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This FI Tech 💩 has pissed me off for the last time. I identified the problem: the injector pulse width doubles/triples when the MAP spikes/dips. It doesn't sound like a big deal until it bogs out of the hole or while passing in 4th gear. It goes pig rich down to 10:1 and floods/bogs. I tried all their suggestions to no avail. It gets rid of about 1/2 the bog, then drivability suffers. They say I can't alter the direct correlation between the MAP and pulse width, so they can eat a bag of djcks. I'm putting a carb back on it.
That's a bummer you had such bad luck with the FiTech system. If I swapped to FI I'd want it to run flawlessly.
My 71 98 has a Summit carburetor on it. It's a clone of the old Holley 4010, which is in turn a clone of the Autolite 4100 (originally used on classic Thunderbirds). It runs well and is easy to tune. I guess a traditional Holley might be more tunable for someone who races or uses an O2 sensor to tune. I rebuilt my Summit carb once and getting it dialed in is easy enough to do with a vacuum gauge and tachometer.
I was a little reluctant to post to this thread initially since the question in the poll seemed to be directed at carbs for racing applications, but I see others are posting for their street cars, so here goes. I have a '67 4-4-2, 400ci E block, ported and polished C heads, hardened valve seats with 3 angle valve job, with hydraulic lifters, fed by a Holley/Street Demon 750cfm thru an Edelbrock 2151 Performer intake. Cam is an Engle, 496/512 Lift, with 226/230 Duration at .050. Even with the moderately aggressive cam the Holley/Street Demon was easily tunable to maintain a steady, albeit lopey street idle. I don't feel any lag/bog thru the entire power band. The car starts (Mallory ignition) right up and runs very strong, great street car. I am very happy with the performance of the Holley/Street Demon carb. For those who may not be aware, Holley bought out the parent company of Street Demon around 2011 and continues to make them today.
Last edited by Dream67Olds442; Apr 12, 2022 at 07:50 AM.
Which is it, a Holley or a Street Demon? Or, is it one of the old Street Demons that look like a Holley?
It's what I would call a high performance street car. I don't own a trailer, and drive it anywhere, including to and from the track to run low 12s (11s once I figure it out).
I’m only running street cars but every one of them (4)has a quadrajet on them and they all work great .The more I work on them the easier they get .I’m sure they could all be fine tuned with a wide band and o2 bungs and all that jazz but I like to keep it simple.
Which is it, a Holley or a Street Demon? Or, is it one of the old Street Demons that look like a Holley?
It's what I would call a high performance street car. I don't own a trailer, and drive it anywhere, including to and from the track to run low 12s (11s once I figure it out).
Holley still makes the Street Demon model carbs. Mine is from 2015, and looks like the attached pic. I'm sorry, I don't remember the actual model # of mine off the top of my head. Sounds like you've got your car running strong, good luck getting into the 11's!
The way I look at it is you pick with what you feel comfortable with as long as the carburetor fits the application. The tricky part is really deciding on what your application really is / what you want out of it. I typically go with a Holley 4150 as it offers a wide variety of choices.
I'm out on the FI stuff, don't need all the electronics. I like the simplicity of the 4150/60 carbs. Nothing wrong with a Quadrajet or Edelbrock, I'm just more comfortable with the Holleys. The 4500 is more for the track and big cube engines in my opinion.
Sorry to hear you had such a lousy experience with the FI Tech. I would not consider it or the Sniper, both have flaws and they are cheap for a reason. The Street Demon is basically a Carter Thermoquad that uses a 3 barrel base and they fixed a bunch of the factory issues. The SD are only available in 625 and 750 cfm, a bit small and one member had issue with it running lean on full throttle when checked with a wideband, like 13.3 AFR. I do have an 800 cfm Quadrajet that I totally rebuilt using a Cliff Ruggles Premium kit, including primary shaft bushings that is set up for a pretty radical camshaft. If you are interested, I will let it go for a good price. Good luck.
I'm leaning heavily towards a q-jet, mainly because I don't like the block off plate on the spreadbore intake. I'm sure it works fine; I just don't like it.
Trimble wants me to put a 4500 on it, but then I need to change the intake and it needs cut, anyway.
I heard that the HP series 4150s are less cfm than their names suggest, like a 950HP is 750cfm. Don't know how much truth there is to it, but it makes shopping difficult.
I can say that the Edelbrocks and goggles are not even considerations.
I'm leaning heavily towards a q-jet, mainly because I don't like the block off plate on the spreadbore intake. I'm sure it works fine; I just don't like it.
Trimble wants me to put a 4500 on it, but then I need to change the intake and it needs cut, anyway.
I heard that the HP series 4150s are less cfm than their names suggest, like a 950HP is 750cfm. Don't know how much truth there is to it, but it makes shopping difficult.
I can say that the Edelbrocks and goggles are not even considerations.
Get the one you are comfortable taking apart and putting back together. Some engine builders hate Quadrajets. A few of those "off brand" carbs have a slight advantage on a dyno.
4 of my 5 Oldsmobiles have Rochester carbs. 3 of 5 have Quadrajets, 1 of 5 (57 Olds) has a 4 GC. 1 of 5 has an off brand carb (Holley Avenger 870) that was on the car when I bought it.
You already have the fuel system, buy a better TBI. The Terminator X is far superior to ANY TBI with an onboard ECU. For best results add spark control.
I inderstand all the aspects of a carb vs EFI. But I put EFI on my car in ‘04. Granted it’s multiport but I’d never go back to carb, ever.
You already have the fuel system, buy a better TBI. The Terminator X is far superior to ANY TBI with an onboard ECU. For best results add spark control.
I inderstand all the aspects of a carb vs EFI. But I put EFI on my car in ‘04. Granted it’s multiport but I’d never go back to carb, ever.
I'm not made out of money, and I'm sick of the "voodoo". I don't know enough to be proficient with it. I've got probably $1500 tied up in an $1100 unit between all the replacement parts, and that doesn't count the hours of brainfvcking it.
If you're racing, you should really just go with a 4150 design.
They're great on the street, the strip...
Not taking anything away from the quadrajet as a great carb, but there's a reason the 4150 is the goto carb for racing.
I'd call quickfuel and talk with them(yes, I know they're owned by Holley now).
Their advice is great and they're carbs are amazing for the price.
I'm running 10.50's with an 850 carb when everyone tells be I should have a 950 or 1050.
If you're racing, you should really just go with a 4150 design.
They're great on the street, the strip...
Not taking anything away from the quadrajet as a great carb, but there's a reason the 4150 is the goto carb for racing.
I'd call quickfuel and talk with them(yes, I know they're owned by Holley now).
Their advice is great and they're carbs are amazing for the price.
I'm running 10.50's with an 850 carb when everyone tells be I should have a 950 or 1050.
Duly noted. I happen to know where a fairly new 850 Brawler is. Only a couple hours runtime.....
Oh, and an AFR gauge has been on the to do list regardless of where this debacle ends.
Last edited by fleming442; Apr 12, 2022 at 05:08 PM.
Seeing as this is primarily a restoration site your poll results are going to be biased towards the Quadrajet. My recommendation is a 4150 style carb of some sort. I have a Holley 4781 on my 65 tuned in using an AEM air/fuel gauge.
If you are considering a Quadrajet then why aren't you also looking at a 4160?
IMHO for your application I think a Holley/Quickfuel 4150/60 is the way to go.
It’s hard to beat a well tuned Q-Jet, especially on the street. The people who say they are too complicated are either too lazy, too stubborn, or too stupid to figure out how to make them work. The engine does not care what carb is bolted to it, as long as it’s properly calibrated. I don’t believe that one carb design over another will provide a huge difference in performance, all things being equal.
Seeing as this is primarily a restoration site your poll results are going to be biased towards the Quadrajet. My recommendation is a 4150 style carb of some sort. I have a Holley 4781 on my 65 tuned in using an AEM air/fuel gauge.
It was getting a little stale; figured I stir the pot a bit.
I need a something over 800cfm. I looked at the 4160 series yesterday, and they were 600s. I've never heard of a 4781.
I also want to be a little different without getting pigeon holed into having something i can't find parts for if necessary. It's hard enough being Oldsmobile.
I believe 4781 is the actual part number. 4150/60 is the style or series.
An 850 Brawler is a good choice. Changeable air bleeds and power valve circuit as well as different options for the aggressiveness of secondary opening. I’ve purchased and tuned dozens of these. Best bang for the buck in my experience.
My best carburetor experience was with a 670 CFM Holley Street Avenger on a Chevy 327 built to L-79 specs. Ran well literally out of the box, and if yours doesn't, it's infinitely tuneable.
I'm currently running a Q-jet (which has been great but is less user-friendly) on my 4-4-2 for the sake of authenticity, but if that wasn't a concern, I'd consider the Holley even though it would necessitate a manifold change.
It was getting a little stale; figured I stir the pot a bit.
I need a something over 800cfm. I looked at the 4160 series yesterday, and they were 600s. I've never heard of a 4781.
I also want to be a little different without getting pigeon holed into having something i can't find parts for if necessary. It's hard enough being Oldsmobile.
The difference between a 4150 and 4160 is the 5160 uses a metering plate in the rear bowl instead of a metering block.
How did you come up with your CFM demand? Do you have a post with more details about your combo?
It's over on ROP under builds- pump gas 468, but the top end has changed. This stupid site software is giving me fits trying to post a link.
63cc Edelbrock Gen 1s w 2.15/1.7 valves, BAM solid roller lifters from Travato, and a Holley Street Dominator intake.
I haven't dynoed it, so I still have the chip at 6k. It might make more revs; don't know yet.
Last edited by fleming442; Apr 13, 2022 at 10:02 AM.
Like I said, if you want to give this Qjet a try, I will let it go with what I have in it for parts. I tapped the air horn and slotted the APT, so part throttle AFR adjusts very easy with a small standard screwdriver. I will also include Cliff's power piston spring assortment, some bigger primary jets and secondary metering rods and hangers. I actually have the secondary air door adjusted to the max 1.270" opening, the same as the old Edelbrock 850 cfm Qjet. The Quickfuel carbs have almost no bad feedback and everyone seems to love them. Almost anything will be an improvement over the FI Tech.
It's over on ROP under builds- pump gas 468, but the top end has changed. This stupid site software is giving me fits trying to post a link.
63cc Edelbrock Gen 1s w 2.15/1.7 valves, BAM solid roller lifters from Travato, and a Holley Street Dominator intake.
I haven't dynoed it, so I still have the chip at 6k. It might make more revs; don't know yet.
I Found it on ROP. It sounds like you don't have any real port work done. If that's true you probably have a few more usable RPM. A 1.562x1.750 (850) Holley would work well in all out performance application with a standard booster. Since you street drive drive it and have a 4 speed I would pick something smaller. For a double pumper I like a 950HP (Holley 0-80496-2). The only down side is no choke and it can run rich at part throttle. If I'm not worried about racing I would go vacuum secondary 780 (QF SS-780-VS). This will give you excellent drivability right out of the box.
It’s hard to beat a well tuned Q-Jet, especially on the street. The people who say they are too complicated are either too lazy, too stubborn, or too stupid to figure out how to make them work. The engine does not care what carb is bolted to it, as long as it’s properly calibrated. I don’t believe that one carb design over another will provide a huge difference in performance, all things being equal.
I don't disagree with you, but I would like to point out that this is the most common argument of those in the Q-Jet camp: "The people who say they are too complicated are either too lazy, too stubborn, or too stupid to figure out how to make them work." But you also said,"The engine does not care what carb is bolted to it, as long as it’s properly calibrated. I don’t believe that one carb design over another will provide a huge difference in performance, all things being equal," which is basically contradicting the argument in favor of the Q-Jet.
The Q-Jet, when properly tuned as you said, is a great carb, but if someone doesn't already own a Q-Jet, why would anyone suggest that they buy one for a performance application? The Holley 4150 cheap, plentiful, and easy to tune. You can walk into virtually any auto parts store in America and get parts for a 4150. And there is nothing wrong with having a carb that is easy to tune and modify for your specific application, and there is no need to denigrate those who prefer Holleys over the Q-Jet by saying that they are lazy, stubborn or stupid.
Are you referring to my post, because that is exactly my point.
Just in general, I was trying to have a nice discussion. 😁
I'm so freaking pissed with fitech right now, I could chew steel and spit nails. I lit them up on IG, and now they're trying to be nice, all the while belittling me and my car. It's their junk; I was trying to make it better! The frustrating part is that I have the tune pretty good, but no matter what I do, it goes pig fat (10:1 AFR) when the MAP jumps from low/mid to high. They have told me the injectors are too small, the pump is too small, I didn't put the injector information in, yada, yada, yada. I'm no software engineer, but even the fundamentals say that AFR will go LEAN if there's not enough fuel. It actually runs REALLY WELL, most of the time. The issue is affecting general drivability. Now, if it all gets straightened out and it starts leaning out on the top end, yeah, maybe I need a slight upgrade in fuel delivery. I'm not there yet. The kicker is their flat out inconsistency. I tried to put a Walbro 450 340lph pump in on the initial install. It was overloading the regulator and they said to put the 255/190lph back in. I did, and now this fvckface is telling me to put the 450 back in. I don't think I need to say how outright mad I will be if it floods the engine or doesn't fix the problem.
The problem with the Qjet is you also need a fuel system that can feed the single fuel bowl
As Hp/ TQ / RPM increases the fuel supply issues are amplified with the Qjet
The stock and super stock cars run some very expensive fuel systems
The problem with the Qjet is you also need a fuel system that can feed the single fuel bowl
As Hp/ TQ / RPM increases the fuel supply issues are amplified with the Qjet
The stock and super stock cars run some very expensive fuel systems
It was good on the even smaller (50lph?) efi pump with the Holley Barry (Holley 800 main body, old school Demon metering blocks, bowls, ans base). I have a big Mallory regulator, so I'm playing volume off increased pressure. The problem is returning enough fuel pressure to the tank and venting the excess. It works, but has its downsides. I like not hearing the pump over a big, obnoxious rail mount.
