[soon2be]

buildin up a 408 and im lost in the motor world now. to start off, it was a built 406 with 305 heads and was suppose to take higher octane then unleaded... =cracked piston. so i bought it and bored to 408. i dont know the cam or specs though and that where i get lost at. i want 400hp on pumped gas to the wheels though and so far its just:

400 block bored .40 over with clean and all that extra stuff
stock crank thats been polished and balanced
.40 over piston but not too sure of the brand or specs at this point (10:1)
holley 750 carb
air gap intake
hooker headers, 3in exhaust and dump offs

would it be better to get a new cam (want a nice lope)that i know the specs and then gets the heads? also which heads (iron) will you think can accomplish this task? and what other parts should be bought to also do the 400hp?

[DoubleVision]

You won`t reach 400 horses with 305 heads. Flow is the key to power so the heads play a big role but don`t let this mislead you, the whole combo must work together as a team to make max performance. Unless we know what pistons you have then we really can`t recommend a set of heads, to survive on pump gas the compression ratio needs to be in the 9.5:1 range, the 305 heads have small 58cc combustion chambers and if ran on a 400 with dished pistons and pump gas put the compression ratio over 10:1, detonation likely set in and that`s what took out the piston. Let us know what pistons you have and what your looking to do, street? street/strip? and we can line up a combo for you.

[soon2be]

Sorry for the confusion, but the car no longer has the 305 heads. When it was with the previous owner it did but since then has been scrapped. Motor is strictly street use and if it ever sees the track, it'll be just to see what time it puts out. Ill go to the shop and see what the specs are one the pistons. Also is there any way to look at a cam and know the specs?

[cobalt327]

Originally Posted by soon2be

is there any way to look at a cam and know the specs?

See if there's a manufacturer's stamp on the end of the cam, often that's enough to pull up the specs from their website.

If not, it can be carefully measured with it in the engine and with one cylinder mocked up, valve train-wise. You'll want to use a degree wheel and dial indicator.

[soon2be]

Originally Posted by cobalt327

See if there's a manufacturer's stamp on the end of the cam, often that's enough to pull up the specs from their website.

If not, it can be carefully measured with it in the engine and with one cylinder mocked up, valve train-wise. You'll want to use a degree wheel and dial indicator.

seems like alot. think ill be better off going new and knowing what it is then playin the guessing game and being dissapointed when its running.

[F-BIRD'88]

How will you be using this motor? Installed in what?

Are you willing to buy the right pistons to match the heads correctly?

Gear ratio, torque converter stall? willing to match them to a easy to build kick *** street 400sbc combo?

Budget for cylinder heads?

400+.040
O deck the block
stock reground 400 crank
5.7 350 rods. (chev oem type rods with thru bolts will require minor rod/cam lobe clearancing preparation)
KB 147 +.040 Pistons
the rotating assembly must be rebalanced.
felpro 400 heaqd gasket
Comp cams Xe284H-10 cam 1.5 rockers
GM big port Bowtie vortec heads GM pn#25534446
Performer rpm air gap (vortec) manifold. felpro #1255 manifold gasket
1-5/8" long tube headers.
750+cfm carb

92 octane gas

[soon2be]

Originally Posted by F-BIRD'88

How will you be using this motor? Installed in what?

Are you willing to buy the right pistons to match the heads correctly?

Gear ratio, torque converter stall? willing to match them to a easy to build kick *** street 400sbc combo?

Budget for cylinder heads?

400+.040
O deck the block
stock reground 400 crank
5.7 350 rods. (chev oem type rods with thru bolts will require minor rod/cam lobe clearancing preparation)
KB 147 +.040 Pistons
the rotating assembly must be rebalanced.
felpro 400 heaqd gasket
Comp cams Xe284H-10 cam 1.5 rockers
GM big port Bowtie vortec heads GM pn#25534446
Performer rpm air gap (vortec) manifold. felpro #1255 manifold gasket
1-5/8" long tube headers.
750+cfm carb

92 octane gas

86 monte ss, street machine. No strip but will run a race on street. Thinking about starting over and getting new pistons and going from there. Goal is atleast 400 to the wheels. I have the block work done and crank turned. Is forged internals only necessary if going spray or power adders? Rear end is stock 7.5 with 4.10 gears. Going with 400 turbo tranny. Like I said pump gas is a must. Is aluminum heads only really needed to reduce weight?

[F-BIRD'88]

Originally Posted by soon2be

86 monte ss, street machine. No strip but will run a race on street. Thinking about starting over and getting new pistons and going from there. Goal is atleast 400 to the wheels. I have the block work done and crank turned. Is forged internals only necessary if going spray or power adders? Rear end is stock 7.5 with 4.10 gears. Going with 400 turbo tranny. Like I said pump gas is a must. Is aluminum heads only really needed to reduce weight?

The trick is to figure out what you want to achieve.
For pump gas on a 400SBC you want a true 10.5:1 cr or less:

flat top 400 pistons: use a 70 to 76cc combustion cylinder head

64cc heads require a 18cc to 22cc dish piston for pump gas friendly 9.8 10:0 cr.

( based on a net (with gasket) .040" piston/head quench clearance)
0 decked block Yes it matters.

Aluminum heads cost more and weight less.

When compared to a identical cast iron head 9 times out of 10 the cast head will make more power. The iron head is more heat efficient than same aluminum head.

I've run many stock cast bottom end motors on nitrous without failure. Forged pistons are a good idea thou. Forged pistons will take more abuse than cast pistons. If you abuse a motor (fuel lean out, detonation, extreme rpm, improper nitrous tune, excessive timing, low octane fuel/excessive compression ratio, valve float etc, you will break the forged stuff too.

If you have good flat top pistons ready to go already then there are other good similarly priced larger chamber heads to choose from eg: Brodix IK-200
(70+cc combustion chamber) That will give the right pump gas cr on a 400 with flat top pistons.
www.brodix.com
www.airflowresearch.com

[soon2be]

Originally Posted by F-BIRD'88

The trick is to figure out what you want to achieve.
For pump gas on a 400SBC you want a true 10.5:1 cr or less:

flat top 400 pistons: use a 70 to 76cc combustion cylinder head

so if i keep the flat tops and go withthe Brodix IK-200 itll would produce the power im wanting? also and if there forged i can use nos from tiem to time and be ok? will the cr have to change when using nos?
when looking for a cam, will the exact specs on the pistons effect what route ill need to take?

oh and by the way F-BIRD'88 and all that responded, your helping me soo much. appreciate it all.

[soon2be]

anyone?...

[barnym17]

Flat tops and the brodix heads should get you what you want.Either go with the cam F-bird recomended or call a grinder for recomendation.

[soon2be]

Got back from shop and found out specs:
817 block from 71-77 truck bored .40 (but not decked)
stock crank thats been turned
stock 5.56" rods (doubt they were balanced)
TRW h400cp-40 flat top pistons.
brass freee plugs plugs
-------------------------
running those brodix ik200
a 750 carb
air gap intake
Comp cams Xe284H-10 cam 1.5 rockers
what type of numbers do you think itll put out?

[BBCMudbogger]

Oh god.....moderators see street racing....we d not condone street racing.....LOL........

[soon2be]

Originally Posted by BBCMudbogger

Oh god.....moderators see street racing....we d not condone street racing.....LOL........

sure u dont... sure everyone here has raced someone atleast once on the street, but to those who can answer that last question would be very appreciated.

[ericnova72]

My rough guess would be around 460-475 hp, you will need more cam than what you plan if you want more than that.