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Predator carb on a big six?

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motzingg
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Predator carb on a big six?

Post #1 by motzingg » Fri Jan 31, 2014 10:22 am

I was just talking to my boss (a crazy awesome dude that has built and raced everything from baja to airplanes) yesterday and we got talking about these 'Predator' carbs, some kind of wacky box-shaped variable venturii thing.

We got on the subject talking about how motorcycle carbureation (which hit its peak in the mid-late 90's sportbikes) was vastly superior to anything that ever came out of detriot, mostly because they had to make a CV carb that delivered 3-4 HP/CI with radical cams, valves and porting, while still making something that drunk Bros could get started when leaving the bar at 3 am, and have a somewhat 'streetable' performance curve.

Anyhow, the CV thing.. It came up in that other thread talking about a mikuni 48 mm single venturii, but other than that not many automotive CV's are out there. The predator seems kinda cool, and at $500 its really pretty reasonable, especially for something that is made in the USA and appears to have pretty good support.

All I know about them is the little bit i could read on their website, anyone run one of these on a six? The only people i've seen running them in real life is some of the lower-powered bracket drag race guys.

So they cant run blow-through turbo... bummer, and they say '600 cfm' and '3000' rpm as the low end of their performance... so that would be like turned-up smallblock territory.

But since its variable venturii would it run good smaller?

Of course this is only for racing, but if i happened to be racing on a long mountainous track while pulling a trailer with my pickup...

Seattle Smitty

Re: Predator carb on a big six?

Post #2 by Seattle Smitty » Fri Jan 31, 2014 1:19 pm

Drag boat racers used them a lot. But David Vizard was quite impressed with them too, with a couple of caveats. Look at his book on carburetion, there's a whole section on the Predator.

The enormous CFM capability of the thing would seem rather much for a mid-sized, relatively low-revving six. Sure, it will only open as far as it needs to, but it just seems like a lot of wasted capacity. This is especially true when you consider that when Predators are mounted on V-8s for street use rather than racing, they are put on dual-plane manifolds, which tends to halve the capacity of any carburetor, as seen at the individual cylinder. With nearly all carbureted inline sixes, the whole capacity of whatever carb is there, 1bbl, 2bbl, or 4bbl, is used by each cylinder.

I almost bought a swapmeet Predator to use on a 300, but fooled around and it was gone when I came back. My idea was to take it apart and see if there was a way I could divide it in half, with a splitter in the middle of the airbox. This would have required splitting the spraybars as well, a little tricky, but I think this kind of thing is fun to try. I would have mounted my split Predator atop an older Clifford single 4bbl manifold which I had already split with a sort of wedge-shaped divider in the middle of the plenum so that it was effectively two manifolds, one for 1-2-3 and one for 4-5-6. But as I say, I missed out on the used Predator, never saw another at the swap meets, and didn't feel like spending enough to buy a new one for an experiment that might not have worked out.

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Re: Predator carb on a big six?

Post #3 by CNC-Dude » Fri Jan 31, 2014 1:32 pm

They did seem innovative, but they never were really accepted by the masses so much. Holley had been the top dog for so many decades before the Predator came along it just couldn't break thru. Even when Barry Grant came along as competition for Holley, they still struggled at first, now Holley owns Barry Grant.
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Re: Predator carb on a big six?

Post #4 by Baron Von Ottomatic » Fri Jan 31, 2014 6:52 pm

As a matter of fact I've got a Predator carb that I plan to give a go on the Bronco. I need to finish fabbing up bracket to hold the throttle cable/bell crank before I can try to drive it. Bolted it up and and let it idle and hand revved it a few times just for fun, it responded very well. I'm interested to see how it drives because Predators are supposed to be aces on rough terrain and at steep angles.

They're totally simple - no jets, no power valve. Just a couple of spring loaded air flaps, one of which turns a cam that rides on the metering rod. I posted some photos over at FTE: http://www.ford-trucks.com/forums/11827 ... retor.html

Seattle Smitty

Re: Predator carb on a big six?

Post #5 by Seattle Smitty » Sat Feb 01, 2014 1:26 pm

Baron, maybe you know this, but the Predator website has a good article by the chief tech guy on how to dial in his carburetor. Pretty simple compared to the carbs we usually deal with. And your library might have that Vizard book, if you don't.

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Re: Predator carb on a big six?

Post #6 by BIG 6 farmer » Sat Feb 01, 2014 5:52 pm

Back in the mid 80s, when we did a lot of Drag racing. We used a borrowed Predator Carb. on my Brothers 67 Cougar. :thumbup: After some minor adjustments, it performed very close to the heavy moded 780 vacuum sec. Holley we had been running. Almost no one was running one then(Predator). I think it was rated @ 930 CFMs ? Seems they made a smaller one too? :hmmm: The Cougar had a 1970 351C, 4v heads. hot Hyd. cam, single plane Holley intake, Headers. 3k rpm stall converter, 4.56 gears, and 10 inch slicks...With our Holley Carb., Ran 12.90s in the 1/4, 11.80 with a 100 HP shot of Nitrous oxide. :D From my experience, im sure a Predator Carb. would work well on a 3/4 Race or hotter built 300 six :nod:
83 F 150 SB 4x4 300 six NP 4speed - - 1950 IHC L162 (1&1/2 ton?) - 87 & 88 T-Bird Turbo Coupes - 2000 Triumph Tiger , 76 Honda GL 1000 , & other toys and parts (& junk) -

Seattle Smitty

Re: Predator carb on a big six?

Post #7 by Seattle Smitty » Mon Feb 03, 2014 1:46 pm

the post-WW2 Fish carburetor was the ancestor of the Kendig/Predator carb. I mailed a old (Fifties) article from a Popular Science magazine with a good article on Fish and his carb down to Texas to Gary "Stubby" Stubbs, with the intention that he would scan it and post it here. But Stubby disappeared form these pages right after that. If anyone knows how to reach him . . . .

Baron Von Ottomatic
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Re: Predator carb on a big six?

Post #8 by Baron Von Ottomatic » Mon Feb 03, 2014 6:22 pm

Here's a pretty cool 1972 Hot Rod magazine article on the Predator's cousin, the Kendig carburetor:

http://www.yellowbullet.com/forum/showp ... tcount=111

motzingg
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Re: Predator carb on a big six?

Post #9 by motzingg » Tue Feb 04, 2014 1:15 pm

hmm interesting.

its tough for me to take my 'motorcycle carb' brain and twist it around to understanding one of these.

the more i get into auto carbureation, the less i buy into the whole 'cfm' rating system. there are so many variables that its just about impossible to go from one model/configuration, to another, and have that rating mean anything.

I think they are probably taking the 'industry standard' holley and approximating their carb performance based it being equivalent to a 750 double pumper, per se.

Either way it doesn't look like the tuning parts are out there. I'm pretty happy with the 2100, its a nice carb, works good and simple. The future came, went, and it has chosen conventional EFI... maybe these odd duck carbs have a place, maybe not. Probably not on a six either way.

Seattle Smitty

Re: Predator carb on a big six?

Post #10 by Seattle Smitty » Tue Feb 04, 2014 1:25 pm

motzingg wrote: Either way it doesn't look like the tuning parts are out there.


If you're referring to the Predator, one of the neat things about that carb is that there are few tuning parts needed, and they're still available. In fact, if you find a racing carb at a swapmeet, whether set up for alcohol or gas, you can retrofit it as a street carb, including an accelerator pump that the pure racing carbs didn't use. One of the things David Vizard remarked on in his section on the Predator was the ease of dialing it in as compared to nearly anything else, including fuel injection (although he might not have been thinking of the Holley Pro-Jection, another system that is generally simple to tune).

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Re: Predator carb on a big six?

Post #11 by motzingg » Tue Feb 04, 2014 1:37 pm

i mean the tuning parts to make this work in a ~400 cfm application.

since its CV it can run efficiently at 10, 20 30% alpha, but the parts listed on the website start rich (rich assuming a heavy breathing race motor) and only go richer from that.

We over-carb our two stroke race motors all the time, guys running 24 mm carbs on a 50 cc cylinder that is only 40 mm bore! Crazy! That would be like having a 2 1/4" carb on each cylinder of a big six!

You just have to tune the idle and needle jets for the lack of airflow at low rpm, the CV doesn't care, but when its wide open it will support crazy power.

I dunno if this would work the same way, but i'm guessing it would be similar, just get bitchy to tune at those low flow conditions.

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Re: Predator carb on a big six?

Post #12 by motzingg » Tue Feb 04, 2014 1:38 pm

nevermind.. weird double post
Last edited by motzingg on Fri Feb 07, 2014 4:03 pm, edited 1 time in total.

Seattle Smitty

Re: Predator carb on a big six?

Post #13 by Seattle Smitty » Tue Feb 04, 2014 3:12 pm

I see (twice, tee hee). That's why, as I said farther up the page, that I wondered if the carb and manifold could be divided in half, so that any cylinder only "saw" half of the carb, as with a dual-plane V-8.

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Re: Predator carb on a big six?

Post #14 by Baron Von Ottomatic » Tue Feb 04, 2014 5:36 pm

Predator carbs are made to run a bit rich (12.5-13:1 afr).

There's only one screw to raise/lower the metering block (and an idle speed screw). The fuel cam only affects performance above 3,500 rpm. If it's super rich Predator sells blank spray bars that can be drilled smaller than stock. The only other adjustment is spring tension on the air doors. Supposedly most cases will just require a couple of 1/8 turns on the metering block adjustment screw.

They're supposed to be a hot ticket off road, they just ignore rough terrain and steep grades. We shall see.

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Re: Predator carb on a big six?

Post #15 by nightwatchman59 » Wed Feb 05, 2014 12:35 pm

THANK ALL OF YOU!!!! This is the info I was hoping to see when I posted the question about the Mikuni carb.
The early BIGFOOT monster trucks were powered by tunnel ram / blown 460's topped w/ Predators. I knew a couple people running BB Fords / Clevelands w/ Predators in the early 80's - the carb was not street savvy, requiring high idle speeds which would chirp the tires when you didn't want to- drawing attention when you didn't want it (stoplight near a cop). Fastest cars I ever rode in.
The Q-jet is damn close, and the varajet is a Q-jet sliced down the middle... My thoughts are that for racing a hot 300, a Predator would be Ist choice; For street / mud pit, a Q-jet; commuting / trash runs, varajet / motorcraft 2100-2150; stock replacement...yf or....maybe a mikuni??
There is some interesting reading at SPEEDTALK regarding carb CFM. When my right foot does not receive the required (desired) results, I will change that... by any means necessary.
p.s. the Predator sits kinda tall,and might be a problem even under an F150 hood.......

Seattle Smitty

Re: Predator carb on a big six?

Post #16 by Seattle Smitty » Wed Feb 05, 2014 1:14 pm

Check out the street version of the Predator, with accelerator pump (that also can be retro-fitted to race-only Predators.

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Re: Predator carb on a big six?

Post #17 by BIG 6 farmer » Wed Feb 05, 2014 5:13 pm

From what I remember about running the Predator Carb. was, that it seemed to be a bit of a hard cold starter (ran it only in the summer) Prob. from lack of an accel. pump? :hmmm: But once it was running, it idled so smooth. :thumbup: The response was like nothing anybody ever saw... Like I said, the car wasn't any faster with the Predator compared to our 780 Holley. But we didn't put much time tuning it ( changing fuel cams in it) I think that's why we took it off? Cool nights street racing, it was a pain to start...
83 F 150 SB 4x4 300 six NP 4speed - - 1950 IHC L162 (1&1/2 ton?) - 87 & 88 T-Bird Turbo Coupes - 2000 Triumph Tiger , 76 Honda GL 1000 , & other toys and parts (& junk) -

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Re: Predator carb on a big six?

Post #18 by Baron Von Ottomatic » Wed Feb 05, 2014 6:35 pm

It's got no choke. Nothing. Easy to see how cold starts might be squirrely.

The Predators I've got have accelerator pumps. The Kendig carbs didn't because he figured guys at the track would just use a squirt bottle of gas to start. It shouldn't need one once the engine is running. In theory anyway. It's supposed to run a rock solid a/fr from idle to redline with the variable venturis.

High idle speed is the other thing I've heard. If you can get her down to 800 rpm you're doing well. It's easy enough to add a vacuum port above the throttle plates so at least I can try it with ported vacuum and see if it's any better.

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Re: Predator carb on a big six?

Post #19 by motzingg » Fri Feb 07, 2014 4:19 pm

hmm that is interesting stuff...

kinda seems like everyone on the greater internet has about the same level of experience, you don't hear the keyboard jockeys talking about them much, maybe everyone who has figured it out is keeping the secret...

basically it comes down to what tuning parts are available and what the Mfg. has designed for/tested.

they probably are set up for a wild cammed small block v8. good setup for something where you need a lot of power but don't want to be constantly thinking about pushing your engine to the limit... something like mud bogging, monster truck, off road, bracket racing, etc.

maybe a 300 with a big cam and some custom tuning parts you could get it working, but i think its just not set up for what our engines are meant to do.



this 'Varijet' hmm... going to have to look into that, i have thought many times 'i wish i could cut a q-jet in half'

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Re: Predator carb on a big six?

Post #20 by Baron Von Ottomatic » Fri Feb 07, 2014 6:49 pm

I've spoken to a guy at Predator a couple of times and he's set them up for 300s before. They offer a rebuild service for $99 labor which includes run testing. He said to send the carb and engine/vehicle specs and he'd do it up. I'm thinking about boxing up the one I've got and letting him play with it. Give them a call.

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Re: Predator carb on a big six?

Post #21 by Baron Von Ottomatic » Fri Feb 07, 2014 6:54 pm

motzingg wrote:i have thought many times 'i wish i could cut a q-jet in half'


One inch spacer, a couple of freeze plugs, a couple of hex head screws to fit the jet orifices, maybe a little epoxy on the accelerator pump nozzle - voila!

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Re: Predator carb on a big six?

Post #22 by BIG 6 farmer » Sat Feb 08, 2014 3:03 pm

What about the early Ford Variable venturi Carb. ? The later ones were wired for feed back. :hmmm: Back in the day, I worked on some Ford cars that ran them. Seemed to run well and smooth. :thumbup: I have 2, thinking someday trying them on a six cyl., or a small V8...
83 F 150 SB 4x4 300 six NP 4speed - - 1950 IHC L162 (1&1/2 ton?) - 87 & 88 T-Bird Turbo Coupes - 2000 Triumph Tiger , 76 Honda GL 1000 , & other toys and parts (& junk) -


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Re: Predator carb on a big six?

Post #24 by nightwatchman59 » Sun Feb 09, 2014 7:20 pm

I had an early 80's wagon w/ the vv carb on a 302. When it was running good, it pulled as hard as my 1970 LTD wagon w/ a 2150 motorcraft atop a 351W (I ran a carpool). I miss none of it.

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Re: Predator carb on a big six?

Post #25 by sdiesel » Fri Feb 21, 2014 12:28 am

the fish is a similar idea to this predator
throttle response like a bat from heck.
good design

lots of fun on a six!
a long love affair with the 300 six.
my lastest and final fling is a fresh 300 in an 88 ford f350 dually 4X flatbed

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Re: Predator carb on a big six?

Post #26 by woodbutcher » Fri Feb 21, 2014 3:27 pm

:hmmm: Seems like I read an article about a 2bbl version of the Qjet.IIRC,it was used on some (maybe 4 or 6cyl) GM motors.
Good luck.Have fun.Be safe.
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Re: Predator carb on a big six?

Post #27 by motzingg » Fri Feb 21, 2014 4:02 pm

yeah that would be the 'varijet' that came on some of the small GM v6's

i did some research into it, not very popular. seems to be kinda complex and most of them had a bunch of emissions crap stuck on them.

looks like they also used them on some of the I-4's if that gives you an idea of the HP capacity.


if i happened upon one cheap that was in decent shape i'd give it a shot, but it looks too fidgy for my tastes

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Re: Predator carb on a big six?

Post #28 by woodbutcher » Sat Feb 22, 2014 11:42 am

:hmmm: Hi motzingg.The "Varijet" is IIRC a whole different critter.
Good luck.Have fun.Be safe.
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Re: Predator carb on a big six?

Post #29 by Baron Von Ottomatic » Sun May 04, 2014 8:50 pm

FWIW, I was able to run the Predator carb on my Bronco and it howls. Need to fool with return spring bracket to see if that helps with the idle speed - it idles ~800=900 rpm I'd guess, need to confirm the vacuum advance port is high enough above the throttle plates so as not to pull the can at idle. It runs like crazy with no tuning or adjustment. The throttle response is incredible.

http://www.ford-trucks.com/forums/11827 ... tor-2.html

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Re: Predator carb on a big six?

Post #30 by motzingg » Thu Jul 03, 2014 1:16 pm

somehow i missed this update... sweet!!!

the rich thing is to be expected but it sounds like you'll be able to figure it out.

i think the fact that it is able to meter fuel based on flow in the transient, while accelerating, is going to be a huge advantage to the kind of useful torque that you need, rather than incorporating accelerator pumps and power valves and all that mumbo jumbo.

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Re: Predator carb on a big six?

Post #31 by MechRick » Thu Jul 10, 2014 10:28 am

woodbutcher wrote: Seems like I read an article about a 2bbl version of the Qjet.IIRC,it was used on some (maybe 4 or 6cyl) GM motors.


This was a dualjet. It was a feedback 2 bbl used on sixes that was, essentially the front half of a Q-Bog.

The varijet was a progressive variable venturi 2 bbl (like a variable venturi Weber 32/36). They suffered from porosity problems that would make them run rich.

I still have a Motorcraft VV somewhere. They only had two issues. The diaphragm would fail and if you overtightened the air horn it would warp the top of the carb so the slides would not work. But they ran well. I wonder if diaphragms are still available?
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