Hi gang, possibly based on conversations revolving around this thread: http://www.ifsja.org/forums/vb/showthread.php?t=154201 Ristow has very graciously volunteered to test the 450 CFM Holley 4548 carb off this '77 work truck against my 600 CFM Edelbrock 1405. Of particular interest in his build would be this page, http://www.ifsja.org/forums/vb/showt...=152113&page=4, which indicates approx. 14 MPG from a 4.10 geared J-20 that is going to pull a bobcat on a trailer. Not too shabby! I suppose the curiosity is mileage and possibly performance vs. my Edelbrock, I'm betting both will be better w/ the Holley. One thing to be clear of please, I'm not an advocate of Edelbrock carbs. I just happened to have this one sitting on a shelf when I bought my J-20 years ago. After spending about 15 min. fiddling w/ its stock MC4350 I threw it in the trash and ordered up the Ford to square bore adapter and dusted off this 1405 I've now been running since around 2005. This isn't a challenge or dare to see if "my" Edelbrock is better than Ristow's Holley, just a comparison to see what happens. While my Edelbrock is fairly well tuned (minus needing to jet up the secondaries) it's likely his Holley is more finely tuned. That is one of the benefits of the Holleys I suppose, is that you actually CAN more finely tune them compared to an Edelbrock, but that's another conversation.
My '76/'79/'81/'85 mutt J-20 is a fairly similar setup to his '77. '76 bone stock motor (360 w/ stock 4V intake, Summit $55 square bore adapter), '79 J-20 chassis, T-18/D20, 4.10 gears. He's running aftermarket full HEI distributor but I'm running HEI/TFI hybrid (stock '79 distrib, AC Delco brand HEI module, Autozone cheap-o TFI coil [haven't gotten around to swapping for MSD 8227 yet], and some wiring), timing chain is stock w/ probably around 43,000 original miles. Our trucks may not be dollar for dollar exact twins but they're close and the only change I'll be making on mine in this shoot-out is that I'll be swapping my Edelbrock for his Holley and redialing my distrib. vacuum advance to match the power stage in the Holley. I'll make sure idle speed is dialed to match mine so it?s not burning extra fuel at stop lights. Driving style and routes will not change; I don't lead a very exciting life these days. This is a comparison of the two carbs, not the two trucks or drivers.
Timing on my rig is advanced until ping then back off just until it doesn't. Vacuum advance will be setup according to another Ristow write-up, http://www.ifsja.org/forums/vb/showt...ht=distributor, which is how I had it on my Edelbrock, matching its 5" enrichment stage. His Holley has either 7.5 or 8.5 power valve so I'll dial my vacuum advance to fully back out at 8.5" that should cover either closely enough.
I've (hopefully) never professed to be an expert at these things, I try to only speak from my own experience and as I understand things I haven?t actually done. I feel w/ an accurate vacuum gauge and a free Saturday afternoon I can reasonably tune my way out of a wet paper bag. Having said that, I'm sure a lot of what I report or describe will be corrected by those who know better than I do. Please feel free if you do, this is an exercise in learning.
At a cursory glance (my first close-up look at a Holley) I can already see this thing is INFINTELY more adjustable than the Edelbrock, which is pretty much only tunable in "stages;" the accelerator pump on the Edelbrock pretty much has three "size" options vs. Holley's changeable squirter and changeable cam (and position thereof) for the accelerator pump. I'm not going to start any religious conversations on "real" mechanical vs. vacuum secondaries but in the most basic sense I would say the Edelbrock is mechanical (twisting the main throttle plate operates some levers that open up the secondary plates [we're not going to discuss the air flapper door cover thing though yes vacuum does come into play] while the Holley appears to be purely vacuum secondary; twisting the main throttle all the way open does not operate the secondary throttle plate, only the vacuum pot on the passenger side appears to operate the secondaries). I'm not going to tear into Ristow's carb to compare internals. His is an electric choke vs. my manual (though I have found at least one manual choke Holley 4548 on the 'bay that I'd like to pick up) so I can't make a whole lot of fair comparisons about choke operation. I'll mooch off something nearby that's hot w/ the key on for the electric choke.
So anyways, w/ a two and a half month old son my time is precious and few to fiddle and tinker w/ the '20. Ristow's carb arrived Friday and I was hoping to at least have it sitting on my truck by Sunday but it hasn't happened yet I'm going to pick up a fresh square bore gasket on the way home today and see if I can either sneak it on before the wife wakes up early tomorrow morning or maybe even drive the '20 to work tomorrow and swap them in the parking lot behind the dumpster tomorrow if I can. I?ll be making every effort to get it bolted on and running on my truck w/in the next couple of days, please bear w/ me and the new youngan.
Stay tuned (no pun intended) and a massive big thanks to Ristow for this opportunity.
My '76/'79/'81/'85 mutt J-20 is a fairly similar setup to his '77. '76 bone stock motor (360 w/ stock 4V intake, Summit $55 square bore adapter), '79 J-20 chassis, T-18/D20, 4.10 gears. He's running aftermarket full HEI distributor but I'm running HEI/TFI hybrid (stock '79 distrib, AC Delco brand HEI module, Autozone cheap-o TFI coil [haven't gotten around to swapping for MSD 8227 yet], and some wiring), timing chain is stock w/ probably around 43,000 original miles. Our trucks may not be dollar for dollar exact twins but they're close and the only change I'll be making on mine in this shoot-out is that I'll be swapping my Edelbrock for his Holley and redialing my distrib. vacuum advance to match the power stage in the Holley. I'll make sure idle speed is dialed to match mine so it?s not burning extra fuel at stop lights. Driving style and routes will not change; I don't lead a very exciting life these days. This is a comparison of the two carbs, not the two trucks or drivers.
Timing on my rig is advanced until ping then back off just until it doesn't. Vacuum advance will be setup according to another Ristow write-up, http://www.ifsja.org/forums/vb/showt...ht=distributor, which is how I had it on my Edelbrock, matching its 5" enrichment stage. His Holley has either 7.5 or 8.5 power valve so I'll dial my vacuum advance to fully back out at 8.5" that should cover either closely enough.
I've (hopefully) never professed to be an expert at these things, I try to only speak from my own experience and as I understand things I haven?t actually done. I feel w/ an accurate vacuum gauge and a free Saturday afternoon I can reasonably tune my way out of a wet paper bag. Having said that, I'm sure a lot of what I report or describe will be corrected by those who know better than I do. Please feel free if you do, this is an exercise in learning.
At a cursory glance (my first close-up look at a Holley) I can already see this thing is INFINTELY more adjustable than the Edelbrock, which is pretty much only tunable in "stages;" the accelerator pump on the Edelbrock pretty much has three "size" options vs. Holley's changeable squirter and changeable cam (and position thereof) for the accelerator pump. I'm not going to start any religious conversations on "real" mechanical vs. vacuum secondaries but in the most basic sense I would say the Edelbrock is mechanical (twisting the main throttle plate operates some levers that open up the secondary plates [we're not going to discuss the air flapper door cover thing though yes vacuum does come into play] while the Holley appears to be purely vacuum secondary; twisting the main throttle all the way open does not operate the secondary throttle plate, only the vacuum pot on the passenger side appears to operate the secondaries). I'm not going to tear into Ristow's carb to compare internals. His is an electric choke vs. my manual (though I have found at least one manual choke Holley 4548 on the 'bay that I'd like to pick up) so I can't make a whole lot of fair comparisons about choke operation. I'll mooch off something nearby that's hot w/ the key on for the electric choke.
So anyways, w/ a two and a half month old son my time is precious and few to fiddle and tinker w/ the '20. Ristow's carb arrived Friday and I was hoping to at least have it sitting on my truck by Sunday but it hasn't happened yet I'm going to pick up a fresh square bore gasket on the way home today and see if I can either sneak it on before the wife wakes up early tomorrow morning or maybe even drive the '20 to work tomorrow and swap them in the parking lot behind the dumpster tomorrow if I can. I?ll be making every effort to get it bolted on and running on my truck w/in the next couple of days, please bear w/ me and the new youngan.
Stay tuned (no pun intended) and a massive big thanks to Ristow for this opportunity.
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