Hey everyone. I have a 67 with a 350 crate motor with a 700R transmission and 3.73 gears. It's mainly for street use and I'm looking for more power with decent gas mileage (everyone's dream right?)
I was originally looking to put in or build a 383 stroker with a carb, but my mechanic has been pushing the idea of swapping in an LS1. I know it would take a lot of fabrication, installing a fuel system, and getting a new tranny.
I'd like to know from you guys with more experience than me, what are the differences between going a 383 stroker with fuel injection vs swapping in an LS1. Besides the all aluminum motor what should I expect to see in mpg, power, torque, reliability etc between the 2 motors.
I've actually done this experiment for you. My now-sold '68 Camaro had a Holley Commander 950 EFI system on it, 11:1 383, backed up by a T56 (0.5 to 1 6th gear) and 4.11s. Best mileage ever, babying it on a freeway on a long trip was right about 18 MPG. More normally it was in the 16.5 to 17 MPG range. An important part of the mileage issue is how well the engine pulls at your cruising RPM (really low end torque perhaps?). My 383 was never really happy running at about 1,600 RPM at 60 MPH. If I put my foot in it in 6th gear, my first reaction was then to immediately downshift to 5th. In order to improve my fuel economy, I think I would have had to gear it even lower to up the cruising RPM, or put in a milder cam to detune it.
My current '68 Camaro has a LS376/480 LS3 in it (376 cubic inches), same transmission, same rear gears and reliably gets 23 to 24 MPG on the freeway. Running along at about 1,600 RPM, it is extremely smooth, and pulls away cleaning (and pretty strongly) in 6th.
The 383 was about 365hp to the rear wheels, the LS3 is 440hp to the rear wheels. The Camaro with the LS3 is the closest I've come in a street car to the passing ability of a motorcycle - it simply flies around traffic on two lane roads - another pretty good indicator of torque. The 383 didn't like local 20 to 25 MPH speeds, the LS3 is smooth at all speeds.
In short, there is no comparison between the two, with the LS3 winning on power, economy and smoothness.
What.is your knowledge level on tuning? A "tuner can come up with a base map and timing curve" Great. What is your comfort level in understanding that and being able to do that yourself someday instead of relying on somebody else? LS motors are cool, no doubt, but that 500 hp comes at a very high rpm that you won't be reaching on the street very often. The 383 will be making more torque down low where you want it and won't cost $6-7K to do it. Half of that will get the job done in all probability. What crate motor? Doe it have a roller cam? If it does, all you need is a stroker kit and some decent heads and you' re there. Need injection and get away from a "locked in" HEI? Put one of the self tuning fuel injection kits on it.
Here's where extreme ignorance rears its head.
First, when any EFI engine is tuned by a competent tuner, that's pretty much all that's needed - the one tune - unless you change something. In an LS motor, the ECU does some additional learning, but that's all done around the base tune.
When you install a aftermarket EFI system on a 383, the first thing you need to think about is tuning. Do you want to and can you tune it? If not, is there a local tuner who knows the system you're using who can tune it?
There are excellent tuners for LS engines everywhere, because there are probably hundreds of thousands of these motors that have been hot-rodded and need tunes. Not so much for aftermarket EFI systems installed on SBCs. For example, I couldn't find anyone in the greater Los Angeles area who knew the Commander 950 system.
Don't get me wrong, I tuned the car myself and got it running well and making good power but remember that best ever 18 MPG? I think with a really good tune, that could have been a touch better.
Similarly, the self tuning systems will get the car running well and making good power, but stop there. For liability reasons the "self-tuning" systems are going to err on the rich side. Running rich is the enemy of fuel economy.
Moreover, any EFI system is going to require fuel system upgrades - one of the major costs of the LS conversions.
The OP has gotten replies from two types of posters - the first is those who have done it, the second is one who has read a little. I leave it to you to decide which advice is most likely closest to reality.