1990 454 carburetor recommendations

pvoth1111 · May 28, 2013, 08:56 PM

What carb do you guys go with for max performance / economy for the chevy big block....

I know q jets suck butt except when they work.....(mine still works....have never liked em)....

what CFM....800....850.....more?

I'm in Florida.....right now.....no emissions...could title it here.....

gimme some feed back

DaveVA78Chieftain · May 28, 2013, 09:28 PM

First, you have a 1990 Winnebago that is mounted on a 1989 P30 chassis. 1989 used a Q-jet where 1990 used TBI injection. An important distinction for parts search.

Either use a quality rebuilt Q-jet, there is a recent thread about this somewhere around here, or use a 750CFM Edelbrock . An RV is not a high RPM race engine. Low end and mid range performance is what you are seeking. Do a thread search for Edelbrock.

Dave

Oz · May 28, 2013, 09:49 PM

850 or more? Sure! On a street rod but not on an RV. There is always a trade-off since "max performance and economy" are at the opposite ends of the spectrum and to get one, you have to make a compromise on the other. I said it before, I'll say it again - The price of "performance" is paid for at the pump.

Dave gave you the right direction to look - no BS.

bluebird · May 28, 2013, 10:52 PM

I'm going to follow suite here. The quadrajet was the BEST carb ever introduced, period. Even though you never liked them. For someone that knows and understands a quadrajet, they are the best of both worlds. You just have to find that someone around you. Talk to some hot rodders around you and you will find a guy that will change your mind. I know a few guys that still run them on their drag cars.

MotorPro · May 29, 2013, 06:32 AM

If your Quadrajet is working good then there is little or nothing to be gained by changing it. If you are having problems with it the best straight out of the box choice is an edelbrock 750. In all my years as an engine builder and racer they are the only carb that I have every had come out of the box,bolt on and run great.

ClydesdaleKevin · June 06, 2013, 05:32 PM

I concur. We put on an Edlebrock 1411 (1141?), 750 CFM, specifically jetted and tuned for a big block Chevy to give you the best power/economy balance. We love ours. We put it on this winter and it ran perfect right out of the box with just a few minor adjustments. Did have to get an throttle adapter and spread bore adapter. Lots of power on hills, and a solid no BS average MPG of 7+.

If your Quadrajet is running fine, leave it alone. Ours still ran crappy after a rebuild, and the Edlebrock fixed the problems we were having.

Kev

Stripe · June 08, 2013, 09:13 PM

7+ mpg

ClydesdaleKevin · June 09, 2013, 09:12 AM

Yep Frederic. At highway speeds of 55-65 getting a solid 7+mpg on average. Goes way up, 9-10, if I stick to back roads and only go 40-45 mph...lol!

Kev

Oz · June 09, 2013, 11:15 PM

There's a whole discussion on 454 gas mileage as well as maximizing and improving it. Check the "sticky" topics.

GONMAD · June 30, 2013, 09:28 PM

Hi All, I first must relate a math formula for CFM on any NA or naturally asperated engine, here goes...
you take the cubic inch & multiply it by the max rpm you plan on turning, divide the sum by a constant '3456' to get a cfm figure. If you want to get fancy subtract ten percent for parasitic losses & reduce cfm even more. Secondly, Try looking up the NEW Demon Street Carb in the 625 cfm. I purchased one, put it on & WOW!. It has TRIPLE venturi boosters & the signal is rapid off idle. It is a real THREE barrel carb based on the Thermoquad design even to the black polymer heat reducing main body. The secondaries are fully tuneable with hand tools. I haven't made a trip yet with one but looking forward to it SOON! It's like having a really good working Q jet only without the inane lack of serviceability. It will supply ALL the needs of any RV engine & priced very right for all you get. I'm trying to get Demon to make a marine version as well.
Here is the formula in numbers: 454 x 4400= 1997600 div by 3456=578 cfm.
Anywhere from 600 to 700 cfm will be OK. Don't forget to use a good air filter such as Amziol or K&N is good
ps. Now they have a 750 cfm version for larger demands
Once again I go. C YA! GONMAD

Oz · June 30, 2013, 11:14 PM

If 600-700 cfm is what you recommend for a 454 based on the formula, why did they equip all the big block motors with 750cfm from the factory?

When I bought my second D24 Indian with 440-3, it had a 600 cfm Edelbrock it for economy. Which it did get... the best I ever had, 8mpg towing a 17' open bow from Connecticut to south-central PA through the mountains. BUT, it was a total dog on hills and acceleration was poor. I normally drive at 60mph anyway but, holding that speed with a 600cfm carb wasn't an easy task. With the 750cfm, no problem at all.

Anything else I've ever read says 750cfm is correct for big blocks and 600-650 for small blocks.

Is this Demon Street Carb a new design that can deliver the performance of a 750?

MotorPro · July 01, 2013, 07:46 AM

Quote from: GONMAD on June 30, 2013, 09:28 PM
Hi All, I first must relate a math formula for CFM on any NA or naturally asperated engine, here goes...

Here is the formula in numbers: 454 x 4400= 1997600 div by 3456=578 cfm.

This and other formulas turn up all the time but dynos and everyday driving prove that they don't work. A 750 cfm seems to work the best for most mild 454's. While the Demon is a decent carb,when we have had problems with them we got little help from Demon. Edelbrock gives great support.

GONMAD · July 03, 2013, 03:47 PM

Hey Gang,
I hope you read the post script about the 750 cfm demon street carb coming out. I have been running an Edelbrock "thunder" series 650 cfm while towing a 10,000 lb. dragster trailer with no problems up to around 80 mph for extended periods while traveling to different tracks. I don't recommend pushing your stock rigs to this extreme, I felt no difference from the 750 Edelbrock I removed to go to this more advanced version carb. The people at demon seemed new at this stuff & I felt I knew as much or more than they did.

I have a 625 cfm demon on a 450 HP small block 55 Chevy with an HHO generator producing 1.7 lph. It gets about 23MPG with the air conditioner on. The triple booster venturies on the very small primaries provide very good throttle response & fuel atomization. I'm NOT a salesman for any of these devices but I have decades of experience & while I'm no expert, common sense prevails & the "seat of the pants" method works good. Everyone will always have a different outlook & thoughts, I look forward to new ideas & opinions so collectively we can come out for the better solution.

I think the factory used 750's & 850 cfm carbs out of convenience & what they had available (I could be wrong) but newer technology hopefully has gotten better & will continue to improve. I have tried an older Holley projection unit with little satisfaction but maybe the newer units aren't so touchy with the barometric pressure as I constantly had to readjust it on the fly or maybe it needed a PWM & Mosfat to calm the units volatility down. I removed it in favor of something I didn't constantly tune. Anyway have a good one folks & as always... C YA! GONMAD

DaveVA78Chieftain · July 03, 2013, 04:32 PM

After watching this type of discussion for several years, the truth of the matter for this subject is, that for ease of installation, satisfaction of the users (from know nothing to pro), and reliability over time, anyone who has replaced the Thermoquad on a Dodge or Quadrajet on a GM motorhome, with a Edelebrock 740-850 CFM carburator has had nothing but rave reviews of the change over. Until someone can match that combination of results it will be very difficult to change that thought pattern. Sure, there will be possible improvements in technology but do those improvements come at the same cost as a Edelbrock change over.

And believe it or not, this observation is coming from a someone who is still using a Thermoquad.

Dave

GONMAD · July 05, 2013, 12:30 PM

You are absolutely right! It used to be an Edelbrock C3B & a Holley 780, mallory distributor & hooker headers & you were ready for anything! Now the possibilities are limitless & it's a matter of personal beliefs & tradition. This keeps some stuck in ancient paradigm & some dare to be adventurous & sometimes make mistakes. (I claim no exception) Everyone should do your own homework & your own conclusions. Advice can be good & bad I try to stay on the good side after weighing both views & try to be constructive in the outcome.
I hope everyone had a good 4th, As always C YA! GONMAD

maxximuss · July 06, 2013, 02:32 AM

As past experience building engines & carb's when I was young with older muscle cars I have to agree with Mark's & Dave's post. I learned all this by trial and error through my 20's. As I worked in aftermarket parts for many years I also read allot of info on this too. It's usually the norm for 600cfm - 650cfm for small block engines and 750 - 850 for big block engines. Undercarbed engines is not a good thing. Of coarse were talking about mildly modded engines RV cam, headers, etc.

bluebird · July 06, 2013, 07:32 PM

QuoteI think the factory used 750's & 850 cfm carbs out of convenience & what
they had available.

If you really think the manufactures just thru stuff together because it's what they had, nothing I say will change your mind. There is a heck of a lot more to a carb besides the cfm rating. You probably can stick a 625 cfm demon on a big block, but it won't have near the power and torque that it does with the proper carb. If you really have a 450 hp small block, with a 625 demon, I know for a fact you are leaving a lot on the table. I've been pissing with sbc for 47 years, and still running one in a 96 firebird, that takes a 3300 lb car to 6.40s @ 103 mph.
I wouldn't consider anything less than a 750 on a STOCK big block anything.

By the way I'm running a Holley 950hp on my small block, and it'd probably go faster with a 1050 dominator, but we're just bracket racing.