redwolf624 Posted August 17, 2014 Author Share Posted August 17, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better? we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 17, 2014 Share Posted August 17, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better? we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf Well, do the math and let us know. Inquiring minds want to know. You asked, so let's see what ya got for an answer. Link to comment Share on other sites More sharing options...
redwolf624 Posted August 17, 2014 Author Share Posted August 17, 2014 just by using Engine size (in Cubic Inches) x Max RPMs of motor / 3456 = Max CFM from what eagle told me the cubic lnches was 244 i got 388, but i had to use 5500 for a peak RPMs, Redwolf Link to comment Share on other sites More sharing options...
outlaw star Posted August 18, 2014 Share Posted August 18, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 300 cfm would be ideal. You can get a 4bbl intake from Cliffords and put an adapter plate on it for a simple Holley 2bbl carb or use Cliffords adapter for a 300cfm Weber. My 4.2L in my Xj before I stroked it to 4.9L and added EFI was using a Weber 300 with Clifford 4.0 manifold (I used the 4.0L head) and ran great. Link to comment Share on other sites More sharing options...
yxmj Posted August 18, 2014 Share Posted August 18, 2014 :popcorn: HA HA these posts are always the best for the head shaking entertainment value alone..... :rock on: Link to comment Share on other sites More sharing options...
Eagle Posted August 18, 2014 Share Posted August 18, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better? we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf That's an expensive backup. You'll need a new fuel pump, because carburetors only want about 5 to 7 psi, not 40. You'll need a new distributor, because the one in the 4.0L Jeeps is controlled by the ECU. You'll probably need a new coil to go with the new distributor. And you'll need an intake manifold on which to mount the (expensive) new carburetor. I'd say you're looking at between $500 and $750, minimum, all to avoid buying a used or reconditioned ECU for a Renix 4.0L that you can probably find for $25. Doesn't sound like a great plan to me. Link to comment Share on other sites More sharing options...
Eagle Posted August 18, 2014 Share Posted August 18, 2014 just by using Engine size (in Cubic Inches) x Max RPMs of motor / 3456 = Max CFM from what eagle told me the cubic lnches was 244 i got 388, but i had to use 5500 for a peak RPMs, Why did you "have to" use 5,500 RPM? I know the factory tachometer sets that as the redline, but the 4.0L engine (especially the Renix version) doesn't make any more power above about 4,000 RPM. It's a torque engine, not a race engine. There is nothing to be gained by running any higher than 4,000 to 4,500 RPM. I told you to use 5,000 just to leave some "headroom." Between an '88 XJ, an '87 MJ, and two '88 MJs I don't think I've ever seen the north side of 3,500 RPM in well over 300,000 miles of driving. (The '88 XJ alone has 287,000 on it.) The original 1987 model was rated at 173 horsepower at 4,750 RPM and 220 foot-pounds of torque at 2,000 RPM. The horsepower rating for this version was raised to 177 horsepower at 4,750 RPM and 224 foot-pounds of torque at 2,400 RPM for model years 1988 through 1990. You gain absolutely nothing by revving the engine beyond the horsepower peak, and you get the best driveability by staying closer to the torque peak -- which is 2,200 to 2,400 RPM. Link to comment Share on other sites More sharing options...
outlaw star Posted August 18, 2014 Share Posted August 18, 2014 :popcorn: HA HA these posts are always the best for the head shaking entertainment value alone..... :rock on: Why's that? And are you referring to the whole thread or a single post? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 18, 2014 Share Posted August 18, 2014 :popcorn: HA HA these posts are always the best for the head shaking entertainment value alone..... :rock on: Why's that? And are you referring to the whole thread or a single post? I'm sure it's the thread............. Link to comment Share on other sites More sharing options...
yxmj Posted August 18, 2014 Share Posted August 18, 2014 Yes....like driving by a car wreck.... :shake: ...don't want to look.......but can't turn away..... :popcorn: Link to comment Share on other sites More sharing options...
redwolf624 Posted August 18, 2014 Author Share Posted August 18, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better? we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf That's an expensive backup. You'll need a new fuel pump, because carburetors only want about 5 to 7 psi, not 40. You'll need a new distributor, because the one in the 4.0L Jeeps is controlled by the ECU. You'll probably need a new coil to go with the new distributor. And you'll need an intake manifold on which to mount the (expensive) new carburetor. I'd say you're looking at between $500 and $750, minimum, all to avoid buying a used or reconditioned ECU for a Renix 4.0L that you can probably find for $25. Doesn't sound like a great plan to me. that bein said eagle, could that be half the reason why my MJ runs like crap, the engine i put in it was a 2.8 out of a 93 sonoma and it was fuel injected, we used the distributor off the sonoma? Redwolf Link to comment Share on other sites More sharing options...
outlaw star Posted August 18, 2014 Share Posted August 18, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better? we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf That's an expensive backup. You'll need a new fuel pump, because carburetors only want about 5 to 7 psi, not 40. You'll need a new distributor, because the one in the 4.0L Jeeps is controlled by the ECU. You'll probably need a new coil to go with the new distributor. And you'll need an intake manifold on which to mount the (expensive) new carburetor. I'd say you're looking at between $500 and $750, minimum, all to avoid buying a used or reconditioned ECU for a Renix 4.0L that you can probably find for $25. Doesn't sound like a great plan to me. that bein said eagle, could that be half the reason why my MJ runs like crap, the engine i put in it was a 2.8 out of a 93 sonoma and it was fuel injected, we used the distributor off the sonoma? Redwolf It may be a Chevy 2.8 and various style GM sensors but Jeep had they're own ignition system. You should use the AMC 2.8 distributor and Ignition system with your vehicle. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 19, 2014 Share Posted August 19, 2014 ok so 300CFMs for a carb for the 2.8, say i could get my hands on a 4.0 but couldn't get the CPU, what CFMs would i need for a carb for a 4.0? Redwolf 4 liters is 244 cubic inches. Plug that into the formula, use 5,000 as the peak RPM, and do the math. But WHY would you use a carburetor on a 4.0L when the EFI is so much better?we don't know if the computer for the 4,0 works, just a back up option if it don't, Redwolf That's an expensive backup. You'll need a new fuel pump, because carburetors only want about 5 to 7 psi, not 40. You'll need a new distributor, because the one in the 4.0L Jeeps is controlled by the ECU. You'll probably need a new coil to go with the new distributor. And you'll need an intake manifold on which to mount the (expensive) new carburetor. I'd say you're looking at between $500 and $750, minimum, all to avoid buying a used or reconditioned ECU for a Renix 4.0L that you can probably find for $25. Doesn't sound like a great plan to me. that bein said eagle, could that be half the reason why my MJ runs like crap, the engine i put in it was a 2.8 out of a 93 sonoma and it was fuel injected, we used the distributor off the sonoma? Redwolf It may be a Chevy 2.8 and various style GM sensors but Jeep had they're own ignition system. You should use the AMC 2.8 distributor and Ignition system with your vehicle. Absolutely. Link to comment Share on other sites More sharing options...
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