five7kid

iTrader: (14)

See https://www.thirdgen.org/messgboard/...ML/001092.html for the beginning of the story of my going from an Edelbrock 1901 Q-jet to Holley 80508S (3310 w/electric choke) 750 CFM vacuum secondary.

(Remember this is the '57, all at 5800' Bandimere, the rest of setup in sig.)

Q-jet setup: as-delivered primaries, CK rods, B to K hanger (depending upon air), AV @ 3/16 turn (just enough to close when not running). Best ET 15.02, best speed 94.91, best 60' 2.326, all on one day - never happened again. Typical (a whole different story) 15.4, 93's, and 2.45's. I'd run back-to-back 2.38 and 2.45 60 ft's, 15.2's and 15.7's ET's with no changes (but usually more consistent than that). Almost all runs in late afternoon and evening. If engine temp was over 160 when I pulled up to the box, I was dead (it hated heat). AV just never seemed to open consistently or early enough. There was probably more in it, I just didn't know where to find it.

Ran Holley for the first time this Friday and Saturday. Limited time trials (3 in two days), 5 runs in eliminations. Initial setup: 72 primaries (came w/carb), 76 secondaries (came w/4150 conversion kit), .025 shooter, 6 power valve, 2nd lightest secondary spring. By third run, had lightest spring in, running 15.5-15.6 with terrible air (mid-afternoon). Next day, jetted down to 70/72, best run 15.377 @ 93.33 at 9 pm. All 60 ft's were 2.41-2.43 after light spring installed, both days. Ran best if engine temp was up to 170 by the time I pulled into the box.

Biggest differences:
1) RT - I red-lighted 3 times (My 1st two time trials - .489 & .499; .499 on my last elimination run) - I never do that. I can only attribute that to improved response when punching it. Others (except for the one when I zoned out) were .545, .532, .544, .524 - I never do that, either!
2) Really pulls immediately after the shift to second. Q-jet would take a little time to recover.
3) On the street, much improved. I jetted down again today to 68/70, too lean on the secondaries now, will go back probably to 72-74, leave primaries at 68. Continues to work nicely even after stop-and-go driving. Q-jet hated heat (oh, I already said that).

Also put on regular base air cleaner in place of the dropped-base today. Will go for a .028 shooter to see if that makes any difference (will stumble when you snap it unless revs up first).

Well, I'm sure there's more in it with additional tinkering. It almost seems like it wants the secondaries to open sooner, but I've already got the lightest spring in there. 3.73's would help, I'm sure.

Bottom line: There's a 1901 for sale. The CC q-jet stays on the Camaro, though.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. Cat-back from '91 GTA, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker headers & y-pipe, 3" Catco cat & 3" cat-back, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750 VS, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

SSC

Thats what I figured would happen
The qjet is a "GREAT CARB" no doubt it could out perform the holley with some extra tinkering, but why bother? Time / cost wise you get proven holley setups that run well. With a qjet its pure trial and error.
BTW out of curiosity, if you can put a vac guage on the holley and see if there is more vac with the holley than the qjet.
SSC

RB83L69

I gotta agree, the Q-Jet is a great carb, which I understand well and can coax quite a bit out of, but a properly set up Holley will outrun the best you can do with a Q-Jet every time. They might put up the same numbers on a dyno, but the differences go deeper than that. On the other hand, a Q-Jet is usually alot more pleasant to drive on the street (and buy gas for!) if it's one of the very few that has big enough idle and transition passages to support a large-inch motor with a big cam. There are very few such, and excatly zero computer-controlled ones like that. The CC system automatically impose a limit of either more cubes, or more cam, up to a point, but not both. The "default" behavior of a Holley is to feed more fuel, that is to say, if it can't figure out what to do, it meters more fuel; the corresponding "default" behavior of a Q-Jet is to feed less. That's why the Q-Jet survived in stock applications past the imposition of emissions controls, but the Holley didn't; and also why the Holley will always outrun the Q-Jet: you get power from burning gasoline, period. Pretty basic.

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"So many Mustangs, so little time..."
ICON Motorsports

five7kid

iTrader: (14)

Idle vacuum with the q-jet was 11 in-Hg, the Holley runs 9.5-10. I'm still learning "Holley-speak", but I believe that means I might be better off with a different power valve.

BTW, Ulrich's books says if you eliminate the power valve, jet up 6-8 sizes. Does that mean the secondaries (w/o power valve) should be that much larger than the primaries (e.g., with 68 primaries, 74-76's in the secondaries)? I'll continue reading the plugs, just want a place to start since I won't have many tuning opportunities before eliminations start.

five7kid

iTrader: (14)

One other observation: My previous Holley experience was in the late 70's with a tweaky 302 I had in the '57 - 1st a 600 DP (4776) that didn't cut it with a cam & single plane intake that didn't come in until 2500 RPM with a stock convertor powerglide behind it; then a new "original" 3310 780 CFM VS on that 302. The 3310 was pretty poor quality - loose throttle shafts, leaking gaskets (porous castings, warped surfaces), etc. And, I never really attempted to learn how to tune either one of them.

This new carb is of very high quality. None of the problems the 780 exhibited.

Oh, also a 4165 (or was it 4175?) 850 CFM DP q-jet that a friend tried to make work on his 402 Chevelle. Gave up completely on that one. When I put the 302 into another '57 with a stick, I put the 600 DP back on, traded him the 3310 for his 4165, then sold the 4165 for $50 to a clueless Air Force Academy cadet who wanted to put it on his Vette...

[This message has been edited by five7kid (edited September 03, 2001).]

merf23

I have had similar experiences with holleys and racing. I have been working with circle track cars for quite some time. When the rules allowed us to switch from a rochester 2G to a holley 4412 we started getting "loose" coming out of turns 2,4...increased throttle response. We had to increase the crossweight to compensate for this.
I am now building a VW scirroco stock car...I tossed the FI in favor of a holley 7448 (350cfm 2bbl)and i adapted an HEI distributor in place of the CC piece....If it runs right (I suspect it will run better), it will demonstrate the versatility and tunability of these components.
I do like my qjet on the camaro though.

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1984 Z28 (L69) monochrome tangerine orange with IROC decals and hood
1987 IROC wheels with Goodyear GSC's
305 from 87 IROC with 1994 LT1 cam (203/208 .450/.460")
performer intake
Qjet from 73 Olds
dynomax cat-back, gutted cat
no emissions controls --> passed emissions testing
non WC T-5 with 0.73 5th
3.27 nine-bolt

Biochem

Hey... are you trying to copy ME? I have the same Holley and also have jetted down to #68 primaries (have $66 still in box), but I still have yet to go to a metering block in the secondaries. I think you and I are going to be tossing a few posts back and forth before we both figure out this carb!

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1984 z28 w/ a 357 cu in. monster engine which is looking like the posterchild for Edelbrock with the exception of the Holley 750vac... all the suspension stuff... 9-bolt posi disk is in...

-=ICON Motorsports=-

five7kid

iTrader: (14)

You probably know this, but: Toss the metering plate. Get the 34-13S "4160 to 4150 conversion kit", $32.95 from Summit. Being able to rejet the secondaries makes it well worth it. If you have a solid dual feed fuel line, it will be too short, so a 34-150 line is $21.95.

That's another story - the feed line. In my original post, I related that Summit didn't include the line in the original shipment. Reason: The line comes with the carb, but someone apparently took the line out of the box for my carb. So, they sent me one, but sent the 34-160 line (for the 4160 model carbs)! They offered to reimburse me if I sent it back and picked up the right line locally, but I needed to get running before 9 a.m. Friday. I ended up cutting it and putting in a rubber line from an in-line fuel filter. Side benefit - loosen the hose clamp, you can disconnect one bowl without loosening both inlet fittings (or both bowls w/o loosening either fitting, for that matter). Just looks ugly.

Damon

Getting good throttle response from a QJet is 80% of the "magic" in tuning one. Stock, they NEVER respond well to a quick throttle stab. The design (in stock form) is just not made for that kind of work. Just changing jets and rods won't give you that. It's an emissions carb and will only give you "warp speed" when needed, and you'll have to wait a fraction of a second for it.

Unless you are ready to do some "post-graduate" level tuning on it!

I'll put one of my home-tweaked QJets up against ANY Holley 750 vac sec carb tuned by anybody, anytime, anywhere. Dyno, racetrack, whatever. I'm dying for somebody to take me up on this someday!

SSC

Heh you sound like my dad thats a good thing he builds qjets "for himself and his buddies, not me " These sukers have the throttle responce of FI. Im to dumb to build a qjet right so I stick with holley's


Yea, try a smaller PV. I gained a good 2in of vac when replaceing the qjet and was curiuos what you got.

SSC

five7kid

iTrader: (14)

Damon,
I'd agree with you on factory q-jets. But, the 1901 was supposed to be "fixed" by Edelbrock for all the little quirks the q-jets have. However, I found the AV to be very rough in it's travel (much more so than any of the factory q-jets I've had over the years), with the "bad" pin angle, etc., etc., etc. I'll admit part of the problems were my own fault (took off the pull-off to AV rod 3 years ago, the piece Edelbrock sent was the wrong one), but I didn't cause that rough AV travel. And, the throttle response wasn't bad, the primaries just weren't big enough to feed the engine soon enough.

For a street/strip carb, it sure was sensitive to engine temp. So far, the Holley is proving to be much more flexible. And, who knows, I may put the q-jet back on for that 800-mile roundtrip to the highschool reunion in '03.

In retrospect, I should have layed out the extra $80 4 years ago and gotten the 1910 RPM q-jet. To do so now would have cost a lot more than going Holley. Fear not, though, like the topic says, I have been and will remain a "q-jet guy". It'll just be on the Camaro and van for now, looks like the '57 will stay Holley.

Until the Ram Jet 502 goes in, that is...

C h r i s

Old Topic I know but my thoughts are that the reason Q-Jets typically don't have the throttle response of other designs is simple. When you stab the throttle - and go from those small triple-tier-boostered primaries to those giant secondaries (with an air-door to meter air flow) you are going to get a hesitation unless the perfect balance of forces is established. Of course this balance is affected by many many variables, thus hard to achieve.

Just my thoughts. I have a Road Demon on my Malibu and it's required quite a bit of tuning to get it close to where I want it. As always the biggest room in the world is the room for improvement.

I've run Q-jets, Holleys (4160, 4010 and 4011 style), an Edelbrock (briefly) and now a Demon and they all have their own quirks.

Chris
'78 Bu 350/TH700R4 - new converter very soon
'68 SS396 Chevelle - resto project

five7kid

iTrader: (14)

I'm not done, but 3 weeks down the road I'm still doing okay with the Holley. Went to .028 shooter (why do they only come in pairs - we don't all have DP's), 4.5 PV (original was actually 6.5), 69/74 jets. Haven't played with pump cams yet.

It's not "perfect" yet, but I'm having more success tuning it (even though it's been 22 years between Holleys for me), and it's at least as drivable as the q-jet - better when the engine is warm in stop & go.

Oh, last week went out to test & tune, got in 6 runs. RT's all in .5's, I uncorked the Warlocks - it really liked that. Still haven't matched the ET on that "one good day" with the q-jet, but I set best ever MPH (95.4) using the Holley.

Back to test & tune next Wednesday...

Damon

Chris hits the nail on the head! Transitioning to those monster secondaries is the main challenge in tuning those things. Getting the jetting right is only 1/2 the battle. Getting rid of the "hole" when you put you foot through to WOT is the real trick.

Fortuantely, it's not too tough to do once you figure out that the factory calibration is almost always WAY TOO LEAN on intial secondary opening. Almost anything you do to fatten it up will pay dividends in torque and throttle response.

The difference between a bad factory calibration and one that's ready to race with is about .3-.4 sec in ET on a typical 13 second car.


[This message has been edited by Damon (edited September 23, 2001).]

C h r i s

Wow I didn't expect such a resounding confirmation on my theory from the resident expert. To me anyone who has had a Q-Jet off the car and in their hands could look at those monster secondaries (with no booster!?) and small primaries and (literally) see the main tuning hurdle.

Since we're on the subject of secondary actuation . . . my Road Demon carb (625cfm) puts a fair amount of smoke out when the secondaries open from a full-throttle stab. I've jetted the carb down from 70/78 to 66/76 and reduced the shooter from 28 (I think) to 25 - which helped. My next move is to go down again in the rear to 74s (good thing I bought the big holley jet kit!) Does this sound right? Vacuum pod spring maybe? How will I know when I've gotten too lean on the primaries and secondaries? My mileage is terrible with this carb - 12 compared to 15mpg with the worn-out 1850 I was using.

All help appreciated,
Chris
'78 Bu 350/TH700R4 - trans. in, trans. out, trans in . . .
'68 SS396 Chevelle - resto project