redwolf624 Posted August 14, 2014 Share Posted August 14, 2014 so i found out that i can get all my parts half off through work if i have the parts store order my stuff and charge it through the stores account as long as i pay for it :banana: so i'm wondering what the CFMs for the rochester 2SE carb is, i read somewhere before that it was around 300, if that's true and i slap a holly carb on it (it's still 2 bbl) that has 500CFM? gotta know before i order a carb i can't use, Redwolf Link to comment Share on other sites More sharing options...
outlaw star Posted August 14, 2014 Share Posted August 14, 2014 Weber makes a 32/36 DEGV carb as a replacement/upgrade for the Rochester one. Here's the carb size math formula to help you in choosing CFM size. Engine size (in Cubic Inches) x Max RPMs of motor / 3456 = Max CFM. Now this formula give 100% Volumetric Efficiency and most street motors only run at 70-80% VE IE: (I'll use a 2.5L as an example) 150 x 5,500 / 3,456 = 238.7 CFM. So max CFM size would be a 250 CFM. It's hard to get a carb in the exact CFM size but choose the size closest to the math. Hope this helps. Link to comment Share on other sites More sharing options...
Eagle Posted August 14, 2014 Share Posted August 14, 2014 500 CFM is too big for a 2.8L. Using the formula above, for your engine it would be: 170 x 5500 / 3456 = 270.5 CFM In reality, you probably won't be operating at 5500 RPM anyway, so that 270 CFM for practical purposes will be 245. A 500 CFM carburetor will be twice as much flow as you'll ever need. Link to comment Share on other sites More sharing options...
outlaw star Posted August 14, 2014 Share Posted August 14, 2014 500 CFM is too big for a 2.8L. Using the formula above, for your engine it would be: 170 x 5500 / 3456 = 270.5 CFM In reality, you probably won't be operating at 5500 RPM anyway, so that 270 CFM for practical purposes will be 245. A 500 CFM carburetor will be twice as much flow as you'll ever need. Hence the 70-80% VE rating. Only fully built race motors run close to 100% VE. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 14, 2014 Share Posted August 14, 2014 Get the Weber. Link to comment Share on other sites More sharing options...
redwolf624 Posted August 15, 2014 Author Share Posted August 15, 2014 so ok, i have a 93 gmc sonoma 2.8 and i don't know by max RPMs for the motor, how would i figure that out? also what would happen if i slapped a 500 CFMs carb on my truck? Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 15, 2014 Share Posted August 15, 2014 It would run like $#!&, but doesn't it do that already? Link to comment Share on other sites More sharing options...
redwolf624 Posted August 16, 2014 Author Share Posted August 16, 2014 It would run like $#!&, but doesn't it do that already? yeah :fs1: Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 Do the Weber..... Link to comment Share on other sites More sharing options...
redwolf624 Posted August 16, 2014 Author Share Posted August 16, 2014 Do the Weber..... but what CFM? Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 How many are available for the 2.8? Gimme some links. Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2014 Share Posted August 16, 2014 but what CFM? See posts number 2 and 3. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 http://www.carbsdirect.com/product-p/wk490.htm Link to comment Share on other sites More sharing options...
redwolf624 Posted August 16, 2014 Author Share Posted August 16, 2014 but what CFM? See posts number 2 and 3. see post number 6, i don't know my max rpms, Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 but what CFM? See posts number 2 and 3. see post number 6, i don't know my max rpms, Redwolf Who cares? Redline/Weber has done all the work for you. It works. Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2014 Share Posted August 16, 2014 see post number 6, i don't know my max rpms, 5,000 RPM. And you probably will never actually take it that high. If you do, you'll only do it once and after the engine blows up a carburetor will be the least of your worries. Why do you think we used 5,500 and 5,000 RPM in the examples? You need a 300 CFM carburetor. That Weber kit in Cruiser's link looks like just what you need. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 see post number 6, i don't know my max rpms, 5,000 RPM. And you probably will never actually take it that high. If you do, you'll only do it once and after the engine blows up a carburetor will be the least of your worries. I almost posted that^^ word for word!! LOL. Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2014 Share Posted August 16, 2014 5,000 RPM. And you probably will never actually take it that high. If you do, you'll only do it once and after the engine blows up a carburetor will be the least of your worries. I almost posted that^^ word for word!! LOL. You probably remember, too. When I bought my '88 XJ new, the service manager at the stealership was a racing buddy, and I hung out in the shop fairly often. Back then there were still a lot of 84, 85 and 86 Cherokees on the road, and every time I went to the dealer's shop there would be another one with a connecting rod blown through the side of the block. You DON'T beat on the 2.8L engine. (And what many people consider to be normal driving, unfortunately, is "beating on it" for the 2.8.) Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 5,000 RPM. And you probably will never actually take it that high. If you do, you'll only do it once and after the engine blows up a carburetor will be the least of your worries. I almost posted that^^ word for word!! LOL. You probably remember, too. When I bought my '88 XJ new, the service manager at the stealership was a racing buddy, and I hung out in the shop fairly often. Back then there were still a lot of 84, 85 and 86 Cherokees on the road, and every time I went to the dealer's shop there would be another one with a connecting rod blown through the side of the block. You DON'T beat on the 2.8L engine. (And what many people consider to be normal driving, unfortunately, is "beating on it" for the 2.8.) I remember very well. They would just grenade. Don't know if you've seen this, but in the parts catalog for that POS 2.8 they list shims for the main bearing caps!! Link to comment Share on other sites More sharing options...
redwolf624 Posted August 16, 2014 Author Share Posted August 16, 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 Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 Who gives a $#!& at this point? Link to comment Share on other sites More sharing options...
redwolf624 Posted August 16, 2014 Author Share Posted August 16, 2014 Who gives a $#!& at this point? me, i have a 4.0 in a MJ in my back yard that the computer in the MJ may or may not work, just wondering if i do end up gettin the 4.0, Redwolf Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 Use the formula provided then. Link to comment Share on other sites More sharing options...
Eagle Posted August 16, 2014 Share Posted August 16, 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? Link to comment Share on other sites More sharing options...
cruiser54 Posted August 16, 2014 Share Posted August 16, 2014 Eagle, don't ask................... Link to comment Share on other sites More sharing options...
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