Time for an Engine build

[Handy Andy]

Ok fellas, it's time to start doing some work on the 86 gmc sierra 1/2 ton. I've spent countless nights doing research on LS/vortec swaps, 400 sbc builds, and 383 stroker builds.

My end goal is lower rpm torque. This truck is my hunting/putting around truck and I would love to be able to use it for pulling my boat back and forth to the lake(18' glass boat with a 200 yamaha on it so it's not the lightest boat ever made). I would love to be able to just throw on the cruise and go. Some more fuel economy would be nice, but I'm not 100% convinced I want to take on the task of an LS/Vortec swap. I don't really have the space to work on the truck and have it be out of commission for an extended period of time for now.

I was looking at rebuilding a 400 sbc and dropping it in there. I found one used that supposedly started and ran very well when it was pulled from the truck it was in for $350/obo. BUT, my dad has a disassembled 350 that has supposedly been all machined with camel hump heads just sitting in the shed screaming to be built. He's pushing me to build a 383 stroker. I did some wrenching as a kid, and i do most all of my own mechanic work now (except on my new truck as it has warranty). I'm not too worried about the build part, my dad knows a ton about engines, transmissions and everything automobile related. My question is, with the goal of lower end torque, and somewhat decent fuel mileage, which would you choose? 400? or 383 stroker? I believe the truck has a 700r4 transmission in it. not sure about the rear end, I'll have to get under and look.

Also, I'm looking to stay under around $1700 including machine work for this build. There shouldn't be much for machine work because my dad said it's all been done. I know I know if you want good results you gotta spend money. I'm not looking to make this into a drag truck.

Thanks in advance!

 

[CSFJ]

Hard to beat the ls swaps for power and fuel economy, but to stay in your budget, I think you'll have to stay old school. The trick will be not to kill the 700r. Seems like the last time I looked, you could pretty much order up a rotating assembly from summit or the like for a 383, that was just about drop in. Been a while since I checked though. The only thing to watch out for on a 400, is it's been overbored, how far they went. If I remember correctly the siamesed (sp?) cylinders don't play well above .040? Or was it .060? Anyway plenty of power to be had from a 383, which if you already have a block and heads, is probably the way I'd go.

 

[Handy Andy]

Yea so after doing some investigating, the block and heads that dad had were out of the question. So, I'm going to pick up a bone stock, never been modified 400 SBC that supposedly still runs for $300 tomorrow. Gonna get it to my folks' place and tear it down to see how it looks, If the lower end looks good and usable still, I'll put a better cam, aluminum heads, a decent intake, a new carb on it, and some decent headers on it and see if she does what i want it to do.

 

[Handy Andy]

Ok, so I'm trying to wrap my head around compression ratios, and combustion chamber sizes etc..... Let me ask this, What is an acceptable Compression ratio when wanting to run say 87 or 89 octane fuel? I have done a tone of research over the last week and can't seem to find a general conclusion. From what I've seen anything around 10 is ok, but closer to 9 is more desirable with a DCR of 7.5-8.5. Does this sound right to you guys?

 

[yevgenievich]

9 - 10 sounds correct. Depends if heads are aluminium, size of a cam and ability to tune. 9.5 to 1 would br a safe level.

 

[87scotty]

Yea just stay under 10-1 87 isnt always 87 at the pump better to be safe than sorry

 

[Handy Andy]

Sounds good, thanks guys. The heads I'm looking at are Dart aluminum heads, and the pistons will be speed pro dished 12.5cc so it looks like my SCR will be around 9.44. With the cams I'm going back n forth between i should have a DCR between 7.9 and 8.3 using the stock 5.565 rods. Hopefully this works well. Now for machine work to get done!

 

[rich weyand]

Pay attention to LTZ C20's build in this thread on another forum.

http://forum.73-87chevytrucks.com/smforum/index.php?topic=28581.0

 

[Handy Andy]

Thanks Rich, I did some reading in that thread and it looks like he is doing some stuff the same as me. The heads he's using are 64cc combustion chambers versus the 72's i'll be using. I'm not 100% sure If I entered everything in properly, but when I checked it out on camquest my build looks like I will be around 375hp at 4500 rpm and approximately 480-525 lb-ft at 2500rpm's. I'm sure this is the flywheel ratings and expect to be considerably lower at the wheels.

One other question I have is this, I know the 400's can be pretty temperature sensitive, besides drilling steam holes in the heads, is there anything else I can do to keep temps down?
I was contemplating a 160 degree t-stat, but I was also reading somewhere on the internet about how you can T- off the water pump and feed water into the sides of the block through the ports right under the heads that are usually plugged. Anyone ever done this?
Does it help?
my thoughts on the 160 degree t-stat were that it may help keep from detonation occuring so I may be able to sneak by with a bit more compression ratio. Does this make sense?

I'm new to specing out builds. Any prior builds that I have been involved in were basically just assembly. Dad has always done the hard work lol.

 

[rich weyand]

Running an engine cold will make it run like crap. I replaced the stupid engine propeller with an electric fan because I couldn't get mine to run warm enough.

With those numbers, you need to worry about the rest of the driveline. Easier to replace them from the get-go than piecemeal as you blow them up.

 

[Handy Andy]

ok. so don't run it cold. they come with a 180 tstat from the factory right? My main concern is everything I've read says there is a fairly decent risk for overheating and wrecking these 400's.

I get where you are coming from with the driveline. I do plan to beef it up as I go. But, that will be as money and time allows. I work 50 hours a week and I'm a full time college student right now. I'm not gonna be hot rodding this truck and ripping around town or anything. The only reason I'm building it up is so I can pull my boat with it and to hopefully get a little better fuel mileage. The 700r4 that's in it has already had some work done previous to me owning it. not sure exactly what, but it doesn't shift like it's stock. My plan is to some day swap it out to a 5 speed manual like the one that was in my dads old truck (think it was an nv4500 or something like that).
What else would you suggest I do with the driveline?

 

[rich weyand]

What rear end is in it?

 

[Handy Andy]

Sorry rich, haven't been ignoring you I swear! Busy Busy Busy with work and school. The RPO for the rear end is GT4 which tells me it's a 3.73. It's a 10 bolt, but from what I read, from like 80-the mid 90's they went down to a 7.5" rear end right?

 

[rich weyand]

Better start looking for a 12-bolt if you are going for those numbers.

 

[Handy Andy]

Yea I kind of figured I'd need to go to something a little better. Since I'm gonna need to look at changing the rear end out should i maybe consider trying for something in the 3.55 range? The majority of my driving in this truck will be during hunting seasons but I will also be pulling my boat with it during the summers... I think I made about 25 trips out on the water this summer, but I don't pull my boat more than about 35 miles at a time.