Xephius's unnoffical LT1 conversion thread.

[Xephius]

Hey all,

So I am going to document my conversion from 4.3 to LT1 here. I hope that this will be able to remain for others who hope to try and do the same. Once I am complete, I will do a write up and post it on my website along with all the information I have gathered. So here it goes.

I found a LT1 motor for a great price, so rather than build up a 350, I figured it was worth the money to give it a try. I am going to break down the prices so others can get an idea of the costs involved.
The LT1 motor came out of a 95 Trans Am with a 4l60e. This was ideal, because I have a 4l60e in my van that was just rebuilt with vet servos and should be able to handle the power. Also makes it easy to control because I can use the stock LT1 computer. Also of note, the computer, wire harness and much of the main car harness was also included with the motor. I found that by using LT1Edit I can completely reprogram the computer to do anything I want. So I won't be using my Megasquirt on this project.
The motor was pulled about a year ago, with 90k miles on it. The car was rear-ended, and they pulled the entire front assembly out of the car. You can see by the photo, they just removed the transmission and gave me the rest. (Including a Demon torque converter with 93 miles on it)
As it turns out, the motor was not without problem. Cylinder number 7 was in a position that the valves were left open. So there is some bad pitting on the wall. Everything else in the motor is spotless. No grime, no sludge, everything clean as if it were new. And it is a virgin block. All original GM gaskets, no work has been done on the motor. So a single re-sleeve will be needed, but still a good deal.
Rather than going into to much detail about the plan, I will just run down the list of machine work I am going to have done, and the quoted prices for reference. If anyone sees something that I should avoid or is over-priced, let me know. All my questions are below. I hope that I can get some input from you guys...

Complete LT1 - $650
Elderbrock LT1 Headers - $250
Accell Opti-spark distributor - $250 (ebay)
Vette Cam/springs/roller rockers - $250 (buddy)
Moly Push Rods - $100
Thermostat - $20 (Autozone)
Waterpump - $150 (Autozone)
Fluid Balancer - $100 (ebay)
Gasket/bearing kit - $200 (includes oil pump from my Machinist)
A/C Drier - $30 (Autozone)
A/C Compressor - $225 (Autozone)
Power Steering pump - $55 (Autozone)
Radiator - $150 (Autozone)
Trans Am elect fans - $100 (ebay)
Intake parts - $150 (various filter/pipe/clamps)
Throttle Body - $250 (ebay, but later)
ARP Head studs <not bolts> - $150 installed (Machinist)
Stainless valves and bronze guides - $300 (Machinist)
Re-Sleeve #7 and cam bearings - $150 (Machinist)
Mounts and poly bushing - $100 (Jags that Run) <Will these work with a LT1?>

Yes, its a long list. My plan is to replace anything that could go wrong while I am in the motor. What I don't know, is how all the accessory's are going to work out. I suspect that I am going to have to adapt the LT1 accessories to my van, I hope someone can give me some advice here. Also, how to interface the existing gauges with the LT1 computer. Finally, how to attach the Asto linkage to the LT1 and hopefully keep the cruise control.
Pictures below, more to come. Any advice would be greatly appreciated.

-=John=-

[astrozam]

Cool John,we'll all be lookin forward to seeing this project evolve

[Hotroder383]

I will be watching this closely as i have an eye on a TA with the LT1 and 4l60e that I been thinking about putin in my van. I will be doing nothing to engine or trans just a straight swap, BUT i was wondering about how the comp will go in and how my digital dash will work with this swap.

[SafariRob]

I will be watching this closely as i have an eye on a TA with the LT1 and 4l60e that I been thinking about putin in my van. I will be doing nothing to engine or trans just a straight swap, BUT i was wondering about how the comp will go in and how my digital dash will work with this swap.

Hotrodder, what year is your van? Mine is an 89 with a digital dash and the lack of the ECM only affects torque converter clutch lockup. I got around that by use of a manual switch.

[Rebel]

I got around that by use of a manual switch.

Hey Rob,,tell me about that switch, will ya ? Never mind,,think I got it.

[SafariRob]

I got around that by use of a manual switch.

Hey Rob,,tell me about that switch, will ya ? Never mind,,think I got it.

Be glad to, Lar! Just let me find those schematic drawings...

[SoCalli V8]

Do you have smoglaws to abide by?

[Xephius]

Do you have smoglaws to abide by?

Define "have"...

Here in Texas we have to pass a sniff test on ODB1 or earlier vehicles. If the vehicle has ODB2 then a in car system check is preformed. They do not "inspect" the engine for smog parts, only to check to see if it passes the sniff test.

So the answer is, I only have to pass the sniff test. So I will be stripping off all the crap and give the motor a proper tuning using LT1Edit. I imagine I will get better efficiency and performance once I get it up and running.

I am still hoping to get some help from previous LT1 converts....

[mikedamech]

You can disconnect the Air Pump and block the passages as per the TSB. I am working on a 95 LT1 with iron heads now and found out the core plugs are brass and with 49,000 miles I am fighting the urge to install new ones. Nice find, I also have a few questions about wiring, dash, passkey, but I hope everything works OK for both of us.

[Xephius]

mikedamech,

I am not sure what you are referencing by "TSB", that is unless there is a Technical Service Bulletin that addresses this and I still don't know what you are talking about :O Can you link me?

Also, on the back of the motor, there is a water pipe that goes from head to head to throttle body. I plan to use the same kind of brass plugs used on the front of the heads to block both these holes. On the bottom of the throttle body, there is some kind of sensor, looks like a water temp sensor. If this is un-needed, I will remove all that crap to clean up the look. Then plug the return line on the water pump from the throttle body.

As for the AIR holes on the top of the exhaust manifold, I will plug those with brass or steel pipe plugs if I can find them. If not, I will weld up the stock AIR hose fitting, and screw them back in place. I have some aftermarket headers but they still have AIR fittings.

The EGR should be a easy fix, I am just going to put a plate over both holes and use the existing hardware to bold them down. Lots of unused vacuum holes to plug, and because we don't use vacuum brake booster, that hole can be plugged.

Moving on to other holes, I hope that the oil filler from the V6 will work on the V8 valve covers, and the oil dipstick is able to be adapted. I am planning on having custom lines made for the A/C and power steering to go from the LT1 pumps to the Astro lines. These are some of the things I was really wanting to get some feedback on from other LT1 converts.

Well, I am going home early today to rip out the dash and start on building a custom one. Pics on that soon...

[Mr_Roboto]

Also, on the back of the motor, there is a water pipe that goes from head to head to throttle body. I plan to use the same kind of brass plugs used on the front of the heads to block both these holes. On the bottom of the throttle body, there is some kind of sensor, looks like a water temp sensor. If this is un-needed, I will remove all that crap to clean up the look. Then plug the return line on the water pump from the throttle body.

Moving on to other holes, I hope that the oil filler from the V6 will work on the V8 valve covers, and the oil dipstick is able to be adapted. I am planning on having custom lines made for the A/C and power steering to go from the LT1 pumps to the Astro lines. These are some of the things I was really wanting to get some feedback on from other LT1 converts.

The "sensor" you speak of is the idle air controller. You need it. You can also do a remote mount one if you want, but it's $$$ with no real performance return. Basicly what it does is control the idle RPM of your engine, idleing it higher at lower temperatures.

You may want to check about the PS pump, I don't know if they changed styles on the LT1s or not but if it's the Saginaw "canned ham" style pump chances are it's got an 18mm Saginaw fitting for the high pressure line like all astros have and all other GM cars have since the early 80s. There was a ton of slack in the stock Astro line, I don't see why it would be too difficult to bend it for your application.

[Hotroder383]

I have a 93 GMC dig dsah 4L60E tranny, would like to keep the dash but it wouldnt break my heart to make one up with some aftermarket gauges. My BIGGEST worry isnt in the fitting or bolting but in the wireing, I have shoved v8's in many things but was always carbed. I have no smog laws, well laws start at 96 an up for snffer test. 95 an older nothin.

[mikedamech]

You can disconnect the Air Pump and block the passages as per the TSB. I am working on a 95 LT1 with iron heads now and found out the core plugs are brass and with 49,000 miles I am fighting the urge to install new ones. Nice find, I also have a few questions about wiring, dash, passkey, but I hope everything works OK for both of us.

The TSB # is 01-06-04-011, It states that this vehicle doesn't need the secondary air pump and can be disabled on this vehicle only. Pull the relay and plug the hole going to the air cleaner box.

[Xephius]

Hi all,

I am going to get my LT1 back early next week and am planning on getting it installed ASAP. Can anyone give me a primer on what to expect with the A/C, PS pump, and Alternator? Can I keep my Astro A/C Compressor? Will the accessories all remount? What should I do, I hope to drive the van 1000+ miles in 3 weeks so I need to get her together.

-=John=-

[HPbyStan]

Probably do-able but I'd drive the 1000 miles first and then do the swap,,,,,, just in case.. It always seems a surprise or two lurks in a swap like this.