390 vs 408

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NorthernSwede

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Hi!

I'm having troubles deciding wheter to build a 408 or a 390 I will bring some thoughts and hope you can help me choose!

Pros and cons for the 390

+ Already have the 318
- Less cui

Pros and cons for the 408

+ More cui
- Engine will cost me approx 600USD (I live in Sweden)
+ Cheaper pistons

Other important things to have in mind

I want to keep as mild gears and stall converters as possible

It's a daily driver

A 727 will be parked behind together with a 8.75

It will be driven hard

Fuel economy isn't a top priority but it will be driven a MINIMUM of 60kilometers per day so the more mpg the better. And above all, reliability!

It's a '66 Dodge Dart

Questions

How much power difference will those 18cui make?

Will the 600 USD it'll cost to buy the 360 even the cost out? Or will one or the other be cheaper/more expensive? Oh and the goal is approx 500 horse at the crank

Any good suggestions on parts? I'm 18 and no millionare so it's in a budget but I'm here to teach those plastic and turbo-loving guys and gals that nothing beats cubic inch!

Is the 500hp@crank possible while maintaining idle and mild gears?

I'd rather have torque than horses, what will make those ftlbs show themselves?


Anyway! Best regards! You guys at FABO are the best!
 
The difference in the 18 Cubes isn't going to be that much of a deal, it's the shrouding of the smaller cylinder bore. I would say, you will be maybe 20HP less?

Pro's of a 390?

IMO, less piston surface=less chance of detonation.
You have the 318 already=you know the block is good
I believe, and always have believed the 318 block is stronger than the 360. Say what you will, I have never had a major 318 failure (except for my first go around, a set of KB pistons for my 390, I love my ROSS pistons...), and LOTS of 360 failures. Fluke or fact, thats my OPNION.
I have over 40K on a 390, runs at WOT a ton, and has been flawless as far as internals after the KB's........ I love my 390.

I also have experienced better MPG's with smaller bore engines.

I think the 600 will be more than enough for the little more you will spend on pistons, and the peace of mind knowing you started with an engine that you are familiar with.

My 390, is built for 3500RPM, WOT power. It even has ported small port 302 heads. It is a truck motor, so I keep it on the low RPM, it will zing past 5k, and build power too. It get 12-17mpg, in a dually pickup, with 4:10's.

Pulls the hills better than the 413 dually I used to have, for sure.

Pro's of a 408?
Well........

A little more breathing, a little more cubes, and you can say, "408"..........
 
97.3

3700 pounds, 4:10's

Crappy hookup.

Did a 14.92 with the built 318...... LOL

ran a 14.12 real nice to the throttle, but I only did three runs.
 
Build the 408.. better yet,you can build a stock stroke 360 that will out run stroked318's no problem..my stock stroke 360 has put my '70 duster in the 11.70's...all motor!!!
 
stroked 340 said:
Build the 408.. better yet,you can build a stock stroke 360 that will out run stroked318's no problem..my stock stroke 360 has put my '70 duster in the 11.70's...all motor!!!
Click to expand...

and what is your bases for that ?

everything being equal i would bet on the 390......over the stock stroke 360
 
It may be easier in your case to stroke the 318,with an overbore its not far off a 4in. bore and you already have the block.The main benefit of the 4in. arm is torque anyway and you will not lose anything significant going from a 3.940 to a 4.030 bore size.You can make an average mopar head flow extremely well with a chevy 1.94 intake-or for that matter a 1.88,it really comes down to whats easiest for you to obtain and cost.Either engine built similarly would run similarly-not apples and oranges.
 
There is a 500 Crank HP 390 down here - runs 11.9s -

Frankly I'm having trouble working out why 18 cubes and a minor bore size difference would suddenly make a 408 soooooo much faster than a 390?

Not saying there won't be a difference, but its in the heads that the differences will show.

:rant on: - I think the real issue is, guys who build 390s come from a 318 base point - they still haven't got their heads around the need for big breathing heads!

- Maybe likewise, the 408 guys are already running bigger heads from their stock 360 days and so its less of an "issue" for them? :rantoff:

Either way - The big "must" with any stroker is the heads - you need port volume if you want to MPH.

Remember, DodgetKboy's engine is built for torque, not MPH, so don't judge potential HP on his build - as his is a stump puller! (No disrespect intended) .
 
Moparmal said:
There is a 500 Crank HP 390 down here - runs 11.9s -

Frankly I'm having trouble working out why 18 cubes and a minor bore size difference would suddenly make a 408 soooooo much faster than a 390?

Not saying there won't be a difference, but its in the heads that the differences will show.

:rant on: - I think the real issue is, guys who build 390s come from a 318 base point - they still haven't got their heads around the need for big breathing heads!

- Maybe likewise, the 408 guys are already running bigger heads from their stock 360 days and so its less of an "issue" for them? :rantoff:

Either way - The big "must" with any stroker is the heads - you need port volume if you want to MPH.

Remember, DodgetKboy's engine is built for torque, not MPH, so don't judge potential HP on his build - as his is a stump puller! (No disrespect intended) .
Click to expand...

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.

Anyhow,
I think 18 cubes isnt much to fuss about,
Usually go by a horse per cc.
18 extra cubes, 18 more horses or there abouts
IF 2 builds are the exact same an only difference
is cubes. An obviously more torque in the 408.
But wouldnt be by much....
 
Build the 408.. better yet,you can build a stock stroke 360 that will out run stroked318's no problem..my stock stroke 360 has put my '70 duster in the 11.70's...all motor!!!
Click to expand...

I had a 318 that ran 11.50's all day... Your point is...........


Frankly I'm having trouble working out why 18 cubes and a minor bore size difference would suddenly make a 408 soooooo much faster than a 390?
Click to expand...

It's a cubic inch thing, a simple jet size being off can make a bigger difference than the power capability.

:rant on: - I think the real issue is, guys who build 390s come from a 318 base point - they still haven't got their heads around the need for big breathing heads!
Click to expand...

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

Remember, DodgetKboy's engine is built for torque, not MPH, so don't judge potential HP on his build - as his is a stump puller! (No disrespect intended) .
Click to expand...

True, every intent was to pull trailers........... But, put it in a A body and see what it will do.

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.
Click to expand...

YOUR 318 isn't in a one paddle box shape dually pickup with steel rims, stock low stall converter, and a front to back weight ratio of 70/30. And if you wanted to start in a race, sayyy, from 30mph?

Seeee yaaaaa..........
 
Clearly your offended...

No mine isnt,its an aus charger,
mines manual but has 3.23 not 4.1's like yours.

I didnt tell you my mph,so what makes you think
youl be seeing me?
Im not fussed, or scared to say you have the faster car!

You should put it in a abody ;)
 
stroked 340 said:
How much were you spraying??...if not i'll bet you had a lot more in that 318 then it takes for a 360 to run that fast in the SAME car..
Click to expand...

Your right, because it was a 318, is would always be slower than a 360! Just like my mild 440 will always be faster than wild and crazy's 408! And yeah, I had a lot in it, but your cubic inch logic is flawed.....


Clearly your offended...

No mine isnt,its an aus charger,
mines manual but has 3.23 not 4.1's like yours.

I didnt tell you my mph,so what makes you think
youl be seeing me?
Im not fussed, or scared to say you have the faster car!

You should put it in a abody :wink:
Click to expand...

Well, no, I could really care less, and considering torque is what gets the ball rolling, it is a pretty safe bet that it will twist your 318 backwards... Just trying to make a comparison of torque........ From the line, I don't have enough traction to do nothing but spin. ergh, never mind.

And yes, the project car, will have a 390, big port heads, roller, it will be nice. But for now, I have lots of other things to do.








The only reason I even posted in this dick wagging thread was because I ACTUALLY HAVE A RUNNING 390 sitting right outside my door, that I can go start up and drive....no speculatio, no guessing, it's under the hood of my truck. Want a pic? Wanna hear it run?....... 390's are rare, I guess. Pickin it apart saying it isn't up to it's full power potentioal, ect, is completely ignorant. It is 100% perfect for doing what it was intended to do. To pull three of your VG chargers on a trailer up a hill.......
 
dodgetkboy78 said:
Your right, because it was a 318, is would always be slower than a 360! Just like my mild 440 will always be faster than wild and crazy's 408! And yeah, I had a lot in it, but your cubic inch logic is flawed.....




Well, no, I could really care less, and considering torque is what gets the ball rolling, it is a pretty safe bet that it will twist your 318 backwards... Just trying to make a comparison of torque........ From the line, I don't have enough traction to do nothing but spin. ergh, never mind.

And yes, the project car, will have a 390, big port heads, roller, it will be nice. But for now, I have lots of other things to do.








The only reason I even posted in this dick wagging thread was because I ACTUALLY HAVE A RUNNING 390 sitting right outside my door, that I can go start up and drive....no speculatio, no guessing, it's under the hood of my truck. Want a pic? Wanna hear it run?....... 390's are rare, I guess. Pickin it apart saying it isn't up to it's full power potentioal, ect, is completely ignorant. It is 100% perfect for doing what it was intended to do. To pull three of your VG chargers on a trailer up a hill.......
Click to expand...

Your being a real goose about this you know.

I cbf arguing with you ,mr 318 twister!
Good for you!

An its not called a vg charger....

Anyhow,not
fussed, i own something that will leave you so far behind at a set
of lights youl think someone has hit the PAUSE button on
your LIFE.
I didnt wanna brag but oh well,
now i just did :thebirdm:

Easy on the moon juice redneck an chill.
I wasnt even giving you OR your car crap
til now!
 
You bet that 390 is rare,most people don't even bother dumping big money into 318's...mild 440 no problem for a 360 built right,never mind what a 416 could do to it..you see i actually RACE my car so i know EXACTELY what the 360 and 416 run,no speculations here..only timeslips to prove it..:-D:-D
 
I think that this is getting a little personal. I would like to chime in and I hope that i dont offend anyone. I think, and this is just my opinion based on experience, that the 318s smaller bore may hamper cylinder head flow. The 360s cylinder bore is .090 bigger and in cylinder heads mind its a big jump. 18 cubic inches is not a big difference. It depends on what your trying to do. The truck motor spoken of previously is a good example of a 390s advantages. A 408 would be a better street/strip motor. When the bore crowds the intake valve in the combustion chamber it does hurt flow quite a bit. When a small block gets bigger the need for a better head, whether its built for low rpm torque or high rpm hp, grows exponentially. I like the low buck idea of the 390 and I think the debate of which motor, 360 vs 390, would make more power would only be settled with a dyno. I would put my money on the 360 with all things being equal. There are millions of 318s out there and can be had for pennies, why not make em into tire schredding machines! I say go for it.
 
i guess unless someone will spend the money and build a 390 vs 360 both being equal ..

so all we have is our opinions.....
 
stroked 340 said:
You bet that 390 is rare,most people don't even bother dumping big money into 318's...mild 440 no problem for a 360 built right,never mind what a 416 could do to it..you see i actually RACE my car so i know EXACTELY what the 360 and 416 run,no speculations here..only timeslips to prove it..:-D:-D
Click to expand...

:stop:


You guys need to READ the original post......... Your starting to sound like a bunch of chevy guys.

Again, the ONLY reason I even posted here, in this thread, was because I ACTUALLY HAVE A 390! AND not only do I ACTUALLY HAVE A 390, it is BUILT FOR A REAL CLOSE TO WHAT HE IS WANTING......

READ.......


I'm having troubles deciding wheter to build a 408 or a 390 I will bring some thoughts and hope you can help me choose!

Pros and cons for the 390

+ Already have the 318
- Less cui

Pros and cons for the 408

+ More cui
- Engine will cost me approx 600USD (I live in Sweden)
+ Cheaper pistons

Other important things to have in mind

I want to keep as mild gears and stall converters as possible

It's a daily driver

A 727 will be parked behind together with a 8.75

It will be driven hard

Fuel economy isn't a top priority but it will be driven a MINIMUM of 60kilometers per day so the more mpg the better. And above all, reliability!

It's a '66 Dodge Dart

Questions

How much power difference will those 18cui make?

Will the 600 USD it'll cost to buy the 360 even the cost out? Or will one or the other be cheaper/more expensive? Oh and the goal is approx 500 horse at the crank

Any good suggestions on parts? I'm 18 and no millionare so it's in a budget but I'm here to teach those plastic and turbo-loving guys and gals that nothing beats cubic inch!

Is the 500hp@crank possible while maintaining idle and mild gears?

I'd rather have torque than horses, what will make those ftlbs show themselves?
Click to expand...

OK, hopefully you read that......



I think that this is getting a little personal.
Click to expand...

Every time I bring up a small port head, stroked 318, it gets personal. SOME people don't understand that there is a BIG DIFFERENCE between MAX POWER OUTPUT, and what someone wants. Every argument against the 390 I am aware of too, but, HE HAS A 318 ALREADY. I built mine with MPG in mind, the smaller bore does do better MPG wise, and the closed chamber small port heads help with MPG, and low end torque, not to mention the small bore and closed chamber heads help with detonation, something that I am worried about considering the engine run WOT for longer than any of your cars, way longer, minutes and minutes at times. In his case, big port heads would be better, since he doesn't need the 2.5K and down torque like I do.

And for the street, the 4" stroke of the 390 will offset the valve shrouding. Hands down.

READ his post. And remember, I HAVE a 390........... :munky2:
 
My opinion for whatever it is worth.Maybe not much to some people.I just sold my '70 Challenger I built a Hughes 390 stroker motor with the Magnum heads and loved it. If you build the 408 you will get a little more power.Depending on what you are driving now you might be perfectly happy with the 390. I had 3.55 gears in mine then when i went on road trip i used hwy gears and with the torque the stroker puts out either will still keep a smile on your face.
 
Like someone else said the 340/360 bore will un shroud the intake valve and help the engine breath a little better. The difference in cubic inches is not really that big a deal. But if the original poster is over seas, on a budget, and already has a good 318 block I think he would be happy to build a 390. Now if he has money to burn by all means pick up a 360 block and get the advantage of the larger bore.
 
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?
 
I dont think there is any documented numbers. I do have experience flowing heads on a flow bench. Let me give you a little background. When someone flows a head on a flow bench, we use a bore plate that simulates the bore in an engine. Lets take a big block chevy for instance. Typical 454 bore is 4.280 and when heads are flowed for advertisement purposes they flow them with a 4.500 bore. Now I know that it is a .220" difference but its a good illistration. There is typically a 10% difference between the 2. I know that when I flowed my edelbrock RPMs on a bench they flowed 220 cfm, well below what they advertise. That was with a 4.030 bore. I figure Edelbrock flows them with a 4.100 bore which is .070 bigger and their numbers come in at 250 cfm. This is just speculation on my part and I have not confirmed this with Edelbrock. So if you take the cfm results and times them by 2 to get a theoretical hp potential for a given engine, I would lose out on 60 hp. 60 hp is a lot to lose to a smaller bore. I know that some of the guys here are running 390's and they are getting quite defensive about it. I have never said a 318 is a boat anchor, as a matter of fact I have support you guys and I believe that your 390s run hard! So please just take this as an information source for our friend across the pond can take into consideration for his personal car. All cars are different and our expectations are different so everyone needs to find a combo that they like. I have read every word that is on this thread and it doesnt change what I am saying or my opinion and this is just what it is, an opinion. Go back and read my posts and it may change how you feel.
 
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