaust into dual exhausts.  Rear exit tailpipes are a mandatory for wife, children, driver and other living creatures!  Headers, with the concerns I mention, are a consideration, there's certainly some benefit over the stock manifolds.  As for the induction, a dual-plane manifold is essential, I would consider a small AFB (not the Edelbrock equivalent if a stock OEM AFB carburetor is available) or a smaller application Rochester Quadrajet.  The original Rochester 2G or 2GC is a failsafe alternative, there is adequate CFM with a "blueprint rebuild" of the stock carburetor, and the intake manifold is not that bad.  Choice is governed by your budget here.

20 minutes ago, Stefan L said:

I plan on running a mild lift with either 32 or 33 inch tires and 4.10 gears. The motor that is in the jeep now has the stock ignition but I have a spare motor that has an HEI set up that I was planning on using.

Good plans.  Be certain to widen the track width with negative offset, wider wheels.  4" lift, 33x12.5x15 on a maximum 10" wheel with negative rim offset would be the limit.  Make sure you have the fender and frame clearance for the tires and wheels, test a set of wheels and tires at a reputable tire store before spending money here.  You may need a smaller tire, though many run 33" with a 4" or so lift and negative offset wheels.

That Delco-Remy HEI ignition needs to be odd-fire era 1975-77 GM/Buick 231 V-6 type.  If you have a complete 231 odd-fire V-6, that's a possible buildup, though I would opt for the 231 even-fire engine like I address in my Jeep CJ Rebuilder's Manual:  1946-71 (Bentley Publishers).  In the book, I discuss engine details mentioned here as well.

29 minutes ago, Stefan L said:

I live in North Central Florida where everything is flat and we probably never get above 750ft of elevation. I wouldn't mind a TBI system, what is out there? Perhaps I am barking up the wrong tree? Maybe I should be trying to build that power internally? Let me know what you think! 

TBI is always an option.  There were OEM GM 3.8L V-6 engines with TBI in the early 'eighties.  If you're good with electronics and wiring, an OEM boneyard or Craigslist donor might be available.  Another route would be Howell Engineering TBI.  This system is compatible with your standalone ignition and has been popular for Jeep 258 inline six retrofits.  Howell sells various segments of the kit, including the TBI unit and computer (essentially 4.3L GM V-6 pieces) plus a wiring harness interface and correct pressure fuel pump.  Using an adapter, you can mate the TBI unit to your current intake manifold or a 4-barrel manifold, either would work...This is mostly OEM, proven GM parts, and the system would not be overkill for a Buick 225/3.7L V-6, especially with oxygen sensor feedback and electronic fuel metering.  Worth visiting the Howell site.

There are distinct gains with TBI.  On the Jeep 258/4.2L, TBI delivers approximately 50 extra horsepower over stock while using the OEM (i.e., poor flow) intake manifold.  TBI is not altitude sensitive when using O2 sensor and MAP feedback.  TBI would certainly deliver more performance gains than any other modification we're discussing.  Headers would work very well with TBI and offer the kind of exhaust flow you need with EFI.  The O2 sensor bung can be installed on any exhaust system, though it needs to be located at the right point with regard to engine heat and accurate exhaust content readings.

Carburetion is acceptable with your fixed altitude plans, and even the 390 CFM Holley could be made to run well at this narrow range of elevation.  It would come down to cost and your budget.  If it comes down to headers versus a four-barrel intake and carburetor, I would start with the headers and a complete dual exhaust system to the rear of the tub (stock exit locations).  In the event you want more induction after that point, you would have the required exhaust modifications in place.

Moses

 

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Hello again Moses. I have been working a lot and haven't had a chance to start my Jeep project yet but I do have Any laying around the shop. I thought it be way too big though. I think it is the smaller version, 750 cfm. I agree with that being a much better carb but again will the 225 be able to handle it? Can I jet it way down? Let me know. I am very interested in going that route if possible. Thanks!

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Stefan L...The 750 CFM would be way too much flow.  The venturi bores are not desirable, and "jetting down" is not practical or likely to produce good results.

300 CFM would be plenty, 350-400 CFM would be more than enough even with the headers.  Think in terms of approximately 1 CFM per cubic inch of engine displacement to spin the engine at 4,000 rpm.  350 CFM would provide 6000-plus rpm capability.

Moses

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