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355 vs. 406 w/vortec heads

21K views 35 replies 8 participants last post by  cr480r 
#1 ·
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)
 
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#2 ·
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
 
#3 ·
thanks guys i appreciate the input.


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.



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.

Hyd cams are for the girlie man. ;)
i know, i know... :D 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...
 
#7 · (Edited)
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...:confused:

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:D

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.

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.
 
#6 ·
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.
 
#9 ·
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.
 
#10 ·
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?
 
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#14 ·
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.
the old cam was flat tappet and it wiped a lobe. I was lashing cold, but its a pain in this truck while basically sitting on the motor. The old truck had no fenderwells so i could sit on the tire and go through them very easily. I went hydraulic because my springs were too weak for a solid roller, and i read many horror stories of cheap roller lifter failing with street use. pressure fed lifters are alot of money.

with my intake valve closing at 74 on the new cam i figured i could up the compression to 11:1.. i dont remember the intake closing on the old cam but with a 102 installed ICL it was trapping over 200psi with no pump gas issues. I always spiked the fuel before races, but i did plenty of street flogging on pump 91. always had 32* total timing. I always figured the stall speed and tight quench made it more forgiving
 
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#15 · (Edited)
Don't buy into the dynamic cr BS.
Its is way to simplistic.
Yeah, I can see where it makes way more sense to just pick a cam out of thin air and hope for the best. Holy Jesus H. Christ !!!!!!!!!!!!!! :boxing:
You seem intent on calling BS to most everything I write, so I'm gonna start bitin' back. You don't know all the answers and neither do I.

Can't you give some sound engineering reason as to why you don't like DCR or is it just that I happen to champion it and you have to try to call it BS just because I like it.

Let the biting back begin, here and now. I'm tired of you and your punk attitude. Several board members have PM'd me and asked why you are the way you are toward what I write, so it's not just me. Others see your attacks also. So, either lighten up or I'm gonna have something to say about every damned thing you write.

For the rest of you, here's an article written by Pat Kelley that might explain some of the process of choosing components....
http://cochise.uia.net/pkelley2/DynamicCR.html
 
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#17 ·
Its real simple. The dynamic compression ratio is based on simplictic intake valve closing point.
When for 1 is very hard to accuratily establish.
I call BS. The mfg will give you the intake closing point down to minutes and seconds if you ask for it and it's not that difficult for a home garage builder to find 1 degree.

2. the RUNNING engine's real in cylinder pressure has nothing to do with the cranking compression.
when its running at speed.
I call BS. Show your scientific data to support that statement.

In the real world, engines do not operate in a tightly controled environment.
Gas quality changes, operating temps change, air inlet temp changes widely.
The knock tolerance of a engines varies widely based on the actual operating conditions at any one time.
I call BS. What are you going to do, reach out into thin air and pick a cam?

As a general statement engines that operate in the real world with more than 10.5:1cr that are not computer electronic controled will be knock sensitive on even good pump gas reguardless of the cam used.
When things get hot they get hot.
I call BS. What data do you have to back up what you say?

For every internet guru that claims that you can do this and that there are 4 guy who found out how the real world really works.
You don;t pick a cam based on simple dynamic compression ( theory).
I call BS. Where's your data to prove what you're saying?

You cannot predict the cranking compression based on published cam specs.
These are not the true running open close specs of a RUNNING engine.
I call BS. Where's your data?


Your cam picks are always lame and wrong fo both power and .....
I call BS. Sounds like one punk's opinion to me.

Your power estimate are always wrong and lame based on over simplistic $20 computer programs and wrong inputs./
I call BS. Sounds like one punk's opinion to me.

In short you are full of BS,,,, SIR. have a nice day.
Again, BS. Just one punk's opinion.

That seems to be all you have is opinions with nothing scientific or mathematical to back them up. I call BS on your entire agenda.

Just for the record, I have PM'd you in the past and tried to make friends. My PM was never answered, leaving me to think that you are just a punk who is devoid of honor and integrity and chocked full of BS opinions.
 
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#21 ·
Thank you for the article. I read it. While it addresses air fuel ratio and spark timing, it stops short of explaining what camshaft timing needs to be used to complement the max 10.5:1 static compression ratio. Could a guy supposedly use any cam he feels like using? That's what the article suggests. In other words, you could use a cam that closes the intake valve at 20 degrees and have the same results as another cam that closes the intake valve at 60 degrees. I call BS. If that's your "real world", I call double BS with sprinkles.
 
#20 ·
I see a lot of new cars with 12:1 CR and mazda uses 14:1 for both gas and diesel economy engines.None of those cars are running lumpy cams? BMW has a lot of 11:1 and higher engines.
Maybe tech is not that far off? He uses friendly and conservative numbers.
I like to debate with him.
 
#23 ·
OMG! I feel sorry for the poor car hop girl at the drive in that gets the combo wrong! wrong tomato:cheese ratio with the wrong amount of onion rings.Wont get enough quench with a small rootbeer.Have to watch the compression in order to get the bun at the correct installed height. The roller skate wheels are the wrong diameter causing poorly matched RPM for the distance to the kitchen.
 
#24 ·
anybody have the capability to computer simulate the 355 vs 406 combos? I am curious just how much the theoretical numbers would differ and at what revs the action would happen at. So far only one guy has posted about an actual experience w/ a vortec headed 400.. and honestly its sounding pretty good to me. The rest have just said "no gains" or "less rpms than a 355" or "you need change everything" I need to know what 51 cubes would actually change.. when using MY stuff.. lose 500rpms? 1000 rpms? gain 15lbft? 40lbft? help me out here.

clearly there is some other unfinished off topic business goin on here..
 
#26 ·
anybody have the capability to computer simulate the 355 vs 406 combos? I am curious just how much the theoretical numbers would differ and at what revs the action would happen at. So far only one guy has posted about an actual experience w/ a vortec headed 400.. and honestly its sounding pretty good to me. The rest have just said "no gains" or "less rpms than a 355" or "you need change everything" I need to know what 51 cubes would actually change.. when using MY stuff.. lose 500rpms? 1000 rpms? gain 15lbft? 40lbft? help me out here.
clearly there is some other unfinished off topic business goin on here..
OK, this is just my opinion.
L31 heads, as good as they are, are still heads that were designed by engineers to feed a 350 cubic inch engine up to about 5000 rpm's. 350 cubic inches theoretically passes 506 cfm @5000 rpm's. 400 cubic inches theoretically passes 509 cfm @4400 rpm's. So, you might make the argument that the L31 heads on a 400 are theoretically done at 4400 and could stall at rpm's over that.

I'm aware that other members of this board will suggest that L31 heads will make power to XXXX rpm's and that's fine. I'm just trying to make some sense to the OP.
 
#25 ·
350 vs 400. With the 400, you are looking at an extra 40lb. ft of torque and an extra 40 horsepower, with the same cam as the 350, all of which will occur lower in the RPM range. You can also cam up a step or 2 with the 400 which will handle a larger cam. Peak Hp will be 400-500 rpm lower in the 400. Torque will be good right from idle with the 400. A 350 has to rev up to 2500 to start making good torque. 1 3/4 headers are good for a 400. 1 5/8 headers are probably better suited to a 350 street motor 400 hp or less. 3 in exhaust is a little large. for the 350. 2 1/2 may give better torque on the 350. 3 in exhaust may work fine with the 400.

It is all about hte combination of parts working together. larger exhaust is good for high rpm power - all out racing. smaller headers and exhaust work better for a street driven car. I hope this is helpful.
 
#28 ·
350 vs 400. With the 400, you are looking at an extra 40lb. ft of torque and an extra 40 horsepower, with the same cam as the 350, all of which will occur lower in the RPM range. You can also cam up a step or 2 with the 400 which will handle a larger cam. Peak Hp will be 400-500 rpm lower in the 400.
even if there was zero HP gain, and I gained 40 lbsft at launch rpms... thats worthwhile IMO..
 
#31 · (Edited)
The thing about how new cars w/o a lumpy cam can run higher CR than we can w/sbc carbed engines is mainly because we don't have electronic feed back from sensors to a computer that can retard timing when knock occurs, trim the fuel/air ratio, and change the cam timing just to name a few.

Now that's not to say we cannot use higher than 'normal' compression on a finely tuned engine. But w/only about a 4% (according to prevailing opinion) gain- all else being equal- to be had for each point of CR, I see no reason to run at the ragged edge of detonation. And I don't believe that's what TI is saying to do, either, but I do not presume to speak for him- he can do that just fine w/o my help.

Too much of ANYTHING is not good. Like the medical profession says, "The only difference between a poison and a cure is the dosage." I keep the CR for pump gas engine w/iron heads in the 9.5:1 range and aluminum a point higher, max. BUT- the Vortec (and other) modern fast burn chambers allows more CR w/o detonation than what could be safely used in the older heads. Obviously cam timing matters, as does ignition timing, air/fuel ratio, plug heat range, air inlet temps, engine coolant temps, etc. So there is no ONE right way. ALL the parameters have to be considered.


DCR vs. the real world:

The thing about DCR is (IMO) it DOES try to account for what an engine "sees" in in a running condition. That's the whole reason in calculating DCR in the first place. Now, if DCR used cranking pressure as a datum point, I could see how an argument could be made that it doesn't reflect what a running engine sees, but it doesn't.

DCR is not the end all, do all of engine parameters. But it IS a 'tool in the chest', so to speak. I think the more info the better, at least if that info is able to tell something useful. And DCR has- in the right hands- been shown to do just that.


Vortec heads vs. cam timing:

The following are my opinions.

The L31 Vortec head is probably the most over-cammed head GM has ever produced!

Guys think that because it's said to flow better than the old Bow Tie heads, they can run 240 degrees @ 0.050" duration, no problem. If it were only that easy...

The facts are the heads do not continue to flow well cammed much more than about 0.500" lift and 224 degrees on the intake side. And even there the exhaust is lagging well behind the intake, ratio-wise, and needs help. A split pattern cam will help but the exhaust port actually should be ported to gain the intake to exhaust ratio that's needed. And to use more cam effectively, the head needs help on both sides.

I say to use the Vortec head as-is (with the usual clean-up, valve job/guides, etc, as needed). If more head flow is needed, go to the aftermarket.
 
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