Cylinder head upgrade for my SB400
 

Many years ago when I built the drivetrain for my '69 C10 I considered going big block but the costs scared me away. The truck was originally a small block truck so I would have needed everything including brackets, etc. which gets pricey. Anyway, I'm more of a small block guy anyway so I went with a '76 SB400 out of a '76 Blazer. I installed 5.7 rods and built a really nice just-a-notch-above-stock engine. The primary role of the truck was to be a nice driver and workhorse so I didn't want to hot rod it. It ended up with a Crower Baja Beast flat tappet cam:

Lift: .414 - I / .417 - E
Full duration 258/264
Duration at .050 204/208
Lobe separation 112

It idles pretty smooth and has a lot of low end grunt, pretty much done by 4500 RPMs though. Power runs through a TH350 with a mild shift kit and a 12-bolt truck posi with 3.73 gears. I've always thought a more modern auto with overdrive would be nice but I've never pulled the trigger on that. I retained the original tiny valve heads, just a 1.76 intake, but I did later upgrade the intake manifold to an Edlebrock Performer Q-Jet. The original quadrajet was used but slightly modified to run better than in it's original smogger motor configuration. Carb works excellently. The ignition is stock HEI with better advance weights for a more aggressive curve, 36 degrees all in by 2800 RPMs. I used the stock rams horn exhaust manifolds down to 2-1/4 dual exhaust with no crossover. I originally had a crossover downstream but it made working on some things tough and caused a broken exhaust manifold since the system wouldn't really rock with the engine. It has about 38k on the rebuild. Runs fantastic.

BUT, I'm bored. I've been wondering how it would do with much better heads. I've become a fan of AFR Enforcer heads and was thinking of adding these to the mix: https://www.summitracing.com/parts/afr-1011ft

They are as-cast aluminum heads with 2.02/1.60 valves. Would certainly improve breathing. Might cause the compression to go up as the smogger heads I have probably have a 76cc or larger combustion chamber and the AFR ones have 64cc chambers. I roughly calculate the current set up is running about 10:1 compression. I pretty much have to run 91 octane gas or I have to really back off the timing and it will still knock under load.

But I wonder if the heads would be a waste with such a mild cam. I could upgrade the cam too, but I still want the truck to pull and haul well and remain super reliable as it has been.

Re: Cylinder head upgrade for my SB400
 

Never have I seen a 400 with a 1.76 intake valve, But what I would do is just get a good pair of 350 heads and have them gone through with the 1.94s and have the exhaust valve opened up to the 1.60. The 350s will have to be drilled for the steam pocket holes, but the machine shop can do that without blinking. I'd get the corvette rams with the 2.5 opening and work the exhaust to a single 3'' pipe with a dynaflo

Re: Cylinder head upgrade for my SB400
 

You might look into the GM Vortec heads. 1988 to 1996. You would need to modify your intake or get a different one.

Re: Cylinder head upgrade for my SB400
 

I have been wondering the same thing about a swap on my 406. It just runs so good that I can't take it apart. I opened up the stock heads to 2.02s and bowl blended them. They have been fine for 20 years but need valve seals. I think pulling it apart will be a rabbit hole and would end up being a 6.0 LS swap. I think I will just let it run til it fails.

Re: Cylinder head upgrade for my SB400
 

AFR's are available with 65 or 75cc chambers. Vortec heads are going to be 64cc chambers.

Re: Cylinder head upgrade for my SB400
 

The AFR heads would by far be more cost effective and probably flow a lot better than anything GM ever provided.

Re: Cylinder head upgrade for my SB400
 

That is probably true but all those improvements would be mostly wasted with the small cam. So then I'd want a bigger cam but, with all the flat tappet cam issues I'd have to have a hydraulic roller, and by the time I reached the bottom of the rabbit hole it would be a $4000 head swap. It might be better to get a good set of Vortec heads that will work nicely with a cam of that size. Modify the intake and be done for a $1500 or so.

That's only my opinion which along with a sawbuck will get you a steaming hot cup of joe just about anywhere. :lol:

Re: Cylinder head upgrade for my SB400
 

According to the information provided by the OP. He will not be able to run the smaller chamber vortecs. Without, also a piston change. Plus, an aluminum head, will also help with his knocking/octane issue.

Re: Cylinder head upgrade for my SB400
 

That is true and for personally for myself I would have to pull a head and determine the deck height and the piston dish/dome and valve relief CC's before deciding what heads I would use. Just too many variables to allow me to roll the dice and still be able to sleep at night. :lol:

Re: Cylinder head upgrade for my SB400
 

Flat top pistons. No domes or dishes.

Re: Cylinder head upgrade for my SB400
 

Part of the problem with your current set up is. Small valve, oem cast iron heads, small RV style cam. 10:1 compression.

The general rule of thumb on a street vehicle. With stock type cast iron heads is 9:1 compression. Also with such a small cam. It's probably not bleeding off much of the dynamic compression. Because of the small amout of valve overlap.

Rule of thumb on a aluminum head street vehicle is 10:1. Going with a slightly bigger cam on your 400sbc. Probably won't hurt it any, on the low end. Probably would actually gain some. Especially with quality aftmarket heads.

Rule of thumb on a vortec head swap (if you could use them ) is 35-45hp iirc. AFR's wouldn't be any worse than that . . .

You also may want to look at the Brodix IK 180 line of heads. With some 1.6 rockers. Especially if you don't want to change the cam.

Re: Cylinder head upgrade for my SB400
 

Already considering 1.6 rockers if I do the heads.

Re: Cylinder head upgrade for my SB400
 

My 2 cents for what is worth (not much). You are already around 10:1 compression with the 76cc heads - and yes you could get a 400 SBC with 1.76 intake valves from 1976 to 1980. I would consider the AFR head with a 75c chamber - aluminum head will help with the timing issue as will a fast-burn chamber. Once you have chosen a head you can think about a different cam if you wanted, as others have mentioned the cam you have is small and a little more duration would help bleed off some compression. If you still want to maintain low end grunt, I would keep the .050" intake duration between 214* and 220*.

Re: Cylinder head upgrade for my SB400
 

So the AFR heads I want have gone on sale and I'm really considering pulling the trigger but one more thing came up. My current set up has an Edelbrock Performer Q-Jet intake and of course a Q-Jet which I want to retain. The carb uses a divorced choke, however, none of the decent aftermarket heads have a heat riser port in them. The truck is pretty cold blooded as it is. I don't often have to drive it in cold weather, but today I needed it and it was about 15F out and it took forever to warm up even with cardboard in front of the radiator. Heads with no heat riser would cause the choke to take forever to open even in more moderate weather.

Re: Cylinder head upgrade for my SB400
 

Heads are on the way. They DO have a heat riser passage. Got an amazing price through Jegs.

Re: Cylinder head upgrade for my SB400
 

I like the AFR Enforcer heads great choice!

Are you going to do a cam change and if so what did you decide?

I'm curious as I want to do a head swap and cam change on my 383.

Great thread!

Re: Cylinder head upgrade for my SB400
 

Thats a real mild RV cam almost stock

I like those ATF heads

GM Vortex heads are thin casting and real prone to cracking. Junk

Re: Cylinder head upgrade for my SB400
 

Thats a real mild RV cam almost stock

I like those ATF heads

GM Vortex heads are thin casting and real prone to cracking. Junk

Re: Cylinder head upgrade for my SB400
 

Going to stick with the current cam for now.

Re: Cylinder head upgrade for my SB400
 

Looking forward to your results!

Re: Cylinder head upgrade for my SB400
 

Got all the gaskets the other day. Heads will be a few more weeks, probably because I purchased the additional machining to have the steam holes drilled.

Got these today:

Re: Cylinder head upgrade for my SB400
 

Holy crap, you are right next to me in Omaha! Let me know if you ever need an extra pair of hands! Excited to hear how the heads work for you as I have a set of ported AFR195s on my 383 that is currently awaiting installation in the truck.

Re: Cylinder head upgrade for my SB400
 

AFR FINALLY got around to drilling those steam holes and shipping my heads to me.

Re: Cylinder head upgrade for my SB400
 

Very cool !

Looking forward to hearing about the results. Once you bolt them on.

Re: Cylinder head upgrade for my SB400
 

It will be a while yet, but I will post back when the time comes.