408 stroker engine build

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schultec14

schultec14

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Hi I have an early 1974 dodge 360 engine with original bore with the low compression 8.4:1 dish pistons and rotating assembly.. I have completely redone, unshaved 1971 360 J heads with the 1.88 intake valves and the 1.60 exhaust in it with a set of new, original style rocker assemblies. I have a new edelbrock performer (not rpm style) 360 intake for it. I want to make it a 408 for an every other day driver 1970 dodge dart swinger that will be sort of a sleeper running a stock converter and 2.76 gears. First, I want to know what it takes to make it a 408, what kind of 4" crankshaft I should buy, can I use the stock rods for up to 5500 rpm, what camshaft I can run, and with trying not to touch the heads (shaving) or the block (decking), but boring's ok, what kind of pistions I should get that will get me the most possible compression on today's 92 or 93 octane pump gas with no additives. ( I have 2 sets of stock 1968 340 pistons, and 1 set of '68 340 rods, and 1 5/8" long tube headers to work with also ) Is the intake I have any good for this application? Also what carb size should I use with this application? What horsepower should I expect (rough estimate)?
Please advise!
-ANTHONY
 
Welcome to FABO Anthony!

I am no expert on strokers, but I am learning. Use the search feature and search for strokers. There are more than enough threads to keep you busy and answer some of your questions while you wait for the experts to chime in!
 
schultec14 said:
Hi I have an early 1974 dodge 360 engine with original bore with the low compression 8.4:1 dish pistons and rotating assembly.. I have completely redone, unshaved 1971 360 J heads with the 1.88 intake valves and the 1.60 exhaust in it with a set of new, original style rocker assemblies. I have a new edelbrock performer (not rpm style) 360 intake for it. I want to make it a 408 for an every other day driver 1970 dodge dart swinger that will be sort of a sleeper running a stock converter and 2.76 gears. First, I want to know what it takes to make it a 408, what kind of 4" crankshaft I should buy, can I use the stock rods for up to 5500 rpm, what camshaft I can run, and with trying not to touch the heads (shaving) or the block (decking), but boring's ok, what kind of pistions I should get that will get me the most possible compression on today's 92 or 93 octane pump gas with no additives. ( I have 2 sets of stock 1968 340 pistons, and 1 set of '68 340 rods, and 1 5/8" long tube headers to work with also ) Is the intake I have any good for this application? Also what carb size should I use with this application? What horsepower should I expect (rough estimate)?
Please advise!
-ANTHONY
Click to expand...

I would expect with all the limitations you have that power would be low (375'ish) depending on the cam.
TQ should be great though.
I would use comp's new thumpr cam, works very well and it sounds nasty.
Carb I would use would be a 750DP Holley.
I'm a Scat dealer so that is what I use. 9000 series crank, I beam rods and KB IC745 piston.
 
ou812 said:
I would expect with all the limitations you have that power would be low (375'ish) depending on the cam.
TQ should be great though.
I would use comp's new thumpr cam, works very well and it sounds nasty.
Carb I would use would be a 750DP Holley.
I'm a Scat dealer so that is what I use. 9000 series crank, I beam rods and KB IC745 piston.
Click to expand...

Anthony,

Brian know his $$hitttt...........Listen to what he is telling you and your project will hit the target you intend it to for sure!!
 
ou812 said:
I would expect with all the limitations you have that power would be low (375'ish) depending on the cam.
TQ should be great though.
I would use comp's new thumpr cam, works very well and it sounds nasty.
Carb I would use would be a 750DP Holley.
I'm a Scat dealer so that is what I use. 9000 series crank, I beam rods and KB IC745 piston.
Click to expand...
Is the intake I have one of the limitations? And is there any way I can use the stock 340 pistons in my build? And how much do one of those 9000 cranks cost?
 
yes, your intake is a limtation...it belongs on a 318 not a 408.

you can not use stock 340 pistons in a 408..due to the longer stroke the compression height of the piston must change...the compression height is the center of the wrist pin to the top of the pistons...

the 340 has a CH of 1.84 inches....4 inch stroker pistons are generally around 1.45...

a 340 piston in the stroker would hit the cylinder head....

the scat 9000 is a cast crank .......if you use ebay for pricing they are selling for around 265 bucks....
 
70aarcuda said:
yes, your intake is a limtation...it belongs on a 318 not a 408.

you can not use stock 340 pistons in a 408..due to the longer stroke the compression height of the piston must change...the compression height is the center of the wrist pin to the top of the pistons...

the 340 has a CH of 1.84 inches....4 inch stroker pistons are generally around 1.45...

a 340 piston in the stroker would hit the cylinder head....

the scat 9000 is a cast crank .......if you use ebay for pricing they are selling for around 265 bucks....
Click to expand...

What intake manifold would you suggest? I also have a torker TM5 single plane aluminum intake in the back...
Could I also stick with the stock rods? are they good up to 5500 rpm?
Is there any other piston that you would suggest that runs a little cheaper, and what c/r should I expect with the 72cc j heads and standard head gaskets running the cheaper piston?
Thanks,
-ANTHONY
 
A stroker assembly from me is around 1600.00 balanced with race bearings, I beam rods, cast crank and forged pistons.

If the heads are not going to get any port work, then the rpm intake will work a little bit better but maybe not worth the cost in this case.

You can use stock rods, but by the time you resize them and install good bolts you'll have at least 175.00 in them and they are much much heavier than the Scat I beam rod and the Scat will clear the block much better (less grinding for clearance because of the stroker crank).
 
schultec14 said:
What intake manifold would you suggest? I also have a torker TM5 single plane aluminum intake in the back...
Could I also stick with the stock rods? are they good up to 5500 rpm?
Is there any other piston that you would suggest that runs a little cheaper, and what c/r should I expect with the 72cc j heads and standard head gaskets running the cheaper piston?
Thanks,
-ANTHONY
Click to expand...
Best intake for street duties is the Eddy Air-gap,the TM5 is a single plane and is best for higher RPM,s.
 
ou812 said:
A stroker assembly from me is around 1600.00 balanced with race bearings, I beam rods, cast crank and forged pistons.

If the heads are not going to get any port work, then the rpm intake will work a little bit better but maybe not worth the cost in this case.

You can use stock rods, but by the time you resize them and install good bolts you'll have at least 175.00 in them and they are much much heavier than the Scat I beam rod and the Scat will clear the block much better (less grinding for clearance because of the stroker crank).
Click to expand...
Is there a set of pistons for the 408 stroker engine that are cheaper than $600 that can get me in the range of 9.5-10.0:1 compression ratio with 72cc 360 j heads and stock head gaskets?
 
Not trying to hijack this thread or anything. I've thought about buying a assembled 408 stroker from someone like Summit. Are these engines worth the money?
 
I don't know but we build, dyno and ship engines. Everything we do is custom so nobody gets the same thing...unless a customer wants a build we've done in the past.
It's all about budget vs. power vs. reliability....
 
ou812 said:
I would expect with all the limitations you have that power would be low (375'ish) depending on the cam.
TQ should be great though.
I would use comp's new thumpr cam, works very well and it sounds nasty.
Carb I would use would be a 750DP Holley.
I'm a Scat dealer so that is what I use. 9000 series crank, I beam rods and KB IC745 piston.
Click to expand...
Would you happen to have a link to the KB IC745 pistons? I can not seem to find them. All I could find was a KB 356 piston listing...
Thanks,
-Anthony
 
SRP has a set with a smaller dish... 16cc IIRC that is $560/set too.
 
The Scat stroker kit comes with the KB 745 step dish forged pistons, Scat I-beams, and Scat cast crank along with bearings and rings. You need to have a reputable engine shop balance the rotating assembly. Don't pay to have Scat do it they do a horrible job and when you call and complain they do nothing so don't let them balance.

It makes a lot more sense to buy new Scat I-beams instead of running those stock rods. The Scat rods are lighter, stronger, and you won't have to notch the block for rod bolt clearance. You should have the block line honed and put some ARP main studs in there too.
 
Mopar 408 Magnum
Engine Specs

408 Cubic inches
Bore 4.030
Stroke 4.00 Ohio Crankshaft 4340
Rods Cat 6.123 H-beam
Pistons Probe
Compression 11.5
Cam Comp XFI Lobe HYD roller (236/236 duration at 0.050-inch, 0..576/0.576-inch lift). Heads Edelbrock RPM Magnums Ported
Intake Mopar M1 single plane Ported
Comp 1.6 ratio exhaust roller rockers
Carb 1050 Quick Fuel
DYNO RESULTS Mopar 408 Magnum Stroker SuperFlow 901 Engine Dyno
STP Correction Factor Tested

RPM TORQUE HORSEPOWER
3200 491 299
3400 495 321
3600 496 340
3800 508 368
4000 509 388
4200 517 414
4400 522 438
4600 529 463
4800 532 486
4900 533 497
5000 532 506
5200 528 523
5400 522 537
5600 513 547
5800 501 553
6000 484 553
6100 477 554
6200 468 552
 
Your original post said you plan to run 2.76 gears and a stock converter. In that case I would probably not run a 750DP carb. You'll be much happier with vacuum secondaries, or an AFB style carb (Edelbrock).
 
C130 Chief said:
Your original post said you plan to run 2.76 gears and a stock converter. In that case I would probably not run a 750DP carb. You'll be much happier with vacuum secondaries, or an AFB style carb (Edelbrock).
Click to expand...
Ok, then I'll start looking around for one of these carbs.
Thanks!
 
I have a 68, 340 block that will be stroked. The best source for stroking small blocks arew contained in a book by a Chrysler engineer. The things that instantly come to mind are the limitations of the small block HP at approximately 420HP before longevity is comprimised. Richard Ehrnberg of Mopar Action also expresses this concern and a friend gernaded a 500 HP 340, so your application appears approtiate. Eill try to find the book title and post here.
 
G. G. LEVERETTE said:
I have a 68, 340 block that will be stroked. The best source for stroking small blocks arew contained in a book by a Chrysler engineer. The things that instantly come to mind are the limitations of the small block HP at approximately 420HP before longevity is comprimised. Richard Ehrnberg of Mopar Action also expresses this concern and a friend gernaded a 500 HP 340, so your application appears approtiate. Eill try to find the book title and post here.
Click to expand...

I guess my 560Hp 360 is out to lunch...LOL!!
I've been running it for 5 years and I can tell you it's the most reliable engine I've had to date.
Took it apart to inspect things and it was a waste...so I changed the cam and carb for more HP and put it back in.
Made 560HP on my DTS and runs 10.50's in my 3350lb. duster (w/me).

Biggest problems are the oil pump inlet, or I should say pickup tube and making sure the pressure side is 1/2 and port the main cap area some.
Once you open the inlet of the oil pump to 3/4 you eliminate all oiling issues.
It's actually ridiculous how easy it is to upgrade the sb oiling system!!
 
You said that you didn't want to deck the block but would bore it. The cost to deck block is minimal once it's cleaned and at machine shop. Decide what compression ratio you want for the heads and deck to zero deck height or something close. Spend the money on block and the base of engine and save on intake and parts that can be upgraded easily later.
If you use your existing heads with bigger chamber go with lower CR and then you could change heads with smalller chamber later and get higher CR. I have a 360/408 that made 520 hp with 10.5 CR and runs on pump gas 91 octane. It idles well and has great torque. Makes peak HP at 6000 rpm. Cast crank should live at 6500 rpm and lower. or with liss than 500 HP. Good luck with decisions.
 
G. G. LEVERETTE said:
I have a 68, 340 block that will be stroked. The best source for stroking small blocks arew contained in a book by a Chrysler engineer. The things that instantly come to mind are the limitations of the small block HP at approximately 420HP before longevity is comprimised. Richard Ehrnberg of Mopar Action also expresses this concern and a friend gernaded a 500 HP 340, so your application appears approtiate. Eill try to find the book title and post here.
Click to expand...

420 hp is it for a stock block? Wow! I'll have to tell my buddy with the 590 hp 408 (stock block) he runs at the track every weekend.

GG don't believe everything you read. Especially in the magazines. I have read some of the stupidest stuff in magazines.

BTW: How did your friend's 340 grenade? Was it block failure? If so that's the first time I've heard of one.
 
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