high performance/gas mileage trick carb idea

[SleeperZ]

Originally posted by 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.

MO, if you want fuel economy, you will find it difficult to beat a fuel injection setup. You will probably not go too far wrong with a carbs either, provided you can tune the (small) primaries to run lean and back it up with some responsive secondaries that will give you good airflow at WOT.

[Guest Ziggy Vulcan]

the thing is, it's not just fuel economy, it's fuel economy then switching to high performance. That's the tricky part. I could do what a lot of people have already suggested, and run a carb with tiny primaries and huge secondaries. I think this setup would work quite well considering I have the secondaries open at about 4000 rpm. (I plan on getting to 6500) Normal driving shouldn't exceed that. Or, do secondaries open by pedal pressure? Like I said, kinda lack some knowledge.

 

Then again, with FI, I can run two different fuel maps. Hmmm, choices.

[Chaparral2f]

Tee Zee,(oh most magnificent Guru) I'm from Penna, but I tell everyone that I'm from Oregon!! I never knew much about Goats, When I was young I had a great job, and was into Mopar. ('66 Charger with Street Hemi) first new car I ever owned. Oh well. Dodge has long been replaced with Wife, Kids, Grandkids, Great-grandkids, Mortgage, and a Peterbilt. Haven't had a fast car in centuries. But I do have this ratty old 300zx. Now you know what I'm doing here.

[Mike C]

What do you consider high perf and what is economy? How big a factor is your wallet? Those are probably the questions to answer first. IMO, mid 13's in a daily driver IS a high performance car, and anything above 25 mpg is reasonably fuel efficient. This very accurateley describes the 235 hp 5.0 5 speed 91-92 Camaro/Firebird TPI motor. And with a cam change and exhuast it would not surprise me if it ran 12's. My friends 3700# '74 'vette convertible with non-roller cam TPI 305, headers, and an SLP cam ran 13.97 with the TH700 and 3.07 gears (in Baytown, which DOES help...) and it knocked down 27 mpg on the way there! Knock off 1000# and 25% of the frontal area and you can see as how the Z could run 12's and return better than 30 mpg. Considering my 2.4L 6 gets around 20 mpg with the 5 speed and it would be lucky to crack the 16's, I think relatively, the 305 MORE than meets your goals. The smaller the engine the easier your mileage goals can be met, and the TPI setup is much better suited to 5500 rpm with a 305 than with the 350 because of airflow.

[Guest Ziggy Vulcan]

Wow. Fuel economy isn't as important as I thought it was! I was hoping to make 22mpg. Maybe less. Budget isn't really a problem because I have time and I'm gonna save up part by part. I would rather save for a couple of months to get the right part that just buy something sooner and regret it later. This car is going to be a very long term project. It's going to have all the right stuff. I'm just trying to figure out what the right stuff is. I was hoping to run a little bit better numbers than that however. I guess I'm willing to give up some fuel economy for more power, but the optimum setup for me would be to be able to switch.

 

Maybe I was aiming to high, but I wanted to run 10 or 11s. This is with the help of high perfomance cams, heads, pistons, carb/FI, ram air, nitrous, and anything else I can come up with.

 

I'm leaning more towords carb with big secondaries, but most of the quadra-jet carbs I've seen are an ugly brown color. Gotta go chrome. Under hood appeal is a concern, too.

 

I've also looked into a 3x2 carb setup with progressive linkage but where do you find an air cleaner? I wanted to run a street scoop from Mr. Gasket through the hood. I like being different.

 

Maybe I could just be simple and do one normal, polished carb with the street scoop. Is it true you have to change jets at different altitudes? That's a turnoff for me because right now I'm in south carolina and I plan on road tripping it out to see some friends in Utah (used to live there) and I want to go to various events to show it off with other Zer's and I'm sure there will be altitude changes.

 

Maybe I'm expecting too much. A reliable daily driver strong enough to road trip that can go to the strip and run 10's? Is this physically possible? My budget is pretty stretchable.

[Guest m35514h]

IMO all of the parts you listed above is going to cost you a lot of money, and seeing as how this is your first car maybe you should look into a few simple mods on a 350 and get it to run. Then you can see where you are at on your 1/4 times and go from there.

[Guest Ziggy Vulcan]

I like a under-hood setup that is very clean and uncluttered with lots of chrome. Shiny is good To me, chrome can't be over done if it's clean. I saw a magazine feature where everything under the hood that could be chromed, was chrome. It was clean and very purdy.

 

Like I said before though, I'm willing to save up the money for the right parts. Maybe the chrome is a little unnecessary. But I will invest in the nitrous.

 

Scottie's numbers are perfect. How did he get a buick in there? I didn't really want to go lt1 or ls1 due to the less aftermarket support. I guess it's still an option. I do want a T56 however.

 

Is an lt1 harder to get in and set up than a 350?

[Mike C]

It is possible. The drivability factor almost dictates FI in my opinion. The LT1 and T56 are the best choice to go with if you want 8 cylinder power for economy and performance IMO. If you want to see how it can be done, look at Scottie GNZs car. 10.50's at 129 and gets 26 mpg on the highway. 3.8 SFI turbo from a Buick GN. I am of the school if it don't go, chrome it. I personally like clean, detailed engineering and not expensive dress up parts, but hey, it's your money.

[Mike C]

Honestly, there is as much if not more support for the late model powertrains than the early models. With late model stuff you get roller cams and high tech cylinder head design. The Buick turbo 6 has been know to make in excess of 1200 hp, as they say, "There's no replacement for displacement except cubic dollars and turbo chargers." The $ is usually the single driving factor in my world and the best bang for the buck IMO, power and economy, is the LT-1 T56 combo. Follow the advice above and start mild. Just getting the combo in and running will be a significant learning experience, and like motorcycles, fast cars should be worked up to in stages. If you want a carb, you can still get an LT1 and buy a Gen II 4 barrel intake from the General. That's what I did just to get my LT1 running in my convertible. Eventually when finances allow, I will buy the DFI setup and go FI.

[John Scott]

I know this started as a carb question, MikeC started to mention a 6speed trans, but it needs mentioning again. Overdrive transmissions will really help the milage issue, weather its a 4 speed auto , 5-6 speed standard. Cruising down the highway at idle rpms is sweet! My .02 thinks that an over drive trans. strong bottom end engine, forged pistons, and a big nitrous system will get you closer to your goal. Mild manners, great milage, AND fast at the touch of a button. The only other way to get high hp is big cams/ compression, cubic inches= worse milage, or turbo/supercharger higher initial investment, effort, tuning FI & $$. W/unlimited funds I'd Turbo, being the most elegant and sophisticated, nitrous will get you there w/o an engineering degree and fewer headaches, but still need a strong engine and a fair amount of work to get you into the 10-11s.

John

[Guest Ziggy Vulcan]

I was under the impression that major low end torque wasn't really needed in a car so light. I was watching popular hotrodding TV yesterday and they said in race cars, they have more high rpm horsepower because of their lightness, but street cars should have more torque to get them off the line faster. Since they were refering to cars like chevelle's and the like, I was thinking that since the Z is so light, it should have more high rpm power.

 

The T56 is a must. A 5 speed tranny plus a 6th gear overdrive to cruise down the highway is a good idea. Gas mileage!

 

I still would probobly rather go with an old fashioned, carb'd 350 than a newer LT1. It just seems easier.

 

My opinion about the parts is that a cam is going to have to be put in either way, why buy a cheaper cam only to replace it down the road? To me, that seems like a waste of money and extra work. The same goes for all the other parts. If you're gonna do something, might as well do it right the first time. So, it's easier to buy parts and install them to meet my goals from the start rather than having to upgrade. Also, that way, I can buy parts knowing i'm getting a specific other part. For example, I'd go ahead and by stronger forged pistons knowing I'm going to put nitrous on, rather that getting cheaper pistons then having to replace them when I get the nitrous. So my setup will work together from the start and save me money and work.

 

I was thinking, a 350sbc with a 750cfm vac. secondary carb, forged pistons, righ rpm heads and cam, and a very healthy shot of NOS, mounted to a T56. Does 750cfm give enough fuel to run the nitrous? Maybe someone can give me insight on a carb with really small primaries and large secondaries. I think this setup with a strong clutch and fat tires should get me pretty good numbers while maintaining fair fuel economy. I can make sure the engine is strong enough.

[Guest Anonymous]

search somwhere in here for a Lingenfelter corvette (some help on where i posted it please guys) that got 30mpg and a 12 sec pass without no2

 

the details were a tpi 383 with a 700r4 auto 4spd tranny with an aux overdrive added (gear vendors) for double overdrive mpg

 

I think the 383 had only 380hp? but a big tourque curve to handle the steep gears over the double over drive.

 

It could be done to a z but getting dive line angles could be tricky since a the drive shaft on a doubl overdrive z would be 12"

 

also a good aticle to pick up is the "mistake 500 hp" car craft dec issue and what bsfc means for selecting efficent powerful engines.

 

for my setup of a mpg high hp on a student budget (you said you were a student didn't you) a 350 or preferably 383 overdrive trans carbed with 200hp of no2. that way if you want to go for FI later or DBL overdrive you can save you money up for it later but for now have some fun with your car while you can.

BTW why the concern with mpg?

[Mike C]

The T56 IS a double overdrive, no extra attachments required. As noted, you need low speed torque and throttle response in order to use the overdrive(s). We are now back to FI as the solution to a broad powerband. FI is not more fuel efficient than a properly tuned carburetor in a narrow rpm band, it is reduced engine speed where gains can be made. But in order to get proper flow at low speeds with a carb, you must have small ports, runners, and camshaft. With FI you can have much more highperformance engine and maintain the smooth lowspeed performance.

[Brad-ManQ45]

One possible alternative is a dual 4 bbl manifold and using a couple of Holley 390 CFM carbs.

 

I personally like this better than the idea of small primaries/big secondaries because of fuel distribution issues.

 

W/the 2 small 4's you get pretty even distribution front to rear and when all 4 ~equal size barrels open it gets even better!

 

Best of all would be FI, but everyone has beat that horse....

 

BTW Chrysler Tri-Power setups on teh Trans-Am Cudas/Challegeres and the 440 six-packs were vacuum operated. A single 4 bbl got better mileage/power though (Ask Dick Landy who had a purple Challenger 440 6Pk convertible).

 

Brad

[Moridin]

A lot of the FI people will wire in secondary injectors. I'm guessing this is really only useful on a turbo. Does it work with the nitrous? They program them in to come on under WOT, throttle point, etc... I'm not an expert, so don't quote me on this. I know the rotary guys use this a lot too for the demands of fuel for a big turbo. Anyways, just a thought.

[Guest Ziggy Vulcan]

The only reason MPG is an issue is to save some money but I get the impression that the gains are not that noticeable. So I guess power is more prefered. It seems everyone likes FI better.

 

I know I'm gonna have a T56. The only thing with nitrous is I want to have a big shot and I want to make sure I can get it enough fuel. I'm assuming I can get an EFI system with sensors to compensate for this so that isn't really a problem.

 

Is there any difference between the FI that goes in the carb spot or the DFI with fuel rails? If I do FI then I think I want the fuel rails. Another thing I have to worry about is my Mr. Gasket street scoop. The biggest thing there is the butterflies hook to the throttle linkage. I have seen DFI setups that have the rails running down the the side of the manifold and a simulated chrome carb-like thing. That one looked the best to me. I think I can hook the scoop up to the fake carb. It was on the Jegs website, I think holley makes it.

 

Maybe I'm not getting something but, do carbs have to have different jets for different altitudes? If that's the case I'm sold on DFI.