[Chadman]

A few month ago I posted a thread on possible carbeurators that would work well with the ZZ4 crate motor while at the same time give the correct Hood clearence for the shaker hoodscoop on an 81 Trans Am (stock carb was a Rochester Q-Jet). Now I finally have the motor and I'm dropping it in by next weekend and the only carbs i found were the edelbrock Q-Jet series replacement carbs

( http://www.jegs.com/cgi-bin/ncommerc...95&prmenbr=361 )

of these I wish for an electric choke (, but the only one w/ that is a 850 CFM, which I beleive would severely be overcarbing the ZZ4 crate, could someone verify this for me? In the pace performace magazine they sell a demon carb tuned for the zz4 thats a 650 cfm, but that carb would not work due to the aircleaner housing diameter (where it is attached to the carb) and the carb height (not allowing clearance for the shaker). I was also told holley makes a carb that has the same dimensions as the stock rochester Q-jet aswell,does anyone know of any of these carbs? Finally, if this post hasn't confused you enough, would anyone know the "suggested" cfm carb for a ZZ4? Or, if anyone could answer this question all my problems would be solved, does anyone know of a correct CFM carb that would work with my setup allowing the shaker to fit?



....whew


Any help would be greatly appreciated

One more question ...

Do the edelbrock performer carbs have the same dimensions as the Q-jet replacement carbs




Performer carb

http://www.jegs.com/cgi-bin/ncommerc...91&prmenbr=361


Q-Jet series replacement carb
http://www.jegs.com/cgi-bin/ncommerc...95&prmenbr=361


Thanks in advance!

[johnsongrass1]

850 are big but with tunable secondary's I don't see why you should have a problem. You will probably find you'll need to tighten the secondary's so they come in way late but you should still get great drivability and response. Tuning will be the key here. Just in case that scares you than you can let someone else do that. You need to know whatever carb you get, you will need to fine tune it to you specification.

[Dradee]

I use the holley HLY-0-80555C on my 74 vette 350 because of the hood clearance issues,I have to use the stock air cleaner.These are spreadbore replacement carbs for the quadrajet,I dont even know what style of intake the zz4 crate engine uses,square flange or spreadbore?

[killerformula]

I agree with Johnson. Q-jets are really not like any other carb. Its almost like they don't play by the same rules. For example, I'm not sure they ever made one that flowed less than 750 cfm. They'd stick those suckers on 305's and whatnot. THey always worked great too. I miss my q-jet, I think they're probably more fun than any other carb. The induction noise is killer... sorry about the digression.

My point is that with some tuning you can run a big Q-jet. The small primaries are cool too because you can save some gas mileage if you keep your foot out of it (right, like that's gonna happen ).

Sure you can't set up a heat-riser choke? THey're not that hard to install and they're pretty reliable.

K

[Dradee]

The holley spredbore is just like a q-jet but more easily tunable,you can always get away with a big cfm carb that is spreadbore than a squarebore on a smallblock for just that reason of it having the small primaries.

[hotwheels55]

The ZZ4 was GM tested for hp/torque specs using a HOLLEY 750 cfm. Don't let that influence you decision on cfm ratings, since that was at maximum rpm to obtain the specs. Street cars don't get driven at those rpm levels for extended periods. The testing also doesn't consider street driveability, fuel economy, etc...they're looking for maximum hp/torque figures to sell the public on that motor.
I use a DEMON 625cfm on my ZZ4, but I made the classic mistake of not inquiring with DEMON tech support to determine the best product for my specific application. A "crate motor 650 cfm Speed DEMON" is what I probably should have used. It would have minimized the tuning problems I had with the DEMON 625cfm. DEMON will tell you that they "wet flow" their carburetors and therefore a 650cfm is actually very close in characteristics to a typical HOLLEY 750cfm. My DEMON works great now on my ZZ4 in a '57 150 sedan. BUT, it tooks weeks of eye burning exhaust, oil diluting and spark plug fouling over rich conditions and general discontent with the carburetor before their tech support advised me how to correct the problems.
In your case, you're trying to maintain the oem shaker hoodscoop so while I would lean towards a DEMON or HOLLEY (square bore)for some performance improvement, the EDELBROCK or HOLLEY (replacements for ROCHESTER) type spread bore Q-Jet will probably give you less headaches in accomplishing you goal of maintaining originality. If you can get the spread bore tuned, then you'll have the best of both worlds.

[mstngjoe]

Originally posted by hotwheels55
.....DEMON will tell you that they "wet flow" their carburetors and therefore a 650cfm is actually very close in characteristics to a typical HOLLEY 750cfm.......

I don't get this part I'm afraid .....Holley bases their cfm ratings on wet flow testing.

[hotwheels55]

Go to the member list of this site and search for "tech @ BG". This is a BARRY GRANT/DEMON technical support advisor who used to regularly post on this site regarding carburetor questions.
When you find his profile, click on the gray button for "search" and you'll find all 68 of his previous postings.
My comment was based on what I was told by the BG technical support staff when I called about my DEMON carburetor issues. I recall "tech @ BG" commenting about the same thing.
I may be misquoting his remarks, but I recall it being stated that a lower cfm rated DEMON flows a higher cfm than a comparative HOLLEY carburetor. That was why they recommended a 650cfm carburetor for a ZZ4 (where a HOLLEY may've been at 750cfm).

[mstngjoe]

Based on my personal experience with a tech at Demon, I was not impressed. They recommended a 575 cfm carb for my 331 stroker. Not close I'm afraid, as proven on a chassis dyno with a 750 cfm carb.

I inferred from your post that you were under the impression that Holley had another way of rating cfm (dry flow?). Sorry if I misunderstood.

Given your example of BG vs Holley, I guess I don't understand how a 650 Demon would be equiv to Holley 750 relative to flow. Be it wet or dry. I understand your info was based on something someone else has posted, but it still is a mystery to me.

Maybe "tech@bg" will show up and clue me in.

[hotwheels55]

I got a tech inspection card with my DEMON that gave the specs that the carb tested at. Apparently, all DEMON carbs have to comply with certain wet flow rate standards before they are shipped.
I don't think that every HOLLEY (or EDELBROCK) carburetor is tested in the same manner before it is packaged and shipped for consumer use. I would think that the HOLLEY custom shop that builds their custom carburetors probably does the same type of specific testing.
My understanding of DEMON having superior flow characteristics to a HOLLEY has to do with the shape of the bowl castings. I don't profess to be an expert as demonstrated by my DEMON issues.
I was impressed with their tech support. I wrote several e-mails to them as well as phone calls. They lead me through the progressive steps of modifying the carburetor until the problems were resolved. The manager of that department even took the time to call me from GA to make the final changes. His name is Doug. at x125.

[mstngjoe]

Originally posted by hotwheels55
....... The manager of that department even took the time to call me from GA to make the final changes. His name is Doug. at x125.

Maybe had I talked to Doug I'd have a different opinion....You obviously had a better experience than I did.

Glad you got your carb situation straightened out. It can be frustrating I know.

BTW, didn't mean to highjack this thread Chadman.

[Chadman]

Hey guys, thanks for all the great info.

Dradee, the manifold is a quadrajet spreadbore, i took the cover off last night. (resemblance in this website http://pacifico.off-road.com/~wagone..._compared.html -the one marked q-jet spreadbore.)


killerformula, would you happen to know of a place where I could find an elec. choke rochester (either new or refurbished, preferably new) for under $500. I've seen them around but I can't remember where.


hotwheels, i would love to use the demon, but it just won't work for my application , so like you said, i'll probably end up either detuning an edelbrock or go with the holley. currently I'm looking into the "spreadbore" holley


Thanks for all you guys help, if anyone else out there has 2 cents to throw in etc. etc. please do

Quick question, would anyone know the height and circular dimension of the edelbrock carb and the holley spreadbore. Or are they both stock dimensions? I beleive the edelbrock is while the holley is not. This is an important factor

[Dradee]

The HLY-0-80555C neck diameter was 5 1/8 and the height was slightly higher,I dont remember now maybe about a 1/4 inch,but it still fit with no problems.

[Chadman]

dradee, did your holley work with the stock accelorator linkage from the firewall across the manifold?

[Shortblock]

The Edelbrock !904 Q_Jet Has an electric choke. Summit and Jegs carry them.



Vendor: Edelbrock Corporation
Product Line: Edelbrock Performer Q-Jet Series Carbs
Material: Cast Aluminum

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