I have begun discussions with a local machine shop to have them put together a shortblock for me. The owner happens to have 400 block available.

Since I initially wanted a 383 stroker would a 400 shortblock get me similar performance? I have read that a 400 will provide really good torque at low rpms.

This will be going in a 77 with a THD 350 and 3:08 gears. I already have 186 heads w/ 64cc chambers. I was told these could be used with a gasket that blocks the steam holes.

Any opinions would be appreciated.

 

Get an internally balanced aftermarket crank and go with the 400.

 

The larger cubic inches built the same will always provide more HP. Your problem is those heads. The yare barely e enough for a 350 motor. On a 400 they would be starving it for air. If you have to order a crank anyway why not get a stroker 400 to 415 or even 421 ci. You will definitly need a bigger head for that. Something in the 220 range would work.

 

The heads are 3927186 camel humps from a 1970 LT1. I was kind of committed to them since I have spent considerable money to have them totally reconditioned. They have 64cc chambers, 2.02/1.6 valves and 170 intake runners.

It was my understanding that a smaller intake runner was better for low end torque. Since this will be a weekend street driver I want all the torque possible. Not so concerned with the top end. Will never go to the track. Just want a good launch.

Do I really need to ditch these heads if I go with the 400 block? Does the 400 block offer enough additional performance / torque to justify selling the current heads and buying others?

 

A 170 head is barely adequate for a 350. Back in 70 this was about as good as it gets but by todays standards these are puny heads. For a 400you will need more head. You can use them and it will provide good torque but if you put in a decent cam those heads will be done at about 4500 rpm. I have a set of AFR 190 heads tha tflow very well, better tha nsome 210 heads and on my 385 SB these are barely adequate. The minuimum I would run on a 400 is a good flowing 195 head and a 210 would be better.
If you are commited to these heads they will work and provide good torque but will not produce the HP that a 400 is capable of making.

 

Follow the advice, ditch the puny heads and go with the 400ci block, see my sig for a video of my 406ci @ 6500RPM, 546HP and 510ft/lbs

 

First of all I would find out what 400 block casting the guy has available and what the current bore size is...standard, 30 over etc. I would not want anything over 30 or 40 max over on a 400.

Here is the low down on GM 400 blocks. Best casting number (last 3 #'s top or rear block) is 509, next 511, and last is 817 (soft). An 010 or 020 in the front timing cover denotes a higher nickle content which is good. You will want a 2 bolt main in a 400, the main webs are stronger than the 4 bolt blocks (prone to crack). If you are not making much over 400HP and keep RPM's around 5500 then a 4 bolt can be ok.

Inspect the block and look at the area around the front and rear cam hole. There will be a raised area around this hole that looks like a washer, you want this "washer" to be even all the way around. there is no hole but the rear of the block has the same raised area. If it is thicker on one side than the other then there was significant core shift when the block was made. You can also look in the lifter valley and see if all the lifter bores are centered down the valley front to rear. If these are off the wall thickness will vary from one side of the cylinder wall to the other (not good). If these look good then the next thing is have the cylinder walls sonic tested for thickness.

On the heads...DO NOT block the steam holes with the gasket!!! Have steam holes drilled in the heads to match the gasket in whatever heads you decide to use. With 64 cc combustion chambers you will want to run a pretty good size dish piston to keep compression in the pump gas friendly area. I also recommend using head studs as the decks on 400's sometimes crack around the head bolt holes. inpect that area too. Would do well to have deck and main web areas mag checked.

The heads you have are outdated but you could use them IMHO. As you stated you want torque so those heads would keep the powerband lower in the RPM range. Your heads with 202 valves will flow better on the 400 due to the larger bore size. There will be less restriction and increased flow around the valve closest to the cylinder wall. If the car will not see track time you may not notice the difference. You could sell your heads and get some better ones though. A set of late model vortec heads should be considered and will work nicely on the 400 and are affordable, but you have to get a new intake to match them. if you go with 195 or 210 CC heads you will gain HP in the upper RPM range but your torque curve will also move up.

Also agree with above posts, if you have to buy a crank kit go internal balance and step up the stroke to 3.8. I would not go more than that on a GM block. Lots of people do YMMV. Get some 5.7" rods and the lightest forged pistons you can afford. 6" rods and pistons are more $$$ and not necessary IMO.

You will be much happier with a good 400 than with the 383 I think.

 

Great write up Chevyreb.

 

I'm not sure, but I don't think it is a good idea to block the steam holes on a 400 block. IMO, you should drill holes in the heads and use a head gasket with steam holes. I will look for others with more knowledge than I to chime in.

But, I would go with the 400 with the 3.08. I built a 400 for a Jeep in '76 for off-road use. I had a mild cam, with 64cc angle plug heads, 500cfm 2brl holley, headers, close-ratio 4 speed, aluminum fly wheel, 3.73 gears. Peaked out by 5000, but it was a stump-puller from 800 to 5000 rpm.

 

Good write-up chevyreb.You covered most of the bases.I didn't know that the 817 block was weaker than the 511.I thought that it being a two bolt would make it a better candidate than the 511 4 bolt.I actually have all three blocks.They are all std.bore.I also have a set of SRP .040 dished pistons,and I'm still debating whether I should bore that big.My 509 block looks good as far as core shift.Anyways I'm first building my 455 Buick,so it will be awhile before I get to the 400.One other thing I am going to do is tap the large water jacket holes on the deck,and install those plugs to stiffen up the deck.I would suggest to myc3 to buy the book on building a small block chevy by John Lingenfelter.He has good info on the 400.

 

400's had steam holes for a reason! If you are going to use those heads then I would definitely have the steam holes drilled. 400's were known for overheating as it was. You may be able to get away blocking them if you invest in a good sized alum radiator and twin electric fans.

 

Stick with the steam holes, any machine shop can drill them into a head for you. The 400 is great engine for the street. Torque is king on the street!

Do your homework around cam selection too. 400s exhibit behavior closer to a big block. They can take more duration.

 

YEP! 400's love big cams, a cam that sounds like a race only cam in a 350/383 sounds stock in a 400 LOL, can you say "sleeper?". but you still need to match the cam to the heads. Build the bottom end as good as you can afford and upgrade the heads and cam later if you decide to.

Thanks for the complements guys! nice to hear those kind words.

Yes do drill whatever heads you choose for steam holes
! very important! I post again "DO NOT BLOCK STEAM HOLES!!!"

Wish I had a 509 2-bolt... I have a 511 and an 817, both have little to no core shift and are std bore :-)

If I can get away with it I will be using std pistons and internal balance on both with 5.7" rods.

BLACKHORSEVET

If you can I would save those 40 over pistons for a down the road rebuild when nessasary. No need to waist the bores! "One other thing I am going to do is tap the large water jacket holes on the deck,and install those plugs to stiffen up the deck." good plan there, I forgot to mention that...but for his stated purpose not critical. Actually you want to restrict some of the water passages and enlarge others to promote even cooling. I will have to look that up again to tell you wich ones to modify. And an aluminum radiator is always good insurance.

509 2-bolts are the mac daddy's, but as long as everything mag checks and you are careful in selecting parts and operating range I think its all good.

 

Problem is finding a 509 or 511 2 bolt, lots of 4 bolts out there. My 550HP 406ci is a 817 (2 bolt) and it is doing fine with over 25,000 miles on it now and I just recently picked up another 817 for my next motor

 

MotorHead, I hope mine turns out that good too! They are out there you just have to look. I found a few 509's for sale after buying my 511 and 817.

As I posted above "509 2-bolts are the mac daddy's, but as long as everything mag checks and you are careful in selecting parts and operating range I think its all good."

Starting off with a good core is the key IMHO. Then taking the proper precautions should prevent or limit most problems. My point is that 400's can be tempermental and you should know the ins and outs are before building one.

 

.060 over is fine on a 400 with a good casting.

 

My 406 started with the same conversation with an old timer at my local machine shop. The cost of the build is the same,the extra cubes is like free horse power. The heads you have can be used,but I'd set the bar at around 400-450 hp max.If you want to catch Motorhead,and me....you're going to need some good heads.But if you want to build what you've got,(to save cash),I'd keep the cam in the 220-230 range,CR in the 10:1-10.5:1 area,and you'll have a torque monster for sure.You can always change the cam and heads later.

Check my site if you want to see what I did.

 

A friend of mine just bought one of those aftermarket 400 blocks. Really neat setup. They changed the cooling setup -- no steam holes. Supposedly better oiling too.

The only problem is you butt will clinch up as the $$$ is ripped out of it.

 

I am always on the hunt for a good 509. Have been looking for over one yr. VERY hard to find now-a-days.
Had to buy an entire engine in one case...block questionable.
Bad core shift on another....
Damaged cylinder on another...
Bored to .060 on another....
ARGGGGGG....
Plenty of good 817's out there however.
Eddie

 

4-bolt blocks will hold up just fine if the rotating assembly is well balanced. Problems usually occur if the balancing is not perfect.. I made 180+ drag strip passes with my 4-bolt 400 block with 600 - 650 HP with no issues.. Even ran a 100 shot of nitrous (750 HP total) and the block held up..