high performance/gas mileage trick carb idea

[Guest Ziggy Vulcan]

I'm new to this board but I've been reading a lot. This looks like a cool place to get advice and trade info. I've decided I'm probobly going to put a 350sbc in a 240 and I'll need help with it later. But now I've just been planning and looking up parts (that's the fun part, right?)

 

Anyway, I'm planning on making my car a daily driver with fuel economy in mind but with on demand power for when I don't care about economy and just want to smoke someone at the strip. I was thinking about some rather different ideas. I'm new to this area so help me out.

 

I was thinking about running duel carbs with someway to activate the second carb when I want it. First, tune the first carb to run the engine alone with driveability in mind. Then tune the second carb with horsepower in mind. Rig up some switch to acivate it inside the car by electric choke or maybe a second fuel pump hooked only to that carb that can be turned off by switch.

 

Also, you can add nitrous to come on when the second carb is active for more power or to solve air/fuel ratio problems. Also, if your really going big, you could hook the second carb up to it's own small fuel cell and put high octane race gas in it and run more nitrous (with the engine internals reinforced.)

 

Assuming all this works like I think it should (working on limited knowledge), you would get a fuel efficient daily driver that you can take to the strip, flip a switch, and run insane compression ratios for really high horsepower.

 

Tell me what you guys think about this and some problems with it. (there has to be problems or someone would have done it already) I admit I don't know as much about this as some people but this is just a concept I came up with.

 

(btw this site rocks! )

[80LS1T]

Sorry to burst you bubble but I doubt that would work and here's why I dont think it will.....

 

By having a duel carb manifold and only running one carb during "daily driving" you would have a lean mixture in the cylinders farthist from the carb and a rich mixture in the cylinders closest to the carb.

 

And the running race gas in the second carb wouldn't work either cause if you were to run really high compression you would have to run high octane gas all the time to help stop detonation.

 

Like you said if this could have been done it most likely would have been done!

 

That's my $.02

[denny411]

That idea might work better with a tri power setup that operates on one two barrel at part throttle and all three at wot.

[Guest greimann]

It would be very difficult to build a "Jekyl and Hyde" motor that transforms itself from economy motor to race motor by suddenly opening another carburetor. You need to build a motor that has a singular focus so that you can choose complimentary components. The one thing that may come remotely close to that small and large idea is to use a spreadbore carburetor like the old Quadrajet (AKA Quadra-bog) that has tiny primarys and huge secondaries, but, the internals of the engine are what will really determine how the fuel is used.

 

The compression ratio is a fixed relationship between the cylinder, bore and piston, that cannot be changed with the flip of a switch.

 

Your bet for a fuel efficient performance motor is to go EFI.

[Guest subdermal]

I am also new to this and may be way off base here, but here's my 2 cents:

 

Run two carbs with a progressive linkage between the two. Normal driving, only the first gets opened for the most part. At WFO, both are completely open. I'm currently running this setup and although its new and I haven't "tested" it a lot yet, it seems to work pretty well.

[Guest jens]

EFI the new hotrockers variable rockers and overdrive will help mileage. But you have to drive many miles every year because the investment is $$$$$$$

[utvolman99]

One way to save on the gas is to use a vacuume secondary carb. They only have jets in the secondary plate. The primaries are preset and very small! If running only on the primaries your engine will sip gas like its a fine wine. One thing to watch out for though is that all new carbs must be tuned! You need to talk to Holley to find out what power valve and secondary spring you should start with. Most people who just bolt a carb on have really poor gas miliage due to the default power valve.

[Mike C]

Obviously that is the idea behind a spread bore carb. The easy way to do this is with an Offenhauser Dual port intake. It is the same idea behind the ZR1 corvette intake with its multiple throttle bodies. There are two complete sets of runners. One small set that uses the primaries only for high velocity and a second set that uses just the secondaries for power. Combine this with a Q-jet. OR, just swap in a port fuel injection motor and it will do both VERY well. Actually, even the CPFI Vortec motor would be an excellent swap for a Z and they get pretty good economy even in full size pickups and vans. If economy is primary and performance secondary, the 235 hp T5 TPI 305 from a 91-92 Camaro will run low 13's and possibly high 12's whhile returning nearly 30 mpg on the road. (Assuming 70 mph or less) Best way to improve economy is reduce displacement then engine speed.

Volvo has a prototype engine that tilts the cylinder head changing the mechanical compression ratio.

You can have that Jekyll and Hyde transformation with the push of a button...N20. Or turbo, no button, but on and off to some degree. Look at Scottie GNZ. His car runs 10's and knocks back 26 mpg on the road!

Most common Holley vac secondary carbs are square bore and not spread.

Most carbs have progressive linkage so there is no point in running multiple carbs when a single one will work fine unless you are trying to maximize performance from each cylinder in which case you need a venturi for every port by using 4 downdraft webers or something similar.

[deMideon]

An option I use is mechanical secondaries with slightly heavy springs on the secondaries. This way you know when you are useing them. That way you run 2 barrels when you need good millage and you really know it when you get into the secondary. Of course I get into the secondary waayyy more than I should

[Guest Ziggy Vulcan]

See, I knew it wouldn't work.

 

Nitrous probobly is the best thing for this as well as having large secondaries. I completely forgot about finding some way to evenly distribute the first carb.

 

What I was thinking was to have the pistons and valves and cam and everything set up to handle high compression but just supply it with less fuel and air by means of having a small primary carb. I don't think I understand compression ratio completely.

 

I think the main problem is the fuel distribution. Maybe a trick manifold? I'm just trying to come up with something new and different and I thought this might work. Another thing I just thought of but is probobly overdoing it, what about running one carb and DFI? Get one of those manifolds that has the fuel rails off to the side next to the cylander and have the fake carb lookin thing on it to except air, then replace the fake carb with a real carb. Then do the same thing. Get the carb to activeate later at the same time as a shot of nitrous. Nevermind, thats just unnecessary.

 

Anybody else have some really creative jeckyl and hyde ideas?

[Heavy Z]

For serious on/off action, how about an electric blower like the one's on ebay?

 

A leafblower mod has been done with some success.

 

Or Estes model rocket engines - maybe 200 or so of the "D" type mounted in a custom rear valance...

 

Kidding aside, I think you'll be real close to your ideas with a tripower setup. Look around and see what you think, they were on some 60's vettes and other GM cars.

 

Heavy Z

[Pop N Wood]

Tri power set ups were not progressive. All three carbs were synced just like a set of triple webers. I have also read many a magazine that says they got better economy and performance out of a basic 4 barrel set up than a tri power.

[Mudge]

The Rochester QJet was invented for this purpose, small primaries, and big secondaries.

[Chaparral2f]

I'm not real sure, but if my faulty memory serves me right, back in the fifties the Olds J2 ran tripower, and the linkage was progressive. The one I had worked very well for the time. Of course that was when dynosaurs ruled the earth, and most of you weren't born. But like I said, My memory may be faulty.

[Guest Anonymous]

Where you from Chaparel?.........Pontiac GTOs had progressive linkage TRI-Power (3 carbs) but as the 4 barrel carburator developed it developed more power and economy. Three carbs under the hood is a fantastic site though.

[Mike C]

The big block chevy tri-power had a mechanical center carb and vac actuated front and rear carbs. Even Chevy went to a single carb on the L-88 and Zl-1, their highest horsepower motors. Fuel Injection solves all of your problems, why are you shying away from that?

[Guest Ziggy Vulcan]

Fuel injection would be good. The reason I am shying away from it is one kinda good and one really stupid reason.

 

First, this is going to be my first "rod" and I want to keep it relativly inexpensive and simple (yeah, having duel carbs set up to run jekyl and hyde is simple ).

 

The main reason is really stupid. My dad used to have a car (a comet I think) and he always talked about cruising on the primaries and then popping open the secondaries to pass someone or other wreckless things. The way he described it the secondaries were a very dramatic transition and DFI doesn't have secondaries.

 

Although, I could get a cool ECU and program it to either open up at a certian RPM or make separate programs for performance and economy. I've seen some good looking ECUs. I might look into fuel injection a bit more.

 

I am very seriously looking into nitrous. It sounds like the perfect thing for my set up and it has a very broad appeal. ("What's a datsun?" "It has NOS." "COOL!!")

 

Oh and just because it's my first car don't try to tell me it's too complicated for a beginner. I want to do this car because of the awsome power to weight ratio and streetability. Plus, it's not a very common car. And, it has a manual. (thanks JTR!!)

[Tim240z]

It really sounds like you aren't really all that worried about fuel economy.

Just build up a nice reliable SBC, with a holley double pumper, and tune it well. IMHO, a well tuned Holley will barely sip fuel in such a light car, as long as you have an OD tranny and don't get carried away with the grin factor of jumping on the loud pedal to open up the secondaries.....not a very easy thing to resist.

 

If you don't want to go FI because of the complications, why are you even considering your original question here? If ease and simplicity is what you're after, go with something tried and true.

 

Just my 2c worth........

 

Tim

[Mike C]

My 2 cents again (you must have several dollars of my money now...) I have a 1040 CFM Barry Grant Stage III 750 Holley on my Camaro. It doesn't make the same sound as the Q-jet on my truck when the secondaries open, but it DOES absolutely ANNIHLATE the tires. Don't make performance decisions based on sound... Just because it worked better then doesn't mean it will now. If it didn't cost $3000 for a Super Ram, my car would be FI now. Someday all of my vehicles will be converted. You just can't beat it. Best bang for the buck is to buy a wrecked 93-97 Z/28 or Trans AM with a 6 speed. For less than the cost of the Super Ram you can have FI and a 6 speed manual trans. Then (if you have been reading some of the other posts) just pocket port the heads and add the LT4 Hot Cam kit you will have 300 rear wheel HP. This would/will pound the crap out of your old man's Comet.

[Guest Ziggy Vulcan]

I really am concerned about fuel economy, that's the reason for the whole jekyl and hyde thing.

 

This has started to turn into a FI vs. Carb argument. I'll end up doing something relatively simple (scrap the trick carb thing) and what it boils down to is whether I want DFI or Carb. I am going to have nitrous. I've pretty much decided on it. I need to look into fuel injection more.

 

I was considering putting in fuel injection a while ago because I was going to put a computer in the car. I don't know if I'm going to do that anymore, but the thought of programming every aspect of the fuel and spark delivery is tempting, with or without the onboard computer.

 

I'm gonna look into it.