318 to 390 stroker

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dieselman966

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I figured I would start another thread for the stroker build for our 78 w200 build. I'd put it over on one of the truck forums but there doesnt seem to be much activity on them.


I'll try to keep this thread more about the engine and any issues we run into while building it.

Basically we are stroking the stock 318 to a 390 and adding some of these heads
Mopar Edelbrock LA Aluminum Cylinder Heads
Along with probably a pretty healthy cam What ever that ends up being. Were planning on a pretty big stall converter now too. Probably 3000 rpm higher


Just trying to make this easy to search for people maybe considering doing a similar build. Were kicking around the idea of getting a 408 ci short block from blueprint engines also. We see what we decide to do here.
 
Thinking about the same thing myself. I have a pair of Speedmaster aluminum heads and a roller cam 318 block. Subscribed.
 
I think the money best spent would be the short block from blueprint engines. The other thread I have someone posted a link to the thread of of it. $2799 I believe they said for the 408 ci engine.
 
I'm doing one using a Magnum 5.2L block for my '99 Dakota R/T. Using a SCAT crank and I-beam rods, ICON forged dished pistons, Indy RHS 2.02 heads, M1 2bbl intake, 53mm TB and a VooDoo hyd. roller cam (219/227*@.050", 112*LSA, .550" lift). I'm hoping to peak around 5000rpm with gobs of torque from 2000+rpm. I have a bigger cam that would probably work fine, but I want good driveability and that thing is HEAVY (ext. cab)!!!
 
PS: I also have a flat-top Diamond .040" forged piston set that I'd like to do a flat-tappet 392" setup with aluminum heads with, for a carb'd setup someday.
 
We have the machine work done on the 318 finally. The builder is wondering how high we want to go with the compression ratio. He is suggesting keeping it around 9.6 to 1 with the dishes pistons. Were wondering if we should push it over 10 to 1 while were at it?
 
I have also started thinking of a 318 magnum stroker, I have a new 4 inch stroker crank that I was going to use in a 340 but ended up staying with a stock stroke for that build.
I was thinking that a 318 magnum block is at least $500 cheaper than a 340 block...plus the 318 magnum is a roller cam block
 
What cam are you considering? Ultimately, what you care about is dynamic compression ratio to be low enough to stay away from detonation, not static CR, and the cam plus the static CR sets that. You have a heavy vehicle, so more care is typically needed for DCR.

You mention high stall and big cam so your DCR will tend to be lower with the big cam and you ought to push up the static CR as a consequence to avoid excess loss of low RPM torque. But that also depends on the use; the high stall TC hints that this is not a farm truck LOL. So what is the planned use and operation of this truck/engine?
 
nm9stheham said:
What cam are you considering? Ultimately, what you care about is dynamic compression ratio to be low enough to stay away from detonation, not static CR, and the cam plus the static CR sets that. You have a heavy vehicle, so more care is typically needed for DCR.

You mention high stall and big cam so your DCR will tend to be lower with the big cam and you ought to push up the static CR as a consequence to avoid excess loss of low RPM torque. But that also depends on the use; the high stall TC hints that this is not a farm truck LOL. So what is the planned use and operation of this truck/engine?
Click to expand...

Intended use for the truck is a very spirited cruiser. There might be some truck pulling and drag racing being done with it also. He doesnt really care how the street manners are as long as it's not completely ridiculous.

I guess the idea is that he's spending the money and if we can see a significant improvement by bumping up the compression ratio and running a bigger cam to get an overall better running truck when he gets on it is it worth it? Otherwise well probably just go with a milder cam and stick with the static of 9.6 or so.
 
From how you describe the potential uses, then it seems clear that you want a bigger cam and that leads to a higher compression ratio to avoid the low RPM range from getting too soft and being 'completely ridiculous'.

The stroke is helping the low RPM end, but IMHO, might as well select parts based on solid principles. And stroking tends to limit high RPM range, so IMHO you shouldn't sactifice a lot of the low RPM range, like you could more easily get away with in a higher revving, shorter stroke motor.

I'll let others step in and comment on the flow of those heads in a 4" stoker application, which are gonna be the main source of top end RPM limitations. Once there is a handle on that, then the lower RPM range ought to be set based on having a decently wide RPM range, and that will drive cam selection, which will finally drive the static CR selection. Clear as mud huh? LOL

Is the plan to use pump fuel?
 
Yes pump fuel is the plan. We have a few places close to us with non ethanol 91 gas. E85 is pretty prevalent around us also but I'm not sure we will go down that road.

Yes this is all clear as mud lol.
 
91 minus it a bit. At 10-1, I would think you would be OK.
I’ll need a correction from the BTDT crowd.
 
Right NM
no use going to a bigger cam than the heads can use throughout the intended range
you loose on the bottom and don't gain on the top
speaking of the to
the higher compression does not help the top more than a few percent
great in a heads up class but a PITA on a street/strip build
It helps mostlylower and mid range as AJ has said so many times
So pick the rpm range you want to run and build the motor to match
otherwise you end up having to match you use to the motor- tail wagging the dog
10:1 should be ok unless it costs a lot to get there
otherwise a REAL 9.2 can make an amazing broad power curve
 
I'll take a stab.... Sounds like the owner will not mind keeping the RPM's up, what with the 3000 RPM stall TC.... 'making a statement' and all that every time the throttle is applied LOL. No real consideration for fuel mileage. And since there is consideration for truck pulling etc. (sustained high RPM's), and since we are stroking, some cam like a 290-295* advertised w/ 245* or 250* @ .050" seems like a decent place to start. (I'll guess that the heads will be a bit limiting at the top end for this cam.... but that is just a guess. And this is based on an HFT cam specs; translation to a SFT cam specs would be another step.)

With that, and a .039" thick Felpro 1008 head gasket, 108 LSA and 106 ICL, then a 10.5 static CR would give a dynamic CR of 8.0 with that kind of cam. Should be tunable for 91 pump fuel.

With that, the cam can be increased if desired and not drop the DCR too much at all. A step smaller cam would be partially accommodated by going to a thicker head gasket plus careful tuning of timing.

That leads to a piston that has a 10-15 cc dish + eyebrows....but then the usual issue with 318's arises: limited piston selection. I've looked and mostly you have flat tops (too high for CR with the range of cam) and dishtops at 23 cc dish+ eyebrow size. The only thing close to the 10-15 cc range is the Diamond 50010 set, at 16.7 dish + eyebrows.

Using those, you could:
  • Mill the LA block about .020" to get the pistons flush to the deck
  • Mil the heads about .020" to get the chamber size down to 60 cc's
  • Use the Felpro 1008 head gasket
Now you are at 10.2 for static CR, and 7.8 for dynamic CR with the proposed cam durations. You could still move the cam size up/down 1-2 notches and not get out of control for CR, etc.
 
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Yeah there isn't a lot of piston choices for the 318. He has some from diamonds that have a 16cc dish and with the PIE 62cc heads it should be at 9.6 to 1. Kind of sounded like it would cost quite a bit more to go higher in compression.
 
KB Icon has flat top and dished pistons available....not much available...

I have a set of the Icon dished pistons for my 390 if I ever get around to assemble it....have complete balanced rotating assembling waiting...
 
I didn't see anything from KB that is a 3.94 bore piston. There was a kit out there that had some option for stroker kits but the next jump up for compression from the 9.6 is 11.7. That seems like to much of a jump. I'll talk to the engine builder monday and see what he has to say. NM I'll look into the came you suggested.
 
dieselman966 said:
Yeah there isn't a lot of piston choices for the 318. He has some from diamonds that have a 16cc dish and with the PIE 62cc heads it should be at 9.6 to 1. Kind of sounded like it would cost quite a bit more to go higher in compression.
Click to expand...


Icon makes a nice piston for that.
 
The Icon's have 2 choices... where I went 1st. 5 and 23 cc dish+eyebrow volume is quite a spread as noted. I looked into SRP, JE, Wiseco, and DSS. For the rather high cost of the Diamonds (around $800 from Campbell !), you could get some custom pistons made.

Or perhaps mill out some shallow dishes in some of the Icon flat-tops with the same or less $$ versus milling heads and block. A .060" deep dish will add 4-5 cc's; the piston crowns would have to be checked before doing this but I suspect they are thick enough for that amount of milling. You'd end up with the 10.5-ish static CR range, right where you want to be. That might be the simplest solution

As far as the cam, again, it should be chosen with your use, the stroker app, and heads in mind. I am just making what I hope is a good guess. You could look at the cams used in 340 and 360 4" stroker builds to see what has been used; 390 to 408 to 416 will all share the same basic characteristics.
 
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