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Discussion Starter #1
Hi

I’m currently rebuilding a ’96 LT-1 engine. I’m starting to consider the possibility of purchashing a GM carb conversion intake, install a conventional distributor/quadrajet carb, and doing away with the PCM/wiring harness. I will lose some fuel economy and response; however, there are some pluses including initial cost savings and confidence in my knowledge base with carbureted troubleshooting etc. All comments welcome…..Thanks, Jimmy
 

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Jimmy, I would say stay with the FI. If you buy or have a complete LT1, your costs will be negligible. The PCM is very tunable for different cams, heads, intakes, exhaust, etc. If you are worried about the Opti-spark, you can always install the LSX direct ignition. Personally, I wouldn't give up the computer controls. I do speak from some experience here as I have a 95 Z28 as my daily driver.

Barry
 

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I'd stay computer. MSDs distributor for the LT-1 will probably be good.

Can a conventional distributor be installed on a LT-1?
 

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Discussion Starter #5
Yes, a conventional distb can be installed, but only with a special intake manifold (APROX 270.00). I'd like to keep the LT-1 stock but a "stand alone" harness itself will cost about 750.00 (I'm installing engine in a '37 Stude pick up). It's gonna be a hard decision. That's why I'm asking for imput. Thanks, Jimmy
 

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A stock LT1 PCM is very compliant and easily re-writable with its flash memory. I would suggest getting a 94-95 PCM since its OBD1 and a bit easier to deal with, but steer clear of 92-93 boxes unless you're more comfortable with PROM chips.

An LT1's head ports are exact duplicates of vortecs, (actually its the other way around, but...) so converting an LT1 to a carb is just an expensive way to basically duplicate the operating parameters of a vortec 350. The EFI is the only real different part of an LT1... I know they're different engines, but pistons, rods, 1-piece rear cranks, bore spacing, etc are all the same or at least interchangeable, so aside from the obvious differences, they're the same where it counts as far as making power.

Keep the EFI.
 

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Jimmy,
I’m not saying this to contradict what others are saying but rather
give you another view. I am involved with a car that is running a
LT1 with a carburetor and a MSD ignition with a distributor. The
car runs great, really no problems at all with the conversion.
 

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Discussion Starter #8
Curtis73,

Do you know if the Vortec incorporates reverse flow water cooling? Also, I'm not as concerned with the PCM reprograming itself, as I am with the expense of a replacement "stand alone" harness needed for a complete swap. Jimmy
 

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No, Vortecs do not use reverse cooling. Many of them have serpentine belts meaning they have reverse rotation pumps, but they still pump the coolant in the same direction as traditional small blocks.

You don't need a standalone harness. Just get the harness with a PCM from the junkyard. Should be $100-150 if you search hard enough. Then use a wiring diagram to see which ones you need to keep and which ones are for things like headlights and windshield washers. The only real benefit to a standalone harness is that it comes with only what you need and instructions on what to do. If you have a wiring diagram and a stock harness its the same thing except you use your noggin to figure it out. The connectors are easy since they only fit their matching connector. Even if you have two connectors that are the same, the wire colors will match.

I've done a few LT1 and LS1 swaps that way with no troubles.
 

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GM Performance PArts p/n 24502592 is the carb intake for the GEN 2 engines you are talking about, the 350 LT1 V8 and the 4.3L L99 V8 Caprice engine.
This carb intake has longer runners and GMPP states the carb intake is worth 30 lb/ft MORE than the EFI LT1 intake with its 4" intake runners.

The LT4 carb intake manifold is GMPP p/n24502574. The intake ports are 1.100" higher than the LT1 intake ports.

BOTH of these intake manifolds are machined for use with a conventional distributer and have flanges for both a Q jet AND a Holley carb.
There are NO water holes whatsoever on either of these manifolds.

If you stay with teh injection you dont necessarily stay with the LT1 {CM. You could use a TPI ECM with the ECM controlled distributer and simply run the injectors in batch mode. The LT1's in 1992 and 1993 ran in batch mode along with being Speed Density, in 1994 the LT1's went MAFS and SFI.

It really depends on what you intend to install this engine into.

Tunercats makes various products to tune the Lt1 PCM's (both OBD1-1992-95 or OBD2 1996-97). The OBD2 stuff is now sold by Jet as teh JET Dynamic Spectrum Tuner (DST).
http://www.tunercat.com/

peace
Hog
 

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Discussion Starter #11
Hogg,

Your absolutely correct. To my knowledge the GM performance 24502592 is the only conversion intake manifold offered. Apparently when GM introduced Gen II many subtle differences were made in almost all components (mainly because of reverse flow) , that it makes conversion with anything other than direct model replacement parts a must. Although it might seem that retrofitting most GEN I internals would be a match, rebuilding a LT-1 by Mavrigian, and TPI/TBI Eng swapping by Knell, warn against it, with good reason. My question/problem doesn't concern the mechanical rebuilding aspect, as I plan on using correct LT-1 parts. My concern is exclusively with the wiring harness. My '96 LT-1 came out of a Caprice ("P" code), and if I were replacing the engine in a Caprice, I wouldn't have a problem. A rod swap is a different animal all together though. I need to wire it in a "closed loop" NON- emissions format (only 2 fwd O2 sensors, non- egr, air pump, purge canister etc. etc.). Simply stated, the cost of converting fuel inj vice carburation is pretty significant (not to mention the application headaches), and just wanted some feedback to help me decide.
Thanks a bunch for your input. Jimmy
 

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Other intake manifolds work

If you're proficient with a drill, you can modify most any sbc intake manifold to work on the lt1. I purchased Summit's stage II (similar to Edelbrock's Performer RPM) and modified it to work on my '95 lt1, and it was a lot less $ than buying GM's manifold.
1. match the lt1 intake manifold gasket to the replacement manifold and mark where you want to drill new bolt holes. The ports match, as do the far outside holes.
2. drill small pilot holes where marked. Note, the new holes are at aproximately 73 degrees to the heads--the generation I sbc manifolds bolt to the heads at 90 degrees. Once you drill the holes, match the new holes and angles by sitting the manifold on the engine--may take some filing, but worth the effort.
3. remove the distributor drive gear from the lifter valley before installing the replacement manifold so a conventional distributor can be installed.
4. the rest of the installation is pretty much the same as any manifold installation. One thing i don't normally do--not very professional, is i layed a bead of silicone around each port to ensure sealing since the manifold isn't designed for the lt1
5. you can remove and plug the optispark hole, but I simply disconnected all the wires and left it in place--didn't want to spill antifreeze all over removing the water pump to get to the optispark--maybe someday.
6. i used the stock harmonic balancer and indexed it and added a timing reference pointer. I set my initial timing at 15 degrees after priming the oil pump and installing the distributor.

Advantages of the conventional manifold/carb combination were immediately apparent--30 ft-lb torque for about $120 isn't a bad purchase; adjustable timing without using a laptop; and a lot less wires, connectors, and sensors! With the lt1's 10.5 to 1 compression and reverse cooling to stay ahead of head heat and related detonation, I'm really happy with conversion. In all honesty, I would have left the engine SFInjected if I could have worked out numerous bugs that come with buying a junkyard project...
 

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I am currently installing an LT1 in a 64 chevy SWB truck me and my son are doing as a Rat Rod. We want to keep to the traditional old school look of a carb so we are converting it over. I will be modifying a professional products intake to complete the process. If ppl are still interested in this topic I will try to document as much as I can with photos along the way. Also I will be dynoing the truck once i get it running. The LT1 is out of a friends Z28. Has ported heads and the Comp cams 290hr Xtreme cam in it. was 405 Bhp and the car ran 12:20's on radials. Will see if there are any real gains to carb vs efi.
 

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LT1 Rebuild...

Sounds like its going to be a great setup! Since putting mine together and installing in my '86 Blazer, I've been very happy with the performance (and its getting about 14-15 mpg Vs. the 8-10 I was getting with the previously installed 454). The nit-noys are a pain: Had to convert to electric fuel pump; electric cooling fans (assembly from mid '90s Vette); longer high pressure power-steering hose; and the most difficult, building a mount for the original Air Conditioning compressor. I tried both a Q-Jet and 600 CFM 4150 Holley. I already owned the Holley or would have gone with at least a 750. Anyway, I definitely like the 4150's manual secondaries--much more responsive. If you do the air conditioning, be ready to redrill the pulley since the LT1 harmonic balancer bolts are not symetrically placed--offset to ensure it only bolts up the correct way.
 

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I will be doing an Alternator only set up from Madman racing. It lowers the alt. next to the balancer and you run a little short belt. Loosing the weight and crank drag of the A.C., smog pump and P.S. is an instant 40 or so H.P. plus the truck doesnt have any of it in the first place. I have put the truck on a diet and today we rolled my rolling chassis and the rolling chassis of the 95 donor z28 across the scales. My truck is right at 500lbs lighter. If i can get it to hook on the street it should run pretty good for how little I have in it.
 

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Rannos said:
I will be doing an Alternator only set up from Madman racing. It lowers the alt. next to the balancer and you run a little short belt. Loosing the weight and crank drag of the A.C., smog pump and P.S. is an instant 40 or so H.P. plus the truck doesnt have any of it in the first place. I have put the truck on a diet and today we rolled my rolling chassis and the rolling chassis of the 95 donor z28 across the scales. My truck is right at 500lbs lighter. If i can get it to hook on the street it should run pretty good for how little I have in it.
Instead of hijacking this thread you can start your own in the hotrodders lounge.
 

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One More Engine Drag Reduction

Don't know if you previously mentioned it, but going with the electric water pump will also free up power if the alternator can be disabled so all electric load is fed strictly off the battery during speed/acceleration runs. That's not too difficult, but recommend a related multi-battery package be switched in that will give a system voltage of 14VDC when the alternator is isolated--at least to feed the ignition/computer/fuel injector systems.
 
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