305 to 350 LT1
10-21-2008, 09:44 PM
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305 to 350 LT1
A friend of mine is giving me a complete LT1 out of a 1996 Cadillac Fleetwood. I have been told that the LT1's which came out of these Caddy's, are pushing far beyond 300hp. Is there any truth to this rumor ? Also, will I be able to keep my existing exhaust set up which consists of Edelbrock ceramic coated headers and a single 3" catback ?
Last edited by ERICSCHEVY; 10-22-2008 at 11:25 PM.
10-21-2008, 10:41 PM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
300 HP? Not stock, at least not net.
Exhaust? Yes. Sorta. See next observations.
In order to be emissions legal, you have to swap over everything related to the engine to your car. That means things like dual O2 sensors (see "Exhaust" comment above). Cat(s). Evap system. Everything.
You do realize that LT1 is Gen II, while the 305 is Gen I. significant differences between them.
See the LT1 swap sticky in the top section of this forum.
Exhaust? Yes. Sorta. See next observations.
In order to be emissions legal, you have to swap over everything related to the engine to your car. That means things like dual O2 sensors (see "Exhaust" comment above). Cat(s). Evap system. Everything.
You do realize that LT1 is Gen II, while the 305 is Gen I. significant differences between them.
See the LT1 swap sticky in the top section of this forum.
10-21-2008, 11:40 PM
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Car: 82 Camaro Z28
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Re: 305 to 350 LT1
300 HP? Not stock, at least not net.
Exhaust? Yes. Sorta. See next observations.
In order to be emissions legal, you have to swap over everything related to the engine to your car. That means things like dual O2 sensors (see "Exhaust" comment above). Cat(s). Evap system. Everything.
You do realize that LT1 is Gen II, while the 305 is Gen I. significant differences between them.
See the LT1 swap sticky in the top section of this forum.
Exhaust? Yes. Sorta. See next observations.
In order to be emissions legal, you have to swap over everything related to the engine to your car. That means things like dual O2 sensors (see "Exhaust" comment above). Cat(s). Evap system. Everything.
You do realize that LT1 is Gen II, while the 305 is Gen I. significant differences between them.
See the LT1 swap sticky in the top section of this forum.
http://caddyinfo.ipbhost.com/index.php?showtopic=13281
10-21-2008, 11:48 PM
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Re: 305 to 350 LT1
I (admittedly) don't know anything about a '1996 Cadillac Fleetwood' - but I suspect that you'll want to make sure that it's not a Northstar engine, rather than an LT1. (Heck, make sure that it's not a 4.3 LTx V-8 for that matter!)
The Northstars make decent power (from what I've heard), but AFAIK it's not one of the LTx family, & thus the swap info here on TGO may or may not be applicable. Also, there's significantly less aftermarket support.
Good luck.
The Northstars make decent power (from what I've heard), but AFAIK it's not one of the LTx family, & thus the swap info here on TGO may or may not be applicable. Also, there's significantly less aftermarket support.
Good luck.
10-21-2008, 11:51 PM
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Car: 82 Camaro Z28
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Re: 305 to 350 LT1
I (admittedly) don't know anything about a '1996 Cadillac Fleetwood' - but I suspect that you'll want to make sure that it's not a Northstar engine, rather than an LT1. (Heck, make sure that it's not a 4.3 LTx V-8 for that matter!)
The Northstars make decent power (from what I've heard), but AFAIK it's not one of the LTx family, & thus the swap info here on TGO may or may not be applicable. Also, there's significantly less aftermarket support.
Good luck.
The Northstars make decent power (from what I've heard), but AFAIK it's not one of the LTx family, & thus the swap info here on TGO may or may not be applicable. Also, there's significantly less aftermarket support.
Good luck.
10-22-2008, 12:25 AM
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Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
This is where I saw the quoted HP in the Caddy LT1:
http://caddyinfo.ipbhost.com/index.php?showtopic=13281
http://caddyinfo.ipbhost.com/index.php?showtopic=13281
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10-22-2008, 11:21 PM
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Re: 305 to 350 LT1
It also says that "as used in the 95/96 Cadillac Fleetwood. This is a head and cam package that claims and apparently delivers 370-390 rear-wheel hp (RWHP) for the LT1 350 cubic inch engine".
10-23-2008, 12:11 AM
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Right. Heads/cam/exhaust.
But, "out of the Caddy", they ain't "pushing far beyond 300 HP," like you said.
But, "out of the Caddy", they ain't "pushing far beyond 300 HP," like you said.
10-23-2008, 10:33 AM
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Car: 82 Camaro Z28
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Re: 305 to 350 LT1
LOL... Its not what "I" said, please do not quote me on those findings. As I "originally" stated, I am just trying to find out the facts before I proceed with this install, thanks. By the way, where exactly do I have to make the notch in my K-member and where do I relocate the motor mounts to ? Is there any measurements or pictures on where and ho to do this?
10-23-2008, 04:56 PM
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Re: 305 to 350 LT1
All the info you need is in here.
https://www.thirdgen.org/forums/ltx-...questions.html
https://www.thirdgen.org/forums/ltx-...questions.html
10-23-2008, 05:51 PM
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Car: 82 Berlinetta/57 Bel Air
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Anyway, the sticky has the information you're looking for.
10-25-2008, 09:09 PM
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Car: 82 Camaro Z28
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Re: 305 to 350 LT1
Well I finally got my LT1 at my house with all the trimmings. Question, should I keep and rebuild the factory LT1 Harness and use it on my car , or should I go with an aftermarket harness like Painless or something ?
10-27-2008, 11:55 PM
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10-28-2008, 12:01 AM
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Re: 305 to 350 LT1
Well, this is just my 2c worth, I suspect you'll get your fair share of opinions...
If the factory LT1 harness is in good shape, & you have pinouts/wiring diagrams available to you, then it would be a good deal cheaper for you to modify it yourself. The added bonus is that you'd be familiar with it if/when problems arise, & you'd be able to customize lengths so that you could route it however you'd like.
If you have more money than time (or just don't want to deal with it), then a pre-fabbed harness might be what you need. Advantages there are that they're supposed to be fully labeled, & a lot of the time you (theoretically anyway) can be up & running by hooking up just 3 or 4 wires. They're definitely not cheap though...
Good luck.
If the factory LT1 harness is in good shape, & you have pinouts/wiring diagrams available to you, then it would be a good deal cheaper for you to modify it yourself. The added bonus is that you'd be familiar with it if/when problems arise, & you'd be able to customize lengths so that you could route it however you'd like.
If you have more money than time (or just don't want to deal with it), then a pre-fabbed harness might be what you need. Advantages there are that they're supposed to be fully labeled, & a lot of the time you (theoretically anyway) can be up & running by hooking up just 3 or 4 wires. They're definitely not cheap though...
Good luck.
10-28-2008, 12:07 AM
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Car: 82 Camaro Z28
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Axle/Gears: 3:23
Re: 305 to 350 LT1
Well, this is just my 2c worth, I suspect you'll get your fair share of opinions...
If the factory LT1 harness is in good shape, & you have pinouts/wiring diagrams available to you, then it would be a good deal cheaper for you to modify it yourself. The added bonus is that you'd be familiar with it if/when problems arise, & you'd be able to customize lengths so that you could route it however you'd like.
If you have more money than time (or just don't want to deal with it), then a pre-fabbed harness might be what you need. Advantages there are that they're supposed to be fully labeled, & a lot of the time you (theoretically anyway) can be up & running by hooking up just 3 or 4 wires. They're definitely not cheap though...
Good luck.
If the factory LT1 harness is in good shape, & you have pinouts/wiring diagrams available to you, then it would be a good deal cheaper for you to modify it yourself. The added bonus is that you'd be familiar with it if/when problems arise, & you'd be able to customize lengths so that you could route it however you'd like.
If you have more money than time (or just don't want to deal with it), then a pre-fabbed harness might be what you need. Advantages there are that they're supposed to be fully labeled, & a lot of the time you (theoretically anyway) can be up & running by hooking up just 3 or 4 wires. They're definitely not cheap though...
Good luck.
10-28-2008, 12:10 AM
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Re: 305 to 350 LT1
I'm sorry, I don't know - if you haven't already checked the LT1 sticky post at the top of this forum, that's where I'd start... 
10-28-2008, 07:09 PM
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Re: 305 to 350 LT1
also give lt1swap.com a try. Lots of good stuff on there.
11-01-2008, 08:16 PM
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Re: 305 to 350 LT1
Just a little side note - that LT1 has cast iron heads. Lots of Corvette and F-body guys that use these motors change those for the factory aluminum heads.
DON'T do that... in stock form (I assume you wouldn't be porting any heads for this engine) the cast iron heads flow noticeable better than the aluminum heads do - around 20cfm almost all the way accross the board on the intake and exhaust ports.
Leave the cast iron heads on there, they will support more power than the aluminum heads will. The LT1 aluminum heads can't keep up without porting, and the LT4 heads are about equal with the iron heads, at least flow-wise.
That engine won't be making more than 260hp as it is, but with a set of headers, a less restrictive air intake, and a good exhaust system, you'd get pretty close to 300 crank HP. Put in a bigger cam too, like the Y/F-body LT1 cam or an LT4 cam, and you'd pass 300hp pretty easily.
DON'T do that... in stock form (I assume you wouldn't be porting any heads for this engine) the cast iron heads flow noticeable better than the aluminum heads do - around 20cfm almost all the way accross the board on the intake and exhaust ports.
Leave the cast iron heads on there, they will support more power than the aluminum heads will. The LT1 aluminum heads can't keep up without porting, and the LT4 heads are about equal with the iron heads, at least flow-wise.
That engine won't be making more than 260hp as it is, but with a set of headers, a less restrictive air intake, and a good exhaust system, you'd get pretty close to 300 crank HP. Put in a bigger cam too, like the Y/F-body LT1 cam or an LT4 cam, and you'd pass 300hp pretty easily.
Last edited by Air_Adam; 11-01-2008 at 08:19 PM.
11-01-2008, 08:20 PM
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Car: 82 Camaro Z28
Engine: 305 Crossfire
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Axle/Gears: 3:23
Re: 305 to 350 LT1
Just a little side note - that LT1 has cast iron heads. Lots of Corvette and F-body guys that use these motors change those for the factory aluminum heads.
DON'T do that... in stock form (I assume you wouldn't be porting any heads for this engine) the cast iron heads flow noticeable better than the aluminum heads do - around 20cfm almost all the way accross the board on the intake and exhaust ports.
Leave the cast iron heads on there, they will support more power than the aluminum heads will. The LT1 aluminum heads can't keep up without porting, and the LT4 heads are about equal with the iron heads, at least flow-wise.
DON'T do that... in stock form (I assume you wouldn't be porting any heads for this engine) the cast iron heads flow noticeable better than the aluminum heads do - around 20cfm almost all the way accross the board on the intake and exhaust ports.
Leave the cast iron heads on there, they will support more power than the aluminum heads will. The LT1 aluminum heads can't keep up without porting, and the LT4 heads are about equal with the iron heads, at least flow-wise.
11-01-2008, 08:35 PM
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Re: 305 to 350 LT1
Those iron LT1 heads flow quite well anyway, somewhat better than the L31 Vortec heads, and about the same as the Corvette LT4 heads. They have plenty of breathing capacity for a decent street/strip 383, and make for a very torquey engine. Just have the heads checked for straightness, cracks, etc when you build the engine, and have them rebuilt (new seals, springs, retainers, valves, etc) and you should be just fine. Have screw-in studs installed too, like the aluminum heads had.
Should have them check too, to see what kind of valve lift clearance those heads have. I know the aluminum LT1 heads can handle around .580" lift stock, but I don't know if thats true for the iron heads as well.
Those heads are better for a 383 anyway, compared to the aluminum LT1/LT4 heads, because they have larger 64cc chambers instead of the tiny 54cc chambers of the aluminum heads. Its easy to have compression get way too high with the aluminum heads with a stroker setup, so the 64cc heads would be good to keep. (longer stroke with the same style piston = higher compression ratio).
Your iron head LT1 was rated 9.5:1 CR with those heads, and the aluminum head motors were 10.4:1. With a 383 kit, you'd need pistons with a BIG dish to keep the CR under control with the aluminum heads. Not a problem with the bigger 64cc chambers your heads have.
11-01-2008, 08:50 PM
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Re: 305 to 350 LT1
No. Stroking an engine has nothing to do with the heads. Porting is done to increase airflow through the ports and chambers. But I wouldn't recommend trying it unless you know EXACTLY what you are getting into, because doing it incorrectly can make performance worse, rather than better. Its not about how much metal you can grind out, its all about knowing where to grind metal out.
Those iron LT1 heads flow quite well anyway, somewhat better than the L31 Vortec heads, and about the same as the Corvette LT4 heads. They have plenty of breathing capacity for a decent street/strip 383, and make for a very torquey engine. Just have the heads checked for straightness, cracks, etc when you build the engine, and have them rebuilt (new seals, springs, retainers, valves, etc) and you should be just fine. Have screw-in studs installed too, like the aluminum heads had.
Right on bro. Excellent info to keep in mind during my build up after the Holidays. I'll probably be on from time to time with questions here and there, but when the build up gets under way, I know I'll probably be spending many a nights on this website asking questions to knowledgeable members such as yourself...Thank you .
Should have them check too, to see what kind of valve lift clearance those heads have. I know the aluminum LT1 heads can handle around .580" lift stock, but I don't know if thats true for the iron heads as well.
Those heads are better for a 383 anyway, compared to the aluminum LT1/LT4 heads, because they have larger 64cc chambers instead of the tiny 54cc chambers of the aluminum heads. Its easy to have compression get way too high with the aluminum heads with a stroker setup, so the 64cc heads would be good to keep. (longer stroke with the same style piston = higher compression ratio).
Your iron head LT1 was rated 9.5:1 CR with those heads, and the aluminum head motors were 10.4:1. With a 383 kit, you'd need pistons with a BIG dish to keep the CR under control with the aluminum heads. Not a problem with the bigger 64cc chambers your heads have.
Those iron LT1 heads flow quite well anyway, somewhat better than the L31 Vortec heads, and about the same as the Corvette LT4 heads. They have plenty of breathing capacity for a decent street/strip 383, and make for a very torquey engine. Just have the heads checked for straightness, cracks, etc when you build the engine, and have them rebuilt (new seals, springs, retainers, valves, etc) and you should be just fine. Have screw-in studs installed too, like the aluminum heads had.
Right on bro. Excellent info to keep in mind during my build up after the Holidays. I'll probably be on from time to time with questions here and there, but when the build up gets under way, I know I'll probably be spending many a nights on this website asking questions to knowledgeable members such as yourself...Thank you .
Should have them check too, to see what kind of valve lift clearance those heads have. I know the aluminum LT1 heads can handle around .580" lift stock, but I don't know if thats true for the iron heads as well.
Those heads are better for a 383 anyway, compared to the aluminum LT1/LT4 heads, because they have larger 64cc chambers instead of the tiny 54cc chambers of the aluminum heads. Its easy to have compression get way too high with the aluminum heads with a stroker setup, so the 64cc heads would be good to keep. (longer stroke with the same style piston = higher compression ratio).
Your iron head LT1 was rated 9.5:1 CR with those heads, and the aluminum head motors were 10.4:1. With a 383 kit, you'd need pistons with a BIG dish to keep the CR under control with the aluminum heads. Not a problem with the bigger 64cc chambers your heads have.
11-08-2008, 07:20 PM
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Re: 305 to 350 LT1
I am having difficulties separating the Transmission from the Motor. As shown in the pic, it wants to come apart but just won't. Is there anything holding it or a technique to make this easier ?
11-08-2008, 09:57 PM
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