From 318 to 390 Stroker

[Mecki]

Does anyone have any experience of this conversion ?

I was thinking of a low $ build for a 318 C body. Don't really need so much more power, but some added torque would be nice. I know that the stroker pistons are about $600, a cast 4" stroke crank is about $300 and has to be balanced, but over here a 360 is very expensive. I will soon have to do something to my -68 Fury and was thinking if this would be worth to do.

Cast crank and stock rods will limit the revs, but reving is not the goal. How would this work with stock 318 heads (pre -75) with small valves and even with a 2 bbl? Would 1.88 and 1.60 valves make any difference in 318 heads, together with a small 4 bbl and headers?

Would be interesting to hear how much better torque could be expected without harming the high way mpg too much?

Thanks!

[TrashedCharger]

318 heads work okay for a 318 displacement, but you will be choking your engine with those heads if you build any more cubic displacement, through stroke or otherwise.

With a 600cfm 4bbl and headers, into 2 1/2" dual exhaust with a good electronic ignition distributor and aftermarket ignition control, your car will be pulling about all that it can from those heads.

Most guys that hotrod 318's end up going with aluminum closed chamber aftermarket heads.

I don't know if the magnum 318 heads are any better than a standard LA 318 head for flow, but someone here might know.

The problem with going with a 360 head on a 318 is that they are too open to gain anything in performance from their added flow capability over a 318 head.

You will see a significant improvement with even a 340 cam and a 4 barrel with dual exhaust in that car.

A friend of mine is building a '67 and has plenty of torque to get it moving.

If shipping weren't so expensive, or if you were willing to pay crate shipping, I could get you into a 360 for cheap.

[thatwasfunny]

I haven't tried 318 stroked 390 yet but liked the idea of ported 1.88 1.60- 360
heads on one.
Correct piston dome shape would be very beneficial with open chamber and could help a little I think with what trashedcharger is saying.

[Mecki]

Hey Trashed!

I was playing with the Comp Cam's Cam Quest program with the different options and came to something like what you are saying here. Upgrading to 4 bbl and headers/dual exhaust would probably give a lot even with the stock heads. I don't know if there is any point to put in bigger valves other than if they have to be replaced anyway. I have already had one valve job done to these heads and it sounds like it's time again. New heads are no option, way too pricey and I really don't know if a low rev engine would need so much better flow. I can't rev it anyway with stock rods and the goal is to keep good high way mileage with low rear axle ratio.

I must say, that a 390 long stroke sounds more interesting than a 360 and the fact that I already have it makes it a good option. Looks like this engine could produce easily 450-500 ft lb and 250-280 hp below 4500 rpm. That's a huge torque increase for a 318.

Those Xtreme Energy grinds seems to be fitting torque engines very well. Any experiences?

[Mecki]

Originally Posted by thatwasfunny

I haven't tried 318 stroked 390 yet but liked the idea of ported 1.88 1.60- 360
heads on one.
Correct piston dome shape would be very beneficial with open chamber and could help a little I think with what trashedcharger is saying.

Would the 318 port flow gain anything from bigger, 1.88 1.60, valves? Without extensive porting (too expensive), just blending the valve job?

The pistons available for this build are only flat top or dished. Early 318 closed chamber heads could be an option, but it could result in too much compression trying to build a quench motor with that long stroke. Have to check that out. So far I have just calculated with a rough estimate of 9.5-10:1 to see how it works.

[TrashedCharger]

The problem really isn't compression, even with the closed chamber '67 318 heads.

My friends '67 318 has those heads on it and it runs quite well with the 600cfm edelbrock AFB, the 340 cam and dual 2 1/4" exhaust through 360 manifolds.

It's just that if you stroke the 318, you will need more flow than what those heads are capable of doing.

This is why most people who build 318's go with an aluminum head that has a closed chamber and more flow.

[Mecki]

I can see the problem. But is the head/port really the first restriction. Should not headers and intake already help a lot, as it does on a stock 318? As long as the revs are below 4500, mostly 2000-3000, does the port need to flow so much more. A good cam should also help. I realize that I will kill the upper end, but where would the limit approximately be and would it really be a total death?

[TrashedCharger]

You are going to notice restriction issues across the entire span of RPM ranges, because you have to figure that your piston on a stroked crankshaft is moving up and down further in the cylinder, no matter the RPM.

The added stroke simply needs more flow to run at any RPM without restriction.

The only way I could see getting around the restriction coming from the intake is if you boosted the engine, but then you are throwing more gasses into the chamber and those gasses will expand even more when combusted, and will need to exit through a less restrictive exhaust valve port and exhaust system.

A 4bbl intake manifold and less restrictive exhaust will help the existing system out, but it will only flow as much as the piston size and stroke can push through that head at any rpm.

If a 360 can't handle a 318 head and needs a better flowing head, you can imagine how a 390 stroker would react to a 318 head.

Your best bet is to go with the highest lift and duration camshaft that you can for the RPM and flow limits of a 318 head and tune the rest of your engine, torque converter stall and rear gears from there.

[Mecki]

Originally Posted by TrashedCharger

If a 360 can't handle a 318 head and needs a better flowing head, you can imagine how a 390 stroker would react to a 318 head.

Good point. Seems that there is no easy (cheap) way around this.

[440roadrunner]

A stock 360 (even over there) is that much more that all that expensive engine work? I'm amazed.

I'm also continuously amazed at the amount of U.S. iron that's found it's way overseas. Just incredible.

Good luck to ya.

[70AARCuda]

Actually, if you get a set of I beam rods such as Scat that weight in at 595 grams, plus the KB pistons are down in the low 400 grams which sell around $355.00 dollars, the balancing should be pretty simple.

[Mecki]

Originally Posted by 440roadrunner

A stock 360 (even over there) is that much more that all that expensive engine work? I'm amazed.

I'm also continuously amazed at the amount of U.S. iron that's found it's way overseas. Just incredible.

Good luck to ya.

Most of the 360 are in running cars here, many 318 have been replaced with 360. So 318 can be found in almost every garage cheap (I have a couple in original cars and one on the floor), but 360 engines are not lying around. An available 360 is most probably shipped from a US scrap yard (add shipping and dealer profit to the US price) and needs the same or maybe more work.

I was just thinking that if I have a 318 which needs to be bored, crank grinded, new cam and a valve job, why not do the stroker? The heads are the problem and i don't see the point to invest big $ in a high flow set. SB heads are surprisingly pricey. Same goes for rods. It's better to go BB instead of 360 then.

The torque produced with 4" stroke is still interesting, even if the power would not increase. That's why I'm asking if anyone has any experience with a 390 stroker with 318 heads and stock rods.

[valiant64]

318/390 in a C-body (4k + lbs.), highway gears & mileage? The money spent to build this engine would be better off spent on a near stock 400 engine. Plenty of torque to move the car, and high revving enough to make good hp. These engines are still relatively plentiful & cheap in most bone yards since many pull them to replace with the 440. However, since many of these are being built into low-deck strokers these days they may get harder to find. Still, even a 383 would be a better choice than the stroked 318 for this combo.

[owatajrkiam]

Now,..if you can find a set of magnum heads over there and throw them on that 390,...now were talkin'!!!!

Glen

[valiant64]

Something about a smaller engine having to work harder to propel the mass of a C-body still comes to mind. And the amount of $ and effort to make it capable of doing so when a stock big block can do it easier & for less $....

[thatwasfunny]

I think the stock 360 rods or mid-late 70's 318[same as 360]rods would hold up fine w/4inch stroke 6000 rpm and below especially with 430+/-gram piston.
You can go 318 1.88 1.60 heads but as someone else said it's not enough flow to get the power easily had with 390 inches +360 ports 1.88 1.60 .

[TrashedCharger]

My friends 318 driven fury has plenty of torque and power with the 4bbl, 360 truck manifolds into 2 1/4" exhaust with a 340 cam.

He did the exhaust first, but when he went away from the stromberg 2bbl, to the edelbrock setup, it was quite noticably louder and had a lot more power range in RPM.

Then, when he had the closed chamber heads redone and installed the 340 cam, it pulled a lot more torque.

His car was running a 17.70 deadly consistantly at the track at 6,000ft of elevation. I know of A bodies that don't run those numbers with a 318 4bbl.

He was staged against a Pontiac Grand Prix with a stock 455 and beat him, bracketted, but they both dialed a 17.70 and he still ran him!

The problem with going to a stock 400 over a modded 318 is that you do have the capability to make more power with the 400, but if you are going to leave it stock, you end up with a car that makes more power, but weighs significantly more in the front, so it's a wash... Except that you get worse gas milage, the car handles worse and parts are more expensive.

I don't see any benefit in going to a smaller cid big block over a modded small block in a C body. If you are going to go big, go with a relatively stock 440.

The 383 2bbl cars are actually slower than the 318 cars. I know that for a fact.

[Mecki]

If I had a pair of 360 heads, or some one would just give them to me for almost free, then it would be a clear case. But that's the limit for what I would do. Anything more and I would take a BB instead

The money spent on a 390 build - compared to rebuilding a 318? Crank journals ready to go - saved grinding cost. More expensive pistons - difference about $200-300. Totally $400-5oo more in the short block - 70 cubes more.

As I said earlier, I'm not looking for power and the rotating assembly will certainly limit the revs, but such difference in stroke should make a huge difference in the torque characteristics even with very restricted heads. There are other engines with extremely long stroke and tiny valves running just great.

I'm not saying that I will make this build, but it would be interesting to see how radical the change would be, 4" is .25" more than BB. That's why I'm hoping to get some real facts and figures, if some one has actually tried this. A theoretical analysis would also be appreciated.

Thanks!

[Mecki]

Originally Posted by TrashedCharger

The problem with going to a stock 400 over a modded 318 is that you do have the capability to make more power with the 400, but if you are going to leave it stock, you end up with a car that makes more power, but weighs significantly more in the front, so it's a wash... Except that you get worse gas milage, the car handles worse and parts are more expensive.

I don't see any benefit in going to a smaller cid big block over a modded small block in a C body. If you are going to go big, go with a relatively stock 440.

The 383 2bbl cars are actually slower than the 318 cars. I know that for a fact.

I agree, I have been able to get enough speeding tickets with my 318 2 bbl Fury and the noticeable difference to a similar 383 2 bbl is the added weight on the front wheels - worse handling. And the gas mileage of course.

That was mainly the idea: more low end torque even if upper end suffers and keep it light and cheap.

[TrashedCharger]

If you pay shipping, I can get you a set of 360 heads for free, if that will make it easy for you to do this project. They come with valves, but need rebuilt and don't have any cracking, etc. Allthough I think they already have hardened exhaust valve seats in them.

If you are interested in them, send me a PM and I can figure out who to go through for shipping. They are heavy, but I will ship them if you are willing to pay shipping, just to get them out of here.

[Mecki]

Originally Posted by TrashedCharger

If you pay shipping, I can get you a set of 360 heads for free, if that will make it easy for you to do this project. They come with valves, but need rebuilt and don't have any cracking, etc. Allthough I think they already have hardened exhaust valve seats in them.

If you are interested in them, send me a PM and I can figure out who to go through for shipping. They are heavy, but I will ship them if you are willing to pay shipping, just to get them out of here.

Now that's being helpful! OK, it's a deal, PM coming. Thanks a lot!

I don't want to sound cheap, but those 340/360 LA heads are not so easy to find lying around here and the guys having them are asking way too much.

[thatwasfunny]

Thats pretty frikin cool right there!

[valiant64]

Hey, Trashed. Way to help out our Mopar brothers in Finland! Maybe you have a wiper motor for a 67' Coronet you wanna get rid of?

[TrashedCharger]

Possibly. I'll shake down my friends yards and see what's up.

[owatajrkiam]

Here's something you probably didn't think about,but i went through this problem!. No one builds headers for a "C" body with a small block as the torsion bars interfere as they are wider apart on a "C"!. When i was running my 340 in my 69' Monaco 500,i was using the stock 69' hp manifolds from a Dart,and they cleared everything quite well!. I bought stainless shorty headers for a Dakota magnum and i have done a preliminary fit as i was tearing down the 340 to make way for my 418" stroker,...the top of the steering box is very close to the #1 cyl tube,but i will be wrapping part of that tube with a heat wrap i have purchased!. However,.....you could use the exhaust manifolds for a 5.9 Dakota or Ram and they flow as good,if not better than the HP manifolds!. I've got a set that i paid $25 from E-Bay! Lokk for the ones WITHOUT the EGR pad!. Example- http://cgi.ebay.com/ebaymotors/Exhau...spagenameZWDVW The early ones are the good ones!. The Magnum manifolds will bolt right up to an LA head!

Glen

[rumblefish360]

Mecki, this has been a good thread. Trashed , IMO, has some real good words there. The one thing I think the thread has missing besides the been there and done that is you have not exactly looked into a "theoretical analysis" of a strokers mileage yourself. No matter the block size to start with, the cubic inchs have gone up a great deal. Short stroke or long, it's still 400+ inchs. And you'll need to feed that.

Even if you keep the rebuild very simple and cam specs mild, it's still a big engine. The main argument others have brung up make sense. Big Block it for less. The extra weight can be off set largley in lighter parts bolted on later and a stiffer T-bar and sway bar.

As I see it, @ 400+ cubes, mileage is no longer an issue since there will be none or very little on a economy build.

O, the 318 head with 1.88/1.60 valves will need to be at least bowl blended and portsized enlarged to even consider it on a 390 cid.

For the C body, I think the best move is a 383/400. A 440 would be better.
I think tti has headers. Double check with major manufactures to be sure.

[Mecki]

Originally Posted by rumblefish360

Mecki, this has been a good thread. Trashed , IMO, has some real good words there. The one thing I think the thread has missing besides the been there and done that is you have not exactly looked into a "theoretical analysis" of a strokers mileage yourself. No matter the block size to start with, the cubic inchs have gone up a great deal. Short stroke or long, it's still 400+ inchs. And you'll need to feed that.

I agree and have been convinced that 390 is too much for 318 heads. Still, it would be interesting to see a simulation of this setup, torque and power curves.

You could see this discussion more as an experimental, educational thing comparing different stroke/bore ratios. Actually a 273 4" stroker, 330cid, with 318 heads would be a good comparison to a stock 318.

Most of the information I have found is aiming at maximum power output and I'm not able to make a scientific analysis my self. Basically my question is how the torque and power curves of a 1.5:1 stroke/bore ratio engine looks like compared to a 1:1 ratio engine with same displacement and upper end? Further more, would same alteration, like headers or porting, give same results on both engines? Thinking mainly on port velocity affect on lower end torque.

This may sound crazy (You don't have to be crazy messing with old cars, but it certainly helps.), and it probably is, but i hope that it's not considered completely stupid.

Thanks for all your inputs!

[owatajrkiam]

As Rumblefish mentioned,...about the "C" body,Big block headers,...Yes,they do make them,..Hooker and TTI for sure! (TTI is WAY better quality). The only other problem,when swapping to a big block,....is.....you need a different 727 also,as the big and small blocks have different bolt patterns! Alway's something,eh'!!!!

Glen

[TrashedCharger]

I know someone with a mandrel bender that goes to 2"... My friend has a '67 Fury with a smallblock... Hmmm...

[valiant64]

Trashed, let me know if you find a wiper motor for my 67'. PM if ya find one. Thanks! 273ci to 330? Unless for a "stealth" appearance, not worth it IMO. A stock 318 is only 12ci smaller, a 340 is 10ci bigger, and a 360 is... well you get the point! I agree that for any real rpm on the 390ci stroker that the 318 head will probably not cut it. Too small of a port for the extra cubes.