408/360 question

-
dartkory

dartkory

Well-Known Member
Joined
Nov 22, 2007
Messages
301
Reaction score
3
Location
Portland Oregon
So I've been doing a lot of thinking and I might just bite the bullet and do a 408 build but I just had a few concerns but my main one; is can I just simply take a 360 block (obviously after being bored and shop prepped) and drop in a 408 rotating assembly? I know the basics to building but will the extra stroke require any grinding of the bottom of the piston bores? Because if that's the case I'd be willing just to do a nice 360 build but the 408 kit is internally balanced so I can use my 318 flex plate, stall, and harmonic balancer. So I was wondering if any of you know of a company that sells internally balanced stock stroke 360 cranks? Thanks for any help -kory
 
Your answer is yes you can do that though I'd suggest a new balancer a d order it up after the over ore is done. Leave the block at the machinists and let him check it out and final fit it unless your capable of such work.

Start at Summitracing.com
 
dartkory said:
So I've been doing a lot of thinking and I might just bite the bullet and do a 408 build but I just had a few concerns but my main one; is can I just simply take a 360 block (obviously after being bored and shop prepped) and drop in a 408 rotating assembly? I know the basics to building but will the extra stroke require any grinding of the bottom of the piston bores? Because if that's the case I'd be willing just to do a nice 360 build but the 408 kit is internally balanced so I can use my 318 flex plate, stall, and harmonic balancer. So I was wondering if any of you know of a company that sells internally balanced stock stroke 360 cranks? Thanks for any help -kory
Click to expand...

grinding at the bottom of the bores with a stroker will depend on connecting rod choosen,,,scat 4340 I beams or any other I beam rod does not required grinding....a stock rod or H beam rod will require a small notch at the bottom of the bores to clear the rod bolts..

Eagle and Scat both make a forged steel 360 crank...make it for both 360 mains or 340 mains...but like anyother crank, the rotating assembly must be balanced....

I have a scat forged crank in a 408 and it still took 2 slugs of mallory metal to balance it internally...
 
Ok thanks for the replies. I had read in a how to build a small block stroker book for mopars that you would need to drill extra oil holes which didn't make too much sense. Did any of you have to do that?
 
my cast scat took 314.00 of mallory not sure how many slugs that is
 
extra oil holes? maybe in the front oil galley plug to lubricate the chain....i did not drill any extra holes except in the oil filter mounting plate and in the mentioned plug.

I´ve got a scat cast crank assembly with the mentioned I-beam rods - went in with absolutely no problems, no grinding necessary. It´s easy to do, take your time, check the clearances and clean everything twice.

your other question: scat sells 360 cranks for internal balance, check their website.

Michael
 
What kind of hp are you getting 360duster with your scat assembly? I have edelbrock rpm heads and dougs headers I'll be using so I hope it gets at least 425 hp. Is that a pretty reasonable estimation?
 
I think that 425hp is an easy to do goal @ 400+ inch's.
 
I don´t know, no dyno time and no full quarter mile run up til now.

I expect the engine in the 450 hp / 450 ft/lbs range, checked a lot of builds and it seems my components should do this too, proper tuned (still working on that ;)). It feels really strong with power everywhere up to 6000 - my personal rev limit.

Specs: 360 LA roller cam block .030" over; scat 4" cast crank / i beam / hyper-u-piston (KB356) assembly, internally balanced; RHS X-Heads from IMM Engines, 10:1 compression; XR286HR cam 236°/242°@.050", around .540" lift. Performer rpm intake, 750 cfm EDE (for now, will change to 750DP).

I think with the EDE Heads you should reach your goal 425 HP, pretty reasonable to me.

Michael
 
My cast 4" Scat crank with I-beams and Icon flat tops balanced internally with no heavy metal. This is a 318/390 so maybe that swung it for me.
 
dartkory said:
So I've been doing a lot of thinking and I might just bite the bullet and do a 408 build but I just had a few concerns but my main one; is can I just simply take a 360 block (obviously after being bored and shop prepped) and drop in a 408 rotating assembly? I know the basics to building but will the extra stroke require any grinding of the bottom of the piston bores? Because if that's the case I'd be willing just to do a nice 360 build but the 408 kit is internally balanced so I can use my 318 flex plate, stall, and harmonic balancer. So I was wondering if any of you know of a company that sells internally balanced stock stroke 360 cranks? Thanks for any help -kory
Click to expand...

Yes. My 408 is a bored and stroked 92 360 magnum block. I push just over 500hp out of it. You would do well to get a good stall if you don't have one already. Here is what I run:

1992 magnum block
scat 4" stroke crank
Scat forged i-beam rods
Diamond flat top pistons (11.8:1 compression)
total seal rings
Engine Pro main, rod, Cam bearings
Fluid damper
cloyes double roller timing set
Cometic head gaskets
Edelbrock performer rpm heads (gasket matched w/ light porting)
Smith bros pushrods
Comp 1.5 ratio shaft mount billet roller rockers
comp hydraulic roller lifters
Comp Cam
242/248 Dur@ .050, .3660/.3630 lift @ .050, 112° lobe sep. 549/544 gross valve lift
Comp valve springs, retainers, keepers, locators
ARP head studs
ARP bolts used throughout
melling hv oil pump
Edelbrock RPM Air Gap intake
MSD Pro Billet distributor
bronze dist gear
Taylor wires and looms
New ngk plugs
Holley 750dp mech secondary manual choke
Mopar MSD 6 Ignition box
Blaster2 Coil
Adjustable rev limiter

It is a beast and it will never get good mileage. Original dyno was 498 peak hp and 528 ft/lb torque. I have done a little to it and figure it is low 500's now.

I love this car and every time I get on it all I can think is "Holy ****! This thing is fast!"

So .... do it. You will never regret it.
 
Damn that's a bad *** build! I saw you have those total seal rings, do those require to be filed at all? Or do they come ready to roll?
 
MoparAnglia said:
My cast 4" Scat crank with I-beams and Icon flat tops balanced internally with no heavy metal. This is a 318/390 so maybe that swung it for me.
Click to expand...

that is correct ...the 318/390 combo with scat I beams will internally balance with cast crank due to the pistons being lighter...
 
408 will work good in your car, lots of torque! I've had a 318, 360 and 408 in my car which is very similar to yours. You can build a 408 to 450 hp and it will be very streetable. Your stock motor mounts will not hold up, and drag radials will be the only way it will hook on the street. The Dougs headers are great but for a 408 I like bigger primary tubes like tti's.
360 or 408, it will run good, mine ran 12.50's with the 360 and 11.80's with the 408.
 
I always thought the 360 would be much cheaper to build but no matter how I add it up they're both about the same. Going the 360 route I can save a few hundred bucks but at that I might as well do the 408! I always kinda wanted to try the 392 out of the 318 since I already have it ready to go but does anyone know the hp difference between the 392 and 408? And would the 392 get more hp than the 360? I know the 392 might have more cubes but the 360 has a bigger bore! Decisions decisions!
 
The 390/318c.i can produce upward of 500hp with the right heads/cam/carb.The 390 will have a longer stroke due to the 4 inch crank over the 360,s 3.58 crank.I run a 408 .040 over(410ci) with ported Eddy heads,M1 intake,850dp,.631 lift solid roller cam/lifters/rockers.I first bought the Dougs headers(1 5/8)but after having head work done I bought the Hedman Husler 1 7/8 fenderwells(TTI didn,t make the 1 3/4 step hedders yet)My 66 Dart was used double duty street/strip,but decided to just use it for racing(I like my licence LOL)I,m guessing I,m in the 525-540hp range,car runs mid to high 10,s and I,m now going transbrake.Should work well with the Dana.Build the 408 you won,t regret it.JMO
View attachment 340 dyno 4.JPG
 
When I built my stroker, my Eagle steel crank, Scat I-beams, and Diamond pistons didn't need any heavy metal to balance it. Lite pistons are good for soooo many reasons (in conjunction with lite rods). With careful planning, you should be able to build a stroker for close to the same money as building a 360 (assuming you were going to have to buy a rotating assembly either way).
 
dartkory said:
Damn that's a bad *** build! I saw you have those total seal rings, do those require to be filed at all? Or do they come ready to roll?
Click to expand...

Ready to roll. And, since I went to overdrive at the same time, I drive this thing everywhere when the weather is nice. I put 7400 miles on it last summer. The only time the rpm gets over 2800 is when the tires are smoking or when I am blowing some Mustang away. It's funny, the ones that want to race me the most are Mustangs and Subaru WRX's. I am 31-0 against all Mustangs, but the newer supercharged are so close it's scary. You might even say I'm 30-0-1, but I'm sure my chrome bumper was ahead of his molded one. WRX get beaten by blocks, and then I slow down and they blow by me at 130 like they win. Sorry dude, you already lost!
 
My Scat 4" steel crank, Scat H-beams, & Probe flat tops took no Mallory to balance internally!
 
I run pump gas most of the time at 26 degrees timing, but it costs power. I get the itch and tune it up to 38 degrees and run 110 octane race gas. Night and day difference. I have been talking about E85 for a long time. I need to pull the trigger on it before spring. Then I can run tuned up all the time.
 
What do you think is the max compression I could run (keeping in mind I have the aluminum heads) while being able to still run pump gas?
 
Mopar to ya said:
I have been talking about E85 for a long time. I need to pull the trigger on it before spring. Then I can run tuned up all the time.
Click to expand...

I have an E85 station right up the street from my house and have been contemplating the same thing for my stroker. I have read quite a bit on the subject and unfortunately it's not in my budget right now.
 
I have almost 12:1 and I run pump gas most of the time. The issue is, you spend all that money building the motor, you hate to hamstring it with pump gas. It is kind of nice to have the choice. I have been talking with Rob Mix about his E85 carbs. If interested, check out this site. http://www.e85carbs.com/ 105 octane out of the pump. And cheaper. It requires 30% more fuel, however. I have a Clay Smith high volume fuel pump and am going to run 10 AN from the tank to the pump. I already have 8 AN to the fuel rail. Gotta buy that carb! I live in a small town, but it five gas stations, four of which have E85.
 
You must log in or register to reply here.
-

Back
Top