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lt1 or 350 truck motor for 307 eng swap?

2K views 10 replies 7 participants last post by  9c1 Brougham 
#1 ·
im looking to swap in a little more power in place of the original 307 in my 89 fwb. i have a 350 out of a 90 2wd chevy pickup. i also have access to a lt1 motor and trans out of cop car. im not looking for crazy power. but more for the most adaptable installation.....

which would be the easiest?
 
#2 ·
The 90 350 will be the easiest (but not a walk in the park). You will need all the accessories/mounts, the transmission, the complete wiring harness, the computer, a set of motor mounts from a 90-92 5.7, and likely a driveshaft from the same car. Same for the LT1, but more wiring, and the crossmember will need to be notched for clearing the AC compressor.
 
#4 ·
The LT1 has more power & is better in some ways.
The 90 5.7 truck engine is a workhorse & easier to maintain.

Both engines would require a different transmission as the bell housings are different.

Common problems with the 5.7 when they were almost new was head gasket leaks, valve guide seals, oil leaks, & the blocks wern't as durable as older Chevy 350s. They were lightened & would crack in the valley area with overheating abuse. Might have had a piston slap noise issue, can't remember for sure. Replacement parts should be cheap, relaiable, & plentifull.

LT1 in 96 has OBD2 with more emmision control sensors that can cause nussance codes from the emmision system not meeting orignal specs. 95 & 94 were a bit simpler IMO but require outdated OBD1 testing equipment.

The worst problem with the LT1 is the distributer behind the water pump. It can be about a days job to fix a distributor problem. While the engine is out you can replace the ignition system & water pump. The photo distributor pickup is much less reliable probibly because of visual contamination then the maqnetic pickup coil used on earlier SBC.

The other problem is the LT1 had a limited production run and some parts are not compatible with any other SBC.
As Chevy came out with more modern engines it seems that the LT1 has faded in terms of performance aftermarket.
GM has completly forgotton about this engine. Not much for factory replacement parts.
Items such as replacement distributors are primarly sold by unreliable manufactures.
Other parts such as a distributor cap costs a primiumn for a brand name.

IDK if the LT1 computer may have a problem not having other modules / computers to communicate with.
Such as the VATS security / body computer it may not start. In 90 the C/K truck EMC was a stand alone. It has some connections on the trans though.

They might be harder to find now because they stopped making about 40 years ago but a Olds 350 would drop right in with the same trans, motor mounts, air cleaner, accessories.
Between what you have the Olds 307, a 350 Olds, 455 Olds, & every other size like the Olds 400, 403, & 425 they are almost identical. The BB Olds head deck is taller on the big blocks which required different accessories.
But you would also need to get rid of the 307 computer quadrajet that never worked well in the 1st place & disconect the ECM / SES light.
 
#5 ·
I put a 95 LT1 in a 91 Brougham and it was an extensive piece of work but with very rewarding results. With some slight upgrades to the engine and pcm it more than doubled the hp and torque of the factory 5 point slow that the car came with. Keep in mind that this swap was a fuel injected Chevy small block for a fuel injected Chevy small block so it was much more straight forward than what you're attempting. Also the transmission was a 4L60 being replaced with a 4L60E again very straight forward as they are dimensionally the same using the same mounting. The bulk of the work was electrical such as weaving the LT1 harness into the broughams factory harness to replace the ecm with the LT's pcm and installing the LT1's cluster in place of the broughams for actual gauges and a functional speedo while using the broughams existing idiot light locations. It was pretty slick once it was done but took a lot of hours.

Now to your situation. Nothing matches for a Chevy conversion. Your parts sourcing will be extensive and expensive. Transmission, driveshaft and crossmember will all have to be replaced unless you use a 2004R for a chevy which is a weak and trouble prone tranny but then just the trans has to be replaced. Starters are on opposite sides meaning you will have to source a new battery tray and move the evap container to the other side. Fuel lines, electrical, radiator and ac hoses will all have to be replaced. New engine mount frame brackets will have to be sourced, the list goes on and on.
If your insistent on swapping the engine do as LV Cady suggested and look to a small block Olds engine. A 350 or 403 will suit your needs and possibly double the power of the mooring anchor under your hood now with some easy and mild mods without the need for replacement of so much else. I wouldn't recommend an Olds 455 because even a weak 75-76 one will destroy that transmission in short order. The only strong enough transmissions for those engines are 3 speed turbo 400's which will lead to another whole expensive mess. If you already possess the 2 engines you mentioned sell them to source yourself an Olds engine and get to work.
 
#7 ·
I put a 95 LT1 in a 91 Brougham and it was an extensive piece of work but with very rewarding results. With some slight upgrades to the engine and pcm it more than doubled the hp and torque of the factory 5 point slow that the car came with. Keep in mind that this swap was a fuel injected Chevy small block for a fuel injected Chevy small block so it was much more straight forward than what you're attempting. Also the transmission was a 4L60 being replaced with a 4L60E again very straight forward as they are dimensionally the same using the same mounting. The bulk of the work was electrical such as weaving the LT1 harness into the broughams factory harness to replace the ecm with the LT's pcm and installing the LT1's cluster in place of the broughams for actual gauges and a functional speedo while using the broughams existing idiot light locations. It was pretty slick once it was done but took a lot of hours.

Now to your situation. Nothing matches for a Chevy conversion. Your parts sourcing will be extensive and expensive. Transmission, driveshaft and crossmember will all have to be replaced unless you use a 2004R for a chevy which is a weak and trouble prone tranny but then just the trans has to be replaced. Starters are on opposite sides meaning you will have to source a new battery tray and move the evap container to the other side. Fuel lines, electrical, radiator and ac hoses will all have to be replaced. New engine mount frame brackets will have to be sourced, the list goes on and on.
If your insistent on swapping the engine do as LV Cady suggested and look to a small block Olds engine. A 350 or 403 will suit your needs and possibly double the power of the mooring anchor under your hood now with some easy and mild mods without the need for replacement of so much else. I wouldn't recommend an Olds 455 because even a weak 75-76 one will destroy that transmission in short order. The only strong enough transmissions for those engines are 3 speed turbo 400's which will lead to another whole expensive mess. If you already possess the 2 engines you mentioned sell them to source yourself an Olds engine and get to work.
How about a few words on the performance and economy of the '92 once your work was completed? TIA.
 
#6 ·
Perhaps an LS swap would fix the Opti issue. Check out the LT1 LS forums, there are several. That might get you away from the Opti and give you better options. I'm not saying it will but it is a thought.
 
#9 ·
The Olds would be the simplest.
Still see a few in the yards.
Olds & SBC in the full size GM sections of salvage parts.
Just seen a 70' Tornado with probibly the orignal 455 in the salvage yard.

The TH200 was very weak. Can be built to handle.
But I think that the OP doesn't want to spend $2-3K on a suped up trans.

The LS would probibly be the most complicated & costly.
But the LS has more stock HP & potential.
 
#10 ·
I've seen mods done to LT1s like the LS update. $1K at least but you still use the Opti as a pickup sensor. Then there was a guy who machined his intake to install a distributor. Got rid of the Opti completely. Biggest issue is finding someone to program the computer to not monitor certain things and I was told a 95 one is more stable than a 96. I have both, might get the 95 one programmed and run it until I need an inspection then swap back temporarily. Lost of things you can do.
 
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