Since I am thinking about buying a 04 GTO, my 95 T/A will become a race car only. I would then like switch over to a carburetor because it would be cheaper. Using the GM Performance Parts Carbureted LT1 Intake Manifold, what problems would I run into?? I have already planned for the obvious like a electric fuel pump for a carb, and the small things, but what about my tranny and computer functions?? Any input or help is appreciated.

Thanks, Nick

 

Generation and engine specific tech questions should be posted on the appropriate "tech" forum. Moving to "LT1 Tech".

 

Not a whole lot I guess except cutting up the cowl to fit the carb. I believe it will still run off of the optispark so you will still need the computer anyway to control the tranny if you have auto, and to comprehend the opti signals.

One question though, how do you figure its cheaper to go carb? You will spend close to 1000 on a goood carb, and 200 on the intake, for that amount of money you get the only things that make FI more expensive (injectors and tuning) other than that the car will be identical unless you go to a whole new ignition system which requires putting a old type distributor under the cowl. Plus you arent figuring in the fact that FI is much more efficient and powerful, or else they wouldve never invented it. I remember on HP TV once they put a Accell EFI on a chevell wagon or whatever it was, didnt change anything but that and say 60hp at the wheels from a good carb too!!

If you think about it in the fact that injectors and dynotunes are really the only things that make FI more expensive, it really isnt that bad. If you buy 40+lb injectors for $350 that will do for whatever you throw at them, a 58mm TB for $309, and a good dynotune for $400, you are at about the cost of converting, plus it fits under the hood and is more powerful, oh forgot about the hood, you wont fit a carb under a stock hood either.

Just sayin before you do it think about it somemore, not tryin to change your mind!

 

No problem, I understand where you are coming from. But for me it would be cheaper to go to a carb setup, then to get DFI, tuning, injectors, and a fuel pump to run a good race setup on a FI engine. I already have a 4" Ram Air Hood, and the only other things to consider are what will and won't work. I am also a mechanic so the labor is free too. Plus I need a carb box to run my procharger and I could sell my old parts for some $$$. I am really looking for information and help on the process of converting.

Thanks, Nick

 

Ok thats cool, I just always question people that are thinking of converting, whether they know what they are getting into and whether its worth it, but you seem to know whats up and made your mind.

On the conversion subject again, with the GM manifold there shouldnt be much of anything else, it should still run off the opti and you probly already have an MSD or something. The computer will still run the A4. The only thing that gets weird is the MAF, MAP, TPS, IAC. I would guess those could all be programmed out by someone that knows what they are doing.

I think this thread couldve very well stayed in Advanced, but its here, hope you find out what you need. Sorry I cant give you forsure answers.

 

I have a question for you. Why do you think you need to run DFI if you stayed FI? Running the stock pcm with a tune will work well too. Also, someone correct me if I'm wrong, but can't you run higher levels of boost in a FI application with less chance of going lean and burning up opposed to a carb setup?

 

You aren't gonna make power worth a damn with that cheesy GM intake. You will go down in power.

If you want carb, put a Gen1 smallblock in there.... good Edelbrock intake, low profile aftermarket distributor.... build a faster motor for less money. Converting a Gen2 LT1 is not gonna save you a dime, and it wastes a great fuel injected motor that someone could use for a project car (notice how popular FUEL INJECTED LT1's are in hotrod projects?)

Keep in mind, you can't pass inspection with a carb in a 1995 model... Even if you don't have smog where you live now, they will eventually. Just decide if you really want to make your car so that it can never be used on the street again...

-Michael

 

I'm not sure you are going to get the Opti plus stock PCM to supply the ignition needs of a carb'd setup. The PCM needs MAP to use the timing tables. Hooking up a MAP sensor is not that hard, just tap into a full-port vacuum connection on the intake, and keep the connecting line short. Then there is the elusive 3deg of timing advance that seems to be tied into IAT, so you need to keep an IAT sensor. No problem.

But.... and the big "but" here... I don't think the PCM is going to provide usable timing info with the codes for "no injectors", "no MAF", "no TPS".... maybe you could throw a 15ohm resistor into the injector harness plugs. And you would be missing a MAF signal, unless you used a 93 ECM - probably not a bad idea, or simply program the 94+ PCM to run speed-density. And you might need to attach a TPS sensor to the carb linkage.

Then the PCM will be trying to adjust the idle, but there won't be an IAC valve.... again, something you could add in the form of a bypass around the carb.

Doubt you will have O2 sensors, so you will have to program for full-time open loop.... which doesn't realy matter since you aren't controlling fuel with the PCM... but the point here is that the stock PCM may have some defaults impacts on ignition timing when all these codes start to appear..... may just go into "limp" mode and pull all the advance.

So..... a conventional distributor becomes necessary.... squeeze it under the cowl (goodbye windshield wipers - but its a track car").

You can see where a better solution might be to just get a Gen 1 SBC block, and set it up with a belt driven/front mount distributor like the one MSD makes. That would be an infinitely less expensive solution, since with the SBC you will have a huge selection of high flowing heads, intakes, and other performance parts.... things that will cost 1/2 of what the equivalent part for a Gen 2/LT1 part will cost.

You will also need a new fuel system. The carb needs 7psi, not the 45psi you get out of an EFI fuel system.

 

HEy guys I am running that cheesy GM lt1 intake that the one guy was talking about and my car runs 11.4 with stock ported lt1 heads. So no the intake isn't all that bad. And I have went 10.7 on a little juice. And who pays 1,000 for a carb anyway. I have a 750 speed demon and it cost 389.00 new off ebay and it is plenty good enough for most any small block combo. When you talk about cost you can pick up one of these lt1 blocks of ebay for 100.00. Then Buy a set of stock heads for 200.00 to 300.00 dolars. Port the heads yourself. Spend the same money on the bottom end that you would anyway. Through in a 249.00 intake from gm and 400.00 carb any run 11's. Those carb aren't so bad. I do wish that someone made a direct fit single plane and am sure you could pick up some with one. And guys I am noway putting down the EFI thing. I know that they run great too. They just seem to cost a little more to make work and for some of us it is just more simple to run a carb .And for those guys that ask why not build a first gen small block with a carb I say that the lt1 and lt4 heads are just better bang for the buck. Look at afr lt4 heads there 220 head flows 296 at .700 lift. Pretty good but there is alot of brodix and dart heads that will flow that on the intake side. But look at the exhaust flows. The lt4 afr flows 230 at .700 and like 210 at .400 . Most dart and brodix heads will only flow like 195 to 205 on ther exhaust. So to me there is alot to be said about the lt1 lt4 heads that make them worth wild to build no matter if you use a carb or fuel injection. Hell lets all take are lt1 fuel injected and carb cars and go beat up on some mustangs

 

Thanks Injuneer, I am looking into some of those computer issues. I have seen TPI Thirdgens go to a carb setup and use their computer with modifications, of course. My brother has TunerCat and I will see what can be done with that but it might not be enough.

Hey Jonesy91z28, how is your setup hooked up?? Do you have any input for me??

Thanks, Nick

 

Okay First my lt1 is in a 91 z28 so I cant really help with any clearance problems but I can tell you a little about my set up. The motor is a 383 with eagle crank rods and srp pistons. The intake is the gm and it bolts right up. I am running msd pro billet dist and 6al box with blaster coil and msd adjustable timming control. When I done away with the lt1 front dist I just made a plug out of aluminum and had it inserted into the the hole in the timming cover. I then bought a aftermarket timming pointer moddifed it for my harmonic damper so I could have a timming mark. I tried running the stock fuel pump in the tank with a regulator but at 7psi it would not keep up with the carb. The bowls were running dry on the big end.So I had to install a holley rail fuel pump and ran a 1/2 line up to the front. I am using a lt4 timming set and comp 306 cam. I am running a mega rapotor 700r trans so I have no computer issues when it comes to the trans. BUt they do make a stand alone system for the 4le60 thats does away with the factory comp and makes it manual shift so that might make the carb switch a little more easy for you. AS far as that I didn't run into any real promblems going to a carb on the lt1. Oh ye I did have to block off some of the lines on the water pump that runs back to the throttle body but no big deal.

 

Im glad I ran into this post. Im currently taking my LT1 out of my 96 Z for a rebuild and was strongly considering using gms cheesy intake for a carb set up. In my case, I was just planning on junking all of the factory wiring/comp stuff thinking this would make things easier. But im seeing you guys talking about using the factory pcm and opti. How exactly would that work??

My plan was to use a old school, or regular dist., with a crab style cap, and run a crank trigger. All msd stuff straight out of summit. The main problem with that of course is that if for any reason you need to take out the dist., well, you cant without pulling the motor loose. Other than that one prob, I figured it would be much easier to go that way than try and keep the factory pcm and wiring. And what about the hole for the dist. on the gm intake?? What do you do about that if you plan on running the factory opti/wiring??

After taking in everything cost wise, Id dont think Id be saving a whole lot in my current situation, so Im thinking I might just stay with the efi. My main reasoning for considering switching to carb was tuning/programming down the road and being somewhat "limited" if you wil, by the pcm. I talked to a guy locally that owns a shop and does tuning about a stand alone system for down the road. They start at about 1,5k and then theres the descent labtop, prolly another 1k at least. Then he tells me you have to be pretty talented to even use the darn thing. Not to mention have patient galor.

So down the road if or when I decide to get REALLY serious, when time, money, and space arent a problem, I will prolly end up switching to a carb'd set up of some sort. But for now I will probably continue with my plans, and have the pcm sent off to pcmforless to be programmed.


Thanks for any info or reply, Jon

 

Here you go guys....I found this on ebay. Its LT1 converted to carb setup, never run.

http://cgi.ebay.com/ebaymotors/ws/eB...tem=2451269586


The pistons/cam and such are not the best, but its a good setup for the most part for what you want. Its worth a look.