[cr480r]

I have my 355 apart and it needs a few more things than I had planned. Actually, it only needs one piston(skirt has a crack) and all the basic overhaul items. No big deal. I was just about to pull the trigger on all the needed parts, But then over the weekend I went to a garage sale at a neighbors house and saw he was selling a complete 400 core for $100. Supposedly he drove it home, but it smoked. I started thinking that if this 400 core was in fact useable I could gain 51 cubes with just some new pistons and the typical block machine work + balancing... the other stuff i need to buy anyways. The engine is used in my K30 truck that is mud raced and sometimes street driven. i could always use more torque. My new cam set-up is probably gonna be rpm limited by the lifters, so I am thinking the larger displacement may really help me. Just looking for some opinions on rather the potential gain is worth the cost. I have no experience with the larger small blocks. I dont have alot of money, but i could make this happen if its worth it.

my current combo is:

10.68 CR @ .038 quench (was planning to mill for 11.2)
062's w/stock valves bowl blended to 88% throat.
RPM air gap
750 DP holley
1.75 headers/3" pipes
10" converter (3400 stall)
street hyd roller lifters (recommended for 6200-6500 max)
new custom cam is 240/244 @ .05 108lca .535" w/ 1.6 rockers std. base circle. IVC 74 abdc.

went to a hydraulic roller for reliability, and i really hate setting the lash on a lifted truck. I already had appropriate springs.

old cam was solid tappet, 248/256 @ .05 106lca .550/.572"(net)

[techinspector1]

Originally Posted by cr480r

I have my 355 apart and it needs a few more things than I had planned. Actually, it only needs one piston(skirt has a crack) and all the basic overhaul items. No big deal. I was just about to pull the trigger on all the needed parts, But then over the weekend I went to a garage sale at a neighbors house and saw he was selling a complete 400 core for $100. Supposedly he drove it home, but it smoked. I started thinking that if this 400 core was in fact useable I could gain 51 cubes with just some new pistons and the typical block machine work + balancing... the other stuff i need to buy anyways. The engine is used in my K30 truck that is mud raced and sometimes street driven. i could always use more torque. My new cam set-up is probably gonna be rpm limited by the lifters, so I am thinking the larger displacement may really help me. Just looking for some opinions on rather the potential gain is worth the cost. I have no experience with the larger small blocks. I dont have alot of money, but i could make this happen if its worth it.

my current combo is:

10.68 CR @ .038 quench (was planning to mill for 11.2)
062's w/stock valves bowl blended to 88% throat.
RPM air gap
750 DP holley
1.75 headers/3" pipes
10" converter (3400 stall)
street hyd roller lifters (recommended for 6200-6500 max)
new custom cam is 240/244 @ .05 108lca .535" w/ 1.6 rockers std. base circle. IVC 74 abdc.

went to a hydraulic roller for reliability, and i really hate setting the lash on a lifted truck. I already had appropriate springs.

old cam was solid tappet, 248/256 @ .05 106lca .550/.572"(net)

I wouldn't bolt L31 heads onto a 400 block and expect more hp. You can expect more torque up to the torque peak, but those heads, as good as they are, I don't think will feed 400 inches to the revs you are currently seeing with your 355. A 400 block deserves AFR 195's or 210's in my opinion. Scroll down here to 413 and 406 dyno tests.....
http://www.airflowresearch.com/chevy_dyno.php

[F-BIRD'88]

You will really like the 400SBC. Build with 5.7" rods and -18cc dished pistons.
will work very nice with what you got.

Hyd cams are for the girlie man.

[cr480r]

thanks guys i appreciate the input.

Originally Posted by techinspector1

I wouldn't bolt L31 heads onto a 400 block and expect more hp. You can expect more torque up to the torque peak, but those heads, as good as they are, I don't think will feed 400 inches to the revs you are currently seeing with your 355.

i am more concerned with the output than rpms... as long as i dont lose hp or go slower. I know that the rpms will drop with added cubes, but i have no idea how much so that where i need help. I originally had the solid valve train so i could "operate" it @ 7200... which was well past peak and ideal, but it helped me "hang on" with a 4spd truck that was often "inbetween" gears... It worked quite well in fact. But that cam lost a lobe and my new truck is auto trans so it can shift wherever it needs to.

Originally Posted by techinspector1

A 400 block deserves AFR 195's or 210's in my opinion. Scroll down here to 413 and 406 dyno tests.....
Air Flow Research

very good stuff there. But unfortunately, i don't see them in my future. I know my stuff is less than ideal, but its what i have.

Originally Posted by F-BIRD'88

Hyd cams are for the girlie man.

i know, i know... the internet had me thinking the cheap solid rollers were failure prone. and its a pain to check lash on this rig.. gotta make the best of it now...

[454C10]

read this. Bigger heads on a 406 worth 60 hp with a moderately sized cam. Would be even more with a bigger cam.

Chevrolet 406 CI Engine Build - Chevy High Performance


Anything over 0.525" is a "Waste of lift" on vortec heads.

[cobalt327]

First things first- go get the 400 before someone buys it out from under you. If it's a good engine (block and crank mainly, stock heads are junk), it's well worth $100.

[vinniekq2]

The vortec heads will only support so much HP like Tech already mentioned.The 350 will make as much power as the 400 just at a higher RPM.The roller cam you bought will likely make power sooner than the solid you had.I bet the 400 will be all in by 5800- 6,000.
Work with Tech on the CR thats best suited to the fuel you will use.If you want more power then get better heads.

[cr480r]

Originally Posted by 454C10

read this. Bigger heads on a 406 worth 60 hp with a moderately sized cam. Would be even more with a bigger cam.

its not hard to understand that a bigger engine would ideally have better heads.. Everyone knows that. I am just trying to figure out if my existing 355 combo would be worth adding cubes? or if its a waste of my time? I am considering a new short block, not a new engine.. So far i am getting opinions going both ways...

Originally Posted by 454C10

Anything over 0.525" is a "Waste of lift" on vortec heads.

this is why i went with a custom grind. So I could reduce lift without buying new rockers... .535" is pretty close, and with potential lifter collapse and pushrod flex the valve may really only see .525

Originally Posted by cobalt327

First things first- go get the 400 before someone buys it out from under you. If it's a good engine (block and crank mainly, stock heads are junk), it's well worth $100.

thats what started this lol.. i am sure its still there. not many chevy heads around here these days.. and its christmas time.

Originally Posted by vinniekq2

The vortec heads will only support so much HP like Tech already mentioned.The 350 will make as much power as the 400 just at a higher RPM.The roller cam you bought will likely make power sooner than the solid you had.I bet the 400 will be all in by 5800- 6,000.
Work with Tech on the CR thats best suited to the fuel you will use.If you want more power then get better heads.

If i could make the same horsepower, and get a harder punch at launch rpms i would consider that worth it.. this rig is heavy. if the gain is substantial i can justify the effort. I understand the heads are the limiting factor, but i am not ready to upgrade. Besides aluminum heads usually get you thrown right in with the faster rigs... I would rather remain stealthy and give the appearance that nothing has changed.

[vinniekq2]

I dont see any improvement,unless lower RPM is an improvement?You can buy very good cast iron heads

[ap72]

like most people you probably don't want to hear this, but your cam is WAY too big. You'll make more power if you lose about 15 degrees duration on the intake and exhaust.

So many people overcam Vortec heads, they are good STOCK heads, they are NOT a race head.

To handle the cam you have those heads need to be ported out to the max, pick up about 25-35cc's of runner volume and maybe a larger valve after that.

Your combo really should have large port bowtie vortecs, not the tiny 062 vortecs.

[cr480r]

Originally Posted by ap72

like most people you probably don't want to hear this, but your cam is WAY too big. You'll make more power if you lose about 15 degrees duration on the intake and exhaust.

So many people overcam Vortec heads, they are good STOCK heads, they are NOT a race head.

To handle the cam you have those heads need to be ported out to the max, pick up about 25-35cc's of runner volume and maybe a larger valve after that.

Your combo really should have large port bowtie vortecs, not the tiny 062 vortecs.

i know this. But how will less duration make more power?In my mind if the compression ratio is enough for the valve timing, and a narrow powerband is acceptable then where is the problem? i thought limited heads liked duration? My solid cam with "way too much lift" was stronger than the previous 355 combo was. it was 10:1 and a comp 280H.. some would say that cam was too big also.. so how did going even bigger gain? I know these are not race heads, but people do race with them. the roundy rouind guys make power with them. Trust me i wouldnt go this route again, but i own them, they have been freshened, and i dont mind doing more porting. This is not a street car... everything would be different if it was.. All i care about is the output from 3500-6200... I am not changing the converter, the heads, the cam, or the lifters.. so with that considered would a 406 short assembly help, hurt, or do nothing for me?

[ap72]

Originally Posted by cr480r

i know this. But how will less duration make more power?In my mind if the compression ratio is enough for the valve timing, and a narrow powerband is acceptable then where is the problem? i thought limited heads liked duration? My solid cam with "way too much lift" was stronger than the previous 355 combo was. it was 10:1 and a comp 280H.. some would say that cam was too big also.. so how did going even bigger gain? I know these are not race heads, but people do race with them. the roundy rouind guys make power with them. Trust me i wouldnt go this route again, but i own them, they have been freshened, and i dont mind doing more porting. This is not a street car... everything would be different if it was.. All i care about is the output from 3500-6200... I am not changing the converter, the heads, the cam, or the lifters.. so with that considered would a 406 short assembly help, hurt, or do nothing for me?

It will not hurt, and help a little, BUT your money would be better spent on a cam. If you're looking at 3500-6200 then a tight lash solid cam in the 235/240 range would be a LOT closer to what you need. For a hydraulic roller you'd want about 225/230 maybe a little more, but not much. As you can see your current cam isn't even close.

Restricted heads DO NOT want more cam, they work best with smaller cams and less compression. If you want more cam, compression, and RPM then you need a bigger head. For your RPM range on a 350 a 190cc port is about right- hence that is one of the most popular intake port sizes. Even then your cam would be too big though, a HR in the 235/240ish range would be about as big as you would want to go.

If you don't mind me asking, what cam company spec'd the cam you're currently using?

[F-BIRD'88]

My 406 screams with my vortec heads on it.
revs right up to 6700rpm. pulls like a frieght train. well past 6000 rpm.
The vortec heads are ported but not max ported by any means.

The solid roller cam that you have will work really well in the 400 with your vortecs.
re valve lash:
I trust you were not trying to set the lash "hot".

Its a lot easier to set the lash "cold" a lot more pain free.
You won;t hate doing it either.

Set the lash cold about .004" tighter than the hot lash spec.
I'd reconsider using that cam in your 400 w the vortecs. IMHO it is just right for your 400 w vortecs.

Ap72 has no clue.

The Hyd roller you got is just dandy too. Just not my preference.
These cams are just right.

If you liked the vortec heads on your 350, you are going to really like them on a 400SBC.

Use a -18cc dished piston on your 400 for pump gas compatability with 64cc heads.

A flat top piston 400 with vortecs will need about a 100 octane fuel to keep it happy.
A bit much for pump gas.

[cr480r]

Originally Posted by ap72

It will not hurt, and help a little, BUT your money would be better spent on a cam. If you're looking at 3500-6200 then a tight lash solid cam in the 235/240 range would be a LOT closer to what you need. For a hydraulic roller you'd want about 225/230 maybe a little more, but not much. As you can see your current cam isn't even close.

Restricted heads DO NOT want more cam, they work best with smaller cams and less compression. If you want more cam, compression, and RPM then you need a bigger head. For your RPM range on a 350 a 190cc port is about right- hence that is one of the most popular intake port sizes. Even then your cam would be too big though, a HR in the 235/240ish range would be about as big as you would want to go.

If you don't mind me asking, what cam company spec'd the cam you're currently using?

another tight lash flat tappet was not an option for me. The truck often sits for long periods, and although they work fine for most i didnt want to risk another lobe failure. I feel the dry starts may have been a factor, as well as my springs. And In my new neighborhood a camshaft breakin with 3" exhaust isnt a good idea. I dont wanna name drop the cam company on a open forum. not til after i use it anyways. Initially the rep suggested a 236-240 cam on a 110 lca. staying under .500-525" lift for the vortecs. But when we discussed this being a max effort with my existing parts and usage we decided to change it. After I stressed I had a loose converter, as well as a true 10.7 CR he decided to bump it up one step for pump gas. The LCA was tightened to 108 because i have no vacuum acessories. He felt my previous 106 was too tight for the 5.7 rod length? the cam lobes are .501" with 1.5 rockers and it was the closest lobe master he had in this duration range that would let me keep my 1.6 rockers without the lift going sky high...

[F-BIRD'88]

One thnig with the 400 is when using stock style 5.7" GM style rods in the 400 you must check for cam lobe to connecting rod bolt clearance. A few of the rod bolt heads will need to be clearance ground to clear the cam lobe
unless the cam is a small base circle cam.

many of the aftermarket rods like scat H beam etc etc are designed to clear the cam in a 400.

Its no big deal to clearance the "stock" chev style rods (rod bolt head), but must be checked.

Just something you need to be aware of.

On my 400SBC I did not drill the 400 steam holes in my vortec heads.
But I did do a very simple heater hose reroute that achieves the same thing.
Just connect the heater hose or by pass from the top of the water pump to the drivers side rear water port on the intake manifold by the distributor.
The cooling system works a lot better overall and the 400 does not get the steam pocket cooling issue.
Its simple but again a must do.