Hey. I bought my car a few months ago and the previous owner dropped in a zz1 350. this originally came with a carb intake mainfold, but he put the stock tpi from the 305 on top instead. now, i bumped into a zz1 intake manifold and it got me thinking about a carb conversion again. What type of power loss or increase would i see? also, what effect will it have in gas mileage? and also, i dont really know much about carbs in general, so like what size should i get, 650? mechanical or vaccum? is this a bad idea for a daily driver? i really dont know where to start, but for anyone that has done the conversion or knows about carb and tpi, please let me know anything i might need to. thanks a lot for the help guys.

 

What kind of mileage do you get with it now?

For reference, SDPC put a stock TPI on their nifty Vortec base on a 330 HO crate engine, and produced a very disappointing 275 or so HP. What they had to do to get a Vortec-headed 350 TPI to produce at least 330 HP borders on insanity.

So, a 355 HP engine being saddled with TPI is going to be an even bigger difference. A 650 carb on the crate intake is going to make a huge difference.

Mechanical secondary carb would be my choice, assuming the torque converter is loose enough to keep the engine out of bog-land. A 650 would probably be adequate, although a 750 would probably do better at the strip if all other support members are in place.

You'll also need a different distributor, and will need to provide some means of locking up the torque converter clutch.

Whether it is a bad idea for a daily driver depends upon what is more important to you - economy or performance.

 

well right now i get about 15 miles a gallon on premium. but i drive the car very light (most of the time ) would i have a torque loss though? what would be the big deifferences between the 650 and 750, and is there anything inbetween? how much am i looking at for distributor and how could i provide some means of locking up the torque converter clutch? you have been very helpful and i appreciate it.

 

anybody that can help?

 

a distributor could be gotten from nearly anything from 1974 up. Buddy scored one at a junkyard for about 30 dollars i think. I thought that was a bit of a rip off considering how readily available those things really are.

a properly tuned 750 will do just fine on a 350. A 750 would be more likely to bog than a 650, but it'll do better up top. You can just make sure that bog is tuned out, then you don't have to worry about the supposed bad side of the 750.

The torque convertor clutch lockup is pretty easy. I'm sure someone can offer up some wiring diagrams. I have done it, but i don't have anything in front of me. All you need is a toggle switch and the stock connector to the tranny. You just set the toggle switch on a ground...then, when you need to lock it up, you just flip the switch. You can do this with a vacuum switch as well so that, if and when you come to a stop but forget to turn off the lock up, the vacuum switch will have already ungrounded the system.

 

so what price range would i be lookin at for everything, and how much work?

 

Well...

you need an intake. i've got that ZZ1 intake that i'd like to get about 75 dollars for.

Carb...depends on what you'd like to go with here...and if you are buying my intake, i happen to have two carbs as well .

Personally, i prefer holley's. however, they do sacrifice a bit of fuel economy for the little bit extra power they can give.

I have a nice 750 cfm Holley vacuum secondaries carb that has a metering block in it so you can adjust the jets in the back. A lot of them just have a plate and aren't adjustable. I'd like to get $150 dollars for this.

I also have a brand new in box edelbrock 750 manual choke carb. I've never run it, but it was bolted to an engine on a stand for mock up purposes. I bought it from a friend who didn't need it. I'd like to get $175 dor this.

You'll need the distributor of course. You could get one at a junkyard for under 35 dollars. A new cap and rotor and you'd be all set.

One thing i had forgotten to mention, i assume you plan to continue running the TPI fuel pump but use it to feed the carb. To do it properly, you should use a bypass style fuel pressure regulator. These aren't cheap. I'm running an aeromotive unit which is 150 dollars plus the ridiculous price of AN fittings. This is a more expensive one however, there's an aeromotive 3 port bypass style reg for about 100 dollars.
You could, however, use a cheap $25 holley regulator. I've used one of these in the past on a TPI pump and it worked ok. it basically acts as a Y, you have to restrict the return line a bit to allow it to build the right amount of pressure to the carb, otherwise it all just goes back into the tank. I have one of these lying around too... I'd like to see $10 for it.

INTAKE 75 dollars
CARB 175 dollars
DISTRIBUTOR 50 dollars (after new cap and rotor)
FUEL REGULATOR 10 dollars for the cheap way, 100 for the proper way

That should be it. An intake gasket of course, but that's just 12 dollars or so. With that gasket, that's about 325 to do it with a cheap regulator. I ran for two seasons on a cheap holley regulator with a restriction in the tank return. it works just fine. I upgraded my regulator when i went with a Walboro 340 force induction pump as I'm willing to spend the extra 125 dollars on a better regulator when i'm dealing with boost.

The work itself, that's really pretty easy. You could go from TPI to Carb in an afternoon...the other way is certainly not that easy though lol.


as an aside. I have a ZZ1 in my car. Or rather, i had one. I've changed heads, cam and intake now.

If you use aol or msn, feel free to hit me up
aol: nousablenames
msn: pinnaclepartsdepot@hotmail.com

 

how would you compare the power gains and feul economy losses to that of an lt1, because i have found a modified lt1 as well for just a little more than this whole setup, but its all together and it might be easier.

 

As long as there is a proper chip tune, a LT1 setup shouldn't lag behind a carb intake at all in terms of power. They're decent intakes. It would likely get better fuel economy too.

However, keep in mind you need to tune the fuel injection to take advantage of new found power from that intake as compared to the TPI intake. Without a good custom chip, you would certianly be better off with a carburetor since you can tune that yourself, without any extraneous equipment. I'm not talking about a hyperchips chip or soemthing...you need a chip that is especially tuned for your car. Getting someone to do it for you isn't cheap and the learning curve is fairly steep. i'm just learning this fuel injection tuning myself.

My other concern with the LT1 intake is the disorganized look of all the hoses and the remote T stat. Its just not a clean look because you're adding even more hoses to the engine bay.

 

yea, i knew that tuning was going to come into the picture with that. plus the guy wants 500 for the setup, which isnt bad, but carb is cheaper. anyhow, i drive my car everyday, so which setup do you think would be better to go with in terms of the carbs? what are the advantages of vaccum secondaries, and what are the disadvantages of having a manual chocke instead of electronic. i am selling one of my guitars on ebay right now and at the looks of things it should sell for around 700 all of which i can use. i just really dont know anything about the carbs. thanks a lot for all the help you have provided.

 

Well...
Vacuum secondaries can save you a little on gas. All edelbrock carbs and Q jets are vacuum secondaries. Some holley's, the Double pumpers, have mechanical secondaries. For all out drag strip performance, you'd want mechanical secondaries. On the street, Vac secondaries don't give up too much, there's just a slightly longer transition to WOT....but they can save you a bit in terms of gas. Vacuum secondaries open as the engine needs them, whereas mechanical secondaries open based on where your foot is in the throttle and tells the engine it better take that air. They use an extra shot of fuel to keep it from bogging.

Personally, i run a proform built holley Double pumper. There's no choke at all on this sucker, but my car is only driven in teh summer.

A manual choke means you would have to run a choke cable into your cabin and pull it out, like a lawn mower. It's pretty simple really. I had one on a Jeep.

The edelbrock carb i have would need you to run a cable, or buy the conversion kit to make it electric (about 40 bucks). The holley carb i have already has an electric choke, you just need to give it a power lead.


Since i like holleys, i'd say you should go with the vac secondary holley i have. Its a 750 dual feed carb. I ran that carb with the zz1 intake and had lots of fun with it. I've only changed carbs and intakes because i'm in the middle of a twin trubo project and boost likes single plain intakes and doesn't like choke towers.

If you have the money, i'd buy the aeromotive bypass style regulator. if not, the cheap used holley one will work, but it's not going to be optimal. You may have the occasional pressure surge or drop.

 

i should have money by the end of the week (my guitar is ony ebay for about 800). are the prices you mentioned shipped? I would give you 225 shipped for the manifold, carb, and cheap regulator if you want. let me know.

 

If you could do 235, that would offset the shipping a bit better.

Thanks,
Jay

 

OK. So lets make an official list of parts I would need.
1. Intake manifold
2. Carb
3. Distributor
4. New cap and rotor
5. Regulator
6. How many gaskets?
7. Toggle switch for lockup
8. Air cleaner
Is that all?
Also what exactly is bogging, and why would it be bad?

 

Intake, carb mount, air cleaner mount gaskets.

You'll also need fuel line, throttle cables, probably upper radiator hose, thermostat housing, heater hose.

"Bog" is a lean condition when the secondaries open. Fuel hasn't been flowing through the secondary metering circuit, and when the secondary throttle blades open up, you'll get immediate air flow but it takes a moment for the fuel to get sucked through the secondary circuit. So, you either have to gradually open the secondary throttle blades, gradually allow air to flow through the secondaries, or provide a shot of gas to the secondary air flow when the accelerator is stabbed to WOT.

 

so is bogging a bad thing, or just undesirable? and can it be eliminated easily?

ok, so I need all those parts if I am converting from tpi?

how much do you think all the parts will cost me minus the manifold and carb?

 

and so, i dont need a feul pump? did you mean the same thing as radiator fluid neck? did you mean throttle cables, or throttle cable bracket? throttle studs? quick change secondary kit and springs? jet assortment? carb studs and intake manifold bolts? vaccum caps? return springs and bracket?

I was just reading this form the technical articles section.

http://5finger.8m.com/tpi2carb/tpi2carb.html

maybe some of these are included on the carb...or you forgot about them?

 

i can include the quick change secondary kit and springs. teh carb will have the vacuum ports you don't need capped properly.

 

im almost definantly buying your parts. i just want to make sure i know absolutely everything I need and what I need to do before I do anything.

thanks for being so helpful with this.

 

AHH! Im going nuts. I got this and an lt1 conversion Im looking at. sway me one way or the other. the entire lt1 conversion minus a chip and the tstat housing will be around 450. do you think it will be more worth it to do that in the long run. it seems like it will be much easier and with much less parts than this would take. i didnt realize how many little things needed to be added and replaced. what should i do?

 

Raced a ZZZ 350 for almost 10 years. Great little engine. Use a RPM Performer airgap manifold with a 750 holley mechanical secondary carb, great combo with the .480/235 dur@.050 cam makes good streetable power and will run solid 12 sec times with a 5 speed and 3.73 gears. mine made 343 hp at the wheels.

 

they're rated at 345 at the crank though...

and i'm not belittling your engine...i've got one. Least it was before I got better heads, cam and intake on it.

 

the swap to carb is really not tough at all plus we are all here to guide you through.

on the other hand, yeah the swap to an LT1 intake would be easier install wise. I still don't like how messy it looks with the remote T stat. Don't forget you need to have it tuned properly on top of everything else. If you can't do it yourself, that's for sure another 150 dollars min.

I used to be all about fuel injection... I'm not so sure anymore. I've had it pretty good with carbs as of late.

 

so i would need to do the chip and the tuning? or is the chip the tuning you were talking about. im having a really hard time deciding.

 

yeah the chip is the tuning

but don't think you can just buy some chip off the shelf. You have to get it made for your car specifically or you're not going to get the same gains as just swapping to a carb would get you.

 

so you think there is more power available with a 750 than an lt1? plus what would be the difference in price and difference in gas mileage?

 

There's really only going to be a difference between teh systems if you don't get the LT1 tuned

If you tune the EFI, its going to get better gas mileage than the carb and it'll be just as nice at WOT...i doubt it will leave more than a couple hp on the table as compared to what the carb will give you.

 

but then i have the ability to get it tuned (custom chip, right?) and make even more than that? plus get better gas mileage. but it will cost me a couple hundred more in the long run. but it will be an easier swap. so many factors!!!

 

no no

If you don't tune the LT1 intake from the get go, it will be no where near where a carb will be.

Once its tuned, ie, once you spend the 150-200 bucks on a dyno tune for the LT1 intake, it will perform like the carb.

 

so basically after tuning the complete lt1 conversion would cost around 700. how much would the complete carb conversion cost...maybe 400?

 

yyyea....
my transmission blew out today. doesnt look like ill be getting this stuff anytime soon. man i was all saved up for the swap and now i need a tranny?! wat the hell. at least its a good excuse (especially to my parents) to swap the manual in. sigh.

 

Yeah, go for the manual tranny and find the next weakest link.

I don't go for this "vacuum secondaries get better gas mileage" stuff. If you don't open the secondaries, it isn't going to make a difference. In fact, a vacuum secondary carb will open the secondaries when the primary flow allows it, while a mechanical secondary carb will only open the secondaries when you put enough foot into it to do so. It's an unsubstantiated argument. And, if you go with a manual tranny, vacuum secondary would not be the best choice.

You still haven't said what's more important to you, power or economy. It matters, since the only way to have both is to spend a lot more money (which kind of detracts from the economy part, doesn't it?). The TPI will be the best choice for economy, since you don't have to spend any money to get the economy it has now (15 MPG does seem a little low, though - I get 16 MPG with my CC carb commuting, 20+ highway). The modified LT1 will probably not do as well on economy as the TPI, although it will do better on power. The carb will produce the best power for the least up-front money, but will be poor on economy if you don't keep your foot out of it.