Dual Quad Manifold - One TBI, one Carb?

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Dual Quad Manifold - One TBI, one Carb?

Postby pobrien327 » Tue Feb 20, 2007 12:05 am

I have a holley 670cfm TBI kit. It is great on torque and driveability, but can only put out 275 hp. Could I put this on for one of the two carbs, and a carb on the other? I'd love to use it for low speed and have the carb feed the high end power. My concern is that neither is really a "primary" spot - or is one?
Thanks
Pat
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Postby Sirshredalot » Wed Feb 21, 2007 12:18 pm

I have often pondered that myself.

Although I am not terribly familiar with the TBI stuff I would think that they might be difficult to tune together.

Also...this dual quad setup...are we talking low-rise or tunnel ram?
The low rise intake would be a little more forgiving as they arent really that effecient in power production anyways...

One cool thing though is that you could run the carb off of a mechanichal fuel pump and the tbi off the electric...interesting.
Would have to get a different "fuel map" or somthing because at idle the TBI unit doesnt see air demand like a carb....it sees how many cylinders its programed to see.

So you be supply 16 cylinders worth of fuel to only 8 cylinders.
IM not sure how tuneable the TBI's are either.


Either way dont let this sound pesemistic ...I say GO FOR IT!
I like the ugly ducklings and the odd ball stuff.
If someone says "you cant do that" Im usually the one thats more determined than ever to prove them wrong.

Good luck and God bless
-Shred
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Postby ColinOpseth » Wed Feb 21, 2007 2:08 pm

I have a Moates.net AutoProm and I can tune my TPI/OBD-I/TBI/GMC Syclone/T-Type real-time. It's possible.

Why don't you blend the both together? Run a TPI-style harness with a dual/single plane manifold and a standard throttle body plate on top? You get tunable performance that's EFI and carb-like. I've been toying with doing that on a 454 engine I have.

Later,
Colin
'72 Vega with '93 Camaro LT1/M29 T56/12 bolt 3.31. 16" IROCs all around. Sanderson headers into duals with an H-pipe and Flowmasters. It's loud but at least it's faster than your grandma's Buick. pwned.
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Postby NixVegaGT » Wed Feb 21, 2007 3:02 pm

I like the concept... How do you think the linkage would work? Maybe the carb could be actuated by vacuum... Like a vacuum secondary. A secondary curcuit is usually pretty simple... I'm not sure which side would be used as primary. Do guys build tunnel rams with a primary carb?
- Nic '73 Vega GT "DogBoxx" Batwing LS1
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EFI and Carb

Postby pobrien327 » Thu Feb 22, 2007 8:45 pm

The efi is a funky early era kit. It has a box that sits inside the car that has "thumbnail" rotating controls for choke timing, idle, midrange, and full throttle rich/lean controls. It might work very well and enable the carb to help out at higher rpms. I had this on a strong 327-- and it ran hard to 5000 rpm and then the power stopped increasing.

Thanks for the encouragement
Pat
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RE: Carb/EFI combo

Postby vegadad » Sat Jun 30, 2007 7:15 pm

Why not go for a dual TBI system. Ron White used that setup on a couple of the "Super Muscle Cars" he built for TV. Seems like a pretty good situation as if you used direct linkage (1:1) you would only need one throttle position sensor and could run the other TBI as a slave unit. Let me see 670 + 670 equals a bunch of CFM if they would handle the required fuel load. Just another idea to ponder. Good luck.
John b. (in Missouri)
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Postby Sirshredalot » Sun Jul 01, 2007 11:00 pm

Yes...guys do build tunnel rams with a primary carb...but that is less popular with the tunnel rams than the low rise dual quad crowd.

Usually they get them to run better through the transition from part throttle to wot by staggering jet sizes and varying power valve sizes.

Stage the carbs with a progressive linkage when onecarb opens 100% at 30% linkage travel and the primary carb opens at the normal rate.

Kinda like a second carb for full throttle usage and the primary carb for driving on.

Gahh...I love tunnel rams.

God bless
-Shred
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Postby greg72 » Tue Jul 03, 2007 9:57 am

Sirshredalot wrote:Gahh...I love tunnel rams.

God bless
-Shred



Me too , me too!
Greg
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Postby Sirshredalot » Tue Jul 03, 2007 10:38 am

Greg,

What are you running as far as your setup?..Carbs, intake, cam, jets, PV's, mods, etc.

I always love to swap engine specs and tips and tricks.

God bless
Please and thank you
-Shred
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Postby greg72 » Tue Jul 03, 2007 5:44 pm

I put together that current engine way back in 1986 or 7 . As a result I am a bit foggy on the details.....however I have it all written down......somewhere :)

I built it because have always loved the looks of dual quad tunnel rams and could not afford my first choice, a polished 6-71 blower! Also I was told you could not run a tunnel ram on the street....so of course i had to do it :lol:

I do know that it is a Edlebrock intake. I liked it better than the Weiand intake which had larger runners. The Edlebrock looked like it would work better at lower rpms than the Weiand.

I started off with two 390 cfm Holleys, put powered seemed to drop off on the top end. I then put on 465 Holleys , they worked better. I don't remember what jets or PVs are in it though .... most likely i have it written down. If nothing else I will know when i open them back up . They definitely need a rebuild . The whole car has sat idle since 1990!!!!

They are vac secondary carbs with a vacuum equalizer tube running between them. crud i know i changed the springs in there too.... I hope i wrote that down as well!

The cam is either a Crane or TRW , I have had many cams in this block , not sure which one I ended up with but i will look it up this week. I have a complete folder on all the parts for the car ....again, somewhere.....

It is a hydraulic cam , makes power from 2500 to 5500 or so.

I set up the whole drivetrain to maximize power within this range , 2500 to 5500 ... the cam and intake start making power about there and the torque converter locks up at about 2500 ....

The pistons are flat top , works out to about 10:1 CR with the iron camel hump heads, 2.02 intake valves (remember it was the mid-80's LOL) .

All in all it worked great. I drove the heck out of it . And it ran low 12's in the 1/4 with 8.5 " wide street tire using a 7.5 rear end ....3:73 gears. Now that I have put the narrowed Ford 9" in it with a 29" tall tire (vs a 26" tire) I will probably use a 4:56 gear or at least a 4:10.
Greg
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Postby greg72 » Sat Jul 07, 2007 9:49 am

Shred, I looked over all the paperwork I have on the car (brought back a bunch of memories :D ).

This is what I have found .

The current cam is a Crane hydraulic (again this was put together in 1985 / 86 so much of this is old school).

Intake side .510 lift 292 duration
Exhaust side .512 lift 302 duration
Lobe centerline 112 degrees


I am not sure where I have ended up with the carbs. If memory serves I blocked off the power valves and went bigger on the primary jets - I know we tried a couple of set ups unfortunately i don't remember what worked best ..... for sure it is what is in the carbs now. I just cannot take them apart at this time ...too many other projects .

The carbs have a seconadary metering plate as opposed to jets , we did go to a richer plate. and we went with a lighter spring in the vacuum secondary diapraghms.

The fuel pump is a Carter race pump pn 4594 , a Fram cartridge style fuel filter pn. HPG1 and a 12-803 Holley regulator. I am not even sure if these parts are still available !!

I hope this is some of what you were looking for . It was fun lokking through all my old files! Next time we should go over the ignition system , it is MSD based , back when everything was a separate component from MSD , rev limiters etc , were not included in one box like they are now. The car was fun to wire :lol:

Now back to the original thread , with apologies to Pat
Greg
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Postby greg72 » Sat Jul 07, 2007 9:54 am

Years ago I sold one of those Holley TBI kits (1991 ? ) to a guy who was going to run 2 of them on a tunnel ram. He had thought it out pretty thoroughly but I lost track of him and never found out how it worked.

But get this , the engine was going in a tubbed Monza hatchback ! I don't recall the year.
Greg
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