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Discussion Starter #81
COOL! 馃憤

I've elected to whittle it down to 1, Tom Mobley's carb. Its much closer to being correct, while my other is way, way off. And I mean at easy part throttle response, not WOT. With Tom's QJ throttle response is OK. yet the idle quality is ratty. And not easily adjusted. I don't want lumpy idle here.

So just today posted Tom's carb down to Vintage Musclecar Parts , so Eric can maybe take it one step further and make it work as best it can on this beast. And maybe make it look nice too. ;) Bonus is that Eric knows the engine builder some, and the engine.

PS last year Cliff wouldn't take my order fwiw. You must ask nicer than me! ;)
 
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PS last year Cliff wouldn't take my order fwiw. You must ask nicer than me! ;)
Maybe if you signed your name "Jean" instead of Gene , he might be more interested !
LOL, I probably caught him at the right time.
You are using one of the bigger qjets ? The primaries are 1/8" bigger on the 76-79 carbs, or edelbrocks.
 

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Discussion Starter #83
Yes, a truck carb apparently. Hey Beth, do yourself a favor and NEVER throw a 850 Holley DP on top to see how it will go. Ma'am a big DP, stick and a rat are a natural combination!
 

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Yes, a truck carb apparently. Hey Beth, do yourself a favor and NEVER throw a 850 Holley DP on top to see how it will go. Ma'am a big DP, stick and a rat are a natural combination!
I have a new vac secondary holley 850 that came off a crate ZZ502. Got it for $300 years ago. It gets a bad rap but it's hard to figure why when the 780 vac sec is so loved ? Once I optimize my 489, I will have some spare carbs to sell. LOL
Ever tried a 950HP on your beast ? Heard good things about them
 
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Discussion Starter #85
No ma'am. but reckon it cold stand a Dominator of some sort, as I've been told ( not with its stock 3.31 gearset imho) .. My 70's vintage Holley seems to fit just right. Any further experiments after getting a Qjet to run ACCEPTIBLY, would be EFI I would think.
 

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Initial report:

The carb arrived today, and I put it on the live test engine to see where things are at as-delivered.

Idle mixture screws were 4 turns out on the drivers side and 6 turns out on the passenger side. The transfer slot was exposed quite a bit, probably half again as much as it should be. I fired it up and it was idling at about 1050 rpm with an air/fuel ratio around 14-1 on my meter--which tends to read about 1 point richer than what I've seen when running on a few local dyno's.

I re-set the mixture screws to 5 turns out each and the idle smoothed up a bit and richened about 1/2 point. I dropped the curb idle down to ~800 and took the mixture screws out to 6 turns each and the ratio richened up to about 13-1. I also noted that I could not drop the curb idle speed down any lower as the throttle shaft was no longer in contact with the curb idle speed screw. I also noted that the primary throttle shaft is notably bent upwards at the throttle operator, so that may have something to do with that situation.

I ran the engine up to ~3K, and the air/fuel ratio was in the high 15's, which is obviously WAY lean for something like one of Mark's tire shredding rat motors, so there's ample room for improvement there.

I didn't have time to delve into the carb today, I'm still pretty swamped with other work so it'll be at least a few days before I can get back to it.

Tentative plans are to see where it's at in regards to jetting & metering rods and go from there. I'll also make the APT externally adjustable for further refinements. The throttle response was OK but a little soft, so the discharge orifices may get opened up a bit. The rest of my plans I'm keeping under my hat for now.

More later.
 

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Discussion Starter #87 (Edited)
NICE! Man-o-man, having the ability to bench it like that is priceless.

Brother if you think that one was lean, the pretty one was a mess trying to run that engine. "'Big Ugly" was just OK, but idle was clearly way too lumpy. You found that straight away. Holley idles @ 950rpm, 14.X " Hg, smooth as can be.

PS I've never idled it down to 800; a vestige of my solid cam days where low idle speed = no oil splashing about. And I am liking a "classic" muscle car idle these days, not the L88 type idle I had before.

No rush Eric, I hope to FINALLY run the 1/4 mile this Sat or next or both with the Holley on; and then I don camo during the weekends until past Thanksgiving.

PS if anyone wants a nice Qjet to TRY and have Eric build back up, let me know. I have a core, the one that came from Mark. Its very pretty looking externally, unlike the big ugly I sent Eric. I would NOT use it for a 600 hp rat, even with Eric's expertise. To me, its still Mark's carb in a way, so if you want to pay for it, the $ would go to him. This is not a for sale ad.

Mr Jones was kind enough to have a friend build me a Qjet that he felt might support the very special engine he made for me. ( it has multiple upgrades, including full dress down of those 049s.) Unfortunately, through no fault of Mark's that didn't work out as planned.

TO me, there's only Two guys that can build a Qjet to do a MJ special justice, Mark himself ( his race Q rocked!), and this fella down in Union Ohio right here!

Well, we're going to find out shortly, empirically, about that fella in Union OH. ;)

Even our local retired ME from RPD, couldn't make his "baby" feed the MJ right.

And oddly, I cannot dismiss the fact that my ancient race Holley fits and runs the MJ special like an old pair of well fitting hunting boots, like they were MADE for one another. PERFECTLY, with no more than a pri accel pump tweak. AS much as I want to get a RPD carb on there.......its hard to give up on natural symmetry!

Mr Jones warned me, and that why he went above and beyond to try and source a Q that would be acceptable.

Dont know if it will pull the same 583hp /580 ft lbs as Mark's race Qjet Eric, but anything close,with the low speed drivability of the race Holley ( I know its weird) would be acceptable.
 

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I ran the engine up to ~3K, and the air/fuel ratio was in the high 15's, which is obviously WAY lean for something like one of Mark's tire shredding rat motors, so there's ample room for improvement there.
Eric... why do you say high-15s is too lean for light load / light throttle @ 3k rpm? I have a 9.6:1 355 and it runs great at mid-15s highway cruise. This is with a 217/225 @ 0.050, 108 LSA cam. The way I see it, go as lean as possible at light throttle until the engine starts to protest. Engineering texts from the pre-emissions era showing A/F vs load seem to back this up.

Maybe I mis-understood and you are talking about higher load?
 

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Eric... why do you say high-15s is too lean for light load / light throttle @ 3k rpm? I have a 9.6:1 355 and it runs great at mid-15s highway cruise. This is with a 217/225 @ 0.050, 108 LSA cam. The way I see it, go as lean as possible at light throttle until the engine starts to protest. Engineering texts from the pre-emissions era showing A/F vs load seem to back this up.

Maybe I mis-understood and you are talking about higher load?
In a nutshell, it's not about making the carb as lean as possible at cruise in this instance. If Gene were after eeking out every last .001 MPG, saving the planet from Greenhouse gases and keeping his spark plugs ash white then I would be, but in this case it's about driveability and response.

This is a great example of one of those double-edged sword scenarios that's evolved since wideband O2's became so popular--people seem obsessed with shooting for some magical target A/F ratios esp. at cruise. I don't take that approach--instead of telling the engine what it can have, I prefer to let it tell me what it wants.

Gene stated that with this QJet on the engine drives like a stock L35, but with the 850 Holley it goes from Dr. Jekyll to Mr. Hyde mode. What's the difference?--I'd be willing to bet that Holley isn't cruising at 15-1+. Granted the Qjet will never have the same "pedal response" as an 850 simply due to the amount of throttle opening required by each respective carb to provide the same amount of air, but comparing Mark's ~600HP engine to an L35 pretty much screams the engine is starving for fuel.

I'm not going to go nuts on Gene's carb--there are a lot of modifications that can be done to eek out every last ounce of power, but this situation doesn't warrant that amount of work--or cost. I'm just going after a few "low hanging fruit" gains and making the APT externally adjustable so Gene can fine tune it after he gets it back.

FWIW, Gene's carb ran very "soft" or "lazy" as delivered on my test engine which is a mild 406" small block with a 216掳@.050 flat tappet hydraulic cam. The 750 QJet I built for the 358" in my wagon is snappy as hell on my test engine, so I know there's plenty of room for improvement.

Here's the 800 QJet I built for Mark running on my test engine:

 

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I'd say pretty snappy.(y)
 
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In a nutshell, it's not about making the carb as lean as possible at cruise in this instance. If Gene were after eeking out every last .001 MPG, saving the planet from Greenhouse gases and keeping his spark plugs ash white then I would be, but in this case it's about driveability and response.

This is a great example of one of those double-edged sword scenarios that's evolved since wideband O2's became so popular--people seem obsessed with shooting for some magical target A/F ratios esp. at cruise. I don't take that approach--instead of telling the engine what it can have, I prefer to let it tell me what it wants.

Gene stated that with this QJet on the engine drives like a stock L35, but with the 850 Holley it goes from Dr. Jekyll to Mr. Hyde mode. What's the difference?--I'd be willing to bet that Holley isn't cruising at 15-1+. Granted the Qjet will never have the same "pedal response" as an 850 simply due to the amount of throttle opening required by each respective carb to provide the same amount of air, but comparing Mark's ~600HP engine to an L35 pretty much screams the engine is starving for fuel.

I'm not going to go nuts on Gene's carb--there are a lot of modifications that can be done to eek out every last ounce of power, but this situation doesn't warrant that amount of work--or cost. I'm just going after a few "low hanging fruit" gains and making the APT externally adjustable so Gene can fine tune it after he gets it back.

FWIW, Gene's carb ran very "soft" or "lazy" as delivered on my test engine which is a mild 406" small block with a 216掳@.050 flat tappet hydraulic cam. The 750 QJet I built for the 358" in my wagon is snappy as hell on my test engine, so I know there's plenty of room for improvement.

Here's the 800 QJet I built for Mark running on my test engine:

Very nice carb you built me!
 

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Eric, I'm curious, on the carb you built for Mark's Stock Elim Buick, did you retain the primary metering rods or remove, plug vacuum hole, and upjet? With the unlimited duration allowed on Stock Elim engines (stock lift req'd) I could see idle vacuum being a problem. If this is classified info I understand.
 

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Eric... thanks for the reply. I agree there is no one-size-fits-all A/F ratio. I just know that my engine seems to like running at 15.3-15.5 range at 70 mph cruise (~3200 rpm). Tip-in response is great... can't see how it could be any better. I've played with APT and gone richer at cruise, but it didn't really see to help anything in terms of drivability or response, so no reason not to keep the cruise lean.
 

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Gene's carb is done and will be headed back to him tomorrow.

I'll wait until he gets it reinstalled and we'll see how the tuning changes I made work out for him before I go into more details.

I took a pretty big swing at a couple of areas, others not so much--don't want to try to go all the way on the first date kind'a thing. I made the APT externally adjustable (along with several other things), so it may take a little refinement on Gene's end to find the sweet spot, but it ran beautifully on post rework live test--so much so that I'll probably be picking up another identical core to do further development work on.
 

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Discussion Starter #96 (Edited)
TOO COOL! Hey, i'll be following Mark's orders and not racing with a Qjet on, tomorrow or next Sat, our "last chance saloon" this year. After I get some ET's I'll swap the Qjet back on.

High of 55 late in the day tomorrow, so the air ought be near identical to the 118.75 mph run Old Red made years back with the 4 bbl L88. Finally get to see if the MJ467 can "keep up" with my home built L88.

Eric, it will be some time before the swap is done as I have to have my resident sheet metal pro.fabricator alter a drop base air cleaner to fit that choke underneath. It will not fit under the stock OER 2" drop base. Its going to be nice to have a choke for once in 20 years of ownership.

PS, as I mentioned, whether you want it or not Eric, I'll ship back the carb that Mark had made for his engine. He paid for it, its HIS. But for now, it ought hit your hands first. Runs like crap on his 600 HP 467. Unbelievably bad in fact. Yet, I think you could make it PERFECT for a 525 hp MJ, if he can use it. I'll leave that up to you and Mark. It DOES NOT have a choke provision; that's the way I ordered it. Looks pretty as heck tho. Nice green sheen.

False confidence on my part? Heck no! Eric I have little doubt in my military mind you got that thing 90+% of the way there. It will NEVER have the utter snot of the 850 race dp, but as long it preforms acceptably, I'm happy.

Plus, my good buddy mr 4 speed shared that fakebook video with me. So my confidence in you also has some "data points"! Sounds mean! Idles smooth! That's what we're shooting for , a very soft walk, and a VERY BIG STICK.

PS no new fuel pump yet, I'll rig it with the Carter 172 regulated down to 5.5 psi. I have oem 325 hp QJ hard lines to rig a FP once its dialed it.
 

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This generic Summit drop base air cleaner will work as is with the QJet.

 

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Anyone ever try these on a Qjet?

 

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Discussion Starter #99
The oer one was rather spendy, but nice. I already had to alter the PCV breather tube to clear the Holley rear accel pump arm. This will be more severe and I d rahter use another, CHEAPER base to cut on. Or not if SUM-G300 works out ofhe box. THNX for the tips!

Jim, I used the OER 2"drop base for the non choke Qjets just fine. An integral choke wouldnt be a problem, this one is the big electric one. I want it hidden anyhow.
 

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Where doe it hit? The plug for the power?
 
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