258 intake

[craveman85]

I'm switching my 81 CJ8 build from the original iron duke to a AMC 258 i6 / 4.2l . I have the t176trans for it already. I plan on doing a cam, rebuild, 4.0 head, 4 barrel intake and headers. Offy makes 2 intakes. One is a single plane and the other is their dual port. Do any of you guys have any input of which is better. This will be a 95% street driven jeep. I'm thinking of a holley 390 4 barrel. I'd go with the 470 truck avenger but it's probably too big.

 

[mtnwhlr]

My vote is for a dual plane. I think a 4bbl on a AMC 258 i6 / 4.2l is a bit much but I'm sure others will disagree.

 

[gert]

the dual port is an interesting design, how well it works compared to modern intakes Im not sure. Their idea was the primaries are fed by one set of ports to try and give a better vacuum signal and more torque, and when you floor it to open the secondaries they flow thru the other port which is larger to give you the required volume of air to support wide open throttle. It seems to be a design lost to time, My personal option I would stick with the single plane so that you have the option of adding a throttle body injection system at a later date.

 

[mtnwhlr]

This what I base my post on. http://www.google.com/url?url=http:...ggcMAI&usg=AFQjCNHNrIuqbNevY0mq1_r3iDllVoRFcA

 

[craveman85]

I think factor intakes are technically a single plane aren't they?

 

[gert]

I think factor intakes are technically a single plane aren't they?

Yes the factory 6 cylinder intake is a single plane, the V8 is a dual plane, a dual plane splits 1/2 the cylinders to one plane and the other half to the other plane, so that one primary and one secondary feed halftime the cylinders the offy dual port is different it's like 2 single planes put together one plane does the primaries and the other plane does the secondaries, so normal operation the engine runs on both primaries it's a different style of intake


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[Lumpy Grits]

The AMC 258 i6 / 4.2l was based off a tractor engine. It's 'redlined' at 4500rpm.
The factory went with a single plane intake for a reason.......
LG

 

[mtnwhlr]

The AMC 258 i6 / 4.2l was based off a tractor engine. It's 'redlined' at 4500rpm.
The factory went with a single plane intake for a reason.......
LG

And a 2bbl for a reason.

 

[gert]

And a 2bbl for a reason.

Lol ya it's a Jeep, they were probably afraid of you spinning the hubs off the AMC20


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[craveman85]

What's the main thing holding it back from going past 4500?

 

[Lumpy Grits]

Just the way the engine is built. Torque drops off past 4K.
Look how low a diesel engine is redlined.
LG

 

[jakeh937]

Just the way the engine is built. Torque drops off past 4K.

Look how low a diesel engine is redlined.

LG

I got the chance to work on a big cat engine.. operated about 1100 rpm. ALL torque.


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[gert]

I got the chance to work on a big cat engine.. operated about 1100 rpm. ALL torque.


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Lol my Cummings makes 650 ft/lbs at 1400rpm =0


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[jakeh937]

Lol my Cummings makes 650 ft/lbs at 1400rpm =0


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Cummins are awesome. I think the best thing to do with amc straight 6's are build em for low end torque. Just my .02


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[Captainlance]

Cam in block engines rarely can be successfully operated above 4000 rpm. for any length of time. Overhead cam engines can go to over 10K rpm with ease.

 

[mtnwhlr]

Cummins are awesome. I think the best thing to do with amc straight 6's are build em for low end torque. Just my .02


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that is what they were built for. This is why I think guys that are adding 4bbl carbs and headers to them are just throwing money away.

 

[jakeh937]

that is what they were built for. This is why I think guys that are adding 4bbl carbs and headers to them are just throwing money away.

I have done a lot of reading as far as 4bbl cards and ALOT of people say one of the best carbs to throw on that engine is the mc2100. Once mine is finished being built that's what I'm gunna throw on.


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[mtnwhlr]

I have done a lot of reading as far as 4bbl cards and ALOT of people say one of the best carbs to throw on that engine is the mc2100. Once mine is finished being built that's what I'm gunna throw on.


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[jakeh937]

U take ur jeep in the mountains? If so, how's it do with that carb if that's what ur running?


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[Lumpy Grits]

Cam in block engines rarely can be successfully operated above 4000 rpm. for any length of time. Overhead cam engines can go to over 10K rpm with ease.

Stock V-8s RL at 6500rpm most of the time. They are not an overhead cam.
LG