replace 260hp 350cid with LT1???

[thundercat 9]

Hey guys,

I just got my hands on a LT1 350 vortec motor out of a 95 buick roadmaster stationwagon, is it a good motor to replace my 87 merc 350(260hp) with. Should I put a different cam in it to bring the powerband down to around 4500rpm or is it already there? I run an Alpha 1 outdrive. Has anyone ever did this swap? Would there be any unexpected downsides to the swap? Any info at all would be greatly appreciated.

As always, thanks in advance

Jeff

 

[180shabah]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

does the new engine have the "reverse flow" cooling?

 

[bandit86]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

bottom end probably not going to stand up to marine use

 

[Mkos1980]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

It wont work without significant modifications. The water pump is gear driven, as mentioned above "reverse cooling", and no distributor. Its not a vortec motor eather. The heads are similer to the vortec in design but thats it. Move on to something else.

 

[wca_tim]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

ditto on above. chance are you could buy a new / reman vortec longblock for the time and money you'll go through getting it to work right...

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

It is the "reverse flow" motor, allowing for higher compression because the water flows from the heads down. Why wouldn't the bottom end hold up? It is an LT1 with 260hp and 330 ft/lbsof torque.

LT1

GM LT1 from a 1993 Chevrolet Camaro Z28.In 1992, GM created a new-generation small-block engine called the LT1, recalling the 1970 LT-1 moniker. It displaced 5.7 liters and was a 2-valve pushrod design. The LT1 used a reverse-flow cooling system which cooled the cylinder heads first, maintaining lower cylinder temperatures and allowing the engine to run at a higher compression than its immediate predecessors.

This engine was used in:

Y-body:
1992-1996 Chevrolet Corvette C4
F-body:
1993-1997 Chevrolet Camaro Z28
1993-1997 Pontiac Firebird Formula and Trans Am
B-body:
1994-1996 Buick Roadmaster
1994-1996 Chevrolet Caprice
1994-1996 Chevrolet Caprice Police Package
1994-1996 Chevrolet Impala SS
1994-1996 Chevrolet Caprice Wagon
1994-1996 Buick Roadmaster Wagon
D-body:
1994-1996 Cadillac Fleetwood

In the early-'90s, GM introduced the Second-Generation LT1 small-block. It featured reverse-flow cooling and an aluminum cylinder head with a new port configuration. In essence, the company created the best small-block Chevy cylinder head ever put into mass production. It was released on top of the '92 LT1 Corvette engine and later on the '93 LT1 Camaro. The new port/chamber design that began life as an aluminum casting eventually carried over in a cast-iron version. Unfortunately, just as the LT1 concept began its ascension, GM executives decided to put an end to its production. This superstar cylinder head dropped off the performance map because both the aluminum and cast-iron heads lacked a coolant crossover passage, rendering them useless to any engine series other than the discontinued LT1.

The LT1 prospered from 1992 to 1996 in various vehicles, but its days were numbered. In 1997, GM released its Third-Generation small-block engine, the LS1. While the new Corvettes and Camaros were about to receive yet another cylinder head breakthrough, the engineers at GM's truck division knew that the LT1 port still had something to offer. Subsequently, the '96 truck engine series hit the market with the infamous LT1 port in cast-iron production. It was called the Vortec design and became the most efficient mass-produced small-block Chevy cylinder head ever created.

 

[Bondo]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

Ayuh,..... Then Go For It...

Just don't come back here Complaining that Nothing Fits,+ it Won't run Right....

The LT1s were never used in Boats,+ there's No marine parts to fit them.....

 

[mylesm260]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

I had a really good result putting a 1997 chev astro motor into my boat.

Just make sure you watch for fuel leaks, properly vent your engine area (with a blower motor) and replace your starter + alternator + distributer cap (or entire unit if need be) with the marine versions.

An oil cooler and sythetic oil will help your engine last aswell.

The gm marine and gm automotive 4.3's have the same internals and same cam shafts. And you will ALWAYS make more HP in a boat because of the exhaust scavenging effect of the exhaust leaving the prop.

The same motor that makes 200 HP in an AWD chev astro van makes 238 HP in a boat.


I know the LT-1 has the same rear bolt patter (bellhousing) as the 350, but I'm not sure about the exhaut manifold spacing.

you NEED to run marine exhaust manifolds, and I don't know if anyone makes an LT-1 marine manifold or not. I'm 99% sure the exhaust manifold port offset and bolt pattern is different between a 350 and an LT-1


My boat went from 160 HP 1985 4.3 that did 45 MPH to a 238 HP automotive 4.3 that does 62 MPH and gets much much better economy, and never stalls or stutters.

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

I plan on installing all the marine goodies from my original 350,if they will fit.There is a couple of things I have to change like the intake, I really don't want the headache of hooking a computer up to manage the fuel injection system, although I know it can be done by installing MIL eliminators and remapping the ecm. I just want to put my 4bbl back on. What type of distributor was on your 4.3? I would like to use my thunderbolt IV ignition but the system on the LT1 is located on the front of the block which probably means that I can't, unless I swap cams. The original cam in my LT1 has 191/196 duration and .418/.430" lift with 111 LSA , which is almost perfect for the torque curve I'm looking for(idle - 3000rpm with peak power at 5000rpm). Anyway, I'm still surfing this and other sites trying to dig up usefull info.

 

[tarheelebbtide]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

I don't know if I'd go through the trouble of trying to get it to work in a marine application, but I can say that in my experience, it's the best v8 that Detroit ever turned out. I keep my late grandmother's '94 Roadmaster Limited for sentimentality and it will still to this day blow just about anyone off the highway when you need it to and get 26-27 mpg floating that big boat down the highway.

 

[mylesm260]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

I just made a custom wiring harness for my chevy ECU.

Because chev uses MAF based mapping, no re-mapping is required. Only real issue was getting 75 PSI of fuel presure to the rail in a boat safely. I ended up using hydrolic hose and fittings for everything, because I know it will never leak.

And the factory cam was perfect for a boat, I make my peak HP at 4600, and with my prop that I have, my motor bogs down at about 4900 at 62 mph.

There's a crank angle sensor at the front of the motor, a cam angle sensor up top, air intake temp, coolant temp, MAF, map, TPS and that's about it. on the output side, you've got your idle control stepper motor, your ignition driver (then to coil) and your injectors. A soldering gun, some heat shrink tubing and some patience, and you can get it done no problem. I added a couple relays aswell, one for main power, one for shift interupt, and one for starting (my merc wiring couldn't handle the current of the new starter solinoid for some reason) too much voltage drop.


The GM ecu's are already really water-proof, I just mounted it up beside the motor. you can presure wash it and everything

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

Thanks for the input Myles. I have the whole car so I can rob anything off of the harness that I need. I just might have to utilize the injection system. I'll have to do a little more research to make sure that the exhaust port dimensions are the same for my 95 LT1 as they are for my 87 350 merc. I might PM you in the near future and pick your brain some more...

 

[mylesm260]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

FI is sooooooo much better than carbs!

I *love* the computer controlled idle vs my old carb

my boat hasn't stalled or needed to be re-started once since I installed the new motor. Nor have I had to make a sigle carb or tunning adjustment.

 

[Mkos1980]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

Ayuh,..... Then Go For It...

Just don't come back here Complaining that Nothing Fits,+ it Won't run Right....

The LT1s were never used in Boats,+ there's No marine parts to fit them.....

Ditto, but Indmar or PCM used an LT1 or LT4 in for one of their towboat motors.

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

doesn't that mouse look sweet....and it's nice to see the marine exhaust manifolds and riser bolted onto it...thanks for the pic..

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

If anyone plans on doing something similar, you can take the fuel injection intake off of the LT1 and install GM intake part # 24502592. This will alow you to run your marine carb and thunderbolt sytem. The only drawback with this intake is that it doesn't have a cavity for the mechanical choke on the carbs. Also, I'm currently trying to track down a headgasket that can be used for marine motors. Supposedly, the LT1 block already has brass frost plugs, when I find out for sure,I'll post my findings. One other thing, you might want to upgrade the valves to stainless, just a thought.
I'm sure I don't have to ask but if anyone else has something to add, please do so....good or bad..

 

[mylesm260]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

Rather than changing parts on your LT for marine (I'm refering to your head gasket, and asumeably your water pump) Go get yourself a heat-exchanger. That way you can run an automotive water pump, automotive frost plugs, head gaskets, etc etc.


There are lots of advantages to heat-exchangers.... mainly winterizing related. Never have to worry about a cracked engine block over the winter time if you've got a heat-exchanger because you can simply run 50/50 water/antifreze through your engine (what your LT1 was designed for)

 

[thundercat 9]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

That's not a bad Idea. I previously thought about installing a closed loop system, but since I aquired the LT1, that thought never crossed my mind. Have you ever mocked one up?

 

[Bondo]

Re: replace 260hp 350cid with 350 vortec???

Re: replace 260hp 350cid with 350 vortec???

mainly winterizing related. Never have to worry about a cracked engine block over the winter time if you've got a heat-exchanger because you can simply run 50/50 water/antifreze through your engine

Ayuh,....
Then it's Just the heat exchanger,+ manifolds that'll need Replacing when they Freeze...

I'm just wonderin',....
Why do you guys want to Reinvent the wheel,..??
When a 350 block,+ Stroker crank will push a Bigger boat,.. Faster,..??
Cheaper, Easier,+ Simpler,..... Remember KISS,..??

 

[mylesm260]

Re: replace 260hp 350cid with LT1???

Yup, I"m running one with my automotive vortec 4.3... it's pretty simple...


Just loop the coolant lines where your heater core would normally go, your two rad hoses go the exchanger. Your raw water goes from the exchanger to the manifolds and out with the exhauste.

I mounted my exchanger in my bilge in front my my crank pully (Well below and in front of)

And yes, you still have to drain your exchanger and manifolds, but it's less work than pooring anyfreeze into your engine every year.


Why do I re-event the wheel? it's in my nature. I hate carbs and like FI, tha'ts why how my boat project started.

My other project is a 3.5L interpid ES engine and transmision into a tube-framed dune buggy. Finished that about 2 years ago, and it's been a blast to drive ever since.

Past projects include a 450 HP datusun 260Z. I built, installed and tuned a "megasquirt" which is a DIY fuel injection system.