NC Engine Builder
Grumpy Old Man
- Joined
- Oct 10, 2008
- Messages
- 7,248
- Reaction score
- 12,264
I have built a handful of them, they work fine, yeah the bigger bore of the 360 and 340 is better, but in a mild street build it doesn't matter.
Thoughts on a 390 cu in. stroker from a 318?
- Thread starter volaredon
- Start date
-
I agree. 318s have always been total workhorses. They're like Rodney Dangerfield. They don't get no respect. I've always liked um.
Cool. So is stroker 360 an option or just stock stroke 360? Do you have crankshafts for either motor?
3forty
"Raw Power"
RRR likes to be in control!
I’m pretty sure you know I’m not anti 318, but to me we’re not talking about 318’s a 390 isn’t a 318 anymore, your stated goal was low end torque aka displacement, to me we’re talking 365 vs 390 vs 408, a 365 can make decent low end but if more is needed/wanted than a 390 gonna make about 30 tq more and for similar price 408 will make 50 tq more than a 365, obviously there could be other factors but for the dollar per lbs-ft the 408 would be the wiser move. But if you chose 390 or even a 323 that’s up to you and I’ll try my best to help with whatever choice is made.
Hardly.
I don't think that the hp or torque increase just based on displacement increase alone is accurate. If we're talking same EVERYTHING else between one CID and another.. carb intake cam heads ignition EVERYTHING then maybe... But stroke it then that means bigger cam, different carb, may head work you wouldn't have "wasted time on" on a stocker and that's all out the window
If you're going to be using stock magnum heads with upgraded valve springs and typical air gap intake, then a 318 magnum stroker will be plenty. Perfect or your build description. Just send your cam to Oregon and have Ken give you a recommendation. Stock 318 magnum hydraulide rollers usually have a W-I-D-E LSA and very low lift, so the core can make a mild idle torque brute with adequate .050 duration and decent lift.
Hp ain’t overly connected to displacement but torque is, a decent built street engine gonna make around 1.15-1.25 lbs-ft per cid depending on the build so say 1.2tq:cid, that’s around 365/438tq 390/468tq and 408/490tq give or take some lbs-ft’s.
If you would build each engine vastly different from one another that’s up to you. But I don’t see the need especially for a mild truck engine.
Last edited:
Check your numbers.
Is a 360 stroker on the table then?
Without knowing the heads and thinking they’re going to somewhat stock magnums heads, a .030 over 318 with a four inch crank here is PLENTY enough for towing and whatever else you’re intending on doing with it. Hopefully it’s got a Power-lock Dana rear under it. Club cab W-150 with 3.90 gear and 35 inch tires. 391 inch stroked 318 backed an NV4500 gas transmission. This the 11.4:1 Eddy head/comp 274XE variant, but a 9:1 junk gas build with a mild torquey cam would blow the rear tires away at will.
This is 2wd 3/4 ton. It will be an nv4500 behind the engine, and I have a (currently) "open" Dana 60/3.55 in place at the moment...
Yeah looking towards using stock magnum heads possibly cleaned up a bit. I have 2 used/verified uncracked and 1, NOS bare stock magnum head on hand at the moment...
And if I build a stock based 360 vs a 390 vs a 408 all with same heads same cam etc only difference is bore x stroke and all other parts the same, CR same between them and everything else, the difference in torque is that consistent?
Another consideration everyone talks about "small bore this, bigger bore that"
I remember (I think it was) the show "engine master," where they compared same (or really "close") CID engines but with different combinations of bore : stroke but I don't remember the outcome.
My son has a 408 in his ramcharger and I'm sorry I'm not impressed. It's a 1976 360, EQ heads 0.030 over I honestly don't know what cam etc... Even he says it doesn't run as strong as he would have expected...
Back to a stock motor for a minute,
IDK if I've mentioned it here in this thread , but my biggest complaint about the 360 has been that Mopar castrated every one I have seen with low comp and dished pistons, plus too little cam. And of those that I've been inside of for some reason most 360s have seemed to have been more likely to be "sludge monsters" than the 318s I've worked on, especially when talking the LAs...
Yeah looking towards using stock magnum heads possibly cleaned up a bit. I have 2 used/verified uncracked and 1, NOS bare stock magnum head on hand at the moment...
And if I build a stock based 360 vs a 390 vs a 408 all with same heads same cam etc only difference is bore x stroke and all other parts the same, CR same between them and everything else, the difference in torque is that consistent?
Another consideration everyone talks about "small bore this, bigger bore that"
I remember (I think it was) the show "engine master," where they compared same (or really "close") CID engines but with different combinations of bore : stroke but I don't remember the outcome.
My son has a 408 in his ramcharger and I'm sorry I'm not impressed. It's a 1976 360, EQ heads 0.030 over I honestly don't know what cam etc... Even he says it doesn't run as strong as he would have expected...
Back to a stock motor for a minute,
IDK if I've mentioned it here in this thread , but my biggest complaint about the 360 has been that Mopar castrated every one I have seen with low comp and dished pistons, plus too little cam. And of those that I've been inside of for some reason most 360s have seemed to have been more likely to be "sludge monsters" than the 318s I've worked on, especially when talking the LAs...
Last edited:
If it's going in a truck, a longer stroke than the bore is big (under square) makes for a really torquey truck motor.
4" stroke and a 3.910 bore, right? That's a big difference. That added .090" to the stroke instead of making the bore 4" is adding 74 cubes.
I'd run a stock stroke, pick the engine with the least wear and go with that. Have one of the cams reground and talk to a cam grinder. It is that simple and cheap.
I would never stroke a 318" personally do to the bore size.
To make power in a normally aspirated engine you need room (bore) for the valves to be able move air freely.
I've sold 390" kits, but it would be a far better engine using a larger bore 360/340 block.
Plus you'll then have a 408", or 416". However, having more room for the valves is far more important to me than the extra cubic inches.
Tom
To make power in a normally aspirated engine you need room (bore) for the valves to be able move air freely.
I've sold 390" kits, but it would be a far better engine using a larger bore 360/340 block.
Plus you'll then have a 408", or 416". However, having more room for the valves is far more important to me than the extra cubic inches.
Tom
Doesn't mean all 3 would make the exact same torque to Cid ratio but should be fairly close to each other, making the difference in torque somewhat consistent between the displacements. Obviously the 408 should peak at lower rpms than the 390 than the 360.
In my opinion if all you intend to use is a set of stock magnum heads there is no way I would spend the money to stroke any engine.
If you want a little more go in a truck just put a warmed up 360 in and call it a day.
To gain 30 or 40 extra cubics for the cost is just not reasonable justification for a pickup truck engine in my book.
A good OEM 360 roller block with a reground cam and a good intake will get you a lot of improvement over a 318 for very little cost.
To step up to a stroker will add another $3000 to $3500 to the equation. Not a very good bang for buck in my world for that application.
Tom
If you want a little more go in a truck just put a warmed up 360 in and call it a day.
To gain 30 or 40 extra cubics for the cost is just not reasonable justification for a pickup truck engine in my book.
A good OEM 360 roller block with a reground cam and a good intake will get you a lot of improvement over a 318 for very little cost.
To step up to a stroker will add another $3000 to $3500 to the equation. Not a very good bang for buck in my world for that application.
Tom
I agree to a point.
It sure makes sense to use a roller block if you can find one. The roller LA or Magnum is a great way around flat tappet cam and lifter troubles.
I have an LA 318 and 360 that I may never use.
Then use a 5.2 Magnum.
Yeah, That would be smart.
Wiping out cams really sucks. The factory switchover to roller camshafts makes building a flat tappet LA much less desirable.
Wiping out cams really sucks. The factory switchover to roller camshafts makes building a flat tappet LA much less desirable.
-
Similar threads
