Okay. ive been debating whether or not to go with a 350 or a 400 small block. either way i want to bore it and stroke it. question is...are headers interchangeable among these two. i know headers from a 305 will fit a 350 but will they fit a 400. i want the hooker super comps 1 3/4. will the 400 bolt right in?? will i need a special chip or computer to swap a 400 for my 305 tbi?? the 400 will be carb'd. thanks for all your help.

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Rick
90 Camaro RS 305 TBI
350 on the way!!

 

400s will interchange with 350s. It should be a drop-in if you have everything for a 350. the only difference in the blocks is the larger bore of the 400 and they have steam holes in the deck.

Don

 

The fitting of headers (and other accessories) is dependent on the choice of heads rather than the block. Remember to drill steam holes in the heads if you put them on a 400.

 

The 400's are externaly ballanced so you can not use a small 305 flexplate with it. You will have problems getting a starter for it. I am having the same problem with my 350 with the large flexplate. As soon as I find the solution I will post it.

 

Is there any particular sb400 blocks to stay away from even if you are going to do a complete rebuild? Also how does the cost of building a 400 vs a 350 compare? Are the internal parts any more expensive? Would vortec heads work on these or would you need something with bigger runners? Also would votecs need to be milled down or would they be able to make ~10:1 compression?

 

A 400 is more expencive to build. The pistons are more but to do a decent rebuild you would want to put longer 350 rods in it (400's come with a 5.5 rod and a 350 comes with a 5.7 rod). The short rod puts alot of pressure on the outside walls of the cylinder and ends up making the cylinders eggshaped this is why you put the longer rods in to cure this and it also free's up a little more RPM. The Vortec heads will work on the 400 just fine and with the stock type dished pistons you will have 10 to 1 compression. if you put a flat top piston in it you will have close to 11 to 1 with the stock Vortec heads.

 

About the blocks a 2 bolt main 400 is a better casting than the 4 bolt main 400. The 4 bolt main 400s have a very weak webbing and are much more likly to crack. Your best bet would be to get a 2 bolt main 400 and put some splayed main caps in it. I know it is a little more expencive but it is worth it if you are going real ratical. If you are doing more of a street type set up (under 6500 RPM) then leave the 2 bolt mains in it and don't worry about it. You only need a 4 bolt main bottom end if you are running alot of compression or a big power adder (bower with alot of boost, 350 shot of nitrous or more, or a turbo with alot of boost) if you are not then a 4 bolt main bottom end is just there for you to talk about because the bottom end is not being stressed.

 

I agree both with the rods and 2 bolt vs 4 bolts on the 400s. The rods are actually a tad longer than 5.5 (5.56" IIRC). But they are shorter than the stock 5.7" in other SBC.

 

5.565 to be exact.

KR

 

actually its 5.5650

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Rick
90 Camaro RS 305 TBI
400 on the way!!

 

Well I have solved my starter problem the most expencive way I knew how. I had to break down and buy a minni starter. Even after that I had to reclock the starter and put the silinoid on top of the starter and trim one corner of the mounting flange a little to clear the header collector and, voila, it worked. I have found that all Corvette's from 84 and up and all F-bodies from 82 and up run the small 305 flywheel/flexplate and the 305 starter so if you have a 350 or 400 with the larger flywheel/flexplate then you have to runa $200 minni starter.

 

In regard to my above post. I found a 1974 400sb with 2 bolt mains. Think this would be a good starting point. Price is $125. Motor mounts should be the same right? Obviously they didn't have the 700r4 back then. Will my tranny need adaptation.

 

No you won't ! You can use the 305 starter on a 168 tooth flywheel (14" dia.) by changing the starter drive housing. I did it on a 406. Here are the part numbers.

168T flywheel = 3986394
Starter drive housing (iron) = 1984098
Starter drive housing (alum.) = 1984097

I wish i had seen your post sooner i could of saved you a lot of money.

-Auggie-

 

I wish you would have seen it earlyer also.. I have bot a 350 starter and a 305 starter sitting in the back of the car right now...So all I had to do was swap the nose cone on them... I could have done that for free. Oh Well live and learn.

 

are those gm part numbers? i am going to be building a twin turbo 400sm and this is useful info for me to write down. So i just use the stock starter with the parts you listed?

 

Yes those are GM part numbers, but remenber when you change the starter drive housing for the lager flywhell this will move the starter away from the block and towards the hwaders. Had to do a lot of grinding to get the headers to fit. Pain in the *** . If i had to do it over again i would use the small flywhell (153t 12.75") with a bolt on pork chop flywheel balancer and a 400 harmonic balancer. NO header clearance problems!!

-Auggie-

 

well, i wont have that problem because this is going to be a twin turbo 400 and the headers will be out of the way.

 

I am also building up a engine/tranny combo, and some of my friends told me that the th400 would be a very good tranny. It was used on the old big blocks and the one ton trucks, so it can handle a little torque.

Also for the heads, I heard that the Fast Burn heads are really good. On Horsepower TV they got a 350 to do ablot 450 HP on those heads, a cam, and an intake manifold.

have fun, beat imports

 

Glad I read this post! I didn't know about the starter problem, does that matter with a regular manual tranny flywheel?

My engine is going to be a bored and stroked 400 out to a 427, duel Holey 670 TBI's, Fast Burn heads, huge cam, SLP 1 3/4" headers, all forged Lunati internals, fogged, and backed with a T-56/9".

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1992 RS
327, Modded TBI, Rebuilt WC T-5 5-speed, PRO 4 15" rims, Nitto's, 3.73's, SLP 1 5/8" headers, and a few other things.

 

I didnt have a problem with my starter. My car is an auto, I used a stock 400 sb starter and flexplate. I had no clearance, problems except for the dust cover on the tranny was to small. What problems did you guys have with the stock starter? Just curious why you went to all that trouble?

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

[This message has been edited by MikeH (edited November 22, 2000).]

 

to ad to the starter debate- i used the gm ministarter for the 502- the stock starter wouldn't come close with the headers installed. if i had known before i would have the block drilled for the inline bolt pattern , mine had the diaganol pattern

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86 camaro 405 sm. blk. th 350 tranny 3.42 gears

 

craig...so the stock 400 starter was hitting the header? There wasnt enough clearance? What headers did you use?

The first 406 i built I used the Hooker shorty headers with no problems.

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Black 90 IROC, L98, A4, 323 gear. SuperRamed 406 in the works!

 

This will probably start some spirited counter-arguments, but here goes anyways,...

In a recent story in a car magazine(PHR I believe, but it's at work so I'm not positive) someone from World Castings described the new "Motown" blocks. It was mentioned that they specifically avoided using a splayed configuration for the four-bolt main caps. The reason being that splayed caps are more likely than straight caps to cause cracking and distortion. They did not elaborate if this was a problem common to all splayed caps under most circumstances or whether there special circumstances. Anyways,... food for thought!

Auggie,

Thanx for the info on the starter. I recently picked up two 400 blocks(at a price I couldn't resist). The four-bolter is destined to become a truck motor(when I find the "right" donor). As this will be a low-budget build-up I'd really like to reuse one of the starters i have lying around. The two-bolter will be destroked to 352 cid so that I can use 11.5+ compression on a street TPI engine(the 6.25" rods should keep the detonation at bay) and the requisite high-torque starter means I won't be able to save any money there.

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He who hesitates,... is lost!

 

Your Welcome !

-Auggie-