390 vs 408

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.060 360 =372cid
390/391cid 18 cube diff

Big bore with short/er stroke=hp/tq with emphasis on hp.

big arm with lil bore=mostly torque think 225 slant 6 but without the cubic handy cap.

built the same while compensating @.050 dur for the cid increase on the 390 and both having cid matched port volumes, the cid will reflect the power.

If just built the same, the 390 should make close if not more but at a lower rpm.jmo

But there too many variables.
 
If you put real pistons in it (meaning forged, not the hypers) then the cost for the 390 is a little more as not everyone has a piston for it. Otherwise, same same. If you have the 318, use it. It's prob cheaper than finding something near you bigger. There will be more bore shrouding, and I agree it's around 6-8% loss in all lift ranges as a result. Only you can decide if that's acceptable. I had plans to build one for my plow truck but that changed. I think it's a great potential engine. But eventually when looking for max power the bore size will limit things.
 
I'm doing a 408 now because i found a 5.9 magnum motor for $250. If i were i would do the 390 due to you already have the block. no need to spend more money on a different block that could be junk. Plus if you want that extra little hp then put some nitrous on it for the track.
 
Be a real ***** if you ended up with a 600$ 360 block that needs tons of work too...........

I have asked this before, and no one can tell me......

HOW much does .060 bore size difference make with valve shrouding? Is there any documented numbers?

Dare I say anything? Well here I go....

I have to agree with the bore shrouding.But it can be alleviated by notching the bores beside the valves.

Cubic inches doesnt always win.A well built 470 stroker will spank bigger 500+ inch motors all day long. Just depends on how much your willing to do/spend.IMHO this has something to do with the 400 blocks large bore and humble 3.92 stroke.

The driveability/street manners of the bigger motor will likely be better.
 
Wow! This turned out a bit hotter than i thought! Calm down people!
I have gotten a lot of help from this thread though! Thanks for that!
More opinions will absolutely not hurt, and hey, I think the 318 that's in the car is pretty fast :cheers: but I have an undying urge to build crazy engines and go fast :snakeman:. At this point, having read the whole thread I'm actually leaning towards a 390.

But hey! Anyone else?
 
.060 360 =372cid
390/391cid 18 cube diff

Big bore with short/er stroke=hp/tq with emphasis on hp.

big arm with lil bore=mostly torque think 225 slant 6 but without the cubic handy cap.

built the same while compensating @.050 dur for the cid increase on the 390 and both having cid matched port volumes, the cid will reflect the power.

If just built the same, the 390 should make close if not more but at a lower rpm.jmo

But there too many variables.

Justin....... *this has taken a lot out of me to ask this, hey, I am growing... LOL*

What are the chances of you having a set of heads, and access to a flow bench, to see the difference between a 3.94 bore and a 4" bore? I have always heard 4%, 10%, 10HP per .010......... It would be nice to actually have some numbers. Not to mention I would think the bigger thebore, the smaller the difference would be...... in other words, the difference between 3.91 to 3.94 would be greater than say 3.94 to 3.98......

Just a thought.
 
Just for kicks I was playing with areas of circles and assuming a lot it looks like about 8% more area is shrouded witht he 3.91 vs the 4.04 (340) bore using the 2.02 valve. I would think by getting less generalized that percentage will go up rather than down but that's just a guess. You could clearnace or notch the bore... but really, you are minimizing the shrouding. Not stopping it. The only way to stop it is to keep the walls away from the flow path IE hemis.
 
I find that the small bore of the 318 might have an advantage over a 408. This smaller area is capable of holding fuel and air molecules together, tighter, therefore increasing flame propagation and flame speed, increasing in cylinder temperatures, all this helps make more power and economy as more fuel is burned during the process. A head with a good combustion chamber and engine tune would be necessary to take advantage of this scenario. This can also help decrease the chance of detonation.
 
Dodgeketboy -

Firstly - I think you might want to look at Nemesis 1st post with less arrogance and more intelligence - - he is a BIG supporter of 318s, as I am.

YOU started the p1ssing contest, , and he was not "having a go" at your engine - in fact he was trying to help the thread starter - YOUR behaviour was pretty childish however.

Now -

Really? I don't know any 390 besides mine. And I know about big heads, the next 390 I built bill be X heads........


Maybe theres a language problem here? But just so you don't die completely "pig ignorant", I'll explain that i was also not "having a go" at your engine choice!

FWIW - My comment re- the attitude towards suitable cylinder heads comes from our experience in Australia, where most guys have run or built a 318 (because 360a cost $$$)

It stands to reason that because most guys only know small cube V8s, they assume they can get away with factory 360 heads on a bigger cube stroker.

.....and when they realise they can't, they go "cold" and build a 360 instead.

In fact it was Moper on this forum that set me straight on why a stroker needs a lot of attention to induction and head flow.

So - to be clear - I'm not saying everyone down here gets it wrong - but the reason 390s aren't popular is because it's common for 318 guys (Like me) to overlook the BIG difference in $$$ between std stroke engines and stroker induction.
 
Dodgeketboy -

Firstly - I think you might want to look at Nemesis 1st post with less arrogance and more intelligence - - he is a BIG supporter of 318s, as I am.

His first post questioned the speed my truck ran in the 1/4, then added a "so what", my stock 318 does that.......


YOU started the p1ssing contest, , and he was not "having a go" at your engine - in fact he was trying to help the thread starter - YOUR behaviour was pretty childish however.

O, ya, I always say peoples engines are not putting out the power they have the potential too. Which, BTW, is complete BS, my motor puts out the power it was intended and has the potential too.......

Maybe theres a language problem here? But just so you don't die completely "pig ignorant", I'll explain that i was also not "having a go" at your engine choice!

Quit picking a sentence out and Read the whole thing, and no, you weren't "having a go", you got it, but hey, if you think I am pig ignorant........ (Couldn't be further from the truth.)

FWIW - My comment re- the attitude towards suitable cylinder heads comes from our experience in Australia, where most guys have run or built a 318 (because 360a cost $$$)

It stands to reason that because most guys only know small cube V8s, they assume they can get away with factory 360 heads on a bigger cube stroker.

.....and when they realise they can't, they go "cold" and build a 360 instead.

In fact it was Moper on this forum that set me straight on why a stroker needs a lot of attention to induction and head flow.

So - to be clear - I'm not saying everyone down here gets it wrong - but the reason 390s aren't popular is because it's common for 318 guys (Like me) to overlook the BIG difference in $$$ between std stroke engines and stroker induction.

I agree, but lets stand back for a second. What HARM do small port heads, or stock 360 heads, do to a stroker?
Less than a non stroker, here's why.

There is a point, where the piston is starting it's stroke, and stopping it's stroke, in a stroker, the area where the piston is traveling at full speed, is longer and faster. Therefore, you have more chance of making power out of less head with a stroker, and also more of a chance to make power, and low end torque out of a bigger cam, because the piston speed it higher. I am not the best at explaining things, so I hope this makes sense. The reason why the power band on MY 390 is so high, but yet it has small heads, and tons of low end torque, is from the velocity of the air ramming itself into the cylinders long after the piston is don'e moving. (overlap) IMO The small port heads, and single plane manifold help this.

Like I said, he has a 318, why not stroke it? My 390, in a A body, would be flat fun, and feel way fast, spin tire, with minimal throttle, AND get good MPG. And be way snappier than a 360.
 
DBoy - Alright mate - I apologise for the "pig ignorant" comment - but you did come out swinging for NO reason -

Its a communication thing - Here's the quote -

Thats right Potential.... It doesnt make the hp,but has the potential TO make it.
My 318 is dead stock,aside from cam an carb pretty much
an does a mid 14.

The way I read it - He was agreeing that 318s had GOOD potential to make HP - his quote on his qtr times was supporting the 318's potential.............. not comparing it to anyone elses!

When you get that straight, everything else will fall into place, so i won't bother grinding through the p1ssing contest.

Re small heads on a stroker - I understand that a stroker will make more from less - but in the end, you want more from your heads with a SB stroker.
 
Man, you ASSUMED i added a ' so what'....
I never said it!!!!!!
If i wanted to make fun of peoples motors,id be on a CHEVY forum.
NOT a mopar one..

I think were all on here to HELP each OTHER go FASTER right?
If not,then wtf are we doing?

I know that you built your 390 for its intended purposes,an it
does its job well right?
Then thats all there is to it!
If your happy with it,who cares!
I was taking away ANYTHING from your car/motor at all!

I just wanted an insight to it.
An it was clearly built 1st an foremost to tow heavy sh** !

So just chill already an get northern swede well on hes
way on building that 390!
Hurry up an do it swede so this thread ends lol.
 
that is whay my next guild is 318 030 diamond pistons scat ibeam rods and mopar cast 4 inch crank eddey heads crower solid cam air gap intake and 750 hp carb for a little street/strip action.Bradley
 
Haha not going to happen soon ;D When summer comes though! Anyone who can give me some hints on what stock heads to use, I have a set of pre-magnum 360 on the 318 now, how well will they do if ported? How 'bout a crank? Which one? I'm not one who uses top of the line stuff when it's not needed so I want something that will hold up to about 500 horses but hey, no reason for it to be built for 1000... What pistons? I'm going forged, just to be on the safe side, you can never spend to much on pistons, I learned that the hard way. Help, help help =D You are great! Thanks for all the answers, just amazing!
 
almost all 340/360 heads flow the same. cept' for the X-head. doubt you'll find one of those for under $1000. i would
suggest using the "302" cylinder head. clean the bowls, port match it, and put in some 2.02"/1.60 valves. you'll love it.
pistons as you said, go the the best you can afford. cast cranks are good for about 550 donkeypower or 500 hp
whichever way you wanna look at it. ONCE you decided what you really want, build it like anyother normal 318.
PS
no need to champher the intake side of the bore with the 302 head.
PSS
dodgetkboy78 had some pretty good advice.
 
i will sell ya a set of x heads for 500 bucks....LOL
 
almost all 340/360 heads flow the same. cept' for the X-head. doubt you'll find one of those for under $1000. i would
suggest using the "302" cylinder head. clean the bowls, port match it, and put in some 2.02"/1.60 valves. you'll love it.
pistons as you said, go the the best you can afford. cast cranks are good for about 550 donkeypower or 500 hp
whichever way you wanna look at it. ONCE you decided what you really want, build it like anyother normal 318.
PS
no need to champher the intake side of the bore with the 302 head.
PSS
dodgetkboy78 had some pretty good advice.

you are saying that x heads dont sell for less then 1000.00....

i have a prefectly good set that i will sell YOU for 1/2 that....and they are not cracked....in fact a stock elminator friend was wanting them....but hell...i can get a better price from you...
 
obviously you missed the j/k (JUST JOKING) part. the $1000 was for HIS PART OF THE WORLD.
but yah.. if you wanna sell me your set for $500. where do i send the money order too?
 
dodgetkboy78 had some pretty good advice.

What, you mean like ...

Ergh........

LOL!!!

Anyhow, back on topic........


i would
suggest using the "302" cylinder head. clean the bowls, port match it, and put in some 2.02"/1.60 valves. you'll love it.

So 360Z28, do you reckon those 302s will flow enough to feed a swept area of 390 cui? Sorry to sound like I doubt you, but I do!! LOL!

Reason? - Ive been told by experienced people on this board that 200 cfm which is about what you'd get at .500 from a set of 302s will never feed that size engine well enough and I'd be leaving plenty of HP on the table.

If you disagree, I'd like to hear why? ...it might get some discussion happening.

NorhernSwede- FWIW I'm getting a 390 built currently - its specs are:

KB 847 flat tops
Eagle crank and rods,
Comp 282S cam 245/250 @.50
360 cast heads that flow 243 @.550 (2.02 valves)
Compression will be about 10.2:1

FWIW - I pumped the head flow and cam figs into Dyno 2000 and it came up with 425 Crank HP at 5500 rpm

Camquest came up with 445 which is probably a bit high.

Reality is, the only thing "318" about most 390s is the block!

I'll be sure an let the whole board know how it runs ;)
 
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