Help with 400 build (or do I do an LS swap?) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

C.I.Blazer · 09-02-2019, 08:48 AM

Well it looks like the engine is bad on my new to me 71 Blazer. Although it came stock with a 350 and 4 speed manual, the truck currently has a 400 (511 casting) with a two barrel carb mated to a TH350. Trying to figure out what to do now. I am very new to this so please bear with me and excuse my ignorance.

My ultimate goal is to simply have a streetable, driveable vehicle. Only off pavement driving would be forest service roads and very mild trails. I do limited towing of a couple of jetskis and maybe a trailer of dirt or gravel every once in a while. I would prefer something that has some oomph to it just for fun. I want to keep the horsepower reasonable and not have to start upgrading all the other components of the truck (at least not yet). I would love it if I could keep running 87 octane but will get better gas if I need to.

Does something in the 300 HP range sound about right for this motor and this application? What is the best way to get this horsepower? I would like to start with the things that are easiest to do now with the motor out and maybe leave me some options for increases down the road that are easier to add. Not sure if that makes sense.

My plan is to start by sending everything to the machine ship to be cleaned and checked. I have read that the 400s (especially the 511 casting) are prone to cracking so they will magnaflux the block and see if I have a good foundation to start with. Assuming that is all good, how would you build this? I have read all about vortec heads, lift rods, cams, boring .030 over, etc. but have not idea how to build a complete package that works together and meets my needs. I also want to start pricing the parts out and get an idea of what this will take.

I love the idea of an LS swap and it sounds like that may be in the same price range. Especially if my block and crank are bad. I need to try and get a better handle on the cost of each. Actually, more importantly, I need to get a handle on the expertise needed for each.

Thanks for the help everyone. This is quite learning journey for me.

09-02-2019, 08:48 AM	#1
C.I.Blazer Registered User Join Date: Aug 2019 Location: WA State Posts: 186	Help with 400 build (or do I do an LS swap?) Well it looks like the engine is bad on my new to me 71 Blazer. Although it came stock with a 350 and 4 speed manual, the truck currently has a 400 (511 casting) with a two barrel carb mated to a TH350. Trying to figure out what to do now. I am very new to this so please bear with me and excuse my ignorance. My ultimate goal is to simply have a streetable, driveable vehicle. Only off pavement driving would be forest service roads and very mild trails. I do limited towing of a couple of jetskis and maybe a trailer of dirt or gravel every once in a while. I would prefer something that has some oomph to it just for fun. I want to keep the horsepower reasonable and not have to start upgrading all the other components of the truck (at least not yet). I would love it if I could keep running 87 octane but will get better gas if I need to. Does something in the 300 HP range sound about right for this motor and this application? What is the best way to get this horsepower? I would like to start with the things that are easiest to do now with the motor out and maybe leave me some options for increases down the road that are easier to add. Not sure if that makes sense. My plan is to start by sending everything to the machine ship to be cleaned and checked. I have read that the 400s (especially the 511 casting) are prone to cracking so they will magnaflux the block and see if I have a good foundation to start with. Assuming that is all good, how would you build this? I have read all about vortec heads, lift rods, cams, boring .030 over, etc. but have not idea how to build a complete package that works together and meets my needs. I also want to start pricing the parts out and get an idea of what this will take. I love the idea of an LS swap and it sounds like that may be in the same price range. Especially if my block and crank are bad. I need to try and get a better handle on the cost of each. Actually, more importantly, I need to get a handle on the expertise needed for each. Thanks for the help everyone. This is quite learning journey for me.



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.