360 Magnum / stroker build question

[eholster]

In a different thread I had posed the question of 340 vs. 360 with lots of input. I was thrilled to find a Magnum 360 for sale locally, listed as complete from a running vehicle - picked it up on Saturday afternoon and tore into it that evening only to find... missing a piston and a crack between the valves on the same cylinder. ARRGGGHHH:angry7: I was tempted to call the seller at 10:30 p.m. when I discovered this but figured that wouldn't be conducive to getting my money back. Fortunately, in the morning when I explained to him what I found he told me to bring the motor back for a refund. Upstanding guy - thanks M. in Lynnwood. So, the search is on again...
Since I didn't get any response when I posted this in my 340 vs 360 post, I thought I'd try it here. This is in regard to building a 408 stroker -

Thanks all, for your replies. Didn't mean to leave the thread hanging with all the input and no response... Busy with the day job, night job (15 y.o. daughter - lot's of overtime!) and had a work related trip to Central America...
But - I did manage to find a 360 Magnum local for a fair price. I went through and re-read the posts here and now have a bit to consider - the motor is a completer runner, with almost all ancillaries included. This means if I want to I can retain the fuel injection. I also ordered a couple of the "How to..." books - Larry Shepard's How to Hot Rod SB Mopar Motors and Jim Szilagyi's How to Build Big Inch Mopar SB, the latter of which is very informative. In particular I found his recipes on 6 different engine packages interesting. Anyone here have any experience with his 'recipes'? I am specifically interested in the Magnum Muscle Car 408 build from J. Szilagyi, as the motor I'm buying is the basic core for what is laid out. For those who haven't seen the breakdown, here it is -

4.030 bore / 4.000 stroke
block - Magnum 5.9l
Crank - Forged Mopar #P5007254 - internally balanced
Damper - stock 318 w/ neutral balance
Rods - Eagle SIR
Pistons/Rings - Diamond #51405, Speed pro moly
Oil pan and pump - Moroso deep sump # 20730, p/u #24700, Mopar #P4286589
Cam - Hyd roller cam - Mopar #P4876348 230/234 dur. @ .050, .0501/.513 lift, 108 deg. centerline
Tappets - Hyd. roller - included w/ cam
Pushrods - Stock Magnum
Rocker Arms - Stock Magnum
Cylinder Heads - Mopar Magnum R/T - Big Valve #P5007141 w/ porting done
Intake - Mopar M1 Single PLane #P5007380
Carb - Holley 750 cfm
Ignition - Mopar #P3690426
Ign. timing - 35 deg.


The claim is that it will make 505HP @ 5900 and 525 ft-lb @ 3800. Seems impressive... Realistic??

I'm going to price out parts to stroke it. I already have a pretty good idea of the bill at the machine shop. Then there's the whole transmission component to determine...

Another day.

Any input??

Thanks guys.

 

[dodgetkboy78]

Howdy Ed!

Sounds good to me.

Sheepherders recipes are pretty vague and outdated, IMO. Never read big inch, so I couldn't say......

retaining the mpi is possible, but a programmed puter and bigger injectors are needed to feed the stroker.

 

[eholster]

Erin, not Ed!! Didn't we go through this once before? Oh, the recipe was from Jim Szilagyi's book...

 

[dodgetkboy78]

Yes, we did, me and Frank determined you were special!

 

[eholster]

Yes, we did, me and Frank determined you were special!

Ahh, yes... it was Frank the first time.

Special??

 

[moper]

Something to remember is ther are a lot of MP part numbers that are backordered, and there are non-MP parts that IMO will do a better job. Otherwise it's a good build and a decent book to buy.
Just out of curiousity... I'm assuming the piston broke and that's why you say it's missing... Is the bore ok, and how big are the peices?

 

[dodgetkboy78]

The motor he has now isn't the one with the broken piston, if I read it right.

 

[eholster]

The first motor I bought was missing a piston and had a cracked head. The bore that was minus a piston was scored real bad all down both sides from the wrist pin... seller took it back. Presently I don't have another Magnum motor, but plan to go up north of where I live this week to look at a '98 Magnum, runner, for $400... I will give a report.

 

[dodgetkboy78]

You are buying new Mopar heads, right? So the head cracking issue isn't a big deal at all.

Are you serious about retaining the MOPAR MPI? I have done that, a few times, be why's I'm asking.

 

[airwoofer]

That damn cat has to go!

As for that build, 500+ HP at only 5900 RPM with a 750 Holley? Sounds optimistic.

BTW, I am in the planning stages of building a stroker from an old 71 360 block myself.

 

[eholster]

You are buying new Mopar heads, right? So the head cracking issue isn't a big deal at all.

Are you serious about retaining the MOPAR MPI? I have done that, a few times, be why's I'm asking.

I will likely replace with Edelbrock or RHS heads. Not too serious about the MPI... I like the simplicity of the carb set up. Am open to input on that, though. It sounds like the motor I am looking at this week has everything but the ECU, so I could go either way.

 

[moper]

Thanks. The reason I was asking was all the bullshit others were giving me about saying the hyper pistons "exploded"...lol. You saw exactly what I have on another dodge, 3 Chevies, and 5 4.6L mod motor mustangs. The piston fails and basically there are few large chunks left.

Back on topic... If the bores were solid and it sonic tested well, then you could have sleeved that one bore pretty inexpensively. In terms of stroker engine bores, thicker is better. The Magnum blocks seem to be cast fairly well.

 

[eholster]

Thanks. The reason I was asking was all the bullshit others were giving me about saying the hyper pistons "exploded"...lol. You saw exactly what I have on another dodge, 3 Chevies, and 5 4.6L mod motor mustangs. The piston fails and basically there are few large chunks left.

Back on topic... If the bores were solid and it sonic tested well, then you could have sleeved that one bore pretty inexpensively. In terms of stroker engine bores, thicker is better. The Magnum blocks seem to be cast fairly well.

With the bad head and the missing piston / scored barrel I wasn't about to put much more time/energy/$$$ (paid $300) into it as the seller had billed it as a runner...
Which is what I'm going to look at this week. At $400 it sounds like it may have a not more going for it. One thing that I could use some input on is - the seller said the motor was mated to a manual trans. and the output shaft is different for a automatic... if I order a new crank I need to specify a manual or auto, correct? I have read Mancini offers an adapter...
Thanks!

 

[moper]

No, I agree, unless you got it free, it's not worth your time. There are millions of Magnum engines out there so I wouldnt feel obligated to use one that's not good already. I also like to see them running in the vehicle if possible. Then you know the fluids aren't mixing and there's nothing major bad with it without having to check everything closely. On the cranks... They all come drilled for the pilot bushing. That's the difference between them. There is no "manual" or "automatic" carnks in the aftermarket 4" stuff. Least none I've ever seen.

 

[dodgetkboy78]

Thanks. The reason I was asking was all the bullshit others were giving me about saying the hyper pistons "exploded"...lol. You saw exactly what I have on another dodge, 3 Chevies, and 5 4.6L mod motor mustangs. The piston fails and basically there are few large chunks left.

I'm right there with ya'.... But they are so popular, people turn a blind eye and run them.


Eholster.....

The MPI is easier than you think, however, without a core for the re-programmed PCM, it would cost more than a nice 4bbl Carter/Holley based performance carb of your choice.

 

[eholster]

Just bought another Magnum motor - unbelievable... another cracked head!!! Fortunately it has all the pistons this time...
I called the PO after I pulled them and he is giving some of the payment back. Nice guy, he even drove down from Redmond to deliver and is driving down to give some of the money back. I guess in the end I'll probably go with the some aftermarket heads anyway...

 

[AdamR]

You probably will never find a magnum head that isnt cracked.

 

[moper]

They all have cracked heads. Sometimes it does not affect performance at all. But you will ALWAYS find cracks in the heads.

 

[eholster]

They all have cracked heads. Sometimes it does not affect performance at all. But you will ALWAYS find cracks in the heads.

And always right between the valves, at the narrowest point?

 

[moper]

Yeah. I'm told it's a combination of the heat treat, base material, and not enough material there. Not all cracks go to the coolant jaackets, some never will reach it. But a crack is a weak point regardless. That was the main reason for the Engine Quest replacement heads. They have a much thicker area between the valves (thickness, not distance)