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Old 01-09-2018, 11:27 AM   #1
SilverMiner
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400/406/409 Head suggestions

About a year ago this board provided me some good advice on modifying a rebuilt 400 SBC that I had acquired - thread is here. Unfortunately, either the cam I selected was just a touch too hot or the rebuilt smog heads weren't up to the task because in the span of less than 150 miles of break-in a majority of the rocker studs pulled out or broke. Not the end of the world - I yanked it out and slapped the original tired 350 back in and have been motoring happily since.

The tired original engine may be reliable but I still want more pep, so I'm eager to throw some cash and effort to getting the 400 back into service. It is sitting in my shop as a short block.

The question is: What combination of parts should I use to make the best engine I can to motivate my 1980 Suburban?

Here are the specs as they stand now with the short block:

BLOCK - T0505TLS casting 2-bolt 400 SBC bored .040 over according to the piston tops and my crude caliper measurement (HEY, I GOT A 409!)
Dished Sealed-Power 40 over pistons sitting 0.025 in the hole
CAM - Lunati 10120701LK hydraulic flat tappet, 213/219 duration at 050, 0.454/0.468 lift, 112 LSA
EXHAUST - Currently cast logs into 2-1/2" duals and Flowmasters. Not a fan of headers, but will probably give them a try again this go around.

SUBURBAN - 1980 K10 converted to 1978 K20 running gear
rebuilt TH400 trans with an 1350 stall converter, NP205 t-case
3.73 gears running ~32" tall 255/85/R16 tires

BUDGET - Although I know it would be smarter to just buy a new crate HT383, that isn't in the cards. I can spread ~$2,200 out over the next four months easier than I could plonk down $5K for the crate setup.

I want to buy a set of quality assembled heads that I can bolt on and run with, and I'm willing to spend as much as $800 each from Summit if that is what it takes. After reading many threads here I don't think I want to go the Vortec route - I'd prefer to use my current Edelbrock 2101 intake that I know will work with my Harrison A6 AC bracket. I'm already buying premium 91-octane fuel because that is the non-ethanol option in my area, so a higher compression ratio is possible but who knows what kind of fuel I may have to buy on a long trip.

My goal is to achieve the highest level of reliability and longevity with maximum area under the HP/torque curve from off idle to a max of 3500 rpm. Thanks in advance for sharing your knowledge and experience.
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Old 01-09-2018, 04:26 PM   #2
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Re: 400/406/409 Head suggestions

Here is what I'm considering purchasing:

Dart Iron Eagle S/S Cylinder Heads 10024360A
76cc chamber with 165cc intake runners

Cometic MLS Head Gaskets C5248-027
4.165 bore and 0.027 compressed thickness

Using Summit's compression calculator, this puts me right at 9:1.
But is it reliable to use the thinnest head gasket available? Are there any risks?
An alternative would be a 72cc head with 0.036 gaskets - better, or not?
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Old 01-09-2018, 04:55 PM   #3
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Re: 400/406/409 Head suggestions

Quote:
Originally Posted by SilverMiner View Post
Here is what I'm considering purchasing:

Dart Iron Eagle S/S Cylinder Heads 10024360A
76cc chamber with 165cc intake runners

Cometic MLS Head Gaskets C5248-027
4.165 bore and 0.027 compressed thickness

Using Summit's compression calculator, this puts me right at 9:1.
But is it reliable to use the thinnest head gasket available? Are there any risks?
An alternative would be a 72cc head with 0.036 gaskets - better, or not?
Your head and gasket selections are spot on. Cam is good also. You don't need anything fancy for headers. 1-1/2" primary tubes are fine on this deal.

Would be nice if pistons were not as far down in hole. .040 total deck height is great number to shoot for, you will have .052, which is still good.

Has block been decked? If not it is always a good thing. But you don't want to end up much less than .035 deck height.

Make sure you check springs on new heads. Make sure you frill steam holes on new heads.

Your stud pulling ordeal was a combination of stronger springs and a more aggressive cam profile...

Hope it all comes together. I have a friend that had a 66 C10 with similar combo. It was a screamer!
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Old 01-10-2018, 12:22 PM   #4
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Re: 400/406/409 Head suggestions

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...
Has block been decked? If not it is always a good thing. But you don't want to end up much less than .035 deck height.

Make sure you check springs on new heads. Make sure you frill steam holes on new heads.

Your stud pulling ordeal was a combination of stronger springs and a more aggressive cam profile...

Hope it all comes together. I have a friend that had a 66 C10 with similar combo. It was a screamer!
I don't know if the block was decked before I acquired it - it appears to be quite level based upon my measurements with a machinist straightedge. It is an assembled short block as it sits now, so to get it decked at this point I'd have to tear everything apart. Is it worth that level of effort?
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Old 01-10-2018, 03:43 PM   #5
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Re: 400/406/409 Head suggestions

Using the .027 head gaskets will help. Do they make any slightly thinner?

What you have WILL work fine, though. Zero deck height is best.

If the pad forward of the pass side cyl bank still has stampings on it, it has not been decked...
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Old 01-10-2018, 04:45 PM   #6
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Re: 400/406/409 Head suggestions

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Using the .027 head gaskets will help. Do they make any slightly thinner?

What you have WILL work fine, though. Zero deck height is best.

If the pad forward of the pass side cyl bank still has stampings on it, it has not been decked...
.027 is the thinnest available for a 4.165 hole at Summit. For convenience I'm organizing everything on my list there.

The pad just behind where the alternator would reside is stamped TO505TLS, so no decking seems to have occurred.
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Old 01-10-2018, 04:58 PM   #7
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Re: 400/406/409 Head suggestions

Get them ordered!

What carb/intake?
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Old 01-10-2018, 05:54 PM   #8
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Re: 400/406/409 Head suggestions

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Get them ordered!

What carb/intake?
Sure do appreciate your input. My enthusiasm to get started is getting hard to deal with.

The carb will be my favorite Rochester Quadrajet, a 17080292 given the benefit of a full Cliff Ruggles kit and calibration. This will be on top of an Edelbrock 2101, but I admit to being swayed by Ruggles' assertion that the original factory dual-plane is the full equal of a 2101 at the top end and quite possibly superior in the bottom. I'm partial to a stock look, but not at the expense of performance or reliability.
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Old 01-11-2018, 12:04 AM   #9
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Re: 400/406/409 Head suggestions

Is that .027 thick head gasket for a SB400? The bore being 4.165, it is exactly the same as your block bore size. Typically you want the gasket bore a bit bigger than the block bore.
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Old 01-11-2018, 09:58 AM   #10
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Re: 400/406/409 Head suggestions

Need to check to make sure gasket bore fits the chamber on the head AND the block. I'm wondering if the gasket has holes for the steam holes, OR of that specific is supposed to be modified for the steam holes, I'm not sure how the steam holes are sealed on the gasket.

The best intake for your engine is the early Edelbrock performer. It has bigger runners. my buddies 400 had one of these on it with a Holley 3310 (750 vac carb). I've bought parts from Cliff. The Q-Jet is a good choice!!! Any advice you get from Cliff is always good!!!
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Old 01-11-2018, 11:02 AM   #11
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Re: 400/406/409 Head suggestions

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Is that .027 thick head gasket for a SB400? The bore being 4.165, it is exactly the same as your block bore size. Typically you want the gasket bore a bit bigger than the block bore.
How much larger than the bore should the gasket be? 4.165 is nearly the top of the range for what is available from Summit, although there are a small handful of gaskets for 4.166 and 4.180. If there is a better site I should be trying to source these from please let me know. I'm only partial to Summit out of habit.

Jumping only one thousandth larger to 4.166 seems odd. The thinnest gasket available for the 4.180 diameter is 0.045 which would suggest I need to step down to a 64cc chamber in order to stay near 9:1 compression.
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Old 01-11-2018, 11:29 AM   #12
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Re: 400/406/409 Head suggestions

Going directly to the Cometic catalog reveals some additional options over what Summit has available for sale.

Oddly enough, their catalog does not list a 4.180 bore gasket for sale although Summit claims to have some in stock. In the catalog all Gen 1 SBC head gaskets jump directly from 4.165 to 4.200 with a wide range of thicknesses available (but much more expensive as they could be a "build to order" deal).

Would a 4.200 bore gasket be preferable? Should I be looking elsewhere such as FelPro besides the Cometic MLS?
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Old 01-11-2018, 03:55 PM   #13
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Re: 400/406/409 Head suggestions

I'm not computer/internet savvy. I used to sell auto parts. I sold Fel Pro gaskets. I know that they specifically sell SBC 400 gaskets, don't remember any specifics. I will try to find an old catalog later, see what gives....

Do they make those specific heads with the steam holes already in them???
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Old 01-11-2018, 05:02 PM   #14
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Re: 400/406/409 Head suggestions

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I'm not computer/internet savvy. I used to sell auto parts. I sold Fel Pro gaskets. I know that they specifically sell SBC 400 gaskets, don't remember any specifics. I will try to find an old catalog later, see what gives....

Do they make those specific heads with the steam holes already in them???
All of the heads from Summit will require drilling for steam holes by a local shop. Not a huge problem for me, but it would be more convenient if I could order them already done.

Both Cometic and Fel Pro sell 400 SBC gaskets with steam holes, so that's nice.
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Old 01-12-2018, 12:32 AM   #15
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Re: 400/406/409 Head suggestions

The last SB400 that my son built, he ordered Cometic MLS gaskets to the exact thickness he needed to achieve proper quench. They weren't cheap. I don't remember if he ordered them thru Summit or elsewhere. It has been several years ago. I believe you will have to go with a gasket bore of 4.200 to get a 400 specific gasket with the steam holes already present.
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Old 01-13-2018, 10:37 PM   #16
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Re: 400/406/409 Head suggestions

I have 86 K20 Suburban with a 406. Very similar cam, maybe 5 more degrees of duration. I have these heads from summit.

https://www.summitracing.com/parts/sum-152123/overview/

They are built on the old camel hump specs and I have been very happy with them. Made a 6500 mile road trip this summer with the family and all was good.
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